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Copper pour is an important part of PCB design. Whether it is made by Chinese PCB design software or some foreign Protel, PowerPCB provides intelligent copper pour function. Then how can we make copper pour? I will share some experience with you here, and I hope it will benefit you. The copper pour is to use the idle space on the PCB as the reference surface, and then filled with solid copper, which is also called copper filling.The significance of copper coating is to reduce the ground impedance, improve the anti-interference ability, reduce the pressure drop and improve the power efficiency, connect with the ground wire, and also reduce the area of the loop. Also for PCB welding as far as possible without deformation, most PCB manufacturers will also require PCB designers filled copper wire or grid in the PCB free area, if the improper processing of copper, the copper is "The loss outweighs the gain., whether the advantages outweigh the disadvantages" or "more harm than good? We all know that in case of high frequency, capacitance wiring on printed circuit board will play a role, when the noise frequencies greater than the length of the corresponding wavelength 1/20, will produce the antenna effect and noise will be emitted outside through wiring, if there are bad grounding copper clad in PCB, copper became the spread tool of noise. Therefore, in the high frequency circuit, do not think a place connects ground, this is the ground ,the space is less than λ/20, placed via on the wiring , ground plane and multilayer board "well grounded". If copper pour is properly treated, the copper cladding can not only increase the current, but also play a double role in shielding interference. Copper pour generally has two basic ways, that is large area of copper clad and grid copper. It is often asked that large area copper pour is good or grid pour copper is good. This is not a good generalization. Why? The large area of copper pour, with the double effect of increasing current and shielding, but if welding, the plate may be warped up, and even bubble. Therefore, a large area of copper will also open several grooves to relieve blister of copper foil. The pure grid copper pour is mainly shielding effect, and the effect of increasing current is reduced. From the point of view of heat dissipation, the grid is beneficial (it reduces the heating surface of copper) and acts as a certain electromagnetic shielding.However, it is necessary to point out that the grid is composed of alternating direction line, we know that for the circuit, walk the line width of the operating frequency for the circuit board is its "electric length" (digital frequency corresponding to the actual size divided by the working frequency can be specific to the relevant books). When the working frequency is not very high, the function of the grid can not be very obvious. Once the length of the electric power matches with the working frequency, it will be very bad. You will find that the circuit is not working at all, and the signal of the jamming system is being launched everywhere.So for the people who use the grid, the individual proposal is based on the design of the circuit board work and choose not to hold a thing. Therefore, the high frequency circuit has a high demand for multipurpose grid, and the low frequency circuit has a full current of copper with large current. In order to achieve the desired effect, we need to pay attention to the following questions: 1.If PCB is more SGND, AGND, GND, etc., will be based on the PCB plate in different position, with the main "place" as reference to independent copper, analog ground and digital ground to separate copper from the few words, while copper before power connection the first phase should be bold: 5.0V, 3.3V and so on, as a result, on the formation of a number of different shapes of structure deformation. 2.For different single point connections, the practice is connected by 0 ohm resistors or magnetic beads or inductors. 3.Copper pour in the vicinity of the crystal oscillator, the crystal oscillator in the circuit is a high frequency emission source. The method is to cover the copper with the crystal oscillator, and then separate the shell of the crystal oscillator from the ground. 4.The problem of a solitary island (dead zone), if it is very large, it’s easy to define a via in a field. 5.When starting layout, the ground should be treated equally. When the line is taken, the ground wire should go well. It can not rely on copper overlaying to eliminate the unconnected ground pins by adding vias. This effect is not good. 6.It is best not to have a sharp angle on the board ("=180 degrees"), because from the point of view of electromagnetics, this constitutes a launching antenna! It is only big or small for others that have some influence, and it is recommended to use the edges of the arc. 7.Do not pour copper at the middle layer of the multi-layer plate in free area. Because it's hard to make this copper "good ground". 8.The metal in the equipment, such as metal radiator and metal reinforcing bar, must be "good grounding". 9.The heat dissipating metal block of the three terminal regulator must be well grounded. The grounding isolation zone near the crystal oscillator must be well grounded. In conclusion, if the grounding problem is handled well, the copper pour on the PCB will be more effective than the disadvantages. It can reduce the backflow area of the signal line and reduce the electromagnetic interference of the signal.
