If you open up any electronic device and see that green (or other colored) circuit board, its most fundamental material is copper clad laminate. But do you really understand this seemingly simple material? It's like the foundation of a house—it determines the entire structure's stability and lifespan.

What Exactly is Copper Clad Laminate?

Simply put, copper clad laminate is an insulating substrate material covered with copper foil on one or both sides, bonded together firmly through a hot-pressing process. You can think of it as a "sandwich":

• Top layer: Copper foil (conductive layer)

• Middle layer: Insulating substrate (support layer)

• Bottom layer: Copper foil (conductive layer)

This "sandwich" is the starting point for all printed circuit boards. When we etch away unwanted copper from this base, leaving behind the designed circuit pattern, we get the familiar PCB.

The Three Components of Copper Clad Laminate

1. Copper Foil: The Circuit's "Highway"

Copper foil isn't ordinary copper sheet—it's an extremely thin copper layer produced through electrolysis or rolling processes, typically ranging from 0.5 oz to 2 oz (approximately 18 to 70 microns). To put that in perspective, a human hair is about 70 microns in diameter, so the thinnest copper foil is finer than a hair strand.

The surface treatment of copper foil is also crucial. Proper roughness improves bonding with the substrate, but excessive roughness affects high-frequency signal transmission—it's like setting appropriate friction on a highway: not too slippery, not too rough.

2. Substrate: The Real "Unsung Hero"

The substrate determines most of the circuit board's performance:

The Most Common: FR-4 Material
This is a composite made from glass fiber cloth impregnated with epoxy resin. Its popularity stems from its good balance of mechanical strength, electrical properties, cost, and processability. However, "FR-4" is actually a broad category, with significant variations in formulations between manufacturers.

Specialty Substrates:

• High-frequency materials: For 5G, radar, and other high-frequency applications, typically with more stable dielectric constants

• High thermal conductivity materials: For high-heat applications like LED lighting and power modules

• Flexible substrates: Polyimide film for bendable flexible circuits

• Metal-core substrates: Aluminum-based boards with excellent heat dissipation

3. Adhesive: The Invisible "Super Glue"

Special adhesives are needed between the copper foil and substrate. These must remain stable under high temperatures and humidity while offering good insulation and chemical resistance.

Types of Copper Clad Laminates and Their Applications

Rigid CCL

The most common type, like a rigid sheet. Classified by reinforcing material:

• Paper-based: Lowest cost, used in consumer electronics

• Glass cloth-based: Better performance, for most industrial products

• Composite-based: Mix of paper and glass cloth, balancing cost and performance

Flexible CCL

Uses polyimide film as substrate, capable of bending thousands of times without damage. Your laptop screen connectors and foldable phone internal connections use this material.

Special CCL

• Metal-core: Directly bonded to aluminum or copper plates, excellent for heat dissipation

• High-frequency: Very stable dielectric constant and loss factor, suitable for high-speed signals

• High Tg: Remains stable at higher temperatures, suitable for lead-free soldering processes

Key Parameters Affecting CCL Performance

Glass Transition Temperature (Tg)

Think of it as the temperature where material changes from "glassy" to "rubbery." Standard FR-4 has a Tg around 130°C, mid-range about 150°C, and high Tg above 170°C. Higher Tg means better heat resistance and less deformation during soldering.

Dielectric Constant (Dk) and Loss Factor (Df)

These are crucial for high-frequency circuits:

• Dk affects signal propagation speed

• Df determines energy loss during signal transmission

• Standard FR-4 performance degrades at high frequencies

Coefficient of Thermal Expansion

How much material expands when heated. Ideally, CCL's thermal expansion should match copper foil's; otherwise, temperature changes can cause separation between layers.

Peel Strength

Measures how firmly copper foil bonds to the substrate. Too weak causes peeling; too strong makes intentional removal difficult.

Manufacturing Process Overview

Making copper clad laminate is a precise process:

1. Resin preparation: Mixing resin, hardeners, fillers per formula

2. Impregnation: Passing glass cloth through resin bath for thorough saturation

3. Drying: Removing solvents to produce "prepreg"

4. Lamination: Stacking copper foil and prepreg, curing under heat and pressure

5. Post-processing: Cutting, testing, packaging

This sounds straightforward, but each step requires tight control. A few degrees temperature variation or slight pressure changes can affect final product performance.

How to Choose the Right Copper Clad Laminate?

When selecting CCL for your project, consider this decision process:

Step 1: Define Application Requirements

• What frequencies will your product operate at?

• What's the operating temperature range?

• What mechanical stress must it withstand?

• What's the cost budget?

Step 2: Identify Key Performance Needs

• Consumer electronics: Usually standard FR-4, focus on cost

• Automotive electronics: Require high Tg, high reliability materials

• Communication equipment: May need high-frequency materials

• Power products: Focus on thermal conductivity and voltage withstand

Step 3: Consider Manufacturing Process

• What materials is your PCB manufacturer familiar with?

• Is the material suitable for your design (multilayer, HDI, etc.)?

• Is material supply stable?

Step 4: Balance and Compromise

Few materials excel in all aspects. You'll typically trade off between performance, cost, and availability. For example, high-frequency materials perform better but cost more, while standard FR-4 costs less but has limited high-frequency performance.

A Real-World Example

Imagine designing a home router:

• It handles Wi-Fi signals (2.4GHz and 5GHz) → needs good high-frequency performance

• Generates heat during prolonged operation → requires decent heat resistance

• Cost-sensitive → can't use expensive materials

In this case, you might choose mid-Tg FR-4 material, possibly using better-performing material only in critical high-frequency areas while using standard material elsewhere—this "hybrid use" strategy is common in engineering.

Future Trends

Material Innovations

• Lower loss materials for 5G and future communications

• More environmentally friendly halogen-free materials

• Higher thermal conductivity materials for increasing power demands

Process Advances

• Thinner copper foils (below 12 microns) for finer lines

• Better dimensional stability for higher density designs

• Improved heat resistance for lead-free soldering requirements

Sustainability

More manufacturers focus on material recyclability and environmental friendliness, changing material formulations and manufacturing processes.

Final Thoughts

Copper clad laminate might not be as attention-grabbing as chips, but it's the foundation of the entire electronics industry. Just as you wouldn't build a skyscraper on sand, without proper CCL, even the most sophisticated circuit design can't be realized.

Understanding CCL basics not only helps you choose the right material but also helps avoid potential issues during the design phase. After all, a good start is half the battle, and good CCL is exactly that "good start."

About us: Kaboer is a PCBA company with its own manufacturing factory located in Shenzhen, China. We handle PCB designs using various copper clad laminates daily. If you have questions about material selection for a specific project, we're happy to share our practical experience.