Fluxes Cleaning issues

Flux and Cleaning Issues Related to Lead-Free Soldering... 

Continued decline in performance indicates a membrane cleaning or compatibihty issue. The adequacy of the cleaning step is determined by the recovery of at least 80 percent of the initial normalized water flux. Although some variability in water flux is typical, any consistent dechne reflects an inadequate cleaning procedure. 

The real advantage of semi-aqueous processes is that they provide acceptable-to-excellent cleaning for heavy oils, greases, flux and flux residues, waxes, and tars — especially compared to aqueous cleaning technology. Yes, the cleaning quality with volatile halogenated solvents is at least equivalent. But those solvents raise concerns about SHE issues (Ref. 3, Chapter 20), and solvents used in the semi-aqueous process do not. 

Certain no-clean fluxes are not compatible with each other. Their chemical interaction could result in corrosion on the PCA. To avoid corrosion issues, solder paste flux, wave solder flux, and repair flux should be tested separately and in combination for SIR and ECM with the board surface finish. 

Over the last decade, the industry has studied a wide range of alloys to replace the tin-lead alloy. The alloy selection has been based on the following considerations (Ref 12-15) toxicity, physical properties (melting temperature, surface tension and wettability, thermal and electrical conductivity), mechaiucal properties, mi-crostructural characteristics, electrochemical properties (corrosion, oxidation and dross formation, and compatibility with no-clean fluxes), manufacturability, cost, and availability. Yet another important consideration for selecting the lead-free solder alloy for commercial use is whether or not the alloy may be covered by any patents. Lead-free alloy selection, as weU as associated patent issues, have been described in detail in toe literature in Ref 16-20. 

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