The University of Osaka · Engineering
Professor Hiroaki Tatsumi's research lab specializes in advanced interconnection technologies for high-performance electronics, focusing on solid-state bonding, laser soldering, and high-thermal-conductivity joint materials. The lab investigates fundamental mechanisms of interfacial diffusion, void closure, and microstructural evolution in Cu-based joints using molecular dynamics simulations and experimental validation. Key research directions include low-temperature Cu–Cu bonding, novel composite joint materials (e.g., anisotropic microcomposites and TLPS joints), and next-generation bonding techniques such as blue diode laser soldering for improved efficiency and reliability.
Figures are computed from collected data and may differ slightly.
Laser soldering has been widely used to connect electronic components to printed circuit boards (PCBs), owing to its significant advantages, including localized heating, noncontact heating, rapid temperature rise and fall, good controllability, and high adaptability. However, poor absorptivity of the metals involved is one of the main drawbacks of traditional infrared (IR) laser soldering. In this study, we constructed a novel blue diode laser soldering system to validate its higher heat efficie
The evolution of the transient liquid-phase sintered (TLPS) Cu–Sn skeleton microstructure during thermal aging was evaluated to clarify the thermal reliability for die-attach applications. The Cu–Sn skeleton microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds partially filled with polyimide resin, was obtained by the pressure-less TLP sintering process at 250 °C for 1 min using a novel Cu-solder-resin composite as a bonding material in a nitrogen atmospher
High-density electronics are hindered by the constraints of Sn-based solder joints, necessitating the exploration of Cu-Cu solid-state bonding. However, current bonding methods are expensive and time-consuming; therefore, understanding the Cu-Cu bonding mechanism is crucial for optimization. This study utilizes molecular dynamics (MD) simulation to elucidate the Cu-Cu solid-state bonding behavior, focusing on interfacial densification and diffusion phenomena. Furthermore, it highlights the influ
The miniaturization of power conversion systems requires high-power density operation of power modules, causing the heat-density increase. Therefore, it is essential to develop bonding technology to realize highly thermally conductive and reliable high-temperature joints. In this study, we propose a novel anisotropic microcomposite (AMC) joint that integrates a lotus-type porous Cu (LPC) sheet and Sn-based solder for high-temperature electronic applications. The AMC joint was successfully fabric
In recent years, solid-state bonding has attracted attention for various electronic packaging applications as an alternative to conventional solders. Surface-nanostructured materials enable solid-state bonding without complex surface modifications and operate at a low bonding temperature and pressure. Therefore, in this study, molecular dynamics simulations were conducted to investigate the solid-state bonding behavior between surface-nanostructured Cu and Au, with a focus on diffusion phenomena
• Molecular dynamics simulations reveal atomic transport mechanisms in Cu bonding. • Grain boundaries supply atoms to voids, promoting closure in nanocrystalline Cu. • Complex grain boundary migration enhances atomic mobility and void closure. • Nanotwinned Cu maintains quasi-stable energy state, limiting void closure. • Study enhances understanding of void closure for optimizing Cu–Cu bonding process. Low-temperature Cu–Cu solid-state bonding is key for interconnect miniaturization and higher c
The advancement of power modules demands more reliable insulating circuit substrates. Traditional substrates, comprising Cu and Si3N4, are produced using active metal brazing (AMB). However, AMB substrates have reliability concerns owing to electrochemical migration and void formation from brazing filler metals. This study introduces a quasi-direct Cu–Si3N4 bonding technique using a Ti/Al bilayer active metal deposition at the bonding interface. A sputtered Ti/Al bilayer was formed on the Si3N4
Transient liquid-phase sintering (TLPS) using a Cu-solder-resin composite for the die-attach application of high-temperature silicon carbide (SiC) power modules was evaluated with the goal of controlling the joint stiffness. The Cu-solder-resin composite mainly contains Cu particles, Sn-3Ag-0.5Cu solder particles, and polyimide-type thermosetting resin. Microstructural observations, shear strength tests, and thermal cycling tests of the SiC die-attached specimens bonded through the pressureless
We have proposed a low-temperature bonding technology utilizing the sintering of Cu particles with transient liquid-phase of Sn-based solder, called transient liquid-phase sintering (TLPS), as a die-attach solution for high-temperature power modules. A copper-intermetallic compound-resin (Cu-IMC-resin) microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds (IMCs) partially filled with polyimide resin, is obtained by the pressureless TLPS process at 250 °C for
Sintered silver bonding processes are expected to offer bonding solutions with high heat endurance for power modules using wide bandgap semiconductors. This study reports the die-attach reliability of the bonding process under thermal cycling tests, focusing on the metallurgical and mechanical properties of sintered silver joints. A nanocrystalline (NC) structure with 150-nm-sized grains was observed in the as-sintered state, while a coarsened structure with microsized grains and pore coalescenc
Transient liquid phase sintering (TLPS) using copper (Cu)-solder-resin composite was investigated for die-attach applications of high-temperature power modules. The copper particles were connected with Cu-Sn IMCs through transient liquid phase reaction at about 220 °C. The Cu-IMC skeleton structure was partially filled with polyimide resin. The joint strengths of die-attached specimens were tested. The die-attached specimens showed superior reliability through thermal cycling tests. These result
We have proposed a novel bonding process using composite Ag nanoparticles composed of Ag metallo-organic nanoparticles and Ag2CO3 for an application to the assembly of electronic devices. In this research, the sintering mechanisms of the composite Ag nanoparticles are discussed based on the results of the observation of the sintering behaviors and the investigation of the thermal characteristics. Moreover, Cu specimens were bonded using the composite Ag nanoparticles for measuring the bonding st
Sintered silver bonding processes are expected to offer bonding solutions with high heat resistances for power modules using wide-bandgap semiconductors. This study reports the die-attach reliability of such a bonding process under thermal cycling tests, focusing on the metallurgical and mechanical properties of sintered silver nanoparticles. A nanocrystalline structure with a grain size of approximately 150 nm was observed in the as-sintered state, while a coarsened structure with a grain size
In the face of escalating thermal challenges in power modules, this study proposes a novel thermal bonding approach. Traditional Sn-based solders, limited by their lower thermal conductivity, are inadequate for dissipating the increased heat flux. Addressing this, our research introduces a composite joint utilizing lotus-type porous copper (LPC) integrated with Sn-based solder, enhancing thermal management capabilities. By exploiting the anisotropic properties of LPC, we developed a lotus-type p
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