Method for regenerating gold plating solution

Abstract

To provide a method for regenerating a plating solution, capable of improving the bath stability of a gold plating solution including formaldehyde or its precursor as a reducer and removing metal ions from the gold plating solution to prevent plating performance from reducing.SOLUTION: A method for regenerating a plating solution comprises removing iron ions from a gold plating solution by contacting the gold plating solution including gold cyanide salt, a reducer being formaldehyde or its precursor and an iron cyanide compound without including a chelate compound having two or more iminodiacetic acid groups or amino methylene phosphonic acid groups with a chelating resin having an iminodiacetic acid group or an amino methylene phosphonic acid group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for regenerating a gold plating solution.

Background Art

[0002] Gold has the next highest electrical conductivity after silver and copper, is excellent in physical properties such as connectivity by thermocompression bonding, and is also excellent in chemical properties such as oxidation resistance and chemical resistance. Therefore, gold plating using gold is widely used as the final surface treatment method for circuits of printed circuit boards, mounting parts and terminal parts of IC packages, etc. in the electronic industry field.

[0003] As this gold plating process, for example, there is a method of immersing an object to be plated such as a printed wiring board in a gold plating bath and performing a reduction process to apply gold plating to the surface of the object to be plated. However, the gold plating solution used in the gold plating bath contains, in addition to gold ions, a reducing agent, a chelating compound, etc. When the gold plating process is repeated, there is a problem that impurities such as metal ions accumulate and the plating performance such as the plating rate decreases.

[0004] Therefore, as a countermeasure against this, a method of bringing a chelating resin into contact with a gold plating solution has been proposed. For example, a method for regenerating a gold plating solution for removing copper ions by bringing a chelating resin having an iminodiacetic acid type ligand into contact with a gold plating solution containing a gold salt, a reducing agent, a conductive salt, a complexing agent, and thallium has been proposed (see, for example, Patent Document 1). Further, a method for treating a gold plating solution for removing iron ions by bringing a gold plating solution containing iron ions, citric acid, and at least one selected from cobalt ions and nickel ions and a reducing agent into contact with a chelating resin having an aminomethylenephosphonic acid type ligand has been proposed (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Here, in the conventional gold plating solution, since a reducing agent is contained, metal adheres to objects other than the object to be plated (for example, containers such as plating tanks in which the gold plating solution is housed), resulting in a problem of reduced bath stability.

[0007] In particular, in recent years, from the viewpoints of bath stability and deposition rate, gold plating solutions using formaldehyde or its precursor as a reducing agent have been proposed. In gold plating solutions containing formaldehyde or its precursor, there is an urgent need for a method to suppress a decrease in bath stability and a decrease in plating performance caused by the accumulation of impurities such as the above-mentioned metal ions.

[0008] Therefore, in view of the above problems, the present invention aims to provide a regeneration treatment method for a plating solution that can improve the bath stability of a gold plating solution containing formaldehyde or its precursor as a reducing agent, remove metal ions from the gold plating solution, and prevent a decrease in plating performance. [Means for Solving the Problems]

[0009] In order to achieve the above object, a regeneration treatment method for a plating solution according to the present invention comprises contacting a gold plating solution containing a gold cyanide salt, a reducing agent which is formaldehyde or its precursor, and an iron cyanide compound and not containing a chelate compound having two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups with a chelate resin having an iminodiacetic acid group or an aminomethylenephosphonic acid group to remove iron ions from the gold plating solution. [Effects of the Invention]

[0010] According to the present invention, since the bath stability of the gold plating solution can be improved and iron ions can be removed from the gold plating solution, a decrease in plating performance can be prevented.

Embodiments for Carrying Out the Invention

[0011] Examples of the plating solution to which the regeneration treatment method of the present invention is applied include a reducing type gold plating solution used for forming circuits of printed wiring boards, mounting portions and terminal portions of IC packages, and the like.

[0012] <Gold plating solution> The reducing type gold plating solution is a gold plating solution containing a gold cyanide salt as a gold source, formaldehyde or its precursor substance as a reducing agent, and an iron cyanide compound.

