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Disclaimer :All of the content I mentioned below has been my experience and understanding of the situation and I do not claim that this is the only way to do things. The purpose of this post is to give an idea on how I studied for AIIMS PG entrance exam. Also I am not getting paid by any institute or authors to promote them, this is an honest review of the material I used. Feel free to disagree with me totally!!(edit: I decided to add a section of FAQ at the end of this post based on the questions I received…so keep on contributing as questions/comments and I will keep on adding more to this article…the aim is to compile everything for your prep…what to study and HOW TO STUDY!)(the FAQ section has my approach to “smart study” in somewhat detail so even if that FAQ is not your question still give it a read because it might help you in some other way)(also the aim of this post is to connect to you as a fellow student so i have written it in a very informal way with a lot of “…”and ”!! “.)Credentials for answering the question :I joined AIIMS NEW DELHI as a MBBS Student in 2013 (All India Rank - 7).Completed my Internship during Jan 2018 to Dec 2018 period from AIIMS.Gave AIIMS PG entrance exam in November 2018 during my internship :RANK 152 ( the old pattern exam)Joined as a Non academic Junior Resident in AIIMS NEW DELHI in Department of Cardiac Radiology & Endovascular Intervention from January 2019( which I am continuing at the time of writing this post) .Gave AIIMS PG entrance again in may 2019 :RANK 26 (the new pattern exam)(For the exam pattern of AIIMS PG entrance and how to tackle the "new pattern" you can refer to another question that I have answered.)Komal Gupta's answer to What do you think about the new paper pattern introduced in the AIIMS PG entrance exam?Now on the topic of preparation :1.I joined DAMS (PG Medical Entrance Coaching Institute, NEET PG )during my pre-final year (from Jan 2016) in foundation batch2. I had joined DAMS and DBMCI ( Dr. Bhatia Medical Coaching Institute ) TND during my internship year (from Jan 2018)3. I was a MARROW(Gold standard for NEET PG & SS ) pro plan B user from July 2018 till may 20194. I had also joined various facebook groups by subject faculties5. I had attended separate classes by various faculties : including -Medicine lectures (10 days) by Dr. Thameem Saif (Welcome to Bright Medicos )Orthopedics lecture(2 days) by Dr. Apurv Mehra (Dr. Apurv Mehra )Ophthalmology lecture (3 days) by Dr. Utsav Bansal (SOCH | Dr. Utsav Bansal )Anatomy lecture (4 days) by Dr. Rajesh kaushal (HUMANANAT-ACADEMIA )6. I had a full subscription for Uptodate (Smarter Decisions. Better Care. ) (which all AIIMS UG & PG students get for free from the institute)(in case you don't know about Uptodate-- it's an online learning platform that is a point-of-care medical resource and is marketed as an evidence-based clinical resource... Envision it as Harrison - but on steroids...online + getting updates ASAP + has information on all the clinical subjects... But super expensive)7. I had a lot of review books and notes.8.I Read few topics which I could not find anywhere else from wikipedia (Wikipedia ) and Medscape (Today on Medscape )too(on a side note : I didn't pay for a lot of these resources or got them on a discount which was provided to me because of my performance in college professional exams)DO YOU NEED IT? ALL OF IT?NOI just mentioned what options I had.Looking back at it now I feel most of it was just to prevent FOMO.(Because FOMO during entrance preparation is a real thing. May be that one lecture or one book can stand between selection and taking another year drop. May be this, may be that, a lot of may be! )In reality i was a very very very very selective reader.And this along with my exam day strategy was what made my preparation "smart work" instead of hard work.(you can read my exam strategy in the article I mentioned above)HOW MANY MONTHS I PREPARED FOR?All the studying i did during 2018 (during internship) was very irregular and rare... But I attended all the lectures and TND that i needed during that time and made good notes so that when I start my "serious" prep for may 2019 I have all the sources already available.Overall i gave it - 4 months of dedicated studyingWith January - February 2019 : focusing on 1st and 2nd year subjectsMarch - april 2019 : for revision of all 19 subjectsAnd I feel 4-6 months is enough time if you have a good understanding of your topics and have read from standard textbooks during your professional exams.You will need to give more time to cover up whatever deficit you have in your knowledge.So decide for yourself.Now...Coming to the actual point...WHAT AND HOW I STUDIED :(again mentioning that this is just my personal experience and we can agree to disagree here...)I studied only the important topics!How i knew what was important?I referred to previous year AIIMS PG question papers and marked all the topics from that subject that were asked previously into my review books even before I would start studying that subjectLogic behind it :1. 60 - 70 % questions in AIIMS are from repeat TOPICS (not saying questions are repeated though they are a lot of times, but the topics which are usually asked are almost consistent)2. Topper scores around 70%-80% marks usually3. No one knows answers to the weird and new and cool questions, not even the topper4. Everything "new" is either something that no one knows or an update to previous guidelines.5. I should know the strength and weakness of my enemy before I start preparing for the fight.6. I didn't want to read all the topics in all the chapters (!)Refer to previous 3 - 4 years of question papers (total 6-8 papers)(older questions based on older patterns and older guidelines are not needed... Also pattern changed a lot from November 2016 onwards and now again from may 2019)Now...The subjects...What I actually studied...ANATOMY :I attended Dr Ashwani's TND class (DBMCI) (Anatomy App by Dr. Ashwani Kumar ), it was really good.But i needed someone to teach me all that is needed for the exam once so that I don't have to read and get lost in anatomy on my ownI attended Dr. Rajesh kaushal 's class... It covered anatomy very well... Almost 100%... If he didn't teach something in the class then I never tried to read it on my own to prevent myself from getting lost in anatomy.(but spoiler alert :class is boring and long... Because that's how anatomy is... He repeats every topic a million times in the class... Listen to it... Imprint it in your brain... Try to survive through it)Must do electron microscopy images of cell from grey's anatomy (41 edition)PHYSIOLOGY :Dr. Somman Manna's review bookFirst aid to step oneGraphs from Ganong review of physiologyALL THE FORMULAS!RBC, WBC and platelet count calculation as we did during 1st year practicalBIOCHEMISTRY :First aid to step oneFew topics from Dr. Rebecca james ' review like porphyria, glycogen disorders.List of all the enzymes affected by insulin and glucagonProtein, starch and ketone testsPATHOLOGY:First aid to step oneDr Devesh Mishra' s reviewIMAGES (in AIIMS images are not asked from any book... They just ask the most typical image from the Google image page... So I compiled screenshot of those... Also Google gives you many perspectives of the same image so that helps too)Blood transfusion protocolMICROBIOLOGY :Dr. Apurb Shastri's review bookTND notes of Dr. Shivika (DBMCI)First aid to step oneIMAGESParasitology life cyclesFORENSIC :Dr Magendran 's review book ( felt more colourful and readable than sumit seth... I didn't die of boredom while reading it!)PHARMACOLOGY :Dr. Gobind rai garg' s review bookALL THE FORMULAS!(I was told to read the new drugs that are approved from FDA in the previous year.. Just Google it and you will find the list.. I tried... Couldn't memorize even 1... So decided to take the risk of leaving that question if asked.. It wasn't asked)Make a lists of drugs safe & Contraindicated in renal disease, liver disease, pediatrics and pregnancyMechanism of action of all drugsList of drugs of choice for infectionsMEDICINE :Dr. Thameem 's notesKnow how to identify ECG, acid - base imbalance questionsSummary of Uptodate articlesNew topics and updates of latest CMDT .