Copper Clad: Everything You Should Know

What is Copper Clad?

Copper clad is a type of laminate material that consists of a layer of copper bonded to one or both sides of a substrate, typically a non-conductive material such as fiberglass or epoxy resin. The copper layer serves as a conductive surface for electronic circuits, while the substrate provides mechanical support and insulation.

Copper clad is widely used in the manufacturing of printed circuit boards (PCBs), which are essential components in a wide range of electronic devices, from smartphones and computers to industrial control systems and aerospace equipment.

Types of Copper Clad

There are several types of copper clad materials, each with its own unique properties and applications. The most common types include:

Type	Description	Applications
FR-4	Flame retardant epoxy-glass laminate	General purpose PCBs
CEM-1	Composite epoxy material with paper core	Low-cost consumer electronics
CEM-3	Composite epoxy material with woven glass core	High-density PCBs
Polyimide	High-temperature resistant polymer	Aerospace and military applications
PTFE	Low dielectric constant and loss tangent material	High-frequency RF and microwave circuits

FR-4 Copper Clad

FR-4 is the most widely used copper clad material for PCB manufacturing. It consists of a woven fiberglass fabric impregnated with an epoxy resin, with a layer of copper foil bonded to one or both sides. The “FR” in FR-4 stands for “flame retardant,” indicating that the material has been treated to resist ignition and slow the spread of flames.

FR-4 offers a good balance of mechanical, electrical, and thermal properties, making it suitable for a wide range of applications. It has a dielectric constant of approximately 4.5 at 1 MHz and a glass transition temperature (Tg) of around 130°C, allowing it to withstand the high temperatures encountered during soldering and other PCB assembly processes.

CEM-1 and CEM-3 Copper Clad

CEM (Composite Epoxy Material) copper clad laminates are lower-cost alternatives to FR-4, designed for less demanding applications. CEM-1 uses a paper core impregnated with epoxy resin, while CEM-3 uses a non-woven glass mat core. Both types have copper foil bonded to one or both sides.

CEM-1 is typically used in low-cost consumer electronics, such as toys and simple appliances, where the performance requirements are not as stringent as in industrial or high-reliability applications. CEM-3, on the other hand, offers better mechanical and thermal properties than CEM-1 and is often used in higher-density PCBs where cost is a concern.

Polyimide Copper Clad

Polyimide copper clad laminates are designed for high-temperature applications, such as aerospace and military electronics. Polyimide is a polymer material that remains stable at temperatures up to 260°C, making it ideal for environments where FR-4 would degrade or fail.

Polyimide copper clad is often used in multilayer PCBs, where the high thermal stability allows for reliable interconnections between layers. It also offers excellent chemical resistance and low moisture absorption, further enhancing its suitability for demanding applications.

PTFE Copper Clad

PTFE (polytetrafluoroethylene) copper clad laminates are used in high-frequency RF and microwave circuits, where low dielectric constant and loss tangent are critical for signal integrity. PTFE, also known by the brand name Teflon, has a dielectric constant of approximately 2.1 and a loss tangent of less than 0.001 at 10 GHz.

PTFE copper clad is available in various forms, including woven glass reinforced, ceramic filled, and low-density foam core materials. Each type offers specific benefits in terms of mechanical stability, thermal management, and controlled impedance for high-frequency design.

Copper Clad Manufacturing Process

The manufacturing process for copper clad laminates involves several key steps:

1. Substrate preparation: The substrate material, such as fiberglass or epoxy resin, is cut to size and cleaned to remove any contaminants that could affect adhesion.

2. Copper foil preparation: The copper foil is also cut to size and cleaned. In some cases, the foil may be treated with a bonding agent to improve adhesion to the substrate.

3. Lamination: The prepared substrate and copper foil are placed in a lamination press, where they are subjected to high temperature and pressure. The heat and pressure activate the bonding agent and cause the copper foil to adhere to the substrate.

