The clever techniques of PCB layout and the processing of technological defects

- May 12, 2017-

Before starting the wiring, the design should be carefully analyzed and the tool software will be carefully set up, which will make the design more in line with the requirements.

1, determine the number of layers of PCB

The circuit board size and wiring number shall be determined at the beginning of design. The number of wiring layers and the mode of cascading (STack-up) will directly affect the wiring and impedance of printed wiring. The size of the plate helps determine the stacking mode and the width of the printed line to achieve desired design results. At present, the cost difference between the multilayer plates is very small. In the beginning, it is better to use more circuit layers and distribute the copper evenly.

2 design rules and limitations

To successfully complete the wiring task, wiring tools need to work under the correct rules and restrictions. To classify all the required signals, each signal class should have a priority, the higher the priority, the tighter the rules. The rules relate to the width of the printed line, the maximum number of vias, parallelism, the influence of signal lines, and the limitations of the layers. These rules have a great impact on the performance of the wiring tool.

3, the layout of components

In the optimization assembly process, the manufacturability design (DFM) rule limits the component layout. If assembly department allows components to move, you can optimize the circuit and make it easier for automatic routing. The defined rules and constraints affect layout design. An automatic routing tool will consider only one signal at a time. By setting up the wiring constraints and setting the layer of the signal line, the routing tool can make the routing tool complete the wiring as the designer envisaged.

In the PCB layout should be the power decoupling circuit design in the vicinity of the circuit, and should not be placed in the power supply part, otherwise not only affects the bypass effect, and in the power line and the ground wire through the ripple current caused by crosstalk;

In addition, we should pay attention to the power supply in the layout, as far as possible on the separate printed board. When the power supply and the circuit are used in the printed circuit board, the layout of the power supply and the circuit elements should be avoided, or the power supply and the circuit can be shared with the ground wire.

4, manual wiring and key signal processing

Manual routing is an important process of printed circuit board design both in the present and in the future. Manual routing is helpful for automatic routing tools to complete wiring work.

By manually routing and fixing the selected network (net), it is possible to form the path that can be automatically routed.

First of all, wiring of key signals, manual routing or automatic routing tools can be used. When the wiring is complete, the wiring of the signals is checked by the relevant engineers and technicians. After checking, the wires are fixed and then the wiring of the remaining signals is automatically started.

Because of the existence of impedance in the earth wire, the circuit will cause common impedance interference. Therefore, in wiring, do not connect the points with ground symbols at random, which may cause harmful coupling and affect the work of the circuit.

High frequency, wire inductance will be larger than the resistance wire itself several orders of magnitude. At this time, even a small high-frequency current on the wire will produce a certain high frequency voltage drop. Therefore, for high frequency circuits, the PCB layout is as compact as possible so that the printed wires are as short as possible.

5, Automatic routing

The wiring of key signal to control some electrical parameters in wiring, such as reduced inductance, in the understanding of automatic routing tool which input parameters and the input parameters of the wiring when the impact of the quality of automatic routing can be guaranteed to a certain extent.

General rules should be used when routing signals automatically. By setting up the constraints and the forbidden wiring area, the routing tools can be automatically wired according to the engineer's design to limit the layers and the number of vias used for the given signal. After setting up the constraint conditions and the application of the rules, automatic routing and expected similar results will be reached after the completion of a part of the design, will be fixed, to prevent the influence behind the wiring process.

6,wiring arrangement

Some little signal constraints, the wiring length, this can be the first to identify the reasonable wiring, wiring which is not reasonable, then by manually editing to shorten the signal wiring length and reduce the number of vias.

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