The Significance and Design Difficulties of PCB Copper Coating

The so-called copper coating is to use the idle space on the PCB as the base level, and then fill with solid copper, these copper areas are also known as copper filling.

The significance of copper coating is to reduce the ground impedance and improve the anti-interference ability. Reduce voltage drop, improve power efficiency; Connected with the ground wire, the loop area can also be reduced. Also for the purpose of making PCB welding as deformable as possible, most PCB manufacturers will also require PCB designers to fill copper or grid-like ground wires in the open area of the PCB. If the copper coating is handled improperly, it will not be worth the loss, whether the copper coating is "more good than bad" or "more bad than good"?

We all know that in the case of high frequency, the distributed capacitance of the wiring on the printed circuit board will work, when the length is greater than 1/20 of the corresponding wavelength of the noise frequency, there will be an antenna effect, and the noise will be emitted through the wiring, if there is a bad grounded copper coating in the PCB, the copper coating has become a tool for spreading noise, therefore, in the high frequency circuit, do not think that, A certain place of the ground wire is connected to the ground, which is the "ground wire", and must be less than λ/20 spacing, punching holes in the wiring, and the ground plane of the multilayer board is "well grounded". If the copper coating is properly treated, the copper coating not only increases the current, but also plays the dual role of shielding interference.

There are generally two basic ways of copper coating, that is, large area of copper coating and grid copper, and it is often asked whether large area of copper coating or grid copper coating is good, it is not good to generalize.

Why is that? Large-area copper coating has the dual role of increasing current and shielding, but large-area copper coating, if over wave soldering, the board may tilt up, and even foam. Therefore, a large area of copper coating, generally open several slots, alleviate copper foil foaming, simple grid copper coating is mainly shielding effect, increase the role of the current is reduced, from the point of view of heat dissipation, the grid has advantages (it reduces the heating surface of copper) and has played a certain role in electromagnetic shielding.

But it should be pointed out that the grid is composed of staggered direction of the line, we know that for the circuit, the width of the line for the circuit board working frequency is its corresponding "electrical length" (the actual size divided by the working frequency of the corresponding digital frequency can be obtained, specifically see the relevant books), when the working frequency is not very high, Perhaps the role of the grid lines is not very obvious, once the electrical length and the operating frequency match, it is very bad, you will find that the circuit does not work properly, everywhere is emitting signals that interfere with the work of the system. Therefore, for colleagues who use the grid, it is recommended that you can choose according to the design of the circuit board, and do not want to hold on to a thing. Therefore, the high frequency circuit against interference requirements of the multi-purpose grid, low frequency circuit with high current circuit and other commonly used complete copper paving.

Having said so much, then we in the copper coating, in order to make the copper coating achieve our expected effect, then the copper coating need to pay attention to what problems:

1. If there are more PCB ground, such as SGND, AGND, GND, etc., it is necessary to use the most important "ground" as a reference reference to independently cover copper according to the different positions of the PCB board surface, and the digital ground and analog ground are separately covered with copper since it is not much to say. At the same time, before covering copper, first bold the corresponding power connection: 5.0V, 3.3V and so on, in this way, a number of different shapes of multi-deformation structure is formed.

2. For different single point connections, the practice is to connect through 0 ohm resistance or magnetic beads or inductors.

3. Copper coating near the crystal oscillator, the crystal oscillator in the circuit is a high-frequency emission source, the practice is to cover the copper around the crystal oscillator, and then the crystal shell is grounded separately.

4. Island (dead zone) problem, if you think it is very big, it will not take much to define a hole to add it.

5. At the beginning of wiring, the ground wire should be treated equally, and the ground wire should be well walked when the wire is wired, and the ground pin can not be eliminated by adding a hole after copper coating, which has a very bad effect.

6. It is best not to have a sharp Angle on the board (=180 degrees), because from an electromagnetic point of view, this constitutes a transmitting antenna! For other things that will always have an impact on just big or small, I recommend using the edge of the arc.

7. The wiring open area of the middle layer of the multi-layer board, do not cover copper. Because you can hardly make this copper coating "well grounded".

8. The metal inside the equipment, such as metal radiators, metal reinforcement bars, etc., must be "well grounded".

9. The cooling metal block of the three-end regulator must be well grounded. The grounding isolation belt near the crystal oscillator must be well grounded.

In short: the copper coating on the PCB, if the grounding problem is handled well, it is certainly "more advantages than disadvantages", which can reduce the return area of the signal line and reduce the electromagnetic interference of the signal.