Just take a look at the cross section of any PCB, and you'll quickly find that they can be very complex. This is especially true with high density designs, high layer count stack ups, and the myriad of materials used in many PCBa. Sometimes, when we look at a very complex board build, we may want to take that board and make it simpler for cost reasons, sourcing reasons, or to eliminate unneeded features.
In this article, we will look at some ways to take a complex board and simplify it for the reasons listed above. Simplification can take many forms, such as the typical approach to optimizing a BOM for a complex prototype, making it much simpler for production. This is part of a process that larger companies will use when moving a board from prototyping volume into high volume. Let's jump in and examine these aspects.
When is it Simplification vs. Optimization?
The term “PCB design optimization” is generally a cost reduction approach, and it typically looks at the BOM for a production build. When quoting a build for high volume, one will find that the parts are probably the most expensive part of the design. You wouldn't know this by looking at a simple prototype with turnkey or quick turn prototyping, where much of the cost is lopsided towards the board build and assembly. That dynamic changes when switching to volume manufacturing, where a more significant driver for a product is the component costs.
PCB design optimization as a process focuses more on reducing BOM cost, while PCB design simplification can focus more on the complexity of the bare PCB. Depending on what the initial board looks like in terms of complexity of the prototype build, cost reduction may not be the biggest benefit in design simplification. There can be several other benefits to design simplification beyond cost which will certainly make it worthwhile in volume production:
- Defect rate - By reducing the complexity of the board, you eliminate features that could be prone to fabrication defects.
- Throughput - Typically, design simplification creates a PCB that requires fewer process steps, and fewer steps means higher throughput at volume.
- Testing requirements - Additional costs related to quality control, such as testing or on-the-line inspection, can be eliminated which then raises throughput.
Just as a final review step, once a design has been qualified and received sign-off, the design and supply chain teams may come together and look for ways to optimize and simplify the design. This is an important final step that should be done before sending the design outputs to a manufacturer for tooling and process engineering in volume production.
Some Ways to Simplify a PCB
Rather than just focus on the cost aspects above, look also at the list of areas in the table below. The points listed above do affect overall intangible costs for a board production run but they were not chosen with only simple cost reduction in mind. Instead, try to find ways to simplify a design by focusing on things like quality and throughput. Let the supply chain folks focus on the bigger cost driver (the BOM) while the design team focuses on the PCB.
Some areas where it makes sense to attempt to simplify a board are outlined below.
Drill and route
Case size and density
The big hazard in PCB simplification is creation of an SI, Pi, or EMI problem where there was none before. Simplification starts by looking at the stack up and proposes to consolidate layers or remove layers, and this is where there is a risk of creating a new problem if this is not modified correctly. Depending on the changes that are implemented, the board may need to go back for another round of pre-compliance testing or SI testing. If design simplification results in major changes to the design, EMC testing may be required.
Therefore, it’s probably best to wait until the design is simplified, and then put the simpler board through EMC certification, while the more complex board only goes through pre-compliance and functional testing. Keep these points in mind when creating a new revision with the goal of design simplification. With a proper data management system, you can keep track of the compliant and non-compliant revisions easily, and of course in a pinch, a more complex but compliant board could still be put into production.
When you’re ready to remove the excess complexity from your PCB, make sure you use the best PCB design features in OrCAD from Cadence. If you’re ready to take even more control over net logic and board layout, you can graduate to Allegro PCB Designer for a more advanced toolset and additional simulation options for systems analysis. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.