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JANUARY 2025 I DESIGN007 MAGAZINE 65 face finish create the solder joint. is interme- tallic is different from the copper–tin created with other finishes and has pluses and minuses, but it does produce solid solder joints for most applications. Like immersion silver, ENIG cre- ates a flat surface but is slightly thicker than immersion silver. e main issue with ENIG is cost. Gold is among the most expensive raw materials, and the electroless immersion pro- cess is more costly than other surface finish application processes. Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) ENEPIG is essentially the same surface finish as ENIG, but with a layer of palladium added between the nickel and the gold. ENEPIG allows gold leads to be wire-bonded to the pads. is method is used for specialized applications that require wire bonding and is typically called out in the design specs. ENEPIG has the same cost considerations as ENIG, plus those associ- ated with adding the palladium layer, which can also create solderability issues that may impact board durability and operability. We recommend using ENEPIG surface fin- ish only on the parts of the board where it is necessary and using ENIG for all other sol- derable surfaces. is can help contain costs, improve manufacturability, and avoid issues with board function. Immersion Tin is method is like immersion silver. e result is a very flat and very thin surface finish that is cost-effective and has a relatively long shelf life. Immersion tin has low insertion fric- tion, making it a viable option where you have press-fit connectors. ough "nothing solders like solder," the introduction of tin makes this a very solderable surface finish. Immersion tin is more vulnerable to environ- mental conditions than immersion silver sur- face finish. Use boards treated with immersion tin promptly or store them with environmental concerns in mind. People use other surface finish methods beyond these five for more specialized applica- tions or to keep production costs down. Some of the more noteworthy ones are: • Electrolytic nickel with hard or so gold • Electroless palladium immersion gold (EPIG) • Organic solderability preservative (OSP) For a deeper dive into these three specialty surface finishes, listen to the Designing for Reality: Surface Finish episode of On the Line With… and keep an eye out for my last article in this series that discusses routing, final fab, and quality control. If you can't wait to learn how the story ends, check out Episode 12. DESIGN007 Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. To read past columns, click here. Download The Printed Circuit Designer's Guide to…Designing for Reality by Matt Stevenson. Designers can direct manufacturers to use multiple surface finishes. In the print, you can specify one surface finish for a specific area on the board and use one or more addi- tional finishes on the balance of the board. A surface finish combination makes sense in several situations, such as when a board uses press-fit connectors rather than solder- ing in one area and gold wire-bonding com- ponents in another. One Board, Multiple Surface Finishes