There are two kinds of substrates used in PCB: organic substrate and inorganic substrate. Among them, the organic substrate is made of several types of materials, these materials refer to reinforced materials, such as glass fiber cloth, fiber paper, glass felt, etc. These reinforcements are impregnated with a resin binder and dried and then covered with copper foil. Under high temperature and high pressure. This type of substrate, known as copper clad laminate (CCL), is the main material used to make PCBs. Copper clad laminate (CCL) uses glass fiber or wood pulp paper as reinforcement material. CCL is a kind of product which is made by soaking in resin and then covering one or both sides of the reinforcement material with copper clad laminate.
What is a good Copper Clad Laminate ( CCL )?
CCL can perform well only when it meets the following performance requirements:
- Appearance. Due to unexpected factors in the manufacturing process (such as dents, scratches, resin spots, wrinkles, pinholes, bubbles, etc.), copper foil may have problems. All these problems will definitely lead to the performance degradation of CCL and PCB. Therefore, the appearance of good CCL should be smooth.
- Size. As CCL is the basic material of PCB, they must meet the size requirements corresponding to PCB. The parameters of CCL size include length, width, diagonal deviation and warpage, and each parameter must meet specific requirements.
- Electrical performance. This is a basic task of PCB, so it is necessary to carefully design any aspects that affect its electrical properties, including dielectric constant (DK), dielectric loss tangent (DF), volume resistance, surface resistance, insulation resistance, arc resistance, dielectric breakdown voltage, electrical strength, comparative tracking index (CTI), etc
- Physical performance. The physical properties of CCL include dimensional stability, peel strength (PS), bending strength, heat resistance (including thermal stress, TD, T260, t288, T300), stamping quality, etc.
- Chemical properties. The chemical properties of CCL must meet the requirements of flammability, chemical reagent resistance, TG, z-cte and dimensional stability.
- Environmental performance. It must meet the requirements of water absorption.
The quality of CCL should be judged by PCB Fab houses. Taking pcbart as an example, it uses ipc-4101c as the manufacturing standard and IPC-TM-650 for CCL test. Therefore, these measures make CCL a qualified PCB substrate.
Copper clad laminate (CCL) materials
Copper foil: copper foil is a cathode electrolytic material deposited on a thin and continuous metal foil layer on a PCB substrate. Moreover, it is easy to bond it to the insulating layer, thus forming a printed protective layer and forming a circuit board pattern with corrosive effect.
Prepreg: prepreg (from prepreg) is a glass fiber impregnated resin. The resin is pre dried but not hardened, so it flows, adheres and completely immerses when heated. Therefore, the prepreg is reinforced by glass fibers through an adhesive layer (similar to FR4 material). And the well-known types of glass fibers.
Different manufacturers have different thicknesses on the type of prepreg. In addition, according to the resin content, there are two versions of “SR” standard resin, “Mr”, “medium resin” and “HR” high resin. The required final thickness, layer structure or impedance, so the above thickness is only an example.