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Equipment, Consumable, and Process Development for Advanced Interconnect
Keywords: Advanced Interconnect, Power Module Market, Copper Cu
There are increased demands in the power module market for higher reliability, higher power density, and higher running temperature. The present Al (aluminum)-based interconnect technology will not satisfy all the requirements and the Cu (copper)-based advanced interconnect has gained more and more interest. The advanced interconnects, including Cu wire, Cu ribbon, AlCu clad wire, and AlCu clad ribbon, have high mechanical strength, low Coefficient of Thermal Expansion (CTE) mismatch with silicon, higher electrical and thermal conductivities. It was reported that a Cu wire bonded power module has >10 times more lifetime compared to conventional Al wire. However, the Cu-based materials are much harder and stiffer than the Al-based materials. The development of new bonding equipment, consumable, and process is crucial to bring the new technology into mass production. Kulicke & Soffa Industries has aggressively invested in this area. A new platform, Asterion, launched this year, has many improved features that make the bonding process more stable. A configurable bond head was released specifically for advanced interconnects. This bond head has several features that are experimentally proven to be necessary for advanced interconnects. A high power ultrasonic transducer works more efficiently with an improved signal-to-noise ratio, providing a more consistent bonding process and reducing bond failure rates. The increased bonding force and force ramp range makes bonding more efficient and produces stronger bonds. The stiffened cutting system enables clean cuts for the harder materials and significantly reducing die damage. The higher clamp force ensures the stiff materials are firmly held during the looping and cutting, improving loop and tail consistency. The harder Cu-based bonding materials wear bond tools and cutter blades much faster than the softer Al-based materials. In order to apply the advanced interconnects to mass production, consumable life has to be increased to reduce the bonding process cost. Material wear will be reduced by better coupling between the bond tool and the wire. The K&S patented bond tool was designed with specific tool geometry and 3 ridges in the tool groove. In our recent lab test of consumable longevity and process stability, the 3-ridge bond tool produced 100,000 bonds. The Cu-based advanced interconnects have different bonding mechanisms from the Al-based interconnects. Removing Cu oxide before a bond is formed is more difficult than removing Al oxide, and how the bond tool interacts with the bonding material is more critical. Several bonding phases were identified, and a segment bonding profile was developed, to optimize the process and achieve the best bond quality. Embedded in the machine's software, the segmented bonding function makes it possible to program multi-segment bonding sequences in order to achieve the best result in each phase of the bonding process. In combining equipment and consumables development with process development, we have improved our capability to provide a production-ready advanced interconnect technology. Our advanced interconnect technology is being adopted by several companies for their production. A damage-free process was recently developed for 80x8mil AlCu ribbon bonding on MOSFET devices and will go into production this year.
Tao Xu,
Kulicke & Soffa Industries, Inc.
Santa Ana, CA

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