Thermo-mechanical stress analysis

This paper reports about the development and application of a new test chip for stress analysis in microelectronic packaging processes and reliability tests. Special focus will be on transfer molding with epoxy molding compound (EMC). The CMOS based stress sensor is able to measure in-plane normal stress and shear stress on the chip surfaces with an absolute stress resolution of plusmn 3 MPa. By the use of a multiplexer and an array of measuring cells on the chip surface we are able to sense temperatures and mechanical stresses space-and time resolved. We analyzed 1^st and 2^nd level encapsulation methods by transfer and injection molding and performed an in-situ relaxation and stress monitoring of the packaged sensor during temperature load and moisture uptake. The experimental results will be compared with numerical simulations. In substitutive application for electronic parts, the test chip implicates a major potential for investigating production processes and lifetime impacts on MEMS. Adjusting material combinations and optimizing packaging processes to achieve reliable products will be the applications on focus in future.