Advantages and disadvantages of PCB copper coating
Copper coating as an important link in PCB design, whether it is the domestic qingyue feng PCB design software, also some foreign Protel,PowerPCB have provided intelligent copper coating function, then how to apply good copper, I will share some ideas with you, hope to bring benefits to the industry.
By copper coating, the unused space on the PCB is used as a base level and then filled with solid copper, which is also known as copper pouring.
The significance of copper coating lies in reducing ground resistance and improving anti-interference ability. Reduce voltage drop, improve power efficiency; Connecting to ground lines also reduces loop area. For the purpose of not deforming PCB welding as much as possible, most PCB manufacturers will ask PCB designers to fill copper skin or grid ground wire in the open area of PCB. If the copper coating is not handled properly, it will not be rewarding. Is the copper coating "more advantages than disadvantages" or "more disadvantages than advantages"?
Under the condition of high frequency is known to all, on the printed circuit board wiring capacitance will work, when the length is more than 1/20 of the noise frequency corresponding wavelength, can produce the antenna effect, the noise will launch out through wiring, if there are bad grounding in the PCB apply copper, apply copper became the noise spreading tool, therefore, in the high frequency circuit, don't believe that somewhere in the ground after the, this is the "ground", must be less than the spacing of lambda / 20, punch a hole in the cabling, and multilayer ground plane "well grounded". If copper coating is properly treated, copper coating not only increases the current, but also plays a dual role of shielding interference.
Apply copper to have two kinds of basic means commonly, it is large area apply copper and grid copper, often also somebody asks, large area cover copper is good or grid cover copper is good, bad generalize. Why? Large area of copper, with increased current and shielding dual role, but large area of copper, if the wave peak welding, the plate may be up, or even blistering. Therefore, a large area of copper, generally will open a few slots, ease copper foil bubbles, pure mesh copper is mainly shielding effect, increase the role of the current is reduced, from the perspective of heat dissipation, the grid is beneficial (it reduces the heating surface of copper) and played a certain role of electromagnetic shielding. But it should be pointed out that, the grid is made by alternating direction of running, we know for circuit line width for the work frequency of the circuit board has its corresponding "electricity" length of
(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, is very bad, you will find that the circuit won't work properly, emission signal interference system work everywhere. So for those of you who use grids, my advice is to choose the circuit board that works according to the design, and not to cling to one thing at a time. Therefore, high frequency circuit is required to fight interference with multi-purpose grid, low frequency circuit has high current circuit and other commonly used complete copper coating.
Said so much, then we in the copper application, in order to make the copper application to achieve the desired effect, then the copper application needs to pay attention to the following questions:
1. If the PCB is more, have SGND, AGND, GND, etc., will be depending on the position of PCB board face, respectively to the main "to" as a benchmark reference to the independent copper clad, digital earth and simulated separately apply copper from a few words, at the same time before the copper clad, first of all, bold corresponding power cords: 5.0 V, 3.3 V, etc., as a result, a number of different shapes are formed more deformation structure.
2. For different single point connections, the method is 0 ohm resistance or magnetic bead or inductance connection;
3. Copper coating near crystal oscillator. The crystal oscillator in the circuit is a high-frequency emission source.
4. The island (dead zone) problem, if it seems too big, would not take much effort to define a hole through which to add it.
5. At the beginning of wiring, the ground wire should be treated equally, and the ground wire should be well laid when wiring, and it cannot be relied on after copper coating to eliminate the ground pin that is connected by adding through holes, which is a very bad effect.
6. It is better not to have sharp Angle on the board (=180 degrees), because from the point of view of electromagnetism, this will constitute a transmitting antenna!
7. Do not apply copper to the wiring of the middle layer of multi-layer board in an open area. Because it's hard for you to make this copper "well grounded."
8. The metal inside the equipment, such as metal radiator, metal reinforcement bar, etc., must be "well grounded".
9. Heat dissipation metal block of three-terminal voltage stabilizer must be well grounded. The grounding isolation belt near crystal oscillator must be well grounded.
In short: the copper coating on PCB, if the grounding problem is handled well, it must be "advantages outweigh disadvantages", it can reduce the backflow area of the signal line, reduce the signal external electromagnetic interference.