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PCB Layout

The technological process of PCB layout design includes design of schematic diagram, login database of electron component, preparations for design, block subdivision, configuration of electron component, confirmation of configuration, wiring, and the final inspection.

Rules of PCB Layout:

1. Under the general circumstances, all the electron components should be set on the same aspect of the circuit board. Only when the components on the top layer overcrowd, can we put the modules with limited height and small-volume of heat emission such as chip resistor, chip capacitor, chip IC, etc. on the lower layers.

2. Under the premise of ensuring electrical performance, the components should be placed on the grid and arranged parallel or perpendicular to each other to keep neat and beautiful. In general, the components are not allowed to overlap; the components should be arranged compactly, and the components should be evenly distributed on the entire layout with consistent density.

3. The shortest distance between different modules and the bonding pad on the circuit board should be over 1mm.

4. The distance to the edges of the circuit board shouldn’t be shorter than 2mm. The best shape of the circuit board is rectangular with the length-width ratio of 3:2 or 4:3. When the circuit board surface is larger than the size of 200mm*150mm, mechanical strength the circuit board can bear should be considered.

Normal Questions in PCB layout

1. How to arrange the PCB layout to reach the best heat emission effect?

Answer: there are three aspects of the heat source within PCB: (1) the heat emission of the electron component;(2) the heat emission of PCB itself;(3) the heat emission from other parts. Among these three heat sources, the heat emission from electron component is the most that it is the main heat source. And then the heat volume of PCB itself comes to the second, while the heat from external environment needs no consideration, since it depends on the overall heat design of the system. Therefore, the goal of heat design is to adapt proper measures and methods to lower the temperature of the electron components and the PCB so that the system can work normally under the proper temperature. It can be fulfilled mainly through reducing the heat emission volume and accelerating the heat emission.

2.How to reduce the electromagnetic interference in the PCB layout?

Answer: for reducing the electromagnetic interference, you need to be careful about matching, decoupling, layout and wiring, layering and other problems. It is reasonable to refer to some information.

3.For signals over 5G, what should be considered specially?

Answer: you should consider the transmission line effect, parasitic effect, and problems about EMI.

4.Should the distance between the thermosensitive element and heating element be considered?

Answer: the heating element should be set at the edge of the PCB in order to emit the heat. If the PCB is installed vertically, the heating element should be set right over the PCB. And the thermosensitive element should be away from the heating element.

5.What should I notice when setting the multilayer board layout?

Answer: when setting the multilayer board, you should notice that suspending ground plane or power layer must be avoided because the power and ground layers are in the interior layers. Besides, ensure that the through holes drilled on the ground absolutely connect the ground plane. In the final step, you need to add some test points for some important signals to facilitate the measurement in debugging.

6. How could I effectively reduce the interference among electrical modules, and how could I set the layout of amplifier to limit the introduction of the ripple at the maximum?

Answer:  the principles of reducing interference are:

1.Reduce the radiation ends;

2.Enhance the isolation, shielding, and decoupling of being interfered;

The principles of reducing ripple are:

1.Reducing the ripple output of switching power supply;

2.Enough decoupling filtering;

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