WO2005095673A1

WO2005095673A1 - Stripping solution and use thereof

Info

Publication number: WO2005095673A1
Application number: PCT/EP2005/001477
Authority: WO
Inventors: Gernot Strube; Manfred Jordan
Original assignee: Dr.-Ing. Max Schlötter Gmbh & Co. Kg
Priority date: 2004-03-25
Filing date: 2005-02-14
Publication date: 2005-10-13
Also published as: DE102004014680B3

Abstract

Disclosed is an acidic stripping solution comprising an acid selected among alkylsulfonic acid, alkanol sulfonic acid, benzenesulfonic acid, phenolsulfonic acid, sulfuric acid, tetrafluoroboric acid, a nitroaromatic compound, and an aminopolycarbonic acid compound. Said stripping solution can preferably be used for stripping a tin-bismuth layer from a substrate, e.g. a copper substrate, a copper alloy, an nickel-iron alloy, a nickel substrate, high-grade steel, or titanium.

Description

Demetallization solution and its use

The present invention relates to demetallization solutions, in particular the use of demetallization solutions for removing tin-bismuth layers.

The tin-lead coatings commonly used in the prior art have recently been increasingly replaced by tin alloy coatings in which the tin is alloyed with more electropositive metals such as copper, silver and / or bismuth. The replacement takes place due to the possible environmental pollution caused by lead. Lead-containing coatings can e.g. lead to contamination of the groundwater by releasing lead from coated products that are disposed of in landfills and converting it into soluble form.

In the said alloys of tin with more electropositive metals e.g. up to 58% by weight bismuth, up to 5% by weight

Copper or up to 5% by weight of silver are present. Ternary or quaternary alloys of tin with the metals mentioned are also used. The binary alloys in which the more electropositive metal is present in an alloy fraction of up to 5% by weight, based on the alloy composition, are particularly preferred.

Process for applying said alloys of tin with a more electropositive metal to substrates, e.g. by electrodeposition are known. The practical one

However, using these methods has the following problem. In processes for coating substrates, especially in automated processes, incorrect coatings cannot be completely avoided. In this case it is necessary to remove the defective coating and to re-coat the substrate. Furthermore, it is necessary, for example, that the Detach frame contacts from galvanized frames of deposited alloy layers in order to be able to use the frames again.

However, the removal of the coating must not lead to an attack on the coated substrate material. The coated substrates generally consist of metals or metal alloys. In the case of electrolytic coating of electrical or electronic components, the substrate is e.g. made of copper, copper alloys or nickel-iron alloys (e.g. Alloy 42). If necessary, the surface of these substrates is provided with a nickel layer, which should also not be affected during the removal of the coating. Stainless steel, e.g. Chrome-nickel steel or titanium is used. Attack of these metals or metal alloys by the demetallization solution should be avoided.

Demetallization solutions for tin layers can be one

Acid (e.g. sulfuric acid, tetrafluoroboric acid, alkyl sulfonic acid or hydrochloric acid) and a nitroaromatic compound. The nitroaromatic compound used is preferably m-nitrobenzenesulfonic acid or its alkali metal salts (US 4,439,338). These demetallization solutions are suitable for removing tin or lead-tin layers from copper or copper alloys and from nickel-iron alloys. However, they are not suitable for removing a tin-bismuth alloy layer. If a tin-bismuth layer is treated with the above-mentioned demetallizing solutions, the tin matrix of the layer dissolves, but the alloy component bismuth remains in metallic form as a black coating on the surface.

US 2698781 A relates to a demetallization solution consisting of water, a strong acid in a concentration of 1% to 50% and a nitroaromatic compound in one Concentration from 0.1% to 25%, which has a potential between -0.50 and -0.90 volts, measured between a nickel plate electrode and a saturated potassium chloride calomel electrode under the following conditions: temperature +80 ° C or -1 ° C; pH between 8 and 13; Sodium cyanide concentration approximately 2 molar, and at a concentration of the nitro compound which corresponds to the saturation value or at approximately 0.25 gram-mol / l solution, whichever concentration is lower.

US 3677949 A discloses acidic, aqueous solutions for selectively removing tin or a tin-lead solder alloy from a copper substrate, which comprise: (1) 0.1 to 180 g / l of a nitro-substituted aromatic compound with at least one -NO ₂ - Group on the aromatic

Ring and a water solubilizing substituent on the aromatic ring; (2) about 3 to 500 g / l of an inorganic acid which reacts with tin and lead to form water-soluble salts and does not form a water-insoluble film with tin and lead and is selected from the group consisting of fluorine-containing inorganic acid and sulfamic acid; and (3) about 0.1 to 220 g / l of a thiourea selected from thiourea, 1-4 C-alkylthiourea and phenylthiourea, the selected thiourea preventing redeposition of the stripped tin on the copper.

