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JULY 2019 I SMT007 MAGAZINE 47 shown in Table 10. Representative pictures of the solder balling in the overprint patterns are shown in Figure 24. These overprint levels are fairly extreme and would not normally be used in typical sur- face-mount technology (SMT) designs. The solder balling generated by Type 3 and 4 sol- der pastes was low and would be considered acceptable on most electronic assemblies. It is evident from these images that Type 5 and 6 solder powders create excessive solder balling with the no-clean solder paste. The water-solu - ble Type 5 solder paste gave better solder ball- ing than the no-clean Type 5. This is likely due to the rel- ative activity levels of these solder pastes. The water- soluble solder paste has a higher activity level than the no-clean solder paste; there - fore, the water-soluble solder paste gives less solder balling with the smaller solder pow - der sizes. Both the no-clean and water-soluble Type 6 sol- der pastes gave excessive sol- der balling. The graping levels of the solder pastes vary with solder powder size (Figure 25). Figure 25: Graping for each solder paste. The graping levels for the no-clean and water-soluble solder pastes were very similar for Type 3, 4, and 5 solder powders. Overall, the graping was very high for Type 6 solder pastes. The water-soluble solder paste gave higher graping than the no-clean solder paste with Type 6 powder. Voiding was measured for each solder paste using the QFN thermal pads. Figure 26 shows the voiding data. Figure 26: Voiding for each solder paste in the QFN thermal pads; no-clean (L) and water-soluble (R). Figure 24: Solder balling in the overprint patterns. Table 10: Solder balling performance of solder pastes that fell within the measurement criteria.