PCB Design Challenges—From the Fabricator’s Viewpoint

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If you’re a fabricator, chances are you have a few things to say about at least a few of the PCB designs that make their way through your shop. I guarantee that you have several well-worn stories about designs that made you scratch your head and think, “Hmmmm.”

So, in this section, we asked PCB fabrication experts to share their thoughts about challenges that PCB designers need to more thoroughly understand. Do you see yourself on either side of these issues?

Dana Korf - Korf Consultancy LLC

What is your main concern for PCB designers?
Impedance and signal loss variability. In recent years the signal integrity that RF designers were very concerned about is now becoming a requirement in standard digital and analog designs. Simulation tools are used to characterize the design nominally and against high and low tolerances of the key specifications. Then a quick prototype is fabricated and tested. Several iterations may be built and assembled until the proper answer is achieved.

The signal performance can be affected by the drilled/lased hole’s inner diameter, plated diameter, material dielectric thickness and electrical properties, solder mask, Dk and thickness, trace-width tolerance, and to a lesser extent its thickness. Yet, the fabricator is rarely required to provide this information to the designer. So, the designer doesn’t know if the PCB was built at the high-end, low-end, or middle of the tolerance range. Designers often complain that a new revision or build didn’t perform like the last version. Of course, it may not. The reason is most likely due to fabrication tolerances.

When the design has tight impedance or loss requirements the designer should require more information about the received PCB critical parameters to better correlate actual performance to the expected performance.

What issue should PCB designers be more aware of?
Over-specification. Significant cost is incurred by over-specifying requirements. One of the most common reasons for this is that requirements get copied from one design to another design without the designer’s full understanding of whether they are applicable. Another reason is that PCB hardware engineers and designers are not sufficiently taught about cost impacts early in their career. For instance, how many PCB fabrication classes are taught at trade schools, community colleges, and four-year universities?

Continue reading the rest of this article in the June 2023 issue of Design007 Magazine.