CH 625274 describes a composition for the selective removal of nickel, nickel / iron alloys or nickel / iron / cobalt alloys from the surface of a

Metal substrate disclosed, wherein the composition is an aqueous bath containing: a) at least one nitro-substituted organic compound, the at least one contains solubilizing group; b) at least one organic

Amine or polyamine or substituted amine or polyamine or an organic ammonium compound; and c) at least one inorganic phosphoric acid or an organic phosphoric acid or a salt thereof.

Patent application JP 2001335969 describes a solution for demetallizing tin-bismuth layers which contains methanesulfonic acid, -nitrobenzenesulfonic acid, sodium chloride and benzotriazole. However, bismuth can only be detached if sufficient sodium chloride and benzotriazole are present in the solution at the same time. If one of the two components is missing or if it is not available in sufficient quantities, the layers are not removed. The use of the solution mentioned is therefore associated with the disadvantage that complex process monitoring is necessary for the constant correction of the concentrations of sodium chloride and benzotriazole.

It is therefore the task of providing a demetallization solution with which tin-bismuth alloy coatings can be removed from metallic substrates without adversely affecting the metallic substrates, and which do not involve any complex process steps during the use with regard to the setting and monitoring of the concentrations of the individual components of the Solution requires.

This object is achieved by an acidic demetallization solution which comprises at least one acid selected from alkylsulfonic acid, alkanolsulfonic acid, benzenesulfonic acid, phenolsulfonic acid, sulfuric acid and tetrafluoroboric acid, a nitroaromatic compound and an aminopolycarboxylic acid compound. The aminopolycarboxylic acid compound mentioned preferably has at least 2 carboxylic acid residues, particularly preferably 3 to 6 carboxylic acid residues, further preferably 3 to 5 carboxylic acid residues.

The aminopolycarboxylic acid compound can e.g. have the following formula (I):

COOR ₂ II ⁽¹⁾ F ^ OOC - R ₄ - N - R ₆ - COOR ₃

wherein R 1, R ₂ ^and R ₃ are independently H, Na, K or NH ₄ ⁺ , where appropriate also one of the substituents R _] _,

R2 and R3 can be a Ci-Ce-alkyl group, and R ₄ , Rs and Rε independently of one another a Ci-Cε-alkylene group which can be substituted with a -C-C4-alkyl group, a hydroxyl group or a Ci-C4-hydroxyalkyl group, or represent a group of formula (II)

wherein R7 and Rs independently of one another are a Ci-Cs-alkylene group which can be substituted by a -C-C ₄ alkyl group, a hydroxyl group or a Ci-d-hydroxyalkyl group, Rs is a group

- (CH2) m-COORιo (with m = 1-6 and Rio = H, Na, K, NH ⁺ or Ci-Cs-alkyl) or a Ci-Cε-hydroxyalkyl group and n = 1-6. The Ci-Cs-alkyl group mentioned is, for example, a methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, or n-hexyl group. The Ci-Cε-alkylene group mentioned is, for example, a methylene, ethylene, propylene, butylene, pentylene or hexylene group. The C 1 -C 4 -alkyl group mentioned is, for example, a methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl or tert-butyl group. The C 1 -C 4 -hydroxyalkyl group mentioned is, for example, a hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxy-n-propyl, 1-hydroxy-n-butyl, 2-hydroxy-n-propyl, 2-hydroxy-n-butyl, 1,2-dihydroxy-n-propyl, 1,2-dihydroxy-n-butyl or 2,2,2-trihydroxy-tert-butyl group. The Ci-Cε-hydroxyalkyl group mentioned is, for example, one of the compounds mentioned as examples of the Ci-Ci-hydroxyalkyl group or a 1-hydroxyhexyl group.

Particularly suitable aminopolycarboxylic acid compounds are nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediamine triacetic acid,

Methylglycinediacetic acid (N, N-bis-carboxy-methyl-α-allanine), a salt of the compounds mentioned or a mixture of two or more of the acids and / or salts mentioned are present in the demetallation solution.

The trisodium salt of methylglycinediacetic acid (HOOC-CH (CH ₃ ) - (CH ₂ COOH) ₂ ) is particularly preferred.

The aminopolycarboxylic acid compound is preferably in a concentration of 0.01 mol / l of de-metallization solution up to the solubility limit of the aminopolycarboxylic acid compound in the de-metallization solution, particularly preferably in one

Concentration from 0.05 to 0.5 mol / 1 in the

Demetallization solution. A compound with one or more nitro groups and one or more hydrophilic groups is preferably contained in the demetallization solution as the nitroaromatic compound.

