Hi Werner
Thanks for replying. My question relates specifically to a heatsink bonded
to the rear surface of the silicon die on top of a Motorola Power PC (which
uses IBM C4 technology) on a ceramic BGA substrate. The silicon surface
area available for heatsink attach is approximately 10mm square and the
chip power dissipation is 7W.
For previous generation (non BGA) products we used adhesive thermally
conductive tape bonded to the top of the ceramic pasckage, which worked
fine as the surface area was about 30mm square. With the BGA package
structure the bondable area is down to 10mm square but the heatsink has to
stay big (20mm square) to get the required heat dissipation.
Motorola sort of recommend mechanically clipped heatsinks, but these are
not practical in our application due to constraints of size and
availability, leaving us for at least the short term with the need to find
an adhesive that can cope with the mismatch in CTE. Tape does not give
enough bond strength.
We are doing trials at present with Berqquist LA1000, a thermaly conductive
low modulus adhesive, which gives good bond strength. The manufacturer
offers versions with glass beads (4.9mil or 7mil) for control of bond line
thickness, which may or may not be useful.
We would like to know more about the long term reliability aspects of this
adhesive. Does anyone have any data in similar applications?
Regards
John
At 18:30 17/11/98 EST, you wrote:
>
>Hi John,
>In a message dated 11/17/98 12:56:44, you wrote:
>>Does anyone have practical experience of the effects of thermal expansion
>>mismatch on a thermally conductive glueline between a silicon die (in our
>>case, Motorola MPC740 BGA Power PC processor) and an aluminium heatsink?
>>
>>We have looked at several adhesives, some of which are much more compliant
>>than others, and are looking for criteria on which to base the final
>decision.
>
>The answer to your question is: It depends (not meant to be funny).
>The higher the power dissipation, the more temp cycling (testing?), the
larger
>the silicon die, the more compliant your die attach needs to be.
>What are you electrically connecting these die to?
>
>Werner Engelmaier
>Engelmaier Associates, L.C.
>Electronic Packaging, Interconnection and Reliability Consulting
>7 Jasmine Run
>Ormond Beach, FL 32174 USA
>Phone: 904-437-8747, Fax: 904-437-8737
>E-mail: [log in to unmask]
>
>
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