AD7142 datasheet(35/68 Pages) AD

35 / 68 page

AD7142

Rev. 0 | Page 35 of 68

PCB DESIGN GUIDELINES

CAPACITIVE SENSOR BOARD MECHANICAL SPECIFICATIONS

Table 18.

Parameter

Symbol

Min

Typ

Max

Unit

Distance from Edge of Any Sensor to Edge of Metal Object

1.0

Distance Between Sensor Edges1

D2 = D3 = D4

Distance Between Bottom of Sensor Board and Controller Board or Metal

Casing2 (4-Layer, 2-Layer, and Flex Circuit)

1.0

1 The distance is dependent on the application and the positioning of the switches relative to each other and with respect to the user’s finger positioning and handling.

Adjacent sensors, with 0 minimum space between them, are implemented differentially.

2 The 1.0 mm specification is meant to prevent direct sensor board contact with any conductive material. This specification does not guarantee no EMI coupling from

the controller board to the sensors. Address potential EMI coupling issues by placing a grounded metal shield between the capacitive sensor board and the main

controller board as shown in Figure 53.

SLIDER

BUTTONS

CAPACITIVE SENSOR

PRINTED CIRCUIT

8-WAY

SWITCH

METAL OBJECT

Figure 51. Capacitive Sensor Board Mechanicals Top View

CAPACITIVE SENSOR BOARD

CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING

GROUNDED METAL SHIELD

Figure 52. Capacitive Sensor Board Mechanicals Side View

CAPACITIVE SENSOR BOARD

CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING

Figure 53. Capacitive Sensor Board with Grounded Shield

CHIP SCALE PACKAGES

The lands on the chip scale package (CP-32-3) are rectangular.

The printed circuit board pad for these should be 0.1 mm

longer than the package land length, and 0.05 mm wider than

the package land width. Center the land on the pad to maximize

the solder joint size.

The bottom of the chip scale package has a central thermal pad.

The thermal pad on the printed circuit board should be at least

as large as this exposed pad. To avoid shorting, provide a

clearance of at least 0.25 mm between the thermal pad and the

inner edges of the land pattern on the printed circuit board.

Thermal vias can be used on the printed circuit board thermal

pad to improve thermal performance of the package. If vias are

used, they should be incorporated in the thermal pad at a

1.2 mm pitch grid. The via diameter should be between 0.3 mm

and 0.33 mm, and the via barrel should be plated with 1 oz.

copper to plug the via.

Connect the printed circuit board thermal pad to GND.

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