MIDI keyboard silicone rubber switch

Layout Footprints
1

Hello!

Is it possible to design this kind of silicone rubber switch in Kicad? Is there any tutorial available? I haven’t found any yet.

I would need to make this kind of switch in Kicad. This is from MIDI Keyboard.

Thanks!,
Pete.

3

There have been several discussions and questions about footprints like this, I think it’s usually called a membrane switch. By doing a forum search with “membrane” I found for example this: Membrane pattern cannot be connected. There’s a footprint file there which you can probably use as a starting point.

As a general rule, you have to create two custom pads from graphic shapes. See for example Create Pad from Selected shapes disappear in KiCad V7.01? - #2 by mf_ibfeew.

4

Thanks for the answers!

One more question: what is this layer in the PCB on the copper layer? It must be some conductive layer. Is this shielding the copper layer and at the same time it’s some conductive material? What is this layer called in Kicad?

Contact_Fingers
Contact_Fingers1000×750 140 KB

Thanks!

5

That stuff is usually some kind of paint or epoxy with a high carbon content to make it conductive. It is usually only used in mass production, and it’s probably difficult to have such PCB’s made in small quantities.

Gold plated copper is a standard process, and it is probably a more sensible option.

6

It must be carbon ink or carbon mask, see for example Advanced PCB Manufacturing Cost Calculator,Get Manufacturing Price of HDI PCBs, High-Frequency and Thick-Copper PCBs - PCBWay :

kuva
kuva1445×712 164 KB

7

PCBWay seems to be able to do it, but the price (for otherwise default 50x50mm board) jumps up from 5 to 120 monetary units.

I wonder if you can buy carbon ink paste and apply it yourself. :smile:

8

I have made switch contacts like that for remote controls with rubber keys. As Paul mentioned, gold is an easy way to go. Standard ENIG (electroless nickel immersion gold, iirc) processing on the pcb leaves a decent finish for these contacts and is not much pricier than hasl. Hard gold (typically used for edge connectors) is pricey and overkill. However, even hasl has worked for me for prototyping these switches – a white plastic eraser works magic on cleaning the surface tarnish off the contacts :slight_smile: You need to make a footprint that has soldermask removed around the contacts, of course.

9

Thanks, guys! Really helpful info. Things are progressing here. :slightly_smiling_face: Ahaa, gold is the way to go.

Now I have to learn to how to remove the soldermask layer around the contacts…

10

25 years ago you could. I still have a bottle. It was some sort of paint/glue with a large content, in suspension, of graphite/carbon.
The paint was usually applied to the base of the rubber key and the PCB was left as gold plated copper.
This was the way of domestic remote control units… TVs, VCRs, DVDs, Domestic Air Conditioners, Computer Keyboards, etc.

11

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