JPS6053120B2 - Base metal hardening gold plating improvement method - Google Patents

Description

[Detailed description of the invention] The present invention relates to the electrodeposition of gold onto substrate surfaces.

The present invention further relates to improving the corrosion resistance of cobalt-cured gold plating films electrodeposited on various substrates. The method of electrodepositing cobalt hardened gold plating films onto substrate surfaces is known in the industry as electrolytic deposition and electroplating.
Typically, an electrolytic bath consisting of the metal ions to be deposited and a suitable electrolyte is provided, and the article to be coated is immersed in or in contact with the bath to serve as a cathode, while the metal electrode is connected as an anode to the same power source. Metal ions deposited during the plating operation are reduced to zero valence in the bath and electrodeposited on the test piece or substrate. Regarding the use of cobalt to harden gold plated films, see, for example, U.S. Pat. No. 2,905.
, No. 601. It is stated in the official gazette.

It has been found that such known cobalt-cured gold plating films do not have a high degree of corrosion resistance and are not suitable for certain commercial purposes.

Therefore, it has been desired to provide a method for making a special cobalt-cured gold electrodeposit with significantly improved corrosion resistance and excellent aesthetics such as gloss and smoothness. In some cases it has been possible to achieve such an objective only if the plated membrane is extremely thin. According to this invention, it has been found that a cobalt hardened gold plated film exhibiting improved corrosion resistance can be obtained by first coating a substrate with a ductile, strain-free nickel film.

The desired nickel plating is produced on the substrate by electrodeposition using a specially prepared electrolytic bath with an insoluble anode.

Generally, nickel electrolytic baths contain a nickel salt such as nickel sulfate as a source of nickel ions and boric acid or citric acid as an electrolyte. Although other known additives may be used, it has been found essential to use a mixture of orthoformylbenzenesulfonic acid as brightener and potassium perfluoroalkylsulfonate (sold under the trade name FC98) as wetting agent. . Following the electrodeposition of a ductile, strain-free nickel plating film, a surface plating film of cobalt-hardened gold is electrodeposited.

The cobalt-hardened gold-plated film obtained by performing the two-stage continuous electrodeposition process as described above has extremely superior corrosion resistance compared to the cobalt-hardened gold-plated film without such a nickel intermediate plating film. It is characterized by high corrosion resistance.

On the other hand, in the case of gold hardened with iron other than cobalt, for example, excellent corrosion resistance cannot be obtained even if a ductile and strain-free intermediate nickel plating film is applied. The corrosion resistance test was conducted according to Western Electric's manufacturing standard WL.
Measured using 23l6.

According to the standard, all gold-plated finished products must be free of blisters and cracks, and test specimens are subjected to the well-known "゜Bend Test,''"゜QuenchTest,'' and ``゛゜Tape Peel Test.'' Even if it is removed, the peeling part must not be visible.

A nickel plating bath useful in the initial coating process according to this invention has the following composition.

Suitable? Wataruji? J metal sources include sulfuric acid, nickel citrate, nickel carbonate, and others.

These salts are preferably used in amounts of about 135 to 470 g/e to provide the preferred nickel concentration. The most effective electrolyte in this invention is boric acid,
The preferred amount of citric acid and others used in preparing the plating bath of this invention is about 22.5 to 45 g/
′.

Particular preference is given to using boric acid. The organic components of this nickel bath are usually brightening and wetting agents. The specific brightener used in preparing the specialized plating bath of this invention is orthoformylbenzene sulfonic acid. RFc98, which is required as a wetting agent, is a trademark of Minnesota Mining and Manufacturing Company, and is a potassium perfluoroalkyl sulfonate compound (purity 9).
This is an anionic surfactant in the form of a stable white powder (bulk density: 0.6) consisting of a heel weight or more. The pH of this electroplating bath
is about 2 to 5 in most cases, preferably 2.
Adjust to a range of 5 to 4.5.

The pH adjusting compound is nickel carbonate sulfate, potassium citrate or citrate. The bath according to the invention has a bath temperature of about 46
5rc and less than about 1000 ASF (108 A/D), preferably about 100 to 60 QASF (11
65 A/Dd).

Enabling the use of such high current densities is another very important advantage of the plating bath according to the invention. Nickel plating films on various substrates using the bath of this invention are characterized by being semi-bright, ductile, and free of distortion.

Additionally, it is possible to use an insoluble anode during both the initial and secondary coating steps. Insoluble anodes used are, for example, platinum-coated titanium, platinum-coated tantalum, platinum-coated columbium (niobium), and also platinum anodes themselves. Additionally, titanium anodes coated with mixed oxide coatings such as ruthenium dioxide titanium dioxide coatings can also be used. Rlnker is used for electrodeposition of hard gold-plated films.
and U.S. Pat. No. 2,90 by Duva (195).
This can be achieved by using the bath and method described in Japanese Patent No. 5,601.

