Furukawa Electric Develops Low-Young’s-Modulus, Heat-Resistant Oxygen-Free Copper “TOFC™”
- Contributing to the enhanced performance of power semiconductor modules by low Young’s modulus, high heat resistance, and high thermal conductivity -
- The stiffness of oxygen-free copper can be maintained even at temperatures exceeding 300 °C, reducing warpage and deformation
- Low Young’s modulus reduces thermal stress at the bonded interfaces with materials having different coefficients of thermal expansion, thereby significantly improving bonding reliability by suppressing delamination
- Mass production and commercial sales are scheduled to commence within fiscal year 2025
Furukawa Electric Co., Ltd. (Head Office: 2-6-4 Otemachi, Chiyoda-ku, Tokyo; President: Hideya Moridaira) has developed “TOFC™,” a low-Young’s-modulus (note), heat-resistant oxygen-free copper that features a lower Young’s modulus than conventional oxygen-free copper while maintaining high heat resistance and high thermal conductivity.
Background
In recent years, the use of power semiconductors for power conversion and control has been rapidly expanding, driven by the adoption of renewable energy sources including solar and wind power, as well as in applications such as xEVs and data centers. In particular, next-generation power semiconductor modules using SiC (silicon carbide) chips generate more heat as output power and performance increase. Oxygen-free copper is widely used as heat-dissipation substrates and terminals in these modules due to its excellent thermal conductivity.
However, exposure to elevated temperatures during soldering or resin bonding processes causes softening and warpage, leading to reduced bonding reliability. Furthermore, differences in the coefficients of thermal expansion between copper and other materials, such as semiconductor chips, ceramics and resins in the module generate thermal stresses during operation, which can cause delamination or cracking at the bonded interfaces between materials, ultimately leading to malfunction.
Details
In addition to conventional oxygen-free copper (C1020), Furukawa Electric has been mass-producing GOFC®, a heat-resistant oxygen-free copper developed using proprietary materials design and manufacturing technologies that suppress crystal grain coarsening during high-temperature bonding. Furukawa Electric has now expanded its product lineup with the addition of TOFC™, a low-Young’s-modulus, heat-resistant oxygen-free copper. While maintaining high thermal conductivity, TOFC™ achieves excellent heat resistance without softening at high temperatures (Figure 1). As a result, TOFC™ maintains its stiffness even at temperatures above 300 °C, where soldering or resin bonding is performed, which is expected to reduce warpage and deformation. Additionally, TOFC™ exhibits a lower Young’s modulus than conventional oxygen-free copper at temperatures up to 600 °C (Figure 2, Table). This property helps suppress delamination at the bonded interfaces between materials with differing coefficients of thermal expansion, significantly enhancing connection reliability.
With these features, TOFC™ is well suited for applications such as heat spreaders and terminals in power semiconductor modules, as illustrated in the schematic cross-section (Figure 3). Furthermore, when applied to high-current busbars requiring high heat resistance, TOFC™ can suppress strength degradation during high-temperature operation compared with conventional oxygen-free copper and tough-pitch copper. These advantages make TOFC™ suitable for broader applications of TOFC™ in areas such as renewable energy inverters and xEV power control units.
Mass production and sales of TOFC™ are scheduled to begin within the current fiscal year.
Furukawa Electric will continue to supply high-performance oxygen-free copper strip products for a wide range of applications, contributing to the advancement and performance enhancement of power semiconductor modules.
| Electrical Conductivity (%IACS) |
Thermal Conductivity （W/ｍ・K） |
Tensile Strength (MPa) |
Heat Resistance Temperature (℃) |
Young’s Modulus (GPa) |
Product Thickness (mm) |
Features | |
|---|---|---|---|---|---|---|---|
| C1020 | 101 | 391 | 220 - 315 | 200 - 300 | 120 | - | - |
| GOFCⓇ | 101 | 391 | 200 - 300 | 200 - 300 | 100 | 0.25 - 2.0 | Suppresses crystal grain growth |
| TOFC™ | 101 | 391 | 180 - 240 | 500 | 85 | 0.25 - 2.0 | High heat resistance, low Young’s modulus |
(note) Young’s modulus is the proportionality constant between stress and strain during elastic deformation, also referred to as the longitudinal elastic modulus. This represents the stiffness of a material and its resistance to deformation. A higher value indicates greater stiffness and resistance to deformation.
“TOFC” is a trademark of Furukawa Electric Co., Ltd. (application pending).
“GOFC” is a registered trademark of Furukawa Electric Co., Ltd. in Japan.
Furukawa Electric Group’s efforts towards the SDGs
Based on the “Sustainable Development Goals (SDGs)” adopted by the United Nations, Furukawa Electric Group has formulated the “Furukawa Electric Group Vision 2030” which sets the year 2030 as its target and is advancing efforts with the aim to “Build a sustainable world and make people’s life safe, peaceful and rewarding, Furukawa Electric Group will create solutions for the new generation of global infrastructure combining information, energy and mobility.” Toward the achievement of our Vision 2030, we will take open, agile, and innovative approaches to promote ESG management that aims to increase corporate value over the medium to long term and will contribute to the achievement of the SDGs.
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