TW202216600A - Potassium gold cyanide crystal and potassium gold cyanide solution - Google Patents

Abstract

This potassium gold cyanide crystal is characterized in that the silicon content is 10 wt ppm or less. This potassium gold cyanide solution is characterized in that, per 10 mL of the potassium gold cyanide solution, the number of pieces of foreign matter having a size of 1.0 [mu]m or greater is no more than 100. The present invention addresses the problem of providing potassium gold cyanide used for forming a gold plating film or a gold alloy plating film, the potassium gold cyanide being capable of reducing swelling of the plating film.

Description

Potassium gold cyanide crystal and potassium gold cyanide solution

The present invention relates to a gold potassium cyanide crystal, in particular to a gold potassium cyanide crystal and a gold potassium cyanide solution which can be used as a gold plating solution or a gold plating alloy solution.

Gold (Au) is used as an electronic component material because of its excellent electrical conductivity or thermal conductivity. Gold plating with higher purity, called soft gold plating, is used for bonding wires of ICs (integrated circuits) because of its low contact resistance and low hardness. On the other hand, gold plating with lower purity, called hard gold plating, is used for connectors and decoration of electronic parts because of its high hardness and luster. As the agent for supplying gold in the gold plating solution, potassium gold cyanide is used from the viewpoint of chemical stability and ease of dissolution.

As a method for producing potassium gold cyanide, there is known a method in which a gold anode is placed in an electrolytic cell of a potassium cyanide solution, a metal plate is placed as a cathode, and electrolysis is performed, whereby the potassium gold cyanide is crystallized and separated. (For example, Patent Documents 1 and 2). In addition, in Patent Document 3, a technique is known in which a gold cyanide salt is crystallized by a diaphragm electrolysis method, the crystals are separated, and then the separated solution is treated with activated carbon, whereby the solution is used as a diaphragm electrolysis method. The anolyte is reused. prior art literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 62-260084 Patent Document 2: Japanese Patent Application Laid-Open No. 6-192866 Patent Document 3: Japanese Patent Application Laid-Open No. 4-221086

[The problem to be solved by the invention]

Gold (Au) exhibits the following excellent properties: excellent electrical conductivity or thermal conductivity, no catalytic effect, resistance to chemical corrosion, and no oxide film formation. In addition, gold-plated or gold-plated alloys have excellent properties such as electrical conductivity, thermal conductivity, corrosion resistance, low contact resistance, bondability, solderability, high-frequency characteristics, and light reflectivity, so they are widely used in various electrical fields in the field of electronics. Contacts, terminals, connector pins, lead frames, ICs, various electrical circuit parts, etc.

However, when the gold plating film is thickly adhered, there is a problem that the gold plating film bulges. The bulging defect of this kind of coating may be the cause of the failure of various electronic parts. In view of such a problem, an object of the present invention is to provide a potassium gold cyanide crystal and a potassium gold cyanide solution for forming a gold-plated film or a gold-plated alloy film and capable of reducing the swelling of the plated film. [Technical means to solve the problem]

A first aspect of the present invention capable of solving the above-mentioned problems is a potassium gold cyanide crystal having a silicon content of 10 wtppm or less. Furthermore, the second aspect of the present invention is a potassium gold cyanide solution characterized in that the number of foreign substances of 1.0 μm or more contained in 10 mL of the potassium gold cyanide solution is 100 or less. [Effect of invention]

According to the present invention, the gold-plated film or the gold-plated alloy film produced by using the potassium gold cyanide solution has the excellent effect that the defects of the coating film bulge are less.

The potassium gold cyanide solution is used as a plating solution for forming a gold-plated film or a gold-plated alloy film. When a gold-plated film or a gold-plated alloy film is formed by using a potassium gold cyanide solution as a plating solution, there is a case where the defect of the bulging of the plating film occurs. In addition, the swelling of the coating film will cause a decrease in the yield of the product. As the main impurities contained in the potassium gold cyanide solution, transition metals such as Ag, Cu, and Fe are known. Even if these metal impurities are reduced, the defect of the coating film bulging cannot be improved.

