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Capacitive Touch Sensing through Soldermask?

eyAyXGhF

Member
Hey everyone,
I'm wondering if anyone has had any success doing capacitive touch sensing through a PCB's soldermask. I see that it works well with bare copper pads, but I have an application where I would like the buttons to appear plain white - so was considering hiding them behind a white soldermask on the PCB.

Thank you
 

gophert

Well-Known Member
Most Helpful Member
Hey everyone,
I'm wondering if anyone has had any success doing capacitive touch sensing through a PCB's soldermask. I see that it works well with bare copper pads, but I have an application where I would like the buttons to appear plain white - so was considering hiding them behind a white soldermask on the PCB.

Thank you
It should work fine if you are truly sensing capacitive response. If your current version only works with bare solder pads, then it may be a resistive sensor.

most touch screens on current cars work through 2.2 to 3.5mm of gorilla glass or polycarbonate.
 

eyAyXGhF

Member
It should work fine if you are truly sensing capacitive response. If your current version only works with bare solder pads, then it may be a resistive sensor.
Thanks gophert, I'm using the "touch" sense pins on a Teensy microcontroller and also the arduino CapicitiveSensor library, both I assume are using capacitance not resistance. I did a test when I covered my copper-tape test pads with masking tape (the regular paper kind) and the response dropped to almost unusable.. so I'm really hoping a thin layer of soldermask wouldn't affect it nearly as much. I suppose at this point the easiest thing I can do is just to order a test PCB to try..
 

ronsimpson

Well-Known Member
Most Helpful Member
Try it. Put some Scotch tape over the copper on your board and give it a try. Thin tape should be much thicker than solder mask.
 

gophert

Well-Known Member
Most Helpful Member
You can also add a capacitive touch sensing chip and simply read the high/low outputs with your microcontroller or even I2c or spi interfaces. The datasheet should have recommended pad designs

 

gophert

Well-Known Member
Most Helpful Member
Try it. Put some Scotch tape over the copper on your board and give it a try. Thin tape should be much thicker than solder mask.
He did try it with masking tape - it didn't work (post 3)
 

gophert

Well-Known Member
Most Helpful Member
Scotch tape is approximately half the thickness of masking tape so it may work.

Mike.
I'm thinking he is doing something wrong if capacitive touch can through a 3mm polycarbonate cover on most cars. or the glass on most tablets, or, (maybe you can name some examples). I've literally never seen a capacitive touch module behind cellophane film.

7B3011C3-29EB-40ED-97A1-9D3203F86524.jpeg
 

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