The researchers found positional accuracy of the paste deposit relative to the pad to be the critical element in ensuring good fine pitch Pb-free assemblies, and is even more critical for some formulations than others. Solder volume can be readily managed across the supplier base with printer variables and stencil design. As with any solder pastes (Pb-free and Pb-bearing), the use of enclosed print heads such as the Rheometric pump will present advantages such as better aperture fill; however, it is not the determining factor for a high quality process. The atmosphere and profile of the reflow oven contribute substantially to the overall quality of the Pb-free assembly, the researchers found.

Coauthor Dr. Gerald Pham-van-Diep, director of advanced development at Speedline Technologies, said, “This study was undertaken to review the full potential for process needs as customers convert to Pb-free process technologies. It demonstrates that the process changes required in most situations to convert to Pb-free are not as daunting as some suppliers would have the industry believe. In essence, with appropriate process review, process development work and management of the variables available to the manufacturer, the switch to producing high-quality Pb-free assemblies is achievable.”