Solder finish has been HASL and also seen with "tinned and fused".

Solder wets to the pads AND there is evidence the ball reflows.

The ball is pushed against reflowed solder on the pad to point it's out of
shape
(water balloon to solder mound).

Defect is not always on the corner pad, but can be the 2nd, 3rd or 4th in
from corner.

Thru destructive analysis have seen at least one example of farther in under
the package (in 5 rows).

RKUBES

-----Original Message-----
From: Earl Moon [mailto:[log in to unmask]]
Sent: Wednesday, November 15, 2000 8:52 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Soldering Problem


Are you soldering to gold pads? If so, have you checked for the black
plague?

Earl Moon

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