Method of controlling solder deposition utilizing two fluxes and preform

Abstract

Method for controlling the deposition of solder on a base metal or substrate is disclosed. The method comprises applying an attaching flux and finishing flux to a substrate, placing a preform thereon and subjecting the same to reflow conditions. The finishing flux is applied to solubilize the normally insoluble corrosive residues that would occur when the attaching flux is subjected to reflow conditions with the preform and substrate. Alternatively, the attaching flux may be applied to the preform and substrate before undergoing reverse reflow conditions and then the finishing flux is applied to the solder deposit and substrate and the same subjected to second reflow conditions. After each method, the residues left from the attaching flux which are solubilized by the finishing flux, are cleaned by washing with a typical solvent.

1 . A method of controlling solder deposition on base metal utilizing two fluxes and preformed solder comprising: 
 a) applying an effective amount of an attaching flux to a base metal or substrate,    b) placing a preform on the substrate containing an effective amount of the attaching flux,    c) applying an effective amount of a finishing flux onto the preform,    d) subjecting the substrate, flux and preform to heated reflow conditions, to form a solder deposit,    e) cleaning the substrate and solder deposit, and    f) drying the cleaned substrate and solder deposit.    
   
   
       2 . The method of  claim 1  wherein the attaching flux may cause the formation of harmful, insoluble, or corrosive residues on the soldered base metal if it is allowed to remain on the soldered base metal.  
   
   
       3 . The method of  claim 1  wherein the amount of attaching flux is sufficient to fill a capillary space between the preform and substrate.  
   
   
       4 . The method of  claim 1  wherein the attaching flux is rosin mildly activated type.  
   
   
       5 . The method of  claim 1  wherein the attaching flux is rosin highly activated type.  
   
   
       6 . The method of  claim 1  wherein the attaching flux is an organic acid type.  
   
   
       7 . The method of  claim 1  wherein the attaching flux is an inorganic acid type.  
   
   
       8 . The method of  claim 1  wherein the preform is placed on the substrate with sufficient force to have it contact the attaching flux on the substrate.  
   
   
       9 . The method of  claim 1  wherein the finishing flux is selected from the group consisting of rosin, rosin mildly activated, rosin activated, organic and inorganic acid fluxes.  
   
   
       10 . The method of  claim 1  wherein the amount of finishing flux is sufficient to solubilize salts of the attaching fluxes on the substrate after reflow.  
   
   
       11 . The method of  claim 1  wherein the reflow conditions cause the solder preform to be liquidus and to wet the substrate.  
   
   
       12 . The method of  claim 11  wherein the reflow conditions comprise heating the preform and substrate at about 20 to about 40° C. above the liquidus of the solder.  
   
   
       13 . The method of  claim 1  wherein the substrate and solder deposit are cleaned by washing with suitable solvents.  
   
   
       14 . The method of  claim 1  wherein the substrate and solder deposit are cleaned by solvents selected from the group consisting of polar solvents and non-polar solvents.  
   
   
       15 . The method of  claim 4  wherein the substrate is selected from the group consisting of platinum, gold, copper, tin, solder, palladium and silver.  
   
   
       16 . The method of  claim 15  wherein the substrate is copper.  
   
   
       17 . The method of  claim 15  wherein the substrate surface is plated with a second metal.  
   
   
       18 . The method of  claim 5  wherein the substrate is selected from the group consisting of nickel, cadmium, brass, lead, bronze, rhodium, copper, and beryllium-copper.  
   
   
       19 . The method of  claim 18  wherein the substrate is copper.  
   
   
       20 . The method of  claim 18  wherein the substrate is nickel.  
   
   
       21 . The method of  claim 18  wherein the substrate is plated with a second metal.  
   
   
       22 . The method of  claim 6  wherein the substrate is selected from the group consisting of nickel-iron, nickel-iron-cobalt, copper and nickel.  
   
   
       23 . The method of  claim 22  wherein the substrate is plated with a second metal.  
   
   
       24 . The method of  claim 22  wherein the substrate is copper.  
   
   
       25 . The method of  claim 22  wherein the substrate is nickel.  
   
   
       26 . The method of  claim 7  wherein the substrate is selected from the group consisting of copper, nickel, zinc, mild steel, stainless steel, nickel-chrome, nickel-copper and aluminum.  
   
   
       27 . The method of  claim 26  wherein the substrate is copper.  
   
   
       28 . The method of  claim 26  wherein the substrate is nickel.  
   
   
       29 . The method of  claim 26  wherein the substrate is stainless steel.  
   
   
       30 . The method of  claim 26  wherein the substrate is mild steel.  
   
