The effect of postbake treatment on whisker growth under high temperature and humidity conditions on tin-plated Cu substrates

For matte tin-plated copper leadframes stored at 55 °C/85% relative humidity (RH) for 1800 h, nodule-shaped whiskers were observed on test samples without postbake treatment (WOPB), while no whiskers were observed on samples with postbake treatment (WPB). The WPB samples show a very regular layer of intermetallic compounds (IMCs) approximately 27% narrower than the same layer in the WOPB samples. The IMCs had two distinct layers divided into large-grains and fine-grains. The large-grain layers located on the Sn side grew before the fine-grain layers. The IMCs in the WOPB and WPB specimens were identified as Cu6Sn5 (monoclinic) and η-Cu6.26Sn5 (hexagonal).