In PCB board design, for engineers, circuit design is the most basic. However, many engineers tend to be cautious and careful in the design of complex and difficult PCB boards, while ignoring some points to be paid attention to in the design of basic PCB boards, resulting in mistakes. A perfectly good circuit diagram may have problems or be completely broken when converted to a PCB. Therefore, in order to help engineers reduce design changes and improve work efficiency in PCB design, several aspects to be paid attention to in PCB design process are proposed here.

Heat dissipation system design in PCB board design

In PCB board design, the cooling system design includes cooling method and cooling components selection, as well as the consideration of cold expansion coefficient. At present, the commonly used cooling methods of PCB board include: cooling by PCB board itself, adding radiator and heat conduction board to PCB board, etc.

In traditional PCB board design, copper/epoxy glass cloth substrate or phenolic resin glass cloth substrate are mostly used, as well as a small amount of paper copper coated plate, these materials have good electrical performance and processing performance, but poor thermal conductivity. Due to the large use of QFP, BGA and other surface mounted components in the current PCB board design, the heat generated by components is transmitted to THE PCB board in large quantities. Therefore, the most effective way to solve the heat dissipation is to improve the heat dissipation capacity of the PCB board directly in contact with the heating element, and conduct or emit it through the PCB board.

Notes for designing heat dissipation system on PCB board

Figure 1: PCB board design _ Heat dissipation system design

When a small number of components on the PCB board have high heat, heat sink or heat conduction tube can be added to the heating device of the PCB board; When the temperature cannot be lowered, a radiator with a fan can be used. When there is a large amount of heating devices on the PCB board, a large heat sink can be used. The heat sink can be integrated on the surface of the component so that it can be cooled by contacting each component on the PCB board. Professional computers used in video and animation production even need to be cooled by water cooling.

Selection and layout of components in PCB board design

In PCB board design, there is no doubt to face the choice of components. The specifications of each component are different, and the characteristics of components produced by different manufacturers may be different for the same product. Therefore, when selecting components for PCB board design, it is necessary to contact the supplier to know the characteristics of components and understand the impact of these characteristics on PCB board design.

Nowadays, choosing the right memory is also very important for PCB design. Because DRAM and Flash memory are constantly updated, it is a great challenge for PCB designers to keep the new design from the influence of memory market. PCB designers must keep an eye on the memory market and maintain close ties with manufacturers.

Figure 2: PCB board design _ Components overheating and burning

In addition, some components with large heat dissipation must be calculated, and their layout also needs special consideration. When a large number of components together, they can produce more heat, resulting in deformation and separation of welding resistance layer, or even ignite the whole PCB board. So PCB design and layout engineers must work together to ensure that components have the right layout.

The layout should first consider the size of the PCB board. When PCB board size is too large, printed line length, impedance increases, anti-noise ability decreases, cost also increases; If PCB board is too small, heat dissipation is not good, and adjacent lines are easy to be disturbed. After determining the size of PCB board, determine the location of special components. Finally, according to the functional unit of the circuit, all the components of the circuit are laid out.

Testability design in PCB board design

The key technologies of PCB testability include measurement of testability, design and optimization of testability mechanism, processing of test information and fault diagnosis. In fact, the design of testability of PCB board is to introduce some testability method to PCB board which can facilitate test

To provide an information channel for obtaining the internal test information of the object under test. Therefore, reasonable and effective design of testability mechanism is the guarantee to improve the testability level of PCB board successfully. Improve product quality and reliability, reduce the cost of product life cycle, testability design technology can easily obtain the feedback information of PCB board test, can easily make fault diagnosis according to the feedback information. In PCB board design, it is necessary to ensure that the detection position and entry path of DFT and other detection heads will not be affected.

With the miniaturization of electronic products, the pitch of components is becoming smaller and smaller, and the installation density is also increasing. There are fewer and fewer circuit nodes available for testing, so it is more and more difficult to test the PCB assembly online. Therefore, the electrical and physical and mechanical conditions of the testability of the PCB should be fully considered when designing the PCB board, and appropriate mechanical and electronic equipment should be used for testing.

Figure 3: PCB board design _ Testability design

PCB board design of moisture sensitivity grade MSL

Figure 4: PCB board design _ Moisture sensitivity level

MSL: Moisure Sensitive Level. It is marked on the label and classified into levels 1, 2, 2A, 3, 4, 5, 5A, and 6. Components that have special requirements on humidity or are marked with humidity sensitive components on the package must be managed effectively to provide temperature and humidity control range in the material storage and manufacturing environment, thus ensuring the reliability of performance of temperature and humidity sensitive components. When baking, BGA, QFP, MEM, BIOS and other requirements of vacuum packaging perfect, high-temperature and high-temperature resistant components 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, humidity sensitive components and PCB board should not exceed 12H at room temperature. Unused or unused humidity sensitive components or PCB board should be sealed with vacuum packaging or stored in drying box.

The above four points should be paid attention to in PCB board design, hoping to help engineers struggling in PCB board design.