[0013] (Gold cyanide salt) Examples of the gold cyanide salt include gold cyanide, potassium gold cyanide, sodium gold cyanide, ammonium gold cyanide, etc., and particularly potassium gold cyanide and sodium gold cyanide are preferable. These gold cyanide salts may be used alone or in combination of two or more.

[0014] In addition, the concentration of the gold cyanide salt in the plating solution is preferably 0.02 to 200 g / L in terms of gold, and more preferably 0.2 to 100 g / L. If it is less than the above lower limit, the deposition rate may decrease, and if it exceeds the above upper limit, the cost may increase.

[0015] (Reducing agent) The reducing agent is for reducing the gold cyanide salt as a gold source to deposit gold. In the gold plating solution of the present invention, formaldehyde or its precursor is used. Here, the "formaldehyde precursor" means a compound that decomposes in an aqueous plating solution and thereby forms formaldehyde.

[0016] Examples of such formaldehyde precursors include acetals, hemiacetals, aminals, and N,O-acetals. More specifically, examples include hexamethylenetetramine, dimethylol glycol, sodium hydroxymethyl glycinate, 1,3-bis(hydroxymethyl)5,5-dimethylimidazolidine-2,4-dione, 1,3,5,7-tetraazatricyclo-[3.3.1.13,7]decane, benzyl hemi formal, 2-bromo-2-nitropropane-1,3-diol, 5-bromo-5-nitro-1,3-dioxane, 1,3-bis(hydroxymethyl)-1-(1,3,4-tris(hydroxymethyl)-2,5-dioxoimidazolidin-4-yl)urea, 1,1'-methylenebis{3-[1-(hydroxymethyl)-2,5-dioxoimidazolidin-4-yl]urea}, 3,5,7-triaza-1-azoniatricyclo-[3.3.1.13,7]-decane-1-(3-chloro-2-propenyl)-chloride, tetramethylol glycoluril, 1,3-bis(hydroxymethyl)2-imidazolidinone, 1,3-bis(hydroxymethyl)urea, 2,2,2-trichloroethane-1,1-diol, and 5,5-dimethyl-1,3-dioxane.

[0017] These reducing agents may be used alone or in combination of two or more.

[0018] Also, the concentration of the reducing agent in the plating solution is preferably 0.01 to 100 g / L, more preferably 0.1 to 10 g / L. If it is less than the above lower limit, the deposition rate may decrease. If it exceeds the above upper limit, the bath stability may decrease and bath decomposition may occur.

[0019] (Iron cyanide compound) The iron cyanide compound is for improving the bath stability of the gold plating solution. In the gold plating solution of the present invention, pentacyanonitrosylferrate(III) acid or its salt, pentacyanoammineferrate(II) acid or its salt, hexacyanoferrate(II) acid or its salt, and hexacyanoferrate(III) acid or its salt are included. Specifically, potassium ferrocyanide (potassium hexacyanoferrate(II)) and potassium ferricyanide (potassium hexacyanoferrate(III)) are included. These iron cyanide compounds may be used alone or in combination of two or more.

[0020] In the present invention, by adding a non-toxic iron cyanide compound to a reducing type gold plating solution using formaldehyde or its precursor as a reducing agent, cyanohydrin is generated by the reaction of formaldehyde or its precursor with cyanide ions liberated from the iron cyanide compound, and until this cyanohydrin volatilizes, it contributes to maintaining the bath stability, so that it becomes possible to improve the bath stability of the reducing type gold plating solution.

[0021] Also, the concentration of the iron cyanide compound in the plating solution is preferably 0.1 to 1000 mg / L, more preferably 1 to 100 mg / L. If it is less than the above lower limit, the above-described bath stability effect may not be sufficiently obtained, and if it exceeds the above upper limit, the deposition rate may decrease.

[0022] (Amine compound) The gold plating solution of the present invention can further contain various known additives blended in the reducing type gold plating solution as needed. Examples of this additive include amine compounds.

