The Advanced Development Group of Speedline, in cooperation with Agilent, concluded a design of experiment (DOE) to understand and quantify variables in lead-free manufacturing. Fundamental conclusions highlight that the positional accuracy of the paste deposit relative to the pad is the critical element in ensuring appropriate fine-pitch, lead-free assemblies, and is even more critical for some formulations than others. Reportedly, solder volume can be readily managed across the supplier base with printer variables and stencil design. As with any solder pastes, 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 quality of the lead-free assembly.
Speedline and Agilent have undertaken these experiments to help board assemblers understand how lead-free technology is likely to impact their established processes. These companies are working from the premise that process characterization, effective monitoring and process control in the lead-free process are essential to maintaining desired yield and lower costs. The goal of this DOE was to understand the impact of the positional accuracy of the printed paste to the component pad, the positional accuracy of the placed component to the pad, and atmosphere and profile of the reflow process. This study took into account all steps in the SMT process. Inspection equipment was employed: after the print to measure volume and position; after pick & place to measure component position; and after reflow to measure the position of components. Solder pastes were selected from three major manufacturers. Data collected was reviewed for volume and position of the paste deposits as well as for presence and position of the placed components. Speedline director Dr. Gerald Pham-van-Diep stated, “This study demonstrates that the process changes required in most situations to convert to lead 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 lead-free assemblies is achievable“. This project is part of a long-term program, specifically aimed at understanding the challenges of the transition to lead-free manufacturing.
EPP EUROPE 409
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