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Testing Todd: How are the Ratings?

Hello, readers! Thank you for stopping by again. Let’s talk about ratings. No, I’m not talking about the latest Facebook likes or Twitter retweets, but a topic that confuses many final QA technicians the world over. I’m talking PCB voltage ratings.

If you are an electrical test engineer/technician, I’m sure you have seen many master drawings that use the term “Maximum Rated Voltage is XXX Volts,” where XXX is a number.

I have seen many final inspection areas that will reject a final ET certificate of compliance (CoC) because they read the master drawing and see a statement such as “maximum rated voltage = 24V” but the CoC  says it was tested at 250 volts! The manufacturing specification is also stated as IPC-6012D(DS). Is the CoC wrong? In most cases, no. “Todd, can this be?” you ask. Well, in this case, it is correct.

Master drawings carry a gambit of information for the manufacture of printed circuits. Many notations are specific instructions and call-outs for the PWB. However, there are many “statements” on the master drawing as well. The term “maximum rated voltage” is one of those statements. In many cases, when you read that statement, you can think, “Thank you for that. Good to know.” Does that mean that  I have to test that PWB at the rated voltage? In many cases the answer is no. 

What that statement is telling you is that in that PCB’s duty cycle (life) it will never see a voltage higher than what is stated. Again, good to know, right?

To read the full version of this article which appeared in the April 2018 issue of PCB007 Magazine, click here.