Treatment methods and solutions for improving adhesion of gold electroplating on metal surfaces

Patent metadata

Field	Value
Publication number	US-11898264-B2
Application number	US-202117479569-A
Country	US
Kind code	B2
Filing date	Sep 20, 2021
Priority date	Sep 21, 2020
Publication date	Feb 13, 2024
Grant date	Feb 13, 2024

Abstract

Treatment solutions and methods for improving adhesion of gold electroplating onto metal surfaces are provided herein. More specifically, the disclosure relates to micro-etching stainless steel surfaces using to remove any organic contamination and chromium oxide formed on the surface, neutralize and strip the surface of any iron content, and repassivate the surface with a thin chromium oxide layer, prior to gold electroplating of the stainless steel surfaces.

First claim

The invention claimed is:

1. A method of treating one or more stainless steel surfaces, comprising:
etching at least a portion of one or more stainless steel surfaces with an etchant solution comprised of potassium permanganate (KMnO4) and sodium hydroxide (NaOH), the one or more stainless steel surfaces including a metal circuit layer disposed on the one or more stainless steel surfaces, wherein a concentration of the potassium permanganate in the etchant solution is between 0.1 M and 0.4 M, and the sodium hydroxide is added until the etchant solution has a pH greater than 12.5;
exposing at least the portion of the one or more stainless steel surfaces to the etchant solution fora period of time between 1 second and 5 minutes and at a temperature between 5.0 and 85 degrees Celsius;
subsequently neutralizing at least the portion of the one or more stainless steel surfaces with a neutralizer solution comprised of ascorbic acid and citric acid;
repassivating at least the portion of the one or more stainless steel surfaces with a chromium oxide layer; and
removing the chromium oxide layer using a plating surface treatment operation.

2. The method of claim 1 wherein a concentration of ascorbic acid in the neutralizer solution is between 75 g/L and 250 g/L, and the concentration of citric acid is between 50 g/L and 200 g/L.

3. The method of claim 1 wherein at least the portion of the one or more stainless steel surfaces is exposed to the neutralizer solution for a period of time between 1 and 300 seconds.

4. The method of claim 1 wherein at least the portion of the one or more stainless steel surfaces is exposed to the neutralizer solution at a temperature between 25 and 85 degrees Celsius.

5. The method of claim 1 , wherein the etching step dissolves chromium metal and converts chromium oxide, present on at least the portion of the one or more stainless steel surfaces, to a soluble form.

6. A method of electroplating gold onto one or more stainless steel surfaces, the method comprising:
treating at least a portion of one or more surfaces of stainless steel by exposing each of the one or more surfaces of stainless steel to a solution comprising potassium permanganate (KMnO4) and sodium hydroxide (NaOH), the one or more surfaces of stainless steel including a metal circuit layer disposed on the one or more surfaces of stainless steel, wherein a concentration of the potassium permanganate in the etchant solution is between 0.1 M and 0.4 M, and the sodium hydroxide is added until the etchant solution has a pH greater than 12.5;
exposing at least the portion of the one or more stainless steel surfaces to the etchant solution fora period of time between 1 second and 5 minutes and at a temperature between 5.0 and 85 degrees Celsius;
subsequently neutralizing at least the portion of the one or more surfaces of stainless steel by exposing each of the one or more surfaces of stainless steel to a solution comprised of ascorbic acid and citric acid;
exposing at least the portion of the one or more surfaces of stainless steel to an oxygen plasma cleaning process and a wet cleaning process solution;
repassivating at least the portion of the one or more stainless steel surfaces with a chromium oxide layer;
removing the chromium oxide layer using a plating surface treatment operation;
immersing the one or more surfaces of stainless steel in a gold electroplating solution; and
applying a voltage between an anode within the gold electroplating solution and at least the portion of the one or more surfaces of stainless steel to generate a current from the anode to at least the portion of the one or more surfaces of stainless steel to electroplate gold from the gold electroplating solution onto at least the portion of the one or more surfaces of stainless steel.

7. The method of claim 6 , wherein the treating step dissolves chromium metal and converts chromium oxide to a soluble form.

8. The method of claim 6 , wherein a concentration of ascorbic acid in the neutralizer solution is between 75 g/L and 250 g/L, and the concentration of citric acid is between 50 g/L and 200 g/L.

9. The method of claim 6 , wherein at least the portion of the one or more surfaces of stainless steel is exposed to the neutralizer solution for a period of time between 1 and 300 seconds.

10. The method of claim 6 , wherein at least the portion of the one or more surfaces of stainless steel is exposed to the neutralizer solution at a temperature between 25 and 85 degrees Celsius.

11. The method of claim 6 , wherein the gold electroplating solution includes:
a gold (III) cyanide compound, the gold (III) cyanide compound being one of potassium gold (III) cyanide, ammonium gold (III) cyanide, and sodium gold (III) cyanide;
a chloride compound, the chloride compound being one of potassium chloride, ammonium chloride, and sodium chloride; and hydrochloric acid,
wherein if the gold (III) cyanide compound is potassium gold (III) cyanide, then the chloride compound is potassium chloride; if the gold (III) cyanide compound is ammonium gold (III) cyanide, then the chloride compound is ammonium chloride, and if the gold (III) cyanide compound is sodium gold (III) cyanide, then the chloride compound is sodium chloride.

12. The method of claim 6 , wherein the method de posits gold on the one or more surfaces of stainless steel that are part of a disk drive head suspension, flexure, an optical image stabilization suspension, or a medical device.

Assignees

• Hutchinson Technology

Inventors

• Pesavento Paul V
• Grove Collin M
• Riemer Douglas P

Classifications

• C25D5/36 Primary

  of iron or steel · CPC title

• C23F1/28

  for etching iron group metals · CPC title

• C23F17/00

  Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25 (coating for obtaining at least two superposed coatings either by methods not provided for in a single one of main groups C23C2/00 - C23C26/00, or by combinations of methods providedfor in subclasses C23C and C25D, C23C28/00) · CPC title

• C25D3/48

  of gold · CPC title

• C23F1/32

  Alkaline compositions (C23F1/42 takes precedence) · CPC title