What is Copper Clad Laminate (CCL)?

As electronic products evolve towards miniaturization, thinner and lighter profiles, multifunctionality, and higher density, the integration level and assembly density of components on circuit boards continue to increase, along with greater power consumption. This places higher demands on the heat dissipation performance of PCB substrates. If a substrate has poor thermal conductivity, it can lead to overheating of components on the circuit board, thereby affecting the overall reliability of the device. Hence, the PCB substrate came into being.

Copper Clad Laminate (CCL), i.e., the PCB substrate used in PCB manufacturing, is the most widely used and important substrate in the production of PCBs. It is a material made by impregnating electronic glass fiber or other reinforcing materials with resin and then cladding it with copper on one or both sides. It is extensively used in electronic products such as televisions, radios, computers, and mobile communications.

What is Copper Clad Laminate (CCL)?

Copper Clad Laminate (CCL), abbreviated as CCL, is a base material for Printed Circuit Boards (PCBs). It is produced using glass fiber or wood pulp paper as the reinforcing material, which is impregnated with resin. Then, copper foil is applied to one or both sides of this reinforced material, followed by lamination.

Types of Copper Clad Laminates

Copper Clad Laminate (CCL) is a material used to manufacture Printed Circuit Boards (PCBs). They consist of an insulating layer (e.g., glass fiber or epoxy) covered with a thin layer of copper on one or both sides. Based on different characteristics, CCLs can be categorized into the following types:

• By Mechanical Rigidity:
  • Rigid CCL: Typically used in devices like desktop computers and servers.
  • Flexible CCL: Primarily used in foldable or bendable devices, such as smartphones and wearables, due to their flexibility.
• By Insulating Material/Structure:
  • Organic Resin-Based CCL: Examples include FR-4 (Glass Epoxy), CEM series (Composite Epoxy Material), etc.
  • Metal-Based CCL: Mainly used in LED lighting and automotive electronics due to their excellent thermal conductivity.
  • Ceramic-Based CCL: Feature very low dielectric loss and high frequency stability, often used in microwave and RF applications.
• By Thickness:
  • Thick Board (0.8–3.2mm including Cu)
  • Thin Board (<0.78mm, excluding Cu)
• By Reinforcing Material:
  • Glass Fabric-Based
  • Paper-Based – Composite-Based (CME-1, CME-2)

Flame Retardant Grade

According to UL standards (UL94, UL746E, etc.), the flame retardant grades for rigid CCLs can be classified into four categories: UL-94V0, UL-94V1, UL-94V2, and UL-94HB.

Other classification methods include categorization by reinforcing material (e.g., paper or glass fiber), the insulating resin used (e.g., phenolic or epoxy), special functions (e.g., high temperature resistance or low dielectric constant), and Coefficient of Thermal Expansion (CTE).

1) FR-4
According to the flame retardancy ratings from Underwriters Laboratories (UL), FR-4 is a grade of flame-retardant material that meets the highest standard, UL94 V-0. This term was introduced by the National Electrical Manufacturers Association (NEMA) in 1968, specifically referring to the insulating epoxy glass fiber fabric used to make rigid Printed Circuit Boards (PCBs). When you look at a rigid PCB board, the visible insulating part is this FR-4 epoxy glass fiber fabric.

When copper is laminated onto FR-4 material, it forms a Copper Clad Laminate (CCL), also known as FR4 CCL. Due to its robust mechanical properties and high-quality electrical insulation, this material becomes the most commonly used substrate for making bare PCBs. However, in PCB construction, FR-4 acts primarily as the main insulating skeleton.

To create double-sided or multilayer PCBs, additional materials such as FR-4 core boards, Prepreg (PP), and copper foil are required. After completing the micro-etching process, these components are stacked together in a laminating press under high temperature and pressure.

2) FR-2
FR2 Copper Clad Laminate (CCL) is another substrate used for producing Printed Circuit Boards (PCBs). “FR2” indicates that the material has a flame retardancy grade of 2. It primarily consists of a phenolic resin binder and cellulose paper as the reinforcing material, giving it different characteristics compared to FR4 CCL.

