Luckily, it's a qty of 25 boards.  For now, I'm avoiding 1mil wide
traces or 1mil diam holes (or similar), as I don't know what that would
do to the cost of the board (other than drastically increase it).

Shawn Upton, KB1CKT
Test Engineer
Allegro MicroSystems, Inc
[log in to unmask]
603.626.2429/fax: 603.641.5336

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Thursday, March 15, 2007 8:40 AM
To: [log in to unmask]
Subject: Re: [TN] Chip Scale Packagine (CSP)

Of the .1 mm paste deposit, about 50% by volume is metal. The rest goes
away, leaving about .05 mm of solder spread across the other BGA land
patterns. The solder mask protecting the land that you want to remain a
no-connect will be about .05 mm thick. The solder balls should collapse
about 25% from .2 mm to .15 mm. I expect the ball will contact the land
pattern an you will be relying on the solder mask to create the
no-connect condition. 

In prototype stages this may be tolerable. In production, it will be a
problem. Remember Murphy was an optimist.  

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