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April 2015 • SMT Magazine 33 rEliaBiliTy aSSESSMENT OF NO-ClEaN aND WaTEr-SOluBlE SOlDEr paSTES, parT ii continues eter after printing (mm) and Df is the diameter after reflow; the wetting percentage (Df/Di) ac- cording to paste type and thermal profile is re- ported as a histogram in Figure 5. Graping was only observed for pastes C and D with an initial diameter of 0.38 mm. Some pictures of wetting are shown in the table below (Table 5). A, B and C solder pastes perform better than no-clean solder pastes D, E and F. Paste A has the largest wettability and paste D the lowest one. The thermal profile has no noticeable influence. The influence of the size of the initial paste deposit is relatively low for pastes D, E and F, a bit more significant for A, B and C. The wettability according the initial diameter size is different for each paste. Table 5: examples of wetting diameters. figure 5: graph of wetting percentage according to paste type and thermal profile. FeAture