Four considerations for PCB board design

In PCB board design, for engineers, circuit design is the most basic. However, many engineers are often careful and careful when designing complex and difficult PCB boards, but ignore some points to be paid attention to when designing basic PCB boards, which leads to errors. It may make a perfect circuit diagram have problems or be completely broken when it is converted into a PCB board. Therefore, in order to help engineers reduce design changes in PCB board design and improve work efficiency, here are several aspects to pay attention to in the PCB board design process.

Design of heat dissipation system in PCB board design

In the PCB board design, the design of the heat dissipation system includes the cooling method and the selection of heat dissipation components, as well as the consideration of the coefficient of cold expansion. Now the commonly used methods of PCB board heat dissipation are: heat dissipation through the PCB board itself, adding a heat sink and a heat conduction plate to the PCB board, etc.

In the traditional PCB board design, since the boards are mostly copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, and a small amount of paper-based copper-clad sheets are used, these materials have good electrical properties and processing properties, but thermal conductivity. Performance is poor. Due to the large use of surface-mounted components such as QFP and BGA in the current PCB board design, a large amount of heat generated by the components is transferred to the PCB board. Therefore, the most effective way to solve the heat dissipation is to improve the heat dissipation of the PCB board itself that is in direct contact with the heating element. The power is conducted or radiated through the PCB board.

When there are a few devices on the PCB board that generate a large amount of heat, a radiator or heat pipe can be added to the heating device on the PCB board; when the temperature cannot be lowered, a radiator with a fan can be used. When there are many heat-generating components on the PCB board, a large heat-dissipating cover can be used, and the heat-dissipating cover can be buckled on the surface of the component as a whole, so that it can be in contact with each component on the PCB board to dissipate heat. For professional computers used for video and animation production, it is even necessary to use water cooling to cool down.

Component selection and layout in PCB board design

When designing a PCB board, it is undoubtedly necessary to face the choice of components. The specifications of each component are different. PCB proofing may have different characteristics of components produced by different manufacturers of the same product. Therefore, for the selection of components during PCB board design, you must contact the supplier to know the characteristics of the components. , and understand the impact of these characteristics on PCB board design.

At present, choosing the right memory is also very important for PCB board design. Due to the continuous updating of DRAM and Flash memory, it is a big challenge for PCB board designers to make new designs not affected by the memory market. Therefore, PCB board designers must keep a close eye on the memory market and maintain close ties with manufacturers.

In addition, necessary calculations must be made for some components with large heat dissipation, and their layout also needs special consideration. When a large number of components are together, more heat can be generated, which will cause the solder mask to deform and separate, and even ignite the entire PCB. board. So PCB board design and layout engineers must work together to ensure that components have a suitable layout.

The layout should first consider the size of the PCB board. When the size of the PCB board is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase; if the PCB board size is too small, the heat dissipation will be poor, and the adjacent lines will be easily interfered. After determining the size of the PCB board, determine the location of special components. Finally, according to the functional units of the circuit, all components of the circuit are laid out.

Design for Testability in PCB Design

The key technologies of PCB testability include: testability measurement, testability mechanism design and optimization, and test information processing and fault diagnosis. The testability design of the PCB board is actually introducing a testability method that can facilitate the test to be introduced into the PCB board to provide an information channel for obtaining the internal test information of the tested object. Therefore, the rational and effective design of the testability mechanism in PCB manufacturing is the guarantee to successfully improve the testability level of the PCB board. To improve product quality and reliability, and reduce product life cycle costs, it is required that testability design technology can easily and quickly obtain feedback information during PCB board testing, and can easily make fault diagnosis based on the feedback information. In the PCB board design, it is necessary to ensure that the detection position and entry path of the DFT and other probes will not be affected.

With the miniaturization of electronic products, the pitch of components is getting smaller and smaller, and the mounting density will also increase. There are fewer and fewer circuit nodes available for testing, so online testing of printed board assemblies is becoming more and more difficult. Therefore, the electrical conditions and physical and mechanical testability of printed boards should be fully considered when designing PCB boards. conditions, tested with appropriate mechatronic equipment.

MSL: MoisureSensitiveLevel, that is, the moisture sensitivity level, which is described on the label outside the moisture-proof packaging bag, and is divided into eight levels: 1, 2, 2a, 3, 4, 5, 5a, and 6. Components that have special requirements for humidity or are marked with humidity-sensitive components on the packaging must be effectively managed to provide the temperature and humidity control range for material storage and manufacturing environments, so as to ensure the reliability of the performance of temperature and humidity-sensitive components. When baking, BGA, QFP, MEM, BIOS, etc. require perfect vacuum packaging. Components that are resistant to high temperature and those that are not resistant to high temperature are baked at different temperatures. Pay attention to the baking time. PCB board baking requirements first refer to PCB board packaging requirements or customer requirements. After baking, the humidity-sensitive components and PCB boards should not exceed 12H at room temperature. The unused or unused humidity-sensitive components or PCB boards that do not exceed 12H at room temperature must be sealed with vacuum packaging or placed in a dry box. put.