I’m currently working on a 4-layer PCB design with FR4 material and a thickness of 1.6mm. I have ICs with 0.5mm pitch pads and some very small LEDs with 0.4mm pitch pads. I’m debating between using ENIG (more expensive) and HASL finish. I’ve read that for BGAs, ENIG is crucial, but I’m unsure about the pitch limit for QFNs where HASL finish would suffice. Additionally, does the choice between leaded or non-leaded solder make a difference in this context?
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ENIG is definitely the best finish for this application. It produces a thin, even coating which is necessary for mounting components this small and has excellent solderability. By comparison, Hot Air Solder Level produces a thick, uneven coating that doesn’t work well at all with fine pitch components. Pitch limit for HASL is considered to be at least 0.8mm but the process is so inconsistent and varies by machine that it’s best to run an F/A. Aside from environmental issues lead and lead-free both have pros and cons but both get the job done. Leaded has a lower melting temp, is easy to work with and a bit cheaper but some believe lead-free forms a better bond as it doesn’t flow as much. Think the main difference is how someone fells about lead.
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