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

Abstract

The object of the present invention is to provide a method for preventing adhesion of particles to a tin or tin alloy plating film, which can prevent particles that are tin compounds from adhering to the tin or tin alloy plating film and forming a co-deposition by selectively removing hexahydroxide stannate (IV) ions from a tin or tin alloy plating solution, thereby reducing the concentration of tetravalent tin ions in the tin or tin alloy plating solution and suppressing the generation of insoluble stannic hydroxide. [Solution] By contacting a tin or tin alloy plating solution containing methanesulfonic acid, tin methanesulfonate, and a nonionic surfactant with a chelating resin, particles which are tin compounds are prevented from adhering to the tin or tin alloy plating film deposited from the tin or tin alloy plating solution.

Description

[Technical field]

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

[0002] Conventionally, solder balls or solder paste have been used as bumps for connection when joining an IC package to an IC, but as electrode areas become smaller, these methods are becoming less effective.

[0003] In recent years, therefore, the formation of bumps using a tin or tin alloy plating solution has been proposed. Such a plating solution contains, for example, a soluble salt containing at least a stannous salt, a soluble salt of a metal nobler than tin, and a tin complexing agent made of a sugar alcohol having 4 to 6 carbon atoms, the content of the tin complexing agent being 0.1 g / L or more and 5 g / L or less, and a divalent tin ion (Sn 2+ A tin alloy plating solution having a tin content of 30 g / L or more has been disclosed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-108290 A Summary of the Invention [Problem to be solved by the invention]

[0005] When a plating process is performed using a tin or tin alloy plating solution containing divalent tin ions as described in the above Patent Document 1, the divalent tin ions are oxidized to tetravalent tin ions (Sn 4+ ) and the hexahydroxide stannate(IV) ion ([Sn(OH)6] 2―) and precipitates into stannic hydroxide (Sn(OH)4). If stannic hydroxide, an insoluble substance, is present in the plating solution, the stannic hydroxide adheres to the surface of the plating film as particles and co-deposits, causing voids during soldering and resulting in poor joints.

[0006] In view of the above-mentioned problems, the present invention has an object to provide a method for preventing adhesion of particles to a tin or tin alloy plating film, which can prevent particles that are tin compounds from adhering to the tin or tin alloy plating film and forming a co-deposition by selectively removing hexahydroxide stannate (IV) ions from a tin or tin alloy plating solution, thereby reducing the concentration of tetravalent tin ions in the tin or tin alloy plating solution and suppressing the generation of stannic hydroxide, which is an insoluble matter. [Means for solving the problem]

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

[0008] According to the present invention, by removing hexahydroxide stannate (IV) ions from a tin or tin alloy plating solution, the concentration of tetravalent tin ions in the tin or tin alloy plating solution is reduced, and the generation of insoluble stannic hydroxide (particles) is suppressed, thereby preventing the adhesion of tin compound particles to a tin or tin alloy plating film and preventing poor bonding of the plating film. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram for illustrating a method for preventing particle adhesion to a tin or tin alloy plating film according to the present invention. [Diagram 2] FIG. 2 is a graph showing the measurement results of the concentration of divalent tin ions (Sn2+) in the plating solution of Example 1. [Diagram 3] FIG. 2 is a graph showing the measurement results of the concentration of tetravalent tin ions (Sn4+) in the plating solution of Example 1. [Figure 4] FIG. 2 is a graph showing the measurement results of the concentration of tetravalent tin ions (Sn4+) in the plating solution of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The plating solution to which the method of the present invention for preventing particle adhesion to a tin or tin alloy plating film is applied is an acidic tin or acidic tin alloy plating solution containing methanesulfonic acid, tin methanesulfonate and a nonionic activator, which is used to form bumps for connecting wafers or IC packages.

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

[0012] Furthermore, the concentration of tin methanesulfonate in the plating solution is not particularly limited, and can be, for example, 10 to 100 g / L in terms of tin concentration.

[0013] The nonionic active agent is not particularly limited, but examples thereof include polyoxyethylene phenyl ether, etc. The concentration of the nonionic active agent in the plating solution is not particularly limited, and can be, for example, 0.1 to 50 g / L.

[0014] <How to prevent particles from adhering to plating film> As described above, when plating is performed using a conventional tin or tin alloy plating solution containing divalent tin ions, there has been a problem in that insoluble stannic hydroxide is formed in the plating solution via hexahydroxide stannate (IV) ions, and the insoluble matter adheres to the surface of the plating film as particles and co-deposits, causing solder joint failure.

[0015] Therefore, the present inventors have investigated the above problems and have found that by contacting a chelating resin having an N-methylglucamine group with a tin or tin alloy plating solution containing tin ions, it is possible to selectively remove the anion hexahydroxide stannate (IV) ion from the tin or tin alloy plating solution, thereby reducing the concentration of tetravalent tin ions in the tin or tin alloy plating solution and suppressing the generation of insoluble stannic hydroxide (particles), thereby preventing the particles, which are tin compounds, from adhering to and co-depositing with the tin or tin alloy plating film precipitated from the tin or tin alloy plating solution.

