PCB gold fingers are the gold-plated conductive areas on the connecting edges of printed circuit boards. Thanks to gold's excellent conductivity and oxidation resistance, they are core components for signal transmission and power supply connections between circuit boards, widely used in computers, smartphones, smartwatches, and other electronic devices. They primarily assist in the connection between the PCB and the motherboard, serving as a key carrier for digital signal communication between devices.
Based on structural design and application scenarios, PCB gold fingers can be divided into three categories. The standard type is the most common, with pads of consistent length, width, and spacing, distributed horizontally or in an array. The non-uniform type has pads of the same width but varying lengths, with some varying spacing; typically used in memory card readers, enabling sequential power supply to devices. The segmented type has pads of varying lengths and inter-pad design, suitable for waterproof, shock-resistant, and other robust electronic products.
The gold plating process directly determines the performance of the gold fingers. The two main methods are chemical nickel immersion gold plating and electroplating hard gold plating. Chemical nickel-plating with immersion gold is less expensive and offers better solderability, with a plating thickness of approximately 2-5µm. However, its soft texture makes it susceptible to wear and tear from frequent insertions and removals, making it suitable for low-frequency applications. Electroplated hard gold, on the other hand, achieves a plating thickness of up to 30µm, making it the preferred choice for high-frequency insertions and removals. Its process involves: first, masking the non-gold-plated areas with blue adhesive, exposing only the gold finger pads; then removing the oxide layer on the copper surface of the pads with sulfuric acid, followed by grinding and multi-stage washing; subsequently, electroplating a nickel layer and cleaning; then electroplating a gold layer on the nickel layer surface and recovering any remaining gold; finally, washing again to remove the blue adhesive, allowing it to proceed to the subsequent solder mask printing stage.
The design of the gold fingers must adhere to specifications to ensure stability and lifespan. Electroplated vias should be kept away from the gold finger area; for circuit boards with frequent insertions and removals, the gold fingers should be plated with hard gold to improve wear resistance. The edges of the gold fingers need to be chamfered, typically 45°, but 20°, 30°, etc., angles can be designed according to requirements. A full-area solder mask opening is required, but no stencil is needed for the pins. The minimum distance between the immersion solder/silver pads and the gold finger tips is 14mil, and it is recommended to maintain a distance of at least 1mm. Copper should not be applied to the surface of the gold fingers; all inner layers require copper cutting, typically 3mm wide, with half-finger or full-finger cutting options available to reduce impedance differences and improve ESD protection.
As a core connection component of the circuit board, the selection of PCB gold finger type, process control, and design specifications must be closely integrated with the actual application scenario to balance performance, durability, and cost, ensuring the stable operation of electronic equipment.