Although not as popular or widely used as FR4 due to its lower thermal resistance and mechanical strength, FR2 CCL is still employed in less demanding, cost-sensitive environments. The copper layer laminated onto the FR2 substrate can be etched into specific patterns to create conductive paths for electrical signals, similar to other types of PCBs.

3) Metal Core Printed Circuit Board (MCPCB)
Metal Core Printed Circuit Board (MCPCB), also known as a thermal PCB or metal-backed PCB, is a type of PCB that contains a base metal material. The metal core serves to transfer heat away from critical board components to less critical areas, such as the metal heat sink backing.

The most common type of MCPCB uses an aluminum alloy, but other metals like copper can be used for better performance. These boards are particularly suitable for high-power applications where heat dissipation is crucial for component function and longevity.

An MCPCB typically consists of four layers:

• Component Layer: This is the top layer where all components are soldered.
• Dielectric Layer: A non-conductive layer designed to provide electrical isolation while still allowing heat transfer.
• Base Metal Layer: Usually made of aluminum or copper, this layer aids in heat dissipation.
• Backing Layer: Often just an additional protective coating, but it may also include more circuitry depending on the design needs.

MCPCBs are widely used in LED technology (for lighting and backlighting) due to their ability to efficiently manage the heat generated at high brightness levels. They are also used in power converters/supplies, automotive systems, RF applications, etc. – essentially anywhere effective thermal management within an electronic circuit is required.

4) CEM Series (CEM-1, CEM-3)
The CEM series of Copper Clad Laminates (CCL) are composite materials used for Printed Circuit Boards (PCBs). “CEM” stands for Composite Epoxy Material. The two most common types in this series are CEM-1 and CEM-3.

• CEM-1: CEM-1 is a laminate made from a cellulose paper base impregnated with flame-retardant epoxy resin and clad with copper on one or both sides. It is often used in cost-effective applications as it offers good mechanical strength and electrical properties at a lower price than other laminates like FR4.
• CEM-3: CEM-3, on the other hand, performs similarly to FR4 but is more affordable. Its composition includes glass fabric and an epoxy resin binder, making it flame retardant. While FR4 is typically opaque due to its woven cloth reinforcement, CEM-3 uses non-woven glass fiber reinforcement, appearing white and slightly translucent.

Both types are widely used in PCB manufacturing due to their good electrical characteristics, heat resistance, and relatively low cost compared to higher-end materials like FR4.

5) Flexible Copper Clad Laminate (FCCL)
Flexible Copper Clad Laminate (FCCL) is a material used to manufacture Flexible Printed Circuit Boards (FPCBs). It consists of an adhesive layer, a copper layer, and a polyimide film. The polyimide film offers excellent heat resistance, chemical resistance, and flexibility.

The main advantage of FCCL is its ability to bend or fold without breaking. This makes them ideal for use in compact devices where space is limited or where components need to move or flex during operation.

There are two main types of FCCL:

• Adhesive-Based FCCL: Comprises a three-layer structure: copper foil, adhesive layer, and base film (usually polyimide). Common adhesives include epoxy and acrylic resin.
• Adhesiveless FCCL: This type lacks a separate adhesive layer; instead, the copper foil is directly bonded to the base film through a special process. Adhesiveless CCL offers better dimensional stability and heat resistance than adhesive-based CCL.

6) High Frequency Copper Clad Laminate (HF CCL)
High Frequency Copper Clad Laminate (HF CCL) is a material used to manufacture Printed Circuit Boards (PCBs) specifically designed for high-frequency circuits. These boards are commonly used in applications such as Radio Frequency (RF) and microwave systems, telecommunications, antennas, radar systems, etc.

The key properties of HF CCL are its low Dielectric Constant (Dk or εr) and low Dissipation Factor (Df). The dielectric constant relates to the amount of electrical energy that can be stored in the material, while the dissipation factor indicates how much energy is lost as heat during storage and release. Both factors directly impact high-frequency signal transmission speed and loss.

Common materials used for HF CCL include Polyphenylene Oxide (PPO), Polytetrafluoroethylene (PTFE or Teflon), Rogers materials (like RO4350B or RO4003C), etc.

