Tin Whisker Growth On The Surface Of Sn(Cu)

Sn whiskers, which grow from the Sn or Sn alloy layer, is a single crystal. It has a very high current load ability, and can lead to serious damage to electronic components. The growth of Sn whiskers is the major challenge in the electronic packaging industry, so the mechanism of Sn whiskers become the focus of present study.We studied the growth of Sn whiskers under different conditions in my paper, in the first part, Sn films, 1200nm in thickness, were sputtered on copper substrates using magnetron sputtering method, which were then annealed in the condition of argon at different temperatures. At the temperature of 50°C, which was considered to be the most appropriate temperature for Sn whiskers growth, the Sn whiskers got the best length and density. While at higher temperature of 150°C, the quantity of the Sn whiskers will decrease because of the disappearance of the internal residual stress and the transformation of the intermetallic compounds.In the study of electromigration, we sputtered Sn and SnCu films on glass substrate using blech structure and mask method. With different addition of Cu, we investigate the electromigration of SnCu films. For the pure Sn film, at lower current density, Sn whiskers and void structures will appear near the anode and cathode respectively, due to the electron wind force and joule heat. At higher current density, Sn hillocks, instead of Sn whiskers, will appear at the anode side. With the addition of Cu, the internal and surface structure of SnCu films will be changed. As the mobility of Cu is quicker than that of Sn, there will be SnCu hillocks forming at the anode side of the samples. With the increase of Cu addition, Sn and Cu will react to form intermetallic compounds due to the influence of the current, this will inhibit the electromigration in some way. The main diffusion mechanism of the samples is found to be grain boundary diffusion and the existence of Sn inhibits the surface diffusion of Cu. As for intermetallic compounds, eletromigration effect is not significant at low current density, while it becomes much more clear with the increasing current density. Compared with that of SuCu, the eletromigration effect is much slower. As to the reason of the migration phenomenon, we use blech effect to explain.