JPH06272098A - Electrolytic peeling solution and peeling method of coating film made of tin or tin alloy - Google Patents

Abstract

PURPOSE:To remove only a plated film without eroding the surface of a base material by dipping a iron product having a tin plated film into a sulfonic acid aq. solution to electrolyze with the iron product as an anode at a constant voltage. CONSTITUTION:The iron product having the plated film made of tin or tin alloy on the surface is dipped into the aq. solution of a sulfonic acid selected from a group of alkane sulfonic acid, alkanol sulfonic acid and allyl sulfonic acid or their salts. The coating film made of tin or tin alloy on the surface is peeled by electrolyzing with the iron product as the anode at the constant voltage. Sulfonic acid of 0.05-5mol/l is contained in the aq. solution. The concn. of metallic ion in the peeling solution at the time of peeling is kept in a low level and since oxidizing components are not present, a sludge like oxide is not formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution used for electrolytically stripping a tin or tin alloy film formed by plating or the like on the surface of iron products (including products made of iron alloys) and the above. The present invention relates to a method of electrolytically peeling a film.

[0002]

2. Description of the Related Art When a lead frame is plated in a non-standard manner in a manufacturing process of an integrated circuit, it is necessary to remove only the plated layer and re-plat without corroding the lead frame of the base material. I won't. When it becomes necessary to peel off the unnecessary plating film in this way, conventionally, a method of immersing the object to be treated in a peeling liquid having the ability to dissolve the plating film has been adopted. A typical example of the stripping solution used at this time is borofluoric acid, which has an excellent dissolving power for tin and lead, as the main agent, and an oxidizer such as m-nitrobenzenesulfonic acid and redeposition of thiourea. An inhibitor and an inhibitor for preventing erosion of the substrate are added.

Further, tin or a tin alloy deposits on the contact portion of the stainless steel jig for plating to form a film, which must be removed at an appropriate stage. In such a case, As a stripping solution, a stripping solution containing high-concentration nitric acid or a stripping solution containing nitric acid as a main agent and an organic carboxylic acid as a tin complexing agent has been used.

[0004]

However, tin ions in an acidic solution are easily oxidized in the presence of an oxidizing agent to form insoluble tin oxide. Since such tin oxide forming conditions are realized using any of the above-mentioned immersion stripping solutions, the stripping solution shows good stripping performance at the beginning of the bath, but tin ions accumulate in the solution. As a result, sludge of tin oxide is generated and a tin oxide layer is formed on the surface of the object to be treated, so that the peeling performance is rapidly reduced.

Further, a stripping solution containing a fluoride requires a great deal of labor and cost for waste liquid treatment, and a stripping solution containing a high concentration of nitric acid requires a measure to prevent diffusion of odor and mist generated during use. However, there was a problem that handling was dangerous. Therefore, the object of the present invention is to remove only the film of tin or tin alloy attached without eroding the surface of the base material made of iron or iron alloy, without generating sludge even after long-term use, Moreover, it is to provide a new peeling means which is excellent in safety in use.

[0006]

The present invention, which has succeeded in achieving the above objects, comprises one or more sulfonic acids selected from the group consisting of alkanesulfonic acids, alkanolsulfonic acids, and arylsulfonic acids or salts thereof. The present invention provides an electrolytic stripping solution, which is an aqueous solution containing 0.05 to 5 mol / liter in total.

The present invention also provides an iron product having a coating film of tin or a tin alloy (hereinafter sometimes referred to as a plated coating) selected from the group consisting of alkane sulfonic acid, alkanol sulfonic acid, and aryl sulfonic acid. And a method for removing a film made of tin or a tin alloy on the surface of an iron product, characterized by immersing the iron product in an aqueous solution of sulfonic acid or a salt thereof and electrolyzing the iron product at a constant voltage. is there.

[0008]

[Function] An object to be treated is immersed in the electrolytic stripping solution according to the present invention,
When electrolysis is performed with the object to be processed as an anode, the plating film on the surface of the object to be processed is rapidly ionized and dissolved, and the dissolved metal ions reach the cathode surface and are reduced there to be deposited as a metal. The metal ion concentration is maintained at a very low level. Dissolved metal ions also do not form sludge-like oxides because there is no oxidizing component in the stripping solution.

