Do projected capacitive touch panels need side clearance to ground metal?

Question

I need to use a TFT module with an integrated capacitive touch. The TFT has it's FFC and the touch controller has its own, with power supply and an I2C interface. Quite standard, I think, since every panel I've seen does it that way.

However I have some doubt about the working ''environment'' of the capacitive touch. The front panel is made of 1.5mm steel and it's grounded. So there will be a cutout for the panel.

My fear is that the steel would somewhat interfere with the projected capacitive fields. I had issues with other capacitive sensors (like single pad touchs) but the technology is slightly different. In short the steel is like a really big finger and even with auto calibration it messed up (also every kind of noise probably converge on that)

Should I make the cut out way bigger than the panel? Assembly tolerance is 0.5mm so 0.5mm extra space on each side should suffice mechanically but I had to do even 5mm of clearance in the past (with the pad touchs).

5mm on each side would be a lot difficult to conceal (unless we find/make a plastic bezel, which seems the most common option).

Do you have some experience or resource on that? the chinglish controller datasheet, as usual, gives no tip about that.

Answer 1

Usually any PCAP controller will do a calibration at some point (either you do it once during manufacturing of your product or via some menu options, or it is done automatically at some interval) to null out any stray capacitance.

So it doesn't really matter what the surroundings look like, as long is it does not dramatically change during operation.