Copper thieving is a technique used to balance the copper distribution on a PCB by adding small copper circles, squares, or even a solid copper plane to larger blank spaces. The added copper is not connected to any nets on the board and should not affect the functionality.
Figure 1: Copper Thieving Pattern
Relations with Copper Pour
The copper pour is another method for managing copper distribution on a PCB. It is typically used to create ground planes or power planes, which can help to improve signal integrity, reduce EMI, and dissipate heat. Copper pours can be used in conjunction with copper thieving to achieve even better copper distribution. For example, you could use copper thieving to balance the copper distribution in areas around high-density components, and then use copper pour to fill in the remaining empty spaces on the board.
Advantages of Copper Thieving
Even Out Plating Current
One of the primary reasons for incorporating copper thieving into PCBs is to ensure a consistent copper plating distribution within the vias or holes. When the copper distribution across the PCB artwork is uneven, problems can arise. In areas with minimal exposed copper, the electroplating process can cause an excessive buildup of copper, potentially leading to short circuits and other complications. Conversely, in regions densely populated with copper, like those surrounding BGAs or connector pin fields, proper plating may not occur, resulting in insufficient copper thickness, which can compromise connectivity and solder joint integrity. Thieving addresses these concerns by intelligently redistributing plating current, striking a balance to achieve a uniform copper distribution across the entire board.
This process is essential in applications where copper shorts can cause problems, particularly in high-power scenarios or situations with substantial current flow through the PCB.
Improve Solderability
Adequate copper thickness provided by copper thieving facilitates reliable soldering of components onto the PCB, which is crucial for solder joint strength and long-term functionality. For example, if the copper thickness is too thin, the solder joint may not be strong enough to hold the component in place. Conversely, if the copper thickness is too thick, the solder joint may be brittle and prone to cracking.
Improve Signal Integrity
Consistent impedance across transmission lines on the PCB is critical for preserving signal integrity, particularly in high-speed digital and RF applications. Copper thieving helps maintain this consistency by ensuring that the copper thickness is uniform across the transmission lines. This is important because impedance variations can cause signal reflections and distortions, which can lead to errors in data transmission.
Considerations for Implementing Copper Thieving in PCB Design
First, Copper thieving should not negatively affect signal integrity, solderability, or mechanical strength. Second, thieving structures must be electrically isolated from the rest of the PCB to prevent unintended circuit connections. Third, Copper thieving should be placed in areas with a risk of uneven copper distribution, such as those with minimally exposed copper or near high-density components.
