Understanding Gold Finger Connectors in PCBs

Gold fingers are specialized connectors located at the edge of a printed circuit board (PCB). These connectors, shaped like fingers, play a crucial role in protecting PCB prototypes from wear and tear. Check out the image below for a visual representation:

Surface Treatments for Gold Finger PCBs

Electroplated Nickel Gold: This treatment, with a thickness ranging from 3-50 microns, offers excellent conductivity, oxidation resistance, and wear resistance. It is ideal for gold finger PCBs subjected to frequent insertion and mechanical friction.

Immersion Gold: With a typical thickness of 1 micron (up to 3 microns), immersion gold is widely used in high-precision PCBs for its superior conductivity, flatness, and solderability. The cost-effective process results in a golden yellow finish.

Design Tips for Gold Finger PCBs

When designing a PCB similar to the example below, look out for gold fingers indicated by pins and a U-shaped groove on both the TOP and BOTTOM sides:

Here are some key design considerations for gold finger processing:

For PCBs requiring frequent insertion, opt for hard gold plating on gold fingers for enhanced wear resistance.
Chamfer the gold finger at a 45° angle to prevent issues; see example below:

Apply a solder mask window treatment to the gold finger area.
Maintain a minimum distance of 14 mils from the tip of the gold finger for immersion tin and silver pads.
Avoid placing copper directly on the gold finger surface.

For a well-designed gold finger reference, check out the image below:

Ensure all inner layers beneath the gold finger have copper cutting to reduce impedance differences and aid in ESD protection.
Consider full copper cutting beneath the gold finger pad for optimal performance.

Important Considerations for PCB Gold Fingers Processing and Production

PCBs with thickness ranging from 1.2 mm to 2.4 mm can undergo processing with a beveled edge. Boards outside this thickness range are not suitable for this method.
The bevel angle typically falls between 20° and 45°. It is crucial to maintain a sufficient distance between the gold finger and the board edge. Depending on the PCB design or thickness, it is recommended to have a distance of 0.6 mm to 1.5 mm to prevent gold finger damage.

Here are some common diagrams showcasing various bevel angles and depths for your reference: