Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 57 temperature at a rate of 1°C/s up to 150°C before slowing to a rate of 0.5°C/s up to 200°C to allow more time for the flux to activate the surfaces. The high-soak profile subjected the test vehi- cle to 50 seconds above liquidus (220°C) with a peak temperature of 240°C on the test vehi- cle. Finally, both air and nitrogen reflow atmo- spheres were evaluated in this investigation to further understand the effect of voiding under bottom termination components. The focus of the investigation involved the use of the micro-flux coated solder preform to increase solder volume relative to fluxing agent and reduce voiding. The use of a SAC305 micro- flux coated solder preform in conjunction with paste was benchmarked against a solder paste only test vehicle for each of the configurations summarized in Table 2. Four replicate boards of each iteration were processed to ensure statistically viable data. Close to 2,000 data points were generated combining 54 components on each test vehi- cle and four replicates of each configuration. The solder paste only benchmark samples were printed in a window pane configuration commonly used in the industry for void reduc- tion and shown in Figure 4. The design of a solder preforms to allow intimate contact with the thermal pad of the component and increase solder volume played a significant role in the results presented in this investigation. Figure 5 represents an example of the use of solder paste only in window pane format on a QFN where mechanical stack-up Figure 3: Reflow profiles using in this study. Table 2: Assemblies' configuration details. Figure 4: Solder paste print configuration. (Examples of window pane solder prints on QFN components used in benchmark samples.)