Here’s a question that came across my desk the other day: What’s the first thing to know when designing a printed circuit board (PCB)? In case you’re not hip to PCBs, let me assure you that you interact with them on a daily basis. They’re found in everything from dollar store toys to radios to continuous glucose monitoring systems.
We asked Agustin Guzman, one of our electrical project engineers, this very question and he didn’t even say, “Gimme a minute.” He just quickly answered, “I need to know what class of electronics I’m making. Class 1, 2 or 3.”
First, a little background. The PCB class definitions and requirements are designated by an organization known as the IPC. The IPC is the global trade association serving the printed board and electronics assembly industries, their customers and suppliers.
Class 1 — These products are very simple, with non-critical electronics. It’s the type of PCB that goes in the trash when you’re done with it. Think greeting cards that play music, cheap toys with LED lights, and key chains that light up one minute and fizzle out the next. The manufacturer needs to make it inexpensively so they use cheap materials and cheaper components. The copper layers are the cheaper options. It’s not exactly a Six Sigma product.
Class 2 — These products actually need to work. Maybe you’re making a car radio. Let’s face it, as much as we love our tunes, a car radio isn’t critical; no one dies if it doesn’t function. However, people do get upset when their radio doesn’t work. So the materials in that radio, including the materials that make up the PCB, need to be more robust and more expensive. Component testing is required before they're put in the PCB, and the finished product will be tested to make sure it works before it leaves the factory.
Class 3 — Two words: mission critical. When a commander hands a soldier a pair of night vision goggles and tells them to complete a mission, they have confidence that the electronics in that product works all the time. When a pacemaker is placed in somebody’s heart, there’s no, ‘Oh well…that didn’t work.’ Because they’re used in critical systems such as those in the aerospace, defense and medical industries, the materials in Class 3 PCBs must be the highest quality, and have to pass very specific UL tests. A lot of individual testing goes into the components before you put them into a Class 3 assembly.
When you look at it that way, it’s easy to understand why this question is the first one that needs to be answered. Understanding which product class the PCB goes in informs everything else — the design, materials, testing, costs. And if you don’t have that information, your quote is meaningless.
Thanks for being so smart, Agustin!
[To learn more about PCBs, check out this blog post: Which Type of Conformal Coating is Right for My PCB?]