Thermal Characterization of Multi Stack Packages Using Linear Superposition Method

As the mobile products have been developed, many devices of various functions should be packaged into the limited space. Therefore, stacking multi-packages is needed for small form factor. Compared with discrete packages, multi stack packages (MSP) can provide better solutions for power saving, EMI reduction, max frequency up-grade in spite of its higher cost, low test yield, poor quality assurance, and more complicated manufacturing process. But, stacking many packages in confined space has raised concerns related to heat dissipation, which has become one of the most serious problems in the design of MSP. Accordingly, a method to obtain Tj for each chip from the power inputs is needed. This is quite significant at the MSP promotion and design stage, though the temperature value would be changed by system environment. In this paper, a new approach to determine the junction temperatures of the MSP is proposed. The average temperature of the chips was calculated by RSM, and the temperature difference from the average temperature was calculated by linear superposition. Using this approach, one can calculate device junction temperatures simply and accurately