Method for preventing particle adhesion to tin or tin alloy plating films

Abstract

To provide a method for preventing particle adhesion to tin or tin alloy plating films that can selectively remove hexahydroxostannate(IV) ions from tin or tin alloy plating solutions, reduce the concentration of tetravalent tin ions in tin or tin alloy plating solutions, suppress the generation of insoluble stannic hydroxide, and thereby prevent particles that are tin compounds from adhering to and co-depositing on tin or tin alloy plating films.SOLUTION: By bringing tin or tin alloy plating solutions containing methanesulfonic acid, tin methanesulfonate, and a nonionic activator into contact with chelate resin, particles that are tin compounds are prevented from adhering to tin or tin alloy plating films deposited from tin or tin alloy plating solutions.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for preventing the adhesion of particles (impurities assumed to be insoluble substances of tin hydroxide) to a tin or tin alloy plating film used for bump formation.

Background Art

[0002] Conventionally, in the bonding between an IC package and an IC, solder balls and solder paste have been used as connection bumps. However, with the miniaturization of the electrode area, it has become difficult to cope with these methods.

[0003] Therefore, in recent years, the formation of bumps using a tin or tin alloy plating solution has been proposed. As such a plating solution, for example, a soluble salt containing at least a primary tin salt, a soluble salt of a metal nobler than tin, and a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, wherein the content of the tin complexing agent is 0.1 g / L or more and 5 g / L or less, and the concentration of divalent tin ions (Sn 2+ ) is 30 g / L or more has been disclosed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, when performing a plating process using a tin or tin alloy plating solution containing divalent tin ions as described in Patent Document 1 above, in the plating solution, divalent tin ions are oxidized to tetravalent tin ions (Sn 4+ ), and hexahydroxidostannate(IV) ions ([Sn(OH)6] 2―Stannic hydroxide (Sn(OH)4) precipitates via ). When stannic hydroxide, which is an insoluble substance, is present in the plating solution, stannic hydroxide adheres as particles to the surface of the plating film and eutectifies, causing voids during solder bonding and resulting in a problem of poor bonding.

[0006] Therefore, in view of the above problems, the present invention selectively removes hexahydroxostannate(IV) ions from a tin or tin alloy plating solution, reduces the concentration of tetravalent tin ions in the tin or tin alloy plating solution, and suppresses the generation of stannic hydroxide, which is an insoluble substance, so that particles, which are tin compounds, can adhere to and eutectify with a tin or tin alloy plating film. An object of the present invention is to provide a method for preventing the adhesion of particles to a tin or tin alloy plating film.

Means for Solving the Problems

[0007] In order to solve the above problems, a method for preventing the adhesion of particles to a tin or tin alloy plating film according to the present invention is characterized in that a tin or tin alloy plating solution containing methanesulfonic acid, stannous methanesulfonate, and a nonionic surfactant is brought into contact with a chelating resin, thereby preventing particles, which are tin compounds, from adhering to a tin or tin alloy plating film deposited from the tin or tin alloy plating solution.

Effects of the Invention

[0008] According to the present invention, by removing hexahydroxostannate(IV) ions from a tin or tin alloy plating solution, reducing the concentration of tetravalent tin ions in the tin or tin alloy plating solution, and suppressing the generation of stannic hydroxide (particles), which is an insoluble substance, it is possible to prevent particles, which are tin compounds, from adhering to a tin or tin alloy plating film and prevent poor bonding of the plating film.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] The plating solution to which the method for preventing particles from adhering to a tin or tin alloy plating film of the present invention is applied is an acidic tin or acidic tin alloy plating solution containing methanesulfonic acid, stannous methanesulfonate, and a nonionic surfactant used for forming bumps for connecting wafers and IC packages.

[0011] The concentration of methanesulfonic acid in the plating solution is not particularly limited. For example, when methanesulfonic acid (70% aqueous solution) is used, it can be 20 to 200 ml / L.

