Method for soldering, fusing or brazing

Abstract

.[.Article.]. .Iadd.An article .Iaddend.to be soldered, fused or brazed is placed in hot saturated vapors generated by continuously boiling .Iadd.a .Iaddend.heat transfer liquid having selected properties including .Iadd.a .Iaddend.boiling point at least equal to, and preferably above, .Iadd.the .Iaddend.temperature required for .Iadd.such .Iaddend.operation. Vapors condense on .Iadd.the .Iaddend.article and give up latent heat of vaporization to heat .Iadd.the .Iaddend.article to .Iadd.the .Iaddend.temperature for soldering, fusing or brazing. .[.Heat.]. .Iadd.The heat .Iaddend.transfer liquid may be a fluorocarbon. Apparatus is shown for soldering, fusing or brazing a single article, a batch of articles, or a continuously moving line of articles. Specifically, mass reflow soldering and mass wave soldering operations are described. .Iadd.

What is claimed is: .[. 
     
       1.  Method for performing on an article at elevated temperature an operation comprising the melting of material, said method comprising: a. continuously boiling substantially at atmospheric pressure a heat transfer liquid having a boiling point equal to the said elevated temperature and at least equal to the melting point of said material, thereby generating a body of saturated vapor of said heat transfer liquid at said elevated temperature;   b. inserting said article into said body of saturated vapor;   c. condensing saturated vapor directly on and in contact with said article thereby to heat said article to said elevated temperature by transfer of latent heat of vaporization from said condensed vapor to said article;   d. performing said operation on said article..]. .[.2. Method as in claim 1 wherein:   e. the operation performed on the article is soldering with solder,   f. the boiling point of said heat transfer liquid is at least equal to the melting point of said solder..]. .[.3. Method as in claim 1 wherein:   e. the operation to be performed on the article is fusing a coating of solder thereon,   f. the boiling point of said heat transfer liquid is at least equal to the melting point of said solder..]. .[.4. Method as in claim 1 wherein:   e. the operation to be performed on the article is brazing,   f. the boiling point of said heat transfer liquid is at least equal to the melting point of the material being brazed..]. .[.5. Method as in claim 1 wherein:   e. said saturated vapor is chemically inert..]. .[.6. Soldering a printed circuit board according to the method of claim 1 wherein:   e. said heat transfer liquid is electrically non-conductive,   f. said saturated vapor is chemically inert..]. .[.7. Method as in claim 1 wherein:   e. said body of saturated vapor overlies said heat transfer liquid and is denser than air at ambient temperature and atmospheric pressure..]. .[.8. Method for performing on an article at elevated temperature an operation comprising the melting of material, said method comprising:   a. establishing substantially at atmospheric pressure a body of saturated vapor at said elevated temperature extending to a predetermined height over a heat transfer liquid having a boiling point equal to said elevated temperature and at least equal to the melting point of said material by continuously boiling said heat transfer liquid,   b. applying a cooling medium to said body of saturated vapor at said predetermined height to condense saturated vapor at said predetermined height and to substantially prevent said saturated vapor from rising above said predetermined height,   c. inserting said article into said body of saturated vapor below said predetermined height,   d. condensing saturated vapor directly on and in contact with said article thereby to heat said article to said elevated temperature by transfer of latent heat of vaporization from said condensed vapor to said article,   e. performing said operation on said article,   f. removing said article from said body of saturated vapor..]. .[.9. Method as in claim 8 further comprising:   g. returning to said heat transfer liquid condensed vapors resulting from steps (b) and (d)..]. .[.10. Method as in claim 8 wherein:   g. the operation performed on the article is soldering with solder,   h. the boiling point of the heat transfer liquid is at least equal to the melting point of said solder..]. .[.11. Method as in claim 8 wherein:   g. the operation to be performed on the article is fusing a coating of solder thereon,   h. the boiling point of said heat transfer liquid is at least equal to the melting point of said solder..]. .[.12. Method as in claim 8 wherein:   g. the operation to be performed on the article is brazing,   h. the boiling point of said heat transfer liquid is at least equal to the melting point of the material being brazed..]. .[.13. Method as in claim 8 wherein:   g. said saturated vapor is chemically inert..]. .[.14. Soldering a printed circuit board according to the method of claim 8 wherein:   g. said heat transfer liquid is electrically nonconductive;   h. said saturated vapor is chemically inert..]. .[.15. Method as in claim 8 wherein:   g. said saturated vapor is denser than air at ambient temperature and   
     
     
        atmospheric pressure..]. 16. .[.Wave soldering an article according to the method of claim 8, further comprising:.]. .Iadd.A method of wave soldering an article, comprising: a. establishing, substantially at atmospheric pressure, a body of saturated vapor at an elevated temperature extending to a predetermined height over a heat transfer liquid having a boiling point equal to said elevated temperature and at least equal to the melting point of solder but below the melting point of the article, by continuously boiling said heat transfer liquid,   b. applying a cooling medium to said body of saturated vapor at said predetermined height to condense saturated vapor at said predetermined height and to substantially prevent said saturated vapor from rising above said predetermined height,   c. immersing said article into said body of saturated vapor below said predetermined height,   d. condensing saturated vapor directly on and in contact with said article thereby to heat said article to said elevated temperature by transfer of latent heat of vaporization from said condensed vapor to said article, .Iaddend.   .[.g..]. .Iadd.e. .Iaddend.generating a solder wave extending into the lower portion of said body of saturated vapor,   .[.h..]. .Iadd.f. .Iaddend.passing said article through said solder wave.[...]..Iadd.,   
     
     
       g. removing said article from said body of saturated vapor. .Iaddend. 17. Method according to claim 16 wherein: .[.i..]. .Iadd.h. .Iaddend.the temperature of said solder wave is higher than the temperature of said body of saturated vapors.