Abstract
The author describes an experimental investigation in which measurements of junction-to-case thermal resistance, theta /sub 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 theta /sub 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 theta /sub 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.

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