[0023] This amine compound is for promoting the deposition of gold when performing plating treatment using the gold plating solution of the present invention. Examples thereof include amine compounds represented by the following general formula (1) or general formula (2).

[0024] [Chemical formula 1] R1-NH-C2H4-NH-R2(1)

[0025] [Chemical formula 2] R3-(CH2-NH-C2H4-NH-CH2) n -R4(2)

[0026] (Here, in General Formula (1) and General Formula (2), R1, R2, R3, and R4 represent -OH, -CH3, -CH2OH, -C2H4OH, -CH2N(CH3)2, -CH2NH(CH2OH), -CH2NH(C2H4OH), -C2H4NH(CH2OH), -C2H4NH(C2H4OH), -CH2N(CH2OH)2, -CH2N(C2H4OH)2, -C2H4N(CH2OH)2, or -C2H4N(C2H4OH)2, and they may be the same or different, and n is an integer from 1 to 4.)

[0027] Also, the concentration of the amine compound in the plating solution is preferably 0.01 to 500 g / L, more preferably 0.1 to 200 g / L. If it is less than the above lower limit, the deposition rate may decrease, and if it exceeds the above upper limit, the bath may become unstable.

[0028] (Chelating compound) The gold plating solution of the present invention does not contain a chelating compound having two or more iminodiacetic acid type coordination groups (iminodiacetic acid groups) or aminomethylenephosphonic acid type coordination groups (aminomethylenephosphonic acid groups).

[0029] More specifically, for example, it does not contain chelating compounds having two or more iminodiacetic acid groups such as ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-propanol tetraacetic acid, glycol ether diamine tetraacetic acid, etc., or chelating compounds having two or more aminomethylenephosphonic acid groups such as ethylenediaminetetramethylenephosphonic acid.

[0030] This is because when a chelate compound having two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups is contained, the complexation with iron ions is stronger than that of the chelate resin described later, making it difficult to remove iron ions from the reduced gold plating solution.

[0031] Therefore, the gold plating solution of the present invention is configured not to contain a chelate compound having two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups, but may be configured to contain other (i.e., chelate compounds not having two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups), for example, nitrilotriacetic acid or nitrilotris(methylenephosphonic acid).

[0032] (pH) The pH of the gold plating solution of the present invention is preferably 5 to 10. This is because when the pH is less than 5, the plating rate may be insufficient, and when the pH is greater than 10, the plating solution may become unstable.

[0033] The pH of the plating solution can be adjusted with pH adjusters such as sodium hydroxide, potassium hydroxide, aqueous ammonia, tetramethylammonium hydroxide, sulfuric acid, hydrochloric acid, boric acid, phosphoric acid, monocarboxylic acid, and dicarboxylic acid.

[0034] (Temperature of the plating solution) The temperature of the plating solution is not particularly limited, but is preferably 50 to 95°C. If the temperature of the plating solution is less than 50°C, the deposition rate becomes slow and the plating treatment time becomes long, which is not preferable. Also, if the temperature exceeds 95°C, the deposition rate becomes too fast, resulting in a rough film, and warping may occur in the object to be plated due to the thermal shrinkage of the film after plating, which is not preferable.

[0035] (Object to be plated) There is no particular limitation on the type of the object to be plated with the gold plating solution of the present invention, and conventional objects to be gold-plated (for example, circuits of printed boards, mounting parts and terminal parts of IC packages, etc.) can be used as the object to be plated.

[0036] <Method for regenerating plating solution> When performing plating using a reducing gold plating solution containing an iron cyanide compound, in the plating solution, iron ions are generated and accumulated from the iron cyanide compound, and due to the iron ions, there has been a problem that the plating rate (gold deposition rate) decreases.

[0037] Therefore, when the present inventors studied the above problems, by bringing a chelating resin having an iminodiacetic acid group or an aminomethylenephosphonic acid group into contact with the gold plating solution containing the above iron ions, it was found that iron ions can be removed from the gold plating solution and the gold plating solution can be regenerated.

