I'm curious what people are using for 0.4 mm pitch BGAs:

 - Copper pad diameter
 - Soldermask or non-soldermask defined?  If NSMD, what size soldermask opening?
 - Paste stencil thickness and aperture size (round or square?)

I'm playing with different designs and it's quite a balancing act between pad size, board suppliers' soldermask registration tolerances, and having pads large enough for suppliers' via in pad design guidelines.  One option is to get rid of soldermask completely from under the part since, except for the outer row, there's no room for trace routing on the outer layer anyway.

Scott Post
Staff Manufacturing Engineer
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana    46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)

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