How thick is PCB gold finger plating?

What are Gold Finger PCBs?

Gold finger PCBs, also known as edge connector pcbs or gold tab PCBs, are printed circuit boards that have gold-plated contact pads or “fingers” along one or more edges of the board. These gold fingers are designed to mate with corresponding connectors, such as card edge connectors or slot connectors, to establish electrical connections between the PCB and other components or systems.

Gold finger PCBs are commonly used in various applications, including:

  • Computer hardware (e.g., memory modules, graphics cards, expansion cards)
  • Consumer electronics (e.g., game cartridges, USB drives)
  • Industrial equipment (e.g., control modules, sensor interfaces)
  • Telecommunications devices (e.g., network switches, routers)

The gold plating on the contact fingers provides several advantages, such as:

  • Excellent electrical conductivity
  • High resistance to corrosion and oxidation
  • Low contact resistance
  • Durability and wear resistance
  • Compatibility with various connector materials

Factors Affecting Gold Finger Plating Thickness

The thickness of the gold plating on PCB gold fingers is an important consideration in the design and manufacturing process. Several factors influence the choice of plating thickness, including:

1. Application Requirements

The specific requirements of the application dictate the necessary gold plating thickness. Factors such as the expected number of mating cycles, environmental conditions, and electrical performance requirements all play a role in determining the appropriate plating thickness.

For example, applications that require frequent mating and unmating of the gold fingers may demand a thicker gold plating to withstand the mechanical wear and tear. On the other hand, applications with less frequent mating cycles or less severe environmental conditions may allow for thinner gold plating.

2. Industry Standards

Various industry standards and specifications provide guidelines for gold finger plating thickness based on the application and performance requirements. Some common standards include:

  • IPC-4552: Specification for Electroless Nickel/Immersion Gold (ENIG) Plating for Printed Circuit Boards
  • IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
  • JEDEC Standards (e.g., JESD22-A105, JESD22-B106)

These standards specify the minimum and maximum plating thicknesses, as well as other requirements such as surface finish, adhesion, and electrical characteristics.

3. Cost Considerations

The thickness of the gold plating directly impacts the cost of the PCB. Gold is an expensive material, and thicker plating requires more gold, resulting in higher manufacturing costs. Therefore, designers and manufacturers must balance the performance requirements with cost constraints when selecting the gold plating thickness.

In some cases, a thinner gold plating may be sufficient to meet the application requirements while reducing the overall cost of the PCB. However, it’s essential to ensure that the chosen thickness provides adequate performance and reliability.

Common Gold Finger Plating Thicknesses

The thickness of gold finger plating is typically measured in microinches (μin) or micrometers (μm). Some common plating thicknesses used in the industry include:

Plating Thickness Microinches (μin) Micrometers (μm)
Flash Gold 3 – 7 0.08 – 0.18
Thin Gold 10 – 30 0.25 – 0.76
Standard Gold 30 – 50 0.76 – 1.27
Thick Gold 50 – 100 1.27 – 2.54
Extra Thick Gold 100 – 200 2.54 – 5.08

The choice of plating thickness depends on the specific application requirements, industry standards, and cost considerations, as discussed earlier.

Flash Gold Plating

Flash gold plating, also known as ultra-thin gold plating, typically ranges from 3 to 7 microinches (0.08 to 0.18 μm) in thickness. This thin layer of gold provides basic protection against corrosion and oxidation while maintaining good electrical conductivity.

Flash gold plating is often used in applications with minimal mating cycles or where cost is a primary concern. However, it may not provide sufficient durability for applications with frequent mating cycles or harsh environmental conditions.

Thin Gold Plating

Thin gold plating ranges from 10 to 30 microinches (0.25 to 0.76 μm) in thickness. This plating thickness offers a balance between cost and performance, providing good corrosion resistance and electrical conductivity.

Thin gold plating is suitable for applications with moderate mating cycles and normal environmental conditions. It is commonly used in consumer electronics and some industrial applications.

Standard Gold Plating

Standard gold plating, also known as medium gold plating, ranges from 30 to 50 microinches (0.76 to 1.27 μm) in thickness. This plating thickness provides excellent durability, corrosion resistance, and electrical performance.

Standard gold plating is widely used in various applications, including computer hardware, telecommunications equipment, and industrial devices. It offers a good balance between cost and performance for most applications.

Thick Gold Plating

Thick gold plating ranges from 50 to 100 microinches (1.27 to 2.54 μm) in thickness. This plating thickness provides enhanced durability and wear resistance, making it suitable for applications with frequent mating cycles or harsh environmental conditions.

