Earl, Romeo, Jim,
Thanks for the good responses. You have given me several paths to consider
beyond what I have already thought of. I have a call in to Motorola to
verify the alloy they are currently using to make sure that hasn't changed.
Oxidation is certainly a concern. I am running the KIC again to verify my
profile regarding preheat, reflow, etc. Although, we don't see this problem
on every board. So far, about 50 boards out of 1000 built over the past two
weeks. Not all the same date code part either. Thanks again.
Bob
Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679
email: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
Sent: Wednesday, November 15, 2000 12:29 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Soldering Problem
I guess pictures would be in order. Verbally, it seems your paste is wetting
as required to the pads but what's with the "mounds?" The solder balls are
deforming but "smershing" down into the COMPLETELY melted solder paste as if
displacing it. So, what's wrong with the missing picture? Why are the solder
balls incapable of wetting? Contamination? Oxidation? Wrong alloy?
I see your HASL finish as acceptable and wetting normally. What's with the
tinned and fused finish. Is it really tin/lead plated and fused?
Anyway, besides the possibility of the solder balls being incapable of
solder wetting, what is the recommended solder paste profile and how close
are you to it - really? And, again, the corner balls will be hotter causing
them, most often, to collapse first though this is dependent upon the rest
collapsing or a non-parallel device to substrate condition will exist and
will be easily seen - leaving the rest to follow, including the ones
internal to the device and array pattern. In other words, the corner balls
will "melt" first but will not collapse until all others do the same
depending on number.
Earl Moon
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