In-situ measurement of curvature and mechanical stress of packaged silicon

This study demonstrates a technique to simultaneously measure stress and strain of a CMOS silicon die in a thin standard package. Exploiting the highly anisotropic magnetic sensitivity of integrated Hall plates, a magnetic field is applied to measure the orientation of the die surface. This is applicable in-situ with the die assembled in the package and the package integrated into a module without any mechanical modifications. The only requirements are a non-magnetic sensor package and module, and a test chip with an array of Hall elements on the die surface. Moreover, the piezo-Hall and piezoresistive effects afford measurements of mechanical stress. The combined knowledge of stress and strain allows for deeper insight into the mechanical behavior of plastic encapsulated packages.