Compared to standard FR4 laminates:

• Performance: At higher frequencies (typically >2GHz), HF CCL performs better due to lower signal loss.
• Cost: HF materials tend to be significantly more expensive than traditional FR4 materials.
• Manufacturing Process: Some high frequency PCB materials require special handling or processing steps compared to standard PCB manufacturing processes.

7) PTFE-Based Copper Clad Laminate
Polytetrafluoroethylene (PTFE) based Copper Clad Laminates are specialized materials used to manufacture high-frequency Printed Circuit Boards (PCBs). These laminates are particularly suitable for applications requiring fast and efficient signal transmission. PTFE fluoropolymer has a low dielectric constant, minimizing signal loss and aiding rapid signal transmission. Its low dissipation factor means less energy is lost as heat during operation, and its chemical resistance ensures durability in various environments.

However, using PTFE-based laminates also presents some challenges. Due to their excellent performance characteristics at higher frequencies (typically > 2GHz), they tend to be more expensive than other types of laminates like FR4. Furthermore, achieving good adhesion between the copper and the non-stick PTFE substrate during manufacturing can be difficult without special treatment methods like plasma etching or chemical roughening. Despite these obstacles, PTFE-based laminates are widely used in areas where high-frequency signal integrity is critical, such as telecommunications equipment production, antenna design, and microwave devices.

What Makes an Excellent CCL?

A Copper Clad Laminate functions well only if it meets performance requirements in the following aspects:

• Appearance: Due to unforeseen factors in the production process, issues such as dents, scratches, resin spots, wrinkles, pinholes, bubbles, etc., may occur on the copper foil. All these issues inevitably lead to a decline in the performance of the CCL and, consequently, the PCB. Therefore, a high-quality CCL should have a flat and smooth appearance.
• Dimensions: As the CCL is the base material for the PCB, it must meet the PCB’s dimensional requirements. Parameters for CCL dimensions include length, width, diagonal deviation, and warpage, each of which must meet specific requirements.
• Electrical Performance: This is a fundamental task of the PCB, so any aspect affecting its electrical performance must be carefully designed, including Dielectric Constant (Dk), Dissipation Factor (Df), Volume Resistivity, Surface Resistivity, Insulation Resistance, Arc Resistance, Dielectric Breakdown Voltage, Electric Strength, Comparative Tracking Index (CTI), etc.
• Physical Properties: Parameters for the physical properties of CCL include Dimensional Stability, Peel Strength (PS), Flexural Strength, Heat Resistance (including Thermal Stress, Td, T260, T288, T300), Punching Quality, etc.
• Chemical Properties: The chemical properties of CCL must meet requirements such as Flammability, Resistance to Chemical Reagents, Glass Transition Temperature (Tg), Z-axis Coefficient of Thermal Expansion (Z-CTE), and Dimensional Stability.
• Environmental Performance: Requirements such as Water Absorption must be met.

CCL quality assessment should be conducted by the PCB manufacturer. Taking PCBCart as an example, they adopt IPC-4101C as the manufacturing standard and use IPC-TM-650 for CCL testing. These measures ensure the CCL becomes a qualified PCB substrate.

Copper Clad Laminate (CCL) Materials

• Copper Foil: Copper foil is a cathodic electrolytic material, a thin, continuous layer of metal foil deposited on the PCB substrate. It bonds easily to the insulating layer, accepts a printed protective layer, and is etched to form the board’s circuitry pattern.
  

• Prepreg: Prepreg (pre-impregnated) is glass fiber impregnated with resin. The resin is pre-dried but not hardened, so it will flow, adhere, and fully immerse when heated. Thus, prepreg is glass fiber reinforced with an adhesive layer (similar to FR4 material). It is also referred to as the glass fabric type.

Prepreg thickness varies among manufacturers. Based on resin content, it is categorized into three types: “SR” (Standard Resin), “MR” (Medium Resin), and “HR” (High Resin). The optimal material is selected based on the desired final thickness, layer stack-up, or impedance. Therefore, the thicknesses mentioned below are for reference only.

What is Prepreg?

Prepreg is the reinforcing material inside the CCL, made from glass fiber that has been baked. Some also call it a bonding sheet. It is composed of epoxy resin, glass fiber cloth, DMF, 2MI, acetone, etc.

