PCB Materials

Complete Guide to PCB Copper Foil

PCB copper foil is a thin layer of copper that is laminated onto a substrate material in order to create conductive traces or pads on a printed circuit board. Copper foil is an essential component in the construction of PCBs and plays a crucial role in the function and performance of electronic devices.

PCB copper foil is an essential material used in the production of printed circuit boards. It serves as the foundation for the conductive pathways of the PCB, determining the board's electrical, physical, and mechanical properties. As a result, selecting the right PCB copper foil is critical to the overall performance of the PCB. In this article, we will go in-depth on the ins and outs of PCB copper foil, covering its features, applications, production processes, selection considerations, and maintenance tips. This guide will provide essential information to help you make informed decisions for your PCB manufacturing needs.

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PCB Copper Foil Definition

What is PCB Copper Foil?

PCB copper foil is a special material used for PCB manufacturing. PCB copper foil is a thin layer of copper laminated onto a substrate material to create conductive traces or pads on a PCB. The copper foil is etched away in certain areas to form the desired circuit pattern. The thickness, width, and quality of the copper foil are important factors that affect the electrical performance and reliability of the PCB.

PCB Copper Foil Types

As mentioned above, PCB copper foil is an important material used in the production of PCBs. There are three main types of PCB copper foil: electrolytic copper foil, rolled copper foil, and deposition copper foil.

Electrolytic copper foil: Electrolytic copper foil is widely used in high-frequency and high-speed digital circuits because it has excellent electrical conductivity, thermal conductivity, and peel strength. It is produced by an electrochemical deposition process in which copper ions are deposited onto a substrate using an electric current.
Rolled copper foil: Rolled copper foil, on the other hand, is created using a rolling process where copper is rolled to the desired thickness. This type of copper foil is mainly used in flexible PCBs due to its excellent flexibility and ease of bending.
Deposition copper foil: Deposition copper foil is made by depositing copper onto a substrate using a physical or chemical vapor deposition process. It has a very smooth surface and is often used in high-density PCBs, particularly those with complex circuits and submicron lines.

It is important to select the appropriate type of PCB copper foil depending on the specific application requirements of the PCB being manufactured. Factors to consider include the operating frequency of the circuit, the thermal requirements of the application, and the flexibility requirements of the PCB.

According to different classification methods, PCB copper foil also has the following types:

PCB Copper Foil Thickness

PCB copper foil thickness you should know

PCB copper foil thickness refers to the thickness of the layer of copper that is applied to the substrate material of a printed circuit board. This thickness can vary depending on the requirements of the particular PCB design, and it is an important factor to consider when designing a PCB, as it can affect the electrical performance, signal integrity, and cross-talk of the board.

The copper foil thickness is typically measured in ounces (oz). One ounce refers to the thickness of copper that evenly covers an area of one square foot, which is approximately 1.4 mils, expressed in weight per unit area. The formula for this is 1oz=28.35g/FT2, where FT2 represents square feet and one square foot equals 0.09290304 square meters. Additionally, there are other common measurement units for copper foil thickness, such as microns and millimeters. These different units can be converted between each other using conversion formulas.

There are several standard copper thickness options that are commonly used in PCB manufacturing. These include:

1 oz copper (35 µm)
2 oz copper (70 µm)
3 oz copper (105 µm)
4 oz copper (140 µm)

The thickness of the copper layer selected for a particular PCB should take into account the amount of current the board needs to carry, the distance between traces, and the amount of heat the board is expected to generate, among other factors.

If the copper thickness selected is too thin, there may be issues with impedance and voltage drop, which can negatively impact the performance of the PCB. On the other hand, if the copper thickness selected is too thick, it can be more difficult to etch the traces and vias, which can increase the cost of manufacturing.

PCB designers need to carefully evaluate the requirements of their particular design to determine the appropriate copper thickness for their board, taking into account factors such as the size and complexity of the board, the expected electrical loads, and the manufacturing process used.

Surface Conductor Thickness (Foil Plus Plating)

If not stated differently in the procurement documentation, the minimum total thickness of copper conductors (including copper foil and copper plating) after processing must comply with Table 3-1 in IPC-A-600G.

