Fatigue strength estimation method of wire protected with silicone gel under vibration environment

Abstract

Silicone gel is usually applied to electrical automotive devices to protect them from corrosion. However, under a vibration environment, the silicone gel vibrates bonding wires in the devices; thus, to evaluate the reliability of the devices, the vibration analysis of the gel/wire structure is indispensable. In this study, we clarify the relation between the fatigue life of gel-protected bonding wires and the geometry of the gel and bonding wires experimentally. It was founded that the diameter of wires and the thickness of the gel have a significant influence on fatigue life. Then, we developed a method, based on a vibration analysis model that takes into account the visco-elasticity of a gel, for predicting the fatigue life of the wires. It was confirmed that the predicted fatigue life showed good agreement with the measured fatigue life. Finally, we developed a design tool for easily calculating the fatigue life of the wires. This tool estimates the strain range by using a response surface, i.e., a neural network. As Bayesian regularization was executed in learning of unknown parameters in the neural network, we could make the response surface and ensure good generalization ability.