Start with the LATEST 2 layer layout and perform the following changes:
1) Move components so that 1cm diameter round area is available in the center of the bottom side. Indicate the area by printing a circle on the board as you do for other components. Layout the components in a space-saving way. Minimal board size is very important!!
2) The LED had to be used and placed in the centre of the touch pad. [url removed, login to view]
3) The contact to the touch pad component should be of normal size. For instance a 5mm large contact could influence the touch pad capacity which mustn't be. At the same time it should be easy and error-prove to assemble the touch pad component (because it is round). You may follow the contact points illustrated in my two images or suggest a different approach.
4) On a separate PCB the touch pad component had to be designed on a two layer PCB. 1cm diameter circle with contact and hole for LED. The hole should be minimal and tightly fit the LED (to allow best capacitive effect and allow easy assembling). The touch pad component should be shielded off against the main PCB. Its layer towards the outside (away from the main PCB) should be used as the capacitive field. The shielding ground layer should be in between the capacitive layer and the main PCB. The outside surface should be blank because it is user-facing.