Pure tin tinning on a component which should have had derogated Pb/Sn tinning? The normal RoHS cheap component getting into the premium priced aerospace/military/medical traditional-solder product stream?
"The problem was related to a cracked solder joint caused by exposure to extreme temperatures."
If I were to render an opinion, pure tin as a mechanical joint is a very ba d idea, nor would I think that a sophisticated manufacturer would do that a s a matter of intent. Pure tin is extremely brittle, and should NEVER be de pended upon in any sort of situation where mechanical stresses (expansion/c ontraction/flexing) will take place. Add to this the whole issue of tin whi skers (which NASA, at least now understands all too painfully). If what you suggest is accurate, this is a design flaw of significant magnitude. If it is present fleet-wide, it is time to ground these beasts until the problem is addressed specifically.
I would hope that aircraft manufacturers by now would have learned that som e admixture to their solders is a necessary step to reliability. And would have learned by now from the Nuclear industry if not NASA that relying on p ure tin is a dangerous practice.
All-and-at-the-same-time, counterfeit parts are getting into the OEM repair stream at every level. It would not be difficult to believe where such par ts may get into the OEM first-install stream as well.
I know from someone in the medical electronics field, that is extremely difficult , if not impossible, to guarantee that PbF components do not get into the derogated product stream, without sample chemical testing of each batch of componnts, done themselves. The supposed accredited documentation is easily compromised and cannot be relied on. With all the extra markup on derogated components, plenty of motive.
In 1990 a US fastener company, Voi-Shan, admitted to supplying thousands of fasteners for aerospace use that were in essence counterfeit in that they had not been tested and were of inferior quality. They falsified inspection reports and even made up names of the inspectors. These fasteners were used in airplanes among other places. So even a large company will supply crap that is meant to be used in life critical situations. If I was making medical devices, or anything that might hurt or kill someone, I would check all the components supplied from others. Eric
I remember the big stink at the time because I was making helicopter and turbine engine parts. Really fussy stuff. When it hapened I remember they started checking all the VSI supplied fasteners and a whole bunch were below the FAA requirements for strength and proper plating. I was talking to an FAA inspector who was checking some shafts I made and he said the FAA was REALLY pissed off. The parts I made were small enough quantity that they were 100% inspected and the FAA inspectors would drop by from time to time to check our inspection procedure and numbers. VSI made such huge quantities, hundreds of thousands of parts, that there was no way to easily check for bad parts intentionally supplied. I'm still pissed off about VSI because they risked the lives of the people flying planes with their fasteners on board. Eric
Back in the day, I worked for a small, family-owned machine shop in Philade lphia that made aircraft and nuclear reactor seals - including liquid sodiu m pump seals for the French power industry. Each day the Foreman would come onto the shop floor and yell out: "REMEMBER, you are being paid by the HOU R, not by the PIECE!" The message was "GET IT RIGHT, take your time to do s o."
Each piece left the shop with the _actual initials_ of every person that ha ndled it on the internal work-sheet. And, the actual signature of the final inspector. The company is still extant (40 years after I left), still payi ng good, living wages to its workers, still family owned, and still operati ng on the same philosophy.
It is here where I learned the specific difference between a carbon-stretch er and a sky-hook.
so what happens in a well run shop when everybody was trying their best, but the fasteners were bogus? For say liquid sodium pumps for the nuclear industry does each critical fastener get some sort of proof test?
If I were to render an opinion (you'll probably agree) there is a differenc e here. THIS IS AN AIRCRAFT NOT A TV SET ! DAMMIT !
They should be using the solder used back in Tektronix scopes, lead/tin and 2 % silver, or maybe more perce3nt silver.
Lead free solder exists in consumer electronics because it gets to the land fill so fast. And stoooopid people htink it gets into the water. That kind of lead does not, I have a lead buyllet in my body and I have no lead poiso ning. That comes from the salts and compounds of lead. Solder is NOT that.
They just got more planned obsolescence now. More sales in the future. You will rue the day you got rid of your old Toshiba CRT TV. You will rue the d ay you got rid of alot of things., Old lawnmowers that used ignition points . They ran after a thunderstorm. (the electronic modules in the newer ones were too susceptible to mini EMPs caused by lightning strikes, until people got pissed off and made them fix it of course, and it ain't really fixed I guarantee)
We made carbon-faced seals in one part of the shop - carbon is rather an un forgiving medium in any form. Something that got too small... well, you get the picture.
We purchased our fasteners from SPS (Standard Pressed Steel at the time). T heir factory was less than 8 miles up the road in Glenside, PA. Several of the workers in our shop would go to their shop and work on the line with t heir people for our orders, just as I went to the heat-treat shop a few mil es from SPS to supervise the heat-treatment of some of the critical parts, sometimes days at a time. Both SPS and Dreaver (now Evans) are still in ope ration today, and still have such intimate relationships with their custome rs. We took great care with the parts we made, and every part that went int o them. Some parts took very nearly two (2) years in production.
Was there political reasons behind no mention in that report about the exact nature of the solder crack? If I was on the analysis team I would have demanded much deeper exploration of the fault. I assume I'm not unique, so was it done , but the result supressed in this otherwise thorough report?
This is a macro-pic of a PbF solder ring crack I took a few years ago, when generally in repair jobs , it started becoming obvious there was a problem with PbF and vibration or thermal-cycling, in operation, after just a few years. Traditional Pb/Sn solder could also get ring cracks but after more like
Inappropriate hole dimension wrt to the diameter of a component pin is far more likely to end up with a ring crack than with traditional solder, with or without plated through pcb production.
I had to fuss with graphite shaft seals a couple times. Yuck.
Interesting. Sounds like you were hands-on with all parts and processes, even external ones.
Larger companies on the other hand probably just have to trust the initials on a test report as long as the 900 barcodes on the packaging scan correctly. I wonder how long it would take Beoing or Digikey to pull bad parts from the warehouse.
In that pic, X, is the component pin. I assume the crazing/furrows at different angles, is related to that sudden freezing optical effect of PbF going solid. Traditional solder just goes from molten to solid with no visual change to the surface appearance. The outer section of the solder blob does not have that crazing, so perhaps differential stressing is built in , before any operational stresses.