[0012] Also, the concentration of stannous methanesulfonate in the plating solution is not particularly limited. For example, it can be 10 to 100 g / L in terms of tin concentration.

[0013] The nonionic surfactant is not particularly limited, and examples thereof include polyoxyethylene phenyl ether. Also, the concentration of the nonionic surfactant in the plating solution is not particularly limited. For example, it can be 0.1 to 50 g / L.

[0014] <Method for Preventing Particles from Adhering to the Plating Film> As described above, when performing plating using a conventional tin or tin alloy plating solution containing divalent tin ions, in the plating solution, insoluble matter of stannic hydroxide is formed via hexahydroxytin(IV)ate ions, and the insoluble matter adheres as particles to the surface of the plating film and eutectifies, causing a problem of poor solder joint.

[0015] Therefore, the present inventors studied the above problems and found that by bringing a chelate resin having an N-methylglucamine group into contact with a tin or tin alloy plating solution containing tin ions, hexahydroxytin(IV)ate ions, which are anions, can be selectively removed from the tin or tin alloy plating solution, the concentration of tetravalent tin ions in the tin or tin alloy plating solution can be reduced, and the generation of stannic hydroxide (particles), which is insoluble matter, can be suppressed. Thus, it was found that particles, which are tin compounds, can be prevented from adhering to and eutectifying with a tin or tin alloy plating film deposited from the tin or tin alloy plating solution.

[0016] Hereinafter, a method for preventing particle adhesion to a tin or tin alloy plating film of the present invention will be described.

[0017] The chelate resin that can be used in the present invention is a chelate resin having an N-methylglucamine group that acts as a chelate group (functional group) for hexahydroxytin(IV)ate ions, represented by the following general formula (1).

[0018]

Chemical formula

[0019] (In the formula, R represents the base material of the chelate resin.) The base material of the chelate resin is not particularly limited. For example, polystyrene resin or the like can be used, but cellulose fiber is preferred in consideration of the separability from the tin plating solution, chemical resistance, and price.

[0020] Then, a chelating resin having an N-methylglucamine group is packed in a column, and a tin or tin alloy plating solution is passed through the column by a pump or the like, and the tin or tin alloy plating solution is brought into contact with the chelating resin packed in the column, thereby removing hexahydroxytin(IV)ate ions from the tin or tin alloy plating solution.

[0021] Hereinafter, with reference to the drawings, a method for preventing particle adhesion to a tin or tin alloy plating film of the present invention will be specifically described. FIG. 1 is a schematic diagram for explaining the method for preventing particle adhesion to a tin or tin alloy plating film of the present invention.

[0022] As shown in FIG. 1, in the method for preventing particle adhesion to a tin or tin alloy plating film of the present invention, first, a tin or tin alloy plating solution 2 (that is, a tin plating solution containing the above-mentioned hexahydroxytin(IV)ate ions or a tin alloy plating solution) accommodated in a plating bath 1 is circulated by a pump 3, and the plating solution 2 is brought into contact with a chelating resin 5 having an N-methylglucamine group accommodated in an ion removal device 4 disposed in the circulation path of the plating solution 2, thereby removing hexahydroxytin(IV)ate ions 6 from the plating solution 2.

[0023] Next, the plating solution 2 from which the hexahydroxytin(IV)ate ions 6 have been removed is circulated by the pump 3 and returned to the plating bath 1 again.

[0024] Therefore, since the chelating resin 5 removes the hexahydroxytin(IV)ate ions 6 from the plating solution 2 and suppresses an increase in the concentration of tetravalent tin ions in the plating solution 2, it is possible to prevent the formation of stannic hydroxide caused by tetravalent tin ions. As a result, in the plating bath 1, when performing electrolytic treatment with the plating solution 2, for example, when forming bumps made of a tin plating film or a tin alloy plating film in a via hole, it is possible to prevent the adhesion of insoluble substances (particles) of stannic hydroxide on the surface of the plating film, so that defects during solder bonding using the plating film can be avoided.