(refer to FAQ section to know more about CMDT)Emergency medicine from emergency medicine module on DAMS emedicoz app by Dr Naman (Emergency Medicine, AIIMS)Dr. Arvind' s notes (DAMS) for CVS examinationSURGERY :ATLS manual (10th edition) (just Google it and you will get the pdf)Few selective topics from Dr. Pritesh Singh' s review(in surgery in AIIMS hardly anything other than trauma is asked... So just read that in very much detail)DAMS DVT (for cannula, sutures & catheters etc)PSM :High yield biostatistics for USMLE 4th editionDAMS DVTMalaria, TB, HIVWhatever new disease is famous that yearUpdates that are added in the latest Parks textbookALL THE FORMULAS!OBS-GYNAEDr. Deepti Bahl's TND / regular batch notesUptodate summaryImagesPEDIATRICSDr Meenakshi Bothra's reviewNeonatal resuscitationI was told to read "AIIMS standard treatment protocol" (they are treatment protocol for all diseases which are published by AIIMS faculty, available on google for free download and also as a book), I didn't get time for it(New Born Baby )AIIMS pediatrics youtube channel ( you will find the video of Silverman score that was asked in November 2018 there)OPHTHALMOLOGYDr. Utsav bansal 's class(for the first time in MBBS i understood what was going on in that subject)IMAGES from GoogleORTHOPEDICSDr Apurv Mehra' s class /review bookImages of tests and x rays from GoogleENTRead the chapter on hearing assessment from Dr. Sakshi Arora's bookThe multiple versions of the image of mastoidectomyANESTHESIADr. Ajay Yadav 's book from dbmiMedscape ( Today on Medscape ) for reading how to do procedures - I read how to take bp, insert foley, ryles, rapid sequence intubation and arterial sampling.RADIOLOGYDr Sumer Sethi' s TND classImages from GooglePSYCHIATRYDr Praveen Tripathi 's reviewFirst aid to step oneDAMS DVTUptodateDERMATOLOGYDr Saurabh Jindal' s review bookDAMS DVTImages from GoogleMISCELLANEOUS STUFF/MUST DO1.PEP & Blood spill guidelines ( just Google "AIIMS blood spill protocol"... A pdf from AIIMS Jodhpur will appear... Read these 2 topics from it)(https://www.aiimsjodhpur.edu.in/quick%20docs/HIC%20FINAL%20MANUAL%20AIIMS%20JDH%202-1-2018.pdf )2.DAMS DVT slides (will cover most images, instruments, clinical stuff and updates )3. IF IT HAS BEEN ASKED IN AIIMS EXAM PREVIOUSLY THEN YOU MUST KNOW IT4. Keep your eyes and ears open during your postings and grab as much information as you can. Examining a patient is the best way of understanding a disease. With the recent trend in the exam of more clinical knowledge and procedures based questions attending postings sincerely will surely give you an advantage.Question practice :1. MUST SOLVE PREVIOUS YEAR AIIMS QUESTION PAPERS (I have done them 5 times till now and revise all the topics from it)2. Give 3 hour grand tests / CBT/CLT (whatever you would like to call it)... Make a strategy on how to attempt questions... Knowledge and information doesn't matter... Just know how to solve questions... Learn how to find answers by logic even when you have no idea about the question. To get knowledge use your books, don't rely on any question bank for that.(read FAQ section below for more on this)3.Know your weakness4. I have given a detailed plan on how to manage time during the exam in the article that I have mentioned above. Give it a try on one of the grand test.In conclusion,Take advice from everyone, but do only what you find Useful/doableDon't go crazy due to FOMOAvailable knowledge in endless but you have a limit to your efforts so be selectiveAll the best.(EDIT!)So I decided to add a FAQ section based on comments I received here and in Facebook messages and to continue updating it frequently . Hope it solves any further doubts you have.FREQUENTLY ASKED QUESTIONSQUESTION : Is DAMS notes (or any other notes that you studied from) enough?ANSWER: I cross checked DAMS notes / DAMS books / review books/ notes from some subject faculties.I felt all these have almost the same content.So I decided to go ahead and read review books ( I am more comfortable reading from a book rather than reading hand written notes…probably because I have a very bad hand writing… so choose one of these sources (or whatever other notes you have) based on what you find most comfortable)I had used my foundation notes from DAMS a lot during my prefinal year when I was reading my final year textbooks for the first time . After that during my final year I felt a lot of topics were updated (like there was a new Parks PSM that year so foundation notes of PSM felt useless) so I read only my standard textbooks . During my internship I read from only the latest review books ( reading 2 year old notes at that time didn't make sense to me) and TND notes of the classes I liked of DAMS/DBMCI.Whatever you choose…just stick to one source…trust them with your heart and soul…don't waste time because of FOMO.QUESTION : How to manage time along with internship /whatever other work post you have.ANSWER :I was very irregular with my studies during my internship (it wasn't because I could not get sufficient time off from postings, it was because I wanted to take some time off from studies for a while)I studied regularly during January 2019 - April 2019 period.I was doing Non Academic Junior Residency in Department of Cardiac Radiology and Endo vascular Intervention at AIIMS NEW DELHI during that time.It helped a lot because :It was only few hours of work in the morning. I used to always get free before 1 pm and I could study in afternoon then.It provided me with a structured day…work every day in morning…study in afternoon… I needed that kind of structure for myself a lot at that time. For the first time during my MBBS I was sleeping on a fixed time and waking up on a fixed timeI have a tendency of binge watching TV series for days but going for work in the morning would break that cycle of endless binge and I would get to study after work so I wasn't binging anything for more than half day.I changed my perspective…I need 8 hours of sleep…at maximum on any day I can study only for 8 hours ( even 8 hours feel like torture to me…4-6 hours is my comfort level)…so even if I have to work for upto 8 hours my schedule should be OK. We worry so much about the time we are working that we ignore that during the time when we are not working we are actually wasting it away on youtube /facebook etc or wasting it on complaining about work. My focus was that non work time and how to utilize it most effectively.I feel I am addicted to my phone (aren't we all these days!)…so I used apps which would block me out of whatsapp/facebook/Instagram /youtube (there are literally endless number of such apps on play store) (also as we say poison kills poison…so using apps for my phone addiction! )…I would adjust block time in such a way to give me 1 hour slots of study and 10 min break after each slot.QUESTION : Which book you used for AIIMS previous year question papers and did you read the explanation?ANSWER : I had used Dr. Pritesh Singh AIIMS essence review and also Aim4AIIMS question papers (for the latest question papers which were not there in my AIIMS essence) … They both need corrections to be made to their answers…when in doubt search that topic (just type the key word in the search option ) in DAMS exclusive facebook page/any other subject faculty facebook page you follow…you will surely find that question already asked by someone and answered by faculty. Stick to that answer instead of what is given in the question paper.Use these books only for seeing the question…then go ahead and read the explanation from your notes /review book that you usually use.QUESTION : Is Harrison a must??!??!??ANSWER : It is not, but reading any good medicine book for building your concepts is.I didn't read Harrison.I gave it a try during my pre final year( read CNS, CVS, leukemia from it) . It was TOO much for me. I could not finish chapters. Those chapters which I could finish didn't make any sense in my head at the end.The best test for knowing whether you understand your topic well is by teaching it to others or trying to write it down for yourself in a single sheet of paper without referring to the book.You will be able to write a flow chart for it if you understand it…there will be deficits of factual values which you can always look up in books/latest guidelines …for example…symptoms /signs of stroke…do NCCT head…it's either hemorrhagic stroke…then do nothing just manage the blood pressure if it is more than *insert the latest BP cutoff for hemorrhagic stroke here*…or it could be ischemic stroke…then check for *latest* contraindications of thrombolysis…if it not contraindicated then check BP…too high BP becomes a contraindication *insert the latest BP cutoff for thrombolysis here*…then do thrombolysis…post thrombolysis management. Hope i made some sense here!I failed both those tests with Harrison. I was trying to read Harrison only because everyone around me was doing it and i had FOMO.I read CMDT + “choti harri” instead.CMDT (CURRENT MEDICAL DIAGNOSIS AND TREATMENT by McGraw-Hill publications) :It's a book which gets updated every year and a new edition is released every year. It has investigations and treatment explained very beautifully…it uses the words like “drug of choice is” (and all everyone cares about is what to answer…I don't want to read 2 huge pages in any book where I am left on my own to decide what should be the drug of choice!)…it doesn't have Pathology part in much detail (I was okay with that because Robbins is the best source to read Pathology from…not Harrison!)…. DR. THAMEEM TEACHES FROM IT DURING HIS LECTURE (I know i could have written just that last line and it would have been sufficient)“choti harri / baby harry (!)” (Harrison MANUAL of medicine):This book is the short version of Harrison PRINCIPLES of internal medicine (badi harri /papa harry) from the same authors. It has ALL the algorithms, flow charts, tables and a summary of everything from badi harri. So you don't have to carry around the burden of badi harri and still you get all the needed information. Highly recommend it.