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] > > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################