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56 SMT Magazine • February 2014 tomatic coordinate measuring machine (CMM) to enable "true" transfer efficiency curves to be generated (as opposed to using stencil Gerber dimensions). experimental run Procedure For each experimental condition, 30 consec- utive prints were made. After the 10th and 20th prints, the stencil was manually cleaned. Print runs were conducted with and without the ul- trasonic squeegee system activated and with both type 4 and type 4.5 solder pastes. The main process parameters are listed in Table 1. Immediately following each print run the individual boards were measured using a CyberOptics SE 500 inspection tool. The 30 board print runs provided 1080 replicates for each individual aperture shape and design. results & Discussion The first important observation to consider arose from measuring the stencil apertures. The data in Table 2 details the actual measurements made for both the circular and square apertures and compares the actual aperture volume to that of the theoretical volume from the Gerber bIG IDeaS ON MINIaTurISaTION continues FEATUrE Figure 5: reducing area array pattern used for generating solder paste transfer efficiency curves. Note: Figures based on a stencil thickness of 100 microns. Table 1: Print parameter summary.