Considerations for Selecting a Printed Circuit Board Surface Finish
Authors: Randy Schueller, Ph.D. Company: DfR Solutions Date Published: 10/24/2010
Abstract: The selection of the surface finish to be used on the PCB could be the most important material decision made for the electronic assembly. The dominant surface finish prior to the implementation of RoHS was SnPb HASL. With the elimination of Pb and the need to attach components with finer and finer pitch, a number of planar surface finishes have recently gained in market share. These include ImAg, OSP, ENIG, ImSn along with some newer options to be discussed. The surface finish influences the process yield, the amount of rework necessary, the field failure rate, the ability to test, and of course the cost. One can be lead astray by selecting the lowest cost surface finish only to find that the total cost is much higher. The selection of a surface finish should be done with a holistic approach that considers all important aspects of the assembly. This paper will weigh the attributes of the various finishes and make suggestions of which fits best with various product applications. In situations where there is no clear fit, various engineering tradeoffs can be made.