Simulation procedure to improve piezoresistive microsensors used for monitoring ball bonding

For the first time, an integrated piezoresistive, microsensor, used for mon itoring ball bonding, is rigorously simulated. The sensor is based on a CMO S n(+)-diffusion and located in situ below a standard bonding pad. It measu res a value related to the ultrasound stress which is dissipated during bal l bonding. We report on a two-dimensional (2D) simulation tool based on the implementation of the governing equation using a finite difference scheme and taking into account the stress-induced local variations of the conducti vity tensor. This tool calculates sensor's sensitivity and electrical poten tial distribution from piezoresistive, coefficients and previously simulate d stress field. Simulation result is verified with measured data. Using our custom program, the geometry parameters of the sensor are optimized, predi cting 4.5 times more sensitivity than that of the prototype sensor. The ana lysis for the sensor was rounded off with an analysis of the influence of b ond wire misalignment on the sensor's sensitivity. (C) 2001 Elsevier Scienc e B.V. All rights reserved.