Thick gold plating is often used in high-reliability applications, such as aerospace, military, and medical devices. It offers excellent corrosion resistance and electrical performance, but comes at a higher cost compared to thinner plating options.

Extra Thick Gold Plating

Extra thick gold plating ranges from 100 to 200 microinches (2.54 to 5.08 μm) in thickness. This plating thickness is used in extreme cases where the gold fingers are subjected to very high mating cycles or severe environmental conditions.

Extra thick gold plating provides the highest level of durability and wear resistance, but it also comes with a significant cost premium. It is typically used in specialized applications where reliability and longevity are critical, such as in aerospace and defense industries.

Gold Finger Plating Process

The gold finger plating process involves several steps to ensure a high-quality and durable finish. The main steps in the process include:

  1. Surface Preparation: The PCB surface is cleaned and prepared to ensure good adhesion of the plating layers. This may involve a combination of chemical cleaning, microetching, and mechanical abrasion.

  2. Nickel Plating: A layer of nickel is plated onto the copper pads of the PCB. The nickel layer acts as a barrier between the copper and the gold, preventing the formation of intermetallic compounds that can degrade the electrical and mechanical properties of the gold fingers.

  3. Gold Plating: The gold plating is applied over the nickel layer using electroplating or immersion plating techniques. The thickness of the gold plating is controlled by factors such as the plating time, current density, and solution composition.

  4. Inspection and Testing: After plating, the gold fingers undergo visual inspection and various tests to ensure they meet the specified requirements for thickness, uniformity, adhesion, and electrical performance.

The quality of the gold finger plating depends on several factors, including the surface preparation, plating parameters, and post-plating processes. Proper control and monitoring of these factors are essential to achieve consistent and reliable gold finger plating results.

Frequently Asked Questions (FAQ)

  1. What is the minimum gold plating thickness for PCB gold fingers?
    The minimum gold plating thickness depends on the specific application requirements and industry standards. In general, flash gold plating (3-7 microinches or 0.08-0.18 μm) is considered the minimum thickness for basic protection and electrical conductivity. However, most applications require thicker plating for improved durability and performance.

  2. Can I use flash gold plating for high-reliability applications?
    Flash gold plating is generally not recommended for high-reliability applications or those with frequent mating cycles. It provides only a thin layer of protection and may not withstand the mechanical wear and tear associated with repeated mating and unmating. For high-reliability applications, thicker gold plating (e.g., standard or thick gold) is typically required.

  3. How does the nickel layer affect the gold finger plating?
    The nickel layer serves as a barrier between the copper pads and the gold plating. It prevents the formation of intermetallic compounds that can weaken the bond between the gold and the copper, leading to delamination or poor electrical contact. The nickel layer also enhances the overall durability and wear resistance of the gold fingers.

  4. Can I specify a custom gold plating thickness for my PCB gold fingers?
    Yes, it is possible to specify a custom gold plating thickness based on your specific application requirements. PCB manufacturers can work with you to determine the optimal plating thickness that balances performance, reliability, and cost. However, keep in mind that custom thicknesses may require additional processing steps and may impact the lead time and cost of the PCBs.

  5. How can I ensure the quality and consistency of the gold finger plating?
    To ensure the quality and consistency of the gold finger plating, it’s important to work with a reputable PCB manufacturer that has experience in producing gold finger PCBs. The manufacturer should have strict process controls, quality assurance procedures, and testing capabilities to verify the plating thickness, uniformity, adhesion, and electrical performance. Additionally, specifying the required plating thickness, industry standards, and acceptance criteria in your PCB design and fabrication documents can help ensure consistent results.

Conclusion

The thickness of PCB gold finger plating plays a crucial role in determining the performance, reliability, and cost of the final product. Factors such as application requirements, industry standards, and cost considerations influence the choice of plating thickness.

Common gold finger plating thicknesses range from flash gold (3-7 microinches) to extra thick gold (100-200 microinches), with standard gold plating (30-50 microinches) being a popular choice for many applications. The gold plating process involves surface preparation, nickel plating, gold plating, and inspection and testing to ensure a high-quality and durable finish.

When designing and manufacturing PCBs with gold fingers, it’s essential to carefully consider the specific requirements of your application and work with a reputable PCB manufacturer to select the appropriate plating thickness and ensure consistent quality.

By understanding the factors that influence gold finger plating thickness and the available options, you can make informed decisions that balance performance, reliability, and cost for your specific application needs.