Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 65 single via design was observed (Figure 14). Most of the voids on filled via pads were on the top of the vias. Void percent in the pads with unfilled vias were lower but based on the X-ray and optical analysis, solder wicking to the bottom of the board was observed in all cases. Joints with filled vias demonstrated larger and more frequent voids. Some of the assemblies were metallograph- ically prepared for microstructural evaluation. Interfacial reaction between the component thermal pad and solder as well as solder and board pad were examined. Uniform and contin - uous intermetallic compound (IMC) layer was formed at all interfaces, acceptable solder joints were built using both configurations (SPO and PF+paste). SEM images of the cross-sectioned assemblies are shown in Figure 15. Figure 14: X-ray images of different via design the larger QFN components assemblies built with (a) solder paste only and (b) PF+paste with different via design. Figure 15: SEM images of the interfacial reaction of the assemblies built using (a) SPO and (b) PF+paste configuration.