There are many board finishes in use today and the EMS provider must learn to use many,if not all of them. However,all board finishes do not perform the same during assembly and test operations,which can impact assembly yield and solder joint reliability. One of the main characteristics the EMS provider wants is consistency. We want consistency in surface topography,appearance,wetting,solder joint formation,surface contact,etc. Consistency permits the EMS provider to tune their assembly process so that they can provide high yields with consistent solder joint formations. In order for a new board surface finish to be accepted for general use,it must be approved by the OEM as well as the EMS provider. The supplier must approach potential EMS and OEM users to determine their interest in the new finish. The EMS providers must run some trials to determine the advantages and disadvantages of the finish,compared to existing finishes. The OEM must determine if the finish is suitable for and compatible with the particular product application. This assessment must consider all of the assembly operations,test,and final field application. The resulting interconnections must provide a long term,reliable product for the OEM and end customer.

Over the last five to eight years the use of HASL alternatives by the OEM’s and CM’s has increased dramatically,particularly in response to increasing board density and the need for a solderable planar surface that increases their yields at assembly. The chemical industry has responded to meet the needs of the OEM’s but unfortunately some of the product offerings and the manner in which they were installed were less than stellar. This paper outlines for the OEM / CM engineer/auditor some of the areas that should be examined in more detail than might otherwise happen. The information outlined should also be used for surface finish engineers at PWB fab houses that might be new to a finish and may possibly save them from some very late nights on a line trying to understand a problem.