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Printed Circuit Board Layout and Manufacture
7 questions By Tony R. Kuphaldt
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Question 1 of 7
When a PCB designer speaks of dimensions in thous or mils, what does he or she mean?
Reveal answerBoth a “thou” and a “mil” refer to one-thousandth of an inch.
Notes:Be sure to remind your students that the “mil” (which is one “milli-inch”) is not to be confused with a millimeter, which is of course a metric dimension rather than an Imperial dimension.
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Question 2 of 7
An important parameter when specifying traces on printed circuit boards is the ounce rating of the copper used. “1 ounce” copper is very common for general-purpose work. Explain how this “ounce” rating is defined, and why you might want to use “2 ounce” or “4 ounce” copper instead of “1 ounce” for certain traces on your board designs.
Reveal answerThe “ounce” rating of PCB copper is defined as weight of that thickness of copper trace, for one square foot of trace area. Heavier ounce ratings are used for high-current and/or high-reliability traces.
Notes:Ask your students to compare and contrast the “ounce” rating of PCB traces to wire “gauge.”
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Question 3 of 7
What is the difference between a pad and a via?
Reveal answerA pad is a ring of copper on one side of the board only, while a via is a “double-pad” where two pads on opposite sides of the board are electrically joined through the board to form one connection.
Follow-up question: vias are often used to do “stitching” in multi-layer printed circuit boards. Explain what this means.
Notes:This question requires the students to do some research into common PCB layout terms.
