Polymer Die Attach Selection Criteria for Low Drift Inertial Measurement Units
Polymer die attach selection governs MEMS IMU bias drift by balancing storage modulus, glass transition temperature, and long-term viscoelastic stress relaxation.
Thermomechanical Shear Stress
Interfacial Stress
Mechanical force acting parallel to the interface of two bonded materials with different thermal expansion rates arises during temperature transitions. In electronic packaging and layered sensor assemblies, thermomechanical shear stress concentrated at the corners of the bonded area can cause micro-cracking or delamination. This stress occurs as a direct result of temperature variations across the assembly.
Thermal Expansion
When the temperature of a multi-material sensor changes, the materials expand or contract by different amounts. This differential expansion generates thermomechanical shear stress that can alter the calibration offsets of the mounted sensor. For instance, the stress between a silicon sensor die and its ceramic substrate can cause a shift in the sensor sensitivity.
Packaging Failure
Severe thermal cycles can cause these forces to exceed the shear strength of the adhesive or solder layer, leading to failure. This failure is a major reliability concern in high-power electronics and automotive sensors that must operate in extreme thermal environments. Engineers select materials with closely matched expansion coefficients to reduce the peak thermomechanical shear stress.
Metrological Tracking
Optical measurement techniques like digital image correlation or piezoresistive stress sensors embedded in the silicon die measure these interfacial forces during thermal testing. These measurements allow technicians to verify the thermal-stress models of the package against actual physical data. This verification is executed across the entire operating temperature range to map out the stress distribution.
The resulting data are used to optimize the selection of adhesives and curing temperatures, ensuring that the sensor housing provides reliable protection and maintains calibration stability over years of service.