Shear strength between Sn–3.0Ag–0.5Cu solders and Cu substrate after two solid-state aging processes for fan-out package process applications

Abstract

Shear strength between Sn-3.0Ag-0.5Cu (SAC) solders and Cu/Ti in under bump metallization (UBM) samples aged using two solid-state aging processes was investigated. One method aged the samples at 200 degrees C for up for five 1-h intervals; the other aged the samples at 200 degrees C continuously for up to 5h in a convection oven. After reflow, all samples showed scallop-shaped Cu6Sn5 intermetallic compounds (IMCs) at the interfaces between SAC solder and Cu substrate. After aging, the Cu layers of all samples were gradually depleted, and lump-shaped Cu6Sn5 was observed to be separated from the SAC/Cu interfaces. The shear strength of all samples was gradually decreased with increased aging due to depletion of the Cu wetting layer, formation of IMCs with solder, and separation of the IMCs from the interfaces during aging. Quantitative analysis revealed that exposed Ti area is an effective predictor of decrease in shear strength generated by the spalling phenomenon.