( on a side note, choti harri is usually released 1 year after that edition of badi harri…so 20th edition of choti harri is yet to be released as of June 2019).I didn't read any other textbook like Davidson /Matthew's. So I don't know how they are and i dont like to give a judgement about a book without actually reading it. So I will suggest you to ask someone who has read it themselves.OrJudge a book for yourself. Take an important topic…say asthma…read it from every source available…Harrison/CMDT/Davidson /whatever book you want to give a try…record how much time it took for you to complete each source, the amount of information given and how understandable it is/ease of reading. Then stick to what you like the most. All 3 factors are equally important.QUESTION :How to memorize so much content available?ANSWER: I feel if you can understand the logic behind something then you can avoid adding it to your things to remember list. And logic stays in your head for much longer. While what you try to memorize, you will eventually forget.I also analysed AIIMS previous year question papers well and felt that they very very rarely ask factual information so I was able to skip those.So I just used a small notebook in which I would write down all that i wanted to memorize for example all the formulas, cutoff for BP in strokes, and other such key information which is relevant clinically . I don't have a good memory for factual stuff so I didn't try to force myself in memorizing stuff which is not asked in AIIMS exam and is not relevant clinically like diameter of eye, length of some nerve etc. If you can look it up in your book then why should we memorize it and thus should not be asked in a good quality exam. The notebook which I mentioned here I used to carry with me all the time, I used to read it if i would get free time during postings and because it had clinically relevant stuff only so I used it few times to look up something for patient management too.QUESTION : I couldn't find the mock test on AIIMS website which you had mentioned in your previous post.ANSWER : It is available on your registration page from where you download your admit card. It will be available 1-2 week before your exam.(I wanted to add screenshots of that page here to give you idea about it in advance but it has already been removed from my page…may be one of you can send those to me when you get to access the mock test in November 2019 session)QUESTION : How much MARROW question bank you used and is it worth buying?ANSWER : I was a MARROW PRO plan B user from July 2018 - May 2019. Plan B contain test series and question bank, it doesn't include lecture videos. I didn't use MARROW much, I had solved only few modules in it. Also as I didn't have access to the videos i dont know how they are. I don't like giving judgement about a source without using it myself. MARROW test series had previous year question papers given in the form of tests which I thought was a great initiative from their side.My view point on the amount of question practice one needs is a little different.What is the logic behind question solving :To know how to apply your knowledge into the questions ( if you can't use your knowledge in getting marks by answering questions correctly then you need to do more practice…no excuses allowed!)Solve 3 hour grand tests /CBT /CLT/whatever your coaching calls it : start around mid year…don't leave it for the end…don't wait till you have “sufficient” knowledge to start solving it…YOU WILL NEVER FEEL YOU HAVE SUFFICIENT KNOWLEDGE…so start today…test takes around 3 hours or 3.5 hours based on the pattern…doing an analysis of the test takes another 5-6 hours (without the analysis part the 3.5 hours that you spent giving the test is almost useless). I used to watch discussion videos of the test at 1.5* times speed and add the new information to my notes…I used to try and see the entire explanation video because even when I knew a topic very well there was always something new that faculty could add and it makes a great revision source as the most important topics get repeated in every test and listening to it again and again just works as revision. ( you have no idea how many times till now I have heard Dr. Deepti Bahl explain the most common and 2nd most common uterine anomaly in a video discussion and I dont think I can ever forget it).Don't leave grand tests for the month just before your exam as I mentioned above each test takes around 9-10 hour (3 hour for the test and 5-6 hours for the explanation)…that's atleast one entire day worth of studying!!…you should be doing revision of your notes during the last month instead.Try to solve every question, especially those that you have no idea about. You learn how to apply logic in question solving by those questions. You will never know all the answers accurately. But you can learn how to rule out options, how to identify keywords, how to increase speed of question solving. Initially you will apply faulty logic, eventually you will learn and get better at it and finally you will have the confidence to take those risks in your main exam. (also if you can solve 150 questions when you have knowledge about just 100 questions sounds like a good deal to me)Make your own exam strategy. (I have mentioned my exam strategy in the post whose link i have mentioned above, feel free to take inspiration from it)Having said all this, don't use question banks as your source of learning a subject (you need notes or textbook for it) and don't do stuff because of FOMO. I feel DAMS /DBMI content in itself is sufficient but you should decide it for yourself.QUESTION : I just have * insert any time duration in months * before exam left, is it sufficient?ANSWER : I think 4-6 months of dedicated studying is sufficient if you already have good understanding of your subjects. If you are weak in any subject then you will need to give it extra timeOf these 4-6 months keep last 2 months for revision and 1 week before the exam for quick revision.QUESTION : How many revisions you did?ANSWER : I did 2 structured revisions before the exam as I mentioned above. Having said that everytime you hear or talk about a topic with your friend is a revision and everytime you solve a question in a grand test and listen to the discussion video is a revision.

1. The pilot who got stuck outside the aircraft at 17,000 ft​This is one of the most fascinating flying stories of all time. I am going to explain this incident by combining, editing and modifying the text from various online sources. I will also be using the screenshots from National Geographic's "Air Crash Investigation."British Airways Flight 5390 left Birmingham Airport at 7.20am on a fine morning in 1990, heading for Malaga in Spain. At the controls were Captain Tim Lancaster, 42, and his co-pilot, 39-year-old Alastair Atchison, both experienced flyers, and their take-off was routine.Co-pilot Atchison handled a routine take-off, and relinquished control to Lancaster as the plane established itself in its climb. Both pilots subsequently released their shoulder harnesses, while Lancaster loosened his lap belt as well.About 15 minutes into the flight, the cabin crew had begun to prepare for meal service. The plane had climbed to 17,300 feet (5,270 m) over Didcot, Oxfordshire. Suddenly, there was a loud bang, and the fuselage quickly filled with condensation. The left windscreen, on the captain's side of the cockpit, had separated from the forward fuselage. Lancaster was jerked out of his seat by the rushing air and forced head first out of the cockpit, his knees snagging onto the flight controls. This left him with his whole upper torso out of the aircraft, and only his legs inside. The door to the flight deck was blown out onto the radio and navigation console, blocking the throttle control which caused the plane to continue gaining speed as they descended, while papers and other debris in the passenger cabin began blowing towards the cockpit.On the flight deck at the time, flight attendant Nigel Ogden quickly latched his hands onto the captain's belt. Susan Price and another flight attendant began to reassure passengers, secure loose objects, and take up emergency positions. Meanwhile, Lancaster was being battered and frozen in the 550+ KMH wind, and was losing consciousness due to the thin air.​Atchison began an emergency descent, re-engaged the temporarily disabled autopilot, and broadcast a distress call. Due to rushing air on the flight deck, he was unable to hear the response from air traffic control. The difficulty in establishing two-way communication led to a delay in British Airways being informed of the emergency and consequently delayed the implementation of the British Airways Emergency Procedure Information Centre plan.Ogden, still latched onto Lancaster, had begun to suffer from frostbite, bruising and exhaustion. He was relieved by the remaining two flight attendants. By this time Lancaster had already shifted an additional six to eight inches out the window. From the flight deck, the flight and cabin crew were able to view his head and torso through the left direct vision window. Lancaster's face was continuously hitting the direct vision window; when cabin crew saw this and noticed that Lancaster's eyes were opened but not blinking despite the force against the window, they assumed that Lancaster was dead. Atchison ordered the cabin crew to not release Lancaster's body despite the assumption of his death because he knew that releasing the body might cause it to fly into the left engine and cause an engine fire or failure which would cause further problems for Atchison in an already highly stressful environment.​Atchison eventually received clearance from air traffic control to land at Southampton, while the flight attendants managed in extreme conditions to free Lancaster's ankles from the flight controls and hold on to him for the remainder of the flight. By 07:55 the aircraft had landed safely on Runway 02 at Southampton. Passengers immediately disembarked from the front and rear stairs, and emergency crews retrieved Lancaster.The captains body had suffered tremendous physical trauma, getting sucked out of the cockpit and getting pinned down by 600 kmph winds on the cockpit window at -17 degree Celsius. He would have also suffered oxygen deprevition for more than 22 minutes.Despite the trauma captain Lancaster suffered, there is a small twist to his story. He somehow survived this horrific ordeal with two bone fractures, bruising ,shock frostbite and a broken finger.There were no casualties on this flight.Less than five months after the accident Lancaster was working again. He later retired from British Airways when he reached the company's mandatory retirement age of 55 at the time. In 2005 Lancaster was reported flying for EasyJet.