the silence is deafening. Guess I'll chime in.

At 06:02 AM 11/10/2010, Post, Scott E wrote:
>I'm curious what people are using for 0.4 mm pitch BGAs:
>
>  - Copper pad diameter

250um is typical

>  - Soldermask or non-soldermask defined?

yes. >:-}

>  If NSMD, what size soldermask opening?

Depends on uVia technology used.

1. Standard copper via in pad: 250um w/ 300um pad

2. ALIVH compromise:
•Via pad size enlarged to 300um
•S/M opening enlarged to 400um.
•S/M dam of 100um width added
• Accept Potential S/M encroachment one side of pad


>  - Paste stencil thickness and aperture size (round or square?)

fielders choice?  :-)

>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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