Copper Clad Board
Copper clad board is simply referred to a substrate covered by a thin copper layer which is used to make a conductive path in the printed circuit board. Copper clad board is also known as laminate. A typical substrate is a multilayer laminated epoxy sheet which is reinforced by a glass film to provide necessary physical strength to survive the manufacturing process and last longer.
The copper layer thickness is designed according to the circuit requirements. The commercially available copper layer thickness is from 0.009 mm to 0.38 mm, and the inner layer is from 0.01 mm to 0.20 mm. However, the copper thickness is not limited to the commercial standards. The clad board have different variants, such as single-sided, double-sided, or multiple layers. The multilayer PCB laminate has more than one copper layer usually stacked above each other with a dielectric substrate to insulate them.
The cross sectional image illustrates the idea of forming a multilayer copper clad board by bonding different layers together. Top and inner copper layers are bonded and insulated by pre-preg solution. This is a composite fiber with a thermoset polymer like epoxy. The substrate is mainly made of FR4. For special applications, few other materials like BT, polyimide and PTFE are preferred. Aluminum is also used as a substrate to dissipate heat which usually are used as heat sinks in LED lighting applications.
FR4 has many variants other than standard production. High temperature or epoxy microfiber FR4 are few modified versions. Clad board are shipped with a protective coating to prevent the copper layer from oxidizing which has to be removed before processing it.