The amount of sulfonic acids or salts thereof contained in the electrolytic stripping solution (when two or more sulfonic acids are used in combination, the total amount thereof) is preferably 0.05 to 5 mol / liter, If it is less than 05 mol / liter, the dissolving power of tin or a tin alloy is low, and it may take a long time to complete the treatment or the peeling may be incomplete. On the other hand, even if the content of the sulfonic acids exceeds 5 mol / liter, the performance is not improved,
It only comes at a cost disadvantage.

Preferred specific examples of the sulfonic acids contained in the electrolytic stripping solution of the present invention include alkanesulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and butanesulfonic acid; hydroxyethanesulfonic acid, hydroxypropanesulfone. Acids, alkanol sulfonic acids such as hydroxybutane sulfonic acid; aryl sulfonic acids such as phenol sulfonic acid, cresol sulfonic acid, nitrobenzene sulfonic acid, and the like. Among the salts of sulfonic acids, particularly preferred are alkali metal salts and ammonium salts. It is salt.

The electrolytic stripping of the plating film using the electrolytic stripping solution consisting of an aqueous solution of sulfonic acids or salts thereof can be carried out by any power source, but particularly advantageous results are obtained when using a constant voltage power source. . That is, when electrolysis is carried out at a constant voltage, the current value decreases as the tin or tin alloy, which is easily ionized and eluted, is separated and reduced, and the current value drastically decreases when the base material is exposed. In addition, the exposed substrate surface is oxidized and passivated. Therefore, the electrolysis is automatically stopped and the substrate does not dissolve.

Even if the same electrolytic stripping solution is used, if constant current electrolysis is performed, a large current is forcibly applied even after the plating film is melted and the base material is exposed. Therefore, the stripping completion is detected by some means. Even if you turn off the power
It is difficult to avoid the substrate surface from being eroded by electrolysis.

When electrolytically stripping a plating film using the stripping solution of the present invention, the stripping rate of the plating film increases in proportion to the anode current density. Anode current density) is about 1 to 60 A
/ dm ² is suitable. If it is less than 1 A / dm ² , the peeling speed is too slow and it takes too much time for complete peeling, while if it exceeds 60 A / dm ² , it becomes difficult to avoid erosion of the substrate. Especially when not using a constant voltage power source, it is desirable to employ a lower current density in order to prevent erosion of the substrate surface due to excessive electrolysis. As the cathode constituent material, any material can be used as long as it has electrical conductivity and does not dissolve in the electrolytic stripping solution, but preferable examples include carbon, stainless steel and the like.

In the electrolytic stripping solution of the present invention containing no oxidizing agent, tin oxide sludge is hardly produced from tin ions during use, but citric acid, malic acid, succinic acid, gluconic acid, lactic acid, Carboxylic acids such as acetic acid, glycolic acid, propionic acid, tartaric acid, oxalic acid, and malonic acid,
And their alkali metal salts, alkaline earth metal salts,
By adding a substance such as an ammonium salt that can serve as a complexing agent for tin ions, it is possible to stabilize the tin ions and more reliably prevent the formation of tin oxide sludge. Also,
The addition of a small amount of nonionic surfactant can accelerate the precipitation of metal ions dissolved in the stripping solution at the cathode.

[0015]

【Example】

Example 1 A stainless steel SUS304 wire rod (3 mmφ × 80 mm) having a thickness of 10 μm solder-plated (tin: lead = 8: 2) was used as a test piece.
Dipping in 1 liter of stripper, using the test piece as the anode, the stainless steel SUS304 plate as the cathode, and selecting the voltage so that the anode current density at the start of electrolysis is 40 A / dm ^2, and performing constant voltage electrolysis. I did. The anode current density dropped to 0.1 A / dm ² in about 30 seconds, and the solder plating film was completely removed, so that the electrolysis was stopped. No damage was observed on the surface of the substrate after the treatment, and the amount of the substrate was not reduced at all.

