A Comparison of Electrodeposited Tin and Tin/Lead Coatings on Nickel Barrier Terminated, Multilayer Ceramic Chip Capacitors

Abstract

Nickel, as a barrier to the dissolution of termination materials, requires a solderable coating to prevent nickel oxidation and preserve solderability of surface mount devices. Most multilayer capacitors (MLCs) are supplied with tin or tin/lead coatings electrodeposited over the nickel barrier layer. There is general disagreement in the electronics industry about preferred solderable finishes and solderability test methods of component leads. Tin and tin/lead finishes have typically been compared on leaded devices. The results of these studies are not necessarily applicable to leadless surface mount chip components. This study compares 100% tin and 60/40 tin/lead electroplated coatings on nickel barrier terminated, multilayer chip capacitors (MLCs). Various thicknesses of tin and tin/lead were compared for solderability after steam‐age, solder joint strength, and chemical and physical composition of the reflowed termination surface. The results show no significant difference between the solderability and joint strength under vapour phase reflow conditions using 60/40 solder paste. The termination surfaces were reflowed at 215°C in the case of both pure tin and 60/40 tin/lead. The tin/lead finish reflowed to a composition of 60% tin/40% lead. The 100% tin finish reflowed to a composition of 90% tin/10% lead. Reflow was caused by diffusion of lead and tin.