The hydrophilic group is e.g. a sulfonic acid group (- SOaH).

Nitrobenzenesulfonic acid or its salts are particularly preferred compounds. Suitable nitrobenzenesulfonic acids are both o-nitrobenzenesulfonic acid, m-nitrobenzenesulfonic acid and p-nitrobenzenesulfonic acid, with m-nitrobenzenesulfonic acid being preferred. In principle, all salts of nitrobenzenesulfonic acid can be used in the

De-metallization solution soluble salts are used, e.g. the ammonium salt, the sodium salt or the potassium salt. The ammonium salt of m-nitrobenzenesulfonic acid, the sodium salt of m-nitrobenzenesulfonic acid and the potassium salt of m-nitrobenzenesulfonic acid are preferably used. The sodium salt of m-nitrobenzenic acid is particularly preferably used. The demetallization solution can comprise a mixture of two or more of the compounds mentioned.

The nitroaromatic compound is preferably present in a concentration of 20 g / 1 demetallization solution up to the solubility limit of the nitroaromatic compound in the demetallization solution. The concentration is particularly preferably 50 to 150 g / l.

The alkyl sulfonic acid and the alkanol sulfonic acid preferably have 1 to 4 carbon atoms. Methanesulfonic acid is particularly preferred as the alkyl sulfonic acid. In practice, a 70% by weight solution of methanesulfonic acid is used in particular. Examples of suitable alkanolsulfonic acids are 2-hydroxyethanesulfonic acid, 2-hydroxypropanesulfonic acid and 3- Hydroxypropanesulfonic acid in question. 2-Hydroxyethanesulfonic acid is particularly preferred.

The concentration of the acid or acids selected from alkylsulfonic acid, alkanolsulfonic acid, benzenesulfonic acid, phenolsulfonic acid, sulfuric acid and tetrafluoroboric acid is preferably 35 to 280 g / 1 demetallization solution, particularly preferably 70 to 140 g / 1 demetallization solution.

The pH of the acidic demetallization solution is preferably in the range of <1.0.

The above-mentioned demetallization solution can be used to pull off a tin-bismuth layer from a substrate. Examples of suitable substrates are copper, copper alloys, nickel-iron alloys, nickel, stainless steel (e.g. chromium-nickel steel) and titanium. In particular, electrical or electronic components made of copper, copper alloys, nickel-iron alloys, which may each be provided with a nickel layer, and frame material made of stainless steel (eg chromium-nickel steel) and titanium can be obtained from the tin-bismuth de-metallization solution according to the invention -Layer will be freed.

The tin-bismuth layer which can be removed using the demetallization solution mentioned is e.g. an electrodeposited layer. The proportion of bismuth in the tin-bismuth layer can be 0.5 to 20% by weight, preferably 0.5 to 5% by weight. In addition to the tin and bismuth components mentioned, the tin-bismuth layer can furthermore contain copper and / or silver as alloy components. The copper and / or silver content in this case is preferably up to 5% by weight.

The removal of the tin-bismuth layer from a substrate can be done by dipping the substrate into the invention Demetallization solution or by applying the demetallization solution according to the invention to the substrate, for example by spraying.

Before the demetallized substrate is coated again, a pretreatment can be carried out in order to activate the substrate. The pretreatment can e.g. include etching the substrate using a solution comprising sulfuric acid and peroxodisulfate. Sodium, potassium or ammonium peroxodisulfate is preferably used as the peroxodisulfate.

The invention is illustrated by the following examples.

example 1

A demetallization solution was prepared which contained the following components:

100 g / 1 methanesulfonic acid (70% by weight)

100 g / 1 m-nitrobenzenesulfonic acid, sodium salt

15 g / 1 methylglycinediacetic acid, trisodium salt

In this solution was at a temperature of 40 ° C.

