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 on a PCB is typically measured in microinches (μin) or microns (μm). In general, a PCB with a gold thickness of 30 microinches or more is considered a thick gold PCB.

Standard Gold Thicknesses on PCBs

The thickness of gold plating on a PCB can vary depending on the manufacturer and the specific requirements of the application. However, there are some standard thicknesses that are commonly used in the industry. The following table shows the standard gold thicknesses and their corresponding micron and microinch values:

Gold Thickness (μin)	Gold Thickness (μm)
3	0.08
5	0.13
10	0.25
15	0.38
20	0.51
30	0.76
50	1.27

It’s important to note that these are just standard thicknesses, and custom thicknesses can be specified based on the specific needs of the application.

Factors Influencing the Choice of Gold Thickness

When deciding on the appropriate gold thickness for a PCB, several factors need to be considered. These factors include:

1. Application Requirements

The specific requirements of the application play a significant role in determining the gold thickness on a PCB. For example, applications that require high reliability, such as aerospace, military, or medical devices, may require thicker gold plating to ensure long-term performance and durability.

2. Environmental Conditions

The environment in which the PCB will be used can also influence the choice of gold thickness. If the PCB will be exposed to harsh conditions, such as high humidity, corrosive substances, or extreme temperatures, a thicker gold layer may be necessary to protect the underlying copper traces and ensure reliable performance.

3. Contact Surface and Wear Resistance

Gold-plated PCBs are often used in applications that involve frequent mating and unmating of connectors or contacts. In such cases, a thicker gold layer can provide better wear resistance and extend the life of the contacts. The thickness of the gold layer can be adjusted based on the expected number of mating cycles and the contact force.

4. Cost Considerations

The cost of gold plating is directly proportional to the thickness of the gold layer. Thicker gold plating will result in higher manufacturing costs. Therefore, it’s essential to strike a balance between the required performance and the cost of production. In some cases, a combination of different gold thicknesses can be used on the same PCB to optimize cost and performance.

Benefits of Thick Gold PCBs

Using thick gold PCBs offers several advantages over standard gold-plated PCBs. Some of the key benefits include:

1. Enhanced Durability

Thick gold PCBs are more durable and can withstand harsher environmental conditions compared to standard gold-plated PCBs. The thicker gold layer provides better protection against corrosion, oxidation, and wear, ensuring long-term reliability and performance.

2. Improved Contact Resistance

Gold is an excellent conductor of electricity, and a thicker gold layer on a PCB can further improve its electrical conductivity. This results in lower contact resistance, which is crucial for applications that require high signal integrity and low signal loss.

3. Better Solderability

Thick gold PCBs offer better solderability compared to standard gold-plated PCBs. The thicker gold layer provides a more uniform and stable surface for soldering components, reducing the risk of defects and improving the overall quality of the solder joints.

4. Increased Shelf Life

PCBs with thicker gold plating have a longer shelf life compared to those with thinner gold layers. The thicker gold layer provides better protection against oxidation and corrosion, which can occur during storage and handling. This is particularly important for PCBs that may be stored for extended periods before assembly.

Applications of Thick Gold PCBs

Thick gold PCBs are used in a wide range of applications that require high reliability, durability, and performance. Some of the common applications include:

1. Aerospace and Defense
2. Medical Devices
3. Automotive Electronics
4. Industrial Control Systems
5. High-Frequency Communication Devices
6. Test and Measurement Equipment

In these applications, the use of thick gold PCBs ensures reliable performance, long-term durability, and compliance with stringent industry standards and regulations.

Measuring Gold Thickness on PCBs

Accurate measurement of gold thickness on PCBs is crucial for quality control and ensuring compliance with specifications. There are several methods used to measure gold thickness, including:

1. X-ray Fluorescence (XRF)

XRF is a non-destructive method that uses X-rays to measure the thickness of the gold layer on a PCB. This method is fast, accurate, and can measure multiple points on the PCB surface. XRF is widely used in the PCB industry for quality control and thickness verification.

2. Microscopic Cross-Sectioning

In this method, a small section of the PCB is cut and mounted for microscopic examination. The cross-section of the PCB is then viewed under a microscope to measure the thickness of the gold layer. This method is destructive and is typically used for detailed analysis and failure investigations.

3. Beta Backscatter

Beta backscatter is another non-destructive method that uses beta particles to measure the thickness of the gold layer. This method is based on the principle that the intensity of the backscattered beta particles is proportional to the thickness of the gold layer. Beta backscatter is a fast and accurate method for measuring gold thickness on PCBs.

Frequently Asked Questions (FAQs)

1. What is the minimum gold thickness required for reliable PCB performance?

The minimum gold thickness required for reliable PCB performance depends on the specific application and environmental conditions. In general, a gold thickness of 10-15 microinches is considered sufficient for most applications. However, for high-reliability applications or harsh environments, a thicker gold layer may be necessary.

1. Can thick gold PCBs be used for high-frequency applications?

Yes, thick gold PCBs are well-suited for high-frequency applications. The thicker gold layer provides better electrical conductivity and lower contact resistance, which is crucial for maintaining signal integrity in high-frequency circuits.

1. How does the cost of thick gold PCBs compare to standard gold-plated PCBs?

Thick gold PCBs are generally more expensive than standard gold-plated PCBs due to the higher amount of gold used in the plating process. The cost difference can vary depending on the specific thickness and the PCB manufacturer. However, the added cost is often justified by the improved performance, reliability, and durability of thick gold PCBs.

1. Can thick gold PCBs be used for lead-free soldering?

Yes, thick gold PCBs are compatible with lead-free soldering processes. The thicker gold layer provides a stable and uniform surface for soldering, ensuring good wetting and strong solder joints. However, it’s important to control the gold thickness to avoid embrittlement of the solder joints due to excessive gold dissolution.

1. How can I specify the gold thickness when ordering PCBs?

When ordering PCBs, you can specify the desired gold thickness in either microinches (μin) or microns (μm). Most PCB manufacturers have standard gold thickness options, but they can also accommodate custom thickness requirements. It’s important to communicate your specific requirements to the manufacturer to ensure that the PCBs meet your performance and reliability needs.

Conclusion

The thickness of gold on a PCB is a critical factor that influences its performance, reliability, and durability. Thick gold PCBs, with a gold layer of 30 microinches or more, offer several advantages over standard gold-plated PCBs, including enhanced durability, improved contact resistance, better solderability, and increased shelf life.

When choosing the appropriate gold thickness for a PCB, it’s essential to consider the specific application requirements, environmental conditions, contact surface and wear resistance, and cost considerations. Accurate measurement of gold thickness using methods like XRF, microscopic cross-sectioning, or beta backscatter ensures quality control and compliance with specifications.

Thick gold PCBs find applications in various industries, such as aerospace, defense, medical devices, automotive electronics, and high-frequency communication devices, where high reliability and performance are paramount.

By understanding the importance of gold thickness on PCBs and selecting the appropriate thickness for your application, you can ensure optimal performance, reliability, and longevity of your electronic devices.