Calibration of piezoresistive coefficient and stress measurement

Abstract

Thermal and mechanical loadings often produce stresses in integrated circuit (IC) chips, which are incorporated into elecronic packages. Some factors can lead to premature failure of the package due to such causes as fracture of the die, severing of connections, die bond failure, solder fatigue, and encapsulant cracking. Piezoresistive stress sensor, in which the electrical resistivity changes in proportion to the stress applied, can be used to predict those changes mentioned above. In this thesis, design of the piezoresistive sensors, which fabricated in the test chip and used to predict the thermal and mechanical stresses produced in electronic packages is presented. Three-element "off-axis" 0°-45°-90° rosettes were designed to calibrate temperature compensated piezoresistive coefficients p44 for P-type resistors and difference of coefficients (p11- p12) for N-type resistors. The four-element Dual Polarity Rosettes were designed and fabricated for the measurement of in-plane normal stress difference (s'11- s'22) and the in-plane shear stress s'12 after acquiring the value of p44 and (p11- p12). The value of (s'11- s'22) and s'12 are sufficient for comparison with finite element simulations. For calibration of piezoresistive coefficients using pure bending theory in mechanical engineering, a four-point-bending fixture to fulfil the calibration work was designed and manufactured. Comparing to common four-point-bending fixture has been made.The results on the value p44, (p11- p12), and temperature coefficient a are figured out. Error analysis and summary of the test are also presented. It can be seen that the testing method is correct, but the equipment and environment still need to be improved for getting more accurate results. /Kir10