Hi Peter,

We recently had some problems with voiding in the solderjoints of ceramic BGA's on pads with via's. Per design the via's are overplated with copper and leadtin, but the actual bare boards had some problems with dimples and sometimes bad overplating.
So for one batch we made notes of the pads that were not according to the design specificaytion, and afterwards we tried to correlate this with the voids. Correlation was 100%. No void if the pad was flat and had good plating, and voids (up to 50% in diameter !!) whenever the pad didn't look right.

Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

>>> Peter Lee <[log in to unmask]> 12/19 8:20 am >>>
Hello,

We have encountered major BGA voiding issue. The void is sometimes up to
70% of the joint. Under X-ray inspection we found a blind 0.006" uVia,
0.01" deep under each void. Other BGA solder joint on board w/o uVias do
not have any void problems. Board is gold over Nickel finish and 2mm
thick.

Things we tried:
Reflow profile - WS/ no-clean paste, longer soak
Washing/ baking the bare PCB
Reworked by cleaning the uVias/pads and filled with solder but still
seeing void

Has anyone seen this before? Micro-sectioning clearly showed the void
originated from the uVia. We are trying to convince the board house that
it's not our process.


Rgds,
Peter



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