The increase in current density in future power semiconductor chips requires an increase in the wire’s cross-sectional area within the power module. Today, ultrasonic wire bonding is used for electrically interconnecting semiconductor chips. This manufacturing process is to be further developed in order to reliably bond producer goods with large cross-section, which requires high ultrasonic power. However, current methods cannot be simply upscaled, because this would result in high loads and consequently to the damage of the components to be bonded. A multidimensional and possibly multi-frequency excitation is intended to introduce the necessary ultrasonic power into the contact zone economically and efficiently without causing any damage.
Due to the increased ultrasonic power in a newly designed oscillating system, the soldering process in power semiconductor modules can be substituted, while increasing bonding quality, efficiency and flexibility of the production process. Thus, a wide variety of interconnects can be performed with a production machine just by changing the tool.
Significantly more ultrasonic power than provided by current bonding machines is required for bonding producer goods made of copper with a large cross-section area (up to 1 mm2, currently 0.3 mm2). For simplicity, it is assumed that the bond quality depends on the amount of friction per surface area. Thus, as the cross-section area increase, so does the amount of friction required to facilitate a process-safe bond at usual process times increase. Basically, the friction welding of producer goods with a large cross-section area cannot be achieved by an increase in the process time since a certain activation energy or the exceeding of the stick-slip-limit and thus a minimum amplitude is necessary. A novel oscillation system is designed to avoid damage by a multidimensional and possibly multifrequency excitation, since a dimension adaptation or scaling of current oscillation systems with correspondingly increased absolute oscillation amplitudes would lead to a very high load/stress on the components to be interconnected.
The project has three goals:
- Firstly, the design and construction of a suitable ultrasonic oscillation system, which can provide the necessary bonding friction.
- Secondly, the design of the appropriate tool for different producer goods that are resonantly tuned to the set-up vibrating system.
- Lastly, the high amount of friction in the bonding plane due to the large cross-section area and the use of producer goods made of copper must be accommodated, depending on the application, by a suitable clamping of the power semiconductor module.
Project duration: 01.04.2016 – 31.03.2019
Project contributor: Leitmarktagentur.NRW
Project partners: Hesse GmbH, Infineon Technologies AG
Associated partners: Weidmüller Interface GmbH