JPH0317913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to electroplating baths. More particularly, it relates to bath compositions suitable for electroplating highly positive metals, such as aluminum and tungsten in particular.

[Conventional technology]

Strongly positive metals such as aluminum and tungsten are quite difficult to electroplate. Such metals have a strong affinity for atmospheric oxygen. Because of this property, a dense oxide layer is formed on the surface of the metal that is permanently present. Formation of this layer occurs within seconds after the fresh surface of these metals is exposed to oxygen. This oxide layer makes these metals very difficult to plate. And even if plated, the adhesion is often very poor.

Conventional methods for plating such metals include extensive surface pretreatment. In the case of tungsten, the parts to be plated must be frequently moved from bath to bath while being electrically biased, creating a safety problem due to the possibility of electric shock. Additionally, conventional plating methods for these metals generate significant amounts of harsh wastes such as hydrofluoric acid.

Therefore, there is a need for better methods and plating bath chemistries for plating these difficult to plate metals. U.S. Patent No. 3769179, U.S. Patent No. 4242181
No. 3,923,613 exemplify the prior art of copper plating. In particular, the first two are applied to the printed circuit manufacturing industry.

[Summary of the invention]

The present invention provides a method including a bath composition for depositing copper on difficult to plate metals such as aluminum and tungsten. The bath composition of the present invention is an acidic copper bath containing additives for specific purposes. The method of the present invention does not require surface pretreatment or etching prior to plating, thereby reducing the amount of chemical waste associated with the method. Additionally, the present invention provides for the removal of oxides from hard-to-plate metals in the plating bath, thereby minimizing the chance of new oxide formation on the clean surface, thereby reducing the chance of formation of new oxides on the deposited copper and base metal. A good metallurgical bond between the two can be achieved.

The method of the present invention provides higher yields and better adhesion while minimizing costs associated with waste disposal.

[Description of preferred embodiments of the invention]

A preferred aqueous plating solution contains 0.5 to 0.75 moles of sulfuric acid/
, hydrated copper sulfate 0.3-0.5 mol/, urea 1-
2g/, wetting agent 1~2g/, sulfonic acid 1~
2 g/and 800-1000 ml of deionized water.

Urea is included for its properties as a smoothing agent. Sulfonic acid is used for its gloss properties. Suitable wetting agents include cationic surfactants such as sodium lauryl sulfate.

This bath is prepared by sequentially adding all of the chemical reagents listed above to deionized water. This solution is mixed and filtered if necessary to remove any undissolved particles. The metal to be plated is first cleaned to remove dirt, mud and other surface contaminants and then rinsed in deionized water. This metal is then placed in a plating tank containing the prepared bath.

Preferably, the part is allowed to sit in the plating solution for 2 to 3 minutes before electroplating of the copper begins by applying a negative bias. However, it is noted that in difficult cases, especially where there is an insoluble naturally grown oxide layer, it may be removed by applying a positive bias for 30 to 60 seconds before applying a negative bias to the part.

Typical plating process parameters include bath temperature in the range of 20-30℃, current density of about 11-22mA/cm2 (10-22mA/cm2 ⁾ ,
20A/ft ² ) and continuous strong agitation.
The duration of the plating process can be varied depending on the desired copper thickness.

The sulfuric acid in the plating bath is at a sufficient concentration to remove the oxide layer during the 2-3 minute soak before introducing the electrical current. Since no full-scale surface pretreatment or etching is required before plating, the number of man-hours, the amount of chemical waste generated, and the associated costs can be reduced.

〔Example〕

The following examples illustrate various aspects of the invention.

Example 1 Aluminum and tungsten workpieces are cleaned in a mild alkaline cleaning solution and plated in the following solution. Sulfuric acid 74g/, copper sulfate 72g/, urea (smoothing agent) 1g/, sulfonic acid (brightening agent) 1
g/, sodium lauryl sulfate (surfactant)
1 g/1 part of deionized water.

The work piece is immersed in this solution for 2-3 minutes and then a bias voltage is applied. Approximately 11mA/cm ² for plating at room temperature
(10A/ft ² ) for 20 minutes. The deposited copper is smooth and free of defects such as skip plating. Adhesion strength tests using the base grain test method and the quenching method showed no poor adhesion.

Example 2 Another example of the present invention was carried out in the same manner as in Example 1. However, the amount of sulfuric acid was reduced to 50g/. The quality and adhesion of the deposited copper were the same as in Example 1.

