Impact of Solder Powder Size on Cleaning Efficiency in Chip Resistor Assemblies for Future Advanced Packaging

This study evaluates the efficiency of various cleaning chemistries under controlled process conditions, including conveyor belt speed and concentration, for the removal of water-soluble flux residues using a test vehicle incorporating different chip resistors, MLF and BGA components. The influence of solder powder size on flux composition was examined, with smaller powder sizes exhibiting increased flux activator content, leading to higher residue accumulation and greater cleaning complexity. By systematically testing different solder powder sizes T5 (25-15 μm), T6 (15-5 μm), and T7 (11-2 μm) this research aims to elucidate their effects on defluxing efficiency and residue removal. Experimental procedures involved assembling test vehicles having MLF-68, BGA-208 and resistors of varying sizes, followed by controlled reflow and standardized defluxing using aqueous-based defluxing systems. Post-defluxing, analysis was conducted using visual inspection to quantify and characterize flux residues. The study specifically addresses the challenges of flux removal under low-standoff components, where restricted access exacerbates residue entrapment. Results indicate that different solder powder sizes require selection of defluxing chemistry and process parameters. Further studies will aim to refine cleaning methodologies and investigate interactions between solder powder size, flux chemistry, and process conditions to enhance cleanliness and reliability in advanced semiconductor packaging.