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66 I-CONNECT007 MAGAZINE I APRIL 2026 considerations as ENIG, plus those associated with adding a palladium layer. That additional layer can also create solderability issues that may impact board durability and operability. We recommend using ENEPIG surface finish only on the parts of the board where it is necessary, and ENIG on all other solderable surfaces. This can help contain costs, improve manufacturability, and avoid issues with board function. Immersion Tin As the name suggests, this method is similar to immersion silver. The result is a very flat and thin surface finish that is cost-effective, with a relatively long shelf life. This surface finish has low insertion friction, making it a viable surface finish where you have press-fit connectors. Though "nothing sol- ders like solder," the introduction of tin makes this a very solderable surface finish with a copper-tin intermetallic bond. Immersion tin is more vulnerable to environmen- tal conditions than immersion silver surface finish. Boards treated with immersion tin should be used promptly or stored with environmental concerns in mind. These five methods represent the most com- mon surface finishes, but there are others used for more specialized applications or to keep produc- tion costs down. Some of the more noteworthy finishes include: • Electrolytic nickel with hard or soft gold • Electroless palladium immersion gold (EPIG) • Organic solderability preservative (OSP) I-CONNECT007 For a deeper dive into the wide range of surface finish options, listen to the Designing for Reality: Surface Finish episode of On the Line With… . Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. Matt is also the author of The Printed Circuit Designer's Guide to... Designing for Reality To read past columns, click here. C O N N ECT T H E D OTS Surface Finish Selection Tips Every electronic device project has unique priorities that will impact deci- sions made by PCB designers. You often have to balance budgetary constraints with design constraints and functional requirements. Consider: • If containing production costs is your focus, HASL is probably your best bet. It is less expensive than other surface finishes, has good solderability, can sit on the shelf for up to a year, and is durable. • More complex boards—those with high-density interconnects—will likely have fine pitch components. We often use ENIG in these cases because it offers great solderability, resists oxidation, produces supe- rior flatness, and ensures reliable joints. It's a sound choice for boards operating in harsh environmental conditions. • Immersion silver is a solid choice for high-frequency applications because it delivers excellent signal integrity and limited signal loss. • For devices operating in harsh environments, ENEPIG offers solid protection against corrosion and oxidation.