Capactive touch layout design
I am using a MTCH101 microchip component as a proximity detector.
I have bougth and tested the demo board which works well.
I have already designed a custom layout for the pad on a custom pcb and it does not work so well:
- there is sometime no detection putting the finger on the plastic part which is in contact with the pad
- there is sometime false detection
So, after that observations of those erroneous behaviours, i would like to focus more about the layout pad design which must be and can be improved thanks to external advice and point of view.
The context of my project is the following:
- It's a portativ module with a battery
- There is a thin plastic part on the pad, on which i want to put the finger to make the detection.
- there is electronic part (in a casing) behind the pad, so it may be necessary to shield the path
- it's a 4 layers pcb
- I have put in place a 3 sec confirmation time duration for the detection.
For the moment, i have on top plane:
- a 6 mm diameter circle pad, which is filled with copper
- A 2 mm distance of no copper all around the circle pad (1cm diameter)
- a 2.4cm hatched circle of ground around the pad (which is the maximum surface allowed for the whole capacitiv touch pad)
On 1rst inner layer, i have put a full hatched ground plane.
On 2nd inner layer and bottom plane, there is no copper.
Could you give me advice about the design of the capactive touch pad which would fit the best following my configuration?
Thanks a lot in advance,