JPS6312955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stable alloy plating bath consisting of gold, tin and a third element.

Gold and tin alloys have been used for a long time and have a wide variety of uses. Examples include white gold, which utilizes the strong whitening power of tin, and brazing filler metal, which uses a eutectic alloy of 80% gold and 20% tin by weight.

Gold and tin alloys are generally produced by metallurgical methods, but this method has the drawback of being quite expensive due to the complicated process of forming it into the required shape.

On the other hand, several attempts have been made to deposit gold and tin alloys by plating, but it is difficult to obtain gloss, and stannous ions are easily oxidized to stannic ions, so the plating solution However, it had the disadvantage of being unstable.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
The object of the present invention is to provide a multi-element alloy plating bath containing gold and tin that improves the brightness of the precipitate and the stability of stannous ions, and also has improved mechanical properties.

The plating bath of the present invention is an aqueous bath suitable for electrodeposition of gold alloys, and contains 20 to 50% of gold added as potassium gold cyanide.
g/, at least one metal of iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) is 0.5 to 10 g/, and stannous is 20 to 50 g/,
at least one compound that complexes the metal;
600 to 750 g/brightener, 1 to 3 g/brightener, and at least one of the stannous antioxidants 10 to 750 g/b
It is characterized by the addition of 50 g/day and a pH of 4 to 6.

The structure of the plating bath of the present invention is as follows.

The amount of gold added as potassium gold cyanide is between 20 and 50 g/g. If the amount of gold is less than 20 g/g, the stability and gloss of the plating bath will be poor, and the rate of electrodeposition to obtain an excellent deposit will be slow. Also, 50g/
If the amount is more than that, the gold concentration in the plating bath will be too high and it will be uneconomical because of losses due to scooping out by plating.

The stannous ion is 20g/~50g/.
If the amount of stannous ions is less than 20 g, the amount consumed by tin precipitation and oxidation to stannic ions becomes large, resulting in instability, and if it is more than 50 g, it is difficult to form a complex.

Elements added to increase the mechanical strength of gold and tin alloys are group a, group a of the periodic table,
metals of group a, group a, group a, group a and b
Possible examples include those of the group B, group b, and group b. These elements can precipitate into an alloy of gold and tin and significantly improve mechanical strength, and when two or more of these elements are added, their effects are synergistic.

Examples of the aforementioned elements include titanium, niobium, molybdenum, rhenium, iron, cobalt, nickel, rhodium, palladium, copper, silver, silicon, and phosphorus, each of which is added in the form of a compound suitable for the aqueous solution. Ru.

Among these metals, iron, cobalt, nickel, and copper are suitable in terms of ease of addition, ease of complexation, price, and mechanical strength, and the amount of metal ions is 0.5g/~10g. / is. 10g/
If the amount is higher than that, complexation will be difficult and the resulting plating bath will be unstable. If it is less than 0.5g/, mechanical strength will not be achieved.

The amount of compounds complexing the above metals is 600-750
g/. If it is less than 600g/, the stability and buffering effect of the plating bath will be poor.

FIG. 1 shows the current density-gold composition of the deposited film when the amount of gold was 15 g/tin and the amount of citric acid was used as a parameter. As can be seen from this figure, the larger the amount of citric acid, the smaller the change in the precipitated alloy composition with respect to changes in current density, and the more stable plating can be obtained even on the high current density side.
The effect is remarkable when it exceeds 600g/. In addition,
This effect was similarly obtained with organic carboxylic acids other than citric acid.

Moreover, if the amount exceeds 750 g/g, it is not practical because the viscosity of the bath becomes high. The complex compound may be one that complexes the above-mentioned metal even slightly, but organic carboxylic acids such as malic acid, citric acid, gluconic acid, malonic acid, and maleic acid are more preferable. This is because organic carboxylic acids have a strong buffering effect, and gold potassium cyanide can be stably present even on the acidic side.

The alloy composition to be deposited depends on the concentration of each metal ion in the bath, the concentration of complex compounds, PH, bath temperature, and cathode current density. In a range where the bath is stable, components with high concentrations tend to precipitate, and the greater the total amount of metal ions, the faster the precipitation rate. The higher the complex compound concentration, the more stable the precipitated alloy composition becomes, and the more stable the bath itself becomes.
When the pH is high, the electrodeposition efficiency of tin is lower than that of gold, but the appearance of the deposit is improved. If the pH is on the alkaline side, stannous ions become unstable, so the pH of the bath
is 4 to 6, preferably 4.5±0.5. If the pH is less than 4, gold cyanide decomposes, and if the pH exceeds 6, stannous decomposes. A bath temperature of 15 to 90°C can be used; the higher the temperature, the better the plating appearance and the faster the precipitation rate, but the brightener and antioxidant will be consumed more quickly, so the appropriate bath temperature is determined.

