AN2869 datasheet(28/43 Pages) STMICROELECTRONICS

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Surface electrode design

AN2869

28/43

Doc ID 15298 Rev 6

3.5.3

Using electrodes separated from the PCB

It is possible to use surface electrodes which create a sensitive area on the bottom surface

of the panel and are not close to the PCB.

One option is to print an electrode array on the inner surface of the front panel. In this case,

the electrode shape rules are as described in Chapter 3.1, and the materials are as

described in Chapter 2.2.2. The sensors can be connected using spring contacts,

conductive foam or rubber, or a flex tail attached using ACF/ACP (d)(see Figure 22).

Remember that, with this technique, the area where the interconnection is made is touch-

sensitive too.

Figure 22.

Printed electrode method showing several connection methods

ACF/ACP = Anisotropic Conductive Film/Anisotropic Conductive Paste.

MS18979V1

Front panel

(plexiglass or

other suitable

material)

Controller

PCB

Spring

Printed

electrode

PCB pad

Flex PCB

Flex

connector

ACF/ACP

connection

Spacer (cylinder

of hard foam or

other suitable

material)

Printed

electrode

(optional)

AN2869 Datasheet(PDF) 28 Page - STMicroelectronics