Apparatus and method for electroplating tin with insoluble anodes

An apparatus for plating tin into a workpiece, the apparatus comprising:

• a) a process cell including a process anode and a workpiece cathode electrically connected to each other by a process rectifier and a process electrolyte, wherein the process electrolyte includes at least one salt of a platable tin, and wherein the process anode is of titanium coated with ruthenium oxide;
• b) a secondary cell including a secondary soluble anode of the platable metal and a secondary cathode electrically connected to each other by a secondary rectifier and a secondary electrolyte;
• c) a permeability-selective ion exchange membrane dividing the secondary cell into an anolyte compartment containing the secondary soluble anode and a catholyte compartment containing the secondary cathode;
• d) a first conduit in fluid flow communication from the anolyte compartment to the process cell;
• and
• e) a second conduit in fluid flow communication from the process cell to the anolyte compartment.

A method for plating tin onto a workpiece, comprising the steps of:

• a) providing an apparatus comprising:
• i) a process cell including a process anode and a workpiece cathode electrically connected to each other by a process rectifier and a process electrolyte, wherein the process electrolyte includes at least one platable salt of tin;
• ii) a secondary cell including a secondary soluble anode of the platable metal and a secondary cathode electrically connected to each other by a secondary rectifier and a secondary electrolyte;
• iii) a permeability-selective ion exchange membrane dividing the secondary cell into an anolyte compartment containing the secondary soluble anode and a catholyte compartment containing the secondary cathode;
• iv) a first conduit in fluid flow communication from the anolyte compartment to the process cell;
• and
• v) a second conduit in fluid flow communication from the process cell to the anolyte compartment;
• b) operating the process cell by passing a first current controlled by the process rectifier from the process anode to the workpiece to thereby plate the platable tin on the workpiece;
• c) operating the secondary cell by passing a second current controlled by the secondary rectifier from the secondary soluble anode to the secondary cathode to thereby provide a tin enriched anolyte in the anolyte compartment of the secondary cell;
• d) moving the tin enriched anolyte from the secondary cell to the process cell through the first conduit as the process cell is being operated;
• e) removing electrolyte from the process cell to the secondary cell through the second conduit;
• and
• f) a controller connected between the process rectifier and the secondary rectifier.

A method for plating tin onto a workpiece, comprising the steps of:

• a) providing an apparatus comprising:
• i) a process cell including a process anode of tin and a workpiece cathode electrically connected to each other by a process rectifier and a process electrolyte, wherein the process electrolyte includes at least one platable salt of tin;
• ii) a secondary cell including a secondary soluble anode of the platable metal and a secondary cathode electrically connected to each other by a secondary rectifier and a secondary electrolyte;
• iii) a permeability-selective ion exchange membrane dividing the secondary cell into an anolyte compartment containing the secondary soluble anode and a catholyte compartment containing the secondary cathode;
• iv) a first conduit in fluid flow communication from the anolyte compartment to the process cell;
• and
• v) a second conduit in fluid flow communication from the process cell to the anolyte compartment;
• b) operating the process cell by passing a first current controlled by the process rectifier from the process anode to the workpiece to thereby plate the platable tin on the workpiece;
• c) operating the secondary cell by passing a second current controlled by the secondary rectifier from the secondary soluble anode to the secondary cathode to thereby provide a tin enriched anolyte in the anolyte compartment of the secondary cell, wherein the second current compensates for the difference between the anode current efficiency and the cathode current efficiency in the process cell, and the amount of current required to plate tin on the secondary cathode;
• d) moving the tin enriched anolyte from the secondary cell to the process cell through the first conduit as the process cell is being operated;
• and
• e) removing electrolyte from the process cell to the secondary cell through the secondary conduit.