Composition of Copper Clad Laminate

• Prepreg

A prepreg refers to fiberglass that has been infused with resin. Before using, the resin must be dried, but not completely hardened, in order to facilitate flow and complete immersion upon heating. Generally, prepregs are reinforced with fiberglass and fortified by a subsequent adhesive, similar to the FR4 material discussed earlier in this article.

Distinct manufacturers may stipulate varying requirements concerning thickness and particular kinds of prepreg. Additionally, there exist versions known as “SR” (Standard Resin), “HR” (High Resin), and “MR” (Medium Resin), which are distinguished by their resin content. The optimal material choice is determined by the wanted final layer of structure, thickness, and impedance.

• Copper Foil

Copper foil serves as an electrolytic cathode and is applied as a uniform layer on the base of a printed circuit board. It readily adheres to an insulating layer, allowing the formation of a protective printed layer to safeguard the board against corrosion.

The Basic Requirements for Copper Clad Laminates

Before finalizing your choice of a copper clad laminate, it is essential to ensure that it fulfills several fundamental prerequisites, including factors related to its appearance, chemical composition, and physical characteristics. Below are the basic requirements for qualified copper clad laminates:

1. Dimensional Accuracy

The copper clad laminate, serving as the foundation material for a PCB, must adhere to precise size requirements according to the desired end design. Various parameters, such as width, length, diagonal deviation, and warpage, are carefully considered. And meeting these size requirements precisely can ensure the successful application of CCL.

2. Appearance

During the manufacturing process of copper foil, various unforeseen elements can cause a multitude of issues. These problems may include scuffs, dents, resin points,  bubbles, wrinkles, and other defects. The presence of any such issues significantly diminishes the performance of the copper-clad laminate and adversely affects the quality of the printed board it is used for.

3. Electric Performance

The electrical performance must be meticulously designed as it is a crucial aspect. There are several stringent requirements to consider, such as the dielectric loss tangent, dielectric constant (DK), surface resistivity, insulation resistance, volume resistance, electric strength, and so on.

4. Environmental Performance

It is imperative to verify that the copper clad laminate meets essential criteria, such as water absorption and anti-corrosion properties. Failure to do so could result in significant performance issues during the production process.

5. Chemical Performance

Ensuring the chemical performance of a copper-clad laminate is of utmost importance, as it must satisfy stringent criteria related to flammability, Tg (glass transition temperature), resistance to chemical agents, Z-axis coefficient of thermal expansion (Z-CTE), and dimensional stability. Meeting these requirements is essential for its reliable and optimal functioning.

6. Physical Performance

Various requirements pertain to the physical performance of the copper clad laminate, encompassing factors such as Peel Strength, size stability, resistance to bending, thermal resistance, and punching quality.