Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 73 ing common to the industry and are a frequent print challenge for mainstream PBC assem- blers. The test vehicle's area ratios are 0.71 for 0.5 mm BGA and 0.62 for 0.4 mm BGA. These are at eith er side of the threshold of recommended guidelines of 0.66 AR, which has historically been cited as the lowest AR that should be considered when printing T3 solder paste. T3 was not included in this test because T4 is quickly becoming the industry standard it is usually readily available. T5 was also tested, as it is often requested by assemblers who perceive smaller powder size as a fast and easy improvement to a fine pitch printing process. T5 paste indeed brings some print advantages, but also carries with it some inherent disadvan - tages. Procuring T5 paste can present supply chain challenges and it can increase variability in paste print and reflow performance over time due to the higher surface area: volume ratio. Figures 3 and 4 shows the Transfer Efficiency (TE), or the percentage of theoretical aper- ture volume that was deposited and the asso- ciated Coefficients of Variation (CVs) for the Figure 4: Print performance of Types 4 and 5 powder with 0.4 mm BGA. Figure 3: Print performance of Types 4 and 5 powder with 0.5 mm BGA.