# Study on Microstructure and Properties of Micron Copper Powder-Liquid Metal Gallium Composite Interconnect Joint

## TL;DR

This study explores a new copper-gallium composite material for creating strong and conductive electronic connections at low temperatures.

## Contribution

The paper introduces a composite paste formulation that synergistically optimizes electrical and mechanical properties in Cu–Ga TLPB joints.

## Key findings

- A dense intermetallic compound microstructure of Cu9Ga4 and CuGa2 was formed under specific bonding conditions.
- The composite achieved high electrical conductivity (1.1 × 10⁷ S·m⁻¹) and shear strength (52.2 MPa) under optimized conditions.
- Even with rapid bonding, the joint retained significant shear strength (39.2 MPa), indicating potential for high-efficiency applications.

## Abstract

Liquid gallium (Ga) enables low-temperature transient liquid phase bonding (TLPB), but optimizing microstructure and joint performance remains challenging. Here, we developed a copper (Cu)-powder/liquid-Ga composite paste for Cu/Cu interconnects and systematically studied the effects on the interconnect joint performance of Cu powder particle size (CuPS, 10–20, 20–30 and 30–40 μm) and Cu mass fraction (CuMF, 10–30 wt%). The microstructure, electrical conductivity, and shear strength of the joint were evaluated, followed by an assessment of bonding temperature, pressure, and time. Under bonding conditions of 220 °C, 5 MPa and 720 min, a dense intermetallic compound (IMC) microstructure predominantly composed of Cu9Ga4 and CuGa2 was formed, yielding an electrical conductivity of approximately 1.1 × 107  S·m−1 and a shear strength of 52.2 MPa, thereby achieving a synergistic optimization of electrical and mechanical properties; even under rapid bonding conditions of 220 °C, 5 MPa and 1 min, the joint still attained a shear strength of 39.2 MPa, demonstrating the potential of this process for high-efficiency, short-time interconnection applications. These results show that adjusting the composite paste formulation and dosage enables Cu–Ga TLPB joints that combine high conductivity with robust mechanical integrity for advanced packaging.