Laying copper in PCB design is a very important aspect of circuit board design. What is PCB copper laying? It means filling the idle space on the PCB without wiring with solid copper. The significance of laying copper is to reduce the impedance of the ground wire and improve its anti-interference ability; Reduce voltage drop, improve power efficiency, connect to ground wire, and also reduce loop area.
The significance of PCB copper laying
The main advantage of laying copper is to reduce the impedance of the ground wire, which is also a significant part of anti-interference. There are a large number of peak pulse currents in digital circuits, so reducing the impedance of the ground wire is more necessary.
It is generally believed that for circuits composed entirely of digital devices, a large area of ground should be laid, while for analog circuits, the ground loop formed by laying copper can actually cause electromagnetic coupling interference to outweigh the gains (except for high-frequency PCB circuits). Therefore, not all circuits need to be coated with copper.
Advantages and disadvantages of PCB copper laying
1、 For EMC (electromagnetic compatibility) requirements, large areas of ground or power supply need to be paved with copper, which will play a shielding role. Some special areas, such as PGND (protective ground), play a protective role.
2、 For PCB manufacturing requirements, it is generally necessary to ensure a uniform copper plating effect during electroplating or to ensure that the lamination does not deform or bend. For PCB boards with less wiring, copper should be laid on each layer.
3、 For signal integrity requirements, provide a complete return path for high-frequency digital signals and reduce the wiring of the DC network. Of course, there are also reasons such as heat dissipation, special device installation requirements for copper laying, and so on.
1、 If the pins of the components are fully covered with copper, it may lead to rapid heat dissipation, making it difficult to disassemble and repair. So sometimes, in order to avoid this situation, cross connections are used for components (pin contact and solder pad contact are “ten” characters).
2、 Laying copper in the area around the antenna can easily lead to weak signals and interference in the collected signal. The impedance of copper laying can affect the performance of the amplification circuit. So the surrounding area of the antenna section is generally not covered with copper.
The shape of PCB copper laying
Solid shape copper laying
Solid copper coating has a dual effect of increasing current and shielding. However, if there is a certain tension of thermal expansion during wave soldering of solid copper cladding, the board may be warped or even blistered. Therefore, when applying copper physically, several grooves are usually opened to alleviate the tension and cause blistering of the copper foil.
Grid shaped copper laying
Grid copper coating mainly serves as a shielding effect, but increasing the current will reduce the effect. From the perspective of heat dissipation, grid copper coating not only reduces the heating surface of copper, but also plays a certain electromagnetic shielding role. However, the production process has certain requirements for grid shape copper laying, and a small grid size affects the quality yield.
Design of PCB copper laying
When designing a PCB, generally every surface of the PCB needs to be grounded with copper, mainly to prevent PCB bending and deformation, as well as various signal interference and crosstalk.
So when wiring, copper grounding should be applied. However, due to the large number of components and wiring on the outer layer, the copper foil will be divided into many small isolated copper and slender copper sheets by the solder pads and wiring of these components.
1. Handling scrap copper
The thin and long grounding copper with poor grounding can have antenna effect and cause EMC problems. So it is necessary to try to avoid causing copper fragmentation during copper coating, and if it causes copper fragmentation, it can be removed for treatment.
2. Handling isolated copper
Island (dead zone) copper issue, if the isolated copper is relatively small and equivalent to scrap copper, it can be removed and dealt with. If it is very large, it can be defined as a certain place where through hole processing is added, and there is no isolated copper at this time.
PADS photo files coated with copper
The files designed for PADS need to be re coated with copper the second time they are opened, because the copper coating in PADS software is a linear copper sheet, which is also a characteristic of PADS software. There is a large amount of linear copper sheet data. If you close the software and reopen the saved copper sheet, opening the file will be slow and too laggy. Therefore, after the PADS software is closed, only the copper frame of the design file is retained.
PADS copper laying method:
1. 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. Therefore, when opening the design file again, it is necessary to restore the copper filling.
2. Flood
Copper filling is the first time it is used after the PCB layout is completed, or if there are changes to the PCB (such as design rules) that require the use of copper filling again.
3. Flat Link
Flat connection refers to the copper sheet on the inner layer, which is also because the copper sheet designed by the PADS software only retains the outer frame of the copper sheet. The second time you open the copper sheet on the inner layer of the design file, you need to choose a flat connection to restore the copper sheet laying.
Therefore, when outputting the Gerber file in the PADS design file, the second time you open the design file, you need to refill and restore the copper filling. If the board factory assists the design engineer in outputting Gerber, it is necessary to perform a copper recovery operation. Otherwise, the output Gerber file is missing the copper sheet, resulting in production and manufacturing errors, and the product cannot be used.
DFM inspection design copper laying
Regarding the manufacturability issues of scrap copper and isolated copper, scrap copper will be etched off due to its slender characteristics during the production and manufacturing process, resulting in copper separation and detachment in other positions, leading to different network short circuits.
When CAM engineers in the sheet factory process production documents, they will ask and confirm with the design engineer because isolated copper without network links belongs to abnormal design. So isolated copper in the design will waste communication costs and delay production cycles