Boric acid replenishment in electroplating baths

Abstract

Boric acid is replenished in an electroplating bath via a replenishment solution comprising boric acid dissolved in pure water, in which the solubility at room temperature is comparable to that in the plating bath at operating temperature. The replenishment solution may be used to replace all or part of the water lost by evaporation. An automated device may be used to replenish boric acid in the electroplating bath.

1 . A method of replenishing boric acid in a plating bath, comprising the steps of:
 providing a replenishment solution comprising a predetermined concentration of boric acid dissolved in substantially pure water; and   adding a predetermined volume of the replenishment solution to the plating bath so as to maintain the concentration of boric acid in the plating bath substantially at a target boric acid concentration.   
     
     
         2 . The method of  claim 1 , wherein the plating bath is a nickel plating bath operated in the temperature range from 30 to 65° C. 
     
     
         3 . The method of  claim 1 , wherein the predetermined concentration of boric acid in the replenishment solution is in the 30-45 g/L range. 
     
     
         4 . The method of  claim 1 , wherein the predetermined concentration of boric acid in the replenishment solution is equal to or greater than the target boric acid concentration in the plating bath. 
     
     
         5 . A method of replenishing boric acid in a plating bath, comprising the steps of:
 providing a replenishment solution comprising a predetermined concentration of boric acid dissolved in substantially pure water; and   flowing the replenishment solution from a replenishment solution reservoir into the plating bath at a predetermined flow rate so as to maintain the concentration of boric acid in the plating bath substantially at a target boric acid concentration.   
     
     
         6 . The method of  claim 5 , wherein the plating bath is a nickel plating bath operated in the temperature range from 30 to 65° C. 
     
     
         7 . The method of  claim 5 , wherein the predetermined concentration of boric acid in the replenishment solution is in the 30-45 g/L range. 
     
     
         8 . The method of  claim 5 , wherein the predetermined concentration of boric acid in the replenishment solution is equal to or greater than the target boric acid concentration in the plating bath. 
     
     
         9 . An apparatus for replenishing boric acid in a plating bath, comprising:
 a reservoir containing a replenishment solution comprising a predetermined concentration of boric acid dissolved in substantially pure water;   a means of transferring a predetermined volume of the replenishment solution from the reservoir to the plating bath; and   a computing device having a memory element with a stored algorithm operative to effect, via appropriate interfacing, transfer of the predetermined volume of the replenishment solution from the reservoir to the plating bath so as to maintain the concentration of boric acid in the plating bath substantially at a target boric acid concentration.   
     
     
         10 . The apparatus of  claim 9 , wherein the computing device is further operative to determine the predetermined volume of the replenishment solution to be added to the plating bath based an analysis of the boric acid concentration in the plating bath. 
     
     
         11 . The apparatus of  claim 9 , wherein the computing device is further operative to determine the predetermined volume of the replenishment solution to be added to the plating bath based on a volume of water lost from the plating bath by evaporation. 
     
     
         12 . The apparatus of  claim 9 , further comprising:
 a bath level indicator.   
     
     
         13 . The apparatus of  claim 9 , further comprising:
 a means of adding a predetermined volume of substantially pure water to the plating bath.   
     
     
         14 . The apparatus of  claim 13 , wherein the computing device is further operative to determine the predetermined volume of substantially pure water to be added to the plating bath based on the predetermined volume of the replenishment solution and a volume of water lost from the plating bath by evaporation. 
     
     
         15 . The apparatus of  claim 9 , wherein the memory element is selected from the group consisting of computer hard drive, microprocessor chip, read-only memory (ROM) chip, programmable read-only memory (PROM) chip, magnetic storage device, computer disk (CD), digital video disk (DVD), and combinations thereof.