Throughout the agile hardware design process, you’ll need to repeatedly adjust and validate portions of your design in successive development sprints. In a typical waterfall design process, you’ll get through the entire layout and start preparing for manufacturing once your CAD layout is completed. As you prepare your new product for manufacturing, you’ll need to look into the supply chain and check your layout against your design rules to ensure manufacturability. You’ll also need to closely collaborate with your customer and adjust the layout to accommodate changes in functionality.
As your team applies changes during each agile hardware design sprint, it’s always possible to make errors that may compromise product quality, and these errors may even affect fabrication and assembly. As designers, we try to take advantage of DRCs in our PCB layout software as design rules are critical for ensuring your board meets industry standards and passes DFM checks. With these points in mind, you can incorporate DRCs, simulations, and supply chain information into a real agile hardware design workflow.
The Role of DRCs and Simulations in Agile Hardware Design
Your DRCs are critical for ensuring your board will be manufacturable and meet industry standards. You should run a DRC for each functional block in your board multiple times during the design phase in order to catch any design rule violations and other errors that affect manufacturability.
Note that some electrically functional design choices may not trigger a DRC violation unless in your design software you explicitly define certain layout choices as design rule violations. As part of a DFM check, you should check your soldermask dams on components, via density on any thermal pads, and via-in-pad holes when using teardops.
You'll need to run DRCs multiple times during agile hardware design.
Even though a subcircuit in your design may pass DRCs and may be laid out according to industry standards, you shouldn’t assume the layout will function as expected. This is where simulations become a critical part of your workflow. Different simulations should be used to validate your system’s functionality, especially in complex systems. Adapting simulations into your hardware development workflow helps you catch errors before prototyping spins, ultimately reducing the number of design, build, and test runs.
During the design phase, you should run DRCs and simulations from your schematic and from your PCB layout. Simulations from your schematic are SPICE or IBIS-based simulations, so they give you an ideal view of the behavior of your circuit. However, they don’t take account of the geometry of your board; two different layouts that are made from the same schematic will produce different simulation results due to their different geometries. Running a simulation from your layout, particularly an electromagnetic simulation with a 3D field solver, can help you examine problems like crosstalk, reflections, and analog signal resonances at high frequencies in transmission lines.
Check the Supply Chain During Agile Hardware Design Sprints
If you’re using an agile hardware design methodology, it’s in your best interests to check the supply chain repeatedly in each design sprint. The supply chain can change quickly, and critical components in your system might be unavailable at the point you start planning for production. If you wait until the end of your development process to check the supply chain for your desired components, and you find that your desired components are unavailable, you’ll need to swap your components for suitable replacements. If you happen to be farther along in the design process, then the required redesigned can extend beyond the unavailable component.
Dealing with unavailable resistors or capacitors is typically a minor issue as you can usually find a suitable substitute with similar power rating or component value. However, with high pin count components like FPGAs, some SoCs, or even simpler PLDs like MCUs, the swapped component will likely have a different pin arrangement. With a swapped MCU, you’ll likely need to reroute your board to accommodate changes in the pin arrangement on the new component.
If you check the supply chain during successive agile hardware design sprints, rather than just before you move to manufacturing, you’ll be able to anticipate sourcing problems and adjust your design to accommodate. Component shortages and counterfeits are real problems, but identifying them early allows you to reduce the extent of any redesign. As part of an agile hardware design process, any supply chain changes can be addressed during design sprints rather than just before manufacturing.
Design, Build, Test, Repeat
Once your design is finished, you’ll need to produce quick-turn prototypes for testing. If you identify these required changes earlier in the design process, you’ll be able to reduce the number of required redesigns and prototyping runs, ultimately helping you stay within your design and production budget. You'll need to test every aspect of your prototypes and determine appropriate redesigns before you move to full-scale production.
Within an agile hardware design process for electronic products, taking advantage of DRCs in your design software and simulation tools can help you determine appropriate redesigns before you prototype your board. Within each design sprint, these tools allow a design team to identify potential redesigns much earlier in the design process. The goal here is to reduce the number of required prototyping runs and ensure your board meets your basic functionality requirements.
Your documentation and version control processes are critical here, particularly when you begin implementing redesigns after an initial prototyping run. In the event that your board does not function as desired, it is useful to save a previous version of your design before implementing redesigns and beginning a prototyping run. This allows you to revert to an old version of your design in the event your redesign does not improve the functionality of your board. Again, you'll need to use your DRCs and simulation tools during a redesign sprint before moving on to prototyping. However, if you take advantage of your simulation tools numerous times during the initial design phases, you'll be able to identify numerous design options for your system, which can greatly aid in developing proposed redesigns after your first prototyping run.
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