Pin Swapping Without Back Annotation Using Straightforward PCB Design Software

Altium Designer
|  Created: May 18, 2018  |  Updated: September 25, 2020

 Man floating with pins on grid

When working with high pin count, fine pitch components like FPGAs or memories, pin swapping may need to be performed when laying out your PCB. Designing schematics based on these devices that perfectly translate into a sane layout is extremely difficult. But as you start placing components and routing connections, you may find that your initial layout is a tangled, crisscrossed mess. This is where pin swapping becomes invaluable.

Once you start pin swapping, you need to document which pins were swapped and make sure that these changes are updated in your schematic. More complicated layouts with high pin count components tend to require more rounds of pin swapping, and each round of pin swapping requires documentation. Documenting each pin swap operation by hand is extremely time-consuming and prone to errors.

Thankfully, tools are available that make pin swapping quick and easy. After each pin swap operation, your documentation can be updated automatically. This saves considerable time for everyone involved and ensures that others on your team can quickly identify all pin swaps that occur in the layout.

Diagnose Your Design Bottlenecks

If only I could see into the future, PCB design would be so much easier. When placing components on the board, I usually find that my initial placement can be optimized. This usually doesn’t become obvious until I start routing between my FPGAs, DSPs, memories, and the like. Crossover among connections is inevitable and detangling this mess requires pin swapping.

A typical design environment takes the view that PCB layout portion is separate from schematic design and documentation. This lack of integration creates a design bottleneck that requires multiple software products to solve. When swapping pins within a component, and even when swapping parts on a board, you will need to annotate these changes in the appropriate documents.

There is no reason that design and ECO software should be separated from each other. At that point, you might as well manually type up each change in a document with word processing software. Imagine the time it would take to manually document typical pin swapping operations on an FPGA with over 1500 pins. Once you pin swap, your software should also update the schematic to match any layout changes and allow you to seamlessly document your changes.

Complex BGA routing screenshot

Complex BGA routing

Realizing Where the Pain Comes From

Software vendors that try to blend different tools into the same design environment create the potential for back annotation errors after pin swapping. Buying and working with software on a piecemeal basis is no way to design complex systems like PCBs.

Separate software packages, even those produced by the same company, can still reduce productivity when features are separated from each other. Designing schematics in one program, and then moving to another package just to lay out traces, pin swap, and back annotate takes too much time.

Errors can be introduced when you move between software packages. The process for annotating at the board level and the schematic level can also be different. Why spend time learning two different back annotation processes?

Back annotation updates the schematic based on pin swap changes made in the PCB layout. Software packages with complicated back annotation functionality will cause all components in the capture to have incorrect part references and routing, and all because you clicked the wrong option during back annotation. This type of problem may not be easily repaired, and if you did not backup your files, you will have to manually update your schematic to match your pin swaps.

This can take hours of work and can be a real headache. Avoiding this type of error requires learning a complicated back annotation process.

Why You Need Integrated Design and Documentation Software

If you are using two different pieces of software for schematic and PCB layout, you will have to flip back and forth between the two programs. Using a single program presents changes in a single interface and reduces the chances for part referencing errors. Annotating changes between two programs requires a complicated procedure that is not always intuitive. In contrast, working within a single program means that back annotation only takes a few clicks.

Once you back annotate to the schematic, an ECO needs to be generated based on your design changes. Rather than importing files between multiple programs, your ECO can be generated immediately during back annotation. Using a single process to pin swap, back annotate, and generate an ECO all at once is a huge timesaver and prevents mistakes that arise when working with multiple programs.

After performing back annotation, an integrated piece of software can generate a Was-Is file based on the changes made to the layout and schematic. Back annotation at the board level should be no different from the schematic level. A software package with a single back annotation process saves time as you come up to speed and reduces the potential for errors.

 Automated schematic back annotation screenshot

Automated schematic back annotation

How Altium’s Design Environment Can Help You

Pin swapping and subsequent routing don’t need to be a major headache. Altium Designer makes it easy to route connections between components. All you need to do is select the relevant pins on your device and indicate the required connections to external components. Altium Designer’s automated routing features do the rest. Design rules are enforced on your nets, ensuring that your design will meet your basic design requirements.

If you find that you need to swap pins, you can easily limit pin swapping to I/O pins, clock pins, or power and ground pins. Back annotation only requires a couple mouse clicks, and your Was-Is files are automatically updated. The back annotation tool is extremely intuitive. Thorough documentation with step-by-step procedures can be accessed directly from Altium’s website.

A great PCB design software package like Altium Designer can help you save time swapping I/O pins in your layout. Altium Designer’s built-in ActiveRoute tool and massive component libraries give you the flexibility to perform pin swapping on any component. Your changes are seamlessly documented using back annotation.

You can always download a free trial of the board layout software that you want to use for your designs. To find out more about Altium Designer and how it can help you save time with pin swapping and back-annotation, talk to an expert at Altium.

Start the journey to switch over to Altium Designer today.

About Author

About Author

PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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