PCB (Printed Circuit Board) can be developed into two single sided circuit boards, double sided PCBs and multilayer processing circuit boards. Common multilayer PCBs include four-layer circuit boards, six-layer circuit boards and eight-layer circuit boards.Double-sided PCB Simple four-layer board in Top Layer and Bottom Layer furthermore a power layer and ground layer, greatly help to solve the electromagnetic environment interference social problems, improve the reliability of the management system, but also by improving as well as the wires cloth through the rate of reduction of the PCB circuit board area.
The number of PCB multilayer layers is actually very flexible and can be set reasonably according to the actual needs of the designer. So, what kind of layering principle does PCB multilayer have?PCB layer setting should meet the following requirements.
1. The power supply layer should be close to the grounding layer and closely coupled with it, and arranged below the grounding layer. Component layer below the grounding layer, for the top wiring to provide device shielding and reference layer.
2. The signal layer should be adjacent to the inner layer, not directly adjacent to other signal layers, and all signal layers should be adjacent to the ground layer as much as possible.
3. Isolate digital circuits from analog circuits. If conditions permit, analog and digital signal lines are arranged in separate layers and shielding measures are taken; if they need to be arranged in the same signal layer, isolation strips and grounding wires need to be used to reduce interference; the power and ground of analog and digital circuits are to be isolated from each other and not to be mixed.
4. Multilayer boards should maintain a symmetry between the layers of students in the design, preferably an even number of copper layers. If the information is not symmetrical, it is easy to develop and cause serious distortion.
Why ordinary PCB multilayers are even numbered layers instead of odd numbered layers?
Currently there are more than 100 layers of PCB, we usually encountered basically even number of layers of PCB. so why is even number of layers common instead of odd number of layers?
Multilayer PCB circuit boards have the following reasons for the laminated structure:
1. low cost: due to one less layer of dielectric and foil, odd PCB raw material costs are slightly lower than even PCB, but the processing cost of odd PCB is significantly higher than even PCB. when the processing cost of the inner layer is the same, the foil core structure of the odd layer obviously increases the processing cost of the outer layer. Odd-numbered PCBs need to add a non-standard laminated core layer bonding process on top of the core structure process. Factory productivity is reduced with a foil coating on the outside of the core structure compared to the core structure. The outer core requires additional processing before lamination and bonding, which increases the risk of outer layer scratches and etching errors.
2. Balance the development of the structure to avoid the emergence of bending: do not use an odd number of layers to design PCB because odd-layer circuit boards are prone to bending. When the PCB is cooled after the multilayer circuit bonding process, the core structure and the foil laying structure as well as the different lamination tensions during cooling can cause the PCB to bend. As the thickness of our circuit boards increases, the greater the risk of composite PCB bending with the different economic structures of the two Chinese countries. The key to eliminating circuit board bending is that we use this balanced lamination. Although there is a certain degree of culture bending PCB to meet the social norms management requirements, but the subsequent data processing efficiency will be reduced, resulting in an increase in the cost of enterprise costs. Because assembly requires students special equipment and processes, component placement accuracy is reduced, so it will damage the quality of the environment. Simple question to say they are: in the PCB process optimization process, four-layer board than the three-layer board is good control, mainly focusing on the symmetry of the relationship between the four-layer board, the degree of warpage analysis can be effectively controlled below 0.7% (IPC600 standard), but because of the relative size of the three-layer board, the warpage will be more than the U.S. this industry standard, this will affect the SMT patch and the entire company's product Reliability, so teachers are generally designers do not understand the design of odd-layer boards, even if the life needs an odd number of layers to achieve the educational function, but also will be designed as a false even number of layers, that is, the five-layer design into six-layer, seven-layer design into eight-layer board.
For the above reasons, most PCB multilayers are designed with even layers and fewer odd layers.
But if the design has an odd number of PCB layers, how to balance the stackup and reduce the cost? Here are a few ways to balance the stackup, reduce PCB manufacturing cost and avoid PCB bending.
1)Use Signal Layers: This method can be used if the PCB is designed with an even number of power layers and an odd number of signal layers.
2)Add additional power layers:This method can be used if the PCB has an odd number of power layers and an even number of signal layers. An easy way to do this is to add a layer in the middle of the stack without changing the other settings. First route the PCB by the odd-numbered layers, then copy the ground layer in the middle and mark the remaining layers. This is the same as thickening the electrical characteristics of the foil coating in the middle ground layer.
3) Add a blank signal layer near the center of the PCB stack: this method of teaching as well as minimally systematizing the
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