> The two biggest problems I've seen with lead-free solder are the difficul=
ty in
> distinguishing a good joint from a cold one and also the higher temperatu=
re
> needed to melt it.
>=20
> I was fascinated by a problem I had in a car once. I had owned the car si=
nce it
> was new and after 11 years the heater control started behaving erraticall=
y. I
> took it apart and found eventually that the problem was a bad or broken
> solder joint on a 1206 size resistor in the power supply which fed the
> microcontroller  (a PIC interestingly ). It amazed me that this would onl=
y
> appear after 11 years and was not on a large component which was subject
> to vibration. The joint was not visibly cracked - I suppose it is possibl=
e that
> part of the end termination of the resistor was bad - my recollection is =
that
> simply re-heating and adding solder fixed it.

It could just be the temperature cycling. Without knowing just which part o=
f the USA you are in the deep temperature cycling could do exactly what you=
 have described. Remember motor vehicles are one of the toughest environmen=
ts for electronics, hence why RCA and possibly others made special transist=
ors to use in the power stages of car radios.

For our ESA facility qualification for PCB assembly we have to have 5 sets =
of components put through a vibration run that simulates launch, and then d=
o a series of temperature runs which cycle between -55C and +125C and every=
 solder joint has to be good after a total of 500 cycles, done in batches o=
f 100 cycles with inspections between batches for solder cracks and other f=
ailures.

.... and that only gets you qualified for the PCB material used and the comp=
onents fitted. You can get 'tested by similarity' in that if you fit a 1206=
 and an 0402 resistor, and these pass, then 0603 and 0805 are considered qu=
alified by similarity, but in practice you fit them all anyway because you =
don't know if one end is going to fail. And if your test was done with \pol=
yimide laminate double sided, then this test does not qualify 4 layer, or F=
R4 double sided ...



--=20
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