Probabilistic approach to evaluate improvements in the reliability of a chip-substrate (chip-card) assembly

A probabilistic approach is used to evaluate improvements in the reliability of the chip-substrate (chip-card) assembly against cracking of the integrated circuits (IC's). Such cracking is typically caused by bending deformations of the substrate. The suggested model is aimed at the assessment of the effect of the improvements in the IC preparation and encapsulation on the probability of the IC fracture. Examples of possible improvements are: application of low modulus encapsulant and die attach materials, change in the IC thickness and its positioning on the substrate, polishing of the chip's back surface, etc. The developed model enables one to evaluate the in-service variance of the substrate curvature from the reported IC failure statistics and additional experimental data obtained by bending the assembly on a series of circular mandrels. Then, one can evaluate the improvements in the reliability of the chip-substrate assembly from the changes in the mean and variance of the substrate curvature at the point of IC fracture, i.e., to assess the decrease in the probability of fracture for the improved design.