OA Flux Cleaning Studies on Dense Packages

Dr. Mike Bixenman
Kyzen Corporation, Nashville, TN USA

Cleaning flux residues post soldering has been a high reliability criterion practiced by assemblers of military, aerospace, automotive, medical devices and other value offerings. Highly dense advanced packages reduce spacing between I/Os and standoff heights. The complexity of removing flux residue increases, while elevating the risk of white residue under low standoff (gap) components. To address this concern, many electronic assemblers use water soluble solder paste and clean post soldering.

The purpose of this factorial designed experiment is to evaluate multiple water soluble flux materials and cleaning chemistries, including DI water only, to determine the best chemical properties for removing lead-free water soluble flux residues. The optimal process parameters will be defined with data findings analyzed and presented using statistical analysis and models.

Cleaning flux residues post soldering has been a high reliability criterion practiced by assemblers of military, aerospace, automotive medical devices and other value offerings. Highly dense circuit designs reduce component spacing and standoff heights. The complexity of removing flux residue increase as standoff heights reduce. Additionally, lead-free soldering appears to harden flux residues due to higher processing temperatures and flux burn off. The purpose of this research was to test the cleaning parameters needed to remove lead-free water soluble flux residues from under low clearance lead-free components.

When cleaning water soluble flux residues under low clearance components, the data findings indicate that DI water only fails to remove all flux residues. Cleaning agents closely matched to the flux residue improve cleaning results when used at low levels in DI water. With the wide range of soldering materials offered to industry, the data strongly suggests that cleaning agent differentiation comes from knowing how the cleaning agent matches up to the flux soil.

This finding is critical when there is a need to remove flux residue under low clearance components. Cleaning agents closely matched to the flux soil allow for higher throughput rates.

The spray impingement manifold design was also a significant factor when cleaning all flux residues under low clearance components. Literature suggests that high flow, impingement pressure and directional forces improve cleaning under low clearance components. The data findings are consistent with these findings.