How to shield the touch signal cable of an HMI (Human Machine Interface)?

Effective shielding of HMI touch signal lines is crucial for ensuring stable touch functionality in noisy environments. Touch signal lines include the TX drive line and RX sensing line for capacitive touchscreens, or the four-wire analog signal line for resistive touchscreens. For external touchscreen modules, the connecting cables must be shielded FPC or FFC cables, with the shielding layer covered by aluminum foil or braided mesh. The shielding layer must be grounded with low impedance at the touch controller end. Grounding can be achieved by directly soldering the shielding layer to the PCB ground pad, or by connecting it with conductive adhesive or metal clips. For resistive touchscreens, if the leads are long, it is recommended to use shielded twisted-pair cables and ground the shielding layer at one end (usually at the controller end).

Inside the PCB, touch signal lines should be as short as possible and wrapped with ground wires or ground copper foil, i.e., "grounding". In multilayer boards, placing these signal lines on inner layers and clamping them with top and bottom ground planes provides the best shielding effect. The touch chip should be placed in a quiet area of the PCB, and the ground plane beneath it should remain intact. For traces connecting the touch chip to external interfaces, grounding or inner layer routing should also be used. By implementing full shielding from the ribbon cable to the PCB trace, and utilizing Etymotic's shielding materials and good grounding practices, the touch signal lines can be isolated to the greatest extent possible from external interference.