Warpage Analysis of Panelized Molding Process for Plastic IC Packages

Abstract

Panelized molding process is vastly used in low cost molding process for PBGA (Plastic Ball Grid Array), LGA (Land Grid Array), QFP (Quad Flat Pack) and other types of packages. In a panelized molding process, arrays of packages are assembled on a substrate board, which is then molded as a single panel. After the molding process, the package array is cut into single packages. When laminated substrates are used, panel warpage formed during the molding process is very common due to the mismatches of material properties in the substrates and molding compounds. The warpage, however, is one of the major issues in the back-end assembly process. For example, the warpage can cause great difficulties in singulation. Large warpage could also cause high stresses in the components and results in reliability problems in the packages. In this paper, a 3-D finite element model is created to study the relations between the panel warpage and the material properties of the substrate boards and mold compounds. In a 40mmx50mm panel area, the model shows that the global warpage can be as high as +/-10 mils (0.25 mm) using different mold compounds. Test vehicles are assembled to validate the simulation results. The measurement data on warpage from the testing vehicles, although at first seems to vary over a large range across different panel designs, a closer observation and analysis suggests a definite trend and a strong correlation between the substrate panel and the mold compound properties.