This paper describes a square ring on square ring (SoS) strength testing technique for reliability evaluation of ceramic pin grid array (PGA) packages. The unique features of this new technique are that the residual stresses are included in the strength results and that the package does not have to be cut, ground, or modified in any way to test the strength. The testing procedure is simple: after the fixture is calibrated for coplanarity, the package is placed in the SoS apparatus and force is applied until the ceramic fails. The ultimate force to failure is then converted into ceramic strength by using Finite Element Modeling (FEM). This paper also discusses failure analysis of ceramic packages that have been tested to failure with the SoS technique, ceramic strength and statistics, and verification of FEM models. The SoS apparatus consists of cantilevered beams and the free end of the beams come into contact with the edge of the package; therefore, the fixture conforms to the contour of the package during testing. This strength testing technique is currently being used to monitor the changes in strength and Weibull slope of PGAs. It is also being used for reliability evaluation of the heat sink side and cavity side of PGAs as received from suppliers and during the various stages of assembly/environmental processes.