Low CTE LCP for Ultra Low Stress Near Hermetic Package for MMIC Applications

摘要

A low cost, near hermetic, lighter weight than ceramic package with a low coefficient of thermal expansion (CTE) utilizing liquid crystal polymer (LCP) core substrate has been fabricated. An air cavity package is developed to reduce stress on die and warpage while providing better RF performance by reducing the dielectric environment to air. Initial prototypes include a heat sink of metal matrix composite (MMC) AlSiC material, 4 mils core of 5 ppm/K LCP and an LCP lid. The package outline dimensions are 4.0 mm × 7.65 mm × 1.0 mm. Two major issues were discovered during assembly process, the heatsink attach process due to tight dimensions has misalignment problems and caused warpage to the overall package due to pressure applied during assembly. The second issue is the LCP substrate bottom layer has a 5 mil recess from the bottom of heat sink, which does not match IPC standards of 4 mil maximum for level 2 packaging to the board. An alternative approach of embedding AlSiC material shows promise for overcoming the above two issues.