Development of predictive modeling scheme for flip-chip on fine pitch flex substrate

Abstract

A verified/predictive finite element modeling scheme for flip-chip on a fine pitch flex substrate is presented. The scheme is based on the conventional local/global modeling approach to handle complicated three dimensional structures with fine features of interest, but a new formulation is introduced to be able to evaluate time-dependent non-linear stresses induced by hygroscopic as well as thermal expansion mismatches; the proposed model allows design assessment of the packages subjected to a combined temperature and moisture environment. The properties of critical materials are first determined experimentally and their performance in the model is subsequently verified by an interferometric displacement measurement technique. By combining numerical modeling and experimental verification until the results merge, the numerical model becomes more accurate and dependable. Then, the model is applied extensively to optimize the package designs for enhanced reliability.