Table 3-1 External Conductor Thickness after Plating

Weight	Absolute Cu Min. (IPC-4562 less 10% reduction) (μm) [μin]	Plus Min. Plating for Class 1 & 2 (20μm) [787μin]	Plus Min. Plating for Class 3 (25μm) [984μin]	Max. Variable Processing Allowance Reduction* (μm) [μin]	Min. Surface Conductor Thickness after Processing (μm)[μin]
Weight	Absolute Cu Min. (IPC-4562 less 10% reduction) (μm) [μin]	Plus Min. Plating for Class 1 & 2 (20μm) [787μin]	Plus Min. Plating for Class 3 (25μm) [984μin]	Max. Variable Processing Allowance Reduction* (μm) [μin]	Class 1 & 2	Class 3
1/8oz	4.60 [181]	24.60 [967]	29.6 [1,165]	1.50 [59]	23.1 [909]	28.1 [1,106]
1/4oz	7.70 [303]	27.70 [1,097]	32.70 [1,287]	1.50 [59]	26.2 [1,031]	31.2 [1,228]
3/8oz	10.80 [425]	30.80 [1,213]	35.80 [1,409]	1.50 [59]	29.3 [1,154]	34.3 [1,350]
1/2oz	15.40 [606]	35.40 [1,394]	40.40 [1,591]	2.00 [79]	33.4 [1,315]	38.4 [1,512]
1oz	30.90 [1,217]	50.90 [2,004]	55.90 [2,201]	3.00 [118]	47.9 [1,886]	52.9 [2,083]
2oz	61.70 [2,429]	81.70 [3,217]	86.70 [3,413]	3.00 [118]	78.7 [3,098]	83.7 [3,295]
3oz	92.60 [3,646]	112.60 [4,433]	117.60 [4,630]	4.00 [157]	108.6 [4,276]	113.6 [4,472]
4oz	123.50 [4,862]	143.50 [5,650]	148.50 [5,846]	4.00 [157]	139.5 [5,492]	144.5 [5,689]

Reference:

Cu Plating Thickness Class 1 = 20μm [787μin] Class 2 = 20μm [787μin] Class 3 = 25μm [984μin]
Process allowance reduction does not allow for rework processes for weights below 1/2oz. For 1/2oz and above, the process allowance reduction allows for one rework process.

Copper Foil Thickness -Internal Layers

The minimum copper foil thickness (or conductor thickness) represents the highest coplanar thickness that can conduct electric current. Such thickness includes individual scratches, but excludes the saw-toothed dendritic surface that promotes adhesion of the metal-clad surface.

For the minimum internal layer copper foil thickness after processing, Table 3-2 in IPC-A-600G must be followed.

Table 3-2 Internal Layer Foil Thickness after Processing

Weight (oz) [μm]	Absolute Cu Min. (IPC-4562 less 10% reduction) (μm) [μin]	Max. Variable Processing Allowance Reduction* (μm) [μin]	Min. Final Finish after Processing (μm)[μin]
1/8 [5.10]	4.60 [181]	1.50 [59]	3.1 [122]
1/4 [8.50]	7.70 [303]	1.50 [59]	6.2 [244]
3/8 [12.00]	10.80 [425]	1.50 [59]	9.3 [366]
1/2 [17.10]	15.40 [606]	4.00 [157]	11.4 [449]
1 [34.30]	30.90 [1.217]	6.00 [236]	24.9 [980]
2 [68.60]	61.70 [2,429]	6.00 [236]	55.7 [2,193]
3 [102.9]	92.60 [3,646]	6.00 [236]	86.6 [3,409]
4 [137.20]	123.50 [4,862]	6.00 [236]	117.5 [4,626]
Above 4 [137.20]	–	6.00 [236]	6μm [236μin] below minimum thickness of calculated 10% reduction of foil thickness in IPC-4562

Notes:

The reduction of process allowance does not permit rework processes for weights lower than 1/2oz. However, for weights of 1/2oz and higher, the process allowance reduction allows for one rework process.
Please note that any additional plating required for internal layer conductors must be identified as a separate plating thickness requirement.

At JHYPCB, we take pride in providing a wide range of copper weights to meet your requirements for copper thickness, particularly for thick copper PCBs. We offer a variety of options, including 12μm (1/3oz), 18μm (1/2oz, or H oz), 35μm (1oz), 70μm (2oz), 105μm (3oz) and 210μm (4oz), enabling you to select the perfect match for your application.

Our selection of copper weights allows us to provide flexible and reliable solutions to meet your needs. Whether you require a thin copper layer, a high-density interconnect PCB with thicker copper weights or a board with varying copper thickness, JHYPCB has the expertise and capabilities to deliver quality products that meet your specific requirements.

