Development of a Self-Monitored 3D Stress Sensor for Adhesive Degradation Detection in Multilayer Assemblies

In this paper, a novel technique is proposed to provide a 3D piezoresistive MEMS stress sensor with a real-time self-monitoring of its bonding status. Perceiving the degradation of this interlayer due to different environmental parameters is crucial for reliable electronics and sensors assembly. The utilized sensor is featuring strain technology to fully extract the six stress components. Whenever a multilayer assembly, such as a sensor on a structure, is subjected to thermal or mechanical load, out-of-plane shear stress will accumulate at its edge as a reaction for peeling. As any degradation in the adhesion layer causes a significant reduction for out-of-plane shear stress, the capability of the 3D chip to measure this stress is employed to detect the degradation of the adhesive layer. To verify the capability of the current concept to experimentally quantify this loss, thermal energy is exploited for softening the bonding film. Losses up to 28 % for the out-of-plane shear stress are detected at a temperature equal to 80°c, which causes 71.9 percent decrease in the modulus of elasticity of the utilized adhesive. This significant correlation, between the out-of-plane shear stress loss and the bonding layer stiffness, is used to obtain a full picture of the adhesive deterioration in an early phase. The same technique can be utilized as a low profile detector for the debonding in multilayer electronics.