Fluxes removing residues

Flux removal Residual flux should be removed if detrimental. 

Excess flux will not compromise joint quality and provide for flux removal, since residues will be less loaded with metal oxide and more soluble in water. 

Because odd-form components are often larger and/or have more complex constructions (geometry and materials), there is an increased likelihood of flux residues becoming trapped in confined areas. Therefore, the cleaning process must be sufficiently thorough to remove residues from those locations on the component. Similarly, it is necessary to verify that the cleaning solution has likewise been removed from those locations as part of the process. 

Fluxing Is the process to remove residual impurities that remain on the surface of work after degreasing and pickling and to clear the oxides from the surface of the coating bath at the point where steel enters. The flux cover used in wet galvanizing is zinc... 

A circuit test vehicle with both active and passive elements was designed (Ref 44). The passive circuits consisted of band pass filters (6 to 7 GHz range) and T-resonators (5, 10, and 15 GHz), while the active circuits included a mixer device (4 to 6.5 GHz), a VCO module and a wide-band amplifier circuit. The assemblies were tested after soldering and reflow, and again after flux/paste residues had been removed. Variations in signal transmission for two different solder pastes were observed on the passive circuit elements. For the mixer device, variation between signal transmissions for the measurements with/without paste residues was approximately 1%. 

Diversity for DHR in RCS-closed condition At least one SG is required to be operable (secondary side FW available) to remove residual heat (by re-flux condenser cooling mode with the presence of non condensable gas), until a prszr manway is removed. 

Eutectic low-residue solder paste flux removal... 

Materials such as urea, ethylenediamine, monoethanolamine, and triethanolamine, and derivatives such as aniline phosphate are extensively utilized as activators in fluxes. These materials are also temperature-sensitive and, as noted above, have the potential to leave difficult-to-remove residues [102,135]. Structural and empirical formulas of several amine and derivative amine compounds, emphasizing functional features, are given in Fig. 41. 

Testing for complete flux removal is done ly monitoring the presence of chlorides in the final rinse water. An acidified solution of 5% silver nitrate is used to check the final rinse water for clarity. If white chloride residues cloud the water, then salt is still present After several tests on subsequent rinses, the salt is considered removed if the water remains clear. Although this is a simple test, it is quite accurate. 

Flux composition also can have a pnmounced effect if residues are not completely removed. Those from chloride-containing reactimi fluxes can cause severe corrosion if trapped in assemUies. Those from dikxide-free organic fluxes genouUy cause little or no corrosion. All flux residues must be removed when foil or small wire is soldered. Inaccessible or terminal joints where complete flux removal is not possible can be protected by first eliminating moisture, then sealing so that moisture cannot enter the joint... 

Scrap that is unsuitable for recycling into products by the primary aluminum producers is used in the secondary aluminum industry for castings that have modest property requirements. Oxide formation and dross buildup are encountered in the secondary aluminum industry, and fluxes are employed to assist in the collection of dross and removal of inclusions and gas. Such fluxes are usually mixtures of sodium and potassium chlorides. Fumes and residues from these fluxes and treatment of dross are problems of environmental and economic importance, and efforts are made to reclaim both flux and metal values in the dross. 

It is sometimes necessary to remove flux residues after processing due to their corrosive nature. This can be an added source of variability. 

Soldered joints, especially those to be used in a static environment, are, if insufficient care is taken, liable to corrosion by residues of flux, which by their nature as oxide removers are potentially corrosive. It is, however, possible to select fluxes which are active when hot but give non-corrosive residues when cold. 

For optimum corrosion resistance it is recommended that similar composition fillers be used wherever possible, and obviously any flux residues that may be present must be removed. 

The use of solubilizing treatments employing chelants (EDTA, NTA, etc.) is permissible provided that a maximum of 10 mg/kg (ppm) is not exceeded at any time. Complete removal of oxygen should have been achieved prior to injection of the chelant. In boilers having heat fluxes greater than 300 kW/m2 (52,832 Btu/h/ft2/°F) the use of chelants should be avoided because they can decompose to form acidic residues. 

Mitrovic and Knezic (1979) also prepared ultrafiltration and reverse osmosis membranes by this technique. Their membranes were etched in 5% oxalic acid. The membranes had pores of the order of 100 nm, but only about 1.5 nm in the residual barrier layer (layer AB in Figure 2.15). The pores in the barrier layer were unstable in water and the permeability decreased during the experiments. Complete dehydration of alumina or phase transformation to a-alumina was necessary to stabilize the pore structure. The resulting membranes were found unsuitable for reverse osmosis but suitable for ultrafiltration after removing the barrier layer. Beside reverse osmosis and ultrafiltration measurements, some gas permeability data have also been reported on this type of membranes (Itaya et al. 1984). The water flux through a 50/im thick membrane is about 0.2mL/cm -h with a N2 flow about 6cmVcm -min-bar. The gas transport through the membrane was due to Knudsen diffusion mechanism, which is inversely proportional to the square root of molecular mass. 

Trichlorotrifluoroethane (CFC 113) was widely used in the electronics industry for the removal of soldering flux residues from printed circuit boards, for degreasing components in the precision engineering industry, and for the dry cleaning of garments. 

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