SMTA International Conference Proceedings

Determining the Effect of Fine Mesh Solder Powder on Flux Residue Removal

Authors: Timothy O’Neill, Terry Munson, Kalyan Nukala, M.S.Ch.E. and Ravi Parthasarathy, M.S.Ch.E.
Company: AIM, Foresite and ZESTRON Americas
Date Published: 10/14/2018   Conference: SMTA International

Abstract: Solder paste users and developers face an unrelenting drive to miniaturize solder paste deposits. A key element to success is the incorporation of smaller solder particles in the solder paste. New flux formulas have been developed in parallel to enhance printing and soldering performance with finer powder. The focus of this development has been primarily on ‘No-Clean’ chemistries as this flux technology has emerged as the industry standard. While No-Clean flux residue is designed to be left in place after soldering, there are a variety of end use applications that require its removal including coating applications, RF and high voltage circuitry. When flux residue removal is mandated, wash chemistry is required in order to solubilize flux residue so that it can be washed and rinsed away.

At APEX 2018, a study titled ‘Jet Printed Solder Paste and Cleaning Challenges’ was presented whereby data was presented indicating that as solder powder becomes finer, the resulting flux residues become more difficult to remove. As a continuation of the APEX 2018 study, this study will test a common No-Clean flux chemistry with progressively finer SAC305 solder powders with a variety of cleaning chemistries and methods to attempt to quantify the implications of finer mesh powder on flux removal. This study was divided into two phases. For Phase 1, a fully populated ZESTRON test vehicle was assembled and cleaned. Post washed cleanliness levels on the surface as well as under-component were measured using visual inspection. Based on this analysis, Phase 2 trials were conducted utilizing the IPC-B-52 test vehicle cleaning agents yielding best and worst cleaning results from Phase 1. In this phase, cleanliness assessment was conducted using SIR and Ion Chromatography analyses. The results were analyzed to assess the influence of finer solder powder paste deposits on the cleaning process and materials. All cleanliness assessments were conducted in accordance with current IPC guidelines.

Key Words: 

Jetting Paste, Cleaning No-Clean, PCB Cleaning, SIR, Flux Residue Removal, Fine Pitch Solder Paste

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