The practical range of cathode current density is 0.1 to 10 A/dm ² . If the current density is high, the precipitated alloy composition will be tin-rich, and if the current density is low, the deposited alloy composition will be gold-rich.

The plating bath according to the present invention contains gelatin, toluidine, phenylacetamide, sodium arsenite,
At least one of the reaction products such as β-naphthol, peptone, acetaldehyde and o-toluidine
Excellent shine can be obtained by adding seeds. The amount added is 1 to 3 g/. 1g/
If it is less than 3 g/g, no gloss will be produced, and if it exceeds 3 g/g, it will not be very effective and will make the plating solution unstable. The effect of this brightener is particularly noticeable when the plating temperature is below 35°C. This is because tin cannot form a smooth precipitate if the bath temperature is below 35°C. Furthermore, these brighteners have little effect on the stability of the plating bath, the precipitation conditions, etc.

Generally, stannous ions are easily oxidized to stannous ions. Since stannic ions not only do not contribute to precipitation but also have an adverse effect on uniform electrodeposition, it is a practically effective means to add an antioxidant to the plating bath. As the antioxidant, hydrazine sulfate, hydroxylamine sulfate, L-ascobic acid, P-cresolsulfonic acid, resorcinol, formalin, hydroquinone, sodium sorbate, or glucose are effective.

The amount added is 10-50g/. If it is less than 10g/, the antioxidant effect is insufficient, and if it exceeds 50g/, it is not very effective and makes the plating solution unstable.
Furthermore, these antioxidants do not have any adverse effect on the stability of the plating bath, the precipitation conditions, etc.

The anode used in this plating bath is platinum, carbon,
Titanium platinum and titanium rhodium are preferable. Also,
It is desirable that the area ratio of the anode to the cathode is twice or more.

Further, by sufficiently stirring this plating bath, the appearance and uniformity of the precipitated alloy will be improved. As a stirring method, cathode locking, jet flow, or their effects are preferred; air stirring should not be used.

Next, embodiments of the present invention will be described.

Example 1 Gold (as potassium gold cyanide) 20g / tin (as stannous sulfate) 50g / malic acid 600g / nickel (as nickel sulfate) 10g / hydrazine sulfate 30g / gelatin 1g / peptone 0.5g / benzylidene acetate 0.5g / PH 4.5 Bath temperature 20℃ Cathode current density 6A/dm ² anode Titanium platinum plating time 5 minutes When plating was performed with stirring under the above plating bath composition and plating conditions, the result was 72% gold and 27.8% tin.
%, nickel 0.2%, and a thickness of 12 μm, a semi-gloss deposited film was obtained. The appearance of the film is silvery white. When gold wire was bonded to this sample and its strength was measured, all wires were broken.

Example 2 Gold (as gold potassium cyanide) 35g / Tin (as stannous chloride) 50g / Citric acid 600g / Cobalt (as cobalt chloride) 0.5g / Formalin 10c.c. / Toluidine 2g / PH 4.5 Bath temperature 20 °C Cathode current density 2A/dm ² anodes Carbon plating time 5 minutes When plating was performed with the above plating bath composition and plating conditions, the results were 85% gold, 14.9% tin, and 0.1% cobalt.
%, a blank deposited film with a thickness of 4 μm was obtained.
The appearance of the film is silvery white.

Example 3 Gold (as gold potassium cyanide) 50g / Tin (as stannous sulfate) 20g / Malonic acid 600g / Copper (as copper sulfate) 5g / Hydroxylamine sulfate 50g / β-naphthol 1g / PH 4.5 Bath temperature 45 °C Cathode current density 1A/dm ² anodes Titanium platinum plating time 5 minutes When plating was performed using the above plating bath and plating conditions, the results were as follows: 92% gold, 7.8% tin, 0.2% copper, thickness 2.5μ
A shiny deposited film of m was obtained. The appearance of the film is yellowish silvery white.

Example 4 Gold (as potassium gold cyanide) 20g/tin (as stannous chloride) 20g/malic acid 750g/iron (as ferrous chloride) 1g/P-cresolsulfonic acid 50g/o-toluidine 3g/PH 4.5 Bath temperature 45℃ Cathode current density 4A/dm ² Anode Titanium platinum plating time 5 minutes When plating was carried out using the above plating bath composition and plating conditions, 80% gold, 18.8% tin, 0.2% iron, and a thickness of 8 μm. A deposited film was obtained. This film is shiny, has a hardness of 185, and is silvery white.

Example 5 Gold (as gold potassium cyanide) 35g / Tin (as stannous sulfate) 50g / Citric acid 750g / Cobalt (as cobalt sulfate) 5g / Hydroxine 30g / Sodium arsenite 1g / PH 4.5 Bath temperature 45 °C Cathode current density 2A/dm ² anode Titanium white plating time 5 minutes When plating was performed with the above plating bath composition and plating conditions, the results were 88% gold, 11.6% tin, and 0.4% cobalt.
%, a glossy deposited film with a thickness of 4.5 μm was obtained.
The appearance of this film is silvery white.

