Slide switch using ENIG contacts?  - Page 1
Forum section: electronics / projects

author: ebastler
author_rank: Super Contributor
timestamp: June 18, 2024, 10:01:58 am
content: For a little toy/demonstrator, I am contemplating to have my own slide switches incorporated directly into the PCB: Contact pads on the PCB, and a mechanical slider with contact springs guided in a PCB slit. Same principle as the rotary switches in multimeters, but in a linear geometry.(The reason for this approach is that I want largish switches, with 8 positions which align visually with the circuit and LEDs on the board. The idea is to build a demonstrator for magnetic core memory, which should be functional but as simple and visual as possible. 8*8 cores and two slide switches to select row and column address, plus read/write buttons and indicator lights for write current and readout signal.)The proper way to implement this would be hard gold contacts, I guess. But since hard gold is either unavailable or quite expensive at the low-cost PCB manufacturers, I am wondering whether I could get away with ENIG instead. This gadget would be a desk toy for hobbyists, or might be used for occasional classroom demonstrations. Hence, if the contacts are good for a few hundred operations, that should be adequate.Has anyone tried ENIG in settings where it undergoes repeated mechanical rubbing/wiping? How well does it hold up? Thanks for your insights!

author: Haenk
author_rank: Super Contributor
timestamp: June 18, 2024, 12:11:58 pm
content: Sir Clive Sinclair got away with using just tin plated PCBs and ordinary (Nickel?) springy things inside the slider switches on his calculators.So if *he* could do it, and even receiving the knighting, you could do as well. Minus the knighting, I guess...

author: twospoons
author_rank: Frequent Contributor
timestamp: June 18, 2024, 08:39:11 pm
content: Considering the gold will be 3um thick at best, and soft as butter, expect it to be scraped off in a few cycles.

author: wraper
author_rank: Unknown
timestamp: June 18, 2024, 08:57:21 pm
content: Quote from: twospoons on June 18, 2024, 08:39:11 pmGold will be 0.2um at best but most likely several times less, nickel underneath it will be in the ballpark of what you wrote.

author: wraper
author_rank: Unknown
timestamp: June 18, 2024, 09:03:35 pm
content: Quote from: Haenk on June 18, 2024, 12:11:58 pmAFAIK they were notorious for being unreliable. Sir Clive Sinclair produced a lot of cheap shit that did not last.

author: ebastler
author_rank: Super Contributor
timestamp: June 19, 2024, 07:58:34 am
content: Quote from: twospoons on June 18, 2024, 08:39:11 pmWell, yes, the concern is that thismighthappen. But I was wondering whether anybody has ever tried? It's not like I will be applying a lot of force and sharp edges. And people do seem to get away with using ENIG for card edge connectors -- although presumably for very few insertion cycles.I guess I'll have to do some experiments. Have some obsolete, bare ENIG PCBs around, but need to look for suitable springy contacts with a realistic pressure and rounded surface. (Which I would need to locate anyway if I wanted to actually build this.) I'll add an update here when I have some results.

author: jfiresto
author_rank: Frequent Contributor
timestamp: June 19, 2024, 09:09:35 am
content: Quote from: ebastler on June 19, 2024, 07:58:34 amI would be curious how many cycles you get if you were to apply a polyphenyl ether contact lubricant.

author: twospoons
author_rank: Frequent Contributor
timestamp: June 20, 2024, 02:43:28 am
content: ENIG plating will oxidise eventually. I've seen it myself - the pads go black. That tells you how little gold is on there - just enough to maintain a solderable surface for a few months. You'd probably do better with silver plating - its cheaper, thicker and harder. I've seen plenty of rotary switches with silver plating.

author: Whales
author_rank: Super Contributor
timestamp: June 20, 2024, 07:09:15 am
content: Quote from: ebastler on June 19, 2024, 07:58:34 amI'm lead to believe this is "hard gold" not "ENIG". Much thicker, separate process that costs extra.

author: jfiresto
author_rank: Frequent Contributor
timestamp: June 20, 2024, 08:18:08 am
content: Quote from: twospoons on June 20, 2024, 02:43:28 amAttached is an example on its way to black.

author: langwadt
author_rank: Super Contributor
timestamp: June 20, 2024, 08:19:50 am
content: "black pad syndrome" is a defect in the plating

author: jfiresto
author_rank: Frequent Contributor
timestamp: June 20, 2024, 10:20:27 am
content: I do not think anyone was writing about black pad syndrome - just the ENIG plating slowly going black because of the thin, microporous gold layer. I suspect that dragging a switch contact over the layer is just going to make it thinner and accelerate the issue.FWIW, the above PCB has been in storage for a couple years in an atmosphere with a high salt content. I am about 60km from the sea which is close enough to mock stainless steels and provoke galvanic differences.

author: wraper
author_rank: Unknown
timestamp: June 20, 2024, 11:13:35 am
content: Quote from: jfiresto on June 20, 2024, 10:20:27 amIt's going black because plating was defective to begin with. Unless board is kept in highly corrosive atmosphere something like that won't happen unless there were hidden defects under the gold layer. I'm 15km from the sea BTW, and something like this does not happen here because you'd need to put it on the beach for this to happen with properly manufactured board.

