Applied Research for Optimizing Process: Parameters for Cleaning Pb-Free Flux Residue

Abstract

As the electronics industry moves toward the implementation of Pb-free soldering, the impact on the assembly process must be considered. One process that is often over looked is the cleaning of assembled printed circuit boards. How will the introduction of lead free material impact the cleaning process? A number of studies have proven the poorer wetting of SAC 305 alloys and many of the other Pb-free alloys as contrasted to Sn/Pb during the soldering process. To address this issue, solder paste manufacturers researched and advanced flux technologies to improve soldering yields. Many of the advanced flux technologies employ modern “exotic” compounds, which often increase the difficulty of removing post-soldering residues. It is evident that both cleaning equipment and cleaning chemistry must be modified to enable effective and consistent cleaning of Pb-free flux residues. It is also evident that the best overall cleaning solutions will be provided by cleaning equipment and cleaning material companies working together to optimize their products. This paper discusses extensive cleanliness testing of over 70 Pb-free soldering materials. The data suggests increased difficulty when cleaning Pb-free post-soldering residues. Based on the data, this paper discusses advances in cleaning material and cleaning equipment mechanical designs that will optimize the cleaning of Pb-free flux residues. This paper will detail the changes made in the cleaning equipment for optimizing the cleaning material advancements in industry standard cleaning equipment.

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