The effect of Bi addition on the formation of metal whiskers in Ti2SnC/Sn-xBi system

Abstract

The spontaneous growth of tin whiskers on tin-rich solders and platings has haunted the electronics industry for more than 70 years. Reliable mitigation strategies are long-waited with the proceeding of lead-free movement. However, the development of mitigation strategies has been retarded for lack of a clear whisker growth mechanism. Herein, a new research platform of Ti2SnC is developed, in which fast tin whisker growth with excellent repeatability is realized. The sample of Ti2SnC/Sn-xBi is prepared using ball-milling method, to reveal the effect of Bi addition on the growth behavior of Sn whiskers. Compared with the Ti2SnC/Sn system, an extended nucleation period is identified in Ti2SnC–Sn5Bi, Ti2SnC–Sn15Bi, Ti2SnC–Sn20Bi, which mitigates the growth of Sn whiskers in the initial stage; however, when cultivated at proper parameters, the density of Sn whiskers is found to increase with the rising of Bi content. Finally, the growth kinetics was studied using ESEM. A linear relationship between whisker length and square root of the holding time is obtained, suggesting a diffusion-controlled mechanism for the growth of Sn whiskers in this work.