author: ebastler
author_rank: Super Contributor
timestamp: June 20, 2024, 11:50:06 am
content: Quote from: wraper on June 20, 2024, 11:13:35 amI have unused PCBs from JLCPCB which have been sitting on the shelf for five years or so, and the ENIG pads all look like new. I have also used PCBs as front panels repeatedly, using ENIG gold accents a couple of times, and don't see them tarnishing in any way.Quote from: Whales on June 20, 2024, 07:09:15 amYes, that's the proper way, as stated in the OP. But e.g. JLCPCB has a "edge connector" option which comprises purely the mechanical beveling of the PCB edge, and uses their regular ENIG process. I have not used this option but assume that it can't be totally useless, since they continue to offer it.

author: wraper
author_rank: Unknown
timestamp: June 20, 2024, 12:02:50 pm
content: Quote from: ebastler on June 20, 2024, 11:50:06 amIt's OK for prototypes or if it needs to be inserted into the slot only once.

author: jfiresto
author_rank: Frequent Contributor
timestamp: June 20, 2024, 01:19:45 pm
content: Quote from: wraper on June 20, 2024, 11:13:35 amThank you for that and the attachment. That is all good to know in different ways. I am going to watch those blank PCBs and see what develops.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 20, 2024, 07:59:50 pm
content: IMO, you need to think about contact area and pressure. Too high and nothing will hold up. Too low and it will be intermittent. Low but sufficient should get you where you need to go. I've seen this work with non-gold boards, but I don't know what they were plated with. Maybe tin but maybe some kind of nickel.

author: thm_w
author_rank: Super Contributor
timestamp: June 20, 2024, 11:31:52 pm
content: This is no different than the teardown dave did:Add some silicone grease, use low contact force, should be fine.

author: Njk
author_rank: Frequent Contributor
timestamp: June 21, 2024, 06:48:40 am
content: That's a fake chinadevice. A true resistor box is of different appearance

author: tooki
author_rank: Super Contributor
timestamp: June 21, 2024, 12:11:04 pm
content: Quote from: ebastler on June 19, 2024, 07:58:34 amIsn’t this exactly what very cheap multimeters do?

author: Psi
author_rank: Super Contributor
timestamp: June 21, 2024, 12:22:37 pm
content: You can buy hard gold plated metal pads for placement by SMT.Sadly they are a bit pricy if you need lots of them.https://www.digikey.co.nz/en/products/detail/harwin-inc/S70-138305045R/6211249

author: thm_w
author_rank: Super Contributor
timestamp: June 21, 2024, 10:30:19 pm
content: Quote from: Njk on June 21, 2024, 06:48:40 amIts an ultra low cost version, not a "fake", will work fine for light use. Obviously after some time it will wear out, but OP only cares about a few hundred operations.Quote from: tooki on June 21, 2024, 12:11:04 pmExactly, I'm sure a $2 meter doesn't use thick gold plating. They just have very light contact force.

author: wraper
author_rank: Unknown
timestamp: June 21, 2024, 10:33:00 pm
content: Quote from: tooki on June 21, 2024, 12:11:04 pmThey at least have some thin gold or nickel looking plating, not bare copper.

author: tooki
author_rank: Super Contributor
timestamp: June 22, 2024, 11:35:40 am
content: Quote from: wraper on June 21, 2024, 10:33:00 pmNo part of this entire discussion has been about bare copper.The thread title says ENIG. The post I was replying to was about ENIG. So any reasonable person would assume I’m talking about ENIG, the topic of this thread. Literallyno onementioned bare copper here until your response to me.

author: wraper
author_rank: Unknown
timestamp: June 22, 2024, 12:52:19 pm
content: Quote from: tooki on June 22, 2024, 11:35:40 amActually it was, cheap Chinese decade resistor box in Reply #17. I mistakenly thought you were replying to a post about that.

author: tooki
author_rank: Super Contributor
timestamp: June 22, 2024, 12:58:46 pm
content: Quote from: wraper on June 22, 2024, 12:52:19 pmOK. I didn’t bother watching the video.With that said, I used the quote tags to make it unambiguous what I was responding to. The post I quoted came much earlier than the video.

author: ebastler
author_rank: Super Contributor
timestamp: June 25, 2024, 12:50:27 pm
content: Quote from: tooki on June 21, 2024, 12:11:04 pmHmm, if so, buying a very cheap multimeter would provide me with a nice test device. (I was wondering where to get and how to mount suitable sliding contacts for a test.)Is there an unambiguous way to recognize ENIG and distinguish it from proper hard-gold pads? You can always scratch it and see how much damage that does, I guess, but that's not a very clear-cut test and will it depend on subjective interpretation whether a surface behaves "soft" or "hard". Any chemical or microscopic test where the two surface types show qualitative differences?

author: langwadt
author_rank: Super Contributor
timestamp: June 25, 2024, 01:23:01 pm
content: Quote from: ebastler on June 25, 2024, 12:50:27 pmfor fingers the hard gold is plated so all the pads have to be electrically connected and then milling out the board removes the connection

author: tooki
author_rank: Super Contributor
timestamp: June 25, 2024, 10:11:26 pm
content: Quote from: ebastler on June 25, 2024, 12:50:27 pmENIG is generally a much less saturated gold color than hard gold.As for sliding contacts: look at the spring contacts intended for battery packs, like Bourns 70AD series, Samtec SIB series, Kyocera 9155 series, etc. (DigiKey has a bunch of them in Connectors > Rectangular connectors > Spring loaded.) I don’t think most of those are expressly designed for sliding, but I imagine they’d work just fine for this project.