Investigation of the size and spatial distribution of fillers in mold compounds after device packaging

Fillers are used in the molding compounds used to package semiconductor devices, as a means to lower costs and minimize the stress caused by thermal expansion mismatch between the silicon die and the molding compound. With ever finer feature size and increasing die dimensions, control of highly filled molding compound's properties and processing parameters becomes more important. In this study, quantitative measures of the particle distribution of fillers in packaged devices were experimentally determined, including area fraction, size, and interparticle distance. The size and interparticle distance were statistically significant with respect to the position in the package. The difference of filler volume fraction at different positions within a package can be as large as 10%, and can cause a local coefficient of thermal expansion difference of about 4ppm//spl deg/C. A 2/spl times/3/spl times/3 ANOVA test was conducted to assess the statistical significance of these variations.