Electronic Design - Detailed PCB wiring technology

Detailed PCB wiring technology

PCB wiring is a very core process in the entire PCB design. This article will introduce you to this very core process.

1. Circuit board design steps.

1. Circuit schematic design

The design of the circuit schematic diagram is mainly a schematic diagram drawn by the PROTEL099 schematic design system (Advanced Schematic). In the design process, we must fully use the schematic drawing tool in PROTEL99 to help us get a correct and exquisite circuit schematic.

2. Generate a netlist

The netlist is a bridge between the printed circuit board design (PCB) and the circuit schematic design (SCH). The netlist can be extracted from the circuit schematic.

3. Design of printed circuit board

The design of the printed circuit board is mainly for the PCB. In this process, we use the powerful functions provided by PROTEL99 to realize the layout design of the circuit board and complete many difficult and challenging tasks.

Two draw a simple circuit diagram

1 Schematic diagram design process The design of the schematic diagram can be divided into seven steps to complete.

Design drawing size After Protel 99/ Schematic, it is essential to conceive a part drawing. Set a suitable size drawing. The so-called suitable drawing is determined according to the scale of the circuit diagram. The suitable drawing size is the basis for designing the schematic diagram.

(2) Set the Protel 99/Schematic design environment The environment design mentioned here includes setting the grid size and type, cursor type, etc. Of course, most of the parameters can use the default values.

(3) Rotating parts according to the needs of the circuit diagram, the user removes the parts from the parts library and places them on the drawings, and defines and sets the serial numbers and parts packaging of the placed parts.

(4) Wiring with schematic diagram Using various tools provided by Protel 99/Schematic, connect the components on the drawing with wires and symbols with electrical meaning to form a complete schematic diagram.

(5) Adjust the circuit make further adjustments and modifications to the preliminarily drawn circuit diagram to make the schematic diagram more beautiful.

(6) Report output Various reports are generated through various report tools provided by Protel 99/Schematic. The most important report is the network table. The network table is used to prepare for the subsequent circuit board design.

(7) File saving and print output The final step is file saving and print output.

In addition, the following are things that need our attention:

? When designing the printed circuit board of the logic circuit, the ground wire should form a closed loop, which can effectively improve the circuit's anti-interference ability.

? The ground wire should be as thick as possible. We all know that a thin wire has a large resistance, and a large resistance will cause the ground potential to change with the current. This will cause the signal level to be unstable, and then the circuit's anti-interference ability will decrease.

?Pay attention to the choice of grounding point. When the signal frequency on the circuit board is lower than 1MHz, because the electromagnetic induction between wiring and components has little effect, and the circulating current formed by the grounding circuit has a greater influence on interference, it is necessary to use a point of grounding so that it does not form a loop. When the signal frequency on the circuit board is higher than 10MHz, due to the obvious inductance effect of the wiring, the ground impedance becomes very large. At this time, the circulating current formed by the grounding circuit is no longer a major problem. Therefore, multi-point grounding should be used to reduce the ground impedance as much as possible.

In addition to the layout of the power line, the width of the trace should be increased as much as possible according to the size of the current. When wiring, the routing direction of the power line and the ground line should be consistent with that of the data line. At the end of the wiring work, use the ground Lines cover the bottom of the circuit board where there are no traces. These methods all help to enhance the anti-interference ability of the circuit.

? The width of the data line should be as wide as possible to reduce impedance.

? The number of vias should be reduced as much as possible. It is necessary to know that a via on the circuit board will bring about a capacitance effect of about 10pF. This interference is very large in a high-frequency circuit, so the number of vias should be reduced as much as possible. Moreover, too many vias are still Will cause the mechanical strength of the circuit board to be greatly reduced.