Bob,
It is interesting that you have seen these effects in joints made with
Sn-Cu and Sn-Ag-Cu alloys, containing no Bi and presumably
uncontaminated by Pb.

The situation is very complicated of course between alloys, whether
contaminated or not.

1. The solidification shrinkage differs between alloys.
2. The strength and ductility vary between alloy systems, with
temperature of measurement, with thermal history and with sample
configuration.
3. The temperature at which these failures occur will vary with alloy
system and, I guess, type of defect.

Added to these, the adhesion of the copper to the circuit board will
vary with material and process conditions, in both manufacture and
growth.

I think that mechanisms can be devised to explain the various defects
you report. What surprises me is that Sn-Pb alloys do not show these
types of defect...or do they?

Roger Bilham

In message <000a01bff7d7$a5de45a0$0300a8c0@dell>, Bob Willis
<[log in to unmask]> writes
>    Interesting, is also probably even less well known that I have seen
>    fillet lifting in both wave and reflow of through hole
>    parts with SnAgCu and with SnCu in wave in both case the boards
>    were silver finish and we do not believe there was and lead.
>
>    The failures I have seen in my sectioning showed fillet lifting,
>    pad lifting and fillet tearing. To date no one has been able
>    suggest why this has occurred !!!

--
Roger Bilham

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