Tanaka Precious Metals and SUSS MicroTec to Jointly Develop Sub-micron Gold Particle Pattern Transfer and Bonding Technology

This joint development will encompass development of technology for transferring patterns of sub-micron gold particles to a silicon wafer at one time at the low temperature of 150 degrees Celsius on an industrial high volume production basis. Using the transferred pattern of gold particles which have an effect on absorbing wafer surface roughness, it is possible to achieve metal-metal bonding on a wafer level at the low temperature of 200 degrees Celsius, which had been difficult by using conventional technology, with enabling high temperature resistance, high reliability hermetic seals and electrical connections.



Through the joint development, the two companies aim to begin sales of the transfer substrates and the transfer and bonding equipment in March 2012. By implementing the bonding technology in packaging and assembly processes, manufacturers of MEMS (micro electro mechanical systems) devices, LED (light emitting diode) chips and small-sized chip electronic components can form fine patterns on silicon wafers for sealing frames and electrodes at once without any waste and a 100% usage rate (the ratio of material that can be mounted on a product) of expensive gold material. This is expected to lower the effective cost of key processes.



Current technology



Technological development and practical application aimed at reduced size, improved functionality, improved performance and lead-free soldering are currently being accelerated in the advanced device industry. Manufacturers in this industry has formed complex patterns such as hermetic sealing frames and electrodes on wafers with metals such as gold and gold-tin by combining multiple patterning processes such as plating, screen printing and sputtering. This not only lowers rate of the production, but also decreases the efficiency of material utilization by going through several different processes and requires the reduction of material cost.



Furthermore, micro-bump bonding technologies such as gold bumps using plating and solder bumps are currently used in electrical connection processes, but these present issues such as the inability to obtain sufficient bonding stability because of hardness of gold bumps and unexpected contact by fluidity of molten solders. In addition, for hermetic sealing processes, technologies such as conventional anodic bonding and glass frit bonding, along with the recently developed metal-metal bonding using film deposition or plating are currently used, but the need for bonding at high temperatures and reduced yield caused by uneven surfaces have been issues.



Because of above issues, it is becoming difficult to meet all performance requirements such as high heat conductivity, high heat resistance, narrow line width and narrow pitch when using current technologies in the mounting of the latest devices such as high-brightness LEDs, which require stable operation at high temperatures.



Development of pattern transfer and bonding technology using sub-micron gold particles



In order to resolve such issues, through this joint development, precious metal material manufacturer Tanaka Kikinzoku Kogyo has developed manufacturing processes of a substrate for pattern transferring of sub-micron gold particles which offer higher heat resistance and lower stress than existing joints by soldering, and able to be bonded at low temperature due to its size effect. Meanwhile, SUSS MicroTec, which sells wafer bonding devices globally, will develop a wafer-level transfer and bonding equipment using such transfer substrates. This technology development is being carried out with the cooperation of Professor Shuichi Shoji and Associate Professor Jun Mizuno, Nanotechnology Research Laboratory, Waseda University.



The pattern transfer and bonding technology developed here enables electrical connections and hermetic seals with the minimum necessary amount of gold material while also resolving issues faced when using current technologies. It is perfect for the following manufacturing processes.



Hermetic seals in advanced MEMS

One-time processing of hermetic seals and electrical connections in advanced MEMS

Formation of bump electrodes in devices operating at high temperatures, such as high-brightness LEDs and power semiconductors

Formation of minute bump electrodes on small-sized chip electronic components

3D integration of wafers



Tanaka Kikinzoku Kogyo and SUSS MicroTec will have a joint booth at Exhibition Micromachine/MEMS 2011 held at Tokyo Big Sight (Ariake, Koto-ku, Tokyo) on July 13 (Wed.) -15 (Fri.), 2011. The booth (East Hall 2, B-05) will contain exhibits of samples of transfer substrate of sub-micron gold particle and substrate subjected to transferred patterns, and technical staff will be on-site to respond to interviews.