HASL vs ENIG for edge card connectors

[smbaker]

I assume the recommendation would be hard gold, but let's assume that is not an option (due to cost) and the choice has to be made between HASL and ENIG. This would be for hobbyist-grade boards, not commercial products. Of the two finishes, which is better?

My naïve intuition says that ENIG would be better, because it's gold, and because it costs more. But, I've also read that the ENIG is not particularly durable, and scrapes off after relatively few insertions, and for that reason HASL would be preferred.

Thoughts?

[Miyuki]

For single insertion and no touching after ENIG
For inserting ofter HASL is a good option and commonly used in the past

[T3sl4co1l]

Neither is great, because ENIG is thin, wearing through very quickly; while, tin or solder suffers from easy abrasion, and fretting corrosion against the gold-plated connector.  (That is, tin and gold aren't metallurgically compatible, forming a brittle interface layer that flakes off easily under motion.)

ENIG is probably better in general, since neither will be reliable in the long term / over many insertion cycles so at least ENIG gives you better connection at the start.  But over the long term, yeah, neither is great, maintenance will be required (contact cleaning, give it a whack if it starts going flakey..).

Tim

[MichaelPI]

HASL could cause some issues with the planarity of the mating surfaces - so far I have never seen any HASL for edge card connectors. I am not even sure, if there is any connector with tin mating surface available (typically Au over a Ni layer), otherwise as Tim already mentioned you use to dissimilar metals for the mating surfaces.
As far as I know, one would use hard gold plating for edge card connectors, if the board gets assembled multiple times.

[CatalinaWOW]

While I agree with every word in prior replies, there are two other factors which may make a difference in your choice.

1.  In many hobby grade connectors the contacts are not gold, making the metallurgical compatibility issue different if not moot.

2.  Hobby boards are likely using low density connectors.  A little thought on the board edge design will allow enough movement to get fresh contact area on latter insertions.

[T3sl4co1l]

Application is unstated, so in either case the solution is as above.

I think gold plated edge connectors are more common, but there certainly are exceptions.  Most game console cartridges I believe were tin plated!

Tim