PCB Manufacturing

Gold Finger PCBs: Types, Benefits, and Applications

Gold fingers are the gold-plated edges provided at the extremities of any PCB to connect to other boards or devices.  In this article, we are going to briefly discuss the types of gold fingers used in PCBs, the classification of gold finger electroplating, important aspects to remember during the process of electroplating, the benefits of using gold finger PCB and its applications in several domains. As a China gold finger PCB manufacturer, we hope this information will be helpful to people both inside and outside the PCB industry.

What is Gold Finger PCB?

The area or gold-plated pads that provide connectivity and are usually connected to the edges of the PCB are commonly called gold finger PCBs. The reason to specifically use gold for this purpose is that this alloy can help in preventing corrosion, and oxidation and it can last longer.

Communication technology involves sending and receiving signals along several circuits, the important criterion is the requirement of error-free signal transmission. Gold as a superconducting material, can help in proper signal transmission.

Types of Gold Finger PCBs Based on Dimensions

The gold finger PCBs can be classified based on the length, width, and spacing of the gold finger pads.

  • Normal Gold Finger PCB: Here the lengths and widths of each gold-plated finger are the same and they are equally spaced. This PCB gold finger is used in network and graphics cards.
  • Uneven Gold Finger PCB: The length and spacing between each finger are different and the widths remain the same.
  • Segmented Gold Finger PCB: These types of PCB gold fingers have different alignments and spacing. They are usually preferred in memory devices and USB flash drives.

Types of Gold Finger PCBs Based on Plating Methods

  • Gold finger with Thin Electroplating – Electroless Nickel Immersion Gold. 

This is performed by copper immersion. The copper is applied after the solder mask in this type of process. Due to the thin width, the gold fingers cannot tolerate very rough manhandling while removing and inserting the gold fingers. However, they are cost-effective and it is preferable for cheaper PCB varieties.

  • Gold finger with Thick Electroplating- Hard gold.

Nickel is used for immersion and it is harder than the copper plates process. Here, nickel is applied before the solder mask. This type is preferred when the application involves a lot of wear and tear. Due to thick gold plating, the cost involved is high and hence it is opted where quality and robustness are preferred over cost. The thickness, however, should align with the regulations of gold finger PCBs.

PCB gold finger

Benefits of Gold Finger PCBs

  • Corrosion Resistance: Above junction points or interconnecting segments can prefer to use gold fingers due to the advantage of corrosion resistance.
  • Aesthetic Sense: PCB gold fingers also offer an aesthetic sense to the boards and give them good quality and an expensive outlook.
  • High Wear Resistance: Compared to normal wiring, wear and tear is less and hence high wear resistance is offered by connecting through fingers.
  • Low-contact Resistance: Most importantly, gold finger PCBs offer low-contact resistance.

Gold Finger Plating Process

  1. Applying Conformal Coating: The electroplating involves a series of steps which includes preventive action by applying conformal coating on the board as an adhesive.
  2. Cleaning: This is followed by cleaning the gold finger PCB to avoid oxidation. After water washing, the boards are cleaned mechanically using strong abrasives. It is washed several times with deionized water.
  3. Plating Material Selection: This step is the preferred choice of electroplating alloy, for instance, nickel is chosen to be applied over gold fingers, followed by gold.
  4. Secondary Cleaning: The nickel pen is run through the fingers and it is washed with isopropyl alcohol or any acid to be used as per regulation. Again it is cleaned and water washed repeatedly to ensure that the gold fingers are free from dirt.
  5. Plating: After this, a 24k gold pen is used for plating.
  6. Test: Then a series of tests are to be performed before completing the processes of gold finger PCB. Some of the acclaimed tests are:

Chemical Test

In this process, the chemical is applied to the gold-plated area to check the withering of the gold. This can also show the impurities after the plating process.

Visual Test with Microscope

When the board is checked under the microscope, the smoothness of the board can be confirmed through the visual test, to check the roughness of the board. This can help in determining the readiness of the board for production.

Tape Test

A strong adhesive or tape is applied on the board and peeled off with force. Any residue material on the board is seen on the tape after this test. A properly plated board will not have a residue after this test.

Considerations in Gold Finger PCBs Design and Production

gold finger PCBs

There are a few considerations to be taken care of during the plating process of gold finger PCBs.

  • Components and Vias layout: The use of SMD components and VIAs should be avoided by placing them close to the gold fingers. The through holes should be far away.
  • Copper layout: Due to high connectivity, copper inner layers should be avoided, as this can interfere with communication and signal strength.
  • Free from solder masks and silkscreen: We should make sure to avoid solder masks and silk screens during plating as it can affect their performance.
  • Gold fingers should be on edge: The gold fingers should be placed at the edges of the PCB for easy access.
  • Material selection: Gold individually shows very good corrosion resistance, but to add to its strength, the usage of nickel and cobalt becomes essential. Nickel of specific microinches ranging from 100 to 180 is used with gold for its rigidity and mechanical thickness.
  • Beveling: Beveling is always carried out at the edges of gold fingers, to ensure proper connectivity. The fingers are beveled or sloped at an angle of 30 deg or 45 deg for easy connectivity. This is an important step that decides the longevity of the gold fingers as a proper beveling would ensure successful connectivity to the devices and hence the efficiency is high.
  • Integrity of Gold Fingers: To ensure proper connectivity, the fingers should be smooth. This involves a series of tedious processes to be followed before production to ensure proper usage. The damage in the fingers will lead to loss of connectivity and signal transmissions leading to device failure.

Gold finger circuit board

Applications of Gold Finger PCBs

Gold finger PCBs are applied to special connectors and adapters in computers for sound enhancers,  and peripheral devices to computing machines. Gold finger PCBs are indispensable in memory devices, portable devices, embedded systems, and expansion cards.

On the whole, gold finger PCBs are preferred nowadays due to their compatibility with all devices, mostly in adapters. They are available in all sizes and categories in gadgets. Mainly as follows:

Module-to-module Interface

As almost every single electronic device has to connect to the input or output devices that can be used as an additional add-on device, it is important to have the gold fingers to disconnect and connect to devices as required.

Main PCB to Other Module Connections

We know that the embedded devices used for a variety of applications involve several PCBs attached, to maintain modularity and to reduce complexity. This can also help in easy debugging and testing. For instance, communication boards like Zigbee and Wifi boards can be attached or detached from the main PCB as required.

Communication Interface between Master and Slave Modules

In a large and interconnected system, there can be several masters and several slaves performing specific tasks individually and in groups. To ensure easy trackability and for replacements in case of errors, it is reliable to connect the modules separately using the gold fingers and edge connectors.

Power Connections from the Main Module to the Accessory Modules

In cases where there are several boards and a power supply is required for all the boards, it is less complex to connect the boards using the gold fingers instead of a highly complex wiring design.

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