Tokyo  : Tanaka Kikinzoku Kogyo K.K.(*1) (a company of Tanaka Precious Metals), Newlong Seimitsu Kogyo Co., Ltd. and Taiyo Chemical Industry Co., Ltd. commence to provide technology enabling the batch formation of micro-composite patterns on substrates using screen printing with AuRoFUSE(TM) low-temperature bonding material utilizing submicron-sized (1/10,000 mm) gold particles on Wednesday, December 4, 2013. The companies provide AuRoFUSE(TM), printing machines and screen mask technology to customers, including consulting on the introduction of the technology and sample prototype support.

Manufacturers of LED (light emitting diode) chips and MEMS (microelectromechanical systems) devices will be able to achieve the following by implementing the technology.

— Print formation of micro-composite patterns for high heat-resistant and low-resistivity electrode bonding and sealing frames with excellent step absorption on gold (Au) wiring of silicon wafers and substrates is possible.

— Printed sealing frames can create airtight seals by having a finer structure by thermocompression bonding at 200 degrees Celsius.

— Patterns can be formed using high-definition screen printing, and processing can be reduced because the combination of multiple processes such as plating, deposition and sputtering are not required.

— 8-inch wafer size patterns formation is possible.

— AuRoFUSE(TM) enables work to be performed with minimal material loss because it can withstand repeated printing. It is believed that this can practically reduce the cost of key processes.

– Printing technology has been developed to form “thinner, smaller and narrower” AuRoFUSE(TM) micro-composite patterns

AuRoFUSE(TM) is a paste-type bonding material containing a mixture of gold particles with the particle diameter controlled to be submicron sized and an organic solvent. Generally, microscopic particles have the characteristic called “sintering” where particles bond to each other when heated to a temperature under the melting point. If AuRoFUSE(TM) is heated to 200 degrees Celsius, the solvent evaporates, and the gold particles undergo sinter bonding without the application of pressure. Sufficient bonding strength of approximately 30 megapascals (MPa) can be maintained at temperatures under 300 degrees Celsius. Bonding strength at high temperatures can be achieved without pressing the load onto components during bonding.

Tanaka Kikinzoku Kogyo has been examining process technology using AuRoFUSE(TM) to enable users to easily form micro-composite patterns on substrates. It was thought that “thin, small and narrow” formation was essential to use gold material efficiently in the process, and the Company has focused on the combination with high-definition screen printing suit for mass production, and the joint development with Newlong Seimitsu Kogyo and Taiyo Chemical Industry. Tanaka Kikinzoku Kogyo handled printing stability of AuRoFUSE(TM), Newlong Seimitsu Kogyo performed the technical evaluation required for using AuRoFUSE(TM) in screen printing machines, and Taiyo Chemical Industry calibrated the printing mask specifications.

– Effective for airtight sealing of MEMS

As devices become more highly functional, MEMS device manufacturers are facing with the issue of rising packaging costs in wafer-level packaging (WLP). For example, reduced plating costs and improvements in yield are essential in conventional sealing methods using fusion bonding at 200 degrees Celsius by applying multi-layer gold-indium plating on the sealing frame.

Sealing frames formed by screen printing AuRoFUSE(TM) provide densification and high vacuum sealing(*2) as a result of forming gold particle sintered compacts using thermocompression bonding (200 degrees Celsius, 100MPa). Gold sintered compacts have compression deformability able to absorb unevenness on substrate surfaces, and not only can reduce the surface treatment (CMP) that was required by conventional bonding, but also improve product yield. Miniaturization of packages becomes possible by reducing the printing width, and the technology is considered to have extremely versatility for the future.

– Resolution of the issue of “heat” in bonding materials used in power devices such as high-output LEDs

Currently, tin-based and gold-based solder widely used as die bond materials(*3) have heat resistance up to melting point, but there are various issues as a die bond material in next-generation power devices expected to have even higher performance. For example, in the field of high-output LEDs, bonding wire is used to electrically connect the chip surface and the substrate, but it has been indicated that the wire blocking the light emitting surface reduced brightness. Because of this, flip chip bonding is gaining attention for being able to provide better light emission efficiency by using protrusions (bumps) instead of wires as terminals to connect to electrodes. When doing so, the contact area becomes smaller, and the thermal resistance of the solder alloy itself is higher, which reduces the heat dissipation from the element, and results in higher temperature of the element and consequentially lower light emission performance. AuRoFUSE(TM), which is a gold-gold bond, is able to eliminate element damage from the perspective of high heat dissipation.

Furthermore, next-generation power semiconductors using silicon carbide (SiC) and gallium nitride (GaN) have operating temperatures that can exceed 300 degrees Celsius. Because of this, although materials melt in bonds using gold-tin solder, bonding with AuRoFUSE(TM) provides sufficient heat dissipation and bonding strength even at 300 degrees Celsius.

Tanaka Kikinzoku Kogyo has been providing samples of AuRoFUSE(TM) since December 2009, but the commencement of the provision of this technology marks the establishment of a mass production capable to manufacture 200 kg of AuRoFUSE(TM) per year. The company is aiming for annual AuRoFUSE(TM) sales of 2 billion yen by 2020 by providing the material as a standalone product and also providing AuRoFUSE(TM) combined with other technologies as in this case.

Source : ACN Newswire