​Actual photo of the WindshieldBy flying alone, battling 600+KMPH of winds at -17 degree Celsius and oxygen deprivation, Co-Pilot Alastair Atchison's achievement in saving this plane is truly outstanding.First Officer Alastair Stuart Atchison and cabin crew member Susan Gibbins were awarded the Queen's Commendation for Valuable Service in the Air award in recognition of their extraordinary flying under extreme conditions.Accident investigators later discovered that when the windscreen had been refitted to the plane the night before, the wrong bolts had been used to secure it; they were little more than half a millimeter too small, and had failed under intense air pressure. Surprisingly the old bolts were also incorrect ones; the engineer, working under pressure and without reference to manuals, had simply replaced the old bolts with new ones on a like-for-like basis.As a result of the incident, windscreens on British Airways planes are now secured by bolts on the inside of the plane, rather than the outside, putting them under even less pressure.It is highly recommended that you watch the documentary "Aircrash Investigation : Ripped out of the cockpit"Sources:1. Wikipedia: British Airways Flight 53902. June 10, 1990: Miracle of BA Flight 5390 as captain is sucked out of the cockpit – and survives2. Ghost Plane!​SituationA Helios Airways Boeing 737 is circling the city of Athens for more than two hours in a holding pattern. There is no communications from the plane even after multiple attempts. The Greek air force sends two of its fighter jets to investigate the situation. One of them is in a shooting position behind the 737 while the other one is trying to visually access the situation. The fighter pilot can see passengers on their seats but none of them are moving or reacting to the presence of a fighter jet. There is one non responsive person on the pilots seats slumped over the controls.​Then the fighter pilot radios that there is one person moving in the cockpit! But this person is not communicating with the fighter pilot.​Sounds like a movie?This true story is as suspenseful as a good thriller movie. I strongly suggest that you watch this episode of Air Crash Investigation. It is highly dramatized and made nearly like a movie itself.Air Crash Investigation - Ghost Plane - Helios Flight 5223. AirCraft roof ripped off​\\​Aloha Airlines Flight 243 was a scheduled Aloha Airlines flight between Hilo and Honolulu in Hawaii. On April 28, 1988, a Boeing 737-297 serving the flight suffered extensive damage after an explosive decompression in flight. Earlier, in the first incident, we saw the captain enduring a huge physical stress, in this case, the passengers are sitting on an airplane seat with no roof.I suggest you to watch "Air Crash Investigation: Hanging by a thread":Per Page on youtube.com:The flight departed Hilo at 13:25 HST on 28 April 1988 with six crew members and 89 passengers, bound for Honolulu. No unusual occurrences were noticed during the pre-departure inspection of the aircraft. The aircraft had previously completed 3 round-trip flights from Honolulu to Hilo, Maui, and Kauai that day, all uneventful. Meteorological conditions were checked but no advisories for weather phenomenon occurred along the air route, per Airman’s meteorological information (AIRMET) or significant meteorological information (SIGMET). The captain was 44-year-old Robert Schornstheimer. He was an experienced pilot with 8,500 flight hours; 6,700 of those were in Boeing 737s. The first officer was 36-year-old Madeline "Mimi" Tompkins. She also had significant experience flying 737s, having logged 3,500 of her total 8,000 flight hours in them.No unusual occurrences were reported during the take-off and ascent. Around 13:48, as the aircraft reached its normal flight altitude of 24,000 feet (7,300 m) about 23 nautical miles (43 km) south-southeast of Kahului, Maui, a small section on the left side of the roof ruptured with a "whooshing" sound. The captain felt the aircraft roll left and right, and the controls went loose. The first officer noticed pieces of grey insulation floating over the cabin. The door to the cockpit was gone so the captain could look behind him and see blue sky. The resulting explosive decompression tore off a large section of the roof, consisting of the entire top half of the aircraft skin extending from just behind the cockpit to the fore-wing area.​First officer Madeline "Mimi" Tompkins was flying the plane at the time of the incident. After discovering the damage, the captain took over and steered the plane to the closest airport, on Maui island. Thirteen minutes later, the crew performed an emergency landing on Kahului Airport's Runway 2. Upon landing, the crew deployed the aircraft's emergency evacuation slides and evacuated passengers from the aircraft quickly. Tompkins assisted passengers down the evacuation all, 65 people were reported injured, eight seriously. At the time, Maui had no plan for a disaster of this type. The injured were taken to the hospital by the tour vans from Akamai Tours (now defunct) driven by office personnel and mechanics, since the island only had a couple of ambulances. Air traffic control radioed Akamai and requested as many of their 15-passenger vans as they could spare to go to the airport (three miles away) to transport the injured. Two of the Akamai drivers were former medics and established a triage on the runway. The aircraft was a write-off.58 year old Flight Attendant Clarabelle Lansing was the only fatality; she was swept overboard while standing near the fifth row seats. Despite an extensive search her body was never found. She was a veteran flight attendant of 37 years at the time of the accident.​Real photo of the planeSource: Wikipedia Aloha Airlines Flight 2434. Strange Lights around the plane + all four engines fail​British Airways Flight 9, was a scheduled flight from London Heathrow to Auckland, with stops in Bombay, Madras, Kuala Lumpur, Perth, and Melbourne. It is a Boeing 747 Jumbo Jet with 263 people on board.​The plane was flying above Indian ocean near Java at night. After few hours, strange bright lights started appearing all around the aircraft. Despite the weather radar showing clear skies, the crew switched on engine anti-ice and the passenger seat belt signs as a precaution.I strongly suggest to watch this dramatized documentary " Aircrash Investigation: Falling from the sky" here --> youtube.com.This incident is better watched than read. Even a book was written about this incident named All Four Engines Have Failed: The True and Triumphant Story of Flight BA 009 and the Jakarta Incident: Betty TootellBut if you choose to read then continue (otherwise skip to the next incident):As the flight progressed, smoke began to accumulate in the passenger cabin of the aircraft; it was first assumed to be cigarette smoke. However, it soon began to grow thicker and had an ominous odour of sulphur. Passengers who had a view out the aircraft windows noted that the engines were unusually bright, with light shining forward through the fan blades and producing a stroboscopic effect.At approximately 13:42 UTC (20:42 Jakarta time), the number four Rolls-Royce RB211 engine began surging and soon flamed out. The flight crew immediately performed the engine shutdown drill, quickly cutting off fuel supply and arming the fire extinguishers. Less than a minute later, at 13:43 UTC (20:43 Jakarta time), engine two surged and flamed out. Within seconds, and almost simultaneously, engines one and three flamed out, prompting the flight engineer to exclaim, "I don't believe it — all four engines have failed!"Without engine thrust, a 747-200 has a glide ratio of approximately 15:1, meaning it can glide forward 15 kilometres for every kilometre it drops. The flight crew quickly determined that the aircraft was capable of gliding for 23 minutes and covering 91 nautical miles (169 km) from its flight level of 37,000 feet (11,000 m). At 13:44 UTC (20:44 Jakarta time), Greaves declared an emergency to the local air traffic control authority, stating that all four engines had failed. However, Jakarta Area Control misunderstood the message, interpreting the call as meaning that only engine number four had shut down. It was only after a nearby Garuda Indonesia flight relayed the message to Air Traffic Control that it was correctly understood. Despite the crew "squawking" the emergency transponder setting of 7700, the 747 could not be located by Air Traffic Control on their radar screens.Many passengers, fearing for their lives, wrote notes to relatives. One such passenger was Charles Capewell, who scrawled "Ma. In trouble. Plane going down. Will do best for boys. We love you. Sorry. Pa XXX" on the cover of his ticket wallet.Owing to the high Indonesian mountains on the south coast of the island of Java, an altitude of at least 11,500 feet (3,500 m) was required to cross the coast safely. The crew decided that if the aircraft was unable to maintain altitude by the time they reached 12,000 feet (3,700 m) they would turn back out to sea and attempt to ditch into the Indian Ocean. The crew began engine restart drills, despite being well outside the recommended maximum engine in-flight start envelope altitude of 28,000 feet (8,500 m). The restart attempts failed.Despite the lack of time, Captain Moody made an announcement to the passengers that has been described as "a masterpiece of understatement":"Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress."