EMC Question of the Week: March 17, 2025
In products that meet all of their EMC requirements, the circuit boards are typically
- isolated from chassis ground
- shielded
- circular
- green
Answer
The best answer is “d.” Of course, the color of the circuit board has nothing to do with its electrical properties. Nevertheless, historically, green is the most common color of the solder mask used to make printed circuit boards. In honor of St. Patrick's Day, it seemed appropriate for the correct answer to be green.
In some industries (e.g., aerospace and medical products), it is common to provide DC isolation between circuit board current returns and the chassis ground. Nevertheless, this is not typical of most circuit boards. And even in circuit boards where DC isolation is required, high-frequency filtering to the chassis ground is often necessary to meet EMC requirements.
Shielded circuit boards are also common in some industries. Shielding can be found in a growing number of boards that have sensitive analog RF circuits located near fast switching components. Nevertheless, in terms of sheer volumes, it would not be correct to say that most printed circuit boards are shielded (or circular).
Why are most circuit boards green? Historically, solder mask was dyed green to facilitate optical inspections of final board assemblies. That color was found to reduce eye strain while providing excellent contrast with the exposed copper and white silkscreen printing. Over the years, companies began to use other colors to signify different development stages or simply to give their products a unique style. But green has become the default standard and is still (by far) the most common circuit board color.
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