In the method of the present invention in which high-speed nickel plating is followed by high-speed gold plating to form an intermediate plating film on the base surface, it is preferable to apply a gold plating film hardened by cobalt. However, it should be understood that other metal hardeners selected from the metals consisting of indium, nickel and zinc can also be used. Plating baths useful for gold plating processes consist of (1) a stable weak organic acid, (2) gold cyanide (e.g., potassium gold cyanide), and (3) one or more base metal salts soluble in the bath. .

Examples of acids that can be used are formic acid, acetic acid, citric acid, tartaric acid, lactic acid, kojic acid, similar acids or mixtures of these acids.

The acid should be present in a proportion of about 10 to 150 g/e and partially neutralized with ammonium hydroxide or alkali hydroxide to a pH of about 3 to 5. The reason why the gold alloy plated film exhibits the desired effect is due to the use of these weak organic acids and the operation of maintaining the pH of the bath within a certain range. Gold can be added as a gold and alkali metal double cyanide, such as potassium gold cyanide, from about 8 g/e to 26 g/e, preferably 12 g/e.
The percentage of The base metal salts to be added include cobalt,
Nickel, zinc and indium sulfates, sulfamates, formates, acetates, citrates, lactates, tartrates, fluoroborates, borates, phosphates, etc.

These metal salts are added at a rate of 0.5 to 5 g/'. Very satisfactory results are obtained when two such base metal salts are included in the bath. Although the addition of a base metal salt is necessary, it does not matter which salt or mixture of salts is added as long as the added salt is soluble and compatible with all other bath components. Bath is 1 to 100A/F
It can be operated at current densities of t2 (0.1 to 11 A/Dd) and the bath operation can be improved by stirring.

The bath can be operated at normal room temperature (70°F 121.1°C);
This shows the advantage that no temperature regulation is necessary. But higher or lower, i.e. 50 (1Cf'C) to 120'F (48.CfC)
Can be operated within the range. The maximum ratio of cathode to anode should be about 4 to 1. A preferred plating bath useful for the secondary coating process has the following composition: , - -7,
,, Gold (as potassium gold cyanide) 12 to 26
Cobalt (as sulfate) 0.5 to 1.75
The following implementation Ii is described to further explain the invention.
(Example) A first plating bath was prepared by dissolving the following components.

A second plating bath was prepared by dissolving the following ingredients.

The pH of the bath was adjusted to about 4.8 to 5.2 by addition of alkali or acid.

The quality of corrosion resistance in the following experimental examples was determined using Western Electric's Finish Specificat.
The tests were conducted based on the standards for gold-plated finished products described in iOnWL-2316 and the following bending test, quench test, and tape test results. It is directly related to

(Gold-plated finish standards and test methods) All gold-plated finished parts must be free of visible blisters and cracks.

Furthermore, no peeling should occur when the next bending test, quench test, and tape test are performed. Some types of gold plating show cracks during bending tests. However, as long as there is no blistering or peeling, it will be passed.

1 Bend Test The gold-plated area of the panel part is folded 180 degrees so that the diameter of the fold is equal to the thickness of the panel part.

Take out the panel part and tighten both ends of the bent part to approximately 10f1gR.
Visually examine the remaining portion of the plated film for cracks and peeling, and display at 10X as necessary depending on the number and size of cracks and peeling. If there is no cracking or peeling of the plating film on two or more of the three test panel parts, the test is deemed to have passed. For panel parts where bending testing cannot be performed, the bending test shall be performed on another panel of 1.016 mm thickness with the same surface composition and plated under the same conditions as the panel part. . It is permissible to apply mutatis mutandis to the bending test other bending or forming operations that are incidental to the manufacturing process and have conditions similar to those of the above test. 2. Quench Test Heat the plated parts in the open at 150±10°C for 1 hour.

Immediately place the part in water at room temperature, inspect internally for cracks and peeling, and if necessary, display 10X according to the number and size of cracks and peeling. 3 Tape Peeling Test FederaIS SpecificationOnL-T-
12.7 to pass 90D, Type I, C1assA
Pressure-sensitive adhesive tape made of cellophane tape with a width of Tf1m (for example, RTape6OO, 6lO from 3MC0mpany)
or 810 J) firmly across the test surface by at least 50 wn.

The tape should be new and should be applied to three different locations on the part and then pulled away, or if the part is too small to test in three different locations, the peel test should be performed on three different parts. must be done. If even slight peeling of the plating occurs due to tape peeling, it indicates that the adhesion of the plating is poor and the product is rejected. The appearance of the gold-plated film was also tested in accordance with the following test method described in Western Electric's Gold Finish Product Standard WL-2316. 4 Appearance test When visually inspected, the plating film must completely cover the important surfaces and have a uniform appearance, as far as the substrate conditions and manufacturing method allow. It won't happen.

