PCB Design and Risk Benefit Analysis in Component Placement

December 12, 2019 Cadence PCB Solutions

Picture of child playing with toy dinosaurs

 

I don’t know why, but plastic dinosaurs and stuffed animals have to be lined up in a specific order. At least, that’s what my little guy insists on. Perhaps in the world of a 3 year old, this specific pattern has some meaning. I can’t tell you how many times I’ve handed him the stegosaurus only to be told that it was the incorrect dinosaur and I should have known better to hand him the T-Rex instead. With this compulsive need to get the animal placement perfect, I just know that he’s going to grow up to be a great PCB designer.

Placing our components in the right pattern is a very critical part of laying out a printed circuit board design. You need to balance many things during placement including signal integrity, mechanical conflicts, and of course PCB assembly concerns. Doing a risk benefit analysis in component placement becomes second nature to most PCB layout engineers in order to make sure that the parts are placed correctly. If this is new to you, let me explain a little more about what I mean.

What is Risk Benefit Analysis in Component Placement?

Risk benefit analysis compares the risks of a situation with its benefits. In printed circuit board design, the goal is to place the components on the board so that the electrical performance, mechanical constraints, and manufacturability requirements are all met. The risk is that a sub-optimal placement could impact the operation of the board or how it is manufactured, while the benefits are a perfectly running board that is easily manufacturable. 

PCB designers have always relied on their skills and experience when placing components to analyze the board and make the best placement choices, but that is changing. Increasingly complex designs and shorter design cycles have highlighted the need for additional help for the designer in making these placement decisions.

There are a number of requirements that a designer must meet when placing components on the board. The first is to lay out the components in such a way that there is enough room to fit in all the trace routing in. For today’s high density complex designs, this can be a big challenge. 

The designer also needs to make sure that the components are arranged to best fit the signal and power integrity needs of the design. There are also mechanical constraints that have to be observed in order for the board to fit correctly together with other system components in the final enclosure. And lastly, the components need to be placed in such a way that the board will go through all of its manufacturing processes without any problems.

All of these requirements must be met for a successful PCB design, and designers are more and more turning to their design tools for help.

 

Picture of the components of an assembled circuit board

Making the right component placement choices is critical to a successful design

 

What Features in PCB Design Tools Can Help with Placement Analysis?

PCB design tools have continued to be enhanced with new capabilities and functionality over the years. They now have several features which can help a PCB designer analyze and make the best component placement decisions. Here are some of those features:

  • Impedance Calculators: Where your components are placed will be based in part on how they need to interconnect with each other. In high speed designs, this involves knowing how many board layers are available for routing and how best to configure the board layer stackup. The impedance calculators in your PCB design tools will help with these decisions.

  • Board Layer Stackup Utilities: These generators will take the board material information that you have, and help you to create the most optimum layer stackup for your design. Starting with a correct layer stackup will prevent you from having to replace the components later on to accommodate any layer stackup changes.

  • Rules and Constraint Management: Design rules can be set up that will govern how close specific components or classes of components can be to other board objects for optimum manufacturability. Additionally, rules can be set up for specific assembly processes which will help prevent DFM placement changes later on in the design cycle.

  • Placement Floorplanning: The rules-driven methodology of the design tools will allow engineers to assign components to specific areas during placement. This will make sure that all required circuitry is accounted for, and there aren’t any components that are left out that would force changes later to fit them back in.

  • Routing Floorplanning: Using the flow planning and route engine features in the tools, PCB designers can see in advance where the high density routing areas will be and plan accordingly. This will allow fine-tuning of component placement to accommodate all of the required routing before the routing is started, saving you from possibly having to rip up the layout later on in order to find more room for routing.

  • Signal and Power Integrity Tools: By analyzing the signal and power needs of your design, you can better position your components for optimum signal performance and clean power distribution. This will save you from having to redo already completed portions of your design to improve design performance later on.

  • 3D Tools: Using your design tool’s 3D viewing and checking features, you can see where the component placement will clash with other components, board mechanical features, and even other system boards and enclosures. This will save you from redesigning major portions of your board to replace a component that wasn’t located correctly in the first place.

This list goes on and on, but the important thing to understand is that PCB designers no longer need to rely solely on their own abilities. With advanced PCB design tools, they have a powerful resource to help them make the right component placement choices.

 

 Screenshot of Allegro 3D layout showing mechanical features

Using all the capabilities of your CAD tools is important for complex designs like this

 

What Kind of PCB Design Tools Should You be Looking For?

An even better question might be, “where should you be looking for to find the PCB design tools that you need?” The answer to that question is that you need to find a PCB design tool vendor that understands both the challenges of today’s complex PCB designs, and the engineers and designers that are using the software. 

The vendor you choose should be well armed with technical resources that can help you set up and run the tools, as well as constantly working to enhance and improve their software. The software itself should have multiple tools and capabilities that are interconnected with each other, and configurable so that you can fine-tune the tools to best fit your needs.

The PCB design tools from Cadence have all the features and functionality that we have been talking about. With its 3D tools, interconnect floor planner, and a host of other calculators, routers, design rules and constraints, Allegro PCB Designer is the design system that can best help you with your component placement.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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