- Aug 14,2018
Careful analysis of the design and careful setup of the tool software should be done before starting the wiring, which will make the design more compliant.
1. Determine the number of layers of the PCB
Board size and number of wiring layers need to be determined early in the design process. The number of wiring layers and the STack-up method directly affect the wiring and impedance of the printed wiring. The size of the board helps determine the stacking and line width to achieve the desired design. At present, the cost difference between the multi-layer boards is very small, and it is better to use more circuit layers and evenly distribute the copper at the beginning of the design.
2. Design rules and restrictions
To successfully complete the routing task, the routing tool needs to work under the correct rules and constraints. To classify all special required signal lines, each signal class should have priority. The higher the priority, the stricter the rules. The rules relate to the width of the trace, the maximum number of vias, the parallelism, the interaction between the signal lines, and the limitations of the layers. These rules have a large impact on the performance of the routing tool.
3. component layout
In the optimal assembly process, the manufacturability design (DFM) rules impose restrictions on the component layout. If the assembly department allows the components to move, the circuit can be properly optimized for easier automatic routing. The defined rules and constraints affect the layout design. The automatic routing tool only considers one signal at a time. By setting the wiring constraints and setting the layers of the signal lines, the routing tool can be routed as the designer envisions.
For example, for the layout of the power cord:
1. In the PCB layout, the power supply decoupling circuit should be designed near the relevant circuits, and should not be placed in the power supply. Otherwise, the bypass effect will be affected, and the ripple current will flow on the power line and the ground line, causing nuisance;
2. For the power supply inside the circuit, the power supply from the last stage should be taken, and the power supply filter capacitor of this part should be arranged near the last stage;
3. For some major current channels, such as disconnecting or measuring current during commissioning and testing, current gaps should be placed on the printed conductors during layout.
In addition, it should be noted that the regulated power supply is arranged on a separate printed board as much as possible. When the power supply and the circuit are used together with the printed circuit board, in the layout, it should be avoided that the regulated power supply is mixed with the circuit components or the power supply and the circuit are used together. Because this kind of wiring is not only easy to cause interference, but also can not break the load during maintenance, only a part of the printed wiring can be cut at that time, thereby damaging the printed board.
Although at present, the changes in the surface treatment process of PCBs are not very large, it seems to be a relatively distant matter, but it should be noted that long-term slow changes will lead to huge changes. As the environmental protection calls are getting higher and higher, the surface treatment process of PCBs will definitely change dramatically in the future.
The most basic purpose of surface treatment is to ensure good solderability or electrical properties. Since copper in nature tends to exist in the form of oxides in the air, it is unlikely to remain as raw copper for a long time, so other treatments of copper are required. Although in the subsequent assembly, a strong flux can be used to remove most of the copper oxide, the strong flux itself is not easily removed, so the industry generally does not use a strong flux.
There are many PCB surface treatment processes, and the common ones are hot air leveling, organic coating, electroless nickel/immersion gold, immersion silver and immersion tin.