Water-Soluble Flux

Water solubility Water-soluble fluxes Water-soluble polymers... 

Hydrosolv. [Alpha Mttals] Liq. organic water-soluble flux. 

The function of a flux is to clean the metal surface prior to coming into contact with the molten matrix. A suitable water soluble flux is K2Zrp6 [20-22,51-55] ... 

As the name impUes, water-soluble fluxes are soluble in water and their soldering residues are also expected to be water-soluble. These fluxes are much more active than rosin fluxes, have a wider process window, and give a higher soldering yield with reduced defects. This means that the final assembly will require less touchup or repair. On the down side, water-soluble fluxes contain corrosive residues that, if not properly removed, will cause corrosion in the field and long-term reliability problems. 

F. M. Zado raised concern in the late 1970s that water-soluble fluxes affect the electrical characteristics of the epoxy-glass laminate by reducing the insulation resistance. This reduction... 

Possible electrical implications for RF drcnitry Flux residues can interfere with some high-speed circnit condnction by changing top surface dielectric properties and increasing parasitic capacitance. It is for this reason that radio-frequency (RF) circuitry is often specified to be assembled nsing water-soluble fluxes. 

No-clean benefits include lower manufacturing costs through fewer process steps, less board handling, less maintenance, and reduced floor space than is required for board assembly via water-soluble fluxing. There are also environmental benefits of no-clean, as there is almost no waste effluent other than from the solvent within the paste or flux that evaporates during the process and from solvents used to clean the stencil, sqneegee blades, and any misprinted boards. 

It has been shown that polyglycols (which are found in water-soluble fluxes) diffuse into the epoxy during soldering. This absorption has been shown to reduce electrical performance by increasing moisture uptake by the substrate. Jachim et al. were the first to link the use of polyglycols in soldering fluxes and fusing fluids to increased susceptibility to CAF formation. 

Ready et al. showed that the use of certain water-soluble fluxes or fusing (hot air solder level [HAST]) fluids could increase CAF formation. In examining a catastrophic field failure (see Fig. 56.9), Ready et demonstrated the presence of a copper-bromide containing salt between an innerlayer power plane and ground pin, separated by 0.005 in. Using a test coupon manufactured in the same lot as the failed product, they extracted the flux residues from an innerlayer of the multilayer board and used ion chromatography to match the residues from the board s innerlayer with the constituents of the flux. 

Zado, F. M., Effects of Non-Ionic Water Soluble Flux Residues, Western Electric Engineer, No. 1, 1983, pp. 41 8. 

Brous, X, Water Soluble Flux and Its Effect on PC Board Insulation Resistance, Electronic Packaging and Production, Vol. 21, No. 7,1981, p. 80. 

Jachim,X A., Freeman, G. B.,Turbini, L. X, Use of Surface Insulation Resistance and Contact Angle Measurements to Characterize the Interactions of Three Water Soluble Fluxes with FR Substrates, IEEE Transactions on Components, Packaging, and Manufacturing Technology, PartB,Vo. 20, No. 4,1997, pp. 443-451. 

All process assemblies in the evaluation passed the SIR testing with high levels of surface resistivity. The SIR criteria of J-STD-OOIC, Appendix B, on all patterns, showed levels above the limits of 100 MO of resistance. All processed assemblies for current water-soluble fluxes and new production water-soluble fluxes passed SIR and visual criteria of the J-STD-OOIC, Appendix B test conditions. A diagram of the SIR test environment used in this evaluation can be seen in Eigure 1. 

Soldering processes associated with Pb-Sn solders have been performed with fluxes from each of three categories, the (natural) rosin-based fluxes, resin-based fluxes, and the organic acid (water-soluble) fluxes. ... 

FIG. 47 Some components of a commercial, nonvolatile, water-soluble flux. 

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