Further, potassium gold cyanide was dissolved in ultrapure water, and impurities were measured by ICP analysis, but no particularly interesting impurities were confirmed. As a result of further investigation, it was found that oxides mainly composed of SiO ₂ were suspended in the potassium gold cyanide solution as foreign substances, and were carried into the plating solution to cause the swelling of the plating film. It is considered that the oxide mainly composed of SiO ₂ cannot be detected by ICP because it exists in the form of a solid rather than an ion.

Based on the above findings, the potassium gold cyanide crystal according to the embodiment of the present invention is characterized in that the silicon content is 10 wtppm or less. By setting the silicon content to be 10 wtppm or less, the number of the above-mentioned foreign substances can be reduced, and the swelling of the plating film caused by this can be suppressed. It is preferably 5 wtppm or less, more preferably 1 wtppm or less. The swelling of the coating film will reduce the product yield, so it is expected that the suppression of the coating swelling will contribute to the improvement of the product yield.

Potassium cyanide is usually produced by reacting hydrogen cyanide with potassium hydroxide, and is produced using quartz as a reaction vessel. Therefore, it is considered that SiO ₂ was mixed in due to the friction during stirring of the quartz. Further, it was found that SiO ₂ was also mixed in from the surrounding environment. SiO ₂ has never been paid attention to as an impurity before, and it is extremely important to be able to suppress the swelling of the coating film by reducing the amount of SiO ₂ mixed in during the production of potassium gold cyanide.

In the potassium gold cyanide solution of the present embodiment, it is preferable that the number of foreign objects of 1.0 μm or more contained in 10 mL of the potassium gold cyanide solution is 100 or less. The foreign matter is composed of oxides mainly composed of SiO ₂ , but those composed of other components may also cause the coating film to bulge, so the composition of the foreign matter is not particularly limited. By setting the number of foreign objects of 1.0 μm or more to 100 or less as described above, the swelling of the plating film can be effectively suppressed.

The potassium gold cyanide solution is prepared by dissolving 1 g of potassium gold cyanide crystals in 10 mL of pure water/ultra pure water. In the potassium gold cyanide of the present embodiment, it is more preferable that the number of foreign substances of 1.0 μm or more contained in the potassium gold cyanide solution is 50 or less. Furthermore, it is preferable that the number of foreign objects is 30 or less, and it is especially preferable that the number of foreign objects is 10 or less. By reducing the number of foreign substances as described above, the swelling of the coating film can be suppressed, and the decrease in the product yield can be prevented.

(Production method of potassium gold cyanide) Potassium gold cyanide can be produced, for example, as follows. A potassium cyanide solution was prepared by dissolving commercially available potassium cyanide crystals in pure water. Next, the potassium cyanide solution is filtered through a filter with a pore size of 0.1 μm to 1 μm. By this filtering step, oxides such as SiO ₂ mixed as impurities can be removed to some extent. Next, in the potassium cyanide solution after filtration, gold was electrolyzed and dissolved as an anode. The cathode is separated by an ion exchange membrane, and an insoluble electrode is used so that gold does not electrodeposit. When the gold concentration becomes a certain concentration, a solution of potassium gold cyanide is taken out from the anode chamber, and heated at 100°C or higher to concentrate (precipitate crystals).

During concentration, about 1% to 10% of the crystals precipitated at the initial stage are removed, and then washed with pure water or alcohol to obtain potassium gold cyanide crystals. Among the crystals precipitated at the initial stage, there are crystals grown with oxides mainly composed of SiO ₂ as nuclei, so these are removed. Then, the potassium gold cyanide crystals obtained above are dissolved in pure water/ultrapure water at a temperature of 50 to 90°C, filtered through an activated carbon filter, etc., and then cooled to 10°C or less to recrystallize. crystallization, whereby impurities can be further removed (recrystallization treatment).

The measurement apparatus, measurement conditions, etc. used for various evaluations are disclosed below. (Measurement of silicon content) Use acid to decompose potassium gold cyanide crystals in a Teflon beaker (dissolve SiO ₂ , etc.), add mixed standard solution to the decomposed gold cyanide solution by acid, and use matrix matching method. , the use of ICP (high frequency inductively coupled plasma) analyzer for the determination of silicon content.

