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For fun, I took a USB keyboard apart as I'd like to use the keyboard circuit board without the actual physical keyboard. I am in need of soldering advice however.

Opening up the keyboard I see this: Plastic sheet taken from keyboard

This is the plastic sheet that is connected to each keys. The pins I have zoomed into are connecting to the circuit board, which looks like this:

Pins that do not accept solder

Unfortunately I can't solder directly to these as they appear to repel solder. I then tried drilling small holes in them and attaching thin wire, and maybe that can hold a while, but it seems very flimsy and is destined to break off.

Do you guys have advice on how to make a fairly robust connection to these pins?

Initially I'd like to connect separate wires and then connect the wires to my breadboard.

I thought about overlaying the plastic sheet on top (as it would have been inside the keyboard), but connecting wires to the plastic pins seems even harder.

T.K.
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  • Have you considered using something like an Arduino Leonardo or ATmega32U4 breakout instead? – Ignacio Vazquez-Abrams Jul 08 '15 at 18:19
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    Try scraping off the mask from the board using a blade or similar sharp object. – Suraj Bhawal Jul 08 '15 at 18:22
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    Indeed as @SurajBhawal writes clean the contacts, I'd expect to see some copper underneath. Also try to use some flux to ease soldering. – jippie Jul 08 '15 at 18:40
  • Yes, that makes perfect sense, I started scraping off with a sharp blade and it came off, exposing the metal below. Good tip about the flux, I will purchase some. – T.K. Jul 08 '15 at 20:34
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    In the past in a very similar situation, I have removed the mask and soldered directly. Be aware that the traces might come off if you pulled on the soldered wire with minimal force. –  Jul 01 '16 at 13:24

2 Answers2

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I had the same question a few weeks ago. I wanted to build a presentation footswitch controller - up / down / PgUp / PgDn - using an old Lenovo keyboard.

I found that the coating can be scraped off easily using a flat blade screwdriver taking care not to damage the copper. The material is like a powder coating and is hard but brittle. Careful tinning with a fine solder left me with a neat tinned edge connector.

enter image description here

Figure 1. (1) The Lenovo keyboard controller PCB. (2) The 'rows' membrane (18 lines). (3) The columns membrane (8 lines).

Examining the keyboard matrix I was able to determine that there were 26 'pins' split into 18 rows and 8 columns. Plugging the USB connector into my computer and running KeyboardTester.com's online app I was able, by carefully connecting rows and columns, to find the matrix points required for my application.

enter image description here

Figure 2. Partially filled out keyboard matrix. I had what I needed. ;^)

Be aware that since both rows and columns are scanned you won't be able to do a simple pull-down or pull-up arrangement from your micro to simulate a keypress.

Transistor
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I have been able to connect thin wires to these using electrical tape. I also passed the wires through the holes in the PCB and added glue to stop them moving around, and folded the exposed wire onto the contact from the other side before carefully pressing the tape on top.

I only used one contact on each side, just enough to create a single keypress.

bdsl
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