Which Surface is Best?

RoHS has been in effect since, when, 2006? Pretty close to five years now. It's been around long enough that there's even talk of follow-on legislation. All of the PCB fab houses have pretty much figured out how to deal with RoHS. There are lead-free versions of every PCB finish at this point. But, we still get questions about the best choice of PCB finish.

I don't think the Industry has selected one PCB finish as the "standard" preferred choice. A lot depends on the application and the componentry being used. For large parts, HASL, leaded or lead-free, is a good choice. It's inexpensive and works well. For leaded work, HASL still seems to be the most common finish. We don't see quite so much lead-free HASL though.

If you're working with small geometry parts, then you really need to go to Immersion Silver or ENIG. The consistently flat surface of those finishes will help keep the small parts on the pads where they belong. The disadvantage of silver is that it requires a little more care in handling and storage. It can oxidize which will make soldering more difficult. ENIG is more expensive, but it tends to work real well and is easier to store. Fingerprints can be a problem though. We've seen the oils from a fingerprint essentially etch the gold surface off. Weird.

OSP becomes a viable choice with high-volume, cost critical applications. It used to be very sensitive to storage and handling, but has gotten a lot better over the last few years. We don't see immersion tin much at all. It apparently is harsher on the environment to produce than other finishes.

All that makes it more understandable that we don't have one preferred finish. It seems confusing, but really it's not that different than any other product. There certainly isn't just one preferred style of tire for all motor vehicles.

Duane Benson
Gotta have those monster truck tires if you live in Kelso

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Comments

Hola!

What are your thoughts on LPI over ENIG?

Eeek! Thanks for pointing that out. Yes, we prefer to do business with "fab" houses here.

Heh, I always wondered what went on behind the scenes! But I think you meant to write "fab house" instead of "fap house." ;)

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