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PCB/PCBA knowledge
What Is PCB Copper Coating – A Complete Guide

PCB, which stands for Printed Circuit Board, plays a crucial role in the world of electronics. Copper coating, also known as copper plating, is an essential process in PCB manufacturing. It involves depositing a thin layer of copper onto the surface of the board to facilitate electrical conductivity and ensure reliable connections. This guide will take you on a journey to explore PCB copper coating. So, let’s dive in and unravel the wonders of PCB copper coating together!

Table of Contents

What is PCB copper coating?

PCB Copper Coating
PCB Copper Coating

PCB copper coating: An area of a PCB layer that is filled with copper. This layer can be the top, bottom, or anywhere inside the PCB stackup, and the PCB copper can be used as a ground, reference, or isolate a specific component or circuit from the rest of the elements on that layer.

Why your PCBs need copper plating

Copper coating and ground copper coating

Copper coating: An area of a PCB layer that is filled with copper. Copper coatings with vias can be used to help dissipate heat.

Ground: An inner layer of a circuit board stackup, completely filled with copper, used as a signal or power ground or reference.

Ground copper coating: A copper coating that is used for grounding and does not occupy the entire layer.

Role of PCB copper coating

1. Grounding on double-layer PCB

Both layers are used for signals, there is no ground plane. For these boards, the ground copper coating can be very helpful in efficient routing by providing a central ground.

2. EMI shielding

For a good multilayer design, you want to have a ground plane between the two signal layers to minimize noise. If there are internal signal layers next to surface signal layers, grounded copper coating can help reduce noise by adding shielding.

3. Heat dissipation

Grounded copper coatings can also be used to draw heat away from high-power components, and thermal vias can then be used to remove excess heat from the circuit board.

4. Copper balance

PCB ground copper coating can also be accomplished by contract manufacturers (CMs) during PCB assembly by balancing the amount of copper on both sides of the board, reducing the possibility of warping during reflow. In this case, a crossed copper grid may be a better alternative to a solid copper ground coating.

5. Large circuit path

Adding surface ground copper coating provides a shorter return path for high-current devices, such as switching converters, instead of connecting longer traces to the ground plane.

6. Convenient for PCB manufacturing

Provides uniform copper distribution on a layer, allowing for better etching and plating processes and reducing the amount of etchant used during PCB manufacturing (reducing costs).

7. RF and microwave design

Grounded copper coatings contain localized areas of electromagnetic (EM) radiation, thereby reducing spurious coupling, radiation, and dispersion.

8. Digital design

The ground plane improves noise immunity, promotes better ground uniformity, and promotes a low-inductance current path.

PCB copper coating method

When should you use PCB copper coating? PCB Copper coating is usually used for low resistance, low inductance, and heat dissipation.

PCB Copper Coating Method
PCB Copper Coating Method

There are generally two basic methods of PCB copper coating: Large-area copper coating, and pure copper-clad grid.

1. Large area copper coating

It has the dual functions of increasing current and shielding, but if wave soldering is used, it may cause the board to warp or even bubble. At this time, several grooves are usually opened to reduce bubbles in the copper foil.

2. Pure copper-clad grid

It mainly plays a shielding role, the effect of increasing current is weakened, and the heat dissipation is better.

Key points of PCB copper coating

1. Copper coating is sometimes mistakenly used just to fill unused space on a circuit board.
2. CAM engineers can add copper stealing patterns to balance the copper distribution on the layer.
3. Floating (unconnected copper) is a real hazard to signal integrity and all copper coatings must be connected to ground.
4. Ground copper coating without ground vias may become a conduit for crosstalk between traces on both sides of the ground shape.
5. By creating the copper layer as part of the ground grid and configuring it as a solid plane, you can provide a well-defined return current path.
6. Any additional planes must be correctly positioned and spaced so that they do not negatively impact the signal integrity of the board.
7. The ground on the microstrip layer changes the transmission line from a microstrip line to a grounded coplanar waveguide.
8. Copper coating can reduce the characteristic impedance and differential impedance of the transmission line.
9. CPW combines electromagnetic fields in a more localized manner than microstrip lines, thereby reducing spurious coupling, radiation, and dispersion.
10. Microstrip lines can radiate. However, since the fields are restricted between ground planes, the same is not true for straplines.
11. When copper is placed close to critical signal traces, the impedance will be reduced by 2–3 ohms.
12. Copper coating at these points may convert differential mode signals into common mode signals, thus affecting signal integrity.

FAQ

PCB copper coating is an area of a PCB layer that is filled with copper. This layer can be the top, bottom, or anywhere inside the PCB stackup, and the PCB copper can be used as a ground, reference, or isolate a specific component or circuit from the rest of the elements on that layer.

1. Grounding on double-layer PCB

2. EMI shielding

3. Heat dissipation

4. Copper balance

5. Large circuit path

6. Convenient for PCB manufacturing

7. RF and microwave design

8. Digital design

1. Large area copper coating

2. Pure copper-clad grid

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