Determination of packaging induced 3D stress utilizing a piezocoefficient mapping device

This paper presents a novel method to determine 3D stress in microsystem packaging. The stress components sigma_xx, sigma_yy, sigma_zz, and sigma_xy are found in an epoxy package using a piezocoefficient mapping device as stress sensor. We spin the current 360deg in a circular n-type (001) Si piezoresistor by contacts located near the perimeter of the resistor and do high impedance voltage measurements on contacts located near the centre of the resistor. By measuring the potential drops in these contacts we can determine the stress in the chip. The epoxy is potted in a polystyrene tube using the same concept as in [1] used for chip packaging for fisheries research. We investigate the EpoTek 305 epoxy and find stress values of sigma_xx ap -23 MPa, sigma_yy ap -1 MPa, sigma_xy = 0.3 MPa, and sigma_zz = 40 MPa. The presented method can be used for 3D stress measurements of various packaging concepts.