Ni barrier for tin whisker mitigation

In the present work, a close-to-product investigation was conducted in evaluating tin whisker growth on electroplated matte Sn films. The matte Sn films were deposited on Cu leadframes (C194). Electroplating Ni film was used as a barrier between the Sn film and the substrate. The experimental results revealed that Ni barrier could completely restrain the tin whisker growth after 8,000 hours storage at 55°C/85%RH. However, it was found that cracks often formed from the surface during forming process, reflow process and even storage under thermal/humidity condition. Crack formation and corresponding stresses in different processes were investigated. The thicker Ni barrier could induce considerable mechanical damage to the matte Sn films of the IC leads. It was found that thinner Ni barrier layer could withstand the forming stress, thermal mismatch stress and IMC-induced stress without causing cracks in the matte Sn films and thus did not promote Sn whisker growth.