Deposition and Utilization of Nano-Multilayered Brazing Filler Systems Designed for Melting Point Depression

As shown in previous investigations a significant melting point depression (MPD) of a brazing filler can be achieved when using nano-multilayered material systems built up from thin films separated with insulating diffusion barrier layers (DBLs) [1], [2]. In this study, nanolayers of Ag-Cu brazing filler insulated by thin film diffusion barrier layers (AlN, W, C) were manufactured by means of a magnetron sputter PVD device. The deposition of the nanolayers was optimized for a customized as well as a commercial sputtering system in order to utilize the process for industrial usage with a focus on a uniform multilayer design. The thickness of the brazing filler was varied between 2-20 nm to analyze the scaling effect. The melting point depression was estimated by the HT-XRD measurements in the temperature range between 25° and 780°C. It was found that besides the thickness of the brazing filler layer, the type of the diffusion barrier layer and the resulting material interfaces are critical for the amount of the melting point depression. The greatest melting point depression of about 100°C was observed for the Ag-Cu/C system.

The flow of the molten brazing filler and the behavior of the diffusion brazing layers during the heating process were observed to utilize the system in the brazing process. Preliminary results show successful formation of the metallurgical bond at temperatures much below the bulk melting point of the eutectic Ag-Cu brazing filler.

[1] Patent DE 10 2008 050 4330A1 2010.04.15 filed by Empa/Behr.
[2] V.Bissig, J.Janczak, Empa Activities 09/10, p.8, Advanced Materials and Surfaces