​Without the engines noise, the planes was totally silent and the lights in the cabin went out!As pressure within the cabin fell, oxygen masks dropped from the ceiling – an automatic emergency measure to make up for the lack of air.Without the engines, most of electronic things will stop working including the public addressing system.Lead Flight attendant came to the the cabin with a megaphone and announced:"Can you hear me. There is a small problem with our public addressing system. Place your mask over your mouth and nose and breath normally"​On the flight deck, however, Greaves's mask was broken; the delivery tube had detached from the rest of the mask. Moody swiftly decided to descend at 1,800 m per minute to an altitude where there was enough pressure in the outside atmosphere to breathe almost normally.​At 13,500 feet (4,100 m), the crew was approaching the altitude at which they would have to turn over the ocean and attempt a risky ditching. Although there were guidelines for the water landing procedure, no one had ever tried it in a Boeing 747, nor has anyone since. As they performed the engine restart procedure, engine number four finally started, and at 13:56 UTC (20:56 Jakarta time), Moody used its power to reduce the rate of descent. Shortly thereafter, engine three restarted, allowing him to climb slowly. Shortly after that, engines one and two successfully restarted as well. The crew subsequently requested and expedited an increase in altitude to clear the high mountains of Indonesia.As the aircraft approached its target altitude, the strange lights on the windscreen returned. Moody throttled back; however, engine number two surged again and was shut down. The crew immediately descended and held 12,000 feet (3,700 m).As Flight 9 approached Jakarta, the crew found it difficult to see anything through the windscreen, and made the approach almost entirely on instruments, despite reports of good visibility. The crew decided to fly the Instrument Landing System (ILS); however, the vertical guidance system was inoperative, so they were forced to fly with only the lateral guidance as the first officer monitored the airport's Distance Measuring Equipment (DME). He then called out how high they should be at each DME step along the final approach to the runway, creating a virtual glide slope for them to follow. It was, in Moody's words, "a bit like negotiating one's way up a badger's arse." Although the runway lights could be made out through a small strip of the windscreen, the landing lights on the aircraft seemed to be inoperable. After landing, the flight crew found it impossible to taxi, due to glare from apron floodlights which made the already sandblasted windscreen opaque.They had landed the jumbo jet blind as their windscreen had nearly became opaque due to scratches caused by the strange lights!The crew received various awards, including the Queen's Commendation for Valuable Service in the Air and medals from the British Air Line Pilots Association. Following the accident, the crew and passengers formed the Galunggung Gliding Club as a means to keep in contact. G-BDXH's engineless flight entered the Guinness Book of Records as the longest glide in a non-purpose-built aircraft (this record was later broken by Air Canada Flight 143 and Air Transat Flight 236).One of the passengers, Betty Tootell, wrote a book about the accident, All Four Engines Have Failed. She managed to trace some 200 of the 247 passengers on the flight, and went on to marry a fellow passenger, James Ferguson, who had been seated in the row in front of her. She notes: "The 28th December 2006 marks the start of our 14th year of honeymoon, and on the 24th June 2007 many passengers and crew will no doubt gather to celebrate the 25th anniversary of our mid-air adventure."​Post-flight investigation revealed that this flights problems had been caused by flying through a cloud of volcanic ash from the eruption of Mount Galunggung. Because the ash cloud was dry, it did not appear on the weather radar, which was designed to detect the moisture in clouds. The cloud sandblasted the windscreen and landing light covers and clogged the engines. As the ash entered the engines, it melted in the combustion chambers and adhered to the inside of the power-plant. As the engine cooled from inactivity, and as the aircraft descended out of the ash cloud, the molten ash solidified and enough of it broke off for air to again flow smoothly through the engine, allowing a successful restart. The engines had enough electrical power to restart because one generator and the on-board batteries were still operating; electrical power was required for ignition of the engines.The strange lights were initially called St Elmo's fire, but later it was found that the glow experienced was from the impact of ash particles on the leading edges of the aircraft, similar to that seen by operators of sandblasting equipment.5. Gimli Glider - Ran Out of FuelOn July 23, 1983, Captain Robert Pearson, 48, and First Officer Maurice Quintal are at the controls of a brand new Air Canada's Boeing 767.At 41,000 feet (12 497 m) over Red Lake, Ontario, the cockpit warning system chimed four times and indicated a fuel pressure problem on the left side. Thinking the fuel pump had failed the pilots turned it off; the tanks are above the engines so gravity will take over and feed the engines. The computer said that there was still plenty of fuel, but this was based on the wrong calculations. A few moments later a second fuel pressure alarm sounded, and the pilots decided to divert to Winnipeg. Within seconds the left engine failed and preparations were made for a one-engine landing.While they attempted to restart the engine and communicate with controllers in Winnipeg for an emergency landing, the warning system sounded again, this time with a long "bong". The sound was the "all engines out" sound, an event that was never simulated during training. Seconds later the right side engine stopped and the 767 lost all power leaving the cockpit suddenly silent and allowing the cockpit voice recorder to easily pick out the words "Oh, f%$#!".The 767 is based on a "glass cockpit" concept in which mechanical instruments are replaced with display screen monitors. The jet engines also delivered electrical power to the aircraft, so most of the instrumentation suddenly went dead. One of the lost instruments was the vertical-rate indicator, which would let the pilots know how fast they were sinking and therefore how far they could glide.The engines also supplied power to the hydraulic systems, without which a plane the size of the 767 could not be controlled.However, Boeing actually planned for this possible failure and included a device known as a ram air turbine that automatically popped open on the side of the plane, using some of the plane's residual velocity to spin a propeller-driven generator and provide enough power to the hydraulics to make it controllable.​RAM Air TurbineWith nothing in the emergency guide on flying the aircraft with both engines out, Pearson glided the plane at 220 knots (407 km/h), his best guess as to the optimum airspeed. Copilot Maurice Quintal began making calculations to see if they would reach Winnipeg. He used the altitude from one of the mechanical backup instruments, while the distance travelled was supplied by the air traffic controllers in Winnipeg, who measured the distance the plane's echo moved on their radar screens. The controllers and Quintal both calculated that Flight 143 would not make Winnipeg, as the plane had lost 5,000 ft in 10 nautical miles (1.5 km in 19 km) giving a glide ratio of approximately 12:1.Stationed at the former Royal Canadian Air Force Base, Quintal selected Gimli to be the attempted place of landing. Since his time in the service, Quintal did not know the Gimli airport had become a drag racing ground. Also not knowing one of its parallel runways was now being used for auto racing. To further complicate the situation, there were many cars, campers and families close to the former runway as it was "Family Day" for the Winnipeg Sports Car Club.As they approached Quintal did a power-off "gravity drop" of the main landing gear, but the nose wheel, despite being built to open by swinging backwards with the force of the wind, would not lock. The ever-reducing speed of the plane also reduced the effectiveness of The "RAT" (Ram Air Turbine, a propeller driven hydraulic pump tucked under the belly of the 767. The RAT can supply just enough hydraulic pressure to move the control surfaces and enable a dead-stick landing) and the plane became increasingly difficult to control. As they grew nearer it became apparent that they were too high, and Pearson executed a manoeuvre known as a "forward slip" to increase their drag and reduce their altitude. This gave passengers on one side of the aircraft a view of the ground while passengers on the other side of the plane seen blue skies. With the reduction of speed and altitude the 767 silently leveled off and the main gear touched down. Pearson "stood on the brakes" the instant the plane touched the runway, blowing out several of the plane's tires.Two kids were cycling at the end of the runway. They looked back and saw a big jet approaching them. The terrified kids tried to outrun the plane.