Properties of PCB Copper Foil

PCB Copper foil is widely used in various fields such as electronics, power transmission and communication systems due to its unique combination of chemical, physical, and electrical properties. Its high conductivity, resistance to corrosion, smoothness, and ease of adhesion to substrates make it an ideal choice for electronic applications. Additionally, its malleability, flexibility, and high melting point enable it to be easily manipulated and formed to fit specific design requirements. PCB Copper foil’s low resistance, high thermal conductivity, low dielectric constant, and low dielectric loss also make it ideal for electrical applications.

Chemical Characteristics:

PCB copper foil is a highly conductive material.
It is resistant to corrosion and oxidation, making it durable.
The surface of the copper foil is very smooth, making it easy to use in etching and printing circuits.
It is also highly adhesive to the substrate which enhances its bonding ability.

Physical Characteristics:

The thickness of PCB copper foil can range from a few microns to several hundred microns depending on the application it is used for.
It is very malleable, ductile and can be bent easily to fit any shape.
The melting point of copper is very high, making it suitable for use in high-temperature applications such as power transmission.

Electrical Characteristics:

Copper is highly conductive, making it an ideal material for electrical applications.
PCB copper foil has low resistance, enabling efficient flow of current through it.
It also has high thermal conductivity, allowing for efficient dissipation of heat.
PCB copper foil has a low dielectric constant and loss tangent, which prevents any signal loss during the transmission of electrical signals.

How is PCB Copper Foil Made?

PCB copper foil used in the industry is more complex than one would imagine. Copper is an excellent conductor and thermal conductor, making it an ideal material for most PCB conductors. Copper foils also have many other characteristics, which are important for engineers to understand.

There are generally two types of copper foil used in the PCB industry: rolled annealed copper (RA) and electrolytic deposition (ED) copper foil. The manufacturing process of RA copper foil starts from pure copper stock, and the thickness is reduced by continuous rolling until it reaches the desired thickness. The ED copper foil is made by electroplating copper onto a rotating titanium drum, and the thickness of the foil depends on the speed of the drum rotation. After manufacturing, both RA and ED copper foils require multiple processing steps.

Copper foil has various processing methods, including passivation treatment that aims to prevent oxidation before use. Other methods aim to enhance the chemical adhesion of copper foil to certain resin systems, such as PPE and PTFE. Different resin systems react differently to each processing method due to their distinct bonding characteristics. Some processing/resin combinations are better than others and achieve good adhesion. Some processing methods can ensure appropriate adhesion at high temperatures, and others can ensure reliable adhesion surfaces for long-term high-temperature applications.

For rigid PCB applications, ED copper foil is most commonly used, but RA copper foil is also used. Generally, RA copper foil is more expensive than ED copper foil unless certain features of RA copper foil have a greater advantage for the application. RA copper foil has a very smooth surface, which is conducive to low insertion loss, making it suitable for high-frequency and high-speed digital applications. RA copper foil has a unique manufacturing process, resulting in in-plane crystal structure, which is advantageous for applications that require circuit bending. However, the downside of RA copper foil is related to this crystal structure, that is, etching of small circuit features, which can be overcome to some extent by using specific etching for RA copper foil.

ED copper foil is widely used in the PCB industry. There are different types of ED copper foil, which are categorized according to their surface roughness and/or processing methods. IPC classifies ED copper foil into different categories based on their roughness, including LP (low profile), VLP (very low profile), and HVLP (extremely low profile).

Applications of PCB Copper Foil

PCB Copper Foil has a wide range of applications in the PCB manufacturing industry, including:

Application in single, double, and multilayer PCBs: In single-sided and double-sided PCBs, Copper Foil is mainly used as a conductor to connect the components and circuits on the board. In multilayer PCBs, the Copper Foil is used as a signal and power layer, providing high conductivity for the circuit connections between different layers.
Application in rigid, flexible, and rigid-flex PCBs: In rigid PCBs, Copper Foil is mainly used as a surface layer or internal layer to provide electrical conductivity to connect different components and circuits. In flexible PCBs, Copper Foil is bonded with a flexible substrate to provide a flexible conductive layer. In rigid-flex PCBs, Copper Foil serves as both a rigid and flexible conductive layer.
Application in high-frequency, high-speed, and high-density circuits: In high-frequency circuits, Copper Foil is used as a signal layer to provide high-frequency transmission lines with low insertion loss and low crosstalk. In high-speed circuits, the Copper Foil is used as a grounding layer to reduce electromagnetic interference and maintain signal integrity. In high-density circuits, the Copper Foil is used as a metal layer to ensure the close proximity of components and circuits, reducing the size of the PCB and improving the system performance.

