How to make a good PCB

We all know that PCB is to turn the designed schematic diagram into a real PCB Board. Please do not underestimate this process. There are many things that work in principle that are hard to implement in the project, or what others can achieve, but others cannot. Therefore, it is not difficult to do a PCB, but it is not easy to do a PCB. The two major difficulties in the Microelectronics field are the processing of high-frequency and weak signals. In this regard, the PCB production level is particularly important. The same principle design, the same components, the PCB produced by different people has different results. How can we make a good PCB? Based on our past experience, I would like to share my views on the following aspects: I. Clear design objectives To accept a design task, we must first clarify its design objectives: General PCB, high-frequency PCB, small-signal processing PCB, or PCB with both high-frequency and small-signal processing, if it is an ordinary PCB, as long as the layout and wiring are reasonable and tidy, the mechanical size is accurate, if there is a medium load line and long line, it is necessary to use a certain means to deal with, reduce load, to enhance the drive for the long line, the focus is to prevent the long line reflection. When there is a signal line over 40 MHz on the board, special consideration should be given to these signal lines, such as crosstalk between lines. If the frequency is higher, there will be more stringent restrictions on the length of the wiring. According to the network theory of the distribution parameter, the interaction between the high-speed circuit and its connection is the decisive factor, you cannot ignore this feature during system design. As the door transmission speed increases, the opposition on the signal line will increase accordingly, and the crosstalk between adjacent signal lines will increase in a proportional manner. Generally, the power consumption and heat dissipation of High-Speed Circuits are also very high, high-Speed PCB should be paid enough attention. When the board has a millivolt or even microvolt level weak signal, special attention is required for these signal lines. Because the small signal is too weak, it is very vulnerable to interference from other strong signals, blocking measures are often necessary. Otherwise, the signal-to-noise ratio will be greatly reduced. So that useful signals are overwhelmed by noise and cannot be effectively extracted. The commissioning and testing of the Board should also be considered in the design phase. factors such as the physical location and isolation of the test points cannot be ignored, because some small and high-frequency signals cannot be directly added to the probe for measurement. In addition, we also need to consider other related factors, such as the number of layers of the Board, the encapsulated shape of components, and the mechanical strength of the Board. Before making PCB, you should be aware of the design objectives of the design. II. Measure the test taker's knowledge about the layout and wiring requirements of the components used. We know that some special components have special requirements for layout and wiring, such as the analog signal amplifiers used by Loti and APH. The analog signal amplifiers require stable power supply and small ripple. To simulate a small signal, try to stay away from the power device. On the Oti board, the Small Signal Amplification part also has a special shielding cover to shield stray electromagnetic interference. The glink chip used on the ntoi Board adopts the ECL process, causing high power consumption and heat dissipation. Special consideration must be given to the heat dissipation problem during layout. If natural heat dissipation is used, the glink chip should be placed in a place where the air flow is relatively smooth, and the heat generated cannot have a big impact on other chips. If the Board is equipped with speakers or other high-power devices, it may cause serious pollution to the power supply.   Iii. Component layout considerations One of the first factors to consider the layout of components is the electrical performance. Put components with close connections together as much as possible, especially for some high-speed lines, the layout should be as short as possible, power signals and small-signal devices must be separated. When the circuit performance is met, components must be neatly arranged and beautifully arranged to facilitate testing. The mechanical size of the Board and the position of the socket must also be carefully considered. The transmission delay time on the grounding and interconnectivity in high-speed systems is also the first factor to be considered during system design. The transmission time on the signal line has a great impact on the overall system speed, especially for the High-Speed ECL circuit, although the integrated circuit block itself is very fast, however, the system speed can be greatly reduced due to the increase in latency caused by the use of common interconnectivity (latency of about 2 NS every 30cm lines) on the baseboard. for example, a shift register, a synchronization counter is recommended to be placed on the same plug-in board. Because the transmission delay time of clock signals to different plug-in boards is not equal, the shift register may cause a master error, if it cannot be placed on a board, synchronization is the key. The clock lines connecting from the public clock source to the plug-in board must be of the same length.