Peter,

You bring up an interesting point. I got involved in an almost hopeless
situation, as usual and love so much, involving incredibly poorly designed
MLB's with interesting BGA's. We've gone over most of this drama before.

First, I don't like tenting/masking over vias of any kind. Second, I like
using blind dogbone vias, temp mask, selective solder pallets, double sided
reflow when possible, and/or solder shields beneath BGA's to prevent solder
welling/wetting up BGA dogbone vias and shorting out my balls - all this not
necessarily in that order.

Question is, what are some good design guidelines so solder shields can be
used under BGA's on the back side if one has to use through hole dogbone
vias? It must be kinda like the .200" keep out for the rework process but on
the back side?

Do you have any thoughts?

Earl

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