Mechanical construction considerations

AN3431

8/18

Doc ID 019017 Rev 1

2.1.1

Insulating layer

The designer can add an optional insulating layer to improve electrostatic discharge (ESD)

protection (if the conductive top cover is driven by an MCU pin) and/or to enhance the look

of the application. This layer can simply be glued onto the top cover and has limited impact

on the behavior of the touch module.

2.1.2

Conductive top cover

The conductive top cover should be designed so that it has a measurable non-permanent

deflection when pressed in the desired sensor area.

For any material sample, it is possible to represent graphically the relationship between

stress (forces which deform a body) and strain (the relative deformation itself). Figure 4

demonstrates the relationship between stress and strain. The first part of the curve is linear

(according to physical laws). Here, the ratio between stress (

Young’s modulus (E). An additional parameter, the elastic limit (1), must also be taken into

account. This applies when the material becomes permanently deformed if the stress

applied is too high.

a.

In this mechanical context, “

measure of deformation representing the displacement between particles in the body relative to a reference

length).