JP4445648B2 - Silver electrolytic stripping solution and silver electrolytic stripping method using the same - Google Patents

Description

【００５１】
表１より、本発明の実施例１〜９及び比較例１の建浴後の電解剥離液を用いて電解剥離した試料は、素地、必要部分銀めっき皮膜及び必要部分銀めっき皮膜と不要部分銀めっき皮膜との境界部において剥離前と比較して変化がなかった。
一方、比較例２及び３の試料にはそれぞれ、素地が褐色に変色し、必要部分銀めっき皮膜に光沢ムラが生じた。さらに、比較例３の試料では、必要部分銀めっき皮膜と不要部分銀めっき皮膜との境界部が黒灰色に変色した。
【００５２】
また、５０℃の恒温槽で２週間保持後の電解剥離液を用いて電解剥離した試験において、本発明の実施例１〜９の電解剥離液を用いて電解剥離した試料は、全ての評価項目で剥離前と比較して変化がなかった。建浴後の電解剥離液を用いた場合に全ての評価項目で剥離前と比較して変化がなかった比較例１の電解剥離液は、５０℃の恒温槽で２週間保持後に用いると必要部分銀めっき皮膜に黄色ムラが生じた。５０℃の恒温槽で２週間保持後に用いた比較例２及び３の電解剥離液では、建浴後の電解剥離液を用いた場合と同様の色調変化が発生した。
【００５３】
以上の試験結果から、本発明の銀電解剥離液は、５０℃の恒温槽で２週間保持した後であっても、被処理物の色調を変化させることなく良好な電解剥離を行うことができることが示された。
【００５４】
【発明の効果】
本発明の銀電解剥離液を用いれば、素地、必要部分の銀めっき皮膜及び必要部分の銀めっき皮膜と不要部分の銀めっき皮膜との境界部に変色や光沢ムラが生ずることなく１０〜１５秒程度の短時間で剥離することができる。また、剥離液中の主成分の濃度が５０ｇ／Ｌ以下であっても剥離することができるため剥離液が安価である。さらに、２週間以上の連続剥離作業が可能であり、剥離液の寿命が長いという利点を有する。さらに、本発明の銀電解剥離液は、弱い攪拌状態下で使用しても必要部分の銀めっき皮膜に変色やムラが生じないため短冊型の被処理物にも使用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silver electrolytic stripping solution and a silver electrolytic stripping method using the same.
[0002]
[Prior art]
When partial silver plating is applied to an electronic component such as an IC lead frame, a portion that does not require plating is masked with a rubber mask or the like, and only a necessary portion is plated. In this case, the plating solution enters the masked portion, and plating is often performed up to a portion that does not require plating. In such a case, it is necessary to peel off the unnecessary plating film after plating. As a method for peeling, the object to be treated is immersed in a stripping solution, electrolyzed using the object to be treated as an anode, and unnecessary plating film is removed.
[0003]
As a stripping solution, conventionally, a cyan stripping solution containing several tens of g / L of cyanide such as sodium cyanide and potassium cyanide is known. Since the cyan stripping solution is highly toxic, the work is dangerous and the wastewater treatment is complicated. Furthermore, when the substrate on which silver plating is applied is copper or a copper-based alloy, there is a problem that the cyan stripping solution cannot be used for the copper or copper-based alloy substrate because cyanide discolors the substrate.
[0004]
Therefore, an electrolytic stripping solution not containing cyan has been proposed. Examples of such an electrolytic stripper include those containing a 5-membered ring and 6-membered ring compound containing -NH- as the main component (Japanese Patent Laid-Open No. 2-175825), and those comprising 2-pyrrolidone-5-carboxylic acid. (Japanese Patent Laid-Open No. 6-41800), those composed of hydantoin compounds (Japanese Patent Laid-Open No. 7-243100), and those composed of allantoin (Japanese Patent Laid-Open No. 8-337900).
[0005]
However, these electrolytic stripping solutions are used by dissolving the main component using a strong alkaline component in order to obtain a practical stripping rate. For this reason, even if the unnecessary part of the silver plating film can be removed, the corrosion dissolution proceeds to the necessary part of the plating film that is not subject to peeling, and the gloss of the required part of the plating film changes or the plating film is partially There is a drawback in that unevenness occurs due to corrosion.
