Development of a laser-assisted drop-on demand brazing process to extend the process limits of conventional wire bonding processes for electronics assembly and packaging (T04#)

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The aim of the proposed research project is the qualification of the drop-jet brazing process - developed within the framework of subproject A04 of the SFB/Transregio 39 PT-PIESA - as an alternative joining process for electronic assembly and interconnection technology (AIT). Ultrasonic wire bonding and soldering currently represent the state of the art in electronic AIT. In ultrasonic wire bonding, copper buffer layers must be applied to silicon semiconductors to prevent mechanical damage to the Si semiconductor during the bonding process. In soldering, the low thermal stability of the soldered joints of approx. 230 °C is increasingly posing a problem for their applicability, for example in power electronics. The drop-jet brazing process promises to avoid the disadvantages of the mentioned standard processes. In this process, a spherical, braze preform is introduced into a capillary, melted by a laser pulse and then expelled from the capillary by inert gas overpressure. Brazing alloys can be processed, which have a melting temperature of approx. 700 °C higher than the solder alloys, which increases the thermal stability of the brazed joint by a factor of three to four compared to soldered joints. Due to the non-contact nature of the process compared to ultrasonic wire bonding, high-temperature stable contacts can also be applied to foils, metallizations or electrode structures with a thickness of only a few micrometers. However, in order to qualify the process for series production in the electronic AIT, metallurgical compatibility between the base and brazing alloy must be ensured, taking into account in particular the passivation layers commonly used in the electronic AIT. The focus of the work is therefore to expand the fundamental knowledge acquired to date to a broader range of materials. It is assumed that both the solder alloy used and the volume of the braze preform as well as the base material, its passivation layer and its geometry have an influence on the process result. In order to be able to quantify these influences discreetly, the investigations are supplemented by numerical simulations. The contacts generated are characterized metallurgically, mechanically and electrically and evaluated with regard to their relevance for AIT. The potential fields of application for such a joining technology range from power electronics to the automotive industry and aerospace. The efficiency of Peltier elements, for example, can also be increased by high-temperature-stable bonding methods. In addition, the technology is also promising for packaging circuit carriers used in harsh environments.