Measurement and Simulation of Stacked Die Thermal Resistances

Packages with multiple dies provide additional challenges when documenting their thermal performance. One style of multiple dies packages stacks the die on top of each other with a die attach adhesive. This paper explores the thermal performance of such packages in a wire bond plastic ball grid array package with three different die configurations. The thermal performance of the package was determined using the JEDEC JESD51 specifications. Since there were three different effective die sizes, the data allowed a better validation of the finite element thermal simulation techniques than can be obtained with only a single die size. Die size is usually the most important predictor of plastic ball grid array thermal performance. In this case, packages built with the same materials and substrate had a Theta-JA (2s2p board, natural convection) that differed by 100% as a result of a change in effective die size. With a validated simulation method, additional power distributions were simulated and compared to results obtained by superposition techniques.