TechNetters, I have a question regarding consistency of 7095 (Design and
Assembly Process Implementation for BGAs), SM-782 (the Surface Mount pad
document), and 7525 (Stencil Design Guidelines), resulting from discussion
with process engineers and techs earlier today.

We were looking at a BGA, 20x20 package, with 1.27 mm pitch.  The stencil
design guidelines (7525, Table 1 on p. 4), call for an aperture of 0.75 mm.
 That table also refers to a 0.80 mm pad.  SM-782 (section 14) says a 20x20
BGA will have 0.75 mm balls that should go onto 0.60 mm pads.  Do these
documents contradict each other regarding pad size, and is 7525 wrong with
regard to BGA stencils?

Further, the bare board does have 0.60 mm pads for the BGA.  7095, in
6.2.1, p. 33, says "land diameter is usually smaller than the ball
diameter..land size reduction of 20 to 25% has been determined to provide
reliable attachment...".

As always, thanks for any comments.  Lou Hart

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