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JULY 2019 I PCB007 MAGAZINE 21 crovia. No CO 2 laser-related melted and recast copper was visible on the target pad. Shown in Figure 22 are images of the CO 2 LDD drilled microvia after desmear and elec- troless metallization. No copper foil brush marks were visible from the deburr process used to remove the surface oxide and the laser formed copper burr. Figure 23 shows a microvia from another supplier's CO 2 LDD microvia process. The out- er layer copper foil was oxidized before LDD ablation. The microvia roundness was better than the CO 2 beam quality of the previous sup- plier's LDD formed microvia. Melted and re- cast copper were formed around the rim of the outer layer copper. Figure 24 shows the CO 2 LDD drilled microvia after desmear and electroless copper. No brush marks were visible following the deburr pro- cess used to remove the oxide and recast copper burr. However some of the copper foil around the rim was damaged, which changed round- ness of the microvia. No melted and recast cop- per anomalies were formed on the target pad. Figure 25 shows CO 2 LDD microvias from an- other supplier. A substantial amount of melted and recast copper was spread on the outer lay- er around the microvia. The roundness of the microvia matched the CO 2 beam quality. The microvia sidewall shows melted and fused tips of glass fibers—a condi- tion typically present with CO 2 laser ablation of glass-reinforced dielectric material. Brush striations can be seen on both the outer layer copper foil and target pad. No melted or recast copper was visible on the target pad. Figure 26 shows SEMs of the CO 2 LDD mi- crovia after desmear and electroless copper metallization. Brush marks were still visible. Figure 22: SEM view of CO 2 laser direct-drilled microvia through oxided 9-mm copper foil after mechanical brush scrub, desmear, and electroless copper at 0° tilt (L) and 45° tilt (R). Figure 24: SEM view of CO 2 laser direct-drilled microvia through oxided 9-mm copper foil after mechanical brush scrub, desmear, and electroless copper at 0° tilt (L) and 45° tilt (R) showing copper foil damage. Figure 23: SEM view of CO 2 laser direct-drilled microvia through oxided 9-mm copper foil from another supplier il- lustrating better beam quality at 0° tilt (L) and 45° tilt (R). Figure 25: SEM view of CO 2 laser direct-drilled microvia through oxided 9-mm copper foil from another supplier showing variation in degree of laser-induced surface copper recast at 0° tilt (L) and 45° tilt (R). Figure 26: SEM view of CO 2 laser direct-drilled microvia through oxided 9-mm copper foil after mechanical brush scrub, desmear, and electroless copper at 0° tilt (L) and 45° tilt (R) showing brush marks on the copper foil.