Issue link: https://iconnect007.uberflip.com/i/1480758
46 SMT007 MAGAZINE I OCTOBER 2022 "Look at the first part of the solder paste spec," Sue said. "It says the recommended ramp rate should be between 0.5°C and 1°C per sec- ond." (Note the red triangle in Figure 2.) "Yeah, then if we look at the reflow profile, by dividing the change in temperature at the melting point (217 - 20°C = 197) by the change in time (230 seconds), we see that the slope is 0.857°C per second, so it is nicely in the spec limits," Andy said. "e time of liquidus is easy, too—just sub- tract the time at D (290 seconds) minus the time at B (230 seconds) and get 60 seconds, also within the spec," Sue added. "e peak temperature is certainly easy to find at point C, or 240°C," Andy said. "And the cooling slope is -2.8°C, also within the spec," Sue chimed in. (Note to readers: Can you calculate this number?) ey then developed the PowerPoint slides to teach this material in their class. "at Excel soware tool you developed to make all these calculations was really impres- sive," Sue complimented Andy. "I heard Mag- gie discussing it with Chuck Tower. ey thought it was amazing." "'Twern't nothing, me lass," Andy responded in a gallant way (Figure 4). Both agreed that the students could use this Excel soware tool aer the class, but they had to know how to perform the calculations by hand. Eighteen months later… Sue and Andy continued their night school classes at the local community college. With the recommendation of Ivy University Pro- fessor Patty Coleman, they received some equivalent credit for work they had performed teaching SMT classes, as well as some other projects they worked on at Ivy-Benson Elec- tronics. Both students were granted their two- year AAS degrees. e more interesting devel- opment was that Professor Coleman pulled some strings and enabled them to transfer to Ivy University as juniors to work on their bachelor's degrees. ey would take a reduced course workload and work at Ivy-Benson part- time. All these events transpired in June and the two future Ivy U students would have to wait until September to start class. Right aer graduation, Andy and Sue were asked to meet with Maggie Benson. Both felt a little nervous. As they entered Maggie's office, they were even more so when they saw that Professor Coleman had joined the meeting. Figure 3: A reflow oven profile.