[0006]
In addition, these electrolytic stripping solutions may be used for strip-type workpieces that are subjected to electrolytic stripping treatment under weak stirring conditions because the plating film in the necessary portions will be discolored and uneven if the stripping solution is not stirred vigorously. However, there is a limitation that it can only be used for a reel-to-reel type workpiece to be electrolytically stripped under strong stirring conditions.
[0007]
Furthermore, these electrolytic stripping solutions need to have a high concentration of 80 to 100 g / L of the main component in the stripping solution in order to prevent unevenness in the plating film in the necessary portions. For this reason, there exists a fault that the cost of stripping solution becomes high.
[0008]
Other electrolytic stripping solutions not containing cyan include those composed of piperazine, piperidine, etc. (JP-A-8-325799), those composed of aliphatic aminocarboxylic acids (JP-A-10-88398), and pyridine derivatives. (Japanese Patent Laid-Open No. 11-106999).
[0009]
These electrolytic stripping solutions have a problem that the stripping rate is low, they cannot be processed in a normal stripping time of about 30 seconds, and the production efficiency is low. Therefore, when the anode current density is increased to increase the peeling rate, the problem arises that the boundary portion between the unnecessary portion plating film and the necessary portion plating film is corroded and turns black.
[0010]
Furthermore, an electrolytic stripping solution containing succinimide and / or phthalic imide and an alkali metal hydroxide as main components has been disclosed as an electrolytic stripping solution not containing cyan (Japanese Patent Laid-Open No. 2-104699). This electrolytic stripping solution has a short time of about 10 to 15 seconds because there is no problem that the boundary between the plating film of the unnecessary part and the plating film of the necessary part is hardly corroded even when the anode current density is increased, and there is no problem of discoloration to black. It can be peeled and removed in time. Furthermore, even if the main component in the stripping solution is as low as 20 to 50 g / L, there is an advantage that unevenness does not occur in the plating film of the necessary part.
[0011]
However, since this electrolytic stripping solution is an alkaline solution containing an alkali metal hydroxide, the main components succinimide and phthalimide are easily hydrolyzed and the stripping function is lost after 3 days or more. Further, during the peeling treatment, a decomposition product of succinimide or phthalic imide adheres to a plating film in a necessary portion, and yellow discoloration or unevenness occurs. Therefore, it must be replaced with a new stripping solution frequently, which is a big practical problem from the viewpoint of work efficiency.
[0012]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems of the prior art, and its purpose is to prevent discoloration and gloss unevenness in the plating film of the necessary part, and to plating the necessary part of the plating film and the unnecessary part. Discoloration does not occur at the boundary with the film, it can be peeled off in a short time of about 10 to 15 seconds, and it can be used even if the concentration of the main component in the peeling liquid is 50 g / L or less, An object of the present invention is to provide a silver electrolytic stripping solution that can be continuously used for 2 weeks or more and can be used for a strip-shaped workpiece, and a silver electrolytic stripping method using the silver electrolytic stripper.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
[1] (a) succinimide, (b) at least one selected from the group consisting of aliphatic aminocarboxylic acids, salts of aliphatic aminocarboxylic acids, aliphatic hydroxycarboxylic acids and salts of aliphatic hydroxycarboxylic acids, and (C) A silver electrolytic stripping solution containing a nitrogen-containing heterocyclic compound is proposed,
[2] The pH is 3 to 10.
[0014]
The present invention also provides:
[3] Silver electrolytic stripping in which a workpiece is immersed in the silver electrolytic stripping solution according to [1] or [2], and using the workpiece to be an anode, a silver plating film at a predetermined portion of the workpiece is removed. A method is proposed.