​The plane came to a stop at the end of the runway in a nose-down position due to the unlocked nose gear, only a few hundred feet from spectators of Family Day and the kids at the end of the runway.None of the 61 passengers were hurt during the landing, the only injuries that resulted from the landing of Flight 143 came from passengers exiting the rear emergency slide, a near vertical angle because of the nose down position of the plane. A minor fire in the nose area was quickly put out by course workers, who rushed over with fire extinguishers.​Real photoWithin two days the aircraft was repaired and flown out of Gimli, after approximately one million dollars worth of repairs, Aircraft #604 the Boeing 767 known as "The Gimli Glider", is to this day still in the Air Canada fleet.Note: The mechanics sent from Winnipeg Airport to repair the aircraft, also ran out of fuel in their van on their way to Gimli.​Why this plane crashed?At the time of the incident, Canada was converting to the metric system. As part of this process, the new 767s being acquired by Air Canada were the first to be calibrated for metric units (litres and kilograms) instead of customary units (gallons and pounds). All other aircraft were still operating with Imperial units (gallons and pounds). The pilots miscalculated the fuel required for the trip in pounds instead of kilograms.Instead of 22,300 kg of fuel, they had 22,300 pounds on board — 10,100 kg, about half the amount required to reach their destination. This simple problem with the units had caused this crash.Sources:- Gimli Community Web, Gimli GliderIf you would like to watch it, then search for "Air Crash Investigation: Gimli Glider"6) Kids fly a commercial jet​Aeroflot Flight 593, an A310 was en route from Sheremetyevo International Airport to Hong Kong Kai Tak International Airport with 75 occupants aboard, of whom 63 were passengers. Most of the passengers were businessmen from Hong Kong and Taiwan who were looking for economic opportunities in Russia.The relief pilot, Yaroslav Kudrinsky, was taking his two children on their first international flight, and they were brought to the cockpit while he was on duty. Aeroflot allowed families of pilots to travel at a discounted rate once per year. Five people were in the cockpit: Kudrinsky, copilot Igor Piskaryov, Kudrinsky's son Eldar , his daughter Yana, and another pilot, V. Makarov, who was flying as a passenger.With the autopilot active, Kudrinsky, against regulations, let the children sit at the controls. First his daughter Yana took the pilot's left front seat. Kudrinsky adjusted the autopilot's heading to give her the impression that she was turning the plane, though she actually had no control of the aircraft. Shortly thereafter Eldar occupied the pilot's seat. Unlike his sister, Eldar applied enough force to the control column to contradict the autopilot for 30 seconds. This caused the flight computer to switch the plane's ailerons to manual control while maintaining control over the other flight systems. A silent indicator light came on to alert the pilots to this partial disengagement. The pilots, who had previously flown Russian-designed planes which had audible warning signals, apparently failed to notice it.The first to notice a problem was Eldar, who observed that the plane was banking right. Shortly after, the flight path indicator changed to show the new flight path of the aircraft as it turned. Since the turn was continuous, the resulting predicted flight path drawn on screen was a 180-degree turn. This indication is similar to the indications shown when in a holding pattern, where a 180-degree turn is intentional to remain in one place. This confused the pilots for nine seconds. During this confusion, the plane banked past a 45-degree angle (steeper than it was designed for). This increased the g-force on the pilots and crew, making it impossible for them to regain control. After the plane banked to 90 degrees, the remaining functions of the autopilot tried to correct its plummeting altitude by putting the plane in an almost vertical ascent, nearly stalling the plane. The co-pilot and Eldar managed to get the plane into a nosedive, which reduced the g-forces and enabled the captain to take the controls. Though he and his co-pilot did regain control and level out the wings, their altitude by then was too low to recover, and the plane crashed at high vertical speed, estimated at 70 m/s (14,000 ft/min). All 75 aboard were killed.The aircraft crashed with its landing gear up, and all passengers had been prepared for an emergency, as they were strapped into their seats. No distress calls were made prior to the crash. Despite the struggles of both pilots to save the aircraft, it was later concluded that if they had just let go of the control column, the autopilot would have automatically taken action to prevent stalling, thus avoiding the accident.The wreckage was located on a remote hillside approximately 20 kilometres (12 mi) east of Mezhdurechensk, Kemerovo Oblast, Russia; the flight data recorders were found on the second day of searching.If you would like to watch it, then search for "Air Crash Investigation: Kids in the cockpit"Source: Aeroflot Flight 593I will add more details and more incidents soon.7. TACA Flight 110 [Remarkable landing]8. Hudson River Ditching9. Air Transat flight 236 [Flying with empty fuel tank]10. Malaysian Airlines MH370 (But I have only theories and assumptions, so I am going to leave it.)by - Kshitij SalgunanPS:- Due to readers demand for explanation of the Ghost plane story, I have written a fully fledged answer here : What happened to Helios flight 522-the ghost plane?

tldr: The scope of this question is potentially larger than it appears. Disadvantages apply to personal, hobby, research-level soldering such as prototype design by engineers. Disadvantage also apply to industrial production, all industries involving electronics.Disadvantages of lead-free solders:The flux core in the wire and lead-free fluxes contain harsh reducing agents that are highly irritating to wet membranes like the sinuses and the eyesThe flux used in lead-free soldering has a shelf life because exposure to oxygen reduces the effectiveness of the core in the solder. For this reason, many solder companies have introduced expiration dates for their flux-core solders instead of just printing the DOM (date of manufacture).lead-free solder is mostly, tin, silver, copper :: Sn, Ag, Cu, or other metals. The temperature required to get a lead-free solder alloy into its molten, “eutectic”* state which allows for proper wetting is greater than that required for soldering with Sn60Pb40 or Sn63Pb37 Lead-tin solder; significantly hotter in centigrade or Fahrenheit (C or F).Table source linkGood old Sn60Pb40 (or Sn63Pb37) undergoes a phase change from solid to liquid (molten) at a [specific] eutectic point. 183 degrees C (highlighted in yellow)SAC (SnAgCu305) is likely the most common lead-free solder. SAC305 is a lead-free alloy that contains 96.5% tin, 3% silver, and 0.5% copper. The phase change from solid to liquid occurs over a range (217–220)The phase change from solid to liquid is not at a single [eutectic] point or temperature value for this lead-free alloy, SAC 305, and so is technically a non-eutectic solder.Wetting is a property of liquids. Wetting is crucial to the formation of acceptable or superior solder joints. Wetting occurs as a phase change from solid to liquid (flux is crucial for this wetting as well), then heating it to the eutectic temperature.Flux allows for heated solid solder to wet and be wet in open air. This is similar to how surfactants such as soaps help water (liquid) become “wetter.”Flux helps solder wet properly, as the solder moves to the two surfaces being heating temporarily with the soldering iron tip.The less-than-desirable “eutectic range” for the alloy itself can account forless than ideal wettinga different appearance from other metallic alloysLead-free solders also differ in their greater surface tension, specifically, and which can be seen exaggerated in specialty solder alloys such as Sn96Ag04, tin solder or Silvergleem. This is a solder alloy used for jewelry, for example. The surface tension of lead-free solders results in playfulness on the tip, flux is essential (but caustic or corrosive)technique must be modified, if accustomed to normal electronicslead-free solder will require specialized, (upgraded) tips, especially if the tip temperature is determined by the model number of the tip (e.g. Metcal brand), and not a variable temperature dial, tips which could be expensive to replace lead-solder tipsthere is a good amount of reason to consider that the higher temperatures required for making good solder joints with lead-free solder could be responsible for the premature failure of active semiconductor components as a trend, some of which have low temperature exposure tolerances.When soldering is done with leaded-solder, there is somewhat of a correlation between the qualitative appearance of the joint (shiny, smooth) and the electrical conductivity and mechanical strength, the two most important qualities provided by Mr. solder joint.When lead-free solder is used, appearance and qualities like “shininess” are not really an indication of a good solder joint.If you are totally new to soldering and you have a lot of it to do (for example, to complete a large engineering project that will determine your final grade)you may not learn how to solder sufficiently well if you use lead-free when learning to solder. (i.e., don’t waste your time!!)This situation would be made worse if one is also attempting to learn using lead-free solder that is old, expired, oxidized or using lead-free flux that is expired.It would be worse or least ideal to the also use old, oxidized