Crack generation in electroless nickel plating layers on copper-metallized silicon nitride substrates during thermal cycling

The reliability of metallized ceramic substrates at high temperatures has been one of the main issues for high-power semiconductor modules. Cracks generated in the nickel plating layers, which prevent oxidation of the metal conductor layers, reduce the reliability. Thus, we evaluated the cracks generated in electroless nickel plating layers on copper-metallized silicon-nitride substrates subjected to thermal cycles of three different temperature ranges in air. The different temperature ranges for the thermal cycles were −40 to 150 \({}^{\circ }\text{C}\), −40 to 200 \({}^{\circ }\text{C}\), and −40 to 250 \({}^{\circ }\text{C}\). The results indicated that the cracks were generated in the Ni layers after 500 thermal cycles in the temperature range of −40 to 250 \({}^{\circ }\text{C}\). These cracks penetrated the Ni layer completely and extended into the Cu layers to a depth of several micrometers. Copper oxide formed under the cracks, part of which ascended through the cracks and deposited on the surface of the Ni layers due to the volume expansion during oxidation. On the other hand, no cracks were observed on the surface of the Ni layers even after 1000 thermal cycles when the upper limit of temperature was 200 \({}^{\circ }\text{C}\) or lower. The thermal cycles with the upper limit of temperature at 250 \({}^{\circ }\text{C}\) or higher strongly affected the formation of cracks in the Ni plating layers.