Example 6 Gold (as potassium gold cyanide) 50g / Tin (as stannous chloride) 50g / Malonic acid 750g / Nickel (as nickel chloride) 5g / Resorcinol 50g / β-naphthol 2g / PH 4.5 Bath temperature 45°C Cathode Current density 4A/dm ² anodes Titanium white plating time 5 minutes When plating was performed with the above plating bath composition and plating conditions, the results were 83% gold, 16.5% tin, and nickel.
A glossy precipitated film containing 0.5% and a thickness of 9 μm was obtained.

The embodiments described above are part of the invention and are not intended to limit the invention.

Next, the effects obtained by the present invention will be listed below.

(1) Metsuki bath is stable.

The larger the amount of potassium gold cyanide and complexing agent, the more stabilized the plating bath will be, but the effect is significant when the amount of the former exceeds 20 g/and the latter exceeds 600 g/. Furthermore, the more gold and complexing agent there are, the less changes in the deposited composition due to current density will occur, and the effect will be synergistic when both are present in large amounts.

(2) Excellent gloss is obtained, and there is no change in gloss, uniformity, or adhesion even with thick plating.

(3) Hardness increases by adding a third element to the gold-tin alloy.

(4) High-speed plating is possible due to the high metal content.

(5) The composition of the precipitated alloy can be changed arbitrarily and over a wide range by changing the bath composition and current density.

(6) Excellent precipitates can be obtained even at room temperature.

This has the effect of further increasing the stability of the plating bath.

(7) If the bath concentration decreases, you can prepare a concentrated replenisher solution in advance and replenish it.
Can be used for a long time.

The plating bath according to the present invention exhibits remarkable effects as described above. The uses of this plating bath include the following.

(a) Decorative gold alloy plating with high hardness (b) Decorative white gold plating with high hardness By changing the composition of gold and tin, a wide range of color tones from gold to white can be obtained.
The hardness of the precipitates is high, so they can be used as decorative plating. Specifically, it can be used for decorative accessories such as wristwatches, eyeglass frames, and net dresses that require excellent appearance, hardness, and corrosion resistance.

(c) Low-grade, high-strength electrical contact material Can be used as an electrical contact material that takes advantage of its excellent wear resistance, corrosion resistance, and conductivity.

(d) Plating for bonding By adding an appropriate amount of tin to gold, the melting point is significantly lowered. Utilizing this, it can be used in lead frames where IC wire bonding is performed. Compared to traditional pure gold plating,
At the same time as the gold phase is lowered, the heating temperature during bonding can be lowered, which has the advantage of shortening the cycle time.

(e) Low melting point, high strength brazing filler metal Alloys of 80% gold and 20% tin, as well as alloys to which a third element is added, have a melting point of approximately 300°C and a strength ten times higher than that of solder. .

Specific uses for brazing metal plating include the following. When the lead wire of the plug tip of a crystal resonator such as a wristwatch is coated with the plating of the present invention, heated and melted to braze the crystal resonator to the lead wire, and when the crystal resonator is enclosed in a package, the plating of the present invention is applied to the lead wire at the tip of the plug. In some cases, the plating of the invention is applied, the material is heated and melted, and the package is sealed by brazing. In addition, when the present invention is applied to a chip or a finger part for brazing an IC chip and a conductive finger part of a tape carrier method, it is also possible to apply the present invention to a chip or a finger part for brazing a circuit board and an IC chip in a semiconductor mounting method called face-down. There are cases where a substrate is plated according to the present invention.

When this alloy plating mainly composed of gold and tin is used as a brazing material, the composition of the precipitates is approximately 10-85% gold, approximately 15-90% tin, and a total of one or more third elements. 0-60%, melting point is 280℃
This is possible as long as the temperature is ~550°C and the plating thickness is 2 μm or more.

As described above, the gold alloy plating bath according to the present invention can be used for various purposes such as decorative plating, functional plating, and brazing material plating, and is therefore an extremely useful invention in practice.

[Brief explanation of the drawing]

FIG. 1 shows a current density-gold composition diagram of a deposited film when citric acid is used as a parameter.

Claims (1)

[Claims] 1. In an aqueous bath suitable for electrodeposition of a gold alloy, the amount of gold added as potassium gold cyanide is 20 to 50%.
g/, at least one metal of iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) is 0.5 to 10 g/, and stannous is 20 to 50 g/,
at least one compound that complexes the metal;
600 to 750 g/brightener, 1 to 3 g/brightener, and at least one of the stannous antioxidants 10 to 750 g/b
A gold alloy plating bath characterized in that 50 g/g/g/g of gold is added and the pH is 4 to 6.