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January 2017 • The PCB Magazine 15 finish is expensive to process and is still rela- tively low-volume in the market. Fabricators are slowly bringing this process in-house as volume makes outsourcing less economical. Things to keep in mind: • Gold and aluminum wire bonding • Applications include medical and U.S. military • Excellent solderability • Mitigation of black pad • Gaining interest and acceptance in the market There are many factors to consider when se- lecting a final surface finish and unfortunately, there is not a universal finish that works best for all applications. Understanding the advan- tages and disadvantages of each surface finish allows the designer to select the surface finish that best fits each application. Chemistry sup- pliers, fabricators and assemblers are all happy to offer suggestions based on their experience, take advantage of the resources available if you have questions or need assistance. PCB Tara Dunn is the president of Omni PCB. To read past columns or to contact her, click here. FINAL SURFACE FINISH: HOW DO YOU CHOOSE? • Easily scratched; sliding connector limitations • Microvoiding is something to be aware of with soldermask defined pads ENIG—Electroless Nickel/Immersion Gold ENIG has become one of the most common surface finishes and is often seen in aerospace and defense, medical, and other high perfor- mance markets. It is also predominant in the flex market. While this process requires many processing steps and numerous chemical analy- ses, fabricators run this process day in and day out with very little issue. Things to keep in mind: • Applications associated with high reliability • Used often in the flex market • High corrosion resistance due to nickel barrier • Aluminum wire bondable • No degradation between reflow cycles; can be held mid-assembly for extended times • Potential for nickel corrosion (aka black pad) if time in gold bath is excessive ENEPIG—Electroless Nickel/Electroless Palladium/Immersion Gold ENEPIG is the new kid on the block. A sig- nificant advantage to this finish is that it is gold wire bondable. Typical applications are in the medical and the U.S. military markets. This Sandia National Laborato- ries researchers have shown it is possible to make transistors and diodes from advanced semicon- ductor materials that could per- form much better than silicon, the workhorse of the modern electronics world. The breakthrough work takes a step toward more compact and efficient power electronics, which in turn could improve everything from consumer electronics to electrical grids. Power electronics are vital for electrical systems because they transfer power from its source to the load, or user, by con- verting voltages, currents and frequencies. Sandia's research was published this summer in Applied Physics Letters and Electronics Letters and presented at conferences. Honey, I Shrunk the Circuit

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