[0038] Hereinafter, the method for regenerating the gold plating solution of the present invention will be described.

[0039] The chelating resin that can be used in the present invention is a chelating resin having an iminodiacetic acid group or a chelating resin having an aminomethylenephosphonic acid group.

[0040] Examples of the base material of the chelating resin include polystyrene resin, cellulose resin, epoxy resin, phenol resin, acrylic resin, resorcinol resin, vinyl chloride resin, polyvinyl alcohol resin, etc. Note that these shapes are not particularly limited, and examples include spherical, columnar, ring-shaped, saddle-shaped, honeycomb-shaped, etc.

[0041] Also, fibers such as natural fibers, regenerated fibers, and semi-synthetic fibers may be used as the base material of the chelating resin, and among these, it is preferable to use cellulose-based fibers such as cotton, hemp, and pulp.

[0042] It is also preferable that the resin has a structure in which an aminopolycarboxylic acid or an oxo acid of phosphorus is chemically bonded to the base material. Examples of the aminopolycarboxylic acid include ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, nitrilotriacetic acid, nitrilodiacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, dicarboxymethylglutamic acid, hydroxyethyliminodiacetic acid, propanediaminetetraacetic acid, diaminohydroxypropanetetraacetic acid, and the like. Examples of the oxo acid of phosphorus include those having a phosphonic acid group, a phosphoric acid group, or a phosphinic acid group, and those having a phosphonic acid group or a phosphoric acid group are particularly preferable.

[0043] In addition, the aminopolycarboxylic acid or the oxo acid of phosphorus may be directly bonded to the base material or may be bonded to the base material via a linking group. Examples of the linking group include -CH2-, -NH-, -CO-, -O-, -S-, and -SO2-. Note that those in which a plurality of linking groups are connected may also be used.

[0044] As the chelate resin of the present invention, for example, a macroporous resin having a polystyrene resin as a base material and having an iminodiacetic acid group or an aminomethylenephosphonic acid group as a functional group can be used.

[0045] Commercially available products can be used as the chelate resin. For example, as a chelate resin having a macroporous resin with a polystyrene resin as a base material and having an iminodiacetic acid group as a functional group, "Sumichelate MC700" manufactured by Sumitomo Chemical Tex Co., Ltd. can be used. As a chelate resin having a macroporous resin with a polystyrene resin as a base material and having an aminomethylenephosphonic acid group as a functional group, "Duolite C747UPS" manufactured by Sumitomo Chemical Tex Co., Ltd. can be used.

[0046] Then, a chelating resin having an iminodiacetic acid group or a chelating resin having an aminomethylenephosphonic acid group is packed in a column, and a gold plating solution is passed through the column by a pump or the like to bring the gold plating solution into contact with the chelating resin packed in the column, thereby removing iron ions from the gold plating solution. The flow rate at this time may be appropriately set according to the treatment performance of the chelating resin used. As the space velocity (SV), for example, 0.2 hr -1 ~50 hr -1 can be adjusted within the range of.

[0047] Alternatively, the chelating resin may be directly added to the gold plating solution, dispersed, and then removed by filtration. For example, there are a method of adding the chelating resin to the gold plating solution stored after the plating process and a method of transferring the gold plating solution used in the plating process to another container and bringing it into contact with the chelating resin.

[0048] Also, the chelating resin may be stored in a fibrous bag, and the bag may be immersed in the plating solution to bring the chelating resin into contact with the gold plating solution.

[0049] The contact time between the gold plating solution and the chelating resin is not particularly limited, but from the viewpoint of reliably removing iron ions, 3 to 2000 minutes is preferable, and 5 to 1000 minutes is more preferable. Also, from the same viewpoint, the usage amount of the chelating resin is preferably 0.1 to 100 g / L, and more preferably 1 to 50 g / L, per 1 L of the gold plating solution.

Examples

[0050] Hereinafter, the invention according to the present application will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples at all.

