Gold Finger PCB: A Tough, Durable Contact Edge for Connecting PCBs

Connectivity is critical for computers, mobile phones, and other devices in the modern technological world. Each connected component resulting from PCB fabrications usually has specific functionality, so bringing them together is essential to enhancing the overall performance of any device and increasing the available features.

The gold finger feature enables this kind of connectivity. Found at the edge of PCBs, this section provides a durable and reliable connection point to transfer data and power signals between the peripheral device and the motherboard.

We will look closer at gold finger PCBs, their types, and how to design them.

What are Gold Finger PCB Boards?

PCB gold fingers are narrow, gold-plated connectors found at the edge of PCBs. They enable connectivity and communication between the boards and contain flesh gold, the most solid and durable gold form with superior conductivity.

But why gold? The material has the highest electrical conductivity and corrosion resistance levels after copper and silver. Usually, the gold gets combined with nickel and cobalt to make the finger surfaces more resistant to wear and tear.

The gold finger PCB edge of a graphics card

This feature is crucial because constant insertion, removal, and reinsertion can peel the gold over time, exposing the contacts underneath.

How Are Gold Fingers Used?

• Interconnection Points: Gold fingers are usually the contact points in several slots, such as AGP, PCI, or ISA, to conduct signals from secondary PCBs to the main motherboard. Thus, they are useful when linking an internal card or peripheral device to a computer.
• Special Adapters: Gold fingers allow you to connect numerous performance enhancement features to your computer. For instance, your computer can deliver high-fidelity sound and better graphics via the secondary PCBs found in sound cards and graphics cards. The cards slot perpendicularly to the motherboard, and the fingers usually outlast them because there's not much wear since the cards seldom get unattached and reattached.

Sound card gold fingers

• External Connections: All outer peripherals (monitors, printers, scanners, etc.) link to the motherboard through gold fingers. They connect to the computer through ports or slots, which direct the signals to the motherboard via circuit boards.

Gold/Edge Fingers Vs. PCB Edge Connectors

PCB Edge Connectors on an Arduino Board. 

Many people cannot distinguish between gold/edge fingers in a PCB and connectors. Check out this:

PCB Gold Fingers Plating Thickness

PCB Gold Fingers on a memory card.

The ideal gold plating thickness is particularly important, especially when handling tear and wear on the edge finger. Ideally, the thickness is within the 0.003 to 0.005 mil range. So, what are some of the different platings and their thicknesses?

• First, the common electroplated hard gold is usually 0.003 mil. Its thickness means it can withstand all abrasions and thus guarantees longevity.
• Also, we have the electroless nickel immersion gold, commonly called ENIG. It is also substantively thick, measuring between 0.002 to 0.005 mil, and less pricey than the former type. In addition, it allows easy soldering, although it's not sturdy against regular abrasion.

What is PCB Gold Finger Beveling?

When making a PCB, the gold finger plating process comes right after depositing the solder mask, and it consists of the following three steps.

• Nickel Plating: Initially, two to six microns of nickel get plated to the finger connector edges.
• Gold Plating: Next, hard gold plating between one and two microns thick gets applied over the nickel. Manufacturers usually add cobalt to the gold to enhance the surface resistance.
• Beveling: Beveling is the last step, and it involves angling the edge connector fingers for easy insertion into the respective slot. The tapering is usually 30° - 45° depending on the port, size of the circuit board, or the client's requirements.

After beveling, the next step is applying the surface finish.

Design Specifications for Gold Finger PCBs

The gold plating process has certain restrictions and design specifications to ensure the fingers function as expected. They include the following:

• Pads, plated holes, and SMD should never be close to gold fingers (within 1 mm).
• The fingers should not contact the screen printing or solder mask.
• Plated pads should not exceed 40 mm lengthwise.
• The inner layers along the PCB edges must be free of copper material to prevent exposure during the beveling stage.
• Maintain a distance of at least 0.5 mm between the PCB outline and the fingers.
• The fingers on PCBs should always face the opposite direction or outward from the center of the board.

Compromising these standards can result in weak or malfunctioning circuit boards.

Types of Gold Finger PCBs

Three types of gold fingers are based on their appearance or the plated gold.

