Collapsing or not collapsing balls? Solder alloys used? Flux activation procedure? Built-in moisture in paste? Coplanarity? Warpage? Black pads? Oxides? Protection gas? Etc. Seem to be a number of causes for 'voids', both big and small ones. From thermomechanical point of view minor voids seem to be a  minor problem (Wassink, Manko etc)in most finepitch joints. We think the problem is to find what KIND of void. If the void is caused by bad wetting or dewetting I think there could be a problem. So, you have to have some distinction between 'good' and 'bad' voids.  Dewetting voids next to the pad interface can't be healthy, while voids on inside of a normal solder joint are widely acceptable. Closer identification of void nature isn't a peace of a cake, you need market's best Xray and possibly also a Sonoscan or other laminograph. Will be interesting to see what TN's gurus will add here...

Ingemar Hernefjord
Ericsson Microwave Systems

-----Original Message-----
From: Thomas Han [mailto:[log in to unmask]]
Sent: den 16 oktober 2000 23:49
To: [log in to unmask]
Subject: [TN] voids in BGA


Hi all,  Customers are finding some opens in the PBGA(292 pin 1.27pitch)
that we installed for them.  X-ray shows good even reflow, but has some
small voids in some of the connections.  The gentleman that took the xray
for us tells me that the voids are caused by moisture in the paste, but
that shouldn't cause opens.  We are running an OA process, and the BGAs are
processed thru PnP and forced convection reflow.  I have increased the ramp
temp and that didn't seem to help.  The profile looks good with reflow of
about 55sec(time above 183C) with max temp at 225C.  The whole profile is
about 4.5min.

Any input is greatly appreciated.

Tom

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