[0016] The method of the present invention for preventing adhesion of particles to a tin or tin alloy plating film will be described below.

[0017] The chelating resin that can be used in the present invention is a chelating resin having an N-methylglucamine group that acts as a chelating group (functional group) for hexahydroxide stannate (IV) ions, as shown in the following general formula (1).

[0018] [ka]

[0019] (In the formula, R represents the base material of the chelating resin.) The base material for the chelating resin is not particularly limited, and may be, for example, polystyrene resin, but cellulose fiber is preferred in consideration of separability from the tin plating solution, chemical resistance, cost, and the like.

[0020] A chelating resin having an N-methylglucamine group is packed into a column, and the 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 hexahydroxide stannate (IV) ions from the tin or tin alloy plating solution.

[0021] The method for preventing particle adhesion to a tin or tin alloy plating film of the present invention will be specifically described below with reference to the drawings. 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, the method of the present invention for preventing particle adhesion to a tin or tin alloy plating film first circulates a tin or tin alloy plating solution 2 (i.e., a tin plating solution or tin alloy plating solution containing the above-mentioned hexahydroxide stannate (IV) ions) contained in a plating tank 1 using a pump 3, and removes hexahydroxide stannate (IV) ions 6 from the plating solution 2 by contacting the plating solution 2 with a chelating resin 5 having an N-methylglucamine group contained in an ion removing device 4 arranged in the circulation path of the plating solution 2.

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

[0024] Therefore, the chelate resin 5 removes the hexahydroxide stannate (IV) ions 6 from the plating solution 2, suppressing an increase in the concentration of tetravalent tin ions in the plating solution 2, thereby making it possible to prevent the generation of stannic hydroxide caused by tetravalent tin ions. As a result, by performing an electrolytic treatment using the plating solution 2 in the plating tank 1, when forming a bump made of a tin plating film or a tin alloy plating film in a via hole, for example, it is possible to prevent the adhesion of insoluble matter (particles) of stannic hydroxide to the surface of the plating film, thereby avoiding defects during soldering using the plating film.

[0025] The ion removing device 4 is not particularly limited, but may be, for example, a cartridge filter. The mesh size of the 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 contained in the filter (i.e., removal from the filter) caused by the circulation of the plating solution.

[0026] The flow rate of the plating solution 2 through the ion removing device 4 may be set appropriately depending on the treatment performance of the chelating resin used. For example, the space velocity (SV) may be set to 1 hr -1 ~10hr -1 can be adjusted within the range.

[0027] The contact time between the tin or tin alloy plating solution and the chelating resin is not particularly limited, but from the viewpoint of completely removing the hexahydroxide stannate (IV) ions, it is preferable to circulate the solution continuously. 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, of the plating solution.

[0028] Alternatively, the chelating resin may be added directly to the tin or tin alloy plating solution, dispersed, and then removed by filtration. For example, the chelating resin may be added to the tin or tin alloy plating solution stored after plating, or the tin or tin alloy plating solution used in plating may be transferred to another container and brought into contact with the chelating resin.

[0029] Alternatively, the chelating resin may be stored in a fibrous bag, and the bag may be 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] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0031] Example 1 <Preparation of plating solution> Methanesulfonic acid (70% aqueous solution) is 100ml / L, tin methanesulfonate (Sn 2+ The acidic tin plating solution (tin plating solution) of the present example was prepared by mixing and stirring the above ingredients so that the concentration of the tin activator (as a tin activator) was 60 g / L and the concentration of the nonionic activator (polyoxyethylene phenyl ether) was 20 g / L. The temperature of the plating solution was set to 25° C., and the pH was set to 1 or less.

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

[0033] Next, the above-prepared plating solution (25°C) was placed in a plating tank, and the above-mentioned substrate (plating area: 3.3 cm x 5.0 cm) was immersed in the plating solution at a predetermined current density (0.5 A / dm 2 ) The tin plating solution was used to form bumps made of a tin plating film on the surface of the electrolytic copper pads while immersing the pads in the tin plating solution for a time set so that the thickness of the plating film would be 15 μm. The tin plating solution was then circulated using a pump.

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

[0035] [ka]

[0036] <Divalent tin ions (Sn 2+ ) Concentration Measurement 100 mL of ion-exchanged water was placed in a 300 mL conical beaker, and 50 mL of 6N hydrochloric acid was added to prepare a solution. 5 g of sodium potassium tartrate (tetrahydrate) was added to this and completely dissolved. Next, 2 g of sodium bicarbonate was added to the solution in which sodium potassium tartrate had dissolved, and dissolved and foamed. Next, the tin plating solution (2 mL) used in the above plating process was taken with a whole pipette and added to this solution.

[0037] Then, 2 mL of 5% starch solution was added as an indicator to the solution to which the tin plating solution had been added, and the solution was titrated with 0.5N iodine solution to determine the amount of divalent tin ions (Sn 2+ ) concentration was measured.

