Bob,
I assume you are working with CBGA? what sort of stand off, package
size etc are you looking at, is it fully populated, or is there a "naked
zone" by the die edge (always liked that phrase, don't know where it came
from, don't hear it often but it brings a smile to my face every time)
sorry, are you cleaning before underfill or using one of them funky flip
chip no clean chemistry type affairs?
During discussions in RL, I was told (so take this with a pinch of
salt) that when selecting an underfill the cure schedule is of critical
importance, if its a high temp fast cure, you run the risk of creating a
material that is quite rigid at operating temps, which can actually decrease
solder ball life, similarly, if you use to low a cure, the epoxy is too soft
to do any good, and when it hits Tg it expands like mad, and can still
reduce life. I gather that these are less of an issue with flip chip and
CSP etc as they are so damn small, but with BGA the large amounts of
material make it an issue. I guess if you're working with PBGA it could be
even worse due to the flexibility of BT compared to a ceramic inetrposer?
Also, isn't this expensive?
Regards,
Roger
Roger Massey
Materials Technologist
Motorola AIEG
UK
-----Original Message-----
From: Bob Vanech [mailto:[log in to unmask]]
Sent: 26 October 1999 07:20
To: [log in to unmask]
Subject: [TN] BGA Under-fill
To Jeff, John, HGross, Kelly, Vidya, ETC.
Quick thank you for your vendor information.
Still need any BGA under-fill guidance that is
out there in TN land of the assemblers. How
about it Kelly? I would think that you might have
some experience in BGA under-fill, or was it too
painfull to remember and you've blocked it out
of your memory?.. ;-> Any war stories would be
appreciated. Have a great Tues.
Regards,
Bob Vanech Bob
BVAN Enterprise
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