[0015]
Here, the predetermined portion is a portion that is not a target to be plated, and was plated because it was not plated by masking the workpiece. This refers to the part (part that does not require plating)
[0016]
Hereinafter, the present invention will be described in detail.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The silver electrolytic stripper of the present invention uses succinimide as the main component. Succinimide is a complexing agent that forms a soluble compound by complexing exfoliated metallic silver, and dissolves unnecessary parts of the silver plating film and also causes oxides that cause discoloration in the necessary part of the silver plating film. Prevent sticking. The content of succinimide in the silver electrolytic stripper is preferably 5 to 100 g / L, more preferably 20 to 70 g / L, and particularly preferably 30 to 55 g / L.
[0018]
If the succinimide content is less than 5 g / L, the peeled metal silver is unlikely to become a soluble compound, so that the peeling action is lowered and peeling in about 10 to 15 seconds becomes difficult. Moreover, the silver plating film of a required part becomes easy to discolor.
[0019]
When the content of succinimide is more than 100 g / L, it is possible to work with a high anode current density, but since the content of succinimide in the stripping solution is large, it adheres to the object to be treated after peeling. The amount of succinimide taken out of the stripper tank with the stripper increases, which is uneconomical.
[0020]
At least one selected from the group consisting of aliphatic aminocarboxylic acid, aliphatic aminocarboxylic acid salt, aliphatic hydroxycarboxylic acid and aliphatic hydroxycarboxylic acid salt is peeled off without reducing the complexing performance of succinimide Maintains high electrical conductivity of the solution and stably dissolves soluble silver compounds in the stripping solution to prevent the decomposition of silver compounds and succinimide from adhering to the necessary silver plating film Have
[0021]
Examples of the aliphatic aminocarboxylic acid used in the silver electrolytic stripper of the present invention include glycine, glycylglycine, aspartic acid, alanine, glycylalanine, valine, leucine, isoleucine, glutamic acid, lysine, cysteine, cystine, methionine and the like. Is mentioned. Examples of the salt of the aliphatic aminocarboxylic acid include the sodium salt and potassium salt of the aliphatic aminocarboxylic acid described above, and examples thereof include sodium glutamate and potassium aspartate.
[0022]
Examples of the aliphatic hydroxycarboxylic acid used in the silver electrolytic stripper of the present invention include citric acid, tartaric acid, malic acid, and gluconic acid. Examples of the salt of the aliphatic hydroxycarboxylic acid include the sodium salt and potassium salt of the above-mentioned aliphatic hydroxycarboxylic acid, such as sodium citrate and potassium tartrate.
[0023]
These aliphatic aminocarboxylic acids or salts thereof and aliphatic hydroxycarboxylic acids or salts thereof may be used alone or in combination of two or more.
[0024]
The content of at least one selected from the group consisting of aliphatic aminocarboxylic acids, salts of aliphatic aminocarboxylic acids, aliphatic hydroxycarboxylic acids and salts of aliphatic hydroxycarboxylic acids in the silver electrolytic stripper is preferably 1 to 60 g / L, more preferably 5 to 40 g / L, particularly preferably 10 to 30 g / L.
[0025]
If the content of at least one selected from the group consisting of aliphatic aminocarboxylic acid, aliphatic aminocarboxylic acid salt, aliphatic hydroxycarboxylic acid and aliphatic hydroxycarboxylic acid salt is less than 1 g / L, a silver electrolytic stripping solution The electrical conductivity of the film tends to decrease, and the peeling operation at a high anode current density becomes difficult. Further, when the plating base is copper or a copper alloy, the plating base is easily oxidized and discolored.
[0026]
When the content of at least one selected from the group consisting of aliphatic aminocarboxylic acid, aliphatic aminocarboxylic acid salt, aliphatic hydroxycarboxylic acid and aliphatic hydroxycarboxylic acid salt is more than 60 g / L, Since the content of the compound is large, the amount of these compounds taken out of the stripper tank with the stripper adhering to the object to be treated after stripping increases, which is uneconomical.
[0027]
Since the nitrogen-containing heterocyclic compound is adsorbed to the necessary part of the silver plating film and covers the surface of the film, the silver compound dissolved in the stripping solution is prevented from adhering to the necessary part of the silver plating film, and Suppresses corrosion of silver plating film by succinimide. Furthermore, in order to prevent the decomposition product of succinimide from adhering to the necessary silver plating film, discoloration and unevenness are prevented.
