This paper presents the results of our study on the development and optimization of lead-free wave soldering process for large and thick printed circuit boards (PCB), through multiple designs of experiments (DOEs) including many variables from design, material, component and process. Design variables were pin-to-hole ratio, pad diameter, annular ring diameter, component orientation, spacing, thermal relief pattern, internal copper thickness, and the number of copper layers connected to PTH barrel. Material and process variables included flux materials, flux amount, preheat temperature, solder pot temperature, conveyor speed, contact time, wave atmosphere and wave system. A variety of plated through hole (PTH) components were tested. Two board thicknesses (2.4mm and 5.0mm) and two board surface finishes (immersion silver and immersion gold) were used. The results showed that there were strong correlations between flux materials, process conditions and hole-fill. Bridging and insufficient solder defects were reduced by optimizing wave process parameters. Design parameter optimization could be used to improve the PTH hole-fill, and reduce defects of PTH bridging, insufficient solder on SMT components, and voiding in the PTH solder joint.
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