Plating Hard Gold onto printed circuit boards is typically done to provide contact points and PCB edge connectors.
Gold contact surfaces are often used on circuit boards with membrane switches which are a technology of choice for industrial, commercial and consumer products. When PCBs will be repeatedly installed and removed electroplated gold is used for edge-connector contacts or as they are more commonly known: Gold fingers. It is difficult to hear the term Gold finger without remembering the villain Auric Goldfinger from the James Bond film of 1964. However, the gold fingers (gold-plated contact pins) found on PCBs are quite unlike Auric’s stubby, fat digits. To begin with, the plating thickness of a PCB gold finger is typically a mere 300 micro-inch. At this thickness the hard gold is expected to survive 1,000 cycles before wear through.
At Omni Circuit Boards, we have the in-house capability to produce the hard gold plating required for both contacts and gold fingers.
The process begins after the copper etch with the PCBs tape laminated to leave only the desired area exposed. A Nickel underlayer is electo-plated onto the PCB with a minimum thickness of 50 microinch. Nickel not only provides mechanical support it also provides a diffusion barrier as well as an inhibitor to pore and creep corrosion. The 24 carat hard gold, immersed in a salt medium, is then electro-plated directly onto the Nickel surface.
Quality control for hard gold finishes include thickness and tape adhesion tests. As you may expect, the price of gold requires solid process controls as the cost for errors would make even Auric shudder.
The calculation to determine the amount of gold required is a function of the plating time.
A simple calculator is provided below to determine the approximate weight of gold consumed for edge connectors. Simply provide the dimensions (in inches), take the resulting weight and multiply by the current price (the London Metal Exchange is a good resource) of gold.
A few design rules are required for gold fingers / edge connectors.
- No plated through holes are allowed in the plated area
- No solder mask or silkscreening can be present in the plated area
- For panelization, always place gold fingers facing outward from the panel center
- Connect all gold fingers with a 0.008” conductor trace at the edge to allow for manufacturing
- Features can be placed on one or both sides to a depth of 25mm from the outside edge
Having the capability to provide 24 carat, hard gold PCB electroplating capabilities in-house not only ensures we have control over the process, it also allows us to significantly shorten the manufacturing lead time of quick-turn PCBs when compared to subcontracting or outsourcing. While Auric may have been “ in love with its color... its brilliance, its divine heaviness “ we believe gold is just one more way to improve our customers PCB sourcing experience.