(Determination of foreign bodies) Dissolve 1 g of potassium gold cyanide crystals in 10 mL of ultrapure water to prepare a potassium gold cyanide solution, and use a particle counter (KS-28 manufactured by Rion, light scattering method) to analyze the potassium gold cyanide solution for the solution. The number of foreign objects larger than 1.0 μm.

(Conditions for electrolytic gold plating) Gold ion supply source: Potassium gold cyanide 12 g/L Free cyanide ion source: Potassium cyanide 20 g/L Conductivity improvement: Potassium carbonate 20 L pH buffer: hydrogen phosphate borate 20/ L pH: 12 Bath temperature: 70°C Current density: 1 A/dm ² Film thickness: 5 μm

(Conditions for electroless gold plating) Gold ion supply source: potassium gold cyanide 3 g/L Ammonium citrate 90 g/L Hydrazine hydrochloride 19 g/L pH: 7.5 Bath temperature: 95℃

(evaluation of coating bulge) The coating film was observed with a SEM (Scanning Electron Microscope: JSM-7000F manufactured by JEOL), and among the unevenness generated on the coating film, the size of the convex portion with a width of 5 μm or more was defined as “swelling”. Example

Next, embodiments and the like of the present invention will be described. Furthermore, the following examples are only representative examples, and the present invention is not limited by these examples, and should be interpreted within the scope of the technical idea described in the specification.

(Example 1) Dissolve 400 g of commercially available potassium cyanide crystals in 1 L of pure aqueous solution. Next, after filtering the obtained potassium cyanide solution with a 0.1 μ filter, the filtrate was used as a solution for an anolyte, and electrolysis was performed using gold as an anode. When the gold concentration became 10 g/L, the liquid was taken out, and thereafter, the liquid was heated at 100° C. or higher and concentrated. At this time, after removing 10% of the crystals precipitated at the initial stage, the precipitated potassium gold cyanide was washed with alcohol to obtain potassium gold cyanide crystals. Furthermore, after that, a recrystallization treatment was performed to refine the potassium gold cyanide crystals.

The silicon content of the potassium gold cyanide crystal thus obtained was analyzed and found to be less than 1 wtppm. In addition, potassium gold cyanide crystals were dissolved in ultrapure water to prepare a potassium gold cyanide solution, and the solution was analyzed for the number of foreign matters of 1.0 μm or more using a particle counter. As a result, the number of foreign objects of 1.0 μm or more was 1 to 3 per 10 mL. Furthermore, electrolytic plating/electroless plating was performed using the potassium gold cyanide solution of Example 1 to form a gold-plated film, and the surface of the obtained gold-plated film was observed. As a result, the number of bulges was 0. The above results are shown in Table 1.

[Table 1] Manufacturing conditions Potassium gold cyanide solution Gold-plated film Si content (wtppm) The number of foreign objects over 1.0μm (per 10 mL) Types of Plating Number of bulges (converted to per cm ² ) Example 1 Filter the potassium cyanide solution with 0.1 μm filter paper + remove the initial 10% of potassium gold cyanide during crystallization + recrystallization <1 3 Electrolytic Plating 0 <1 1 Electroless Plating 0 Example 2 Removal of potassium gold cyanide 5% at the initial stage of crystallization + recrystallization 1 10 Electrolytic Plating 2 1 8 Electroless Plating 1 Example 3 Filter the potassium cyanide solution with 0.1 μm filter paper + remove the initial 1% of potassium gold cyanide during crystallization 3 28 Electrolytic Plating 4 5 26 Electroless Plating 3 Example 4 Remove the initial 10% of potassium gold cyanide during crystallization 10 100 Electrolytic Plating 10 9 96 Electroless Plating 9 Comparative Example 1 The potassium cyanide solution was filtered through 1 μm filter paper twenty one 498 Electrolytic Plating 26 18 458 Electroless Plating twenty four Comparative Example 2 Direct use of commercially available potassium cyanide 52 746 Electrolytic Plating 52 47 718 Electroless Plating 48

