Unfortunately, we can't send Rich HTML format, so my mail became ding-dong. 
I write it again, otherwise.


Many relationships are described, one of which is a Curtiss-Wright report. 
They have exposed identical boards to SnPb soldering/repair and compared 
with same for SACs, and found a significant difference in time to failure.



1st thermal cycle to failure for:
As received boards = 788

1st thermal cycle to failure for:
6 x 230 Celcius =  443

1st thermal cycle to failure for:
6 x 260 Celcius =  4



That is a dramatic change in via failures.  We have seen some failures 
recently on ordinary double sided FR-4 boards, which were exposed to several 
heat exposures in conjunction with electrical testing. Far from 260 Celcius, 
think only 125 Celcius. If we got microvia issues with only 125 C, what if 
we use 260 C (e.g. repeated repair)?

Has anyone seen any signs of via failure due to increased heat exposure in 
practice?


Inge
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