Reverse mount SMT tact switch that can be sub-flush when pressed for protection - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: June 17, 2023, 01:16:18 pm
content: Has anyone seenreverse-mountSMTtact switches that can't easily be damaged from finger push force because their travel can go sub-flush with 1.6mm PCB when pressed?For my application it would need a proper size plunger/button cap, like 4-6mm diameter for use by a finger.

author: PlainName
author_rank: Super Contributor
timestamp: June 17, 2023, 02:32:09 pm
content: If you've got that cap on then presumably the base of the cap would come up against the PCB to restrict travel? If so, why not just have a normal switch and put a spacer around it to achieve the same thing?

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2023, 12:14:39 am
content: I only have ever seen these:https://www.adafruit.com/product/5410Typical pushbutton tactile switch's post length value is usually from the post end to the back of the switch. Others use the switch's pins.These are 6.5mm minus the back of the switch 4.5mm thickness leaving 2mm... and 0.2mm travel.... and PCB thickness 1.6mm ... gives "0.4mm sticking up".Let us know if you find a vendor offering these in other post lengths. I could not find them anywhere else.

author: Psi
author_rank: Super Contributor
timestamp: June 18, 2023, 06:39:37 am
content: Quote from: floobydust on June 18, 2023, 12:14:39 amYeah, I was hoping someone else might have seen them but I knew it was a long shot. I couldn't find them either.

author: Psi
author_rank: Super Contributor
timestamp: June 18, 2023, 06:41:29 am
content: Quote from: PlainName on June 17, 2023, 02:32:09 pmCurrently the cap is a special part for the existing button. It's flat so just passes through the hole. It clicks onto the current tact switch shaft. I was hoping for a button with the cap built in.Like those larger TH tact buttons you can get, but reverse mount and SMT.

author: Psi
author_rank: Super Contributor
timestamp: June 18, 2023, 06:44:09 am
content: I think maybe the best option is going to be a custom height right angle metal frame TH button with extra long shaft.(Shaft needs to be long because there is a USB socket just below the buttons so it needs to go far enough back to avoid that)

author: ebastler
author_rank: Super Contributor
timestamp: June 18, 2023, 07:16:05 am
content: https://www.mouser.de/datasheet/2/140/E_switch_3_28_2023_RT3301-3134489.pdfOnly 3.5 mm button diameter, but the profile seems low enough for the plunger to stay below the surface of a 1.6 mm PCB.

author: Psi
author_rank: Super Contributor
timestamp: June 18, 2023, 08:32:08 am
content: Quote from: ebastler on June 18, 2023, 07:16:05 amWould need a separate button plunger part, but yeah, i guess that's an option.

author: wraper
author_rank: Unknown
timestamp: June 18, 2023, 08:47:03 am
content: The problem is with TACT switch construction. They have almost no further travel after activation point. So just PCB thickness tolerance, terminal height tolerance and overall switch tolerances makes this unfeasible. I guess the only somewhat feasible way is to use travel limited buttons with soft plunger and it still won't be a good solution. You generally don't see such switches used because it's very unreliable to apply lifting force to SMT solder joints.

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2023, 04:11:15 pm
content: I've also tried low profile 0.8mm C&K PTS625 andPTS526series but some are literally just the dome, thicker ones have a tiny 4mm post, then Littelfuse bought them and I gave up following that circus.I think reverse-mount tact switches could use some innovation to allow more protection and button/key caps options. But still seems to be trading off mashed pushbuttons for PC board flex.Designs nowadays are using overlays for front panels and switches. I have used ones with built-in dome pushbuttons and those that have a tact switch underneath. All can get destroyed by gorillas pressing hard on the switches, the overlays crack with sunlight and age when outdoors.

author: Psi
author_rank: Super Contributor
timestamp: June 19, 2023, 09:45:18 am
content: Quote from: floobydust on June 18, 2023, 04:11:15 pmyeah, it does seem that way.

author: thm_w
author_rank: Super Contributor
timestamp: June 19, 2023, 10:17:43 pm
content: Its possible to build a flexure or spring into the button that activates the switch and limit the pushing force to a known amount. Sort of what wraper is saying with the soft plunger.But you'd need a fairly low force tact switch, so it doesn't get torn from the PCB. That in combination with the soft element means the tactile feel is mostly lost.I'd go with the regular tactile dome or SMD tact switch and reinforce the back of the PCB.