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60 SMT007 MAGAZINE I SEPTEMBER 2024 egy, package footprint size, material, and PCB fabricator with respect to a 225 µm coplanar- ity acceptance limit. It shows that, with few exceptions, small- and medium-sized package footprints can achieve low coplanarity require- ments without much consideration for copper balancing. With larger package footprints, the need to balance copper becomes extremely critical. Fabricators did not use the exact same pre- preg glass styles or resin content which resulted in each fabricator having different levels of avail- able resin volume for filling copper void areas under the component at each prepreg open- ing, but nonetheless, coplanarity trends were consistent across fabricators. Based on micro- section analysis, this difference in stackup con- struction likely accounted for most differences seen between PCB fabricators rather than any differences in lamination profiles. Coplanarity and Local PCB Thickness Variations e data obtained from the Interface Analy- sis feature in Akrometrix analytic soware was used to separate the contribution of local PCB thickness variations and the contribution of bow/twist and warpage of the PCB on copla- narity of the component footprint. e inter- face plots also allow analysis of how the super- position of the two contributions resulted in coplanarity differences between front/back and between panels. e methodology of including different copper balance strategies within the same manufacturing panel made it possible to evaluate the progression of total coplanarity and local thickness variations as the profile of local copper changed. Figure 13 shows an example progression for different changes in local copper as well as the coplanar- ity and local PCB thickness for two different materials. Figure 13: Superposition of local PCB thickness variations with general PCB bow/twist.