Examination of Mechanical Stresses in Sensor Devices Induced by the Molding Process

Metrological Instrumentation

The reliability of sensor devices is particularly determined by mechanical stress due to encapsulation. In this thesis an X-ray diffractometer has been realised, that allows the three-dimensional stress state to be analysed in the single crystal silicon substrate of encapsulated chips. This requires different innovative aspects to be developed and approached. Only hard X-rays (>15 keV) can penetrate through the injection molding. Because of the special sample geometry only high order Bragg reflections are available. Therefore it was essential for this experimental setup to optimise the Bragg peak intensity by a combination of a microfocus X-ray source and a specially adapted capillary optics. For a reproducible sample alignment the implementation of an X-ray examination system is necessary. The diffractometer has been developed with a hexapod as sample holder. This feature makes it well suited for different shaped chip packages and spatial resolved measurements. The X-ray stress analysis provides the verification of a piezoresistive force measurement chip, which passes through the packaging process in place of the sensor device. For different packages the results of the X-ray stress analysis have been compared with the results obtained by the force measurement chip and a good qualitative agreement has been reached.

TU Braunschweig
Ph.D. student: