How to Choose Surface Finish

There are many surface finish types to choose when designing a printed circuit board. Do you know how to choose the best one for your electronics assemblies? EPCB lists some common but popular finishes with pros and cons for each.

Hot Air Solder Leveling    HASL has been around for many years. A thin layer of solder is mechanically applied to copper surfaces. A hot air knife is used to sheet the excess solder away to create a flat finish. It is cheap, and available from all PCB suppliers. What’s more, it has really long shelf life, and good resistance against oxidation and against handling.    However, its surface flatness is difficult to control. This could be an issue for components that are sensitive to surface flatness like BGA, fine pitch components, etc. The hole size may not be uniform which could be an issue where press fit connectors are used. And HASL is not suitable for RoHS application.

Electroless Nickel Immersion Gold   ENIG is a chemical plating process where a thin layer of nickel and gold is deposited onto the copper surfaces. The gold preserves the copper below and it remains solderable and conductive with very low contact resistance. ENIG’s surface flatness is excellent, suitable for BGA or other fine pitch components, and also available from all PCB suppliers. Like HASL, it has good shelf life and good resistance against oxidation and handling.    However, it requires a tightly controlled plating process to prevent excessive gold being plated, and not suit some high frequency or high-powered RF application. Besides, its processing cost is much higher because gold is used in plating solution.

To be continued…