I've seen problems with solder wicking from the BGA (.050" pitch) solder joint
down attached vias when no solder mask dams or when small solder mask dams,
i.e. .005" have been used.  Result can be a low/no volume solder joint.   

With a good design and effective SMT process controls in place, my opinion is
that capping vias on the component side of .050" pitch BGA mixed technology
assemblies is not necessary.  But will the same hold true for finer pitch,
.030" or less, BGA assemblies?  I haven't developed an opinion on that
subject, yet.

Tracy Tennant
Micron Technology, Inc.
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                                                              Message#   473671
                                                         7-NOV-1996 20:35:17.14
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Subj:   Capping vias for BGA's

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Date: Wed, 6 Nov 96 08:27:51 EST
From: [log in to unmask] (Charles Elliott)
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Subject: Capping vias for BGA's
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Hello,

My questions has to do with the capping of vias for BGA's.

Why is it recommended that vias be covered on the component side of
BGA boards ?

What are the implications of not following this recommendation ?

Thanks in advance for your input.

Charles Elliott
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