TIN AND TIN ALLOY ELECTROPLATING METHOD WITH CONTROLLED INTERNAL STRESS AND GRAIN SIZE OF THE RESULTING DEPOSIT

Abstract

A method for electrochemically plating tin or tin alloy onto a workpiece to provide a tin or tin alloy deposit on said workpiece having a stress differential and workpieces characterized by a tin or tin alloy deposit having a stress differential.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an electrically mediated waveform.

FIG. 2 is a graph showing the polarization curves for tin deposition in methane sulfonic acid solution and in a commercial tin-lead plating solution.

FIG. 3 is a graph showing the grain size and surface roughness of a tin deposit produced by the method of the present invention, as a function of changing process parameters. The surface roughness is measured in terms of Ra, which is the arithmetic mean deviation of the profile. The profile identified (OW), is a measure of the surface as initially plated. The profile identified (5 W) is a measure of the surface after five weeks of exposure to ambient conditions.

FIG. 4 is a series of scanning electron micrographs showing the change in surface morphology of the tin deposit after one day after and 5 weeks after plating under conditions of a) test D4, b) test P8, and c) test PR16.

FIG. 5 is a graph showing the internal stress in the tin deposit, as a function of changing process parameters.

FIG. 6 is a series of optical micrographs showing the surface appearance of the tin deposit after plating from a tin-methane sulfonic acid plating bath (a, b), and a commercial tin-lead plating bath (c, d).

Claims

1. A method for electrochemically plating tin or tin alloy onto a workpiece, comprising: immersing the workpiece in an electroplating bath comprising stannous ions;immersing a counter electrode in said electroplating bath; andpassing a pulsed current between said workpiece and said counter electrode sufficient to provide a tin or tin alloy deposit on said workpiece having a stress differential.

2. A method for electrochemically plating a metal or a metal alloy onto a conducting workpiece using a cell comprising: a. immersing said workpiece in an electrolyte solution;b. immersing a counterelectrode in said electrolyte solution; andc. passing a pulsed current between said workpiece and said counter electrode sufficient to generate a deposit of metal or metal alloy onto said workpiece wherein said deposit has a predetermined state of stress selected from the group consisting of compressive stress, zero stress, and tensile stress.

3. The method as described in claim 1 wherein said metal and metal alloy comprise tin and tin alloy.

4. The method as described in claim 1 wherein said workpiece comprises a copper substrate.

5. The method as described in claim 1 wherein said workpiece comprises a cathode in said cell.

6. The method as described in claim 1 wherein said electrolyte solution consists essentially of an acid, a wetting agent, and a salt of said metal.

7. The method as described in claim 1 wherein said electrolyte solution consists essentially of an alkane sulfonic acid, a wetting agent, and a stannous sulfontae.

8. The method as described in claim 6 wherein said alkane sulfonic acid is alkane sulfonic acid, said wetting agent is Triton X-100, and said stannous sulfonate is stannous methane sulfonate.

9. The method as described in claim 1 wherein said solution is devoid of organic additives other than methane sulfonic acid and Triton X-100.

10. The method as described in claim 1 wherein said solution is devoid of additives containing hetorocyclic moiety.

11. The method as described in claim 1 wherein said pulsed current includes a succession of alternating cathodic on-times and anodic on-times.

12. The method as described in claim 1 wherein said pulsed current is a pulse-pulse reverse current.

13. A method for electrochemically plating a metal or a metal alloy onto a conducting workpiece using a cell comprising: a. immersing a counter electrode in an electrolyte solution;b. immersing said workpiece in said electrolyte solution; andc. passing a pulsed current between said workpiece and said counter electrode sufficient to generate a deposit of metal or metal alloy onto said substrate wherein said deposit has a predetermined stress gradient from the interface between said workpiece and said deposit to the outer surface of said deposit.

14. The method as described in claim 13 wherein said metal and metal alloy comprise tin and tin alloy.

15. The method as described in claim 13 wherein said counter electrode is a tin electrode.

16. The method as described in claim 1 wherein said workpiece comprises a copper substrate.

17. The method as described in claim 13 wherein said workpiece comprises a cathode in said cell.

18. The method as described in claim 13 wherein said electrolyte solution consists essentially of an acid, a wetting agent, and a salt of said metal.

19. The method as described in claim 13 wherein said electrolyte solution consists essentially of an alkane sulfonic acid, a wetting agent, and a stannous sulfontae.

20. The method as described in claim 18 wherein said alkane sulfonic acid is alkane sulfonic acid, said wetting agent is Triton X-100, and said stannous sulfonate is stannous methane sulfonate.

21. The method as described in claim 13 wherein said solution is devoid of organic additives other than methane sulfonic acid and Triton X-100.

22. The method as described in claim 13 wherein said solution is devoid of additives containing hetorocyclic moiety.

23. The method as described in claim 13 wherein said pulsed current consists of a succession of alternating cathodic on-times and anodic on-times.

24. The method as described in claim 13 wherein said pulsed current is a pulse-pulse reverse current.

25. The method as described in claim 13 wherein said stress gradient is selected from the group consisting of: a stress gradient from zero stress at said interface and compressive stress at said outer surface; a stress gradient from zero stress at said interface and tensile stress at said outer surface; a stress gradient from compressive stress at said interface and zero stress at said outer surface; a stress gradient from compressive stress at said interface and tensile stress at said outer surface; a stress gradient from tensile stress at said interface and compressive stress at said outer surface; and a stress gradient from tensile stress at said interface and zero stress at said outer surface.