PCB Contact Design Guide

PCB Contact Design: SILICONE RUBBER KEYPADS & CONDUCTIVE RUBBER KEYPADS

Typical Gold or Nickel Plated Board Contact Designs

np_pcbcont_02 np_pcbcont_03 np_pcbcont_04 np_pcbcont_01

Typical Carbon Screened Board Contact Designs

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These designs are for reference only. There is no preferred contact design. The important objective is to provide as many contact paths as possible to achieve the best switch operation.

Carbon contacts are normally round. Standard contacts available are 2, 2.5, 3, 3.5, 4, 5, 6, 7 and 8 mm diameter. Other shapes and sizes are available.

The size of PCB electrode should be 1.25 times the size of the carbon contact on the bottom of the key.

If contact resistance of less than 50 ohms is required, a metal contact can be used instead of a carbon contact. The metal contact is molded to the keypad the same as the carbon contacts are. Contact resistance using the metal contacts is typically less than 15 ohms. Metal contacts are not frequently used in rubber keypads because of the high cost and long lead times associated with metal contacts.

Specification
Gold Plating
Nickel Plating
Carbon Screen Contact
Plating:
min. 3 micro inches over 60 micro inches of nickel
min. of 100 micro inches
.001″ over copper traces
Trace Width:
0.25-0.40 mm
0.25-0.40 mm
Minimum distance
between traces:
0.30mm
0.30mm
0.50 mm
Maximum distance
between traces:
0.40 mm
0.40 mm
Electrical contact
resistance:
less than 100 ohms
less than 100 ohms
600-1000 ohms