Example 3 Other experiments were conducted as in Examples 1 and 2. However, the concentration of sulfuric acid was further reduced to 30g/.
A subsequent adhesion test revealed that the test area
25% or more showed failure.

Example 4 Another experiment was carried out under the same conditions as in Example 1, except that the amount of copper sulfate was 50 g. The deposits were smooth, free from uneven plating, and had good adhesion.

Example 5 A tungsten corner piece exhibiting a slightly bluish color (tungsten oxide) was cleaned and then plated as in Example 1. Subsequent adhesion tests showed poor adhesion. However, when the square piece was plated first under a positive bias for 1 minute and then under a negative bias, the plated square piece showed good adhesion. Up to this point, the present invention has described particularly preferred embodiments for reference, but it will be apparent to those skilled in the art that various modifications and details can be made without departing from the spirit and purpose of the present invention as defined in the claims. would be considered easy.

Although the present invention has been described in detail above, the present invention can be further summarized by the following embodiments.

(1) Sulfuric acid is used in the method of copper plating on positive metals.
0.5-0.75 mol/, hydrated copper sulfate 0.3-0.5 mol/, urea 1-2 g/, wetting agent 1-2 ml/
, brightener 1-2g/, and deionized water
Prepare a bath containing 800-1000 ml, immerse the parts to be plated in this bath and approx.
Under the temperature of 20℃~30℃, the current density is about 11~
The method for plating copper as described above, comprising electrodepositing copper from this bath with continuous stirring at 22 mA/cm ² (10-20 A/ft ² ).

(2) The method according to item 1 above, wherein the dipping step is for 2 to 3 minutes.

(3) Under the influence of positive bias, repeat the above immersion process for 30 to 60 minutes.
The method according to item 1 above, which lasts for seconds.

(4) The method according to item 1, which includes mixing the bath components in deionized water in the order described in item 1 and filtering the bath solution as the step for preparing the above.

(5) The method according to item 1, 2, 3 or 4 above, wherein the wetting agent is sodium lauryl sulfate and the brightening agent is sulfonic acid.

(6) Sulfuric acid 0.5-0.75 mol/, hydrated copper sulfate 0.3
The part to be plated is immersed in a bath consisting of ~0.5 mol/, leveling agent 1-2 g/, wetting agent 1-2 ml/, brightener 1-2 g/, deionized water 800-1000 ml and about 20-30 Temperature below about 11 ~
Acidic copper plating bath for positive metals with a current density of 22 mA/cm ² (10-20 A/ft ² ) to deposit copper from this bath.

(7) The bath according to item 6 above, wherein the wetting agent is a cationic surfactant.

(8) The bath according to item 6 above, wherein the brightener is sulfonic acid.

(9) Item 6, 7 or 8 above, where the smoothing agent is urea.
The bath described in.

(10) Sulfuric acid 30-50g/, hydrated copper sulfate 50-72
Aqueous acidic copper for strongly positive metals such as aluminum and tungsten plated with continuous stirring of a bath composition consisting of 1 g/g/g of urea, 1 g/g of sulfonic acid, and 1 g/g of cationic surfactant. Electrodeposition bath composition.

Claims (1)

[Claims] 1. In a method of copper plating a positive metal, sulfuric acid
0.5-0.75 mol/, hydrated copper sulfate 0.3-0.5 mol/, urea 1-2 g/, wetting agent 1-2 ml/
, brightener 1-2g/, and deionized water 800ml
Prepare a bath containing ~1000 ml, immerse the parts to be plated in this bath and approx.
At temperatures between ℃ and 30℃, current density is about 11 to 22 mA/cm ²
The copper plating method described above comprises electrodepositing copper from this bath while continuously stirring at (10 to 20 A/ ^ft2 ). 2 Sulfuric acid 0.5-0.75 mol/, hydrated copper sulfate 0.3
~0.5 mol/, smoothing agent 1-2 g/, wetting agent 1-2 ml/, brightening agent 1-2 g/, deionized water
The parts to be plated are immersed in a bath consisting of 800 to 1000 ml, and heated at a temperature of approximately 20 to 30°C at approximately 11 to 22 mA/cm ² (10
An acidic copper plating bath for positive metals with a current density of ~20 A/ft ² ) to deposit copper from this bath. 3 Sulfuric acid 30-50g/, hydrated copper sulfate 50-72
Aqueous acidic copper for strongly positive metals such as aluminum and tungsten is plated with continuous stirring of a bath composition consisting of: Electrodeposition bath composition.