Comparison of Electroplated Ni and PVD Ni Coating Layers after Soft Soldering Process

Abstract

This work is part of a publicly funded project called ReffiMaL (resource efficient material solutions for power electronics), which aims to substitute electroplated Nickel (Ni) as contact material in power electronic modules. The baseplates of these power electronic modules are based on the metal matrix composite material AlSiC, which needs to be coated to become solderable. Today, it is state-of-the-art technology to coat the baseplate with electroplated Ni to form an adhesive layer to the system solder. In this paper we present a performance comparison of physical vapor deposited (PVD) Ni and electroplated Ni. The main advantage of PVD Ni is a significant reduction of layer thickness compared to the electroplating process. Second advantage of PVD Ni is the limitation of the deposition to areas that get soldered, in contrast to a non-selective electroplated coating. When deposited by PVD at room temperature, Ni exhibits columnar growth patterns, whereas electroplated Ni tends to form a laminar layer. The columnar growth leads to an increase in interface area affecting phase formation behavior. To compare both adhesion layers, we investigate the phase formation after soldering with a Sn based soft solder-copper composite material. The baseplates are reflow-soldered at different temperatures and process times. Temperature varied between 270°C and 400°C. The corresponding process time ranged from 10 to 40 minutes. We inspect the samples optically to determine the phase formation. Intermetallic phase (IMP) composition is evaluated using energy dispersive X-ray analysis (EDX). ReffiMaL is funded by the German Federal Ministry of Education and Research (BMBF).