Issue link: https://iconnect007.uberflip.com/i/1526114
58 SMT007 MAGAZINE I SEPTEMBER 2024 support. For each build lot, four manufactur- ing panels were selected, serialized, and singu- lated into the individual quadrants. e quad- rant level and component footprints were mea- sured from front and back (Figure 8). e area of measurement for each component was 12.5 mm beyond the edge of the component perim- eter. Analysis metrics of warpage and copla- narity were then obtained for front and back of each component footprint. Interface plots were also obtained to evaluate local PCB thick- ness profiles along the diagonals of each com- ponent site in conjunction with the general coplanarity of the site. Physical microsections were also taken aer surface analysis by shadow moire. ese microsections were done on a sampling basis across different build lots, quadrants, and com- ponent sites to confirm PCB thickness varia- tions obtained from the interface plots. Mea- surements were taken every 1 mm along the microsection to generate profiles of PCB sur- faces relative to the PCB centerline (Figure 9). Results and Discussion e differences in copper balance strate- gies had a significant impact on the coplanarity under a component. Figure 10 shows the mea- sured results for the smaller 28 x 28 mm pack- age footprint across the different materials and PCB fabricator build lots. Here, the materials were ordered generically from highest to low- est resin flow going le to right. e selection of material had a very significant impact when the design was not optimized for copper bal- ance. Whereas, when the copper balancing was optimized, the choice of material had lit- tle impact on average coplanarity with only a noted increase in variability for materials con- sidered to be lower flow. is observation matched general expectations based on the delta copper profiles for the 28 x 28 mm foot- print as shown in Figure 7. Figure 11 shows summary results of copla- narity for a selected high-flow, mid-flow, and low-flow material by package size and copper balance strategy, including data across multi- Figure 8: Surface analysis and metrics. Figure 9: Full microsection across the component footprint.