[0025] In addition, the ion removal device 4 is not particularly limited, and for example, a cartridge filter can be used. The aperture of this cartridge filter is not particularly limited, but is preferably 5 μm or less from the viewpoint of reliably preventing the outflow of the chelating resin accommodated in the filter (i.e., filter leakage) caused by the circulation of the plating solution.

[0026] In addition, the liquid passing speed of the plating solution when passing the plating solution 2 through the ion removal device 4 may be appropriately set according to the treatment performance of the chelating resin used. As the space velocity (SV), for example, 1 hr -1 ~10 hr -1 can be adjusted within the range.

[0027] In addition, the contact time between the tin or tin alloy plating solution and the chelating resin is not particularly limited, but continuous circulation is desirable from the viewpoint of reliably removing stannate (IV) ions. From the same viewpoint, the amount of the chelating resin used is preferably 0.1 to 10 g / L, more preferably 1 to 3 g / L, based on the plating solution.

[0028] In addition, the chelating resin may be directly added to the tin or tin alloy plating solution to disperse the chelating resin, and then removed by filtration. For example, a method of adding the chelating resin to the tin or tin alloy plating solution stored after the plating treatment, or a method of transferring the tin or tin alloy plating solution used for the plating treatment to another container and bringing it into contact with the chelating resin can be mentioned.

[0029] In addition, a configuration may be adopted in which the chelating resin is stored in a fibrous bag and the bag is immersed in the tin or tin alloy plating solution to bring the chelating resin into contact with the tin or tin alloy plating solution.

Examples

[0030] 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.

[0031] (Example 1) <Preparation of Plating Solution> 100 ml / L of methanesulfonic acid (70% aqueous solution), 60 g / L of stannous methanesulfonate (as Sn 2+ ), and 20 g / L of a nonionic surfactant (polyoxyethylene phenyl ether) were mixed and stirred to prepare an acidic tin plating solution (tin plating solution) of the example. The temperature of the plating solution was set to 25°C and the pH was set to 1 or less.

[0032] <Plating Treatment> As a substrate to be plated, a silicon wafer (size: φ300 mm, thickness: 0.8 mm) equipped with pads made of electrolytic copper (large diameter pattern: 80 μm, small diameter pattern 20 μm) was prepared.

[0033] Next, the above-prepared plating solution (25°C) was placed in a plating bath, and the above substrate (plating area: 3.3 cm × 5.0 cm) was immersed in the plating solution for a time set so that the thickness of the plating film became 15 μm based on a predetermined current density (0.5 A / dm 2 ). While circulating the tin plating solution using a pump, bumps made of a tin plating film were formed on the surface of the pads made of electrolytic copper using the tin plating solution.

[0034] In addition, 1 g of a chelating resin having an N-methylglucamine group represented by the following formula (2) was added to the housing of a cartridge filter (manufactured by Advantec, product name: Compact Cartridge Filter, aperture: 1 μm), which is an ion removal device, in the circulation path of the plating solution, and 1 L of the tin plating solution was circulated to bring the tin plating solution into contact with the chelating resin having an N-methylglucamine group, and electrolysis was performed until the energization amount (aging degree) of the tin plating solution reached 100 AH / L.

[0035]

Chemical Formula

[0036] <Measurement of the Concentration of Divalent Tin Ions (Sn 2+ ) in the Plating Bath> 100 mL of ion-exchanged water was placed in a 300 mL conical beaker, and 50 mL of 6N hydrochloric acid was added thereto. Then, 5 g of potassium sodium tartrate (tetrahydrate) was added and completely dissolved. Next, 2 g of sodium hydrogen carbonate was added to the solution in which potassium sodium tartrate was dissolved, and dissolved and foamed. Next, the tin plating bath (2 mL) used in the above plating treatment was taken with a whole pipette and added to this solution.

