Thermal evaluation of simulated finish and flatness conditions typical to MCM and MPU applications

This paper describes the variation in contact thermal resistance under controlled and measurable finish and flatness conditions. Special test fixturing was developed to control the mounting pressures while measuring power levels and temperature differentials between hot and cold plates of materials under test. The test platform for this test series was a pair of two inch square aluminium blocks which approximated the contact area of higher power level MCMs or MPUs with their heat sinking devices. Test power levels ranged up to approximately 20 Watts per square inch. These tests were specifically directed at the variable thermal interface conditions relating to surface finish and flatness. Using the simulated microprocessor platform, parametric studies were conducted for different controlled finish and flatness conditions and interface materials as a function of uniform applied interface pressure. Test results showed that both realistic surface flatness and finish conditions have a marked impact on component thermal performance