What Problems Should PCB Copper Cover Pay Attention To?

Copper cladding is an important part of PCB design. The so-called copper cladding means that the idle space on PCB is taken as the datum plane and filled with solid copper. These copper areas are also called copper filling.

 

The significance of copper cladding is to reduce the ground impedance and improve the anti-interference ability; Reduce the voltage drop, improve the power efficiency; Connecting to the ground wire also reduces the area of the loop. Most PCB manufacturers also require PCB designers to fill open areas of the PCB with copper sheeting or grid-like ground wires in order to make the PCB solder as deformable as possible.

 

It is well known that at high frequencies, the distributed capacitance of the wiring on the printed circuit board will come into play, and when the length is greater than 1/20 of the corresponding wavelength of the noise frequency, the antenna effect will occur, and the noise will be emitted outward through the wiring. If there is a poorly grounded copper cladding in the PCB, the copper cladding becomes a tool for spreading noise.

 

Therefore, in high-frequency circuits, do not think that the ground wire is connected to the ground somewhere, this is the “ground wire”. Must be less than λ/20 spacing, holes in the wiring, and the floor plane of the multilayer board “well-grounded”. If the copper cladding is handled properly, the copper cladding not only increases the current but also plays a dual role in shielding interference.

 

There are two basic types of copper cladding, namely large area copper cladding and grid copper. It is often asked that large area copper-clad or grid copper-clad good. It’s not easy to generalize!

 

Large area copper clad, with the dual role of increasing current and shielding, but large area copper clad, if the wave soldering, the board may become warped, or even blister. Therefore, large-area copper coating, generally also open a few grooves, alleviate copper foil foaming.

 

The simple copper-clad grid is mainly shielding, and the effect of increasing current is reduced. From the perspective of heat dissipation, the grid is good (it reduces the heating surface of copper) and plays a certain role in electromagnetic shielding.

 

But it should be pointed out that, the grid is made by alternating direction of running, we know that for the circuit, go line width for the working frequency of the circuit board has its corresponding “electrical length” (actual size divided by the working frequency of the corresponding digital frequency, concrete books), when the working frequency is not high, perhaps the role of the grid lines is not obvious, once the electrical length and working frequency matching, very bad, you will find that the circuit won’t work properly, emission signal interference system work everywhere. So for the use of grid copper cladding colleagues, my advice is to choose according to the design of the circuit board working condition.

Therefore, high-frequency circuits with high interference requirements of multi-purpose grid copper cladding, low-frequency circuits with large current circuits often complete copper laying.

 

In order to achieve the desired effect of copper cladding, what should we pay attention to in terms of copper cladding?

1. If there are more PCB areas, such as SGND, AGND, GND, etc., it is necessary to take the main “ground” as the reference to independently copper-clad according to the different PCB surface positions, and copper-clad digitally and analog separately. At the same time, before the copper coating, first of all, the corresponding power supply connection: 5.0V, 3.3V, etc. As a result, multiple deformable structures with different shapes are formed.
2. For different single-point connections, the practice is through 0 ohm resistor or magnetic bead or inductor connection.
3. Copper cladding near the crystal oscillator. The crystal oscillator in the circuit is a high-frequency emission source by covering the crystal oscillator with copper and then grounding the crystal casing separately.
4. The island (dead zone) problem, if you feel big, then define a hole to add-in also does not cost much.
5. At the beginning of wiring, the ground should be treated equally. When wiring, the ground should be taken well, and the ground pin can not be eliminated by adding holes to the copper cladding.
6. Try not to have sharp angles on the board, because from the perspective of electromagnetism, this constitutes a transmitting antenna, and it is recommended to use the arc edge along the line.
7. The open area of wiring in the middle layer of the multi-layer board should not be covered with copper. Because it’s hard for you to get the copper cladding to “ground well.”
8. The metal inside the equipment, such as the metal radiator and the metal reinforcement strip, must be “well-grounded”.
9. Three end regulator heat dissipation metal block must be well-grounded. The grounding isolation belt near the crystal oscillator must be well-grounded.

 

In conclusion: copper cladding on PCB, if the grounding problem is handled well, it is certainly “more beneficial than harmful”, it can reduce the signal line backflow area, reduce the signal external electromagnetic interference.