Phil- DON'T

Check out John Lau's book on the BGA solder joint reliability. It kind of
says that the joint will fracture somewhere around 17psi if I remember
right. Also, why the big heat sink? Repackaging sounds like a cleaner
soltuion. There are BGA package options out there today that routinely
handle 8 watts without any heatsink, and maintain junction temps well below
125C. Sounds like a 'special' application...

-----Original Message-----
From: Phil Bavaro [mailto:[log in to unmask]]
Sent: Monday, October 04, 1999 6:08 PM
To: [log in to unmask]
Subject: [TN] BGA Solder joint compression


Ok, before I get hammered for posing this question, let me say that
my answer is  "Don't do it, solder will creep and it will short out".
Anyways, here is the question:

Some of our designers have come up with a design using about eight
560 BGAs as well as many other SMT packages on a board which will be
pressed up against a sheet of thermal tranfer type spongy material
which is then pressing against a solid metal chassis.

They are worried about dissipating 6 watts per BGA and therefore need
to envelope the thermal pad around the BGA by applying 30 psi
according to the spec sheet.  This part is only 1.5" square so I
calculate that we need to apply approx 65 pounds of pressure to the
component.

I take this to mean that they want to compress the solid tin lead
solderballs with this huge amount of force and believe that this will
definitely cause the solder to deform/creep.

Any comments (please be nice....).


Phil

Phillip A. Bavaro
QUALCO/\/\/\/\  Incorporated
Manufacturing Engineer, Staff
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Cell (619) 602-8644 (offsite, after hours)
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Tel (619) 658-2542 Office/voice mail
Cell (619) 845-9968 (workday)
Fax (619) 658-1584

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