Pcb multilayer board is a kind of unique printed board, and its existence “address” is generally unique. For example, there will be pcb multilayer board in the circuit board. This kind of multilayer board can help the equipment to switch on and off various routes. It is worth mentioning that it can also have the actual effect of insulating layer, and it is not easy for electricity and electricity to collide with each other, thus ensuring safety.
If you want to apply it to a pcb multilayer board with better characteristics, you must plan it carefully, and then tell everyone how to design the pcb multilayer board.
Design scheme of PCB multilayer board
1. The design, specification and number of superimposed layers of 1.pcb multilayer board are clear.
1) All printed boards have the problem of assembly line matching with other parts. Therefore, the appearance design and specifications of printed boards must be based on the whole equipment structure of commodities. However, from the perspective of production process, it should be as simple as possible, generally a square with a small width-height ratio, so as to improve the productivity of the assembly line and reduce the cost of workers.
2) The stacking layer level must be determined according to the regulation of power circuit characteristics, board specifications and the aggregation level of routes. For double-layer printed boards, four-layer boards and six-layer boards are more commonly used. According to the characteristics of four-layer boards, there are two conductor layers (component surface and electric welding surface), one power layer and one geological structure.
3) Each layer of multilayer board should maintain symmetry, and it is best to have even copper layers, i.e. four, six, eight layers, etc. Because of the different lamination, the surface is very easy to swell and shrink, especially for the multilayer board with surface patches, which should be paid more attention to.
2. Position and placement orientation of 2.pcb multilayer components
1) The position and placement orientation of components should first be considered from the level of circuit principle, and comply with the trend of power supply circuit. Whether the placement is effective or not will immediately endanger the characteristics of the printed circuit board, which is a high-frequency digital integrated circuit. It seems that the requirements for the location and placement of components are more stringent.
2) Effective placement of components, to some extent, has already heralded the success of the PCB design scheme. Therefore, in the case of editing the printed circuit boards and deciding the overall reasonable layout, we should make a detailed analysis of the circuit principle, first identify the positions of unique components (such as large-scale IC, high-power tube, video signal, etc.), and then allocate other components to minimize the factors that will affect it.
3) On the other hand, the overall structure of the printed circuit board should be taken into consideration to prevent the uneven ordering of components and components. This not only jeopardizes the beauty of printed boards, but also causes a lot of troubles in assembly lines and maintenance work.
3. The provisions of the wire cloth layer and wiring area
Under normal circumstances, the wiring of double-layer printed boards is carried out according to the function of power supply circuit. When wiring on the surface layer, it is stipulated that there are more wiring on the welding surface and less wiring on the component surface, which is beneficial to the maintenance and troubleshooting of printed boards. Thin and dense wires and affected power cables are generally distributed on the inner floor.
Large-scale copper deposits should be evenly distributed inside and on the surface, which will help to reduce the expansion and contraction of the plate, and also make the plating process get a more symmetrical coating on the surface. In order to avoid the appearance design, production and processing hurting the printed wires and the virtual beam short circuit fault caused by mechanical processing and manufacturing, the distance between the conductive pattern of the inner surface wiring area and the board edge should exceed 50mil.
4. The requirements of traverse direction and graphic boundary.
Multilayer wiring should separate the power supply layer, geological structure and data signal layer, and reduce the influence of switching power supply, ground and data signal. The wireframes of adjacent double-layer printed boards should be vertical to each other as much as possible, or take slashes and curves, instead of straight lines, so as to reduce the coupling and influence of virtual beams of base steel plates.
And the wires should be as short as possible, especially for the small data signal power supply circuit. The fewer wires, the smaller the resistor and the smaller the influence. The power cord on the same floor should be protected from obtuse turning when changing direction. The width of the wire should be defined according to the current and characteristic impedance of the power supply circuit. The input line of the switching power supply should be larger, and the relativity of the power supply line should be smaller.
Generally speaking, for large digital boards, 50 ~ 80 mil can be used for the key line of switching power supply, and 6 ~ 10 mil can be used for the power line.
Total width of conductor: 0.5, 1, 0, 1.5, 2.0;
Allowable current: 0.8, 2.0, 2.5, 1.9;
Wires: 0.7, 0.41, 0.31, 0.25;
When wiring, we should also pay attention to the total width of the wireframe to be as consistent as possible, so as to prevent the wires from suddenly widening and narrowing, which is beneficial to the matching of characteristic impedance.
5. The regulation of hole size and welding layer
1) The punch size of the components on the multilayer board is related to the pin size of the components used. If the punch size is too small, it will endanger the mounting and soldering of the components; Excessive punching and insufficient round spot welding during electric welding. Generally speaking, the calculation methods of hole diameter and solder layer size of components are as follows:
2) Diameter of component hole = diameter of component pin (or straight line)+(10 ~ 30 mil)
3) The diameter of component welding layer ≥ the diameter of component hole +18mil
4) For the diameter of via hole, the key is to decide the thickness of finished board. For multilayer board with high density, it should generally be controlled in the range of board thickness: diameter ≤ 5: 1. The via layer is calculated as follows:
5) VIAPAD diameter ≥ via diameter +12mil.
6. Provisions of power layer, geological structure system partition and flower hole
For double-layer printed boards, there is at least one power layer and one geological structure. Because all the working voltages on the printed circuit board are connected to the same power supply layer, it is necessary to carry out system partition protection on the power supply layer. Generally, the size of the system partition line is 20 ~ 80 mil, and the working voltage is extremely high, and the thicker the system partition line is.
In order to improve the credibility of the connection between the welding hole and the power supply layer and geological structure and reduce the virtual connection caused by large-scale endothermic reaction of metal materials in the whole process of electric welding, the general connection plate should be designed with a flower hole. Diameter of welding layer ≥ hole diameter +50mil.
7. Provisions of safety interval
The setting of safety interval should consider the provisions of electricity safety. Generally speaking, the minimum spacing of the surface conductor shall not be less than 2mil, and the minimum spacing of the inner conductor shall not be less than 2mil. Under the condition that the wiring can be discharged, the interval should be as large as possible, so as to improve the output rate of plate-making process and reduce the potential safety hazards of common faults of finished boards.
8. Provisions for improving the anti-interference performance of the whole PCB
In the design scheme of double-layer printed circuit board, we must also pay attention to the anti-interference of the whole PCB. The general ways are:
A. add filter capacitors around the switching power supply and ground of each IC, and the volume is generally 473 or 104.
B. For sensitive data signals on printed boards, accompanying shielded cables should be added respectively, and wiring around video signals should be avoided as much as possible.
C. Choose a valid pick-up address.
Have you mentioned many pcb multilayer design schemes and methods for a long time? In response to the high-speed development trend of electronic products nowadays, the pcb design scheme encounters such a development trend of excellent performance, high speed, multi-layer and lightness. The PCB design of high-speed data signals is becoming the most important and difficult problem in the hardware development of electronic devices, and it pays more attention to high efficiency and meticulous care.