(Example 2) A potassium gold cyanide crystal was produced by the same method as in Example 1, except that in Example 2, the filtration was not performed with a 0.1 μ filter and 5% of the crystals precipitated at the initial stage were removed. The content of silicon in potassium gold cyanide was analyzed and found to be 1 wtppm. In addition, the number of foreign objects with a size of 1.0 μm or more contained in 10 mL of the potassium gold cyanide solution was analyzed, and the results showed that the number of foreign objects was 8 to 10. Furthermore, electrolytic plating/electroless plating was performed using the potassium gold cyanide solution of Example 2 to form a gold-plated film, and the surface of the obtained gold-plated film was observed, and as a result, the number of bulges was 2 or 1.

(Example 3) In Example 3, except that 1% of the crystals precipitated at the initial stage were removed and recrystallization was not carried out, gold potassium cyanide crystals were produced by the same method as in Example 1. The content of silicon in potassium gold cyanide was analyzed, and the result was 3-5 wtppm. In addition, the number of foreign objects of 1.0 μm or more contained in 10 mL of the potassium gold cyanide solution was analyzed, and the results showed that the number of foreign objects was 26 to 28. Furthermore, electrolytic plating/electroless plating was performed using the potassium gold cyanide solution of Example 3 to form a gold-plated film, and the surface of the obtained gold-plated film was observed, and the number of bulges was 4 or 3.

(Example 4) In Example 4, except that filtration with a 0.1 μ filter was not carried out, and recrystallization was not carried out, a potassium gold cyanide crystal was produced by the same method as in Example 1. The content of silicon in potassium gold cyanide was analyzed, and the result was 9-10 wtppm. In addition, the number of foreign objects of 1.0 μm or more contained in 10 mL of the potassium gold cyanide solution was analyzed, and the results showed that the number of foreign objects was 96 to 100. Furthermore, electrolytic plating/electroless plating was performed using the potassium gold cyanide solution of Example 4 to form a gold-plated film, and the surface of the obtained gold-plated film was observed, and the number of bulges was 10 or 9.

(Comparative Example 1) Dissolve 400 g of commercially available potassium cyanide crystals in 1 L of pure aqueous solution. The obtained solution was filtered with a 1 μ filter to prepare a potassium gold cyanide solution. In the obtained potassium gold cyanide solution, the number of foreign objects larger than 1.0 μm is 458 to 498 per 10 mL. In addition, the silicon content in the potassium gold cyanide crystal is 18 to 21 wtppm. Next, using the potassium gold cyanide solution of Comparative Example 1, electrolytic plating/electroless plating was performed to form a gold plating film. When the surface of the obtained gold-plated film was observed, the number of bulges was 26 or 24.

(Comparative Example 2) 400 g of commercially available potassium cyanide crystals were dissolved in 1 L of pure aqueous solution to prepare a potassium gold cyanide solution. In the potassium gold cyanide solution produced in this way, the number of foreign objects with a thickness of 1.0 μm or more was 718 to 746 per 10 mL. In addition, the silicon content in the potassium gold cyanide solution is 47-52 wtppm. Next, electrolytic plating/electroless plating was performed using the potassium gold cyanide solution of Comparative Example 2 to form a gold plating film. When the surface of the obtained gold-plated film was observed, the number of bulges was 52 or 48. [Industrial Availability]

The present invention has the excellent effect that the gold-plated film or the gold-plated alloy film produced by using the potassium gold cyanide solution has fewer defects of the coating film bulging. The plating solution containing the potassium gold cyanide of the present invention is useful as a plating solution for various electrical contacts, terminals, connector pins, lead frames, ICs, various electrical circuit parts, etc. in the field of electronics.

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Claims (2)

A crystal of gold potassium cyanide with a silicon content of less than 10 wtppm. A potassium gold cyanide solution, the number of foreign objects above 1.0 μm contained in 10 mL of the potassium gold cyanide solution is less than 100.