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32 SMT Magazine • April 2015 is enhanced for small deposits because of the higher exposed surface area compared to the paste volume, for paste with less activation and for thermal profiles with long and high soak. To perform such tests, FR-4 substrates of 1.6 mm thickness with round copper pads of 5 mm were used. After cleaning the substrates, the pastes were printed through a 120 microns sten- cil with five openings of respectively: 5 mm, 3 mm, 1 mm, 0.76 mm and 0.38 mm diameters. The substrates were placed in the reflow oven using P1 and P5 thermal profiles. Each test was done three times to assure repeatability. The di- ameter after reflow was measured for every pad and any sign of graping was recorded. A gen- eral view of the wetting substrate after reflow is shown in Figure 3. Examples of appearance af- ter reflow are given in Figure 4: graping for 0.38 mm diameter deposit; no graping for 0.76 mm diameter deposit with the same solder paste; diameter measurement for an initial deposit of 0.38 mm. Table 4 presents the mean of the measured diameters where Di states for the initial diam- rEliaBiliTy aSSESSMENT OF NO-ClEaN aND WaTEr-SOluBlE SOlDEr paSTES, parT ii continues FeAture figure 3: Wetting substrate description. Table 4: Wetting diameter. figure 4: (l) graping on 0.38 mm; (ctr) no graping on 0.76 mm; (r) diameter 0.41 mm (initial 0.38 mm).