Dimension optimization of through silicon via(TSV) through simulation and design of experiment (DOE)

Abstract

As the market is desperate for better performed, miniaturized, highreliableand lower-priced electronic devices, nowadays, three dimensional integrated circuit (3D IC) seems to be a promising technology which can meet these requirements. However, many issues hinder this technology from being developedrapidly, among which the reliability of through silicon via(TSV) is one of the major concerns. Because of its complexity of the architecture and miniaturized interconnect, TSVs often undergo relatively high density electric current, which inevitably generates a fair amount of heat during work. What's more, the coefficient of thermal expansion (CTE) mismatch between copper and silicon, thereforestress concentration can easily take place between them, resulting in shorter fatigue life of the device. Since design parameters can have a great effect on these devices' reliability, optimizing these parameters is essential and meaningful. This paper is meant to present the impact of some design parameters such as TSV diameter and pitch, thickness of silicon dioxide (SiO2), die thickness, solder diameter and underfill properties on the thermo-mechanical durability of TSVs and direct chip attach (DCA) solder joints respectively using the design of experiments (DoE) which applies Taguchi experiments and analysis method because of its high efficiency and effectiveness. The two dimensional models are built in numerical experiments under accelerated thermal cycle loading. In the model, solder is assumed to be visco-plastic material and copper interconnects are considered to have elastic-plastic behavior. Two continuum damage models, Coffin-Manson and creep energy damage modelare used to assess the number of cycles before TSVs and solder joints fail to work under thermal cycle loading respectively. The results are analyzed by Minitab to decide the variation tendency of TSVs' and solder joints' fatigue life, which is induced by the parameters with different levels, and general linear model analysis of variance is used to assess significance of each factor in determining durability of TSV interconnects and solder joints. The results reveal that the most influential factor on TSV durability is TSV diameter, while for durability of the solder joints, it is the property of underfill. TSV durability increases as the TSV diameter decreases and solder joints have a longer fatigue life when underfill has a smaller Young's Modulus.