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PCB Tech
What are the basic principles of PCB board design
PCB Tech
What are the basic principles of PCB board design

What are the basic principles of PCB board design


PCB board design

1. The accuracy of electrical connection

The wires to be laid should be consistent with the electrical schematic diagram, and the wires that cannot be laid should be described in the relevant technical documents.

2. The manufacturability of printed circuit boards.

The equipment processing capacity and technological level of the printed circuit board manufacturer should be able to meet the PCB processing requirements.

Under the premise of meeting the requirements, use less thin wires, small holes, special-shaped holes, slots, blind holes, and buried holes.

The number of layers of the printed circuit board should be minimized.

The external dimensions should meet the requirements of GB/T9315.

3. The reliability of the printed circuit board.

Try to use common materials and mature processing techniques.

The design should be simple, symmetrical in structure and uniform in layout.

The number of layers of the printed circuit board should be as small as possible, and the diameter and aperture of the pad, the width of the wire and the spacing should be as large as possible.

The thickness and aperture ratio can be adjusted according to the current process level and product requirements, and 3:1~5:14 is recommended.

4. The maintainability of printed circuit board components.

There should be enough distance between the components to facilitate the maintenance and replacement of the components. Easy to test.

pcb board

5. The cleanability of printed circuit board components.

High-reliability PCBA must be thoroughly cleaned after assembly and welding; when designing and installing components, there must be sufficient gaps between the component body and the PCB to ensure adequate cleaning and cleanliness testing.

6. PCB substrate selection

The substrate should be selected according to the use conditions and mechanical and electrical performance requirements of the PCB during design.

Determine the thickness of the substrate board according to the size of the printed circuit board and the quality of the components carried per unit area.

The selection should also consider factors such as electrical performance requirements, Tg and CTE, flatness and the ability of hole metallization

Unless otherwise specified in the design, the substrate used for the printed circuit board is a flame-retardant epoxy woven glass cloth substrate (FR-4).

The mixed printed circuit board of leaded components and lead-free components should use FR-4 board base material with higher glass transition temperature, and its performance should meet the requirements of GJB2142.

7. Selection of electronic components

Electronic components should be selected according to the electrical performance, reliability and manufacturability requirements of the product, and the type, size and packaging form of the components should be selected, and conventional components should be used as much as possible.

The selected electronic components should be consistent with the design standards, suitable for process and equipment standards, and meet the selection requirements of military electronic equipment electronic components.

The designer should consider the assemblability, testability (including visual inspection) and maintainability of the components; SMD/SMC that does not meet the heat resistance requirements of wave soldering and reflow soldering is not to be used in principle; if needed, For SMD/SMC whose soldering temperature is below 250℃, it should be stated on the circuit design document; for QFP whose lead pitch is less than 0.5mm, it should be carefully considered.

The designer should consider whether the information related to the manufacturing is complete and available (such as the completeness of the components, detailed outline dimensions, lead materials, process temperature limits, etc.)

8. The soldering method determines the layout design of PCBA components and the graphic design of the pad

PCBA soldering process has three forms: reflow soldering, wave soldering and manual soldering; the soldering method is different, the component layout can be designed, the PCB and land pattern design and the via design are also different.