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April 2017 • SMT Magazine 31 Conclusions The three types of rheology measure- ments studied here all show trends that mirror the print volume and volume re- produceability for the three pastes used in this study. A low area ratio, 0.54 ampli- fied the correlation of the rheology mea- surements to the print deposit reproduce- ability. The paste sample size required for rhe- ological testing is an order of magnitude lower than what is required for spiral vis- cosity testing. Both suppliers and users could see a significant reduction in wast- ed material if rheology would become the standard for solder paste inspection. Obviously, more testing, including a round robin test by the IPC-JSTD-005 would be required before this type of test method could be elevated to an industry standard. Acknowledgements The authors thank Simon Ellis and Isabella Millan for preparing the paste samples. SMT Editor's Note: This paper was originally published in the proceedings of SMTA Inter- national, 2016. Mitch Holtzer is the director of reclaim business at Alpha Assembly Solutions. Karen Tellefsen is a senior research chemist at Alpha Assembly Solutions. Westin Bent is a senior process engineer for R&D at Alpha Assembly Solutions. PREDICTING SOLDER PASTE TRANSFER EFFICIENCY AND PRINT VOLUME Figure 8: Oscillation frequency sweep: (a) complex modulus vs. frequency; (b) elastic and viscous modulus vs. frequency; (c) complex viscosity vs. frequency.