Gaby,
   In a previous life, IBM, I saw a similar type BGA defect on several cross
section.   The x-ray revealed irregular shape bumps.   Temp. parameters were
characterized, etc.  The works.   After all the dust settled it came to be a
plugged stencil on the PCB side.   Insufficient solder paste/flux to reflow
the bump to the PCB pad.   This clue came about after several samples
exhibited the same anomaly, PCBA date code dependant.   Others vendors of
the same product line and technology did not exhibit this type of defect.
The stencil was found to be restricted.

Food for thought.

Victor,

-----Original Message-----
From: Gaby Bogdan [mailto:[log in to unmask]]
Sent: Wednesday, June 26, 2002 2:55 PM
To: [log in to unmask]
Subject: Re: [TN] Reflow on Wave.


Maybe this article will help.
http://www.alphametals.com/products/solder_solutions/pdf/pillowhead.pdf

Gaby

----- Original Message -----
From: "Henry Rekers" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 26, 2002 4:07 PM
Subject: [TN] Reflow on Wave.


> Does anybody have any suggestions on avoiding reflow of a 357 ball bga on
> the wave?  I'm dealing with a 6 layer board and I've kept the preheat as
low
> as possible.  Kapton tape doesn't seem to help.  Has anybody tried any
> custom manufactured sheilding?
>
> Thanks.
>
> Henry J. Rekers
> Manufacturing Engineer.
>
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