Whiskers growth on thick tin layers and various types of surfaces

The transition from a highly widespread lead solders to lead-free solder alloy types meant many changes in the electrical industry. This transition has brought many technological phenomena that deserve our attention and they have to be still addressed in order to improve the quality and reliability of manufacturing printed circuit boards. One of them is the presence of small crystalline formations on the surfaces of tin and some tin alloys which are called whiskers. This article focuses on the influence of the used electrical materials and their surface treatments on the growth of tin whiskers. For our experiment were selected two lead-free solders with a high percentage representation of tin, by which are Sn95,5Ag3,8Cu0,7 (SAC 387) and Sn99Cu1. Solders were plated in a thick layer on the three types of metal substrates with various surface finishes. For this experiment was chosen copper, brass and phosphor bronze. The created samples were exposed to static mechanical stresses of compressive force under the action of permanent constant temperature at 50 degrees of Celsius.