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JULY 2022 I SMT007 MAGAZINE 85 "What about the area of the side walls?" Sue teased. Andy paused and seemed stumped. "Well, what is the perimeter of the circle?" Sue teased. "Two pi times the radius?" Andy said with uncertainty. "Yes, so then the area of the side walls would be?" Sue questioned. "Wait, now I see it—two pi times the radius times the stencil thickness!" Andy said trium- phantly. "Isn't it interesting that the area ratio is the same for square apertures?" Sue commented. "And I actually understand how it is derived," Andy said, beaming. As they were chatting, Chuck and Tanya Brooks came to their table. "Andy, Sue, it's great to see you here," Chuck said. Andy, Sue, Chuck, and Tanya shook hands, and Sue and Tanya hugged each other. "is place has the best ice cream around," Chuck opined. All agreed and small talk ensued for a few moments. Finally, all sensed Chuck wanted to say something. "Sue and Andy, you two are the superstars in our SMTA certification prep class. We need some more instructors. How about you two joining our instructor team?" he asked. "Sure," Andy said, "we would love to!" Some more small talk ensued, and eventually the group broke up and headed to the doors of the shop. As Sue and Andy walked to Andy's car, Sue looked extremely upset. "What's the matter?" Andy asked. "I'm afraid to speak to a group; I don't think I can be an instructor," Sue replied. Andy thought for a while and then gave her a hug. "How about this? I will speak and conduct the class and you will answer questions that you are comfort- able answering," Andy suggested. e relief on Sue's face was palpable. "anks, Andy, maybe approaching it this way will make me feel more confident speaking in front of a group," she said with an obvious sigh of relief. Will Andy ever catch up to Sue intellectu- ally? How will Sue handle helping teach the class? Stay tuned to find out. SMT007 All figures are used with permission of the copyright owners, Jim Hall, Phil Zarrow, and Ron Lasky. Reference 1. "Does Solder Paste's 'Five Ball Rule' Remain Valid in SMT Today? by Ron Lasky, Indium Corpo- ration. Ronald C. Lasky is an instruc- tional professor of engineering for the Thayer School of Engineering at Dartmouth College, and senior technolo-gist at Indium Corpora- tion. To read past columns, or contact Lasky, click here. Download The Printed Circuit Assembler's Guide to… Solder Defects by Christopher Nash and Dr. Ronald C. Lasky. You can also view other titles in our full I-007eBooks library here. Figure 3: The area ratio is important in round or square stencil apertures. Note that the formulas are the same for both.