Hi TNLF-ers,

please have a look at http://stevezeva.homestead.com/files/Ioan_Ball.jpg , many thanks to Steve again.
What can I tell you: no-clean SAC305 at the bottom, the balls read a sort of SAC with 3%Ag and 1.75%Cu
The reflow profile seems to be OK, I measure 246C under the periphery of the BGA, with a thermocouple that is squeezed there. I know it is not rigorous, I did not drill, I am not measuring inside the joint. But even if I am 20C off, the materials should be molten and coalesce, isn't it?
The intermetallics solder paste - PCB pad are OK, the wetting is good, the BGA balls seem to have changed shape, they are almost collapsed, there is physical contact between the balls and the paste, but no joint.
The question is: why do I see the separation line? What can cause that? Should I bother investigating the process, or do I have a sort of contamination? Or the BGA ball alloy has a higher melting point?
Thanks,
Ioan




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