Thermo mechanical behaviour of dies in multi material stacks

CiS Research Institute for Micro-Sensors and Photovoltaics is an R&D service provider that carries out the development of micro-sensor solutions from system design to prototyping for industrial enterprises. The main focus of the actual assembly and packaging development is the miniaturisation of smart sensor systems. Three-dimensional integration is a promising solution to meet this goal. New materials in combination with flip-chip techniques can help to realize such modules. But high demands for long-term stability of the electrical signal quality have to conform to demands for smaller size of the complete module. However, the mismatch of thermo-mechanical properties in stacks combined of different materials leads to stress during assembly and lifetime. This limits the reliability and signal stability of such sensor systems. Endurance tests in combination with finite element analyses of deformation and inner strains can help to understand the influence of material properties and to optimise design and assembly processes. Additional use of MicroDAC (Micro Deformation Analysis by means of Correlation) stress chips is possible. With this kind of in-situ measurement it is possible to verify simulation results and optimise thermal processes of assembly. Results of measurements and simulation show the way to create low stress packages and improve lifetime as well as signal stability. Especially chips made of new LTCC materials with adapted CTE show advantages. The investigation can help to adjust design and processing of mixed materials stacks for sensor applications.