I'm trying to modify a small USB keypad to attach a foot switch to it, that would trigger the enter key.

I disassembled the keypad and figured out which pins I need to contact to make an enter keystroke. It's the 8 and 7 in the image below.

the circuit board with connectors

I need to attach wires to these pins (two separate wires, connected to a jack port). Now, I have never ever soldered anything in my life, so I'm not sure what's my best option here.

The 11 soldered pins you see are about 1,5/2mm wide each, so I'm afraid trying to solder there would end up in me soldering two of these pins together.

There is also the other flat areas, but can I solder something there? Will it hold, and will it not melt the board's coating?

Any other options I'd have missed?

Here's the backside of the board, the pins you see on the front come from the black connector in the bottom left.

backside of the board

And, for those interested, here's the contact sheet of the keys:

enter image description here

  • 1
    \$\begingroup\$ If you are inexperienced at soldering, I suggest that you have a bit of practice first on something that doesn't matter. Even having a go at soldering two wires together a few times will be helpful to gain confidence. \$\endgroup\$ – Andrew Morton Oct 13 '18 at 15:22

Soldering would be the best bet, as it would provide the most reliable connection for your specific application. Use a temperature-controlled soldering station at about 300 degrees C to prevent delamination of copper. Also use ample flux to prevent shorts. Use strong, tacky flux and as much as possible.

It's nothing bad if you make a short. It's always fixable as long as you don't delaminate the copper. Apply less heat in short intervals. Be gentle like you are writing with a pencil you won't want to break the pencil tip. Also you can use lead or lo temp solder. You can also operate on the test points which you have circled in the picture.

Use a low guage wire if you are using stranded wire, twist and tin first.

After you are done, fix the wires with hot glue or tape so that the solder pads are not subject to mechanical stress.

  • 2
    \$\begingroup\$ Why in the name of all that's holy do people always recommend flooding things in flux? Use solder that has a flux core. If you need more flux, you are doing something wrong. Stop flooding things and learn to use your soldering iron. The amount of flux in standard solder was intentionally set by engineers who know how it works. \$\endgroup\$ – JRE Oct 13 '18 at 12:39
  • \$\begingroup\$ LOL commentor named JRE you seem to be in a bad mood. Please just relax a little. The person asking is new to soldering. Unless you have a more valid opinion to help him/her (in which case please articulate) or if you could explain why a lot of flux is a bad thing. Flux can always be cleaned afterwards. Tacky flux which has a similar working temperature to the solder also has minimal thermal impact. \$\endgroup\$ – user199643 Oct 13 '18 at 12:45
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    \$\begingroup\$ This is a trivial task. If you can't do it without flux, there's something wrong. The amount of flux in normal solder is completely adequate. It is of no help here, and is one extra thing for someone new to have to purchase. And then, thanks to tips like yours, use unnecessarily for tasks that don't require it. I worked as a radio technician, soldering every work day for over ten years - everything from heavy guage wire, to wire wrap wire, to 0402 sized SMD parts, and never needed extra flux. \$\endgroup\$ – JRE Oct 13 '18 at 13:04
  • \$\begingroup\$ Soldering without "extra flux" is not a normality and certainly on the extreme spectrume. Something that I tend to agree with is that there are multiple ways to do soldering. I'm glad that your way worked out for you but you only stated flux as "needless" there's nothing technically bad or wrong. Or rather your way fits your specific workflow with wire joints TH components and discretes doesn't mean it works for everyone. (or did you use lead solder all the way?) I'd love to hear your opinion on IPC and NASA. \$\endgroup\$ – user199643 Oct 13 '18 at 13:23
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    \$\begingroup\$ I have to agree with JRE. 40 years of soldering, from vacuum tube chassis to SMD parts on circuit boards, and never once have I ever used anything but flux core solder. Not once. Now, for copper plumbing, I use flux, but that isn't electronics work. \$\endgroup\$ – R Drast Oct 13 '18 at 19:07

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