Solving PCB design interconnect challenges: new design tools that incorporate strategic planning, routing guidance and design feedback.

THE RELATIONSHIP BETWEEN PCB interconnect challenges and the CAD tools needed to address them has always been one of leapfrog. In years past, as new interconnect challenges such as surface-mount technology, differential pairs and simple high-speed constraints have emerged they have routinely been met with a continuing evolution of productive and automated CAD tools and features. More recently, however, this is not the case. New interconnect challenges such as high pin-count devices, bussed interfaces and ultra-complex high-speed constraints have once again leapfrogged the CAD tools and are reducing designer productivity. As these challenges proliferate and new challenges appear on the horizon, the current generation of CAD tools falls further behind in delivering the problem-solving solutions that designers need in order to be productive. PCB designers need next-generation technologies and methodologies to efficiently, and more importantly, intelligently address global interconnect challenges.

To fully define the problems that exist today, we need a historical view of how we got here. Interconnect challenges in early PCB designs, such as connection count and interconnect complexity, were within the ability of manual tools and features to solve and designers were relatively productive. As time progressed, PCB feature sizes began to shrink, connection counts increased and interconnect complexity grew to a point where manual-only methods were ineffective and unproductive. To address this increased complexity, automation was applied to various phases of PCB design. Semi-automatic routing is one example of automated implementation that helped the designer get the problem under control and, in turn, become productive once again.

However, designers were still left with the task of actually solving the problems and challenges, such as manually creating the interconnect. To address this, CAD tool automation continued to evolve with automatic route engines to help automate the creation of the interconnect and speed up the process. For a long time, steady evolutions in automation helped the designers stay productive. But technological progress such as industry interfaces, bigger component packages and complex constraints have once again grown beyond the capabilities of current routing automation. This lack of applicable automation in the design process has returned us to where we started--manual design environments. The stalled technological progress and missing intelligent automation features in CAD tools have led to lower designer productivity, much longer design times and delays in getting products into the marketplace. With today's CAD tool automation being several steps behind the interconnect challenges, what's needed to solve the problems is not simply continued evolution, but an entirely new paradigm--one that will provide a significant leap in designer productivity. A new paradigm that provides intelligent, global automation will allow designers to stay a step ahead of PCB design challenges.

Evolution vs. Interconnect Challenges

Further evolution of existing technologies and features might bring automated routing technology that is faster, is more efficient at trace density and supports additional high-speed rules. Some tools may even provide simple planning features that can assist in semi-automatic/manual routing. But simple evolutions such as these will not provide designers significantly more capability to solve existing and future interconnect challenges. More importantly, they will not provide the major leap in design throughput that companies require in order to remain at their competitive peak.

To solve these interconnect challenges, designers must leverage intelligent automation throughout the design process and fundamentally change the way that global interconnect challenges are strategically planned for and routed. In order to efficiently and intelligently solve these interconnect challenges, designers need a design methodology that rises above working with single nets or individual objects one at a time and consider the design as a hierarchy. In addition, this hierarchical approach must consider everything on the design throughout the entire process in order to derive an optimal routing solution. A tool that just looks at a single object at a time is destined to fail. Without forethought or insight into the impact of all the nets to each other throughout the design process, a designer's inherent and intelligent decisions to resolve the interconnect challenges cannot be realized.

Realizing the Designer's Intent

To solve interconnect challenges, designers need to utilize an intelligent planning and routing environment with a global perspective of the design and the routing constraints. This intelligent environment lets designers use their knowledge and design intent in concert with the environment's global, hierarchical view to plan the best interconnect solution possible. With awareness of the designer's intent, the computer--specifically the route engine--performs the mathematical and geometric crunching necessary to solve the interconnect pathways and provide a routed design. This may sound simple in its approach. Many designers today use paper and pencil, or extra layers in their CAD tool, plus interactive and manual methods, to accomplish the same thing. But this is all done manually with little automation or assistance from the CAD tool.

A truly intelligent environment provides more than just simple pathway sketches for routed interconnects. It provides an environment that is intelligent enough to conceptualize the design and make a hypothesis early in the process as to how nets need to be connected. It accounts for the impact of the first net as it relates to the last net, and accounts for the necessary space for all of them. It then continues to refine the initial hypothesis as it works through the interconnect solution with guidance and input from the designers, based on their intent.

Designs today have become so electrically and physically constrained in unique ways that the CAD tools cannot always capture all of the necessary constraints. For example, a rule may require that two buses cannot cross within four inches of the driver and must cross at 90[degrees] to each other at a given location. Bus and circuit tuning for phase control often have very specific requirements such as location, angle or proximity. As a result, it is left to the designer to drive their design intent through manual routing techniques, rendering automatic tools useless. An intelligent interconnect environment would allow the designer to capture this design intent while employing underlying, powerful engines to determine feasibility and, ultimately, the interconnect paths that align with the user's intent.

Using an Intelligent Environment to Solve Problems

Presentation of the design data in a more abstract way allows both the designer and the environment to identify key interconnect associations and groups of interconnects that have common connect locations and common paths through components. Connections that should be routed together, such as a bus or an interface, can be automatically recognized and incorporated into the router's global view of the design.

Using this abstract design data and strategic planning capability, the designer can accelerate processes at any stage of the design because the system provides a visual/spatial map of the open area in relation to the larger interconnect structures and component objects. The designer can strategically plan the abstracted interconnect representations across the board, making tradeoffs and analyzing "what-if" scenarios for component placement, routing, return-path management and layer optimization strategies.

With a global perspective of the design, the routing system would be able to validate the user's decisions and provide feedback throughout the planning process, without the need to route-analyze-reroute. The intelligent environment captures and adheres to a designer's intent and guides the user through each step of the design process until ultimately reaching a routing solution.

By using design data abstraction for strategic planning and the global route engine for guidance and feedback, the user can converge on a successful interconnect solution far faster and more easily than ever before. These features finally give designers what they have needed for a long time: tools that allow them to work smarter, not just harder and a toolset that works with them and does not make them work around its deficiencies.

JOSH MOORE is senior product marketing manager for PCB design tools for the Allegro platform at Cadence Design Systems; [e-mail]. PAUL MUSTO is engineering group director for the PCB Implementation and High-Speed Analysis groups for the Allegro Platform at Cadence Design Systems; [e-mail].