To remove RMA flux residue Mr. (or Ms.) Oppenheimer is looking for a 
     drop-in replacement for Genesolve in a vapor degreaser, and is unhappy 
     with the semi-aqueous option.
     
     I learned just this week about such an approach: 3M has line of clean- 
     ers based on what are called hydrofluoroethers.  You can find out more 
     about it at 800-362-3455 or
     
     www.mmm.com/market/industrial/fluids/cleansys.html
     
     The one promoted as the drop-in replacement for flux removal is called 
     a co-solvent blend.  The solvent is a mixture of two hydrocarbons, one 
     for polar and one for nonpolar residue.  They both have a very high 
     boiling point, and remain virtually unvaporized in the boil sump, so 
     their flammability is not an issue.  The hydrofluoroether (HFE) is not 
     a solvent but a "rinsing agent" that boils at about 75 C (170 F) 
     (depends on the mix ratio with the solvent).  (It is nonflammable, has 
     very low toxicity, is not an ozone-depleter, and has a mean atmospher- 
     ic lifetime of about 4 years.)  Assemblies pass through the vapor into 
     the boil sump where residues are removed, move to the rinse sump, and 
     finally are rinsed by condensing vapor.
     
     When the boil sump becomes contaminated, the solvent can be separated 
     from the HFE by first removing some of the HFE from the rinse sump and 
     then running the boil sump until the rise in boiling temperature 
     indicates that most of the HFE has been boiled off.  The concentrated 
     dirty solvent can then be drained from the boil sump;  3M, under the 
     concept of "environmental stewardship" picks it up for proper dispo- 
     sal.  Fresh solvent is then added to the boil sump and the drained-off 
     HFE is returned to the rinse sump.
     
     The solvent is cheap; the HFE is not.  The rate of loss of the HFE 
     depends on how efficient the vapor degreaser is in preventing vapor 
     loss and how careful operators are in the way they put work into and 
     remove it from the degreaser.
     
     Gordon Davy

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