High frequency electronic equipment is the development trend, especially in the increasing development of wireless network, satellite communications, technology information products trend high speed and high frequency, and communication products trend large capacity high speed wireless transmission of voice, video and data standardization, so the development of a new generation of products require high frequency circuit board. The communication products such as satellite system, mobile phone receiving base station and so on, must be equipped with high frequency circuit boards, which will develop rapidly in the next few years. There will be large demand for high-frequency substrates. The basic characteristics of high frequency substrate materials require the following points: 1.The dielectric constant (Dk) must be small and very stable, usually is the square root of the transfer rate and the dielectric constant of the smaller the better signal is inversely proportional to the high dielectric constant, easy to cause the signal transmission delay. 2.The dielectric loss (Df) must be small, which mainly affect the signal transmission quality, the less the dielectric loss so that the signal loss is small. 3.The thermal expansion coefficient of copper foil is as consistent as possible, because the inconsistency causes the separation of copper foil in the cold and heat changes. 4.The low water absorbability and high water absorption will affect the dielectric constant and dielectric loss at damp. 5.The heat-resistant, anti chemical, impact strength, peeling strength and so on must be good. In general, the high frequency can be defined as above 1GHz. The high frequency circuit board substrate is always use the fluoride substrate, such as polytetrafluoroethylene (PTFE), usually known as Teflon, usually used in more than 5GHz.In addition, it also use FR4 or PPO substrate, which can be used in 1GHz ~ 10GHz products. These three kinds of high frequency substrates are compared as follows: The three kinds of high frequency substrate material Epoxy resin, PPO resin and fluorine resin which are used at present,epoxy resin is the cheapest, and the most expensive is fluorine resin; consider dielectric constant, dielectric loss, water absorption rate and the frequency characteristics,fluorine resin is the best, epoxy resin is the poor.When the frequency of product application is higher than 10GHz, only fluorine resin printed board can be applied. Obviously, fluorine resin high frequency substrate performance is far higher than that of other substrates, but its shortcomings is except high cost also poor rigidity, and high thermal expansion coefficient.For polytetrafluoroethylene (PTFE), in order to improve the performance, a large number of inorganic materials (such as silica SiO2) or glass cloth are used as reinforcing filler materials to improve the rigidity of the substrate and reduce its thermal expansion.In addition, because of the molecular inertia of the polytetrafluoroethylene resin, it is not easy to combine with copper foil, so it is more necessary to deal with the special surface of the copper foil.The treatment methods include polytetrafluoroethylene surface chemical etching or plasma etching, increasing the surface roughness or increasing adhesion between copper foil and polytetrafluoroethylene resin, but it may affect the performance of the dielectric. The development of fluorine based high frequency circuit board requires cooperation among raw material suppliers, research institutes, equipment suppliers, PCB manufacturers and communication products manufacturers, so as to keep up with the rapid development of high frequency circuit boards.
The early process of Rigidflex PCB board is use connector or hotbar process to connect two PCBs with flex board.This combination with the flex board and rigid PCB process is time-consuming and laborious, so customers transfer the assembly to PCB manufacturer to make rigid-flex PCB. In addition to the price, the use of Rigid-flex Board has many advantages, listed as follows: 1.It can effectively save the space on the circuit board and save the use of the connector or the HotBar process,Because of flex PCB and rigid PCB get together, so that require the use of connectors or HotBar process space can be saved, saved space is very important for some high density board,it also saved the cost of using the parts of the connector or the cost of the HotBar process. In addition, the space between the two pieces of the board can also become more compact because it saves the connector. 2.The distance of the signal transmission is shortened and the speed is increased, and the reliability can be improved effectively. The traditional transmission of the signal through the connector is circuit board --->connector--->flex board--->connector--->circuit board. The signal transmission of rigid-flex PCB is reduced to the circuit board--->flex PCB---> circuit board.The distance between signal transmission is shorter, and the problem of signal transmission attenuation between different media is also reduced.The wiring on the general circuit board is copper material, and the contact terminal of the connector is gold-plated. The solder joints are plated with tin, and solder paste is applied to the printed circuit board. The transmission of signals between different metal will be attenuated.If we change to rigid-flex boards, these media will become less, and the ability of signal transmission can also be improved. 3. Simplifying the assembly of products and saving the time of assembly The use of rigidflex PCB can reduce the time of SMT process, because the number of connectors is less.It also reduces the time for the assembly of the whole machine, because it saves the assembly of the flex board into the connector, or saves the process of the HotBar. It also reduces the cost of part management and inventory, because the BOM table is reduced, so management becomes less. The disadvantage of rigid-flex PCB: After comparison,the biggest weakness is that rigid-flex PCB boards is more expensive.The cost is nearly doubled than flex PCB +rigid PCB.But if the price of the connector is deducted or the cost of HotBar, the price is likely to be same. Another disadvantage is that both SMT and carrier may need to use a tray (carrier) to support the part of the flex board, which virtually increases the assembly cost of the SMT. More PCB technology, please visit www.kingsunpcb.com
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