Datasheet
DD2.X
Preliminary
PowerPC 750CL Microprocessor
5.8.3 Adhesives and Thermal Interface Materials
A thermal interface material is required at the package die-surface-to-heat-sink interface to minimize the
thermal contact resistance. For those applications where the heat sink is attached by a mechanical means
(not adhesive), Figure 5-9 on page 60 shows an example of the thermal performance of three thin-sheet
thermal-interface materials (silicon, graphite/oil, floroether oil), a bare joint, and a joint with synthetic grease,
as a function of contact pressure. As shown, the performance of these thermal interface materials improves
with increasing contact pressure. The use of synthetic grease significantly reduces the interface thermal
resistance. That is, the bare joint results in a thermal resistance approximately seven times greater than the
synthetic grease joint. Customers are advised to investigate alternative thermal interface materials to ensure
the most reliable, efficient, and cost-effective thermal design.
An example of heat-sink attachment to the package by mechanical means is illustrated in Figure 5-7,
Package Exploded Cross-Sectional, on page 56. In this case, the synthetic grease offers the best thermal
performance considering the low interface pressure. Of course, the selection of any thermal interface material
depends on many factors: thermal performance requirements, manufacturability, service temperature, dielec-
tric properties, cost, and so forth.
Version 2.5
System Design Information
Page 59 of 70
December 2, 2008
IBM [ IBM ]
