Erni,

Have you done analysis of capacitors (removed them from PWB).  ICT may not
identify these as failures, depending on test program and pass/fail
tolerances.  These capacitors could be by-pass caps which means when ICT
checks the caps from VCC to ground you will get lump summations of values.
 Again depending on the tolerances of test values in program, several of
these could be totally cracked through the inner substrate and ICT will
pass them!

I would be concerned with crack propagation.  If PWB's are subject to
stresses from enviroment (hot/cold) then I would expect the crack to
worsen.


Things to check:

1.  Excessive thermal shock in Reflow or Wave (Moisture in parts)
2.  Excessive mechanical shock during depanel or handling
3.  Check Tooling support inside of automation, supports could cause this
(But since on top and bottom, most likely not)
4.  CTE mis-match of substrates


Tom B.
Manufacturing Engineer

> Greetings to all. We are currently experiencing cracking of the ceramic
> capacitors, on both primary and secondary sides of the PWB. The cracks
> do not appear to alter the electrical properties (PWBs pass in circuit
> testing), but we are concerned with long term reliability. Thermal
> profiling of all processes, and copying same in defect lab, has not
> reproduced the defect! The cracking appears randomly, and is spread
> across several vendors. Any helpful suggestions out there? Thanx for
> your time.
>
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