Both 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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The öunce" 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 öunce" rating of PCB traces to wire "gauge."

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A 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 ßtitching" 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.

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A "blind" via is one that connects a surface layer to an inner layer of a multi-layer PCB. A "buried" via is one that does not appear on any surface layer at all, but rather goes between inner layers.

Notes:
One students grasp the concept of a multi-layer board, the necessity of different types of vias will become obvious. Asking this question, then, is just one more way to communicate the concept of a multi-layer board.

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Hand soldering is exactly what is sounds like: soldering done manually, by a human being.
Wave soldering momentarily passes the PCB just over a bath of molten solder, allowing the solder to "wick" onto the pads and through via holes.
Reflow soldering uses solder "paste" applied to each pad, and a hot oven to melt the solder for joining components to the board.

Follow-up question: which technique is most appropriate for the following applications?

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Mass production with through-hole components

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Mass production with surface-mount components

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Single-board prototyping

Notes:
If possible, show videos of automated soldering processes to your students. It is quite educational (and awe-inspiring) for students familiar with tedious hand-soldering techniques to see how large volumes of circuit boards can be soldered using modern wave and reflow techniques.

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A ßolder mask" is a thin coating of polymer covering every part of the board except for those spots where you intend it to be soldered. A solder mask is absolutely essential if the board is to be wave soldered!
Follow-up question: what is the mask expansion dimension on a PCB?

Notes:
Anyone who has ever worked with a home-made, bare-copper (etched) PCB will appreciate the function of a solder mask, even when the soldering is all done by hand.

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Copper is very chemically reactive, so leaving it exposed invites corrosion, which will cause a variety of electrical problems. Tin is a much less reactive metal, and solder mask is a polymer which cannot corrode.

Notes:
Anyone who has ever etched their own board at home (and not coated it) either has seen or will see what happens to bare, unprotected copper over time!

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