PCB Design Completion Rate And Efficiency Of Design Skills

PCB wiring design, a complete set of methods, to improve the efficiency of this, we improve the design efficiency and provide PCB effective techniques to design efficiency for everyone, not only for customers to save the project development cycle, but also to maximize the quality assurance of the product design.

1. Determine the number of layers of PCB

The size of the circuit board and the number of wiring layers should be determined at the early stage of the design. If the design requires the use of a high-density grid array (BGA) component, the minimum number of wiring layers required for the wiring of these devices must be considered. The number of wiring layers and the mode of stack (stack-up) will directly affect the wiring and impedance of the printed wiring. The size of the board helps to determine the stack mode and the width of the printed line to achieve the desired design effect.

2. Design rules and restrictions

The automatic wiring tool itself does not know what to do. In order to complete the wiring task, the wiring tool needs to work under the correct rules and restrictions.  Different signal lines have different wiring requirements. It is necessary to classify the signal lines of all special requirements, and different design classifications are different. Each signal class should have a priority. The higher the priority, the more strict the rules. The rule involves the width of printed circuit, the maximum number of holes, the parallelism, the mutual influence between signal lines, and the restriction of layers. These rules have great influence on the performance of wiring tools. Careful consideration of design requirements is an important step in successful wiring.

3. Layout of components

In order to optimize the assembly process, the DFM rules will restrict the layout of the components. If the assembly department allows the components to move, the circuit can be properly optimized and more convenient for automatic wiring. The defined rules and constraints will affect the layout design.

The layout path (routing channel) and the over - hole area should be considered in the layout. These areas are obviously on the path and design staff, but automatic routing tools consider only one signal at a time, by setting the routing constraints and setting can be distributed signal line layer, can make routing tools like designers envisioned by complete wiring.

4. Fan out design

In the fan design stage, to make the automatic routing tool can be connected to pin assembly, surface mount devices each pin should have at least one hole, in order to need more connection, the circuit board can be connected, the inner line test (ICT) and circuit processing.

In order to make the highest efficiency of the automatic wiring tool, it is necessary to use the maximum size of the hole and the printed line as much as possible. The interval set to 50mil is ideal. The type of over - hole to make the largest number of lines of cloth should be used. When the fan out is designed, the problem of on-line testing of the circuit must be taken into account. The test fixture can be very expensive, and it usually will be ordered when it is about to put into full scale production. If only this time we consider adding nodes to achieve 100% testability, it will be too late.

After careful consideration and prediction, the design of online circuit test can be carried out in the early stage of design. During the later stage of production, the type of through hole fan is determined according to the wiring path and circuit online test. The power and grounding will also affect the design of wiring and fanout. In order to reduce the filter capacitor connected line inductance, holes should be as close as possible to the surface mount device pins can be used when necessary manual wiring, which may affect the route originally envisaged, even may cause you to reconsider what kind of through holes, because this must be considered the relationship between hole and the pin inductance and set specifications via priority.

5, manual wiring and processing of key signals

Manual wiring helps the automatic wiring tool to complete the wiring work.  Regardless of the number of key signals, these signals are first cabled, manual wiring or combined with automatic wiring tools. Key signals must usually be designed by careful circuit design to achieve desired performance. After the wiring is completed, the relevant engineering personnel to check the signal wiring, the process is relatively easy. After the check is passed, the lines are fixed, and then the other signals are automatically wired.

6. Automatic wiring

The wiring of key signals needs to be considered to control some electrical parameters during wiring, such as reducing the distribution of inductors and EMC, and similar to the wiring of other signals. All EDA vendors will provide a way to control these parameters. After understanding the input parameters of automatic wiring and the influence of input parameters on wiring, the quality of automatic routing can be guaranteed to a certain extent.

The same steps are used to wire the rest of the signal. The number of wiring depends on the complexity of the circuit and the number of general rules that you define. After each kind of signal is completed, the constraints of the other network wiring will be reduced. But it follows that many signal wiring needs to be manually intervened. Now the automatic wiring tool is very powerful and usually can complete 100% of the wiring. But when the automatic wiring tool does not complete all the signal wiring, it is necessary to manually wire the remaining signals.

7. Arrangement of wiring

If you use the EDA tool software to list the wiring length of the signal and check these data, you may find that some signal strings with limited constraints are long in length. This problem is easier to handle, by manual editing, it can shorten the length of the signal wiring and reduce the number of holes. In the process of sorting, you need to determine which wiring is reasonable and which wiring is not reasonable. As with manual wiring design, automatic wiring design can also be arranged and edited during the inspection process.


(Source: Internal information)

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