No clean flux composition and methods for use thereof

Abstract

A flux formulation includes an activator and a protic solvent. The activator may be glutaric acid, levulinic acid, 2-ketobutyric acid, 2-oxovaleric acid, or mixtures thereof. Suitable protic solvents include alkanediol, alkoxy propanol and alkoxy ethanol. The flux formulation may be a no-clean flux formulation that may be used in the soldering of electronic circuit board assemblies, for example, in conjunction with a support fixture having a planar back surface that minimizes vibrations during processing that might otherwise cause misalignment between a chip and a substrate prior to solder reflow.

1 .- 10 . (canceled) 
     
     
         11 . A soldering method comprising:
 exposing a first substrate to a reducing plasma at a temperature from 20° C. to 25° C.;   applying a flux formulation comprising an activator and a protic solvent, wherein the activator is a ketoacid having a boiling, sublimation or decomposition point of from 150° C. to 260° C. onto a surface of the first substrate to be soldered, the surface of the first substrate comprising a plurality of first solder bumps or metal contacts,   contacting second solder bumps disposed on a surface of a second substrate to be soldered with the first solder bumps or metal contacts, and   heating the first solder bumps or metal contacts and the second solder bumps to a first temperature to solder the first solder bumps or metal contacts to the second solder bumps and form a soldered assembly.   
     
     
         12 . (canceled) 
     
     
         13 . The method of  claim 11 , wherein the first temperature is 150° C. to 260° C. 
     
     
         14 . The method of  claim 11 , further comprising cooling the soldered assembly to a second temperature and applying an underfill material between the first substrate and the second substrate at the second temperature, wherein the second temperature is 100° C. to 120° C. 
     
     
         15 . The method of  claim 14 , further comprising exposing the soldered assembly to an oxidizing plasma prior to applying the underfill material. 
     
     
         16 . The method of  claim 14 , further comprising curing the underfill material at a third temperature greater than the second temperature. 
     
     
         17 . The method of  claim 11 , further comprising placing the first substrate on a top surface of a fixture prior to the contacting, wherein the fixture has a planar bottom surface opposite to the top surface. 
     
     
         18 . The method of  claim 17 , wherein the planar bottom surface comprises at least 25% of an area of the fixture. 
     
     
         19 . The method of  claim 17 , wherein the first substrate is placed into a recessed region formed in the top surface. 
     
     
         20 . The method of  claim 17 , wherein the fixture comprises a plurality of apertures extending through the fixture from the first surface to the second surface. 
     
     
         21 . The method of claim  1 , wherein the ketoacid is selected from the group consisting of 2-ketobutyric acid, 2-oxovaleric acid and mixtures thereof. 
     
     
         22 . The method of claim  1 , wherein the flux formulation does not contain halides. 
     
     
         23 . The method of claim  1 , wherein the flux formulation does not contain halides or organic resins. 
     
     
         24 . A soldering method comprising:
 providing a first substrate comprising a plurality of first solder bumps or metal contacts affixed to a surface thereof;   exposing the surface of the first substrate to a reducing plasma at a temperature from 20° C. to 25° C.;   applying a flux formulation comprising an activator and a protic solvent, wherein the activator is a diacid or ketoacid having a boiling, sublimation or decomposition point of from 150° C. to 260° C. onto a surface of the first substrate;   contacting the first solder bumps or metal contacts disposed on a surface of the first substrate to a second substrate, and   heating the first solder bumps or metal contacts to a first temperature to solder the first solder bumps or metal contacts to the second substrate to form a soldered assembly.   
     
     
         25 . The method of  claim 24 , wherein the reducing plasma comprises hydrogen. 
     
     
         26 . The method of  claim 24 , further comprising cooling the soldered assembly to a second temperature and applying an underfill material between the first substrate and the second substrate at the second temperature, wherein the second temperature is 100° C. to 120° C. 
     
     
         27 . The method of  claim 26 , further comprising exposing the soldered assembly to an oxidizing plasma prior to applying the underfill material. 
     
     
         28 . The method of  claim 26 , further comprising curing the underfill material at a third temperature greater than the second temperature. 
     
     
         29 . The method of  claim 24 , wherein the activator is a ketoacid selected from the group consisting of 2-ketobutyric acid, 2-oxovaleric acid and mixtures thereof 
     
     
         30 . The method of  claim 24 , wherein the flux formulation does not contain halides or organic resins.