Re: Help me fix my latest IC7000 failure


montanaaardvark
 


I'd go with the first one.  I've heard of it, but I don't remember seeing one.  It may be that I saw one and forgot about it, although we tend to remember the weird things and not the everyday.

It's possible for chip resistors to be manufactured shorted, but I don't know how they grow shorts and go bad.  It may be that the circuit board can grow shorts because certain solders can grow whiskers or dendrites that short out parts. That depends on time, temperature, humidity, and the type of solder.  That was more common in the early days of lead-free solders, which was around '06 to '08 (very approximately).  Coincidentally that's around the time the 7000 was in production.  

Because we refer to parts being solder coated as being "tinned" it's ironic that the worst solders for growing whiskers were bright tin solders.  Matte tin solder was better, but still not as good as tin-lead. 

I think the European Union was first to introduce laws against tin-lead solders.  The impact on reliability was anticipated; they knew consumer items would fail earlier, but they made specific exceptions for high-reliability stuff like military, space, and civil aviation (where I worked).  The problem was that the people who make components don't want to retool their line for different manufacturing lots of parts for the small market instead of just making different values for everyone, so the high-rel companies had to figure out how to solder the lead free parts onto circuit boards and ensure the leads were covered with solder. 

Being typical regulators, they went after the molehill and not the mountain; the tiny amount of lead used in solder vs. the lead used in batteries.  The total world use of lead is about 90 percent for batteries, and the amount used in electronics (excluding batteries) is all of 2 percent. Further, of the lead in landfills (supposedly what they're trying to reduce), the overwhelming majority is coming from the disposal of TV CRTs and monitors, which can contain up to 2 kg of lead per tube, not from circuit board assemblies, by a massive ratio of 9 to 1.

To reduce the amount of lead in landfills, they went after the tiny amount of lead in solder, and increased the amount of junk in total that would go to the landfills because of the lower lifetime.

Some industry chatter that may be informative.
https://www.aviationtoday.com/2012/07/01/system-design-death-by-tin-whiskers/ 
https://nepp.nasa.gov/WHISKER/background/  (I think this one is worth reading)
https://nepp.nasa.gov/whisker/dendrite/index.html


73,
Bob
--
W4ATM - 35 Miles south of the Kennedy Space Center
Retired RF Design Engineer
Now able to play with all the hobbies I never had enough time for

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