Hi Bob,
Can't answer all your questions, but another option to throw out there is a
"white tin" process.  A Super flat protective coating but not much being
said about it. You might want to ask around about its application to bga.

Good Luck,
JimWalton

-----Original Message-----
From: Bob Walker [mailto:[log in to unmask]]
Sent: Friday, April 16, 1999 9:32 AM
To: [log in to unmask]
Subject: [DC] OSP vs HASL


I've designed a board that has four BGA's on it, the smallest has 272 balls
while the largest has 600. The initial prototypes were made using the HASL
process, but after talking to a contract manufacturer about assembling the
production boards, he is recommending that I use an OSP process to keep the
BGA pads flat. I'm told that because of using the OSP process, there will be
some exposed copper after the boards have been completely assembled, but
that there aren't any negative effects of the exposed areas based on some
studies that he has read about. My questions are as follows:

1. Are there potential reliability problems with the exposed copper?

2. Is OSP a better way to go when dealing with BGA packages?

3. Since I've never dealt with the OSP process before are there any other
design considerations that I need to be aware of?

I'd appreciate any comments or recommendations concerning this situation.

Regards,

Bob Walker
Sandgate Technologies
[log in to unmask]

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