Example 2 A 42 alloy lead frame plated in the same manner as in Example 1 was used as a test piece, and the test piece was immersed in a stripping solution containing 3 mol / l of methanesulfonic acid to make the test piece an anode and stainless steel. A constant voltage electrolysis treatment was performed by using steel SUS304 as a cathode and selecting a voltage so that the anode current density at the start of electrolysis was 50 A / dm ² . Anode current density is 0.1A in about 25 seconds
/ dm ² and the plating film was completely removed, so the electrolysis was stopped. No damage is seen on the substrate surface after treatment,
There was no weight loss of the substrate.

Example 3 In the same manner as in Example 1 except that the electrolytic stripping solution was changed to an aqueous solution of isopropanol sulfonic acid 3 mol / liter,
The plating film on the surface of the test piece was peeled off. The solder plating film was completely removed in about 30 seconds, no damage was found on the surface of the base material after peeling, and the weight of the base material was not reduced at all.

Example 4 Using a 4 mol / liter phenolsulfonic acid aqueous solution as a stripping solution, the plating film of a test piece similar to that in Example 2 was stripped by constant voltage electrolysis. Stainless steel SUS3 for the cathode
No. 04 was used, and the anode current density at the start of electrolysis was 30 A / dm ² . After about 40 seconds, the anode current density dropped to 0.1 A / dm ² , and the solder plating film was completely removed, so the electrolysis was stopped. No damage was observed on the surface of the substrate after the plating film was peeled off, and the amount of the substrate was not reduced at all.

Example 5 To examine the stability and reusability of the electrolytic stripping solution of the present invention, a solder strip (tin: lead = 8: 2) was used in 1 liter of the electrolytic stripping solution used in Example 1. Anode, stainless steel S
US304 is used as a cathode, and constant current electrolysis of direct current 1A is 50
I continued for hours. Due to this electrolysis, the solder plate is about 110
g was dissolved, but tin ions and lead ions dissolved in the stripping solution were successively deposited as a metal on the cathode surface, and the tin ion and lead ion concentrations in the solution were maintained at 100 mg / liter or less. Sludge did not occur at all. When the same plating film peeling test as in Examples 1 and 2 was performed using the peeling solution after the above continuous electrolysis as it was, the same good results as in Examples 1 and 2 were obtained.

Comparative Example The solder plating film of the test piece was peeled off in the same manner as in Example 1 except that constant current electrolysis was carried out at an anode current density of 30 A / dm ² . The solder plating film was completely removed in about 1 minute, and the electrolysis was stopped immediately, but the amount of the base material was reduced by about 1 mg, and the surface of the base material was also roughened.

[0021]

As described above, when the electrolytic stripping solution of the present invention containing sulfonic acids as a main component and containing no oxidizing agent is used, the plating film can be stripped very efficiently. In particular, when constant voltage electrolysis is performed, the current density is sharply reduced after the peeling of the plating film is completed and the electrolysis is substantially stopped.Therefore, there is no risk of damage to the substrate surface due to excessive electrolysis, and process control is also possible. It's easy. Further, since tin ions that have been electrolytically stripped and dissolved in the stripping solution are rapidly oxidized and are deposited on the cathode as a metal without being oxidized, the stripping solution of the present invention may generate sludge of tin oxide even after long-term use. Demonstrate stable processing capacity without. It is also a feature of the electrolytic stripping solution of the present invention that it is easy to handle and can perform safe work.

Claims (2)

[Claims] 1. An aqueous solution containing a total of 0.05 to 5 mol / liter of a sulfonic acid selected from the group consisting of alkanesulfonic acid, alkanolsulfonic acid, and arylsulfonic acid or a salt thereof. An electrolytic solution for electrolytically stripping a film made of tin or tin alloy on the surface of iron products. 2. An iron product having a coating film made of tin or a tin alloy on its surface is dipped in an aqueous solution of a sulfonic acid selected from the group consisting of alkanesulfonic acid, alkanolsulfonic acid, and arylsulfonic acid, or a salt thereof, A method of stripping a film made of tin or a tin alloy on the surface of an iron product, which comprises electrolyzing at a constant voltage using the iron product as an anode.