We think DIY capacitive touch sensing buttons, and sliders are cool. Designing and shaping your capacitive panels can be a pain. Here is an app note by Microchip that covers all the basics required to get your capacitive touch sensing project started.
This app note starts with which pad shape and size is best suited for buttons. How the choice of material, and design of the covering plate impacts the sensitivity of a the design, is covered as well. In the end they give some routing guidelines to follow in designing capacitive touch sensing projects.
One thing to note, that we liked as well, is:
Also, the sensors may be separate from the PCB.
Wires leading off-board may direct the sensors to the
location where they are to be mounted and appropriately
affixed. This can allow for very flexible designs
and permits shapes which are not flat.