6 Basic Processes of PCB Design

Information Required for PCB Design

Basic Processes of PCB Design

1. Preliminary Preparation
2. PCB Structure Design
3. PCB Layout
4. Routing
5. Routing Optimization and Silkscreen
6. Netlist and DRC Check and Structure Check
7. PCB Fabrication

1 Preliminary Preparation

1. This includes preparing the component library and schematic diagram. "If you want to do something well, you must first sharpen your tools." To make a good board, in addition to design principles, you must draw well. Before proceeding with PCB design, you must first prepare the component library for the schematic SCH and the component library for PCB (this is the first step - very important). The component library can use the library that comes with Protel, but it is usually difficult to find a suitable library. It is best to complete the component library yourself according to the standard size data of the selected components. In principle, first complete the PCB component library, then the SCH component library. The PCB component library has higher requirements, which directly affects the board assembly; the SCH component library has relatively loose requirements, as long as you pay attention to defining pin attributes and the corresponding relationship with PCB components. Pay attention to the hidden pins in the standard library. Then comes the schematic design, and when it is ready, you can start the PCB design.
2. When making the schematic library, pay attention to whether the pins are connected to the input/output PCB board and check the library.

2 PCB Structure Design

3 PCB Layout

1. Ensure that the schematic diagram is correct before layout - this is very important! ---- Very important! After the schematic diagram is completed, the check items include: power grid, ground grid, etc.
2. When laying out, pay attention to the surface where the components are placed (especially plug-ins, etc.) and the placement method of components (horizontal or vertical placement of through-hole components) to ensure the feasibility and convenience of installation.
3. Layout is to place the components on the circuit board. At this time, if all the above preparations are completed, you can generate a netlist on the schematic diagram (Design -> Create Netlist), and then import the netlist on the PCB (Design -> Load Nets). You will see the complete component stack and the flying line prompts for connections between pins, and then you can perform component layout.

1. Reasonably divide according to electrical performance, generally divided into: digital circuit area (which generates interference and is resistant to interference), analog circuit area (which is afraid of interference), and power drive area (which is the interference source);
2. Circuits that complete the same function should be placed as close as possible, and the components should be adjusted to ensure the simplest connection; at the same time, adjust the relative positions between functional blocks to make the connection between functional blocks the most concise;
3. For high-quality components, installation position and installation strength should be considered; heating elements should be placed separately from temperature-sensitive elements, and thermal convection measures should be considered if necessary;
4. Clock generators (such as crystals or oscillators) should be as close as possible to the devices that use the clock;
5. The layout should be balanced, sparse and orderly, not top-heavy or sunken.

4 Routing

1. Under normal circumstances, power lines and ground lines should be routed first to ensure the electrical performance of the circuit board. Within these conditions, try to widen the width of power and ground lines. The ground line is better than the power line. Their relationship is: ground line > power line > signal line. Usually, the signal line width is 0.2~0.3mm. The thinnest width can reach 0.05~0.07mm, and the power line is generally 1.2~2.5mm. For digital circuit PCBs, wide ground lines can be used to form loops for forming a ground grid (the ground of analog circuits cannot be used like this);
2. Pre-process lines with higher requirements (such as high-frequency lines). The edges of the input and output terminals should avoid adjacent parallelism to avoid reflection interference. If necessary, add ground lines, and the wiring of two adjacent layers should be perpendicular to each other, as parallelism is prone to parasitic coupling;
3. The oscillator shell is grounded, and the clock line should be as short as possible and cannot be led everywhere. Below the clock oscillation circuit and the special high-speed logic circuit part, the ground area should be increased, and other signal lines should not be used to make the surrounding electric field close to zero;
4. Use 45° broken lines as much as possible, do not use 90° broken lines to reduce the radiation of high-frequency signals; (high-speed lines use double arcs);
5. Do not form loops on any signal lines. If unavoidable, the loop should be as small as possible; the number of vias for signal lines should be as small as possible;
6. Key lines should be as short and thick as possible, and add protection on both sides;
7. When transmitting sensitive signals and noise field band signals through flat cables, they should be extracted by "ground-signal-ground";
8. Test points should be reserved for key signals to facilitate debugging, production and maintenance testing;
9. After completing the schematic routing, optimize the routing. At the same time, after the initial netlist check and DRC check are correct, perform grounding of the wireless area, use a large-area copper layer as the ground line, and connect all unused areas on the printed circuit board to the ground as the ground. Or make a multi-layer board, with the power supply and ground each occupying one layer.

5 Add Teardrops

6 Inspection