What is PCB Copper Pour? What Are the Functions of PCB Copper Pour

1. What is PCB Copper Pour?

2. Copper Pour and Ground Copper Pour

• Copper Pour: A copper-filled area in a PCB layer; copper pour with through vias can be used to assist heat dissipation.
• Ground Plane: An internal layer in the circuit board stack-up, fully filled with copper, used as the ground or reference for signals or power supplies.
• Ground Copper Pour: Copper pour used for grounding that does not occupy the entire layer.

3. Functions of PCB Copper Pour

1. Grounding on Double-Sided PCBs: Both layers of the board are used for signal routing without a dedicated ground plane. For these circuit boards, ground copper pour can significantly facilitate efficient routing by providing a central ground connection.
2. EMI Shielding: For a well-designed multilayer board, a ground plane between two signal layers is required to minimize noise. If there is an internal signal layer adjacent to the surface signal layer, ground copper pour can help reduce noise by adding shielding.
3. Heat Dissipation: Ground copper pour 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 pour can also balance the copper volume on both sides of the circuit board during PCB assembly for the Contract Manufacturer (CM), reducing the possibility of warpage during reflow soldering. In this case, a cross copper grid may be a better alternative to solid copper ground pour.
5. Large Current Path: Adding surface ground copper pour can provide a shorter return path for high-current devices, such as switching converters, instead of routing longer traces to the ground plane.
6. Facilitation of PCB Manufacturing: Providing uniform copper distribution on a layer optimizes the etching and plating processes, and reduces the amount of etchant used in PCB manufacturing (thus lowering costs).
7. RF and Microwave Design: Ground copper pour contains electromagnetic (EM) radiation in local areas, thereby reducing spurious coupling, radiation and dispersion.
8. Digital Design: The ground plane improves noise immunity, achieves better grounding uniformity, and provides a low-inductance current path.

4. PCB Copper Pour Methods

• Large-area solid copper pour
• Copper grid pour

1. Large-area Solid Copper Pour
   It provides the dual functions of current-carrying capacity enhancement and shielding. However, if wave soldering is adopted, it may cause board warpage and even blistering. In this case, several slots are usually cut to reduce blistering of the copper foil.

PCB Copper Pour

2. Pure Copper Grid Pour
   It mainly plays a shielding role, with a weakened effect on increasing current-carrying capacity and better heat dissipation performance. However, it should be noted that the copper grid is composed of staggered and widened traces. For circuits, the trace width has a corresponding "electrical length" related to the operating frequency of the circuit board. The actual electrical length can be obtained by dividing the digital frequency corresponding to the operating frequency, which can be found in relevant books.

5. Correct Methods for PCB Copper Pour

1. Setting Up PCB Copper Pour in CAD Tools
   Increase the isolation clearance to 8mil for 1oz copper, and to 10mil for 2oz copper in CAD tools.

1. The default isolation clearance between the copper layer and signal traces is "6 mil".

Correct Method for PCB Copper Pour

2. To increase the clearance, right-click the edge of the polygon and go to Properties.

Correct Method for PCB Copper Pour

3. In the Properties dialog box, change the isolation value to 10mil, click "Apply", and then click "OK".

Correct Method for PCB Copper Pour

4. The spacing between the copper layer and signal traces will be increased accordingly.

Correct Method for PCB Copper Pour

6. Copper Pour Area Design

Copper Pour Area Design

7. Key Points for PCB Copper Pour

1. Copper pour is sometimes used incorrectly merely to fill unused space on the circuit board.
2. CAM engineers can add copper thief patterns to balance the copper distribution on the layer.
3. Floating (unconnected copper) is a real hazard to signal integrity, and all copper pour must be grounded.
4. Ground copper pour without ground vias may become a channel for crosstalk between traces on both sides of the ground shape.
5. By creating the copper pour layer as part of the ground grid and configuring it as a solid plane, a well-defined return current path can be provided.
6. Any additional planes must be properly positioned and spaced so that they do not adversely affect the signal integrity of the circuit board.
7. Grounding on the microstrip layer changes the transmission line from a microstrip to a grounded coplanar waveguide (CPW).
8. Copper pour can reduce the characteristic impedance and differential impedance of the transmission line.
9. CPW confines electromagnetic fields in a more localized manner than microstrip lines, thereby reducing spurious coupling, radiation and dispersion.
10. Microstrip lines can radiate, while striplines do not, as the fields are confined between the ground planes.
11. When copper pour is placed close to critical signal traces, the impedance will be reduced by 2–3 ohms.
12. Copper pour may convert differential mode signals to common mode signals at these points, thereby affecting signal integrity.