[0037] Then, 2 mL of a 5% starch solution was added as an indicator to the solution to which the tin plating bath was added, and the concentration of divalent tin ions (Sn 2+ ) in the plating bath was measured by titration with a 0.5N iodine solution.

[0038] The measurement of the concentration of divalent tin ions was carried out at each of the energization amounts of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The above results are shown in Figure 2.

[0039] <Measurement of the Concentration of Tetravalent Tin Ions (Sn 4+ ) in the Plating Bath> The tin plating bath (5 mL) used in the above plating treatment was added to a 100 mL volumetric flask, and a solution (Solution A) adjusted to 100 mL with ion-exchanged water was prepared. Solution A (1 mL) and 1.0N NHO3 aqueous solution (50 mL) were added to a 100 mL volumetric flask, and a solution (Solution B) adjusted to 100 mL with ion-exchanged water was prepared.

[0040] Next, quantitative analysis of Solution B was performed by the calibration curve method using an ICP emission spectroscopic analyzer (high-frequency inductively coupled plasma emission spectroscopic analyzer, manufactured by HORIBA, trade name: Jobin Yvon Ultima Expert).

[0041] Note that the calibration curve used was prepared using Sn standard solutions (manufactured by Merck, product name: standard solution for atomic absorption spectrophotometer) with Sn concentrations of 0 ppm (DI water), 50 ppm, 100 ppm, and 200 ppm.

[0042] Then, the concentration of tin (Sn concentration and Sn 2+ concentration) measured by the above calibration curve method, and the difference in the concentration of the above divalent tin ions (Sn 4+ ) were used to measure the concentration of tetravalent tin ions (Sn 2+ ) in the plating solution. 4+ ) was measured.

[0043] Note that the measurement of the concentration of tetravalent tin ions was performed at each amount of electricity passed of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The above results are shown in FIG. 3.

[0044] <Presence or absence of particles> The surface of the bump made of a tin plating film formed by the above plating process was observed with a scanning electron microscope (FE-SEM, manufactured by JEOL Ltd., product name: JSM-7800, acceleration voltage: 5 kv, magnification: 30,000 times), and the presence or absence of particles (stannic hydroxide, which is an insoluble substance) with a diameter of 50 nm or more on the surface of the bump was confirmed.

[0045] Note that the confirmation of the presence or absence of particles was performed at each amount of electricity passed of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The above results are shown in Table 1.

[0046] (Comparative Example 1) A cartridge filter containing a chelating resin having an N-methylglucamine group was not placed in the circulation path of the plating solution, and the plating treatment was performed in the same manner as in Example 1 above, except that the tin plating solution was not brought into contact with the chelating resin having an N-methylglucamine group. The concentration of tetravalent tin ions (Sn 4+ ) in the plating solution was measured, and the presence or absence of particles was evaluated. The above results are shown in FIG. 4 and Table 1.

[0047] In this comparative example, when an electric current is applied, divalent tin ions (Sn 2+ ) decrease, while tetravalent tin ions (Sn 4+ ) increase. When divalent tin ions (Sn 2+ ) decrease, it affects the formation of the plating film (the plating process becomes impossible). Therefore, the concentration of divalent tin ions (Sn 2+ ) in the plating solution was constantly controlled to be 60 g / L.

[0048] Then, based on the difference between the tin concentration (the concentration of Sn 2+ and the concentration of Sn 4+ ) measured by the calibration curve method described above and the concentration of divalent tin ions (Sn 2+ ) (60 g / L), the concentration of tetravalent tin ions (Sn 4+ ) in the plating solution was measured.

[0049] (Comparative Example 2) A plating process was carried out and the presence or absence of particles was evaluated in the same manner as in Example 1, except that a chelating resin having a primary amine group represented by the following formula (3) was used instead of the chelating resin having an N-methylglucamine group.

[0050] [Chemical formula]

[0051] Note that the presence or absence of particles was confirmed at an energization amount of 25 AH / L. The above results are shown in Table 2.