soldering tip(s) and/or a soldering iron lacking power in Wattage available, or temperature prevision.Learning what good soldering looks like, through first-hand experience is easiest achieved by using the old leaded solder, it is the starting point for soldering (even with mandated lead-free ROHS in industry) and how to adjust your technique to the idiosyncratic demands of lead-free alloysIn addition, the inability to make good solder joints leads to other issues:hidden resistances in solder joint(s) and which become worse over timesolder joints so poor that they begin to act as thermal intermittentscold, dry joints that are not conductive as they should be and lack mechanical strengthtrying to troubleshoot the source of an issue when the problem was that one or two solder joints on an IC chip simply do not have a good electrical connection (in terms of conductivity) to the circuit because of a lack of experience in spotting defective solder joints when using lead-free. This could lead to hours pr days of frustration and running in circles when circuit analysis won’t help you figure it out because it could be one crappy solder joint.The alternative:Use leaded solder for your projectsWash your hands every time you touch solder, just as you do after say, doing woodwork or working on a car.Do not eat, drink, smoke, apply cosmetics, till you wash your hands thoroughly and you are done soldering, just like doing any DIY project.Keep your area clean and out-of-reach to children or pets. Wipe up your work area and static-dissipative mat to clean up solder balls and bits.Use a solder (lead-waste) container, or substitute for one, e.g., a medium sized coffee can where contaminated items can be dumped (when they are cool).Contain leaded solder waste such as solder balls and bits in that container such as solder wick, brass wool for conditioning your solder tips, bad components, etc.Dispose of this waste at electronic-recycling collection events or contact your waste management company.Unless you are a business that requires so much soldering that you would be classified as a small, medium, or large waste-generator:you don’t have to use lead-free. Doing so doesn’t mean you are more conscientious or a “better person.” Simply manage the handling and disposal of the waste, just like you do when you change the oil in your car.Alloys containing lead versus lead saltsSolder as an alloy is composed of tin and lead and which has a super-strong outer surface layer of oxidation.Solid solder, as in the case of solder wire, has an oxidative coating on the surface. This coating results from exposure to ambient air which contains oxygen that bonds to surface atoms. The oxidative coating on metals may be held strongly. For example, the oxidative coating on aluminum is an invisible barrier that makes it corrosion proof.Years ago, certain products had lead incorporated into them, notably in indoor house paint. The paint contained lead, but not as metal but as lead salts, or molecular compounds containing lead. If ingested, as paint chips that eroded off walls and eaten by infants, the lead would be easily digested and easily absorbed by the body as toxic, heavy metals.Is it possible to handle pure lead (Pb) metal slabs and get some on the hands? Then not wash one’s then eat a bag of popcorn? Pure lead is “soft” and can rub off on hands but solder is mostly tin, not pure lead metal.Leaded solder is best to learn. In fact, if you paid money to learn from a training organization that offers certifications, you would be trained using leaded solder.They don’t have the time and patience for you to not show some good results from training.Leaded solder is how people have learned soldering and continue to learn to solder correctlyedit, in case this question was meant for industry, I touch upon here, a case where the rubber meets the road regarding lead-free versus leaded solder allows used in automated production:An ideal solder joint with have two (2) key characteristics:good electrical conductivity that results from the proper reflow and wetting within a non-oxidized and contaminant free solder jointmechanical strength of the solder joint that connects two different surfaces togetherIn electronics, through-hole components and through-hole board designs were dominant. The processes for soldering through-hole components into plated through-hole barrels (PTH) that transect the board, were highly reliable yet they were based on lead-containing alloys.Wave machines solder pots, utilizing molten solder pools, to solder all the components to a board well, reliably, and verifiable quickly by visual inspection, were the standard.That said, currently it is not feasible or even possible to maintain pools of molten lead-free solder, using the lead-free alloys currently available.to be clear: It is possible to create a molten pool that is restricted in area during the process of selective soldering, for brief periods, while under or inside a non-oxidative environment. The process is done in a nitrogen gas saturated system and not done in ambient air. I could be done under argon Ar(l) a completely unreactive or noble, gas.here is a wonderful video the demonstrates selective soldering: link I know the video is 10 yrs old but selective soldering for lead-free processes still looks similar to that today in 2020.it’s optional, premium technologyMost electronics today are fabricated using surface mount technology or SMT technology. The components are attached only to the surface of a board, and not through it.SMT technology utilizes solder paste, distributed in precise volumes onto the board surface using stencils and a squeegee. Components (SMD or surface mount devices) are tacked onto a board using a pick and place machine (thousands of them and teeny-tiny). The solder paste provides enough tackiness (stickiness) to hold the components in place and during convection reflow. This process for surface mount components works using lead-free solder pastes works generally well.The exception is for components that are so important that they must be soldered into a board designed for through-hole technologies using plated through-holes and this regards many I/O connectors that provide, for example, many functions or many signal channels and many small pins within many holes.Because molten solder pools are not great with lead-free alloys, such as with wave-soldering machines, many manufacturers must now rely on a process called “intrusive soldering.”Intrusive soldering is the use of surface mount convection reflow ovens to solder through-hole components, while still using SMT-purposed solder paste. Intrusive soldering is also called Pin-in-Paste (PIP) or Pin-in-hole-paste (PIHP) soldering. This is done when waves [of molten solder] were used previously for those. Intrusive soldering is a new approach to soldering based on, and also resulted from, RoHS (lead-free) prescribed protocol.Source, images: http://www.ami.ac.uk/courses/topics/0226_pip/index.htmlNotice the concave shapes (versus convex) or bumpy appearance to the solder. Lead-free solders tend to have greater surface tension. Often will also see darker solder at the surface, usually as partially reflowed solder paste when everything out of a wave machine looks as shiny metal that clearly reached a state of liquidus, displaying properties of wetting and of solder that reached its eutectic temperature—the point or narrow temperature range for phase change; solid becomes liquid.Intrusive soldering however, is mostly experimental since each process and oven temperature profile must be tweaked for every particular assembly. It is an ad hoc process, mostly trial-and-error—tweaking or adjusting oven temperature profiles to produce desirable outcomes. Often the first production run of a single circuit board with these connectors will be defective and scrapped (something now expected), and the oven temperatures tweaked on the next run.Due to the experimental nature of intrusive soldering, agreement by convention will be difficult to standardize or attain.Not everyone agrees that Pin-in-Paste (PIP) or Pin-in-hole-paste (PIHP), aka intrusive soldering, can allow for standardized improvements or even produce acceptable solder joints (results similar to those allowed for previously with leaded solders) with the currently available alloys.For this reason, through-hole connectors must be soldered by hand for lead-free alloys and cannot depend on convection reflow methods whenever a connector is used in a very important circuit board, especially in the case of mission-critical class-3 circuit boards, such as those placed in satellites which are very difficult to service once they’re in orbit. For this reason, intrusive soldering has not yet been accepted by IPC as a reliable method that can be standardized. Instead, IPC urges direct oversight by an astute soldering technician/process engineer and the onus is on them to get the process right by tweaking it for every individual assembly, but for class-2 boards (consumer level) at best.There are some perceived advantages to cost, to using this unconventional means of installing through-hole components with convection reflow of solder pasted just as a reduction in the number of process steps, taken with a grain of salt because the solder joints created with intrusive soldering simply cannot reach target criteria, but only acceptable conditions at best.A solder joint can be Target (nearly perfect), or Acceptable (not too shabby), or non-conforming or Defective.Only hand-soldering of through hole components with lead-free solder wire and not paste, can allow for Target solder