Relationship between the thermal stress and structures of thermal-cycling-induced cracks in electroless nickel plating on metalized substrates

Abstract

The cracking of nickel-plating films, which are typically utilized to prevent the oxidation of underlying metal conductor layers, is an important issue that affects the reliability of metalized ceramic substrates at high temperatures. In this study, we examined the structures of cracks formed in electroless nickel-phosphorous plating films deposited on copper-metalized silicon–nitride substrates, in response to thermal cycling over a temperature range of − 40 to 250 °C. Further, we calculated the stress induced by the thermal cycling and evaluated the relationship between the crack structure and thermal stress. The results revealed that the structures of the cracks could be categorized into three areas of the films. Essentially no cracks are formed in the film corners. In addition, the cracks formed near the film edges were oriented perpendicular to the edges themselves. Finally, the cracks formed in the center of the films exhibited a cobweb-like structure. The reason for the difference in the structures and quantity of the cracks depending on areas was explained by the thermal stress induced in the films. We estimated that the tensile stress induced at lower temperatures, instead of higher temperatures, during thermal cycling could cause brittle fractures in the films, leading to the generation and propagation of cracks. In other words, cracks could be formed at lower temperatures during thermal cycling. Further, we believed that cracking in the nickel-phosphorous plating films could be predicted by estimating the thermal stress induced in the films in numerical calculations.