[0028]
Examples of the nitrogen-containing heterocyclic compound used in the silver electrolytic stripper of the present invention include 2-ethylpyridine, pyridine, nicotine, 4-picolylamine, 3-picolylamine, 2-aminopyridine, 2-amino-3-hydroxy. Pyridine, 3-chloropyridine, 3-cyanopyridine, 2,4-diaminopyridine, 2-hydroxypyridine, 2,6-lutidine, 2-methoxypyridine, nicotinic acid, nicotinaldehyde, 4-picoline, α-picolinic acid, 2,3-picolinediol, quinolinic acid, pyridine-3-sulfonic acid, indole, isatin, lepidin, 2-methyl-8-hydroxyquinoline, quinoline, isoquinoline, 8-quinol, pyrazole, allantoin, 2-ethylimidazole, imidazole Histidine, 2-amino-4-hydroxy -6-methylpyrimidine, 2-aminopyrimidine, 4-aminouracil, 4,6-dimethyl-2-mercaptopyrimidine, pyrimidine, 2-thiouracil, uracil, benzimidazole, aminoimidazole, 3-amino-1,2,4 -Triazole, 1,2,3-benzotriazole, cyanuric acid, 2-vinyl-4,6-diamino-s-triazine, adenine, guanine, 2-mercaptothiazoline, rhodanine, thiazole, 2-amino-6-ethoxybenzo Examples include thiazole and benzothiazole.
[0029]
These nitrogen-containing heterocyclic compounds may be used alone or in combination of two or more.
[0030]
The content of the nitrogen-containing heterocyclic compound in the silver electrolytic stripper is preferably 0.1 to 25 g / L, more preferably 0.5 to 10 g / L, and particularly preferably 1 to 5 g / L.
[0031]
If the content of the nitrogen-containing heterocyclic compound is less than 0.1 g / L, the necessary part of the silver plating film surface cannot be sufficiently covered. It becomes easy to adhere to. In addition, the necessary portion of the silver plating film is easily corroded by the succinimide, and the decomposition product of the succinimide is likely to adhere to the necessary portion of the silver plating film, so that discoloration and unevenness are likely to occur.
[0032]
When the content of the nitrogen-containing heterocyclic compound is more than 25 g / L, the nitrogen-containing heterocyclic compound itself is difficult to dissolve in the stripping solution. Furthermore, the amount of the nitrogen-containing heterocyclic compound taken out of the stripping solution tank with the stripping solution adhering to the object to be processed after stripping increases, which is uneconomical.
[0033]
In the silver electrolytic stripper of the present invention, it is preferable to adjust the pH to 3 to 10 in order to maintain good electrical conductivity and to stabilize the dissolution of succinimide.
[0034]
When pH is lower than 3, dissolution of succinimide becomes unstable and precipitation is likely, and the electrolytic peeling action of silver is lowered. When the pH is higher than 10, the succinimide is easily hydrolyzed. For this reason, it becomes difficult to keep the concentration of succinimide in the stripping solution constant, and the life of the stripping solution is shortened.
[0035]
The silver electrolytic stripper of the present invention can be adjusted in pH using an alkali such as potassium hydroxide, sodium hydroxide or aqueous ammonia, or an acid such as sulfuric acid, hydrochloric acid, nitric acid or acetic acid.
[0036]
Further, a pH buffering agent may be added to the silver electrolytic stripper of the present invention in order to stabilize the pH. Examples of the pH buffering agent include boric acid, potassium borate, sodium borate, potassium phosphate and the like, and one or more of these can be added.
[0037]
Furthermore, a surfactant that lowers the surface tension of the stripping solution can be added to the silver electrolytic stripping solution of the present invention in order to prevent uneven appearance of the silver plating film at a necessary portion. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and polymer surfactants, and one or more of these can be added.
[0038]
The silver electrolytic stripper of the present invention can be applied to both strip-type and reel-to-reel strippers.