Moisture or seepage from parts that have been previously assembled, such as hidden holes or soldering, is a normal occurrence even during good work, and may occur if the spot hits an electrical contact or is subsequently soldered. The test will be passed as long as it is not in any of the following areas. In the case of hard gold finishes, the plating film must be consistently smooth and bright, depending on the tamping solution used and the surface conditions of the base metal.

The content of this smoothness and shine (for example, hue) varies depending on the surface conditions of the substrate, the plating solution used, and the plating method. Hue, gloss and texture do not need to be checked, but
Display conceptually. Experimental Example A A substrate consisting of a commercially available copper-plated circuit board was treated in this nickel plating bath to produce a semi-bright, ductile, undistorted nickel-plated film having a thickness of about 2.5 to 5p. was generated.

The coated substrate was then treated in a secondary bath or gold plating bath to produce a bright, smooth, hard gold plated film.
The coating was about 1 to 2 microns thick. The corrosion resistance of the product is based on Western Electric's manufacturing standard WL23L.
According to No. 6, it was extremely excellent. The nickel plating conditions are PH3, bath temperature 50℃, and current density 300A.
SF (32.3A/DTrl), plating time is 1 to 2 minutes, and the gold plating conditions are PH4. The λ bath temperature was 20°C, the current density was 75 ASF (8.0 A/D77 l'), and the plating time was 1 minute.

Experimental Example B When the electrodeposition step of the nickel plating film was omitted, the corrosion resistance of the resulting plating film failed.

Experimental Examples C, D and E Instead of cobalt in the gold bath, 0.
9g/e indium (as sulfate), 1.8g/e
Example A except that 1.3 g/' of nickel (as sulfate) and 1.3 g/' of zinc (as sulfate) were used, respectively.
This operation was repeated three times.

In either case, a glossy and smooth hard gold-plated film with a film thickness of 1 to 2 microns was obtained. The corrosion resistance of the products was in each case the same as that obtained in Example A. Comparative Example AO - The procedure of Example A was repeated except that saccharin was used in place of formylbenzenesulfonic acid.

Many cracks and blisters were observed on the surface of the product, and it was rejected. Comparative Example B The procedure of Experimental Example A was repeated, except that sodium lauryl sulfonate, a known wetting agent, was used instead of rFC98J (trade name).

Claims (1)

[Claims] A method for producing gold plating with improved corrosion resistance on a substrate, wherein the nickel salt is calculated as 30% nickel.
~150g/l, boric acid and citric acid as electrolyte, 20-100g/l in total of one or both, and 0.25-3.0g/l of orthoformylbenzenesulfonic acid as brightener.
g/l, pH 2-5, bath temperature 46-57°C, from a plating bath containing a potassium perfluoroalkyl sulfonate mixture as wetting agent in a concentration of 0.02-0.2 g/l,
A step of electrodepositing a ductile and distortion-free nickel-plated film on the substrate at an electrolytic density of 11 to 108 A/Dm^2, and (b) a stable gold salt of 8 to 26 g/l, calculated as potassium gold cyanide. 10 to 350 g of one or more electrolytes selected from organic weak acids and their salts.
/l, pH 3 from a plating bath containing one or more base metal salts as gold film hardening agents selected from cobalt salts, indium salts, nickel salts, and zinc salts at a concentration of 0.5 to 5 g/l. ~5, bath temperature 10~49℃, current density 0
．． 1 to 11 A/Dm^2, a method comprising the step of subsequently electrodepositing a base metal hardened gold plating film on the nickel film produced in step (a) above. 2. The method according to claim 1, characterized in that nickel sulfate is used as the nickel salt in the electrodeposition step (a), and boric acid is used as the electrolyte in the electrodeposition step (a). 3. A method according to claim 1, characterized in that the electrodeposition steps (a) and (b) are carried out using an insoluble anode. 4. The method according to claim 1, characterized in that a cyanide gold salt is used as the gold salt in the electrodeposition step (b). 5. The method according to claim 4, characterized in that potassium gold cyanide is used as the gold cyanide salt. 6
The method according to claim 1, characterized in that acetic acid is used as the electrolyte in the electrodeposition step (b). 7. The method according to claim 1, characterized in that citric acid is used as the electrolyte in the electrodeposition step (b). 8. The method according to claim 1, characterized in that formic acid and citric acid are used together as the electrolyte in the electrodeposition step (b). 9. The method according to claim 1, characterized in that cobalt sulfate is used as the cobalt salt in the electrodeposition step (b). 10 Claim 1 characterized in that indium sulfate is used as the indium salt in the electrodeposition step (b)
The method described in section. 11. The method according to claim 1, characterized in that nickel sulfate is used as the nickel salt in the electrodeposition step (b). 12. The method according to claim 1, characterized in that zinc sulfate is used as the zinc salt in the electrodeposition step (b).