Non-Uniform PCB Gold Fingers

As the name suggests, these fingers are not uniform. They have unequal lengths, with some being longer than others. The connection is desirable in PCBs that need to link with the power connection earlier than the rest to get the energy flowing in. A good example is the fingers found in memory card readers.

The non-uniform gold fingers in a memory card and a memory card reader

Uniform PCB Gold Fingers

These fingers are the opposite of the non-uniform type described above. All the connection points are equal in length and width because there's no priority link. Thus, the finger connections power up at the same time.

Segmented PCB Gold Fingers

Apart from varying lengths, some segmented gold fingers appear disjointed among others in the same PCB.

The design is usually present in rugged and water-resistant electronics. They are also the primary connection in modern hybrid technological devices.

Applications of PCB Edge Fingers

Edge Fingers.

Almost every PCB part that requires regular plugging in and out has an edge finger. Hence, you will find PCB edge fingers virtually on any PCB, as they are central to effective transmission.

Some components that feature this part include network transmission cables, memory cards, graphics cards, and industrial control systems.

Quality Measures for PCB Gold Fingers

In addition to the specifications explained earlier, PCB gold finger production standards exist. First established in 2002 and amended several times, these standards include the following.

• Chemical Composition: Use a gold and cobalt alloy with 5-10% cobalt in the plating to maximize rigidity along the edges of PCB contacts.
• Thickness: Ensure the plating thickness is within 2-50 microinches. Most standards are 0.031, 0.062, 0.093, or 0.125 inches. The thinner ones are ideal for board prototypes, while the thicker ones are ideal for "busy" contact edges (regularly inserted, removed, and reinserted).
• Visual Test: Visual inspection is vital for defect tests. Use a magnifying lens to check whether the edge contacts are smooth, clean, and free of excess plating or nickel appearance.
• Tape Test: To check the adhesiveness of the gold plating, place a tape strip along the contact edges, then remove it and visually inspect the tape. If there are traces of the gold plating, the layer lacks enough adhesiveness with the contacts underneath.

Use transparent tape to test the adhesiveness.

It is worth noting that these are IPC standards and are the most widely used when manufacturing PCBs. As technology improves, always check for the latest IPC standard amendments. Also, read and understand other standards, as several exist.

Why Can’t Some PCB Manufacturers Process PCB Gold Fingers?

Toxic Potassium Cyanide.

The manufacturing process of PCB gold fingers is not possible for every manufacturer because of the following reasons:

• First, the manufacturer must be able to handle gold salt potassium cyanide. Due to its toxicity, this chemical is crucial in hard gold plating and requires special handly.
• Also, the chemical waste resulting from the manufacturing process requires special handling. The factory must have the capacity to treat it effectively before disposal.
• Finally, the manufacturing process is quite delicate for top product quality. This is not a standard every manufacturer can achieve.

OurPCB: Your Best PCB Manufacturer with Advanced Gold Finger Technology

At OurPCB, we have invested heavily in streamlining our PCB gold finger processing to ensure we deliver the highest-quality products.

Our Advanced Gold Finger Technology has ensured our success in an area where many manufacturers have failed.

We therefore, guarantee quality products all the time that have impressive abrasion resistance.

Also, our parts match the industrial standards thanks to the extensive tests we do. This is key in ensuring they can fit into any application you use.

How are Gold Fingers Changing The World?

Gold fingers are all about providing reliable connectivity between peripheral devices and motherboards.

This link is crucial in modern-day devices because the rapid development of computers, smartphones, and other devices demands high peripheral connectivity to enhance performance.

Improvements in gold plating technology allow faster insertion and ejection while enabling more connectivity, leading to more productivity in industries.

However, as these technological advances continue to emerge, it is critical to have the circuit board connection points plated and tested according to the highest standards.

At OurPCB, we adhere to these standards and have the experts plus equipment to ensure you get only the best quality.

The gold fingers on two RAM modules

Summary

As you can see, gold fingers are critical in connecting peripherals or cards to the motherboard, such as RAM, graphics cards, or memory cards. However, to ensure perfect functioning, you must follow the latest design specifications and standards when plating them to your circuit board.

We recommend getting experts to do the plating and beveling for you, and our team is best suited for this task. Reach out for any queries or send your PCB designs, and we will give you a free quote.