Advancements in Interfacial Strength and Fracture Behavior of Ag/Si Interfaces: A Breakthrough in Low-Temperature Sinter Bonding

Significance 

In the realm of semiconductor materials, the development of next-generation power devices has been a subject of intense research and innovation. One area of particular interest has been the exploration of low-temperature sinter bonding using metal particles. This bonding technique has garnered attention due to its potential to overcome the limitations of conventional methods and enable the creation of highly efficient and robust devices. However, the understanding of interfacial properties and fracture behavior in dissimilar material interfaces has been relatively scarce.

In this context, a new study conducted by Dr. Tomoki Matsuda, Dr. Ryotaro Seo, and Dr. Akio Hirose from Osaka University has shed light on the interfacial strength and fracture behavior of Ag/Si interfaces formed by a composite paste. Their findings, published in the peer-reviewed journal Materials Science & Engineering A, presented a significant advancement in the field of low-temperature sinter bonding.

The research team utilized a composite paste comprising Ag2O microparticles, Ag microflakes, and terpineol. This innovative paste demonstrated a delayed reduction of Ag2O, leading to interconnection between the Ag grains and Si substrate. The interfacial strength achieved using this composite paste surpassed 30 MPa at a bonding temperature of 250°C. Remarkably, microscale tensile testing revealed the formation of a high-strength Ag/Si interface (>200 MPa) with intrinsic fracture morphology occurring within the Ag layer at a nanoscale. This phenomenon indicated that fracture predominantly transpired within the Ag layer and not at the interface itself.

The utilization of metal particles in low-temperature sinter bonding presents a compelling alternative for the development of advanced power devices. Traditionally, bonding methods have focused on incorporating metallization exclusively on the surfaces of semiconductors or ceramics due to the limited bonding ability of materials other than metals. However, the application of metal particles allows for the formation of robust bonds even with non-metallic materials, thereby expanding the design possibilities for joint structures.

While previous studies have explored changes in microstructure and properties of sintered layers, as well as interfaces formed by plating layers, the investigation of dissimilar material interfaces between the sintered layer and nonmetal has been relatively scarce. The authors provided a comprehensive understanding of the interfacial properties and fracture behavior of Ag/Si interfaces through meticulous experimentation. This fundamental research paves the way for the development of novel interfacial designs and enhances our understanding of the mechanics behind interfacial bonding.

The researchers observed that the formation of the Ag/Si interface involved both direct bonding and nanoparticle layer intermediated bonding. The bonding morphologies varied depending on the distance between the sintered Ag and the interface. In cases where the distance was significant, the formation of a layer with Ag nanoparticles, attributed to the mixture of Ag and organic residue, facilitated interfacial bonding. The delayed production of a large number of Ag nanoparticles, derived from the reduction of Ag2O by an organic lubricant, played a vital role in the interaction among crystallized Ag grains and between the Ag grains and the substrate.

The research team conducted fracture behavior analysis which revealed that the interfacial strength and fracture behavior primarily depended on the morphology of the bonding interface and the sintered Ag layer’s porosity. Fracture initiation either occurred within the interfacial nanoparticle layer or at the interface itself, resulting in rapid fracture propagation within the sintered Ag layer. The presence of significant porosity within the sintered Ag layer contributed to the fracture of the Ag layer. These insights into fracture behavior are crucial for optimizing joint design and enhancing the ductility of joints.

The utilization of a composite paste comprising Ag2O and Ag particles has proven to be highly effective in interconnecting the sintered Ag layer with the Si substrate, effectively filling gaps and mitigating volume shrinkage. The formation of a joint interface through both direct and indirect bonding morphologies, enabled by the composite paste, has improved joint strength by increasing bonding area and inducing fractures towards the sintered Ag layer. This approach holds promise for enhancing joint properties at the micro-to-macroscale level.

According to the authors, the study offers valuable insights into the design and optimization of interfaces for sinter bonding. By advancing our understanding of interfacial properties and fracture behavior, researchers can devise innovative strategies for improving joint performance and developing robust power devices. Further research in this area may involve exploring the applicability of the composite paste in diverse material systems and investigating its potential in various applications beyond low-temperature sinter bonding.

In conclusion, the authors exploration of interfacial strength and fracture behavior in Ag/Si interfaces, utilizing a composite paste comprising Ag2O and Ag particles, has provided crucial insights into joint design and performance. The findings open up new avenues for the development of advanced power devices and other applications that require reliable interfacial bonding. As researchers continue to build upon this foundation, we can expect further advancements in low-temperature sinter bonding techniques, unlocking new possibilities in semiconductor technology.

Reference

Tomoki Matsuda *, Ryotaro Seo, Akio Hirose. Highly strong interface in Ag/Si sintered joints obtained through Ag2O–Ag composite paste. Materials Science & Engineering A 865 (2023) 144647.

Go to Materials Science & Engineering A

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