Issue link: https://iconnect007.uberflip.com/i/1491409
68 SMT007 MAGAZINE I FEBRUARY 2023 rather than having hot slump during reflow, which can also be an issue," Sue said. "We want to make sure that the pick-and-place machine is placing the ball squarely on the pad, not off to the side. It helps to have a solder paste that has a little stringiness to it, so that if the cir- cuit board pad and solder ball do separate, the solder paste will still stick them back together. In these types of situations, an "oxidation bar- rier" in the solder paste helps in the reflow pro- cess, too. e new solder paste that we will be buying to reduce response-to-pause issues also has good HIP resistance. So, that should help a lot." "Will the new square apertures also help?" Carlos asked. "at's a good point. Having more solder paste in the print is definitely a good thing," Sue answered. "Miguel, can you check the printing to make sure we don't have hot slump, and that the placement machines are placing the BGAs squarely?" Sue asked, as he replied, "Sí, señorita Sue." As they were wrapping up, Sue asked, "Car- los, do we have any data on graping since we switched to square apertures?" "Sí, señorita Sue, graping defects are down by 95%," Carlos answered. "Terrific," said Sue and Miguel in unison. At the end of the meeting, Sue gave each man a chaste hug. ey both turned red and looked like they might swoon… Will the HIP decrease? What will Andy teach in his SMTA certification preparation classes? Will you be able to answer some of Andy's quiz questions? Stay tuned to find out. SMT007 References 1. "Pareto chart," Wikipedia.org, Sept. 17, 2022. 2. "Response to Pause: A Critical Solder Paste Parameter," by Ron Lasky, Indium Corporation, Indium.com, Aug. 21, 2019. 3. "SMTA: Certification," SMTA.org. 4. Handbook of Electronic Assembly and A Guide to SMTA Certification, by Ron Lasky et. al, SMTA Publishing. Ronald C. Lasky is an instruc- tional professor of engineering for the Thayer School of Engineering at Dartmouth College, and senior technologist at Indium Corporation. To read past columns, click here. Figure 3: The mechanism of the head-in-pillow defect.