Hello Guys?
Can anybody explain the separation of Solder Bump from UBM after the
Assembly Process?

Solder Bump=95Pb5Sn Alloy
It is plated on a wafer with Under Bump Metal (UBM) of TiCuNi. It then
reflowed to form a bump (And is Fluxed).

The bumped wafer then assembled, after assembly there were weak bumps which
some of them separated from the UBM.
Can you explain this phenomena? would this be intemetallic effects? Is it
possible to have this phenomena that is caused by mechanical vibration plus
the heat applied?
By the way the reflow profile had a peak temp of 285 C.

I can't figure out yet why this happened?
Any inputs would lead me to solve this problem

regards

Jonathan

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