Is a HASL surface finish appropriate for edge connector plating?

I'm working on a daughter board PCB which will plug into a larger board. I'm interested in trying out edge connector plating for the connection type. However, I'm not sure on what surface finish is appropriate for edge connect plating.

Doing a bit of research, I've found that a hard gold finish (gold fingers) is a popular method due to its robustness. However, I'm thinking this is not a cost effective solution.

I know that a lot of board houses use HASL surface finish as default, would it be appropriate to use HASL as edge connect plating? How concerned should I be of ware?

• It also depends on how long you want your products to last. Look around, do you see many edge connectors not gold plated that survived a long time? – PlasmaHH Feb 13 '17 at 19:56
• I don't think so. I have never seen it used that way. – mkeith Feb 13 '17 at 19:57
• @PlasmaHH I'm not quite sure... I just know gold is more common. – Izzo Feb 13 '17 at 20:02
• More common, or the only thing you ever saw? – PlasmaHH Feb 13 '17 at 20:03
• The very lowest cost low quality products sometimes use the HASL finish on edge card fingers. I've seen it many times on scrapped electronics that you may come across at an electronics surplus outlet. With that said I have also noted that many times such connector joints are corroded and oxidized. – Michael Karas Feb 13 '17 at 20:04

Gold is best. Some board houses can do it on a selective area (such as just the connector), for a lower cost.

If you just need a prototype, something that can tolerate bad contacts and does not require high speed, HASL will work, but it is not the best.

Gold is used because it is the most corrosion resistant material with decent conductivity. You have to mate with a edge connector and they are gold plated. You do not want to mate two different materials. Conductivity of solder (HASL) is not that great and makes it a fair to poor contact. HASL has poor surface planarity.

Use gold, does not cost much more.

• At the risk of being off topic, I'm not at all fond of board edge connectors. Better a 2-part connector where you are probably guaranteed quality plating. So tell me I'm wrong. – Robert Endl Mar 23 '17 at 20:24
• I found that gold plating costs significantly more - up to twice as much - on some panel-share services where HASL is the standard option and therefore cheaper. For instance PCBWay quoted me a certain price for HASL, about twice as much to gold-plate the whole board, and four times as much again for HASL with a gold-plated connector. I'm assuming if I wanted HASL with a gold-plated connector they'd have to do a custom run just for me. – immibis Apr 27 '18 at 7:32
• @immibis I have found at PCBWay if you first select immersion gold (ENIG) then gold fingers there is no up charge for gold fingers. I have never done gold fingers with them but assume the fingers will be ENIG rather than electroplated gold. I do use the Immersion gold because it has very good surface planarity for mating with heatsinks. ENIG's is softer and its adhesion is not as good as electroplated. ENIG is very often used for contacts, unless the board is repeatedly plugged in and removed. For electroplated gold, use a fab house that does the fingers separately. – Misunderstood Apr 28 '18 at 16:09
• @Misunderstood Correct, if you want ENIG over the whole board there is no charge for gold fingers (because they're getting plated anyway I assume). It still was about twice as expensive with ENIG as it was with HASL, so if you choose ENIG just to get a gold connector, you're paying twice as much. – immibis Apr 28 '18 at 22:26
• @immibis Depends on quantity and size. It was about 20% for my order of 20 LED strips 560 mm x 9 mm ($169 vs$217). HASL is fine if it's not going to be unplugged, subjected to excessive vibration, or will be used only in-house use. I would not put HASL fingers out in the field. – Misunderstood Apr 28 '18 at 22:58