Learn what design for reliability (DfR) principles are.
Understand the importance of design for reliability (DfR) concepts.
Learn how to implement DfR principles during the PCB design process.
Rather than buying a fancy, new car with state-of-the-art technology, I continue to drive the same dependable, old car. Why? Because I value reliability over having the newest, flashiest model. In electronics, reliability is just as valuable, as it ensures that a product is safe, dependable, and marketable and that manufacturing companies don’t get overwhelmed with returned products that have failed. When you’re working on a PCB, design for reliability (DfR) is one concept that helps to improve reliability by addressing failure points before they become real-world problems.
What is Design for Reliability (DfR)?
DfR is the systematic approach of optimizing a product at the design stage to ensure that possible failure points are identified and addressed before the manufacturing stage. While DfR is a relatively new concept, its implications are becoming more important as companies put an increasing priority on producing products with shorter design life cycles. Cramming more features into a product increases the risk of failures, while public expectations for quality are higher than ever. By putting DfR into practice, a product is allowed to run through its course of lifecycle reliably.
Why Is Designing for Reliability Important?
DfR reduces the chances of PCB failures, particularly in harsh environments.
If you’ve ever seen how a piece of your design is being used in the field, you’ll recognize the fact that passing a lab test does not guarantee a design’s functionality when deployed. There are many external variables that can expose design faults that might be missed during lab testing.
Here are two examples of ways design faults can slip through the cracks during testing:
A PCB will be subjected to consistently high temperatures when installed in some machines and might push electronics to work close to their temperature limits. If some of the components fail to function reliably at higher temperatures, the entire system will be compromised.
Frequent changes in temperature may subject a PCB to thermomechanical effects. Some of the solder joints may crack if continuously exposed to cycles of high and low temperatures. The ability of a PCB to dissipate heat can also aggravate this problem. Thermal management, or the lack thereof, affects lifespan and a PCB’s ability to function properly.
To prevent these types of issues, you’ll want to make using DfR principles a common practice, as it helps prevent PCBs from performance and reliability issues, particularly being a source of electromagnetic interference (EMI). While components may behave as they should in a lab setting, they are not guaranteed to do so in a considerably noisier electrical environment. Instances of corrupted signals are signs of EMI susceptibility, which is very difficult to mitigate once it’s in the field.
Let’s discuss how to apply design for reliability (DfR) concepts to prevent these types of issues.
How to Implement Design for Reliability Concepts in PCB Design
Choosing the right component is an important DfR practice
There are many factors that affect a PCB’s reliability. Some, like the fabrication and PCBA process, are beyond a designer’s control. However, you can still do your part in ensuring your design is reliable and does not require constant troubleshooting.
Considerations for Reliable PCB Design
1. Component Selection
Whether you’re choosing a microcontroller or a plain capacitor, it’s important to ensure what’s stated on the datasheet matches the design requirements. You’ll need to consider the most extreme scenario for the components, as that’s often where failure occurs.
For example, a microcontroller that runs at maximum speed consumes more power and produces more heat than one which runs at minimum capacity. These are issues that need to be addressed in the design. If you’re designing a PCB that runs in extreme environments, you may want to ditch commercial-grade components and go for their industrial or military grade versions.
2. EMI Mitigation
Mixed-signals, RF, analog, and high-speed signals—if your design relates to these terms, you ought to pay attention to EMI radiation and susceptibility. Tips like keeping high-speed traces apart from analog signals are proven to prevent noise coupling from one trace to the other.
It’s also crucial to ensure that high-speed signals have a low-impedance return path that doesn’t traverse into the ground of other components. Plan the placement of components and separate the ground planes for analog, digital, and power modules. While doing so, avoid having ground loops in the PCB, as they can radiate noise.
3. Thermal Management
When you’re designing with microcontrollers and power MOSFETs, it’s inevitable that the PCB will generate substantial heat. It is important to know how well heat disperses to avoid rapid component degeneration.
Using thermal vias is one potential heat dissipation method. Thermal vias should be placed around heat-generating components; coupled with heatsinks and a cooling fan, they’ll allow engineers to avoid heat points building upon the components. It’s also important to ensure the traces carrying high current are routed with sufficient width.
Optimizing a PCB for design for reliability (DfR) is easier with advanced PCB design software. OrCAD not only offers user-friendly PCB layout tools but also analysis and simulation software to ensure design reliability.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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