Evaluation of the Use of ENEPIG in Small Solder Joints in Thermal Cycling
Authors: Ben Gumpert, William Fox, C. Don Dupriest Company: Lockheed Martin Date Published: 9/17/2017
Abstract: The surface finish of a printed circuit board provides a number of functions, with impacts starting at the point of design and continuing through the life of the assembled product. Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) is a surface finish that has been demonstrated to have a variety of benefits, and to be suitable for both SnPb and Pb-free circuit card assembly. Extensive testing of ENEPIG has demonstrated the reliability of this surface finish and resulted in the creation of an industry standard for its application: IPC-4556 Specification for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) Plating for Printed Circuit Boards. When soldering to ENEPIG, all of the palladium is dissolved into the solder joint, and creates a palladium-rich region at the base (Pd source) of the solder joint. This palladium-rich microstructure, which typically exhibits a columnar shape, can spall off, into the bulk solder of the joint. With ever decreasing size of parts used in electronics assembly, the size of the solder joints correspondingly continue to shrink, which causes the relative size of this palladium-rich microstructure to grow relative to the overall joint thickness. In the first half of this work , the impact of industry standard Pd thicknesses on small SnPb solder joints in shear testing was evaluated. In the current phase of the study, similar joints are evaluated for reliability in thermal cycling.