John:
We have a similar product from MEI (Flip chip, C4, in a cavity mold BGA,
die B/S exposed, running 8~9 watts). We put a heatsink/fan on this. Die
area is about 400 mils on a side. We are using Loctitie 315. This is the
same as L384, except the 315 has 5mil silica beads for self-leveling.
Most of our problems came early on from our board assembly houses not
following attachment instructions (this adhesive needs an activator).
Might try this...
> Bill Davis, Ph.D.
> Diamond Multimedia Systems
> Senior Scientist
> Tel. 408.325.7868
> Cell. 408.888.5650
> e-mail: [log in to unmask]
>
>
>
>
> -----Original Message-----
> From: John Loveluck [SMTP:[log in to unmask]]
> Sent: Thursday, November 19, 1998 2:26 AM
> To: [log in to unmask]
> Subject: Re: [TN] Attaching Al heatsink to Si die
>
> 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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