[0051] (Example 1) (Preparation of Gold Plating Solution) A gold plating bath of Example 1 was prepared by mixing potassium gold cyanide, a reducing agent, an amine compound, a chelating compound, and an iron cyanide compound so as to have the concentrations shown in Table 1 and stirring them. The pH of the plating bath was set to 7.0.

[0052] <Bath stability evaluation> Next, this gold plating solution was placed in a container, heated to 80°C, and then held at that temperature for 10 hours. After that, the state of the gold plating solution was visually observed to check for the presence or absence of gold precipitation on the container, which is a sign of bath decomposition. Then, those without gold precipitation were evaluated as ○ (excellent in stability), and those with visible gold precipitation were evaluated as × (poor in stability). The above results are shown in Table 1.

[0053] <Calculation of iron ion removal rate by chelating resin> Next, the gold plating solution held at 80°C for 10 hours described above was brought into contact with a chelating resin having an iminodiacetic acid group (manufactured by Sumitomo Chemical Tex Co., Ltd., trade name: Sumichelate MC700) and a chelating resin having an aminomethylenephosphonic acid group (manufactured by Sumitomo Chemical Tex Co., Ltd., trade name: Duolite C747UPS). More specifically, 10 g of granular chelating resin was added to 1 L of the gold plating solution, dispersed with a stirrer for 120 minutes, and the gold plating solution and the chelating resin were brought into contact. Then, the chelating resin was removed from the gold plating solution by filtration, and the concentration [mg / L] of iron ions in the gold plating solution was measured using an atomic absorption spectrophotometer (manufactured by Hitachi High-Technologies Corporation, trade name: Z-5300), and the iron ion removal rate in the gold plating solution was determined using the following formula (1). The above results are shown in Table 1.

[0054] [Equation 1] Iron ion removal rate [%] = 100 - [(concentration of iron ions [mg / L] in the gold plating solution after iron ion removal treatment by chelating resin) / (concentration of iron ions in the gold plating solution before iron ion removal treatment by chelating resin [mg / L])] × 100 (1)

[0055] <Measurement of deposition rate> First, pretreatment, electroless Ni plating, and electroless Pd plating were performed on a BGA substrate manufactured by Kamimura Kogyo Co., Ltd., and a sample with a Ni / Pd plating film formed thereon was prepared. Next, for this sample, using the prepared gold plating bath, the plating deposition rate (μm / 10 min) of the gold plating film formed when plating was performed at 80°C for 10 minutes was measured using a fluorescent X-ray film thickness gauge (manufactured by Fisher Instruments, product name: XDV-u). The above results are shown in Table 1.

[0056] (Examples 2 to 8, Comparative Examples 1 to 5) A gold plating bath was prepared in the same manner as in Example 1 described above, except that the composition of the gold plating solution was changed to the composition shown in Tables 1 to 2.

[0057] Then, in the same manner as in Example 1 described above, bath stability evaluation, calculation of the removal rate of iron ions by a chelating resin, and measurement of the deposition rate were performed. The above results are shown in Tables 1 to 2.

[0058] Note that since the gold plating solution in Comparative Example 4 does not contain an iron cyanide compound, the calculation of the removal rate of iron ions by a chelating resin was not performed.

[0059]

Table 1

[0060]

Table 2

[0061] As shown in Table 1, it can be seen that in Examples 1 to 8, by bringing the gold plating solution into contact with a chelating resin having an iminodiacetic acid group or an aminomethylenephosphonic acid group, iron ions can be efficiently removed from the gold plating solution.

[0062] In Examples 1 to 8, since formaldehyde or its precursor is contained as a reducing agent, by adding an iron cyanide compound to the gold plating solution, the cyanohydrin generated by the reaction between formaldehyde or its precursor and the cyanide ions liberated from the iron cyanide compound contributes to maintaining the bath stability, and it can be seen that the bath stability of the gold plating solution is excellent.

[0063] On the other hand, as shown in Table 2, in Comparative Example 1, hydrazine is used as the reducing agent of the gold plating solution, and since formaldehyde or its precursor is not used, cyanohydrin is not generated by the reaction between the cyanide ions liberated from the iron cyanide compound and formaldehyde or its precursor, and bath decomposition of the gold plating solution has occurred, and it can be seen that the bath stability of the gold plating solution is poor.

