PCB007 Magazine

PCB-Apr2018

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56 PCB007 MAGAZINE I APRIL 2018 Hello, readers! Thank you for stopping by again. Let's talk about ratings. No, I'm not talking about the latest Facebook likes or Twit- ter retweets, but a topic that confuses many fi- nal QA technicians the world over. I'm talking PCB voltage ratings. If you are an electrical test engineer/tech- nician, 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 rat- ed voltage = 24V" but the CoC says it was tested at 250 volts! The manufacturing speci- fication 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 infor- mation for the manufacture of printed cir- cuits. Many notations are specific instructions and call-outs for the PWB. However, there are many "statements" on the master draw- ing as well. The term "maximum rated volt- age" 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 rat- ed 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? Let's break down our example above: 1. Maximum rated voltage = 24V on the master drawing 2. Specification = IPC-6012D(DS) 3. Certificate of Compliance states 250V Who's right? The certificate of compliance is correct. Why? As we reviewed above, the max- How are the Ratings? Testing Todd by Todd Kolmodin, GARDIEN SERVICES USA

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