PCB News - The core of PCB design-problem solving

Printed circuit board (PCB) design refers to the production of circuit boards at the lowest possible cost through designing principle drawings and circuit layout. In the past, this was usually done with the help of expensive special tools, but now, with the increasing popularity of free high-performance software tools-such as DesignSpark PCB-and design models, the PCB design speed of circuit board designers has been greatly accelerated .

Although engineering designers know that a perfect design plan is the best way to avoid problems, it is still a waste of time and money, and at the same time address the symptoms and not the root cause. For example, if a problem is found during the electromagnetic compatibility (EMC) testing phase, it will cause a lot of cost investment, and even need to adjust and reproduce the original design, which will take several months.

challenge

Layout is the first issue that designers have to face. This problem depends on part of the content in the drawing, and some devices need to be set together based on logical considerations. However, it should be noted that components that are more sensitive to temperature, such as sensors, should be installed separately from components that generate heat, including power converters. For designs with multiple power settings, 12 volt and 15 volt power converters can be set in different positions on the PCB board, because the heat and electronic noise they generate will affect the reliability and performance of other components and the PCB board.

The above components will also affect the electromagnetic performance of the circuit design. This is not only important for the performance and energy consumption of the circuit board, but also has a great impact on the economics of the circuit board. Therefore, all circuit board equipment sold in Europe All must obtain the CE mark to prove that it will not cause interference to other systems. However, this is usually only in terms of power supply, and there are many devices that emit noise, such as DC-DC converters, and high-speed data converters. Due to the flaws in the circuit PCB boarddesign, these noises can be captured by the channel and radiated as a small antenna, resulting in spurious noise and frequency abnormal areas.

The problem of far-field electromagnetic interference (EMI) can be solved by installing a filter at the noise point or using a metal shell to shield the signal. However, adequate attention is paid to the equipment that can release electromagnetic interference (EMI) on the circuit board, which allows the circuit board to choose a cheaper shell, thereby effectively reducing the cost of the entire system.

In the circuit board design process, electromagnetic interference (EMI) is indeed a factor that has to be taken seriously. Electromagnetic crosstalk can be coupled with the channel, thereby disrupting the signal into noise and affecting the overall performance of the circuit board. If the coupling noise is too high, the signal may be completely covered, so a more expensive signal amplifier must be installed to restore normal. However, if the signal circuit layout can be fully considered at the beginning of the circuit board design, the above problems can be avoided. Since the design of the circuit board will vary according to different equipment, different places of use, different heat dissipation requirements, and different electromagnetic interference (EMI) conditions, the design template will come in handy.

Capacitance is also an important issue that cannot be ignored in circuit board design, because capacitance will affect signal propagation speed and increase power consumption. The channel will be coupled with the lines next to it or vertically traverse two circuit layers, thus unintentionally forming a capacitor. By reducing the length of the parallel lines, adding a kink to one of the lines to cut off the coupling, etc., the above-mentioned problems can be relatively easily solved. However, this also requires engineering designers to fully consider the production design principles to ensure that the design is easy to manufacture, while avoiding any noise radiation caused by the excessively large bending angle of the circuit. The distance between the lines may also be too close, which will produce short loops between the lines, especially at the bends of the lines. Over time, metal "whiskers" will appear. Design rule detection can usually indicate areas where the loop risk is higher than normal.

This problem is particularly prominent in the design of the ground plane. A metal circuit layer may form a coupling with all the lines above and below it. Although the metal layer can effectively block noise, the metal layer also generates associated capacitance, which affects the running speed of the line and increases the power consumption.

As far as the design of multi-layer circuit boards is concerned, the through-hole design between different circuit board layers is probably the most controversial issue, because the through-hole design will bring many problems to the production of the circuit board. The through holes between the layers of the circuit board will affect the performance of the signal and reduce the reliability of the circuit board design, so full attention should be given.

solution

In the printed circuit board (PCB) design process, many different methods can be adopted to solve various problems. Among them, there are not only the adjustment of the design plan itself, such as adjusting the circuit layout to reduce noise; there are also methods for the layout of the printed circuit board. Design components can be automatically installed through the layout tool, but if the automatic layout can be manually adjusted, it will help improve the quality of the circuit board design. Through this measure, the design rule detection will rely on technical documents to ensure that the design of the circuit board can meet the requirements of the PCB circuit board manufacturer.

Separating different circuit board layers can reduce the associated capacitance. However, this will increase the number of circuit board layers, thereby increasing costs and bringing more through-hole problems. Although the use of an orthogonal grid power supply system and grounding circuit design may increase the physical size of the circuit board, it can effectively play the role of the ground layer in the double-layer circuit board and reduce the capacitance and complexity of circuit board manufacturing.

Design tools including DesignSpark PCB can help engineering designers solve many problems at the beginning of design, but engineering designers still need to have a full understanding of the design requirements of printed circuit boards (PCBs). For example, if a PCB board(PCB) editor needs to understand the number of layers of the circuit board at the beginning of the design, for example, a double-layer circuit board needs a ground layer and a power supply Layer, composed of two independent layers. The automatic component layout technology is very useful and can help designers spend more time designing the layout area of the device. For example, if the power supply device is too close to sensitive signal lines or areas with higher temperatures, There will be a lot of problems. In the same way, signal lines can also be automatically routed, while avoiding most of the problems. However, the analysis and manual operation of high-risk areas will help greatly improve the quality of printed circuit board (PCB) design, Improve revenue and reduce overall costs.

Design rule detection is also a very powerful tool, which can detect lines to ensure that the distance between the lines is not too close, thus causing the loop to be too short. However, the overall design still has high economic value. The design planning detection tool can also be used to detect and adjust the power layer and ground layer to avoid large associated capacitance areas.

The above tools will also be of great help to Gerber and Excellon, helping them to print circuits and circuit boards, as well as through-hole drilling, in order to produce the final design products. In this way, the technical documentation is closely linked to the circuit board manufacturer.

in conclusion

Many issues need to be considered in the design of printed circuit boards (PCB), and tools including DesignSpark PCB can effectively deal with most of these issues. By adopting certain best practice guidelines, engineering designers can effectively reduce costs and improve circuit board reliability, while meeting system specifications and deflection system certification at a lower cost, thereby avoiding more problems.