[0064] In Comparative Examples 1 and 5, since formaldehyde or its precursor is not used, the reaction between the cyanide ions liberated from the iron cyanide compound and formaldehyde or its precursor does not occur, and in the gold plating solution, the concentration of the cyanide ions liberated from the iron cyanide compound is kept constant, and it becomes difficult for new cyanide ions to be liberated from the iron cyanide compound, so it becomes difficult for iron ions that can be removed by the chelating resin to be generated, and as a result, it can be seen that the removal rate of iron ions is poor.

[0065] In Comparative Examples 2 to 3, since a chelating compound containing two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups (ethylenediaminetetraacetic acid, ethylenediaminetetramethylenephosphonic acid) is contained as the chelating compound, the complexation of the chelating compound with iron ions becomes stronger than that of the chelating resin, and it becomes difficult to remove iron ions from the gold plating solution, so it can be seen that the removal rate of iron ions is poor.

[0066] In Comparative Example 4, since the iron cyanide compound is not contained, cyanohydrin is not generated by the reaction of the cyanide ion released from the iron cyanide compound with formaldehyde or its precursor, and bath decomposition of the gold plating solution occurs, indicating poor bath stability of the gold plating solution.

[0067] In Comparative Example 5, since the bath does not contain a reducing agent, it can be seen that the deposition rate is decreased.

Industrial Applicability

[0068] The method for regenerating the gold plating solution of the present invention is particularly preferably used in the gold plating solution used for forming circuits of printed circuit boards, mounting portions and terminal portions of IC packages.

Claims

1. A method for regenerating a gold plating solution, which comprises contacting a gold plating solution containing a gold cyanide salt, a reducing agent which is formaldehyde or its precursor, and an iron cyanide compound and not containing a chelating compound having two or more iminodiacetic acid groups or aminomethylenephosphonic acid groups with a chelating resin having an iminodiacetic acid group or an aminomethylenephosphonic acid group to remove iron ions from the gold plating solution.

2. The method for regenerating a gold plating solution according to Claim 1, wherein the chelating resin is a resin having a polystyrene resin as a base material and having the iminodiacetic acid group or the aminomethylenephosphonic acid group as a functional group.

3. The method for regenerating a gold plating solution according to Claim 1 or Claim 2, wherein the gold plating solution contains an amine compound represented by the following general formula (1) or the following general formula (2). [Chemical formula 1] R １ -NH-C ２ H ４ -NH-R ２ (1) [Chemical formula 2] R ３ -(CH ２ -NH-C ２ H ４ -NH-CH ２ ) ｎ -R ４ (2) (Here, in General Formula (1) and General Formula (2), R １ , R ２ , R ３ and R ４ represent -OH, -CH ３ , -CH ２ OH, -C ２ H ４ OH, -CH ２ N(CH ３ ) ２ , -CH ２ NH(CH ２ OH), -CH ２ NH(C ２ H ４ OH), -C ２ H ４ NH(CH ２ OH), -C ２ H ４ NH(C ２ H ４ OH), -CH ２ N(CH ２ OH) ２ , -CH ２ N(C ２ H ４ OH) ２ , -C ２ H ４ N(CH ２ OH) ２ , or -C ２ H ４ N(C ２ H ４ OH) ２ ; they may be the same or different, and n is an integer from 1 to 4.)

4. The method for regenerating a gold plating solution according to any one of Claims 1 to 3, wherein the iron cyanide compound is at least one selected from the group consisting of pentacyanonitrosyliron(III) acid or its salt, pentacyanoammineiron(II) acid or its salt, hexacyanoferrate(II) acid or its salt, and hexacyanoferrate(III) acid or its salt.

5. The method for regenerating a gold plating solution according to Claim 4, wherein the iron cyanide compound is at least one of potassium ferrocyanide and potassium ferricyanide.

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