In the pcb design, there are, in fact, long steps ahead of the formal wiring. The following are the main design processes:
1. System specifications
The system specifications for the electronic equipment should first be planned. It includes system functions, cost limits, size, operation, etc。
2. System functional blocks figure
The next step is to make the system's functional block map. The relationship between blocks must also be marked。
3. Splitting of several pcb systems
Splitting the systems into several pcbs would not only be reduced in size, but also give the system the ability to upgrade and exchange spare parts. The system functional blocks provide the basis for our division. It's like computers can be divided into mainframe boards, display cards, sound cards, diskettes and power supplies。
4. Decides to use containment methods and the size of each pcb
When the technology and the number of circuits used by the pcb are determined, the size of the plate is determined. If the design is too large, then the containment technology will change, or be re-divided. In selecting technologies, the quality and speed of the road map are also considered。
5. Mapping of all pcb circuits
Details of interconnectivity between parts are to be shown in the overview. The pcb in all systems has to be mapped out, and is now mostly cad (computer-aided design, computer aided design)。
Pcb circuit overview
The initial simulation was designed to ensure the proper functioning of the designed circuit map, which had to be simulated by computer software. This type of software allows for the reading of overview maps and displays the operation of circuits in many ways. This is more effective than actually making a sample pcb and then measuring manually。
Put the parts on the pcb
The manner in which the parts are placed is determined by how they are connected. They must be connected to the path in the most efficient manner possible. The more efficient the wiring is, the shorter the strings and the fewer the layers, which at the same time reduces the number of pitfalls, the better, although we will revert to it when the real wiring is done. Here's how the currents line up on the pcb. In order for all parts to have a perfect line, the location is important。
Test wiring possibilities and the proper operation at high speed
Part of the computer software is now available to check whether the parts are located correctly or whether they operate at high speed. This step is called the placement of spare parts, but we will not go too far into this. If there is a problem with the design of the circuit, the spare parts can also be repositioned before they are exported from the field。
Export pcb line
The connections in the maps will now be made in the field as wiring. This step is usually entirely automatic, although there is generally a need to change certain parts manually. Here's the model of a two-story steering line. Red and blue lines, respectively, representing the parts and welding layers of pcb. The white text and the quadrilateral representation are the symbols on the print page of the web. Red dots and circles represent drilling holes and guidance holes. On the right we can see gold fingers on the welded side of the pcb. The final picture of the pcb is usually called the work film。
Each design must meet a set of requirements, such as the minimum gap between lines, the minimum width of lines, and other similar practical limitations. These provisions differ according to the speed of the circuit, the strength of the transmission signal, the sensitivity of the circuit to electricity consumption and miscellaneous communications, and the quality of the material and the equipment for its manufacture. If the current intensity rises, the fineness of the fuse must also increase. In order to reduce the costs of the pcb, the reduction of layers must be accompanied by attention to whether these provisions remain consistent. If more than two layers of construction are required, the power layer as well as the surface layer are usually used to avoid damage to the transmission signal on the signal layer and can be used as a shield on the signal layer。
Post-wire circuit testing
In order to determine that the line is functional after the guide, it must pass the final test. This test can also check if there is an incorrect connection and all links follow the profile。
Establishment of production files
Because there are currently many cad tools for pcb design, manufacturers must have a light file to make the tablet. There are several types of light specifications, although the most common is the gerber fields specifications. A group of gerber files consists of a flat map of the signals, the power supply and the surface layer, a flat map of the weldproof layer and the print surface of the netboard, and a specified archive of drilling and extraction。
Electromagnetic compatibility issues
The absence of electronic equipment designed to follow the emc specifications is likely to emit electromagnetic energy and interfere with nearby appliances. Emc imposes maximum restrictions on electromagnetic interference (emi), electromagnetic field (emf) and radio frequency interference (rfi). This provision ensures the proper operation of the electrical appliances with other nearby appliances. Emc has strict limits on the energy of a device to disperse or transfer to another and is designed to reduce the magnetic rate of external emf, emi, rfi, etc. In other words, the purpose of this provision is to prevent the entry of electromagnetic energy or its release from the device. This is in fact a difficult problem, and most of it usually uses power and surface layers or places pcb in metal boxes to address these problems. Power and surface layers can prevent interference with the signal layer, and metal boxes have similar utility. We can only go deeper on these issues。
The maximum speed of the circuit depends on how it's done. The internal emi, like electrical run-off between the conductors, increases with frequency. If the current gap between the two is too large, it is important to keep the distance between the two. It also tells us how to avoid high pressure and minimize current consumption on circuits. The delayed rate of wiring is also important, so naturally the shorter, the better. So a well-wired little pcb would be better suited to operate at high speed than a big pcb。
