Thermo-mechanical analysis of TSV and solder interconnects for different Cu pillar bump types

Abstract

Graphical abstractDisplay Omitted Highlights? FE modelling of Cu pillar bumps of different types. ? Stress distribution in solder interface and TSV interface. ? Reliability of conical frustum type is excellent than other types. The through silicon via (TSV) is a technology for vertical interconnection between multiple chips that employ a hole bored through a Si wafer and stack chips, which is good for securing a number of I/O per unit area reducing the electric resistance. On the other hand, vertical multi-layers are structurally more unstable than a single-layer but are vulnerable to a thermo-mechanical effect. Therefore, in this study, finite element analysis (FEA) of a three-dimensional (3D) multi-layer semiconductor with TSV was carried out to examine the changes in thermo-mechanical stress at the bonding interface with different models of Cu pillar bumps and Sn-3.5Ag solder bumps. A numerical simulation was carried out with different models, such as a plate type, pin type, skirt type, zigzag type and conical frustum type. The height and diameter of each solder bump were 10µm and 30µm, respectively. The distribution of Von Mises stress occurred more at the solder joint interface and TSV joint interface. At the solder joint interface, the stress in the skirt type (100.6MPa) was approximately double that in the conical frustum type (53.1MPa). At the TSV joint interface, the stress in the plate type (17.2MPa) was higher than that in the other types. The stress values were similar in the other types except for plate type Cu pillar bump. Stress in the solder and TSV joint interface was caused partly by the difference in properties between the two materials. In particular, mismatch in the coefficient of thermal expansion (CTE) had the greatest effect on the stress distribution.