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PCB Contact Design: SILICONE RUBBER KEYPADS AND CONDUCTIVE RUBBER KEYPADS
Typical Gold or Nickel Plated Board Contact Designs
Typical Carbon Screened Board Contact Designs
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 |