# Microstructural and Mechanical Characterization of Cu/SnAg Pillar Bumps with Ni-Less Surface Finish Utilizing Laser-Assisted Bonding (LAB)

## TL;DR

This paper studies how laser-assisted bonding affects the strength and structure of copper/silver-tin solder bumps used in electronics.

## Contribution

The study introduces a laser-assisted bonding method for Cu/SnAg pillar bumps with Ni-less pads and evaluates its mechanical and microstructural performance.

## Key findings

- Laser-assisted bonding (LAB) achieved minimal intermetallic compound growth and high bonding strength under optimized conditions.
- Solder splashing occurred at temperatures above 300 °C due to explosive flux vaporization.
- Failure modes shifted from solder to intermetallic compounds with higher laser power density.

## Abstract

In this study, an interconnection was formed between a Cu/SnAg pillar bump and an Ni-less surface-treated Cu pad through laser-assisted bonding (LAB), and its bonding characteristics were evaluated. The LAB process influences the bond quality and mechanical strength based on the laser irradiation time and laser power density. The growth of the intermetallic compound (IMC) in the joint cross-section was observed via FE-SEM analysis. Under optimized LAB conditions, minimal IMC growth and high bonding strength were achieved compared to conventional thermo-compression bonding (TCB) and mass reflow (MR) processes. As the laser irradiation time and laser power density increased, solder splashing was observed at bump temperatures above 300 °C. This is hypothesized to be due to the rapid temperature rise causing the flux to vaporize explosively, resulting in simultaneous solder splashing. With increasing laser power density, the failure mode transitioned from the solder to the IMC.