• Classification of Prepreg. Prepreg can be classified into many types based on different criteria:
  1. By glass fabric style: 106, 1080, 2112, 2116, 1500, 7628;
  2. By application resin and its properties: POLYCLAD Turbo 254/226, ISOLA FR402/FR406, ITEQ IT180, Shengyi S1141-140/170;

The table below shows part of PCBCart’s manufacturing capabilities regarding prepreg. For more details, please contact：sales@pcbtry.com

Prepreg	Gel Time (seconds)	Resin Content	Thickness
1080	135±15	62±1.5%	3 mil
2112 (2113, 2313)	135±15, 115±15	57±1.5%, 59.5%-62.0%	4 mil
2116	135±15	49.5±1.0%, 53±1.5%	5 mil
7628	113±15, 135±15	44±1.5%, 38±1.5%, 41±1.5%	7 mil

Advantages of Copper Clad Laminates

Copper Clad Laminate (CCL) is a base material for Printed Circuit Boards (PCBs). It is made by reinforcing an insulating substrate with copper foil on one or both sides. The advantages of using CCL in PCBs include:

• Electrical Conductivity: Copper has excellent electrical conductivity, reducing resistance to signal transmission and improving the overall performance of electronic devices.
• Thermal Conductivity: Copper also has good thermal conductivity, helping to dissipate heat generated by components on the board, reducing the risk of overheating and improving device reliability.
• Mechanical Strength: The combination of copper and laminate provides mechanical strength to resist bending and breaking, while maintaining flexibility for design purposes.
• Etchability: Copper can be easily etched away during PCB production to create the intricate circuit patterns required in modern electronics.
• Cost-Effective Production: CCL is a relatively cost-effective material used in volume production environments, as they are easy to work with in manufacturing processes like drilling, etching, etc., lowering the per-unit production cost.
• Compatibility with Soldering Processes: Components are typically soldered onto the copper traces on PCBs, so the copper layer makes this process easier and more reliable.
• Durability and Longevity: PCBs based on CCL tend to have long service lives because they offer good resistance to corrosion; this makes them suitable for use in harsh environmental conditions where other types of boards might fail prematurely.
• Dimensional Stability: CCL maintains stable dimensions even with changes in temperature or humidity – an important factor given that many electronic devices operate under varying environmental conditions.

What is the Role of Copper Clad Laminate?

Copper Clad Laminate (CCL) is the foundational material in the production of Printed Circuit Boards (PCBs). It serves several key roles. Firstly, its copper layer forms the conductive pathways or “traces” when etched into specific patterns. These traces enable communication between different PCB components. Secondly, the substrate layer of the CCL provides mechanical support and structural integrity for all mounted components.

Furthermore, due to copper’s excellent thermal conductivity, it helps dissipate heat generated by various electronic components during operation, preventing overheating and potential damage. The insulating substrate also provides electrical insulation by isolating copper traces on different layers, avoiding short circuits between them. Finally, the surface of these boards is compatible with the soldering processes typically used to mount electronic components onto them.

Where Can Copper Clad Laminates Be Applied?

Copper Clad Laminate (CCL) is primarily used as the substrate for Printed Circuit Boards (PCBs), which are found in almost all electronic devices. Here are some specific examples of CCL applications:

• Consumer Electronics: Mobile phones, computers, televisions, game consoles, and other household appliances all contain PCBs made from CCL.
• Industrial Equipment: Machinery controls, power equipment, and automation systems often employ PCBs to manage electrical functions.
• Automotive Industry: Modern vehicles use numerous PCBs for engine control units, infotainment systems, navigation systems, and safety features like airbags and anti-lock braking systems.
• Aerospace and Defense Industry: Avionics systems in aircraft or spacecraft rely heavily on high-specification PCBs; defense applications may include communication equipment or radar devices.
• Medical Devices: Advanced medical equipment like imaging devices (MRI machines), heart monitors, and electric wheelchairs also use PCBs extensively.
• Telecommunications: Network hardware such as routers, switches, and servers contain multiple complex multilayer PCBs.
• LED Lighting Systems: Metal Core PCBs (MCPCBs) are commonly used in LED lighting systems due to their excellent heat dissipation capabilities.
• Wearable Technology: Flexible Copper Clad Laminates (FCCL) find application here due to the need for flexibility, e.g., in smartwatches, fitness bands, etc.

