Principles of PCB Layout
When drawing PCB layout, PCB rookies are better follow the basic principles below.
1.Schematic should be easy to wire and troubleshoot. Use real pinouts and the bus rationally.
2.Before making PCB, hand-made some device packages, fabricating transistor package first.
3.Before wiring, you should make a manual sketch and make a rough layout based on the principle of prioritizing performance.
4.Avoid parallel alignment with the component axis, carefully set the ground, use full or grid copper appropriately.
5.Grounding should be digital in the network circuit, the signal clock line should use snake walking line, and the pad should be soldered properly.
6.Manual wiring according to the principle of network or component wiring, and then carry out the docking and alignment between the blocks.
7.When the layout needs to be modified in an emergency, generally only individual components or one or two networks need to be changed.
8.Make at least five holes, four corners, and one center in the margin when making the PCB for the hole.
9.Before soldering, it is best to first brush the tin and place components on the board with tape, and then soldered.
10.The ADC traces must be separated from the traces of other digital circuits or signal lines (especially clocks) and should not be parallelized or crossed.
11.Crystal oscillation should be as short as possible and surrounded by ground, but be careful not to increase the load capacitance due to small spacing.
12.Single and double panels need at least 50% of the metal layer, multi-layer at least four metal layers to prevent local overheating and fire.
13.Signal line thickness are as consistent and short as possible, the signal line, input and output lines should be added between the ground, the module must also clamp the ground.
14.Use grids instead of large-area copper when contact device pins and ground. To prevent peeling from the skin, the entire board is suggested to use grid.
15.If the PCB board has a large area of copper, open a few small openings on the ground, but the hole can not be greater than 3.5mm.
16.For easy plugging and unplugging do not place the jumpers below large devices such as ICs.
17.Placement and wiring should take full account of the cooling and ventilation of the device, the heat source should be close to the edge of the board, and well design the test location spacing.
18.In the design of multi-layer anti-electromagnetic interference 20H rule and 3W rule should be applied to overcome boundary radiation coupling and logic current magnetic flux interference.
19.Dual signal lines are best not to be the same current direction, and control the minimum parallel length, such as the use of JOG or sine, cosine alignment.
20.Low-frequency line signal changes in the upper and lower edges caused by interference is much larger than the interference generated by the frequency, it should also pay attention to crosstalk problems.
21.High-speed signal line should join the appropriate termination match, keep its impedance in the transmission remain unchanged, and try to widen the width of the line.
22.Do not forget to add filtering and coupling capacitors between the block's power supply and ground to eliminate interference.