The concept of automation is often theoretically satisfactory and unsatisfactory in reality.

As design complexity increases, it becomes more difficult to create and maintain design rules that match the results of wiring that can be manually routed by experienced designers. Some of the reasons designers are avoiding automatic routing include:

1. Trying to set up the auto-router to convert the designer's ideas into screen content, which in itself poses a challenge to the designer;

2. The quality has decreased compared to manual design;

3. The time spent on the cleaning work after the auto-router is sufficient to complete the wiring manually;

4. Too many vias, or the design done by the auto-router generally does not have the refined appearance that rivals the experienced designer.

Is there a trade-off between manual routing and automatic routing?

Both automated routing and manual routing require careful planning strategies and execution to achieve the desired results. In general, if the design team has a dedicated time to fully consider automatic routing and plan, layout, constrain, and prioritize the design database, it is often possible to get the best automated routing results. The success of automated routing also depends on the designer's understanding of its auto-router algorithms and historical performance.

However, the difficulty of PCB design and wiring is increasing day by day. Design is rigorously constrained by increasing design rules, decreasing physical space, signal integrity rules, and many other factors. All of these constraints pose a huge challenge for designers who want to streamline their design processes using traditional automated routing techniques. 

For an independent engineer, it is difficult to complete this task because there is no complete design team to build and maintain a design database specifically for use with the auto-router. Is there a way to combine the convenience of automatic routing with the advantages of manual routing to resolve the growing design challenges?

This article describes how to use the PADS® Professional sketching environment introduced by Mentor Graphics with the proven XpeditionTM technology to enable stand-alone PCB designers and project-based PCB designers to quickly and easily route high-quality rule-driven Designed and styled and styled with manual wiring.

Overview of PCB Designers' Psychological Activities

Typically, when designing a new PCB Layout for the first time, the designer will display the wiring when laying out the components in the design.They must pay attention to the arrangement of the components and how the fan-out mode is generated to ensure that the pins and vias of the components can be used and the routing channels are optimized. At the same time, designers will focus on the networks with the highest priority, identify the networks they need to manually route, and remember all design rules. 

Configuring the auto router to route it as the designer displays can be a daunting task. As a result, most designers turn to manual design for a large number of design cabling tasks, especially critical network cabling, to ensure the desired results.

Rethink automation with sketch routing

Can the routing of critical networks be "automatic"? With the new auxiliary wiring method - sketch routing, you are entirely possible to do this! Mentor Graphics' sketch routers eliminate some of the steps PCB designers need to take care of in their automated routing implementations. With sketch routing, PCB designers can perform complex routing tasks while viewing routing—all operations are done in real time.

The PADS sketch routing environment provides a highly integrated set of automatic routing features such as sketch routers, true trace routing, and dynamic push. Combining these features results in a good cabling experience for high quality, good user control and superior performance    

With sketch routing, designers can:

1. Draw a sketch path to determine the routing of the selected flying leads;

2. High quality design and high completion rate at a speed far beyond manual wiring;

3. Route separate traces or hundreds of single-ended/differential pairs;

4. Automatically optimize the pinout to avoid adding unnecessary vias while enhancing the wiring effect.

Figure 2: PADS Professional makes wiring easier than ever.

How sketch routing works

To use sketch routing, the designer simply draws a line to indicate the path along which the router will automatically eject the selected network. When wiring several, dozens or even hundreds of flying leads, the sketch router is several times faster than manual routing. Twenty-two data lines are selected in Figure 3. The most common sketch routing method uses the existing via fanout without adding any extra vias.

Figure 4: Button routing results obtained from the sketch path in Figure 3.

As shown in Figure 4, the quality of the sketch wiring is excellent, reflecting the quality and features of manual routing. There is very little cleaning required, and in many cases no cleaning is required. Achieving a high completion rate (90% - 100%) thanks to the sketch router's ability to automatically organize the wire so that it can be optimally routed without any additional vias. If you don't care about the results, or want to try an alternative, you can cancel the results and re-execute the sketch routing with just a few clicks. With sketch routing, even the most experienced designers can generate routing results at speeds that are more than 30 times faster than manual routing.

Another useful feature of sketch routing is the ability to route networks in a tight or non-tight mode. As shown in the serial network of the wiring in Figure 5, in the compact mode, the routing pitch is optimized based on the minimum design rule value. In this case, the non-compact mode shown in Figure 6 works better because it provides the most direct network connection and avoids unnecessary overcrowded traces.

Figure 6: Performing sketch routing on a serial network in non-compact mode

Why can sketching wiring greatly improve wiring efficiency?

Drawing sketch paths is easy. The direction of the sketch path determines the start and end pins. As needed, the sketch router will consider up to ten different methods before completing the routing of the selected network, but even so, it can be completed in a short amount of time. Each method considers the wiring results corresponding to the outgoing direction of each pin, and then layouts the traces according to the method corresponding to the best result.

Compression: After determining the best method, the sketch router will run multiple passes to compress the network toward the pins. This will ensure that the routing pins are optimized to accommodate further design routing.

Centered: The sketch router then centers the routing between the compressed pinouts that surround the sketch path drawn by the designer. If no sketch path is drawn, the sketch router places the routing centered between the compressed pinouts.

Smoothing: During smoothing operations, the sketch router can ensure the most straightforward routing by trying to minimize the routing segments.

What if the sketch router cannot route a network?

If sketch routing is not 100% complete in the specified network bundle, designers can use real trace routing and dynamic push to complete the routing.

True trace routing: When you need to route individual networks, you can use real trace routing to generate trace streams through the mouse while moving the mouse, thus minimizing the amount of work required to route single-ended networks and differential pairs of networks. -- No extra clicks required, even when wiring is complete! True trace routing automation uses dynamic visual feedback to guide routing operations, while pushing the vias and traces along the way, even clearing the planar area during routing.

Dynamic Push: To move a large set of wires (even across a regular area), use dynamic push to achieve smooth, fast movement, which automatically removes extra segments and maintains high quality.

In conclusion

If you've tried entering a local destination in GPS and receiving a problematic route suggestion, you may understand that no matter how advanced the technology is, it can't completely replace the route that has been driven by the years. The level of familiarity with accumulation. As an experienced driver, you will eventually choose the best path.

The same is true for PCB layout. Automation does have its role, but it still does not completely replace the knowledge and experience of skilled PCB designers (which also gives these experienced designers a sigh of relief). We believe that our experience can provide guidance and ensure that all design elements “seem correctly”. But in today's market, time is also a key element. 

With the help of auxiliary routing automatically performed in the sketch routing environment in PADS Professional, PCB designers can easily route high-quality, rule-driven designs up to 30 times faster than manual routing, and all wiring will achieve the quality of manually routed PCB designs, appearance and style. By rethinking automation, we have built a methodology that uses advanced routing techniques and combines it with the knowledge and ideas of individual PCB designers.