4. Cooling: After lamination, the copper clad panel is cooled to room temperature while still under pressure to prevent warping or delamination.

5. Inspection: The finished copper clad laminate is inspected for defects, such as voids, blisters, or impurities. Samples may be subjected to additional quality control tests, such as peel strength, dimensional stability, and electrical properties.

The specific parameters for each step, such as temperature, pressure, and duration, depend on the type of copper clad being produced and the desired properties of the finished laminate.

Copper Clad Properties and Specifications

When selecting a copper clad laminate for a particular application, several key properties and specifications must be considered:

Dielectric Constant (Dk)

The dielectric constant, also known as relative permittivity, is a measure of a material’s ability to store electrical energy. In PCB design, the dielectric constant of the substrate material affects the propagation velocity and impedance of signals. A lower dielectric constant results in faster signal propagation and lower capacitance between conductors.

Typical dielectric constant values for common copper clad materials:

Material	Dielectric Constant (@ 1 MHz)
FR-4	4.2 – 4.9
CEM-1	4.5 – 4.9
CEM-3	4.5 – 4.9
Polyimide	3.4 – 4.0
PTFE	2.0 – 2.2

Loss Tangent (Df)

The loss tangent, also known as dissipation factor, is a measure of a material’s tendency to absorb and dissipate electrical energy as heat. A lower loss tangent indicates lower signal attenuation and higher efficiency, which is particularly important in high-frequency applications.

Typical loss tangent values for common copper clad materials:

Material	Loss Tangent (@ 1 MHz)
FR-4	0.020 – 0.035
CEM-1	0.020 – 0.035
CEM-3	0.020 – 0.035
Polyimide	0.002 – 0.010
PTFE	0.0002 – 0.0008

Thermal Properties

The thermal properties of a copper clad laminate determine its ability to withstand high temperatures during PCB assembly processes and in the final application environment. Key thermal properties include:

• Glass Transition Temperature (Tg): The temperature at which the substrate material transitions from a rigid, glassy state to a softer, rubbery state. A higher Tg indicates better thermal stability.

• Thermal Conductivity: The rate at which heat is conducted through the material. Higher thermal conductivity allows for better heat dissipation and reduces the risk of thermal stress-induced failures.

• Coefficient of Thermal Expansion (CTE): The degree to which the material expands or contracts with changes in temperature. A lower CTE mismatch between the copper clad and other PCB components reduces the risk of thermal stress and delamination.

Mechanical Properties

The mechanical properties of a copper clad laminate determine its ability to withstand physical stress and maintain structural integrity. Key mechanical properties include:

• Flexural Strength: The maximum stress the material can withstand before fracturing when bent.

• Tensile Strength: The maximum stress the material can withstand before breaking when stretched.

• Peel Strength: The force required to peel the copper foil away from the substrate, indicating the strength of the bond between the layers.

• Dimensional Stability: The ability of the material to maintain its original dimensions when subjected to changes in temperature, humidity, or stress.

Electrical Properties

In addition to dielectric constant and loss tangent, other electrical properties to consider when selecting a copper clad laminate include:

• Volume Resistivity: The resistance to electrical current flow through the bulk of the material.

• Surface Resistivity: The resistance to electrical current flow across the surface of the material.

• Dielectric Breakdown Voltage: The maximum voltage the material can withstand before electrical breakdown occurs.

• Dielectric Strength: The maximum electric field strength the material can withstand before electrical breakdown occurs.

Copper Clad Thickness and Weight

Copper clad laminates are available in a range of copper foil thicknesses and substrate thicknesses to suit different applications. The thickness of the copper foil is typically expressed in ounces per square foot (oz/ft²) or microns (μm), while the substrate thickness is expressed in mils (thousandths of an inch) or millimeters (mm).

