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38 SMT Magazine • April 2015 The boards were considered clean when no residues were detected. Results are summa- rized in the table below (Table 9). Anionic con- tamination test was performed on the boards regardless of their cleanliness level. This test was done in accordance with the IPC-TM-650, method 2.3.25C: The board is immersed in a solution of water/isopropanol while analyzing the evolution of this cleaning solution contam- ination which circulates in closed-circuit inside the contaminometer. The results are expressed in µg equivalent NaCl per cm² of circuit and are reported in Table 9. A test board with no paste but submitted to the same reflow profile was used as control board: its ionic contamination measured was 0.21µg/cm². Paste A was the easiest to clean, even using cold water, followed by paste C and B for WS solder pastes. Cleanability of pastes D and F was achieved using detergent at 25% whereas E was not (a second cycle in the same conditions was necessary to clean it properly). As long as the cleaning was successful, the ionic contami- nation levels were acceptable and far below the MIL and DEF criteria (respectively 1.3µg/ cm²and 1.5µg/cm²) for all the pastes. But, in case of incomplete cleaning, the level of ionic contamination for WS solder pastes was above Figure 8: Surface insulation resistance graph. figure 9: observation under back-light: (left) dendrites with paste c; (right) no dendrite with paste d. rEliaBiliTy aSSESSMENT OF NO-ClEaN aND WaTEr-SOluBlE SOlDEr paSTES, parT ii continues FeAture