Impact of Copper Densities of Substrate Layers on the Warpage of IC Packages

Abstract

In this paper, the impact of the copper densities of substrate layers on IC package warpage is studiedexperimentally and numerically. The substrate strips used in this study contained two metal layers, with the metal densitiesand patterns of these two layers varied to determine their impacts. Eight legs of substrate strips were prepared. Leg 1 toleg 5 were prepared with a HD (high density) type of strip and leg 6 to leg 8 were prepared with UHD (ultra high density)type of strip. The top copper metal layer was designed to feature meshed patterns and the bottom copper layer was designedto feature circular patterns. In order to consider the process factors, the warpage of the substrate bottom was measuredstep by step with the following manufacturing process: (a) bare substrate, (b) die attach, (c) applying mold compound(d) and post reflow. Furthermore, after the post reflow step, the substrate strips were diced to obtain unit packages andthe warpage of the unit packages was measured to check the warpage trends and differences. The experimental resultsshowed that the warpage trend is related to the copper densities. In addition to the experiments, a Finite Element Modeling(FEM) was used to simulate the warpage. The nonlinear material properties of mold compound, die attach, solder mask,and substrate core were included in the simulation. Through experiment and simulation, some observations wereconcluded.