joints.Intrusive soldering of through-hole components using solder paste in a convection reflow process:results in “Acceptable” solder joints, at bestmore easily allows for non-conforming characteristics (solder joints with insufficient solder, solder joints with voids or pockets of air, cold (non-reflowed) solder jointscomes with a known trade-off of having solder joints that do not have the same conductivity and mechanical strength of through-hole components installed with leaded solders (but may suffice for say, cheap consumer electronics).Soldering through-hole components with lead free solder paste and using SMT convection reflow is often problematic compared to the older process which was highly consistent, highly reliable in producing target solder joints.There was a huge advantage to established processes involving lead-containing solders and technologies, but these are no longer in use whenever lead-free alloys are required, and also because of the different chemistries involved with leaded-and lead free solders.The closest thing today for lead-free solders to the past wave technology with leaded solder, is called selective soldering. Selective soldering requires a specialized machine with cameras and PC, but also cooling with liquid nitrogen. So it add cost to the process where arguably the electronics don’t have to be 100% perfect in aesthetics as long as they’re 100% functional.The disadvantage was that lead-waste in electronics is not and was not being processed as waste, properly, only an estimated 15% of old electronics is recycled appropriately.This is an example of a challenge or disadvantage presented by the transition from leaded to lead-free solders.edit: One other big disadvantage to lead-free solder alloys that should be mentioned involves the formation of microscopic metallurgical “whiskers,” more specifically “tin whiskers” and also “zinc whiskers” that have been increasingly associated with lead-free solder alloys.Image:Image, same source:The formation of these whiskers is as yet not well-understood. What is clear from just the images above is that these develop over time and essential create tiny short-circuit or bridging conditions, instead of discrete, isolated components.For this other reason, highly and critically important soldering electronics does not use lead-free solders. The best examples of highly critical soldering involves Class 3 electronics [mentioned above] (mission-critical electronics with absolutely the lowest possible fail rates, such as in jet planes, defense applications, rockets and satellites, other examples follow), which still utilize lead-based alloys still, because of the tin-whisker problem correlated with lead-free solder alloys in electronics.[Effects of]:Whiskers [Wikipedia] can cause short circuits and arcing in electrical equipment. The phenomenon was discovered by telephone companies in the late 1940s and it was later found that the addition of lead to tin solder provided mitigation.[4]The European Restriction of Hazardous Substances Directive (RoHS), that took effect on July 1, 2006, restricted the use of lead in various types of electronic and electrical equipment. This has driven the use of lead-free alloys with a focus on preventing whisker formation, see § Mitigation and elimination. Others have focused on the development of oxygen-barrier coatings to prevent whisker formation.[5]Airborne zinc whiskers have been responsible for increased system failure rates in computer server rooms.[6]Zinc whiskers grow from galvanized (electroplated) metal surfaces at a rate of up to a millimeter per year with a diameter of a few micrometres. Whiskers can form on the underside of zinc electroplated floor tiles on raised floors due to stresses applied when walking over them; and these whiskers can then become airborne within the floor plenum when the tiles are disturbed, usually during maintenance. Whiskers can be small enough to pass through air filters and can settle inside equipment, resulting in short circuits and system failure.Tin whiskers don't have to be airborne to damage equipment, as they are typically already growing in an environment where they can produce short circuits. At frequencies above 6 GHz or in fast digital circuits, tin whiskers can act like miniature antennas, affecting the circuit impedance and causing reflections. In computer disk drives they can break off and cause head crashes or bearing failures. Tin whiskers often cause failures in relays, and have been found upon examination of failed relays in nuclear power facilities.[7] Pacemakers have been recalled due to tin whiskers.[8]Research has also identified a particular failure mode for tin whiskers in vacuum (such as in space), where in high-power components a short-circuiting tin whisker is ionized into a plasma that is capable of conducting hundreds of amperes of current, massively increasing the damaging effect of the short circuit.[9]The possible increase in the use of pure tin in electronics due to the RoHS directive drove JEDEC and IPC to release a tin whisker acceptance testing standard and mitigation practices guideline intended to help manufacturers reduce the risk of tin whiskers in lead-free products.[10]Silver whiskers often appear in conjunction with a layer of silver sulfide which forms on the surface of silver electrical contacts operating in an atmosphere rich in hydrogen sulfide and high humidity. Such atmospheres can exist in sewage treatment and paper mills.(Another such atmosphere that is high is hydrogen sulfide gases and involve humidity is at the deep sea vents at the bottom of the ocean. So very small deep-sea submarines or so submersibles such as the ALVIN may also be susceptible.)Whiskers over 20 µm in length were observed on gold-plated surfaces and noted in a 2003 NASA internal memorandum.[11]The effects of metal whiskering were chronicled on History Channel's program Engineering Disasters 19.image from the link below:Doctoral student unravels 'tin whisker' mysteryYong Sun, a mechanical engineering doctoral student at the University of South Carolina's College of Engineering and Computing, has solved part of the puzzle.…Sun's findings were published in the Scripta Materialia, a materials science journal. This fall he won the prestigious Acta Student Award, one of only six to receive the honor. A team of editors from Acta Materials, Scripta Materialia and Acta Biomaterials evaluated the applications and Sun beat out students from the world's top universities, including MIT."This shows that our research in material science is reaching an international audience," Sun said. "It is nice to be recognized for our work."The importance of that work goes well beyond extending the operating life of consumer electronics. NASA has verified multiple commercial satellite failures it attributes to tin whiskers. Missile systems, nuclear power stations and heart pacemakers also have fallen victim to tin whiskers over the past several decades and they are also considered a suspect in reported brake failures in Toyota vehicles.While manufactures had been able to control some whiskers by mixing small amounts of lead into tin solder, the 2006 European Union ban on lead in most electronic equipment had ignited a debate among scientists about whether whiskers would remain a perpetual problem. Some observers even predict that it's only a matter of time before miniature devices built after the ban start failing en masse.Xiaodong Li, a professor in USC's Department of Mechanical Engineering who served as an adviser on the research, said Yong's work likely will prompt manufacturer to design lead-free products that diffuse stress."This (research) is a very big deal. As we move toward nano-scale devices, this is a problem that needs to be solved," Li said.Read more at: https://phys.org/news/2012-12-doctoral-student-unravels-tin-whisker.html#jCpFinally, it should be noted that IPC, the industry standard setting organization for electronic solder joints, has received and documented examples of 63Sn/37Pb solder with tin whiskers, provided by documented cases from NASA and Goddard Space Flight.So even the usual solder used for aerospace application has been demonstrated to present a potential for tin whiskers if the unit was ultimately retrievable.My first experiences with soldering did not include any mention of safety or the implications of heavy metals, but played with my elder brother’s soldering equipment when he took a course on electronics. I played with solder casually, didn’t even wash my hands, so I look back and wondered if I had been exposed to more-than-healthful levels of lead.There are many threats that are toxic to biological life forms, many of which are never publicized or addressed. The article I recently added mentions that there have been few or singular solutions to mitigate the problem of tin whiskers, besides adding small amounts of lead to mitigate tin whiskers and device failure in the field.Tin whiskers have also been documented by NASA for aerospace electronics on Sn63Pb37 alloy, the standard military/aerospace solder alloy, in very-long-service satellites.It’s “two steps forward, one step back,” (adding lead minimizes the problem better than any alternative)while the good intentions may be misplaced in the first place and possibly a hindrance to engineering pursuits. In the case of cardiac pacemakers, I would think that lead has a sufficiently good reason to be used, perhaps with special insulation, polymeric, or conformal coatings, the RoHS directive in medical devices may be overly rigid when exceptions should be made, such as with pacemakers.Thank you for reading