In summary, PCB Copper Foil plays an essential role in the PCB manufacturing industry, providing high conductivity, signal transmission, and system performance for various PCB applications.

Selection guide for PCB copper foil

A. Considerations for selecting PCB copper foil:

Thickness: The thickness of copper foil affects the conductivity and the ability to carry current. A thicker copper foil has better conductivity and higher current carrying capacity, but it may be more difficult to process and may increase the overall weight of the PCB.
Width: The width of the copper foil depends on the size of the PCB and the width of the traces that need to be formed. The width should be chosen to ensure proper current carrying capacity and to minimize the possibility of over etching.
Density: The density of the copper foil affects the mechanical strength and flexibility of the PCB, as well as its ability to withstand temperature changes. High density copper foil is more rigid and has higher mechanical strength, but it may be more difficult to process due to its thickness.

B. Performance indicators of PCB copper foil:

Purity: The purity of copper foil affects the electrical conductivity and the susceptibility to corrosion. High purity copper foil is less susceptible to corrosion and has better conductivity.
Surface roughness: The surface roughness affects the adhesion of the copper foil to the substrate, and the ability of the PCB to withstand temperature changes and mechanical stresses.
Peel strength: The peel strength of the copper foil affects its ability to adhere to the substrate and the ability of the PCB to withstand thermal and mechanical stresses.

Recommendations for selecting PCB copper foil:

Choose a copper foil with appropriate thickness, width, and density for the specific requirements of the PCB design.
Choose a copper foil with high purity and low surface roughness for better conductivity and adhesion.
Consider the peel strength of the copper foil to ensure a strong bond with the substrate and to withstand thermal and mechanical stresses.
Consult with manufacturers or suppliers for specific recommendations based on the application and requirements of the PCB.

FAQs on PCB Copper Foil

What is PCB Copper Foil and what are its main characteristics?

PCB Copper Foil is a thin layer of copper that is used to create electrical conductive pathways on the surface of circuit boards. Its main characteristics include exceptional electrical conductivity, thermal conductivity, and corrosion resistance.

What are the different types of Copper Foil available for PCB designs?

There are different types of Copper Foil available for PCB designs, including rolled annealed (RA) Copper Foil, electrodeposited (ED) Copper Foil, and treated ED Copper Foils.

What special precautions should be taken when working with Copper Foil during the PCB manufacturing process?

When working with Copper Foil during the PCB manufacturing process, special precautions such as proper handling, storage, and protection against oxidation may be necessary to ensure the quality and integrity of the material.

RA Copper VS ED Copper: Which Copper Foil for Flex PCB Substrate?

Both RA (Rolled Annealed) copper and ED (Electro-Deposited) copper are commonly used for flex PCB substrates.

RA copper is a type of copper foil that is annealed, meaning it undergoes heat treatment to improve its flexibility and ductility. RA copper is suitable for flex PCB substrates because it is more malleable and can better conform to the flexible substrate material.

ED copper, on the other hand, is deposited onto a surface using an electrochemical process. It is a very pure copper with a very smooth surface finish, which can result in better circuit accuracy, but it is typically stiffer and less ductile than RA copper.

In general, RA copper is a popular choice for flex PCB applications due to its increased flexibility and conformity to the substrate.

What is PCB copper foil current carrying capacity?

"PCB copper foil current carrying capacity" refers to the maximum amount of electrical current that a copper foil on a printed circuit board (PCB) can handle without any damage or loss of performance. The current carrying capacity of a PCB copper foil depends on various factors such as its thickness, width, and ambient temperature. It is an important design consideration because using a copper foil with a lower current carrying capacity than what is necessary can result in heat generation, voltage drops, and other issues.

What is the relationship between PCB copper foil thickness, line width, and current?

The relationship between PCB copper foil thickness, line width, and current is complex, but it can be summarized as follows:

The thicker the copper foil, the more current it can carry without overheating and melting. This is because the thickness of the copper foil affects its resistance, and thicker foils have lower resistance.

The width of the copper trace also affects its ability to carry current. Wider traces have lower resistance and can therefore carry more current without overheating. However, wider traces also take up more space on the board, which can be a limiting factor in some applications.

Current carrying capacity is also affected by factors such as the ambient temperature and the amount of heat sinking provided by the board and its components. In high current applications, it is important to choose copper foil thickness and trace width that will allow the current to flow without causing overheating or other problems.

In general, designers should select PCB copper foil thickness and trace width based on the expected current load and the space available on the board. They should also consider factors such as thermal management and the overall requirements of their application.