In my experience the following adv./disadv. apply to carbon and gold
contacts.

Carbon
Advantage               - Built in contact resistance ( typically 30 ohms per square )
                        - No temp. mask required during wave solder as the carbon is not
solderable.

Disadvantage    - Larger footprint required for screen print of carbon
                        - Potential for solder slivers on edge of contacts if design is poor.
Gold
Advantage               - Less process steps ( lower cost? ) if flash plate all over.
                        - Smaller footprint for tight designs.

Disadvantage    - No contact resistance.
                        - Gold sliver potential from electroplated gold.
                        - Extra process steps ( more cost? )if gold contacts and HASL pads are
                        specified.
                        _ Temp mask may be required for assembly process.

The two technologies are widely used and each has benefits. The specific
design requirements, and your fab shop's capabilities, should dictate which
is the most appropriate finish to select.

I hope this helps,

Keith Lumley
RexCan Circuits Inc.

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