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the pros and cons of pcb surface finishes continues • Etching undercut can lead to slivering/ flaking • Not solderable above 17 μin • Finish does not fully encapsulate trace sidewalls, except in finger areas Figure 5: PCB with gold/hard gold surface finish. faces to be soldered, the recommended nominal thickness should be about 5–10 μin. Advantages: • Hard, durable surface • No Pb • Long shelf life Disadvantages: • Very expensive • Extra Processing/labor intensive • Use of resist/tape • Plating/bus bars required • Demarcation • Difficulty with other surface finishes 36 The PCB Magazine • January 2014 Conclusion It is important to select the appropriate surface finish for your project by considering the various options while factoring in performance requirements and material costs. For example, if you are looking for the lowest cost, then tin-lead HASL might seem like a good choice, but it is not suitable for RoHS-compliant products. If your product does require RoHS, you might consider lead-free HASL. But that is only if there are no fine pitch components, since LFHASL cannot be applied perfectly flat. If your design needs to be RoHS-compliant and uses fine-pitch components, then you'll need to select a flat, lead-free finish, such as immersion silver or ENIG. Bear in mind that doing so will necessitate the use of more costly high-temperature laminate. Unsure of what you will need? Consult with a PCB fabricator prior to making a selection. This will ensure that the combination of the surface finish and material will result in a highyielding, cost-effective design that will perform as expected. PCB Al Wright is a PCB field applications engineer with Epec Engineered Technologies.