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Manufacturability and reliability of a custom CSP SRAM mounted on an interposer is discussed in this paper. In order to provide a reliable device for high reliability applications, an SRAM interposer structure was designed to ensure high reliability on every level of solder joint interconnects. Finite element modeling method was used as a mean to evaluate the reliability of various configurations of the protection methods. Test vehicles were built to run reliability tests on selected configurations from FEA simulation to evaluate the integrity and robustness of the SRAM interposer. An under fill process was chosen to be the protection method in production because of its reliability performance. However, extra efforts are needed for implementation during production in order to address the manufacturability concern.