   
       31 . The method of  claim 26  wherein the substrate is plated with a second metal.  
   
   
       32 . The method of  claim 1  wherein the reflow conditions cause the solder preform to be liquidus and to wet the substrate.  
   
   
       33 . The method of  claim 1  wherein the reflow conditions comprise heating the preform and substrate at about 20-40° C. above the liquidus of the solder.  
   
   
       34 . The method of  claim 1  wherein the substrate and solder deposit are cleaned by washing with solvents.  
   
   
       35 . The method of  claim 1  wherein the substrate and solder deposit are cleaned by solvents selected from the group consisting of polar solvents and non-polar solvents.  
   
   
       36 . The method of  claim 1  wherein the solder deposit is free of voids.  
   
   
       37 . The method of controlling solder deposition on a base metal utilizing dual fluxes and preformed solder comprising: 
 a) applying an effective amount of an attaching flux to a base metal or substrate,    b) placing a preform on the substrate containing an effective amount of the attaching flux,    c) subjecting the substrate, flux and preform to heated reflow conditions, forming a solder deposit,    d) applying an effective amount of a finishing flux to the solder deposit to solubilize residues left by the attaching flux,    e) subjecting the substrate, finishing flux and solder deposit to heated reflow conditions,    f) cleaning the substrate and solder deposit, and    g) drying the cleaned substrate and solder deposit.    
   
   
       38 . The method of  claim 37  wherein the attaching flux may cause the formation of harmful, insoluble, or corrosive residues on the solder deposit and base metal if it is allowed to remain on the solder deposit and base metal.  
   
   
       39 . The method of  claim 37  wherein the amount of attaching flux is sufficient to fill a capillary space between the preform and substrate.  
   
   
       40 . The method of  claim 37  wherein the attaching flux is rosin mildly activated type.  
   
   
       41 . The method of  claim 31  wherein the attaching flux is rosin highly activated type.  
   
   
       42 . The method of  claim 37  wherein the attaching flux is an organic acid type.  
   
   
       43 . The method of  claim 37  wherein the attaching flux is an inorganic acid type.  
   
   
       44 . The method of  claim 37  wherein the substrate is selected from the group consisting of platinum, gold, copper, tin, solder, palladium and silver.  
   
   
       45 . The method of  claim 44  wherein the substrate is copper.  
   
   
       46 . The method of  claim 44  wherein the substrate is plated with a second metal.  
   
   
       47 . The method of  claim 41  wherein the substrate is selected from the group consisting of nickel, copper, cadmium, brass, lead, bronze, rhodium, beryllium-copper.  
   
   
       48 . The method of  claim 47  wherein the substrate is copper.  
   
   
       49 . The method of  claim 47  wherein the substrate is nickel.  
   
   
       50 . The method of  claim 47  wherein the substrate is plated with a second metal.  
   
   
       51 . The method of  claim 47  wherein the substrate is selected from the group consisting of nickel-iron, nickel-iron-cobalt, copper and nickel.  
   
   
       52 . The method of  claim 51  wherein the substrate is plated with a second metal.  
   
   
       53 . The method of  claim 51  wherein the substrate is copper.  
   
   
       54 . The method of  claim 51  wherein the substrate is nickel.  
   
   
       55 . The method of  claim 43  wherein the substrate is selected from the group consisting of copper, nickel, zinc, mild steel, stainless steel, nickel-chrome, nickel-copper and aluminum.  
   
   
       56 . The method of  claim 55  wherein the substrate is copper.  
   
   
       57 . The method of  claim 55  wherein the substrate is nickel.  
   
   
       58 . The method of  claim 55  wherein the substrate is stainless steel.  
   
   
       59 . The method of  claim 55  wherein the substrate is mild steel.  
   
   
       60 . The method of  claim 55  wherein the substrate is plated with a second metal.  
   
   
       61 . The method of  claim 37  wherein the reflow conditions cause the solder preform to be liquidus and to wet the substrate.  
   
   
       62 . The method of  claim 37  wherein the reflow conditions comprise heating the preform and substrate at about 20-40° C., above the liquidus of the solder.  
   
   
       63 . The method of  claim 37  wherein the substrate and solder deposit are cleaned by washing with suitable solvents.  
   
   
       64 . The method of  claim 37  wherein the substrate and solder deposit are cleaned by solvents selected from the group consisting of polar solvents and non-polar solvents.  
   
   
       65 . The method of  claim 37  wherein the finishing flux is selected from the group consisting of rosin, rosin mildly activated, rosin activated, organic and inorganic fluxes.  
   
   
       66 . The method of  claim 37  wherein the solder deposit is free of voids.