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The advancement of printed circuit board (PCB) technology is driving the improvement and innovation of device performance, among which the PCB gold fingers is a crucial connection solution, assuming the key role of transmitting data and power, ensuring the complex interaction and efficient operation of modern electronic equipment. Next, this article will have an in-depth discussion of gold fingers, introducing the definition of gold fingers, design requirements, production process and its core role in different applications; I hope you can learn something after reading.

What are Gold Fingers?

PCB gold fingers are a row of narrow, long and thin metal contact areas located on the edge of a printed circuit board (PCB), as shown below:

Because the contacts shown in the figure are long and narrow, like fingers, and are covered with a layer of gold (the metal covered is usually gold, which is used to improve electrical conductivity and corrosion resistance), they are called "gold fingers." These metal contacts are critical to electronic devices because they can provide a physical connection (usually a slot connection) between hardware devices, allowing data, electrical signals, and power to be transferred between different devices or boards. It is widely used, not only for the motherboard connection inside the electronic equipment, such as expansion card, but also as an important physical connection interface is widely used in industrial equipment and communication equipment.

Gold Fingers vs. Other PCB Edge Interfaces

Advantages of Gold Fingers

1. Gold fingers adopts an Electroplated Hard Gold coating and has strong wear resistance. It can withstand thousands of plugging and unplugging operations and is suitable for industrial and high-performance applications.

2. The gold plating process of the PCB gold fingers ensures low resistance, high signal integrity and stable power transmission.

3. Many gold finger PCB designs support power plugging and unplugging, making them suitable for plug-and-play devices.

4. Circuit board fingers provide a connection method with higher density and more space-saving.

Materials and Structural Characteristics of Gold Fingers

The main materials for manufacturing the gold finger connector include:

Copper Base: The base layer of the gold finger is conductive copper foil, usually with a thickness of 1 oz or 2 oz, providing current-carrying capacity.

Nickel Barrier Layer: Electroplating a nickel layer of 100-200 microinches plays a role in blocking the diffusion of copper, preventing copper from migrating to the gold layer and affecting the connection performance and corrosion resistance.

Gold Surface Finish: The outermost layer is a metal coating, usually including:

Electroplated Hard Gold: With a thickness of 30-50 microinches, it is the most common type among PCB gold fingers and has strong wear resistance.

Electroless nickel plating and gold plating (ENIG): It is suitable for occasions with low requirements for insertion and removal or limited budget. It has good flatness but relatively poor wear resistance.

The above three layers constitute the key contact areas of the "gold fingers in PCB," providing guarantees for high-speed transmission and highly durable applications.

Gold Finger Beveling

Chamfering the edge of the gold finger helps improve the smoothness of plugging and unplugging and reduces wear during the process. The commonly used chamfer angles are 30° or 45°, and the specific Angle depends on the structure of the connector and the required insertion force.

The chamfering process is usually carried out after the solder mask is removed and the gold plating is completed, and only the edge part where the gold finger contacts is treated. The chamfer depth needs to be precisely controlled to avoid affecting the contact area or the strength of the plate edge.

High-quality gold finger PCB manufacturers will strictly implement the chamfering process standards to ensure that their products perform well in communication, industrial control and high-end consumer electronics.

Key Design Points of Gold Fingers

1. Thickness

When designing the gold fingers, the length, width and position of the gold fingers should be precisely determined according to the interface specifications of the target device. It usually requires a layer of gold plating to improve electrical conductivity and corrosion resistance (a layer of nickel is usually plated before gold plating to enhance the adhesion and wear resistance of the gold layer), and the thickness is usually between 3 microns and 50 microns. PCBasic can tailor the design to the different uses and applications of the customer's products, and this customization allows each product to perform optimally in its specific operating environment while also extending the service life of the product.

2. Chamfer

The edge of the gold fingers usually needs to be chamfered or rounded to ensure that the connector can be inserted quickly and to prevent the gold fingers from scratching the card slot or exposing the copper during insertion and removal. (This step is usually done after the pad cover is coated and before the surface treatment)

3. Location

The distance between the gold fingers and the PTH hole should be 1 mm, while the minimum distance between the gold fingers and the edge of the board should be 0.5 mm, which can reduce the probability of board failure. And do not place any pads, holes, or screen prints in the gold fingers area, as these elements can cause the gold fingers to be damaged or the electrical connection to be poor during insertion and removal.

4. Electrical and mechanical properties

The electrical properties and mechanical strength of gold fingers should be considered in the design to ensure that they can withstand frequent physical insertion and removal while meeting electrical requirements.

5. Pollution 

Measures should be taken during the design and manufacturing process to prevent oil, dust, and other pollutants from adhering to the gold fingers. Otherwise, it will have adverse effects (such as holes) and affect its electrical performance.

Surface Treatment Methods for Gold Fingers

The surface treatment of the gold fingers is an important step in its design and manufacture, and with the right surface treatment technology, the overall performance and durability of the gold fingers can be significantly improved, ensuring its efficient and reliable connection in a variety of applications. Gold fingers' surface treatment methods include electroplated hard gold, electroplated soft gold, ENIG, ENEPIG, and selective plating. The two most used are Electroplated Hard Gold and ENIG. Here's a table about them:

Standards of PCB Gold Fingers

Gold fingers has been around since the early 20th century in electronics manufacturing. Later, with the rapid development of the electronics industry and the widespread use of computers and mobile communication equipment, the design and application of gold fingers became more and more mature, and the relevant standards were gradually established. Here are some key criteria:

The design and manufacture of gold fingers must comply with relevant standards such as IPC to ensure that the manufactured gold fingers can maintain consistency and interchangeability on a global scale and improve the reliability and market competitiveness of the products.

Applications of Gold Fingers in Electronics

The gold-plated surface of the gold finger has excellent electrical conductivity and wear resistance, making it a reliable and durable edge connection interface for circuit boards, and is highly suitable for high-performance and modular systems. Gold fingers are often used in:

The PCB edge connector for plugging and unplugging the module

Communication equipment: such as routers, base stations, wireless modules and other devices. These devices often adopt gold finger connectors to achieve high-speed and low-impedance signal transmission and modular connection.

Industrial control systems: the connection of PLC expansion modules

Medical electronic equipment: various diagnostic instruments and monitoring devices

Game system

Gold fingers are widely used in modern circuit board edge designs due to their special gold plating PCB process.

Conclusion

The gold fingers is essential for a stable and reliable physical connection of electronic devices. In its design and manufacturing process, it is necessary to strictly follow the corresponding industry standards, so as to ensure that the production of gold fingers in the world to maintain consistency and interchangeability. If you have any questions, please feel free to contact us!

About PCBasic

Time is money in your projects – and PCBasic gets it. PCBasic is a PCB assembly company that delivers fast, flawless results every time. Our comprehensive PCB assembly services include expert engineering support at every step, ensuring top quality in every board. As a leading PCB assembly manufacturer, we provide a one-stop solution that streamlines your supply chain. Partner with our advanced PCB prototype factory for quick turnarounds and superior results you can trust.