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Printed Circuit Board Layout and Manufacture
7 questions By Tony R. Kuphaldt
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Question 4 of 7
What are blind and buried vias, compared to normal vias?
Reveal answerA “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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Question 5 of 7
Compare and contrast these three techniques for printed circuit board soldering:
- Hand
- Wave
- Reflow
Reveal answerHand 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?
- Mass production with through-hole components
- Mass production with surface-mount components
- 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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Question 6 of 7
A solder mask is a very important feature on professional-quality printed circuit boards. Explain what a solder mask is, and why it is so important.
Reveal answerA “solder 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.
