What is Copper Foil (Base Copper Weight)
Copper foil (base copper weight) is the initial thickness or weight of the copper layer applied to the outer and inner layers of a multilayer PCB. It is measured in ounces and serves as an indicator of the overall copper thickness on the layer. The copper foil is typically supplied in the form of rolls and is combined with prepreg to create a rigid or flexible copper clad laminate through heat and pressure. This copper foil is then etched to form conductors for heat and electricity on the conductive layers of the PCB.
Different copper weights are available, including 5oz copper (18μm or 0.7mil thick), 1oz copper (35μm or 1.4mil thick), 2oz copper (70μm or 2.8mil thick), and other options ranging up to 3oz, 4oz, and 5oz. The selection of the appropriate copper weight depends on the specific design requirements and the desired current-carrying capacity of the PCB.
Two common types of copper foils used in PCB manufacturing are Electro Deposited (ED) Copper and Rolled Annealed (RA) Copper. ED copper has a vertical grain structure and a relatively rough surface, which may impact signal integrity and flexibility. In contrast, RA copper has a smoother surface and is well-suited for dynamic, flexible circuitry applications. It offers advantages for high-frequency signals due to its smoother copper surface.
The copper foils used in PCB manufacturing are typically electronic grade, with a purity of 99.7%. The thickness of these copper foils can range from 1/3oz/ft2 (12μm or 0.47mil) to 2oz/ft2 (70μm or 2.8mil). These foils exhibit a lower surface oxygen rate and can be pre-attached to various base materials such as metal core, polyimide, FR-4, PTFE, and ceramic to produce copper clad laminates. They can also be introduced as copper foil layers in multilayer boards before the pressing process.