1. When the distance between the route and the edge of the plate is less than 25 mm, the characteristIC impedance value of the route is 1~4 ohm smaller than the middle of the plate, while when the distance between the route and the edge of the plate is more than 50 mm, the change range of the characteristic impedance value affected by the position hazard is reduced. Under the prEMIse of considering the utilization rate of the panel, it is proposed to select the cutting gauge first, considering that the distance between the characteristic impedance line and the edge of the plate is more than 25 mm;
2. The most critical factor endangering the unity of characteristic impedance of pcb Circuit board assembly is the symmetry of different parts, followed by the symmetry of graphic boundary;
3. The difference of copper residue rate at different parts of pcb circuit board will lead to the difference of characteristic impedance of 1~4ohm. When the uniformity of patterns is weak (the difference of copper residue rate is large), it is proposed to effectively pave the current blocking image and the separation point of electroplating process on the basis of not harming the characteristics of electrical equipment, so as to reduce the difference of dielectric thickness and barrel plating thickness at different parts;
4. The lower the mold closing force of the semi dry fixed sheet, the better the homogeneity of the dielectric thickness after lamination. The alternating flow of glue at the edge of the pcb circuit board will lead to smaller dielectric thickness and larger relative dielectric constant, which will result in the lower characteristic impedance value of the line near the edge of the board than that in the middle of the panel;
5 For the inner course, there is little difference in the unity of characteristic impedance due to the graphic boundary and copper thickness at different parts of the panel; For the surface route, the harm of copper thickness difference to the characteristic impedance is within 2 Ohm, but the difference of etching process graph boundary caused by copper thickness difference is very harmful to the unity of characteristic impedance, so it is necessary to improve the function of surface barrel plating uniformity.
What are the causes of PCB board heating?
1. Incorrect placement of components
Some high-power equipment need to reserve natural ventilation or forced ventilation position to dissipate heat. If there is no proper airflow cooling, the PCB will accumulate most of the heat, causing the temperature to rise, resulting in circuit performance degradation or damage. It should be noted that sensitive components should not be placed near components that emit a lot of heat; The temperature can be kept within a safe range through proper heat dissipation and natural cooling or forced cooling.
2. Environmental and external thermal factors
When using PCB in extreme temperature environment, if the temperature conditions in the target environment are not considered in the design, the electronIC components may be subjected to excessive pressure; Generally, electronic component manufacturers will provide specifications applicable to specific temperature ranges.
3. Wrong part and material selection
During the selection of electronic component materials, failure to follow the recommended guidelines may cause heat dissipation problems. When selecting electronic components, it is important to review detaiLED data and consider all relevant information related to power consumption, thermal resistance, temperature limits, and cooling technology. In addition, a fast power calculation is performed on the resistor to ensure that the rated power suitable for the application is selected. Another problem is the selection of PCB dielectric materials. The printed circuit board itself must be able to withstand the worst thermal conditions.
4. Defects in PCB design and manufacturing
Poor layout and manufacturing process can cause PCB thermal problems. Improper welding may hinder heat dissipation, and insufficient wire width or copper area may also cause temperature rise. To prevent heat dissipation, designers must reduce heat dissipation and use other cooling technologies when natural cooling is insufficient; The thermal optimization design needs to pay attention to the component specifications, PCB layout, PCB dielectric materials and environmental conditions.