[0052] (Comparative Example 3) A plating process was carried out and the presence or absence of particles was evaluated in the same manner as in Example 1, except that a chelating resin having a polyamine group represented by the following formula (4) was used instead of the chelating resin having an N-methylglucamine group.

[0053] [Chemical formula]

[0054] Note that the presence or absence of particles was confirmed at a current application amount of 25 AH / L. The above results are shown in Table 2.

[0055]

Table 1

[0056]

Table 2

[0057] As shown in FIG. 3, in Example 1, by bringing the tin plating solution into contact with a chelating resin having an N-methylglucamine group, hexahydroxidostannate(IV) ions were removed from the plating solution, and it was found that the increase in the concentration of tetravalent tin ions was suppressed at a current application amount up to 100 AH / L. Further, since the increase in the concentration of tetravalent tin ions was suppressed, the formation of stannic hydroxide due to tetravalent tin ions could be prevented, and as shown in Table 1, no particles (stannic hydroxide which is an insoluble substance) were confirmed on the surface of the bumps at a current application amount up to 100 AH / L.

[0058] On the other hand, as shown in FIG. 4, in Comparative Example 1, since the tin plating solution was not brought into contact with a chelating resin having an N-methylglucamine group, hexahydroxidostannate(IV) ions were not removed from the plating solution, and it was found that the concentration of tetravalent tin ions increased at a current application amount up to 100 AH / L. Further, since the concentration of tetravalent tin ions increased, the formation of stannic hydroxide due to tetravalent tin ions could not be prevented, and as shown in Table 1, particles (stannic hydroxide which is an insoluble substance) were confirmed on the surface of the bumps at a current application amount up to 100 AH / L.

[0059] Also, as shown in Table 2, in Comparative Examples 2 and 3, since the tin plating solution was not brought into contact with the chelating resin having an N-methylglucamine group, similar to Comparative Example 1, hexahydroxidostannate(IV) ions were not removed from the plating solution, and it is considered that the concentration of tetravalent tin ions increased. Therefore, the formation of stannic hydroxide due to tetravalent tin ions could not be prevented, and particles (stannic hydroxide, which is an insoluble substance) were confirmed on the surface of the bumps at a current amount of 25 AH / L.

Industrial Applicability

[0060] The method for preventing particle adhesion to the tin or tin alloy plating film of the present invention is preferably used particularly in a tin or tin alloy plating solution that can be used for forming bumps.

Explanation of Symbols

[0061] 1 Plating tank 2 Tin or tin alloy plating solution 3 Pump 4 Ion removal device 5 Chelating resin having an aminopolyol group 6 Hexahydroxidostannate(IV) ion

Claims

1. By bringing a tin or tin alloy plating solution containing methanesulfonic acid, stannous methanesulfonate, and a nonionic surfactant into contact with a chelating resin, particles that are tin compounds are prevented from adhering to a tin or tin alloy plating film that precipitates from the tin or tin alloy plating solution. A method for preventing particle adhesion to a tin or tin alloy plating film, characterized by this.

2. The method for preventing particle adhesion to a tin or tin alloy plating film according to Claim 1, characterized in that the chelating resin has an N-methylglucamine group as a functional group.

3. The method for preventing particle adhesion to a tin or tin alloy plating film according to Claim 2, characterized in that the chelating resin is a resin based on cellulose fiber as a base material.

4. The method for preventing particle adhesion to a tin or tin alloy plating film according to Claim 2 or Claim 3, characterized in that the plating solution is circulated from a plating bath containing the tin or tin alloy plating solution, and the chelating resin is brought into contact with the tin or tin alloy plating solution, thereby preventing the particles from adhering to the tin or tin alloy plating film.

5. The method for preventing particle adhesion to a tin or tin alloy plating film according to Claim 4, characterized in that the chelating resin is housed in a cartridge filter disposed in the circulation path of the tin or tin alloy plating solution.

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