Estimated reading time: 5 minutes

Elementary Mr. Watson: Ensuring a Smooth Handoff From PCB Design to Fabrication

At the 2020 Tokyo Summer Olympics, the U.S. men's 4x100-meter relay team had high hopes of winning a medal. The team comprised some of the fastest sprinters in the world, but something went wrong. 

In a relay, four runners must smoothly pass their baton to the next runner inside a zone on the track. If a runner drops the baton or it’s passed outside the zone, the team risks disqualification. The U.S. team’s pass between the second and third runner was messy, slowing them down. By the time the last runner received the baton, the team had lost too much time. They finished sixth in their heat and didn’t qualify for the final.

Many people were surprised because the U.S. has a long history of winning relay medals. After the race, some former athletes and coaches said the team needed more baton passing practice. Legendary sprinter Carl Lewis called their efforts a "total embarrassment." My point is, although they were considered the best team, their downfall was the result of what some consider a simple task: handing off the baton. 

I have seen the same problem with PCB designers. You can be one of the best, but if you cannot transfer the crucial information and your vision to the fabricator and assembler, then you are destined to fail. 

However, there is an inherent problem with every PCB design you undertake. Whenever an internal or external entity on your team passes information, that is the weakest link in your process, with the greatest risk of miscommunication, problems, and errors. 

I’ll discuss in other articles the problems of poor components, incorrect trace widths and spacings and other issues. The list is endless. I have seen firsthand several underlying problems that I would label as the root causes of every issue in the design, fabrication, and assembly phases. Since these are the root causes of problems, this is where I would focus my time to fix issues. Some of these issues include:

Lack of Communication
Clear communication is key to any successful project, especially in PCB design. We should be communicating well before, during, and after the project. The design and fabrication teams must work together closely. When communication is poor, it's easy to make mistakes. For example, if the design team doesn't explain specific details clearly, the fabricators may misunderstand how to make the board. This will lead to a variety of problems. When fabricators ask for clarification, it can slow down the process, especially if communication takes time.

Sometimes, designers assume fabricators know what the board should look like. This is where clear communication matters. For example,  a designer might not mention the exact size of a hole or the materials needed for the PCB, which can lead to mistakes during manufacturing, using incorrect materials, or designing holes too small to fit the components.

To avoid these issues, both teams must keep an open line of communication. They should check in with each other regularly and ensure everyone understands the design and expectations. Clear and detailed notes about the design, shared through emails or meetings, can reduce confusion. Collaborative tools like video calls or online platforms, where everyone can review the same documents in real-time, can also be invaluable.

Failure to Follow Standards
Standards ensure that people do things the same way every time. They help designers and fabricators understand what is needed and avoid errors. For example, the industry widely uses IPC standards. It always surprises me when I ask designers about the standards they follow, and their reply is "none." That's like guiding a ship through the ocean with no compass or rudder.

Designers who fail to follow standards may create difficult or impossible boards to build. For instance, a designer might use non-standard hole sizes or spacings that a fabricator cannot work with. If the designer does not follow the proper rules, the board may not meet the necessary safety or quality standards, which can lead to failure during testing or use.

Fabricators are generally used to specific standards and may struggle if the design doesn't follow them. This can cause delays because the fabricator must figure out how to fix the design. By following the standards, designers can help prevent these issues and make the process smoother. When everyone uses the same guidelines, the design is more likely to be manufacturable and meet all the requirements.

Inadequate Tolerances
Tolerances refer to the allowable variation in measurements. In PCB design, they are critical because even small changes can affect how well the board works. If a designer does not define tolerances clearly, the fabricators may not know the acceptable variation. This can lead to too thin traces or holes too small for the components to fit. For example, if the designer doesn't specify the exact size of a hole, the fabricator might assume a standard size, and that may not work with the components.

When tolerances are unclear, ensuring the board is made correctly becomes more difficult. If the designer doesn't tell the fabricator the exact limits for things like hole size or trace width, the fabricator might make the wrong choice, leading to a board that doesn't meet the requirements. This can delay the process as designers correct or redesign the design.

Over-tolerance also contributes to this issue by imposing such strict requirements on the design that no fabricator wants to take on your project.

To avoid these issues, designers must clearly define tolerances for all essential board features, such as specifying the holes' size, the traces' width, and the exact alignment of different layers. By doing this, the fabricator ensures the board meets the correct specifications and functions as intended.

In conclusion, poor communication, failure to follow standards, and inadequate or over-tolerances are common problems that can delay PCB projects. These issues can lead to mistakes during the design or manufacturing process, causing costly delays. To prevent these problems, it’s essential to keep communication open between teams, follow industry standards, define tolerances, and use consistent file version control. By addressing these issues, designers and fabricators can work together more efficiently and create high-quality PCBs that meet all requirements.

John Watson is a professor at Palomar College, San Marcos, California.