Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 61 solder volume from the preforms plays a criti- cal role in void reduction. Voiding of QFN Packages (Small, Medium and Large Pads) Results A QFN is a bottom termination component in which both thermal pad and signal leads terminate under the body of the component. Figure 9 summarizes the results of the voiding of those components based on the combination of PF+paste and SPO configuration as well as types of vias on the board. The PF+paste configuration with no vias or unplugged vias provide excellent voiding results below 5%. Plugged vias had slightly higher voiding but remained lower than SPO configuration. The PF+paste configuration reflowed in nitro- gen environment produced the most impres- sive voiding results, averaging between 5–10% under all three package sizes. It was observed during X-ray analysis that assemblies built with PF+paste configuration had a greater consistency in voiding and pad coverage from one component to another. Void distribution was much tighter for the PF+paste configurations compared to SPO configuration. Those differences could be clearly observed in Figure 10. In the SPO example, a wider distribution of voids was present in which voiding between 11% and 37% was present on the same board for like components in similar board locations. As evident in Figure 10, a greater consistency void percent was achieved for the same situa- tion when a micro-flux preform was used. This consistency will result in a reduction in defect Figure 9: The overall void results of QFN packages. Figure 10: X-ray images of the QFN components assemblies built with different solder material configurations.