Introduction
Copper clad laminate (CCL) is the fundamental building block material used in the fabrication of printed circuit boards (PCBs). CCL consists of a central insulating core laminated between layers of copper foil. The properties and quality of CCL have a major impact on the performance and reliability of completed PCBs. This article provides an in-depth overview of CCL technology, manufacturing processes, materials, properties, and applications.
CCL Basics
CCL provides the starting point for rigid PCB fabrication. The basic construction consists of:
- Central insulating core layer
- Copper foil laminated to one or both sides
- The core is pre-impregnated (prepreg) with adhesive resin
The core gives mechanical support while the copper foil allows formation of conductive pathways by etching. The adhesive resin bonds the foil to the core.
Typical CCL Composition
Standard grades of CCL suitable for most PCB applications consist of:
- Core: Woven fiberglass pre-impregnated with epoxy resin (FR-4 Grade)
- Copper foil: 18um to 70um electrodeposited copper foil
The fiberglass reinforcement provides dimensional stability while the epoxy resin gives mechanical and dielectric integrity. Copper foil thickness is specified based on current density requirements.
CCL Fabrication Process
CCL undergoes an intricate fabrication process including:
- Core preparation – Cutting, inspection, cleaning
- Impregnation – Core material is dipped in resin solution
- B-stage curing – Partial drying and semisolidifying the resin
- Lamination – Foil application under heat and pressure
- Autoclave curing – Fully cures resin to bond foil
- Finishing – Cutting, machining, edge preparation
Precision controls during each phase ensure reliable, consistent CCL quality.
Applications of CCL
As the foundation of PCBs, CCL is utilized across all segments of the electronics industry:
- Consumer Electronics – Phones, tablets, IoT devices
- Computers – Server boards, workstations, laptops
- Automotive – Engine controls, infotainment, radars
- Aerospace and Defense – Avionics, weapons, navigation
- Medical – Imaging systems, diagnostics, therapeutic devices
- Industrial – Programmable controllers, test equipment
- Telecommunications infrastructure
The properties and cost of CCL directly impact the capabilities and economics of these end products.
CCL Material Grades
CCL is formulated in many specialized grades to meet application requirements:
- FR-4 – Flame retardant, standard grade for most commercial uses
- High Tg – For higher temperature or thermal shock environments
- Low Loss – For high frequency applications
- High Speed – Optimized dielectric properties for fast digital signals
- Halogen Free – For environmentally compliant PCBs
- Aluminum Clad – Using aluminum instead of copper foil
There are over 100 defined CCL grades addressing specific thermal, electrical, and mechanical needs.
Key CCL Properties
CCL is engineered to deliver specialized properties based on chemistry and composition:
- Dielectric Constant (Dk) – Impacts signal propagation delay and impedance
- Dissipation Factor (Df) – Determines dielectric losses for high frequency boards
- Dielectric Strength – Maximum voltage isolation capability
- Thermal Conductivity – Heat transfer capability
- Coefficient of Thermal Expansion (CTE) – Impacts thermal stress and reliability
- Glass Transition Temperature (Tg) – Determines maximum operating temperature
- Moisture Absorption – Critical for preventing electrical leakage
Properties are tuned through resin chemistry, core materials, and processing methods.
CCL Thickness
A standard thickness range for common CCL grades is:
- Core only: 0.002” to 0.062”
- Copper clad: 0.004” to 0.064″
Thickness uniformity is critical across a CCL lot. Thinner cores provide greater layer stacking density in multilayer PCBs.
Copper Foil Types
Several copper foil varieties can be laminated in CCL:
- Standard ED Foil – For general applications
- RA Foil – Rolled annealed, more ductile
- VLP Foil – Very low profile with smooth surface
- EF Foil – Electrodeposited fine grained foil
- OF Foil – Oxygen-free foil for high frequency boards
Foil grain structure, roughness, and thickness impact costs and PCB fabrication processes.
CCL Supply Chain
CCL manufacturers produce raw copper clad sheets that get transformed into finished PCBs at board shops:
- CCL Manufacturers – Fabricate base material in high volume
- PCB Fabricators – Process CCL into finished circuit boards
- Laminate Distributors – Provide inventory and delivery to PCB fabricators
- OEMs – Source finished boards from fabricators
Reliable CCL properties and availability support PCB mass production for electronics supply chains.
CCL Considerations for PCB Designers
Key CCL parameters PCB designers should consider when specifying materials:
- Dielectric Constant – Impacts signal propagation speed
- Loss Tangent – Causes signal loss and degradation
- Thermal Conductivity – Determines ability to dissipate heat
- CTE – Impacts reliability and thermal stress tolerance
- Moisture Absorption – Can reduce surface insulation resistance
- Dk and Df Stability – Ensures stable electrical performance
Consulting your PCB fabricator during material selection ensures manufacturability and performance.
Conclusion
CCL forms the backbone of the PCB industry, providing the insulating structure onto which copper traces are etched. Engineering CCL for optimal electrical, thermal, and mechanical properties enables PCBs to serve reliably in diverse operating environments ranging from handheld devices to cutting-edge aerospace applications. Thanks to continual CCL innovations, PCB technology continues rapidly advancing to power today’s electronics innovations.
Frequently Asked Questions
Q: What is the difference between CEM-1, FR-4, and other CCL designations?
These denominations specify the resin system, glass fabric material, and flame retardance properties of the CCL. FR-4 uses brominated epoxy resin while CEM-1 uses a non-halogenated resin system. Different grades offer tradeoffs between cost, performance, and manufacturability.
Q: What are some key considerations when selecting copper foil type?
Key factors include foil thickness, ductility, profile roughness, grain structure, and compatibility with imaging processes. Thinner foils enable finer lines and spaces while roughness affects bond strength. Discussing requirements with your PCB fabricator ensures the optimal foil is chosen.
Q: What is the difference between woven and non-woven CCL?
Woven CCL uses fiberglass cloth with warp and weft threads held together by resin. Non-woven uses randomly arranged fiberglass strands evenly dispersed in the resin. Each construction offers different thermal and mechanical stability properties.
Q: How tight are the thickness tolerances held in CCL manufacturing?
Standard CCL thickness tolerance is ±10% of the specified value. However, tighter tolerances of ±3% or ±5% are possible for high density designs where thickness uniformity is critical across layers.
Q: What is the difference between double-sided and multilayer CCL?
Double-sided CCL has copper foil on both sides of an insulating core for use in 2 layer PCBs. Multilayer CCL interleaves additional cores with adhesive to bond multiple layers for designing multilayer boards.
