SMTA International Conference Proceedings

Comparing PCB Surface Finishes and their Assembly Process Compatibility

Authors: Rob Rowland and Ray Prasad
Company: Axiom Electronics and Ray Prasad Consultancy Group
Date Published: 9/27/2015   Conference: SMTA International

Abstract: PCB (printed circuit board) surface finishes provide several important functions, the most important being solderability protection. The ideal PCB surface finish does not exist today. Every surface finish has some concerns that keep it from being the ideal finish. Surface finish selection has become more challenging as PCBA (printed circuit board assembly) complexity has increased (e.g. fine pitch components, BGAs, use of less active fluxes, etc.).

A PCB surface finish must be compatible enough with the assembly processes and end use application (i.e. product reliability) to achieve acceptable results. The end user must select the best overall surface finish for compatibility with their assembly processes and end use application (e.g. consumer products or space applications). This is not an easy task because there are so many variables. These variables include the flux chemistry and activity level, soldering environment (air or nitrogen) and the solder alloy. Each variable must be understood to achieve good soldering results and the desired level of solder joint reliability.

This is a user paper based on more than 25 years of experience working with all of the PCB surface finishes. The purpose of this paper is to provide users with a basic overview of the common surface finishes, their advantages and disadvantages, and some key assembly and reliability attributes to keep in mind when selecting a surface finish. The PCB surface finishes addressed in this paper are HASL (hot air solder leveling), OSP (organic surface protection), ENIG (electroless nickel immersion gold), ENEPIG (electroless nickel electroless palladium immersion gold), ImAg (immersion silver) and ImSn (immersion tin).

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