[0039]
The liquid temperature when performing electrolytic stripping using the silver electrolytic stripper of the present invention is preferably 10 to 50 ° C, and more preferably 20 to 35 ° C, in order to obtain a good stripping temperature.
[0040]
When the liquid temperature is lower than 10 ° C., the electrical conductivity of the stripping solution is lowered, so that the stripping time becomes long. When the liquid temperature is higher than 50 ° C., the decomposition of succinimide proceeds rapidly, and the life of the stripping solution is shortened.
[0041]
The anode current density depends on the stirring conditions of the stripping solution is preferably 0.1~30A / dm ^2, more preferably 1 to 10 A / dm ^2. Here, the anode current density is a current density for a silver plating film of a necessary part.
[0042]
When the anode current density is lower than 0.1 A / dm ² , the peeling time becomes longer. When the anode current density is higher than 30 A / dm ² , excessive current flows through the plated portion of the necessary portion. The gloss of the glass is discolored or uneven.
[0043]
An insoluble material is usually used for the cathode. Among these insoluble materials, platinum, rhodium, titanium or tantalum coated with platinum or rhodium, or stainless steel is preferably used.
[0044]
【Example】
EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.
[0045]
A copper alloy (Olin 194) QFP (abbreviation for Quad Flat Package) 144-pin lead frame including a pad portion and an inner lead portion of a 10 × 10 mm region was required for plating, and the other regions were rubber masked. This lead frame was subjected to semi-glossy silver plating using a silver plating solution (S-930, manufactured by N.E. Chemcat) so as to have an average plating thickness of 5 μm to obtain a peeled sample. The plating thickness of the unnecessary portion plated with the plating solution entering the rubber masked portion of this sample was 0.2 to 0.5 μm.
[0046]
This sample was subjected to electrolytic stripping for 15 seconds under the following electrolytic stripping solution and stripping conditions, and each color tone was multiplied for the substrate, the necessary part silver plating film, and the boundary part between the necessary part silver plating film and the unnecessary part silver plating film. Observation was performed with a 30-fold stereomicroscope. The results are shown in Table 1.
[0047]
In addition, after the electrolysis peeling in each Example and a comparative example, the unnecessary partial silver plating film was peeled and removed about all the examples.
[0048]
Moreover, the electrolytic stripping solution of each Example and Comparative Example was put in a plastic container and sealed, and this was immersed in a thermostatic bath at 50 ° C., held for 2 weeks, taken out, and stripped as described in each Example and Comparative Example Electrolytic peeling was performed for 15 seconds under the conditions, and the color tone of the substrate, the necessary partial silver plating film, and the boundary between the necessary partial silver plating film and the unnecessary partial silver plating film was observed with a stereoscopic microscope at a magnification of 30 times. The results are shown in Table 1.
[0049]
Example 1
Succinimide 50g / L
Glycine 6g / L
Citric acid 45g / L
α-picolinic acid 5g / L
pH 5.5
Liquid temperature 25 ℃
Anode current density 4A / dm ²
Example 2
Succinimide 20g / L
Sodium glutamate 15g / L
Nicotinic acid 1g / L
pH 8.5
Liquid temperature 35 ℃
Anode current density 2A / dm ²
Example 3
Succinimide 85g / L
Aspartic acid 35g / L
2-aminopyridine 8g / L
pH 7.6
Liquid temperature 20 ℃
Anode current density 15A / dm ²
Example 4
Succinimide 45g / L
Isoleucine 38g / L
Quinolic acid 18g / L
pH 9.5
Liquid temperature 15 ℃
Anode current density 4.5 A / dm ²
Example 5
Succinimide 45g / L
Gluconic acid 15g / L
α-picolinic acid 5g / L
pH 6.0
Liquid temperature 25 ℃
Anode current density 3A / dm ²
Example 6
Succinimide 10g / L
Sodium tartrate 50g / L
Imidazole 20g / L
pH 8.5
Liquid temperature 20 ℃
Anode current density 1A / dm ²
Example 7
Succinimide 65g / L
Potassium aspartate 20g / L
Potassium gluconate 10g / L
α-picolinic acid 10g / L
pH 4.5
Liquid temperature 25 ℃
Anode current density 7A / dm ²
Example 8
Succinimide 55g / L
