If you were ever curious what went on inside one of those tiny guitar-like Paper Jamz toys that clutter the shelves at your local big box store, then you’ll find Margery Conner’s teardown (literally!) of interest. Printed circuits, capacitive touch, blob-tops; it’s a worthy read.
Getting down to the capacitive electrodes was tricky. The surface art work is printed on a plastic film that lies on top of cardboard, that lies on top of another plastic film that has the actual circuit traces printed on it. Separating this sandwich of hard plastic guitar back/cardboard backing/printed circuit traces on plastic film/paper insulator/plastic film printed with surface artwork involved soaking the sandwich in the tub for about an hour.