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  • Notes for copper clad Print circuit board

    The CCL (Copper Clad Laminate) is to take the spare space on the PCB as the reference level, then fill it with solid copper, which is also known as copper pouring.

    The significance of CCL as below:

    1. reduce ground impedance and improve anti-interference ability
    2. reduce voltage drop and improve power efficiency
    3. connected to the ground and can also reduce the area of the loop.

     

    As an important link of PCB design, regardless of domestic Qingyue Feng PCB design software, also some foreign Protel, PowerPCB have provided intelligent copper function, so how to apply good copper, I will share some of my own ideas with you, hope to bring benefits to the industry.

     

    Now in order to make PCB welding as far as possible without deformation, most PCB manufacturers will also require the PCB designer to fill the open area of the PCB with copper or grid-like ground wire. If the CCL is not handled properly, it will lead to more bad results . Is the CCL ”more good than harm” or “more bad than good”?

     

    Under the condition of high frequency ,it will work on the printed circuit board wiring capacitance, when the length is more than 1/20 of the noise frequency corresponding wavelength, then can produce the antenna effect, the noise will launch out through wiring, if there are bad grounding CCL in the PCB, CCL became the tool of transmission noise, therefore, in the high frequency circuit, don’t believe that if you connect a ground wire to the ground somewhere, this is the “ground”, In fact, it must be less than the spacing of λ/20, punch a hole in the cabling and multilayer ground plane “well grounded”. If the CCL is handled properly, it can not only increase the current, but also play a dual role of shielding interference.

     

    There are two basic ways of CCL, namely large area copper cladding and mesh copper, often also asked, which one is the best, it’s hard to say. Why? Large area of CCL, with the increase of the current and shielding dual role, but there are large area of CCL,the board may become warped, even bubble if through the wave soldering.Therefore, generally will also open a few slots to alleviate the bubbling copper,The mesh CCL is mainly shielding, increasing the role of the current is reduced, From the perspective of heat dissipation, grid has benefits (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 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.Therefore, for those who use grid, my advice is to choose according to the working conditions of the circuit board design, rather than holding on to one thing.Therefore, high frequency circuit anti-interference requirements of the multi-purpose grid, low frequency circuit with high current circuit and other commonly used complete artificial copper.

     

    On the CCL, in order to let it to achieve our expected effect, then the CCL aspects need to pay attention to what problems:

     

    1. If the ground of PCB is more, have SGND, AGND, GND, etc., will be depending on the position of PCB board face, respectively to make the main “ground”  as reference point for the independent CCL, to digital and analog to separate copper , before produce the CCL, first of all, bold corresponding power cords: 5.0 V, 3.3 V, etc., in this way ,a number of different shapes are formed more deformation structure.

    2. For the single point connection of different places, the method is to connect through 0 ohm resistance or magnetic bead or inductance;

     

    3. CCL near the crystal oscillator. The crystal oscillator in the circuit is a high frequency emission source. The method is to surround the crystal oscillator with copper cladding and then ground the shell of the crystal oscillator separately.

    4.The problem of dead zone, if feel it’s very big, then add a ground via on it.

    5. At the beginning of the wiring, should be treated equally for the ground wiring , we should wire the ground well when wiring ,can not rely on add the vias when finished CCL to eliminate the ground pin for the connection, this effect is very bad.

    6. It is better not to have a sharp Angle on the board (=180 °), because from the point of view of electromagnetism, this will form a transmitting antenna, so I suggest using the edges of  the arc.

    7. Multilayer middle layer wiring spare area, do not copper, because it’s hard to make the CCL to ”grounded”

    8.the metal inside the equipment, such as metal radiator, metal reinforcement strip, must achieve “good grounding”.

    9.The cooling metal block of the three-terminal voltage stabilizer and the grounding isolation belt near the crystal oscillator must be well grounded. In a word: the CCL on the PCB, if the grounding problem is handled well, it must be “more good than bad”, it can reduce the signal line backflow area, reduce the signal external electromagnetic interference.