Common copper foil thicknesses:

Ounces (oz/ft²)	Microns (μm)
0.5	17
1	35
2	70
3	105

Common substrate thicknesses:

Mils	Millimeters (mm)
10	0.25
20	0.51
30	0.76
40	1.02
62	1.57
93	2.36
125	3.18

The total thickness and weight of a copper clad laminate depend on the combination of copper foil and substrate thicknesses chosen. Thicker copper foils and substrates result in higher overall thickness and weight, which can impact PCB design considerations such as layer stackup, impedance control, and mechanical handling.

Copper Clad Applications

Copper clad laminates are used in a wide range of electronic applications, from consumer devices to industrial control systems and aerospace equipment. Some common applications include:

Consumer Electronics

• Smartphones and tablets
• Laptops and desktop computers
• Televisions and home entertainment systems
• Wearable devices
• Gaming consoles

Automotive Electronics

• Engine control units (ECUs)
• Infotainment systems
• Advanced driver assistance systems (ADAS)
• Electric vehicle power electronics
• Charging infrastructure

Industrial Electronics

• Process control systems
• Automation and robotics
• Power generation and distribution
• HVAC and building automation
• Medical devices

Aerospace and Defense

• Avionics systems
• Radar and communication equipment
• Satellite and space hardware
• Military vehicles and weapons systems
• Unmanned aerial vehicles (UAVs)

Telecommunications

• 5G network infrastructure
• Wireless base stations
• Fiber optic communication systems
• Satellite communication terminals
• Networking equipment

Choosing the Right Copper Clad

Selecting the appropriate copper clad laminate for a given application involves considering a range of factors, including:

1. Electrical requirements: Dielectric constant, loss tangent, impedance control, and signal integrity needs.

2. Thermal requirements: Operating temperature range, thermal conductivity, and CTE mismatch with other components.

3. Mechanical requirements: Flexural strength, tensile strength, peel strength, and dimensional stability.

4. Environmental requirements: Humidity resistance, chemical resistance, and flammability ratings.

5. Manufacturing requirements: Compatibility with PCB fabrication processes, such as drilling, etching, and soldering.

6. Cost considerations: Material cost, processing cost, and overall impact on product pricing and profitability.

By carefully evaluating these factors and consulting with PCB fabricators and material suppliers, designers can select the copper clad laminate that best meets the needs of their specific application.

FAQ

What is the difference between single-sided and double-sided copper clad?

Single-sided copper clad has a layer of copper foil bonded to one side of the substrate, while double-sided copper clad has copper foil on both sides. Double-sided copper clad is used for more complex PCB designs that require conductive layers on both sides of the board.

Can copper clad laminates be recycled?

Yes, copper clad laminates can be recycled. The copper foil can be separated from the substrate and recycled as a valuable metal, while the substrate can be recycled or repurposed depending on its composition. Many PCB fabricators and recycling facilities offer copper clad recycling services to reduce environmental impact and recover valuable materials.

How do I store copper clad laminates?

Copper clad laminates should be stored in a clean, dry, and temperature-controlled environment to prevent damage and ensure optimal performance. Store the laminates flat, away from direct sunlight, and in their original packaging or protective materials to avoid contamination and physical damage.

What is the shelf life of copper clad laminates?

The shelf life of copper clad laminates depends on the specific material and storage conditions. In general, properly stored copper clad laminates can last for several years without significant degradation in properties. However, it is essential to consult the manufacturer’s guidelines and recommendations for specific shelf life information and to use the laminates within the specified time frame for best results.

How do I choose the right copper thickness for my PCB design?

The choice of copper thickness depends on several factors, including current carrying requirements, trace width and spacing, thermal management needs, and manufacturing capabilities. Thicker copper foils allow for higher current carrying capacity and better thermal dissipation but may require wider traces and spacing, increasing overall PCB size. Thinner copper foils enable finer trace widths and spacing but may have lower current carrying capacity and thermal performance. Designers should work with their PCB fabricator to select the appropriate copper thickness based on their specific design requirements and constraints.