PCB Design Process Essentials for Board Reliability

If you have worked in product development, then you are probably used to solving unique problems with each new project. Sometimes, the complication is fitting all the necessary components into the size and weight budget. Others, it’s figuring out how to explain to a client that the kitchen appliance can’t draw 50 A to power everything they want. Fortunately, when it comes to designing a reliable board, you can follow the same PCB design process. When designing a critical circuit, the first thing is to examine its components. Choosing the correct components at the outset will save time, money, and sanity later on. Next, go over the materials that you want to use on the board and make sure they can go the distance. Finally, you can rely on an old faithful list of conservative design rules that are sure to give your PCB the best chance of success.

PCB Component Selection for Reliability

When you first start prototyping, you often want to use the brand spanking new chips you just read about online. You will quickly learn that early adopters often face a host of unseen issues and start to rely on mature components. The ones with multiple supply sources, lots of documentation and proven reliability. It’s important to have several buying options so that you can bypass component shortages and avoid counterfeit parts. Keeping an up-to-date BOM for your board is also a must. That way, your team can watch out for scarcity and ensure no parts are nearing obsolescence.

Knowing how parts will perform on your board is also very important. This is particularly crucial if you’re designing a device with a higher IPC rating that must adhere to more rigorous standards. If your circuit is going to undergo a lot of mechanical stress or high temperatures, it might be a good idea to use through hole components as they are more physically connected to PCBs. If your board will be in a less demanding environment, you may opt for solely SMT components. Whichever option you choose, you’ll need to coordinate with your CM, as component selection  affects the manufacturing process and the longevity of your board in the field.

PCB Material Selection for Reliability

Choosing the right PCB material for an application is already difficult. The coefficient of thermal expansion and dielectric constant not only affect a circuit’s impedance and signal integrity, but also the board’s longevity.

If you’re designing a high voltage board, you’ll need to pay special attention to material selection. High voltages can break down materials and cause the board to degrade, prematurely. If the material degenerates enough, your creepage/clearance may not be enough and your board could be fried.

The operating environment is also critical when choosing your materials. Skip the environment step in the PCB design process, and the circuit may end up in a very hot area with little cooling. The board could fail during flight. Make sure to consider things like dust, humidity, moisture, heat, chemicals, UV exposure, etc. Some of these considerations can be mitigated by an enclosure.

You’ll also want to check the chemical stability of your board materials. Just like with component selection, you don’t want to be using the latest and greatest materials. For reliability, it is best to stick with materials that have a proven track record and won’t degrade or fail during operation.

PCB Design for Reliability

There are times when an engineer wants their design to be as efficient as possible, meeting their guidelines exactly. When it comes to elevators, that’s not the case, because the factor of safety for those is (generally) turned up to 11. Think of conservative design as a factor of safety for your PCB. There are two easy conservative principles you can apply here.

• More Copper - When it comes to copper and reliability, more is more. Over time, copper can degrade, like when we were talking about high voltages. The thicker the copper layers you use, the less likely it is to fail. Sometimes, users will put your board somewhere it’s not supposed to be and it will get too hot. Wider traces will help your board deal with extra heat and can carry more current. More copper may make your PCB more dependable, but be sure to evaluate how it affects your signal integrity as well.
• Wide Spacing - Fine pitch components will always be more difficult to assemble and thus more prone to failure. If your board has to be reliable, avoid fine pitches. Closely grouped parts can also cause hotspots on your board, which will stress PCB materials and components themselves.

Whether your design has its wings in the air or its wheels on the ground, the PCB design process for reliability remains the same. When it comes to component selection, choose mature parts that have a long track record and multiple suppliers. You’ll want to use tried and true materials for your PCB as well, taking the operating environment and high voltages into consideration. Last but not least, you can add a factor of safety to factors like copper weights and spacing between components.