SMT007 Magazine

SMT007-Feb2023

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66 SMT007 MAGAZINE I FEBRUARY 2023 to share. "Well, Carlos and I developed a Pareto chart of the defects (Figure 1). We started working on the graping issue first. ey were using circular apertures for BGAs, so I recom- mended switching to square apertures. Fortu- nately, their stencil vendor is in town, so they got new stencils and we already have quite a bit of data. It looks like the square apertures have significantly reduced graping, but I don't know the details yet. Next, we are going to work on the head-in-pillow (HIP) defect." Satisfied with Sue's progress, Chuck then turned to Andy and asked, "What about the training plan to help some of the workers become process engineers?" "José identified four potential candidates," he replied. "Aer discussing it, we think the peo- ple should become SMTA-cer- tified process engineers 3 . ey will need a lot of preparation, so I am developing a workshop using the Handbook of Electronic Assem- bly (Figure 2) 4 . I plan to give them a lot of exercises to improve their confidence. is teach- ing project and the process improvement action plan will keep me busy for the rest of the time Sue and I are here." "Sue, I can s ee you have your hands full working through the defects identified in the Pa r e to c h a r t ," Ch u c k said, and with that, the meeting was over. Sue decided to tackle her project right away, so she went to find Car- los to start working on reducing HIP defects. " C a r l o s , l e t 's f i n d Mi g u e l a n d d i s c u s s a p l a n t o r e d u c e H I P defects," Sue said. José had appointed Miguel to be the point per- son on working on defect minimization. ey soon found him and got to work. "Señorita Sue, can you tell us what typically causes the HIP defect?" Miguel asked. "Absolutely," Sue said. "e basic failure mechanism occurs in predominantly ball grid array packages. During the assembly pro- cess, as the circuit board and ball grid array go through the reflow oven, they can oen move relative to each other because of thermal warp- ing of the circuit board and ball grid array package. Sometimes, they'll separate during the reflow process: the solder paste will reflow separately from the ball and a solder connection will not be formed." (Figure 3). "So, what can we do to minimize HIP defects?" Miguel asked. "We want to assure that we have a nice, tall stencil-printed solder paste deposit so that we're get- ting good definition in our printing Figure 1: A Pareto chart of the defects at Castellanos Electronics. Figure 2: The book Andy is using for the SMTA certification preparation classes.

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