PCB Changes: Tips for Updating Old PCB Designs with New Parts

Have you ever opened up an old design and wondered how much of it was still usable? Maybe you were contacted by an old client, and they want you to provide some updates on an old design. No matter what the situation is, there are times where updating old PCB designs with new parts makes sense. If done correctly and when armed with all the right information up front, you can cut down the total design time while preserving the best parts of your design in a new iteration. Here’s what you can do to update your old designs successfully and how your PCB design features can help.

What to Keep in Mind when Updating Old PCB Designs

Before you jump into a design update, there are some important points to keep in mind. This all relates to the extent of the required updates, what the goals of the project are, and where in the project the updates will appear. Here are some questions to consider as you prepare to update an old PCB design.

Which Design Documents Need Updating?

Sometimes, design updates are simple enough that you only need to make changes to components in the schematic. In general, there are updates that might appear in the schematic that won’t result in changes to the PCB layout (e.g., swapping a part number for a standard SMD passive). However, a change to the PCB layout is likely to force a corresponding change in the schematic.

If you want to keep your updates clean and concise, try to confine changes to the schematic if possible. This means that, whatever changes need to happen, they don’t result in a change in PCB footprint or 3D model. Whether or not this is possible depends on which parts are being updated or swapped.

Which Parts are Being Updated?

Whenever I need to update an old design, there will always be a few parts updates. Components sometimes go obsolete, they are simply out of stock, or there are functionality changes to the design that rely on new components. Depending on which parts are being updated, the overall extent of any design changes depends on which components need to be updated.

As was mentioned above, updates will be quick if they can be confined to the schematic. However, this is often only feasible for a connector swap, passives swap, or simple IC swap. Unfortunately, many ICs might have the same package and land pattern, but they’ll have totally different pinouts. Even if the new component has the same package size and land pattern as the old component, swapping the components can force major changes to the layout if the two components have different pinouts.

Is it Easier to Start Over?

Whether you’re a freelance designer or you run a design firm the customer is always right, and if they want you to make massive changes to a design that’s their choice. That being said, it may sometimes be easier to start a layout from scratch, rather than modify an existing layout. Making major changes to an existing layout can involve ripping up routing, moving components, changing planes and polygons, and much more.

With this in mind, it might be easier to just start over with a new layout. If you’re using the right ECAD tools, you can still copy complex layout features like the layer stackup, polygons, pads/vias, copper pours, cutouts, and other components from the old layout into the new layout. It’s up to you to judge whether it’s more convenient to do a completely new layout or modify an old layout. In some cases, where you need to modify a complex layout with extensive changes, you’re better off just starting over.

Some Tips for Updating Various Components

By now, it’s probably become clear that the extent of your PCB layout changes will depend on what happens to the PCB footprint when swapping components. Here are some tips I’ve found useful when updating specific types of components.

• SMD passives and semiconductors: As long as you’re only swapping a component for an equivalent part with the same package and ratings, you won’t make any changes to the layout. Changes will only need to happen in your parts library. 
• ICs: The pinout will almost always change, either partially or entirely, when you’re swapping for a newer component. Some manufacturers produce multiple components that have the same pinout and package size, but different part numbers. 
• Discrete transistors: Aside from SMD passives, these are the next easiest components to swap as so many packages are standardized, which minimizes required layout changes. 
• Through-hole passives and ferrites: These components are not always perfect replacements for each other. For inductors or chokes, the pinout for the updated component may be different, but the level of routing and layout changes are minor. The exception is transformers, which can require significant routing changes. 
• Connectors: As long as pin count and pitch are the same, there will not be any required layout changes as long as the land pattern appears on the same layer. If you’re swapping onto the back layer, now you need to swap pins on each side of the and do some rerouting. 

When you’re updating your old PCB designs with new parts, it helps to use the industry’s best set of layout and routing tools to help you finish up your design updates. The rules-driven design engine in Altium Designer® can help you quickly evaluate your design as you apply updates. All the design and CAD features in Altium Designer will help you stay productive and keep your design error-free.

When you’ve finished your design, and you want to share your project, the Altium 365™ platform makes it easy to collaborate with other designers. We have only scratched the surface of what is possible to do with Altium Designer on Altium 365. You can check the product page for a more in-depth feature description or one of the On-Demand Webinars.