As a PCB engineer, what should I pay attention to in Lay PCB?
1. After the power supply comes in, it goes to the filter capacitor first, and after it comes out of the filter capacitor, it is sent to the subsequent equipment. Because the wiring on the PCB is not an ideal wire, there are resistance and distributed inductance. If the power is taken from the front of the filter capacitor, the ripple will be relatively large, and the filtering effect will be poor.
2. The lines must be exquisite: wide lines should never be thin if possible, sharp chamfers are not allowed, and right angles are not allowed to bend. The ground wire should be as wide as possible, and it is best to use a large area of copper, which can greatly improve the problem of grounding points.
3. Capacitors are provided for switching devices (gate circuits) or other components that require filtering/decoupling. These capacitors should be placed as close to these components as possible, and too far away will have no effect.
When laying PCB (power board), what are the key points to pay attention to in combination with safety requirements?
1. The minimum safe distance between the two wires before the fuse is not less than 6mm, and the minimum safe distance between the two wires and the chassis or internal grounding is not less than 8mm.
3. The minimum creepage distance between the high-voltage area and the low-voltage area is not less than 8MM, less than 8MM or equal to 8MM. A 2MM safety slot must be opened.
2. The wiring requirements after the fuse: the minimum creepage distance of the zero and live wires is not less than 3MM.
4. The high-voltage area must have a silk screen with high-voltage warning signs, that is, a triangle symbol including an exclamation point; the high-voltage area must be framed with silk screen, and the frame strips must be not less than 3MM.
5. The minimum safety distance between the positive and negative of the high-voltage rectifier filter is not less than 2MM
What is the design process of switching power supply pcb?
1. Make the schematic diagram according to the design
2. After the schematic is compiled and passed, the corresponding network table can be generated
3. Make a physical border (Keepout Layer)
4. The introduction of components and networks
5. Component layout: The layout and wiring of components have a great impact on product life, stability, and electromagnetic compatibility, so special attention should be paid. Generally speaking, there should be the following principles: ⑴ Placement order first place the components related to the structure in a fixed position, such as power sockets, indicator lights, switches, connectors, etc. After these components are placed, use the LOCK function of the software to switch them Lock it so that it will not be moved by mistake in the future. Then place special components and large components on the circuit, such as heating components, transformers, ICs, etc. Finally, place the small device. ⑵ Pay attention to heat dissipation The component layout should also pay special attention to the heat dissipation problem. For high-power circuits, the heating elements such as power tubes, transformers, etc. should be placed as close to the side as possible to facilitate heat dissipation. Do not concentrate in one place, and do not have high capacitors too close to avoid premature aging of the electrolyte.
6. Wiring
7. Adjustment and perfection: After completing the wiring, all you need to do is to adjust the text, individual components, wiring, and apply copper (this work should not be too early, otherwise it will affect the speed and bring trouble to the wiring), the same is In order to facilitate production, debugging and maintenance. Copper coating usually refers to filling the blank area left by the wiring with a large area of copper foil. It can be laid on GND copper foil or VCC copper foil (but this way, it is easy to burn the device once a short circuit, so it is best to ground it, unless it is necessary to use it. To increase the conduction area of the power supply, to withstand a larger current before connecting to VCC). Grounding usually refers to wrapping a bunch of signal wires with special requirements with two ground wires (TRAC) to prevent them from being interfered with or interfered with by others. If you use copper to replace the ground wire, you must pay attention to whether the entire ground is connected, the current size, flow direction and whether there are special requirements to ensure that unnecessary errors are reduced.
8. Check and check: Sometimes the network relationship of the board drawn is different from the schematic diagram due to misoperation or negligence on the network. At this time, check and check are necessary. So don’t rush to hand it over to the plate maker after finishing the drawing, you should check it first, and then do the follow-up work.
In the design, how should the PCB design and the mechanism design be unified? The height limit is required, and the component layout should not cause assembly interference; the design of the PCB shape, positioning holes, mounting holes, etc. should consider the PCB shape and size of the PCB manufacturing. The PCB shape and size should be consistent with the structural design. The device selection should meet the processing error of the structure and the processing error of the structure. The PCB layout selection assembly process should maximize the production efficiency; the designer should consider whether the board shape design minimizes the problem of the assembly process, that is, multi-layer board or double board. Can the panel design be replaced with a single panel? Can each side of the PCB be completed with an assembly process? Can manual soldering be avoided as much as possible? Can the plug-in components used be replaced with SMD components? The package of the selected components should be The physical object is unified, and the spacing and size of the pads meet the design requirements; the components are evenly distributed, especially the high-power devices are dispersed, to avoid local overheating on the PCB when the circuit is working, which will affect the reliability of the solder joints; consider the reliability of high-power devices Heat dissipation design; under the conditions of design permission, the layout of components should be arranged in the same direction as much as possible, and modules with the same function should be arranged together; components of the same package should be placed at equal distances for component placement, Welding and inspection; the silk screen is clearly distinguishable, the polarity and direction are clearly indicated, and it is not blocked by the assembled device. What are the materials of the PCB version? What are the commonly used materials for the PCB of the switching power supply? 1, 94V-0, 94V-2 belong to a class of flame-retardant materials, and of these two, 94V-0 is the highest flame-retardant material Kind.
In terms of material, it can be divided into organic material and inorganic material
a. Organic material: Phenolic resin, glass fiber/epoxy resin, Polyimide, BT/Epoxy, etc. are all included.
b. Inorganic materials: aluminum, Copper-invar-copper, ceramic, etc.
2. Aluminum substrate PCB
Briefly describe the material recognition process
1. Carry out a single test on the sample, and put forward a "sample test report". For certain test items that require special equipment, the manufacturer's test can be used as a reference. For foreign well-known brand crystal semiconductors, plastic parts and packaging materials, individual tests are not required, but Various types of material samples need to have practical installation and use tests, and the results will be used as an important basis for the final judgment;
2. Use the test and use the result as an important basis for the final judgment. The R&D department checks the test results of the sample with the specifications in the acknowledgment to determine the consistency of the acknowledgment and the sample, and check the integrity of the content of the acknowledgment;
3. For materials that fail the single test or the approval letter does not meet the requirements, request the purchase to provide a new sample and approval letter;
4. For certain key materials, after the R&D department has passed the monomer test, the R&D department will apply for a small batch trial investment, the production department will lead the trial investment work, and the quality control department will be responsible for the verification of the trial investment materials;
5. After the material sample approval certificate and trial investment (critical materials) are qualified, attach the cover of the "material approval certificate" and seal the sample (plastic parts and packaging materials can only be sealed as samples), and issued after approval by the R&D manager To relevant departments.
