Electronic Design - 5g pcb design specification

1. Terminology
1..1 PCB (Print circuit Board): Printed circuit board.
1..2 Schematic diagram: circuit schematic diagram, a diagram drawn with a schematic diagram design tool to express the connection relationship between various devices in the hardware circuit.
1..3 Network table: A text file that is automatically generated by the schematic design tool and expresses the electrical connection relationship of the components. It generally contains components such as component package, network list and attribute definition.
1..4 Layout: During the PCB design process, the process of placing components on the board in accordance with the design requirements.

II. Purpose
A. This specification defines our company's PCB design process and design principles. The main purpose is to provide PCB designers with rules and conventions that must be followed.
B. Improve PCB design quality and design efficiency.
Improve the manufacturability, testability and maintainability of PCB.
III. Acceptance of PCB design tasks
A. PCB design application process
When hardware project personnel need to carry out PCB design, they must submit a board investment application in the "PCB Design Investment Application Form", and after approval by their project manager and planning office, the process status reaches the designated PCB design department for approval. At this time, the hardware The project personnel must prepare the following information:
Completely correct schematic diagrams after review, including paper documents and electronic files;
Formal BOM with MRPII component code;
PCB structure drawing, should indicate the external dimensions, the size of the mounting holes and the positioning dimensions, the positioning dimensions of the connectors, and the prohibited wiring area and other relevant dimensions;
For new devices, that is, devices without MRPII codes, packaging materials are required;
The above information can only start PCB design after being approved by the designated PCB design department and designated PCB designer.
B. Understand the PCB design requirements and make a design plan
1. Read the schematic diagram carefully and understand the working conditions of the circuit. Such as the operating frequency of analog circuits, the operating speed of digital circuits and other factors related to wiring requirements. Understand the basic functions of the circuit, the role in the system and other related issues.
2. On the basis of full communication with the schematic designer, confirm the key networks on the board, such as power supply, clock, high-speed bus, etc., and understand their wiring requirements. Understand the high-speed devices on the board and their wiring requirements.
3. According to the requirements of the "Hardware Schematic Design Specification", conduct a normative review of the schematic.
4. For the parts in the schematic diagram that do not conform to the hardware schematic design specifications, it is necessary to clearly point out and actively assist the schematic designer to modify it.
5. Develop a single board PCB design plan based on the communication with the schematic designer, fill in the design record form, and the plan should include schematic input, layout completion, wiring completion, signal integrity analysis, and light drawing completion during the design process Time requirements for waiting for key checkpoints. The design plan should be signed and approved by both the PCB designer and the schematic designer.
6. When necessary, the design plan should be approved by the superior.
IV. PCB design process
A. Create a netlist
1. The network table is the interface file between the schematic diagram and the PCB. The PCB designer should select the correct network table format according to the schematic diagram and the characteristics of the PCB design tool used, and create a network table that meets the requirements.
2. In the process of creating the netlist, according to the characteristics of the schematic design tool, actively assist the schematic designer to eliminate errors. Ensure the correctness and completeness of the netlist.
3. Determine the package of the device (PCB FOOTPRINT).
4. Create PCB board
Create PCB design files according to the single board structure drawing or the corresponding standard board frame;
Pay attention to the correct selection of the position of the coordinate origin of the veneer, the principle of origin setting:
1. The intersection of the left and lower extension lines of the veneer.
2. The first pad at the bottom left corner of the board.
Rounded corners around the frame, with a chamfering radius of 5mm. Refer to the structural design requirements for special circumstances.
B. PCB design layout
1. Set the size of the board frame according to the structure drawing, arrange the mounting holes, connectors and other components that need to be positioned according to the structural elements, and give these components immovable attributes. Carry out dimension marking according to the requirements of process design specifications.
2. Set the forbidden wiring area and layout area of the printed board according to the structure drawing and the clamping edge required during production and processing. According to the special requirements of certain components, a wiring prohibition area is set.
3. Comprehensive consideration of PCB performance and processing efficiency to select the processing flow.
The preferred sequence of the processing technology is: single-sided mounting on component side-component side mounting, insert and mixed mounting (component side mounting and soldering surface mounting once wave forming)-double-sided mounting-component side mounting and insert mixed mounting, Soldering surface mount.
4. Basic principles of layout operation
A. Follow the layout principle of "big first, then small, difficult first, easy first", that is, important unit circuits and core components should be laid out first.
B. The principle block diagram should be referred to in the layout, and the main components should be arranged according to the main signal flow law of the single board.
C. The layout should meet the following requirements as far as possible: the total wiring is as short as possible, and the key signal line is the shortest; high voltage, large current signal and low current, low voltage weak signal are completely separated; analog signal and digital signal are separated; high frequency signal Separate from low-frequency signals; the spacing of high-frequency components should be sufficient.
D. For the circuit parts of the same structure, adopt the "symmetrical" standard layout as much as possible;
E. Optimize the layout according to the standards of uniform distribution, balanced center of gravity, and beautiful layout;
F. Device layout grid setting. In general IC device layout, the grid should be 50-100 mil. For small surface mount devices, such as surface mount component layout, the grid setting should be no less than 25mil.
G. If there are special layout requirements, they should be determined after communication between the two parties.
5. The same type of plug-in components should be placed in one direction in the X or Y direction. The same type of polarized discrete components should also strive to be consistent in the X or Y direction to facilitate production and inspection.
6. Generally, the heating elements should be evenly distributed to facilitate the heat dissipation of the veneer and the whole machine. Temperature-sensitive devices other than the temperature detection elements should be kept away from the components that generate large amounts of heat.
7. The arrangement of components should be convenient for debugging and maintenance, that is, large components cannot be placed around small components, components to be debugged, and there must be enough space around the components.
8. For veneers that need to be produced by wave soldering, the fastener installation holes and positioning holes should be non-metallized holes. When the mounting hole needs to be grounded, it should be connected to the ground plane by means of distributed grounding holes.
9. When the wave soldering production process is used for the mounting components of the soldering surface, the axis of the resistor and capacitor should be perpendicular to the wave soldering transmission direction, and the axis of the resistor and SOP (PIN spacing greater than or equal to 1.27mm) components should be parallel to the transmission direction; Avoid wave soldering for active components such as IC, SOJ, PLCC, QFP, etc. whose PIN pitch is less than 1.27mm (50mil).
10. The distance between BGA and adjacent components>5mm. The distance between other SMD components>0.7mm; the distance between the outside of the mounting component pad and the outside of the adjacent interposing component is greater than 2mm; PCB with crimping parts, no interposing within 5mm of the crimped connector Components and devices shall not be mounted within 5mm of the welding surface.