Copper sheet dipped with an electrodeposited tin-bismuth alloy with an alloy content of 3% by weight bismuth. The demetallization solution was gently stirred using a magnetic stirrer (stirring speed of the magnetic stirrer: 300 revolutions / minute). After 3 minutes, the tin-bismuth layer was removed with no residue of a black coating. Before renewed coating, treatment (eg dipping) with a sulfuric acid sodium peroxodisulfate solution (containing 100 g / 1 sodium peroxodisulfate and 50 g / 1 concentrated sulfuric acid) can be carried out at a temperature of 20 ° C. Comparative Example 1

A demetallization solution corresponding to Example 1 was prepared, but without the trisodium salt of methylglycinediacetic acid, and the demetallization experiment according to Example 1 was repeated. After a dipping time of 3 minutes, a velvety-black coating remained on the copper sheet, which consisted of undissolved bismuth. Example 2

A demetallization solution according to Example 1 was made up. An IC carrier strip was immersed in this solution at a temperature of 40 ° C. The IC carrier strip (IC = integrated circuit) consisted of a nickel-iron alloy (Alloy 42, 42 wt.% Nickel), which was electroplated with a 10 μm thick tin-bismuth alloy with a bismuth content of 3 wt.% had been. The tin-bismuth layer was completely removed after an exposure time of 3 minutes. The surface of the nickel-iron substrate was bare and no attack of the nickel-iron substrate material could be seen.

Example 3

The resistance of the substrate materials copper, nickel-iron alloy (Alloy 42, 42% by weight nickel) and chrome-nickel steel (material number 1.4571) in the

Demetallization solution according to Example 1 was tested. For this purpose, test sheets measuring 5 x 5 cm were weighed out and immersed in the demetallization solution at 40 ° C. for 10 minutes. The samples were then removed, rinsed with deionized water, dried and weighed out. The following weight differences were found:

Copper sheet: 0.0006 g

Nickel-iron alloy: 0.007 g chrome-nickel steel: 0.0001 g The values for the copper and the chrome-nickel steel are in the range of the measuring accuracy of the analytical balance used, so no attack can be determined. A removal of 0.007 g was determined for the nickel-iron alloy. However, this value is so low that there was no visible attack on the surface and the substrate material could be recoated without any problems.

Claims

claims

1. Acidic demetallization solution comprising - at least one acid selected from alkyl sulfonic acid, alkanol sulfonic acid, benzenesulfonic acid, phenolsulfonic acid, sulfuric acid and tetrafluoroboric acid, - a nitroaromatic compound and - an aminopolycarboxylic acid compound.

2. Acidic demetallization solution according to claim 1, characterized in that the aminopolycarboxylic acid compound contains at least two carboxylic acid residues.

3. Acidic demetallization solution according to claim 1 or 2, characterized in that the solution as aminopolycarboxylic acid compound comprises a compound of the following formula (I):

COOR ₂ IR ₅ (I) R-, OOC- R ₄ -N -R ₆ -COOR ₃ in which Ri, R2 and R3 are independently H, Na, K or NH4 ⁺ , optionally also one of the substituents Ri, R2 and R3 can be a Ci-Cs-alkyl group, and R ₄ , Rs and Rε independently of one another a Ci-Cε-alkylene group, which can be substituted with a -C-C4-alkyl group, a hydroxyl group or a -C-C4-hydroxyalkyl group, or one Represent group of formula (II)

in which R7 and Rβ independently of one another are a Ci-Cε-alkylene group which can be substituted by a -C-C4-alkyl group, a hydroxyl group or a -C-C4-hydroxyalkyl group, R9 is a group - (CH2) m-COORιo (with m = 1-6 and Rio = H, Na, K, H4 ⁺ or Ci-Ce-alkyl) or a Ci-Ce-hydroxyalkyl group and n = 1-6.

4. Acidic demetallization solution according to one or more of claims 1 to 3, characterized in that the solution as aminopolycarboxylic acid compound nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, methylglycinediacetic acid, a salt of the compounds mentioned or a mixture of two or more of the acids mentioned includes.

5. Acidic demetallization solution according to one or more of claims 1 to 4, characterized in that the solution as a nitroaromatic compound comprises a compound having one or more nitro groups and one or more hydrophilic groups.

6. Acidic demetallization solution according to one or more of claims 1 to 5, characterized in that the hydrophilic group is a sulfonic acid group.

7. Acidic demetallization solution according to one or more of claims 1 to 6, characterized in that the solution comprises nitrobenzenesulfonic acid or its salts as a nitroaromatic compound.

8. Acidic demetallization solution according to one or more of claims 1 to 7, characterized in that the number of carbon atoms in the alkyl sulfonic acid and / or the alkanol sulfonic acid is 1 to 4.

9. Use of an acidic demetallization solution according to one or more of claims 1 to 8 for peeling off a tin-bismuth layer from a substrate.

10. Use according to claim 9, characterized in that ^' the substrate is copper, a copper alloy, a nickel-iron alloy, nickel, stainless steel or titanium.

11. Use according to claim 9 or 10, characterized in that the substrate is an electrical or electronic component or an electroplating frame.

12. Use according to one or more of claims 9 to 11, characterized in that the tin-bismuth layer is an electrodeposited layer.