Why these tactile switches fail on me? - Page 1
Forum section: electronics / projects

author: zapta
author_rank: Super Contributor
timestamp: March 09, 2015, 03:48:58 pm
content: I am using these swtiches in a low voltage circuit (3.3V, 10K pullup) and experiencing high failure ratehttp://www.digikey.com/product-detail/en/PTS810%20SJM%20250%20SMTR%20LFS/CKN10502CT-ND/4176673The symptoms are that the failed switches do not make a connection, unless if I press really really hard (though from the outside the look and sounds just fine), and it happens after I assemble the boards. In the last batch for example I soldered the buttons manually and then cleaned the boards with a foam swab and a liberal amount of IPA. Out of 8 buttons, 3 didn't work.I never tested the switches before assembling them.Any idea what's wrong? Is there the cleaning IPA which contains some dissolved flux? Are these low quality switches in general?I found them on DigiKey. They are inexpensive, small and have good tactile feeling.

author: wraper
author_rank: Unknown
timestamp: March 09, 2015, 03:55:41 pm
content: Insides could be corroded too because of the improper storage, however Digikey must have done that properly IMO. I would rip them apart and inspect contact surface under a microscope.

author: ion54
author_rank: Contributor
timestamp: March 09, 2015, 05:45:30 pm
content: I would think is the soldering. They are meant to go in IR reflow oven. Manually soldering might damage them. On top they do not look like sealed switches and cleaning with IPA can transfer some dirt inside.

author: georges80
author_rank: Frequent Contributor
timestamp: March 09, 2015, 07:19:08 pm
content: Likely contaminated contacts after 'washing'. Test a few prior to soldering. Then hand solder and test again.You may want to contact the switch manufacturer and ask what their cleaning recommendations are. Given it is unsealed switch, I'd guess any moisture/flux/etc getting into the contact area will cause issues, especially in a low current application like a uC input with a weak pullup.cheers,george.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 09, 2015, 08:29:36 pm
content: Yes, those seem like the most likely causes of your symptoms:1) Contact overload. But you confirmed that you are using a very "dry" (low-current, low-voltage) signal.2) Storage/shipment contamination. More and more components are specified to be kept in hermetically sealed containers (zip bags, etc.) and with moisture absorption and/or other reduced oxidizing environments, etc. But you said that you didn't test the switches BEFORE soldering, so we don't know whether this might be the problem. But buying the components from a main-line vendor (like DigiKey) would seem to reduce this as a possible cause.3) Contamination from soldering/cleaning is the other likely cause (IMHO). You mentioned hand-soldering and cleaning with IPA, but not really enough info for us to make any kind of meaningful conclusion. Depends on the flux, how much you used, exactly how you cleaned it, etc. etc. Note that some components (switches, connectors, pots, etc.) are supplied with temporary shields to protect them from flux cleaning, and then removed for use.

author: LabSpokane
author_rank: Super Contributor
timestamp: March 09, 2015, 09:33:09 pm
content: Be aware that some "rubbing" IPA contains a small amount of oil and will leave a residue. Might be worth springing for the metal can of industrial denatured alcohol if that's the culprit.

author: electr_peter
author_rank: Unknown
timestamp: March 09, 2015, 09:40:01 pm
content: Possibly severe corrosion in contact area. Give it a bath in IPA/other cleaning solution. Also, check actual DC resistance of a working and non-working switch. I have had problems with seemingly shiny mains switch contacts - slight sanding took care of that.

author: 8086
author_rank: Super Contributor
timestamp: March 09, 2015, 09:43:12 pm
content: I had a similar issue when assembling some boards for a client. The problem was the IPA wash contaminating the contacts. I used some aerosol PCB cleaner quite liberally and it solved the issue. Might not be the same issue as you're having, but worth a try.

author: pickle9000
author_rank: Super Contributor
timestamp: March 09, 2015, 09:45:57 pm
content: Crack a couple open, new and failed ones. Always the best way to start.

author: zapta
author_rank: Super Contributor
timestamp: March 11, 2015, 03:00:18 am
content: Thanks everybody for the information. I followed the suggestions and made an experiment with one new switch.1. Test the switch, no problems.2. Solder it to a clean PCB, leave the solder much longer then needed. Test, no problem.3. Clean it with 99% IPA, use apply liberally with a swab. Dry. Test, no problem.4. Repeat #3 with IPA mixed with ChipQuik tacky flux. Dry. Test, no problem.5. Reflow a large amount of solder paste (Mechanics, Chinese, off ebay) with a solder iron and repeat #3 (IPA mixed with the left over flux from the solder paste). Dry. Test, connection is intermittent.6. Open the switch and inspect under a microscope. The switch has significant amount of dirt above the membrane but no much below it where the contact is made.This made me to believe that the problem was the combination of the Mechanics solder paste's flux mixed with IPA. Also, the upper side of the membrane has a protective adhesive tape and possibly the IPA dissolves it.I need a better cleaning process. Would be nice to protect the switch with some goo that can be easily removed after the cleaning.

author: pickle9000
author_rank: Super Contributor
timestamp: March 11, 2015, 03:29:09 am
content: Have compared the colour of the contact area with a new one. I have had some issues with failure of the conductive ink. This was over 5 years ago but was c&k.

author: JuKu
author_rank: Frequent Contributor
timestamp: March 11, 2015, 09:59:37 am
content: Quote from: zapta on March 11, 2015, 03:00:18 amAs the first thing, you need electronics paste.

author: kjs
author_rank: Regular Contributor
timestamp: March 11, 2015, 10:16:20 am
content: Quote from: JuKu on March 11, 2015, 09:59:37 am+1 to that! Just for fun I tried some of that cheap stuff from aliexpress. Now I know why the expensive Kester I use is darn cheap compared to it.

author: free_electron
author_rank: Super Contributor
timestamp: March 11, 2015, 02:15:27 pm
content: Chinese soldering flux ? There's ya problem matey. ...And eh, ipa only dilutes flux, it does not destroy it. You need a real production board cleaner

author: zapta
author_rank: Super Contributor
timestamp: March 11, 2015, 03:05:50 pm
content: Quote from: JuKu on March 11, 2015, 09:59:37 amIt's Mechanic with capital M. It's a brand of inexpensive electronic solder paste sold on eBay (Small 35g jars which is perfect for me)I also have kester and chipquik solder pastes, I will repeat the experiment with them.Is there any easy removable goo I can use to protect the switches when cleaning?

author: LabSpokane
author_rank: Super Contributor
timestamp: March 11, 2015, 03:08:26 pm
content: Try poster tack on the switches. Not good for production, but cheap and available everywhere.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 11, 2015, 05:38:25 pm
content: Quote from: zapta on March 11, 2015, 03:05:50 pmWhy not just use sealed switches if assembly contamination is a problem for you?