Cysteine 5g / L
Tartaric acid 15g / L
Nicotinic acid 10g / L
pH 5.0
Liquid temperature 25 ℃
Anode current density 4A / dm ²
Example 9
Succinimide 25g / L
Alanine 12g / L
Potassium citrate 25g / L
α-picolinic acid 5g / L
pH 9.0
Liquid temperature 35 ℃
Anode current density 6A / dm ²
Comparative Example 1
Succinimide 45g / L
Potassium hydroxide 7g / L
pH 9.3
Liquid temperature 35 ℃
Anode current density 2A / dm ²
Comparative Example 2
5,5-dimethylhydantoin 75g / L
Sodium hydroxide 30g / L
pH 10.0
Liquid temperature 40 ℃
Anode current density 5A / dm ²
Comparative Example 3
Glycine 50g / L
Sodium hydroxide 10g / L
pH 13.0
Liquid temperature 40 ℃
Anode current density 2A / dm ²
[0050]
[Table 1]

[0051]
From Table 1, the samples that were electrolytically stripped using the electrolytic stripping solution after building baths of Examples 1 to 9 and Comparative Example 1 of the present invention were the base, the necessary partial silver plating film, the necessary partial silver plating film, and the unnecessary partial silver plating. There was no change at the boundary with the film compared to before peeling.
On the other hand, in the samples of Comparative Examples 2 and 3, the base material turned brown, and uneven gloss occurred in the necessary partial silver plating film. Furthermore, in the sample of Comparative Example 3, the boundary between the necessary partial silver plating film and the unnecessary partial silver plating film was changed to black gray.
[0052]
Moreover, in the test which carried out the electrolytic stripping using the electrolytic stripping solution after hold | maintaining for 2 weeks in a 50 degreeC thermostat, the sample electrolytically stripped using the electrolytic stripping solution of Examples 1-9 of this invention is all evaluation items. There was no change compared with before peeling. When using the electrolytic stripper after the bathing bath, the electrolytic stripper of Comparative Example 1, which did not change compared to before the stripping in all the evaluation items, was necessary when used for 2 weeks in a constant temperature bath at 50 ° C. Yellow unevenness occurred in the plating film. In the electrolytic stripping solutions of Comparative Examples 2 and 3 used after being held in a thermostatic bath at 50 ° C. for 2 weeks, the same color change occurred when the electrolytic stripping solution after the building bath was used.
[0053]
From the above test results, the silver electrolytic stripper of the present invention can perform good electrolytic stripping without changing the color tone of the object to be processed even after being kept in a thermostat at 50 ° C. for 2 weeks. It has been shown.
[0054]
【The invention's effect】
If the silver electrolytic stripper of the present invention is used, the substrate, the necessary part of the silver plating film, and the boundary part between the necessary part of the silver plating film and the unnecessary part of the silver plating film do not cause discoloration or gloss unevenness for 10 to 15 seconds. It can be peeled off in a short time. Moreover, since it can peel even if the density | concentration of the main component in stripping solution is 50 g / L or less, stripping solution is cheap. Furthermore, continuous stripping work for two weeks or more is possible, and there is an advantage that the life of the stripping solution is long. Furthermore, since the silver electrolysis stripping solution of the present invention does not cause discoloration or unevenness in the silver plating film at the required portion even when used under weak stirring conditions, it can also be used for strip-shaped workpieces.

Claims (3)

(A) succinimide, (b) at least one selected from the group consisting of aliphatic aminocarboxylic acids, salts of aliphatic aminocarboxylic acids, aliphatic hydroxycarboxylic acids and salts of aliphatic hydroxycarboxylic acids, and (c) A silver electrolytic stripper containing a nitrogen-containing heterocyclic compound. The silver electrolysis stripping solution according to claim 1 whose pH is 3-10. A silver electrolytic stripping method of immersing a workpiece in the silver electrolytic stripping solution according to claim 1 or 2 and removing a silver plating film at a predetermined location of the workpiece using the workpiece as an anode.