Thermosonic wedge-wedge bonding using dosed tool heating

This paper presents a novel thermosonic heavy wire and ribbon bonding process using a laser-heated bonding tool. The proposed thermosonic bonding process uses ultrasonic and thermal energy in a user-definable composition to achieve optimal connections. Through the substitution of vibration energy by thermal energy, ultrasonic vibration amplitude and/or normal force can be reduced, thus lowering the stress to the substrate. This improvement is most significant on substrates which react sensitively during purely ultrasonic bonding like battery caps, copper alloys, coated caps/clips or which are fragile like dies or sensors. Alternatively, the additional power can be used to reduce bonding time and therefore increase throughput and efficiency, or to produce stronger connections within the same bonding time. The temperature distribution at and around the bonding interface is investigated. During the process, it is necessary to ensure appropriate absorption of laser radiation at the tool tip. For this reason, a special tool with integrated optical fibre and optimized laser absorption was developed. Using a pyrometer and a closed-loop controller, the tool tip temperature is precisely controlled in real time. The temperature effect on bond strength is investigated; at a given bond duration and ultrasonic power, tool heating always increased bond strength significantly. Alternatively, the process time required for a desired bond strength could be reduced. Dosed tool heating using laser power is thus a very promising advancement in wedge bonding.