How thick is gold on a PCB?

What is a Thick Gold PCB?

A thick gold PCB refers to a printed circuit board that has a relatively thicker layer of gold plating compared to standard gold-plated PCBs. The thickness of the gold layer can range from 0.5 microinches (12.7 nanometers) to 50 microinches (1.27 micrometers) or more, depending on the specific requirements of the application.

Benefits of Thick Gold PCBs

Thick gold PCBs offer several advantages over standard gold-plated PCBs, including:

  1. Enhanced durability: Thicker gold layers provide better protection against wear and tear, making the PCB more durable and long-lasting.
  2. Improved corrosion resistance: Gold is highly resistant to corrosion, and a thicker layer offers even better protection against harsh environmental conditions.
  3. Superior electrical conductivity: Gold is an excellent conductor of electricity, and a thicker layer ensures optimal signal integrity and reduced resistance.
  4. Better solderability: Thick gold layers provide a better surface for soldering components, ensuring strong and reliable connections.

Applications of Thick Gold PCBs

Thick gold PCBs are used in various industries and applications where high reliability, durability, and performance are critical. Some common applications include:

  1. Aerospace and defense systems
  2. Medical devices and equipment
  3. High-frequency communication devices
  4. Automotive electronics
  5. Industrial control systems
  6. Consumer electronics

Manufacturing Process of Thick Gold PCBs

The manufacturing process of thick gold PCBs involves several steps to ensure the desired thickness and quality of the gold layer. The main steps include:

1. PCB Fabrication

The first step is to fabricate the PCB substrate using standard PCB manufacturing techniques, such as etching, drilling, and lamination. The substrate material can be FR-4, polyimide, or other high-performance materials, depending on the application requirements.

2. Surface Preparation

Before applying the gold layer, the PCB surface must be thoroughly cleaned and prepared to ensure proper adhesion. This typically involves a combination of chemical cleaning, micro-etching, and activation processes to remove any contaminants and roughen the surface for better gold adhesion.

3. Electroless Nickel Immersion Gold (ENIG) Plating

One of the most common methods for applying a thick gold layer to a PCB is through the Electroless Nickel Immersion Gold (ENIG) plating process. This involves first depositing a thin layer of nickel (typically 3-6 microinches) onto the copper surface of the PCB using an electroless plating process. The nickel layer serves as a barrier to prevent the diffusion of copper into the gold layer and improves the overall durability of the finish.

After the nickel layer is deposited, the PCB is immersed in a gold plating solution, where a layer of gold is deposited onto the nickel surface through an immersion process. The thickness of the gold layer can be controlled by adjusting the immersion time and the concentration of the gold plating solution.

4. Electroplated Gold

Another method for applying a thick gold layer to a PCB is through electroplating. This process involves first applying a thin layer of electroless nickel (similar to the ENIG process) followed by an electroplated layer of gold. The electroplating process uses an electric current to deposit the gold ions onto the nickel surface, allowing for a thicker and more uniform gold layer compared to immersion plating.

The thickness of the electroplated gold layer can be precisely controlled by adjusting the plating time and current density. Electroplated gold layers can range from a few microinches to several hundred microinches, depending on the application requirements.

5. Inspection and Quality Control

After the gold plating process is complete, the PCBs undergo a thorough inspection and quality control process to ensure that the gold layer meets the specified thickness, uniformity, and adhesion requirements. This may involve visual inspections, thickness measurements using X-ray fluorescence (XRF) or other techniques, and adhesion tests to verify the bond strength between the gold layer and the underlying nickel and copper layers.

Factors Affecting Gold Thickness on PCBs

Several factors can influence the thickness of the gold layer on a PCB, including:

  1. Application requirements: The specific performance and environmental requirements of the application will dictate the minimum and maximum gold thickness needed.
  2. Cost considerations: Thicker gold layers are more expensive due to the higher material and processing costs involved. A balance must be struck between performance and cost when specifying the gold thickness.
  3. Manufacturing process: The choice of plating process (ENIG or electroplating) and the specific process parameters (plating time, current density, etc.) will affect the resulting gold thickness.
  4. Base material: The type and condition of the base material (copper or nickel) can influence the adhesion and uniformity of the gold layer.

Comparing Gold Thickness on PCBs

The table below provides a comparison of typical gold thicknesses used in various PCB applications:

Application Typical Gold Thickness (microinches)
General-purpose electronics 2 – 8
High-reliability electronics 8 – 30
Aerospace and defense 20 – 50
Extreme environments 50 – 100+

It is important to note that these are general guidelines, and the actual gold thickness required for a specific application may vary based on the unique performance and environmental requirements.

FAQ

1. What is the difference between ENIG and electroplated gold?

ENIG (Electroless Nickel Immersion Gold) and electroplated gold are two different methods for applying a gold layer to a PCB. ENIG involves an electroless nickel layer followed by an immersion gold layer, while electroplated gold uses an electrical current to deposit the gold layer onto the nickel surface. Electroplated gold typically allows for thicker and more uniform gold layers compared to ENIG.

2. How does gold thickness affect PCB performance?

Thicker gold layers on a PCB can enhance its durability, corrosion resistance, electrical conductivity, and solderability. However, thicker gold layers also increase the cost of the PCB. The specific gold thickness required depends on the performance and environmental requirements of the application.

3. What is the typical gold thickness for high-reliability electronics?

For high-reliability electronics, such as those used in aerospace, defense, and medical applications, the typical gold thickness ranges from 8 to 30 microinches. However, the exact thickness required may vary based on the specific application requirements.

4. Can the gold thickness be customized for specific applications?

Yes, the gold thickness on a PCB can be customized to meet the specific requirements of an application. PCB manufacturers can adjust the plating process parameters to achieve the desired gold thickness, ranging from a few microinches to several hundred microinches.

5. How is the gold thickness on a PCB measured?

The gold thickness on a PCB can be measured using various techniques, including X-ray fluorescence (XRF), cross-sectional analysis, and beta backscatter. XRF is a non-destructive method that measures the thickness of the gold layer by analyzing the fluorescent X-rays emitted when the PCB is exposed to high-energy X-rays. Cross-sectional analysis involves cutting a small section of the PCB and examining the gold layer thickness under a microscope. Beta backscatter measures the thickness by analyzing the amount of beta particles scattered back from the gold layer when exposed to a radioactive source.

In conclusion, the thickness of the gold layer on a PCB is a critical factor in determining its performance, reliability, and cost. Thick gold PCBs offer enhanced durability, corrosion resistance, electrical conductivity, and solderability compared to standard gold-plated PCBs. The specific gold thickness required depends on the application requirements and can range from a few microinches to several hundred microinches.

PCB manufacturers use various processes, such as ENIG and electroplating, to apply the gold layer to the PCB substrate. The choice of process and the specific process parameters will influence the resulting gold thickness and uniformity. Proper surface preparation, inspection, and quality control are essential to ensure that the gold layer meets the specified requirements.

When selecting the appropriate gold thickness for a PCB, designers must consider factors such as application requirements, cost, and manufacturing processes. By understanding the benefits and limitations of thick gold PCBs, designers can make informed decisions to optimize the performance and reliability of their electronic devices.