Soldering process

Abstract

A process by which molten solder is purified in-situ, making the soldering process more efficient and yielding better results, particularly for lead-free soldering. Lead-free solder becomes practical for use since the temperature for reliable soldering is reduced. A layer of active additive is maintained on the surface of molten solder for scavenging metal oxide from the solder and assimilating metal oxide into a liquid layer. The active additive is an organic liquid having nucleophilic and/or electrophilic groups. As an example, a layer of dimer acid maintained on a wave soldering apparatus scavenges metal oxide from the bath, and assimilates dross that may form on the surface. Scavenging metal oxide cleanses the bath and lowers viscosity of the solder, and PC boards or the like soldered on the wave have reliable solder joints.

What is claimed is: 
     
         1 . A soldering apparatus comprising:
 a molten solder bath comprising a single layer of an organic liquid active additive on at least a portion of the surface of the molten solder bath, wherein the organic liquid active additive (i) is a liquid at the temperature of the solder bath, (ii) comprises nucleophilic and/or electrophilic groups, (iii) acts as an oxygen barrier to the surface of the molten solder bath, and (iv) assimilates oxide of at least one metal in the bath, to thereby purify the solder bath;   a soldering region where soldering occurs, and   a pump effective to circulate purified solder from the molten solder bath to the soldering region, where the circulating purified solder is devoid of the liquid active additive.   
     
     
         2 . The soldering apparatus of  claim 1 , wherein the organic liquid active additive comprises dimer or trimer acid. 
     
     
         3 . The soldering apparatus of  claim 2 , wherein the organic liquid active additive comprises a major portion of dimer acid. 
     
     
         4 . The soldering apparatus of  claim 3 , wherein the dimer acid is saturated. 
     
     
         5 . The soldering apparatus of  claim 3 , wherein the dimer acid is unsaturated. 
     
     
         6 . The soldering apparatus of  claim 2 , wherein the dimer acid has an average carbon number in the range of from 24 to 60. 
     
     
         7 . The soldering apparatus of  claim 1 , wherein the soldering region comprises a wave, fountain or cascade of molten solder. 
     
     
         8 . The soldering apparatus of  claim 7 , wherein the pump is effective to draw solder from near the bottom of the molten solder bath to the soldering region such that the liquid active additive from the surface of the solder bath is not part of the molten solder in the soldering region for contact with a surface to be soldered. 
     
     
         9 . The soldering apparatus of  claim 1 , wherein the molten solder bath comprises a lead-free solder. 
     
     
         10 . The soldering apparatus of  claim 1 , wherein the molten solder bath comprises a lead-tin solder. 
     
     
         11 . The soldering apparatus of  claim 1 , wherein the molten solder bath is at a temperature of no more than 260° C. 
     
     
         12 . The soldering apparatus of  claim 1 , wherein the amount of liquid active additive is sufficient to maintain a layer at least a molecule thick all across a quiescent surface of the molten solder bath. 
     
     
         13 . The soldering apparatus of  claim 1 , wherein the amount of liquid active additive is sufficient to form a layer at least three millimeters thick on a quiescent surface of the molten solder bath. 
     
     
         14 . The soldering apparatus of  claim 1 , wherein the liquid active additive is liquid at room temperature. 
     
     
         15 . A method of removing dross from molten solder, comprising:
 (i) removing dross from a solder pot in a solder apparatus,   (ii) placing the dross from (i) in a receptacle, and   (iii) adding a liquid active additive comprising dimer acid to the receptacle containing the dross to form a mixture; and   (iv) heating the mixture from (iii) above the melting point of the solder to thereby assimilate dross in the liquid active additive and release molten solder from the dross.