PCB design process

As a PCB engineer, what should I pay attention to in lay PCB?

 

1. After the power supply comes in, first go to the filter capacitor. After the filter capacitor is obtained, it is sent to the following device. Because the cabling on the PCB is not an ideal wire, there is a resistor and a distribution inductance. If the power is obtained from the front of the filter capacitor, the ripple will be relatively large, and the filtering effect will not be good.

 

2. Exquisite lines: if conditions are met, the line shall not be fine, and there shall be no sharp chamfering or right angles. The ground wire should be as wide as possible. It is best to use a large area of copper, which greatly improves the connection location.

 

3. the capacitor is set for the switching device (door circuit) or other components that require filtering/decoupling. The arrangement of these capacitors should be as close as possible to these components, it does not work if you are too far away.

 

When lay PCB (Power Board) is combined with the safety requirements, what should be paid attention?

 

1. The minimum safe distance between the AC power supply wire and the fuse wire is not less than 6 MM. The minimum safe distance between the two wires and the chassis or the grounding inside the cabinet is not less than 8 MM.

 

2. wire routing requirements after fuses: The minimum electrical crawling distance between zero and FireWire is not less than 3 MM.

 

3. The minimum distance between the high-voltage zone and the low-voltage zone is not less than 8 MM, less than 8MM or equal to 8MM. 2MM Security slot is required.

 

4. The high-pressure area must have a high-pressure display logo silk screen, that is, there is a triangle symbol including the exclamation point; the high-pressure area must be framed with silk screen, and the box silk screen must be no less than 3 MM.

 

5. The minimum security distance between positive and negative values of high-voltage rectification filtering is not less than 2 MM.

 

Briefly describe the design and development processes.

 

1. Create a schematic diagram based on the design.

 

2. After the schematic diagram is compiled, a corresponding network table can be generated.

 

3. Create a physical border (keepout layer)

 

4. Introduction of components and networks

 

5. Component Layout

 

The layout and cabling of components have a great impact on product life, stability, and electromagnetic compatibility. In general, there should be the following principles: (1) Place components in fixed positions related to the structure first, such as power outlets, indicator lights, switches, connectors, etc, after these devices are placed, lock them with the lock function of the software so that they will not be moved by mistake in the future. Then place special components and large components on the line, such as heating components, transformer and IC. Finally, place the small device. (2) Pay special attention to the layout of heat dissipation components. For high-power circuits, heat-generating components, such as power pipes and transformers, should be placed in a decentralized layout as far as possible to facilitate heat distribution, rather than concentrated in one place, do not make high capacitance too close to avoid premature aging of electrolyte.

 

6. Wiring

 

7. Improved Adjustment

 

After wiring, you must make some adjustments to text, individual components, and cabling, and apply copper to the cables. (This operation should not be too early. Otherwise, it will affect the speed and cause wiring troubles ), it is also for convenience of production, debugging and maintenance. Copper Coating usually refers to the blank area left after the wiring is filled with copper foil with a large area. Gnd copper foil can be laid or VCC copper foil can be laid (however, once a short circuit is easy to burn the device, it is best to ground, unless you have to increase the conduction area of the power supply to withstand a large amount of current to connect to the VCC ). Generally, a ground wire (TRAC) is used to enclose a signal line with special requirements to prevent it from being disturbed or disturbed by others. If copper is used to replace the ground, you must pay attention to whether the whole earth is connected, the current size, the flow direction and whether there are special requirements, to ensure that unnecessary mistakes are reduced.

 

8. check and verify

 

Sometimes, the network relationship of the painted board is different from that of the schematic diagram due to misoperations or negligence. In this case, it is necessary to check the network. Therefore, after the painting, you cannot rush to hand it over to the plate manufacturer. You should first check it before proceeding with the subsequent work.

 

How Should PCB design and mechanism design be unified during design?

 

The layout of components should not cause Assembly interference. The PCB shape, positioning hole, and installation hole design should be consistent with the structure design in the PCB Manufacturing PCB shape and size, the component selection should meet the processing error of the structure and the processing error of the structure. The PCB layout selection process should have the highest production efficiency. The designer should consider whether the shape design can minimize the assembly process, that is, can the design of multiple or double panels be replaced by a single panel? Can each PCB side be used?

 

Is the assembly process complete? Can we eliminate manual welding as much as possible? Can I replace the inserted components with SMD components? The package of the selected components should be consistent with the physical products, and the welding Pad Spacing and size should meet the design requirements; uniform Distribution of components, especially high-power devices, to avoid stress caused by local overheating of the PCB during circuit operation, affecting the reliability of solder joints; Consider the heat dissipation design of high-power devices; when the design permits, the components should be arranged in the same direction as much as possible, and modules with the same functions should be arranged together; components with the same encapsulation should be placed at an equal distance, for component placement, welding and detection, silk screen printing is clearly identifiable, polarity, direction indication is clear, and is not blocked by the assembled devices.

 

What are the PCB layout materials? What are the commonly used PCB materials for switching power supply?

 

1, 94v-0, 94v-2 belongs to a class of flame retardant grade material, and the two kinds of 94v-0 belong to one of the highest flame retardant grade material.

 

Material can be divided into organic materials and inorganic materials.

 

A. Organic phenolic resin, glass fiber/epoxy resin, polyimide, BT/epoxy, etc.

 

B. inorganic materials such as aluminum, copper-Invar-copper, and ceramic

 

2. aluminum substrate PCB

 

Brief description of material recognition process

 

1. Conduct a standalone test on the sample and propose a "Sample Test Report". For some specialized instrument test projects, the vendor test can be used as a reference. crystal semiconductors, plastic parts and packaging materials of well-known foreign brands may not be tested individually. However, various types of material samples need to be installed and used for testing, and the results are used as an important basis for final determination;

 

2. Use tests and use these results as an important basis for final determination. The R & D department checks the test results of the samples with the specifications in the recognition documents to determine the consistency between the recognition books and the samples, check and acknowledge the integrity of the book content;

 

3. for materials that fail to pass the test or that do not comply with the requirements, the procurement is required to re-provide the samples and the letter of recognition;

 

4. For some key materials, after the R & D department passes a single test, the R & D department applies for a small batch trial investment. The production department leads the test investment, and the Quality Control Department is responsible for verifying the test materials;

 

5. After both the material sample recognition and Trial cast (key materials) are qualified, add the cover of the "material recognition" and seal the samples (Plastic Parts and packaging materials can only be used for sample storage ), approved by the R & D department manager and then released to relevant departments.