# Research on the Influence Mechanism of Thermal Load on the Au-Sn Sealing Weld State on Three-Dimensional DPC Substrates

## TL;DR

This study explores how thermal load affects the sealing weld state of Au-Sn on DPC substrates, identifying optimal welding conditions and microstructural changes.

## Contribution

The paper provides new insights into the microstructural evolution and interface characteristics of Au-Sn sealing welds on DPC substrates under thermal aging.

## Key findings

- The primary reaction in the sealing weld seam involves Ni interacting with Au-Sn to form (Ni, Au)3Sn2 and Au5Sn.
- Optimal welding occurs at peak temperatures of 325 °C to 340 °C, achieving ideal weld seam morphology and Ni diffusion.
- Aging studies show intermetallic compound growth remains controllable under dual atmosphere conditions.

## Abstract

Direct copper-plated ceramic (DPC) substrates have emerged as a favored solution for power device packaging due to their unique technical advantages. AuSn, characterized by its high hermeticity and environmental adaptability, represents the optimal sealing technology for DPC substrates. Through the application of vacuum sintering techniques and adjustment of peak temperatures (325 °C, 340 °C, and 355 °C), the morphology and composition of interfacial compounds were systematically investigated, along with an analysis of their formation mechanisms. A gradient aging experiment was designed (125 °C/150 °C/175 °C × oxygen/argon dual atmosphere × 600 h) to elucidate the synergistic effects of environmental temperature and atmosphere on the growth of intermetallic compounds (IMCs). The results indicate that the primary reaction in the sealing weld seam involves Ni interacting with Au-Sn to form (Ni, Au)3Sn2 and Au5Sn. However, upon completion of the sealing process, this reaction remains incomplete, leading to a coexistence state of (Ni, Au)3Sn2, Au5Sn, and AuSn. Additionally, Ni diffuses into the weld seam center via dendritic fracture and locally forms secondary phases such as δ(Ni) and ζ’(Ni). These findings suggest that the weld seam interface exhibits a complex, irregular, and asymmetric microstructure comprising multiple coexisting compounds. It was determined that Tpeak = 325 °C to 340 °C represents the ideal welding temperature range, where the weld seam morphology, width, and Ni diffusion degree achieve optimal states, ensuring excellent device hermeticity. Aging studies further demonstrate that IMC growth remains within controllable limits. These findings address critical gaps in the understanding of the microstructural evolution and interface characteristics of asymmetric welded joints formed by multi-material systems.