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The significance of PCB copper cladding and its design difficulties
- May 16, 2017 -

The so-called copper coated, the PCB is the idle space as a datum plane, and then filled with solid copper, these copper areas also known as potting copper.

The significance of copper cladding is to reduce ground impedance, improve anti-interference ability, reduce pressure drop, improve power efficiency, and connect with ground wire, and reduce loop area. Also out of the PCB welding as far as possible without distortion of the purpose, most PCB manufacturers will also require PCB designers in the open area of the PCB fill copper skin or mesh ground. If the improper treatment of copper covering, that will not outweigh the value of copper, whether the "advantage outweigh the disadvantages" or "more harm than beneficial"?

We all know that at high frequency, the distribution of the wiring on the PCB will work, when the length is greater than the noise frequency of the corresponding wavelength of 1/20, will produce antenna effect, the noise will be routed out of the PCB, if there is a bad grounding in copper, copper-coated has become the noise of the tool, so in the high-frequency circuits, do not think that the ground of a place to pick up, this is "ground", must be less than λ/20 spacing, in the wiring to punch holes, With multi-layer plate of the ground plane "good grounding". If the copper cladding is handled appropriately, copper clad not only has the increasing current, but also has the double effect of shielding interference.

Copper clad in general has two basic ways, is a large area of copper and mesh copper, often some people ask, large area copper coated good or mesh copper good, not generalized.

Why? Large area copper covering, with increased current and shielding dual role, but large area copper, if the wave soldering, the board may be raised, even foaming. Therefore, large area of copper covering, generally will open a few slots, alleviate blister copper foil, pure mesh CU is mainly shielding effect, increase the role of the current has been lowered, from the heat of the point of view, the grid has advantages (it reduces the copper heating surface) and also played a certain role of electromagnetic shielding.

But it is important to note that the grid is made up of staggered lines, we know that for the circuit, the width of the line of the circuit board for the working frequency of the corresponding "electrical length" (The actual size divided by the frequency of the corresponding digital frequency available, specific books, when working frequency is not very high, perhaps the role of grid lines is not very obvious, once the electrical length and working frequency match, it is very bad, you will find that the circuit is not working properly, Everywhere in the firing of the signal to interfere with the system work. So for the use of Grid colleagues, the proposal can be based on the design of the circuit board to choose the work situation, do not die holding a thing not to put. Therefore, high-frequency circuit against interference requires a multi-use grid, low-frequency circuits have a large current circuit, such as commonly used for the complete copper paving.

Said so much, then we in the copper clad, in order to let copper cladding achieve our desired effect, so the copper covering the need to pay attention to what problems:
1. If the PCB has more ground, have SGND, AGND, GND, and so on, according to the PCB board position, respectively, with the most important "ground" as the benchmark reference to independently copper coated, digitally and simulated separately to cover copper since not much, at the same time before copper cladding, first, the corresponding power supply lines: 5.0V, 3.3V and so on, so that the formation of multiple different shapes of the structure of the deformation.
2. To a single point of connection, the approach is through 0 Euro resistance or magnetic beads or inductance connections.
3. Crystal oscillator near the copper cladding, the circuit in the crystal oscillator is a high-frequency emission source, the method is in the surrounding Crystal copper cladding, and then the crystal oscillator shell separately ground.
4. Isolated island (Dead zone) problem, if it feels very large, that defines a hole to add to the cost of not much matter.
5. In the beginning of wiring, the ground should be treated equally, walking the line should be the ground to go good, can not rely on the copper coated by adding holes to eliminate the connection to the ground pin, this effect is very bad.
6. It is best not to have a sharp angle on the board (= 180 degrees), because from the angle of electromagnetism, this constitutes a transmitting antenna! For the other always have a big or small effect, I propose to use the edge of the arc.
7. Multi-layer Plate middle layer of the wiring open area, do not cover copper. Because you are hard to make this copper coated "good grounding".
8. The metal inside the equipment, such as metal radiator, metal reinforcement bars, etc., must realize "good grounding".
9. Three-end stabilizer of the heat dissipation metal block, must be good grounding. Crystal oscillator near the grounding belt, must be good grounding.

In short: The PCB on copper, if the grounding problem is handled well, it is definitely "advantages outweigh the disadvantages", it can reduce the backflow area of the signal line, reduce the signal external electromagnetic interference.