What is Copper Weight in a PCB?

Copper is a highly conductive material widely used in producing Printed Circuit Boards (PCBs). The extensive use of copper in PCB manufacture is due to its impressive thermal and electrical properties and high corrosion resistance.

However, the effectiveness of a PCB largely depends on the amount of copper present in it, which is referred to as the “Copper Weight." To understand the significance of copper weight in PCBs, it is essential to comprehend how copper is etched onto PCBs. In this article, we will delve into the concept of Copper Weight and its impact on the performance of PCBs.

Copper Fabrication onto a PCB

In a PCB, copper is used as the conductive material for the circuit traces that connect different components of the circuit. Let’s take a look at how the whole procedure takes shape:

1. The circuit traces present in a PCB are etched into a thin layer of copper foil.
2. This copper foil is then laminated on top of a substrate, usually made of fiberglass, plastic, or PTFE.
3. First, the copper layer is coated with a layer of photoresist, which is then exposed to ultraviolet light through a mask that defines the desired circuit pattern.
4. The exposed areas of the photoresist become chemically altered, allowing for selective removal of the unexposed parts using an etching solution.
5. The remaining copper traces form the conductive pathways of the circuit.

Other uses of Copper in PCBs

Copper is used as a component of through-hole plating and surface mount pads on PCBs. Through-hole plating is the process of adding a layer of copper plating to the walls of drilled holes on a PCB, which enables electrical connection between layers of the board. Surface mount pads are small areas of copper on the surface of the PCB that is used for mounting electronic components.

What is Copper Weight?

As discussed earlier, Copper is one of the most crucial components in Printed Circuit Boards. Copper Weight/Thickness is the thickness of the Copper layer on a PCB. It indicates the amount of copper present in a PCB and is measured in Ounces per square foot (oz/ft2). In simpler terms, it represents the thickness of 1 ounce of copper spread over an area of 1 square foot.

Taking an example, if we have a PCB with a Copper weight of 1 ounce, its thickness over a 1 square foot PCB board will be 1.4 mils.

Following is a chart, representing copper weight in oz against copper thickness (mils is one-thousandth of an inch):

Conclusion 

Copper weight is an important consideration in PCB manufacturing and design since it is responsible for overall durability and cost. Additionally, a PCB board’s thermal and electrical conductivity depends on its Cu thickness, hence variations in technical designs bare an effect on them as well. Generally, the thicker the copper layer, the higher the current carrying capacity and thermal conductivity of the PCB. However, increasing the copper weight also increases the manufacturing cost and can lead to other design issues such as impedance control, signal integrity, and board warping.

Copper is one of the most important elements in printed circuit boards (PCBs). Copper Weight or Copper Thickness in a Printed Circuit Board represents the thickness of 1 ounce of copper rolled out over an area of 1 square foot. For example, a PCB that has a copper weight of 1 oz will have a layer of copper that is 1.4 mils in thickness. Copper Weight is measured in ounces per square foot (oz/ft²).

Copper Weight  in oz vs Copper Thickness in Mils

Why is Copper Weight Important for Printed Circuit Boards?

The current carrying capacity of a PCB depends on the thickness of the copper trace. So PCB's with a higher Copper weight will be able to carry more current.