The type of CCL used depends on the requirements of the specific application – some may require higher heat resistance or mechanical strength than others.

Difference Between Laminate and Prepreg

Both Copper Clad Laminate (CCL) and Prepreg are essential materials for manufacturing multilayer Printed Circuit Boards (PCBs), but they serve different purposes. Here are their main differences:

/	Copper Clad Laminate (CCL)	Prepreg
Definition	A base material used in PCBs to provide mechanical support and electrical insulation. It consists of an insulating layer (e.g., FR-4 or polyimide) clad with copper on one or both sides.	Abbreviation for “pre-impregnated,” referring to glass fiber fabric that has been pre-impregnated with a resin system (usually epoxy-based). It is partially cured (“B-stage”), is tacky at room temperature, but is capable of fully curing under heat during the lamination process.
Role in PCB Manufacturing	Forms the external layers where most components are mounted, and the conductive pathways or circuits are etched on its surface.	Acts as an adhesive layer between two pieces of CCL in multilayer boards; when heated during lamination, it flows, and upon cooling, it hardens, forming a mechanically strong, electrically insulating bond. It also provides electrical insulation between different layers inside the PCB.
State Before Use	Fully cured state, meaning they are rigid and non-tacky at room temperature.	B-stage state, meaning they are in a semi-cured state, are flexible and tacky at room temperature.
Thermal Properties	Depending on the specific type, but generally need to withstand soldering temperatures without significant performance degradation.	Needs to be able to flow smoothly under heat and pressure, then solidify upon cooling to form a strong bond.
Electrical Properties	Provides good electrical insulation properties while also providing a conductive surface for circuit formation.	Primarily acts as an insulator, preventing short circuits between layers.
Mechanical Strength/Stiffness	Requires high mechanical strength as it forms the structure of the board. Stiffer than prepreg due to its fully cured nature.	Has lower stiffness than CCL due to its semi-cured nature, but becomes part of the rigid assembly after the final curing step.

Copper Clad Laminate Manufacturing Process

The manufacturing process of Copper Clad Laminate (CCL) typically involves the following steps:

1. Preparation of Insulating Material: The insulating material, typically a glass fiber fabric like FR-4, is prepared according to the required dimensions.
2. Impregnation: The insulating material is impregnated with resin. This step involves soaking the glass fabric in a specific resin solution (e.g., epoxy). After soaking, excess resin is removed, leaving a uniformly impregnated sheet.
3. Drying and Curing: After impregnation, the material undergoes drying and partial curing (“B-stage”). This makes it stiff but still capable of bonding under heat and pressure.
4. Lamination with Copper Foil: Under conditions of high temperature and pressure, a layer of copper foil is laminated to one or both sides of this substrate. The heat causes further curing of the resin, making it solidify while bonding firmly with the copper to form a single, unified structure.
5. Cooling and Finishing: The laminated assembly is cooled, and any excess is trimmed off. Quality checks are performed, such as visual inspection for defects or measurement of thickness.
6. Cutting: Finally, the large panels can be cut into smaller sizes according to market demand.

Conclusion

Copper Clad Laminate (CCL) and Prepreg are two crucial materials for manufacturing Printed Circuit Boards (PCBs).

Copper Clad Laminate (CCL), composed of an insulating layer clad with copper on one or both sides, forms the skeleton of the PCB. It provides mechanical support and electrical insulation while offering a conductive surface for circuit formation. Its manufacturing process involves: preparing the insulating material, impregnating it with resin, partial curing (“B-stage”), laminating with copper foil under high temperature and pressure, and cooling and finishing.

Prepreg is a glass fiber fabric pre-impregnated with a resin system. Before use, it is in a semi-cured state, flexible and tacky at room temperature, but capable of fully curing under heat during the PCB assembly lamination process. Its role is to act as an adhesive layer between CCLs in multilayer boards, while providing additional electrical insulation.

Both Copper Clad Laminate (CCL) and Prepreg possess unique properties that make them indispensable materials at different stages of PCB production – from providing structural integrity to ensuring electrical functionality. Understanding their characteristics is essential when designing complex electronic systems.