Effect of case temperature measurement errors on the junction-to-case thermal resistance of a ceramic PGA

The author describes an experimental investigation in which measurements of junction-to-case thermal resistance, θ_jc , of a 132-pin cavity-down ceramic (PGA) pin grid array package are compared to finite element (FEM) calculations. The initial goal of this work was to validate FEM predictions of θ_jc with measurements in accordance with the established SEMI and MIL standards. A serious problem was discovered in measuring accurate case temperatures, resulting in poor agreement between measured and predicted θ_jc. Detailed 3-D FEM simulations were used to analyze thermocouple measurement problems in the region between the case and cold plate. New methods were developed using fiber-optic thermometry and surface-junction thermocouples