RCCL Classification

Rigid Copper Clad Laminate (CCL) is a type of printed circuit board base material that consists of resin, reinforcement materials, and copper foil pressed together. It is the most mature and diverse category of PCB base materials. Its classification can be listed as follows:

Classification Based on Different Reinforcement Materials in the Substrate

Paper-Based Boards: These use impregnated fiber paper as the reinforcement material and are laminated with copper foil to create paper-based boards. Mainly single-sided copper-clad boards like FR-1, FR-2, FR-3 are prevalent. They exhibit good electrical properties at a lower cost but tend to absorb moisture. They are suitable for general consumer electronic products like radios, and electronic toys, but not for high-speed circuits or high-reliability electronic products.
Glass Cloth-Based Boards(glass fiber board): Comprised of glass fiber cloth impregnated with resin as the reinforcement material. Typically using epoxy resin or other high-performance resins (such as G10, FR-4/FR-5). These boards offer good electrical performance and higher operating temperatures, making them suitable for high-reliability electronic products and high-speed circuit boards.
Composite Boards: Utilize two or more types of reinforcement materials, combining different materials in the surface and core layers. For instance, CEM-I type with a core of epoxy-fiber paper and a surface of epoxy-glass cloth or CEM-3 type with a core of epoxy-glass fiber paper and a surface of epoxy-glass cloth. Composite boards improve upon paper-based boards at a lower cost than glass cloth-based boards, commonly used in civil and general electronic products.
Special Material Boards: Incorporate special functional metals, ceramics, or heat-resistant thermoplastic substrates. These materials are often high thermal conductivity materials used in high-power devices, power modules, automotive electronic products, or IC packaging with high-density assembly. These boards demand increased heat dissipation, making thermal conductivity a critical performance parameter. Materials for these boards include metal-based and ceramic-based substrates.

Classification Based on the Main Resin in the Substrate

The main resin used in the substrate significantly influences its characteristics and reflects certain primary traits. Hence, classifying the Copper Clad Laminate (CCL) based on the main resin in the substrate is another method. The primary resin types employed in the substrate include phenolic resin, epoxy resin (EP), polyimide resin (PI), polyether resin (PPO or polytetrafluoroethylene resin PTFE), bismaleimide triazine resin (BT), cyanate ester resin (CE), among others. When these resins or modified resins are combined with the aforementioned reinforcement materials, the resulting laminated board is generally termed a specific resin-type Copper Clad Laminate. Among these, modified epoxy resin, PI, PPO, PTFE, BT, and CE combined with glass cloth produce copper-clad boards with one or multiple properties surpassing the average substrate level. These substrates are collectively known as high-performance substrates, suitable for various circuit performances and high-speed, high-frequency circuitry in PCB applications.

Classification Based on Outstanding Performance Differences of Copper Clad Boards

Classifying copper-clad boards based on outstanding performance differences aids in selecting substrates with highlighted characteristics, evident from the substrate’s name. The details are as follows:
Flame Retardancy of the Substrate: boards meeting the UL standard’s (Underwriters Laboratories) requirements for the vertical burning test in organic resin materials, achieving a V-level rating as specified in the UL standard, are termed flame-retardant type boards (also known as V0 boards), exhibiting excellent resistance to combustion. Successive levels include V1, V2, and so on. Flame-retardant boards feature superior fire resistance and safety. Boards meeting the UL standard’s HB-level requirements in the burning test are termed non-flame-retardant type boards.

Dielectric Constants: high-speed and high-frequency PCBs are in large need where high or low dielectric constants are becoming important in manufacturing. The dielectric constant of the substrate significantly impacts the characteristic impedance of the printed board. Therefore, classifying materials based on the high or low dielectric constant helps in selecting substrates suitable for high-speed and high-frequency circuits. Generally, materials with a dielectric constant stable at around 3 at GHz-level frequencies and a dielectric loss tangent less than or equal to 10^-3 are termed low dielectric constant materials. They are primarily used for fabricating high-speed and high-frequency circuit boards. In high-frequency and microwave circuit boards, some use low dielectric constant substrates, while others employ materials with higher dielectric constants, with the critical consideration being impedance matching and reducing dielectric loss.

Materials with a dielectric constant above 10, even reaching several tens or hundreds, are known as high dielectric constant substrates and are mainly used in multi-layer printed boards for embedding passive components. Employing these substrates in the ground and power layers of multi-layer printed boards can shorten the connection distance between integrated circuits and capacitors, reducing circuit parasitic inductance, beneficial for decoupling in high-speed and high-frequency circuits, and can lower the resonance noise generated on the ground and power layers.

Outstanding properties: apart from dielectric constant-based classification, substrates can also be categorized based on other outstanding properties, such as heat resistance (reflected in parameters like Tg, Ta, and t260 or t288), coefficient of thermal expansion (CTE), resistance to tracking (CTI), resistance to ion migration (CAF), and environmentally friendly non-halogen properties. Substrates with similar heat-resistant properties can be further divided into multiple grades based on different glass transition temperatures. This classification method assists in finding substrates that meet specific performance requirements during material selection and design processes.

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