Date:2023-09-05 10:35:04
PCB design Copper laying is a very important part of circuit board design. What is PCB copper laying? It is to fill the unused space in the non-wiring area on the PCB with solid copper. The significance of laying copper is to reduce the impedance of the ground wire, improve the anti-interference ability; reduce the voltage drop, improve the power efficiency, connect to the ground wire, and also reduce the loop area.
The significance of PCB copper laying
The main benefit of laying copper is to reduce the impedance of the ground wire. (A large part of the so-called anti-interference is caused by the reduction of the impedance of the ground wire.) There are a lot of spike currents in digital circuits, so it is more necessary to reduce the impedance of the ground wire. It is generally believed that circuits composed entirely of digital devices should be laid on a large area, while for analog circuits, the ground loop formed by laying copper will cause electromagnetic coupling interference that outweighs the gain (except for high-frequency PCB circuits). Therefore, not all circuits need to be covered with copper.
Advantages and disadvantages of PCB copper laying
advantage：
1. Regarding EMC (electromagnetic compatibility) requirements, a large area of ground or power supply needs to be laid with copper, which will play a shielding role. Some special grounds, such as PGND (protected ground), play a protective role.
2. For PCB process manufacturing requirements, generally in order to ensure the uniform copper plating effect of electroplating, or to prevent lamination from deformation and bending, copper is laid on PCB layers with less wiring.
3. For signal integrity requirements, give high-frequency digital signals a complete return path and reduce DC network wiring. Of course, there are also reasons such as heat dissipation, copper laying required for installation of special devices, etc.
shortcoming：
1. If the component pins are fully covered with copper, it may cause heat dissipation too quickly, making it difficult to desolder and rework. Therefore, sometimes in order to avoid this situation, cross connections are used for components (pin contact and pad contact are in the shape of a "cross").
2. Paving copper in the area around the antenna part can easily lead to weak signals and interfere with the collected signal. The impedance of the copper paving will affect the performance of the amplification circuit. Therefore, the area around the antenna part is generally not covered with copper.
The shape of PCB copper
solid shape copper
The solid copper clad has the dual functions of increasing the current and shielding. However, if the solid copper clad is subjected to wave soldering, there is a certain tension of thermal expansion and contraction, and the board may warp or even bubble. Therefore, for solid copper cladding, several slots are generally opened to relieve the tension and cause the copper foil to blister.
Grid shape copper paving
The grid is coated with copper, which mainly plays a shielding role, and the effect of increasing the current will be reduced. From the perspective of heat dissipation, grid copper not only reduces the heating surface of copper, but also plays a certain role in electromagnetic shielding. However, the production process has certain requirements on the shape of the grid, and the grid is too small to affect the quality and yield.
PCB copper layout design
When designing a PCB, generally each surface of the PCB must be covered with copper and grounded. The main reason is to prevent PCB bending deformation and various signal interference and crosstalk.
Therefore, copper should be grounded when wiring. However, since there are a large number of components and traces on the outer layer, the copper foil will be divided into many small isolated copper and slender copper skins by these component pads and their traces.
1. Processing of broken copper
Those thin, long and poorly grounded copper will have an antenna effect, which will cause poor EMC problems. Therefore, it is necessary to avoid causing broken copper when pouring copper as much as possible. If it causes broken copper, it can be deleted.
2. Dealing with isolated copper
Island (dead zone) copper problem, if the isolated copper is relatively small and equal to broken copper, it can be deleted. If it is very large, it can be defined as a certain ground to add vias, and there will be no isolated copper at this time.
PADS light painting file copper pouring
The file designed by PADS needs to be paved again when it is opened for the second time. The reason is that the copper paving of PADS software is a linear copper skin, which is also the characteristic of PADS software. The amount of data on the linear copper sheet is large. If you close the software and reopen the saved copper layer, the file will be very slow and stuck. Therefore, after the PADS software is closed, only the copper skin frame of the design file is retained.
PADS copper laying method:
1. Fill (hatch)
Filling is to restore the copper filling, because the PADS software does not retain the entire designed copper sheet, only the outer frame of the copper sheet, so opening the design file a second time requires restoring the copper pouring.
2. Flood
Copper pouring is used for the first time after the PCB Layout is completed, or if the PCB has changes (such as design rules), copper pouring needs to be used again.
3. Flat link
The planar connection refers to the inner copper sheet. The reason is that the copper sheet designed by PADS software only retains the outer frame of the copper sheet. When opening the design file for the second time, you need to select the planar link to restore the copper covering.Therefore, when the PADS design file is exported as a Gerber file, the design file needs to be refilled to restore the copper filling when the design file is opened for the second time. If the board manufacturer helps the design engineer to output Gerber, the copper filling operation needs to be restored. Otherwise, the output Gerber file will be missing copper, resulting in manufacturing errors and the product cannot be used.
DFM Check Design Copper Laying
Regarding the manufacturability of broken copper and isolated copper, broken copper will be etched away due to its elongated features during the manufacturing process, causing the copper to separate and fall off in other locations to cause short circuits in different networks.
When CAM engineers in the board factory process production files for isolated copper, they will inquire and confirm with the design engineers, because isolated copper without network links is an abnormal design. Therefore, the presence of isolated copper in the design will waste communication costs and delay the production cycle.
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