Switch contact plating - Page 1
Forum section: electronics / projects

author: Rachie5272
author_rank: Regular Contributor
timestamp: November 23, 2021, 06:43:49 pm
content: I'm sourcing tactile switches, but encountered some quality issues. Sometimes the button will depress, but doesn't make electrical contact until it's pressed harder. The manufacturer says they're using titanium copper, plated with silver. Are these quality materials? What would be the best materials and platings to use on low voltage, low current tactile switches?

author: edpalmer42
author_rank: Super Contributor
timestamp: November 23, 2021, 07:23:55 pm
content: All switches and relays should have specs for both minimum and maximum current. The contact material doesn't affect the continuity - you just need to provide significantly more than the minimum current. Having said that, gold-plated contacts typically have the lowest current specs - and the highest cost! Of course, it doesn't matter what the contact is made of or plated with if it gets dirty. Is there any chance that the switch is being contaminated during manufacturing?I've never heard of titanium copper contacts, but I guess it's possible. AFAIK typical contacts are made of beryllium copper. Silver plating is widely used. It works fine - as long as you provide enough current.

author: thm_w
author_rank: Super Contributor
timestamp: November 23, 2021, 10:49:29 pm
content: - What is the part number of the switch?- Is this the case before or after soldering?- If after, how are they cleaned when soldering? (as edpalmer says)- What is the current you are running through the switch?

author: Rachie5272
author_rank: Regular Contributor
timestamp: November 25, 2021, 03:03:28 pm
content: Here is the datasheet. It's a rotary encoder, but only the pushbutton portion is acting up. The problem exists before and after soldering. Normal current is 250 uA, but I've tried up to 50 mA with no change. If they're getting contaminated, it's at the factory.The factory actually asked me to send a few of them back for diagnostics. Hopefully they can fix the problem.

author: edpalmer42
author_rank: Super Contributor
timestamp: November 25, 2021, 06:48:26 pm
content: It appears that both the switch and encoder are rated for a maximum of 5V@10ma., but I can't see any minimum rating. The Switching Characteristics test in Section 2.3 shows 1 ma., but is that under normal operating conditions or an extreme test? And since no specification is shown, it's meaningless anyway. The Sliding Noise specification in Section 2.4 shows 0.1 ma., but again, is that under operating or test conditions?I thought that the lack of minimum ratings was odd, but a quick check at Mouser shows that a lot of mechanical encoders don't explicitly list either minimum or maximum ratings. All they say is that the contacts are rated at 5V@10ma., for example. I did find one from Alps that was rated for min/max values of 1ma / 10ma.All I can suggest is to work with the vendor to confirm that your circuit is compatible with their encoder. I'm far from an expert in this area, but it seems to me that their (and other brands) datasheet could be better.Ed

author: Rachie5272
author_rank: Regular Contributor
timestamp: November 26, 2021, 06:16:27 pm
content: Yes, the datasheet definitely need works. This very much feels like a mechanical issue to me, and at least the vendor is interested in working with us.

author: TimFox
author_rank: Super Contributor
timestamp: November 26, 2021, 09:11:31 pm
content: I had never heard of titanium copper either, but it does exist. Apparently, its properties are similar to beryllium-copper alloy.https://www.nmm.jx-group.co.jp/english/products/alloy/copper/02ticu/c1990hc.htmlWith respect to minimum current and similar questions, the datsheet shows suggested resistive loads for the switches in paragraph 2.3, which imply recommended operating conditions.