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Ultimate Guide of PCB Gold Fingers and Plating Process Updated in 2022

PCBONLINE Team

Thur, Jan 06, 2022

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PCB gold fingers are a narrow column of rectangular PCB pads that are hard-gold plated on the edge of a PCB for connection. Also known as "edge connectors", PCB gold fingers are a common PCB manufacturing requirement for memory sticks, graphics cards, etc.

This article provides a comprehensive introduction to PCB gold fingers, such as PCB gold finger thickness and types, hard gold plating process, and PCB gold finger bevels. You will learn about PCB gold fingers below.

Part 1. Introduction of PCB Gold Fingers

PCB gold fingers

When you open a computer PCB case, you will find graphics cards inserted in the slots. These PCB assemblies have a neat, narrow, and long row of PCB pads on the edge. We call the rectangular row of PCB pads "gold fingers" because these conductive pads used for connection look like fingers.

Compared with other PCB pads, PCB gold fingers have a higher gold thickness. According to IPC-4556, the normal PCB gold finger thickness is 32u" (microinch), and the gold thickness range of PCB gold fingers is 3u" to 50u".

Gold on the PCB gold fingers is a gold alloy with a higher hardness than immersion gold.

PCB gold fingers can be classified into three types:

  • Normal PCB gold fingers - most common PCB gold fingers with a level and even array. The PCB pads have the same length, width, and space.
  • Uneven PCB gold fingers - the PCB pads have the same width but different lengths, and sometimes, different spaces.
  • Segmented PCB gold fingers - the PCB pads have different lengths, and the gold fingers are segmented.

PCB gold fingers is a good option for PCB board connection

PCB gold fingers provide a direct connection to the PCB boards with the system/device. This connection has better conductivity and mechanical strength than PCB connectors and wires. PCB gold fingers are used for connection with slots and interfaces of commercial and industrial systems and devices because they provide:

  • Excellent conductivity because of the direct board connection and more gold thickness,
  • Strong wear resistance so that the PCB can be plugged in and out thousands of times,
  • Good oxidation resistance due to the hard-gold plating process to the PCB pads.

Part 2. Hard Gold Plating - PCB Gold Finger Plating Process

The surface finish to PCB gold fingers is hard gold plating. Hard gold plating, or hard gold electroplating, is a surface finish to electroplate gold alloy on the PCB pads.

To understand PCB gold finger plating, you need to know the differences between hard gold plating and immersion gold:

hard gold plating vs immersion gold

  • Hard gold plating is electroplating gold alloy (gold and nickel), which has a higher hardness, so we also call it hard gold; immersion gold is depositing gold on copper without electroplating, and we also call it chemical gold.
  • In the same gold thickness, immersion gold looks more yellow than hard gold.
  • Hard gold plating has better wear resistance and hardness and is a perfect connection option.
  • Hard gold plating is before the solder mask process, and immersion gold happens after the solder mask process.

Here is the question, what is the PCB gold finger plating process?

At the PCB manufacturer PCBONLINE, the process of hard gold plating to PCB gold fingers is:

Step 1. cover blue glue

Except for the PCB gold finger pads that need hard gold plating, the rest of the PCB surface is covered with blue glue. And we make the conductive position consistent with the direction of the board.

Step 2. remove oxidation layer on PCB pads copper surface

We use sulfuric acid to wash away the oxidation layer on the PCB pad's surface and then use water to clean the copper surface. Then, we grind to further clean the PCB pad surface. Next, we use water and deionized water to clean the copper surface.

Step 3. electroplate nickel on PCB pads copper surface

We power on to electroplate a nickel layer on the cleaned gold finger pads surface. Next, we use water and deionized water to clean the nickel-plated pad surface.

Step 4. electroplate gold on nickel-plated PCB pads

We power on to electroplate a gold layer on the nickel-plated PCB pad's surface. And we recycle the rest gold. Then we still use water and then deionized water to clean the gold finger surface.

Step 5. remove the blue glue

Now, hard gold plating to the PCB gold fingers is done. And we remove the blue glue and continue PCB manufacturing to the solder mask printing step.

hard gold PCB gold fingers

From the above, you can see that the process of PCB gold fingers is not complicated. However, only a few PCB factories (such as PCBONLINE) can complete the PCB gold finger process by themselves.

Why can only a few PCB factories process PCB gold fingers?

Here are two reasons for most PCB factories can't process PCB gold fingers plating:

  • First, the gold salt potassium cyanide (Au(CN)2) used in the hard gold plating process is highly toxic, and only a few factories in the world have the qualifications to purchase and store gold salt.
  • Second, the hard gold plating process discharges chemical wastewater, and factories without a sewage treatment license cannot produce electroplated hard gold.

If you are looking for a PCB manufacturer that can well process PCB gold fingers, please have a look at the manufacturer below.

Part 3. PCBONLINE - Advanced PCB Manufacturer That Meets Your PCB Gold Fingers Demands

PCBONLINE is a one-stop PCB manufacturer that can process PCB gold fingers on its own. Founded in 1999, PCBONLINE has two large advanced PCB manufacturing bases and one PCB assembly factory. Our PCB manufacturing base in Jiangsu Province of China has our hard gold electroplating lines and sewage treatment license.

PCBONLINE's PCB factory that processes PCB gold fingers

Here are PCBONLINE's advantages in meeting your PCB gold fingers demands:

  • PCBONLINE can process the PCB gold finger process by ourselves.
  • We manufacture PCB gold fingers with a gold thickness of up to 50u".
  • Any type of PCB gold fingers is available from PCBONLINE.
  • Both fully-automatic and half-automatic PCB gold fingers beveling are available from PCBONLINE.
  • Besides PCB gold fingers, PCBONLINE also meets any other PCB manufacturing demands.
  • One-on-one engineering support and free DFM, DFT, and DFX.

From prototyping to batch production, you can accomplish one-stop contract manufacturing from PCBONLINE, including PCB manufacturing, electronic components sourcing, PCB assembly, complete testing, value-added services such as conformal coating, IC programming, end-product assembly, etc.

For example, below is a PCB manufacturing and assembly project that has PCB gold fingers manufactured by PCBONLINE. These PCBAs are video capture cards for face recognition. The PCB gold fingers are covered by yellow high-temperature glue, and the gold thickness is 32u".

gold fingers of PCB assembly

If you have PCB gold fingers needs or any advanced PCB manufacturing/assembly needs, please feel free to send your Gerber files and BOM by email to info@pcbonline.com.

Part 4. PCB Gold Finger Bevel

PCB gold finger bevel

A PCB gold finger bevel is an angle on the edge of the PCB sheet material designed for the convenience of PCB insertion in slots. The common angle of a PCB gold finger bevel is 45° (it depends on customers' requirements). According to PCBONLINE's manufacturing experiences, customers may also require PCB gold finger bevels of 20° and 30°.

PCB gold finger beveling is not complicated at all. All we need is to use a machine to cut the edge of the PCB sheet material. The fully automatic PCB gold finger beveling equipment can selectively cut the PCB edges, and it is the only option if the PCB gold fingers are in different directions. The half-automatic equipment cuts the whole edge of the PCB. PCBONLINE has both fully automatic and half-automatic PCB gold finger beveling machines.

Conclusion

PCB gold fingers are a column of hard-gold plated PCB pads for PCB connection with systems/devices. Through this article, you have got a full insight into PCB gold fingers, including gold thickness, gold finger types, hard gold plating process, and PCB gold finger bevels. If your circuit board design has PCB gold fingers, work with the reliable PCB manufacturer PCBONLINE who can accomplish PCB gold fingers and complete the whole project to the best quality.


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