We've found HASL works okay for 1.27mm pitch parts but for anything
smaller our yields have been consistently higher with a flatter finish.
We've used both immersion gold and immersion tin with good results. As
somebody else noted, you need to monitor your board house's performance
but we've not had any issues in this area.  We currently spec one of
those 2 finishes for any boards with BGAs < 1.27mm or any QFPs < .635mm.

Rick Thompson

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Tuesday, November 06, 2001 2:16 PM
To: [log in to unmask]
Subject: Re: [TN] BGA's in design


Thanks to all suggestions.  I found a good app note on the Xilinx site
for Board Routability Guidelines for Fine Pitch BGA Packages which is
very helpful. As I expected, I got a few direct solicitations from board
fab places, mostly US, but no good testimonials of good experienced
Canadian fab houses. I really do not want to go across the border at
this time as we currently do not use any fab places outside the country,
and it adds a whole other level of complexity to shipping as well as
possible delays especially with heightened security these days. Regards,
Genny.

To open another can of worms, most datasheets or app notes have said
'use NiAu or OSP finishes'.  We have 99.99% of the time so far used HASL
(no BGA's), have been made very wary of NiAu and have never tried OSP.
We have tentatively approved immersion Tin as an alternate finish in
select cases but have not used it, and I'm hearing a lot about immersion
Ag these days.
Survey:  What do you use for your BGA board finish?

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