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Figure 3: Print performance of Types 4 and 5 powder with 0.5 mm BGA.
Figures 3 and 4 show that that all the print results were within our prescribed limits of 80% TE and ≤10% CV for both T4 and T5 pastes and coated and uncoated stencils. Comparing the results of T4 and T5, T5 gives very little advantage over T4, with the one slight exception being uncoated stencils on 0.4 mm BGAs with an AR of 0.62.
More striking than the powder size comparison is the impact of coated stencils on print consistency. In every case, the coated stencil deposited similar or greater amounts of solder paste with half the variation. Cutting CV by half is a profound improvement in process control.
Figure 4: Print performance of Types 4 and 5 powder with 0.4 mm BGA.
To the printing specialist, this data should facilitate the decision between finer powder and nanocoating as means to improve release and the overall solder paste printing process. Nanocoating has a significantly more positive effect on both increasing TE and, most importantly, reducing CV.
To read the full version of this article, which was published in the June 2018 issue of SMT007 Magazine, click here.
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