[0038] The concentration of divalent tin ions was measured at currents of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The results are shown in Figure 2.

[0039] <Trivalent tin ions (Sn 4+ ) Concentration Measurement The tin plating solution (5 mL) used in the above plating process was added to a 100 mL measuring flask and adjusted to 100 mL with ion-exchanged water (Solution A). The above Solution A (1 mL) and 1.0 N NHO3 aqueous solution (50 mL) were added to a 100 mL measuring flask and adjusted to 100 mL with ion-exchanged water (Solution B).

[0040] Next, a quantitative analysis of the B solution was carried out by a calibration curve method using an ICP optical emission spectrometer (high frequency inductively coupled plasma optical emission spectrometer, manufactured by HORIBA, product name: Jobin Yvon Ultima Expert).

[0041] The calibration curve was prepared using Sn standard solutions (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] The tin concentration (Sn 2+ Concentration and Sn 4+ concentration) and the above-mentioned divalent tin ion (Sn 2+ ) in the plating solution, 4+ ) concentration was measured.

[0043] The concentration of tetravalent tin ions was measured at currents of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The results are shown in Figure 3.

[0044] <Particles present or absent> The surface of the bump consisting of the tin plating film formed by the above-mentioned 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) to confirm the presence or absence of particles (insoluble stannic hydroxide) with a diameter of 50 nm or more on the surface of the bump.

[0045] The presence or absence of particles was confirmed at current levels of 0 AH / L (new bath), 25 AH / L, 50 AH / L, 75 AH / L, and 100 AH / L. The results are shown in Table 1.

[0046] Comparative Example 1 A plating process was carried out in the same manner as in Example 1 described above, except that 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 tin plating solution was not brought into contact with the chelating resin having an N-methylglucamine group. 4+ The concentration of ) was measured, and the presence or absence of particles was evaluated. The results are shown in Figure 4 and Table 1.

[0047] In this comparative example, when electricity is applied, divalent tin ions (Sn 2+ ) decreases, and tetravalent tin ions (Sn 4+ ) increases, and divalent tin ions (Sn 2+ ) in the plating solution, it affects the formation of the plating film (plating becomes impossible). 2+ The concentration of was constantly controlled to be 60 g / L.

[0048] The tin concentration (Sn 2+ Concentration and Sn 4+ concentration) and divalent tin ions (Sn 2+ ) concentration (60g / L) in the plating solution. 4+ ) concentration was measured.

[0049] Comparative Example 2 A plating process was carried out 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, and the presence or absence of particles was evaluated.

[0050] [ka]

[0051] The presence or absence of particles was confirmed at a current of 25 AH / L. The results are shown in Table 2.

[0052] Comparative Example 3 The plating process was carried out 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, and the presence or absence of particles was evaluated.

[0053] [ka]

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

[0055] [Table 1]

[0056] [Table 2]

[0057] 3, in Example 1, by contacting the tin plating solution with a chelating resin having an N-methylglucamine group, hexahydroxide stannate (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 currents up to 100 AH / L. Furthermore, because the increase in the concentration of tetravalent tin ions was suppressed, the generation of stannic hydroxide caused by tetravalent tin ions was prevented, and as shown in Table 1, no particles (insoluble stannic hydroxide) were observed on the surface of the bumps at currents up to 100 AH / L.

[0058] 4, in Comparative Example 1, the tin plating solution was not brought into contact with a chelating resin having an N-methylglucamine group, so hexahydroxide stannate (IV) ions were not removed from the plating solution, and the concentration of tetravalent tin ions increased at currents up to 100 AH / L. Furthermore, because the concentration of tetravalent tin ions increased, the generation of stannic hydroxide caused by tetravalent tin ions could not be prevented, and as shown in Table 1, particles (insoluble stannic hydroxide) were confirmed on the surface of the bump at currents up to 100 AH / L.

[0059] Furthermore, as shown in Table 2, in Comparative Examples 2 and 3, the tin plating solution was not brought into contact with a chelating resin having an N-methylglucamine group, and therefore, as in Comparative Example 1, hexahydroxide stannate (IV) ions were not removed from the plating solution, and it is believed that the concentration of tetravalent tin ions increased. As a result, the generation of stannic hydroxide caused by tetravalent tin ions could not be prevented, and particles (insoluble stannic hydroxide) were confirmed on the surface of the bump at a current flow of 25 AH / L. [Industrial Applicability]

[0060] The method of the present invention for preventing adhesion of particles to a tin or tin alloy plating film is particularly suitable for use in a tin or tin alloy plating solution that can be used to form bumps. [Explanation of symbols]

[0061] 1 Plating tank 2. Tin or tin alloy plating solution 3. Pump 4. Ion removal device 5. Chelate resin having aminopolyol groups 6. Hexahydroxide stannate(IV) ion

Claims

1. A tin or tin alloy plating solution containing methanesulfonic acid, tin methanesulfonate, and a nonionic activator is contacted with a chelating resin to prevent particles of tin compounds from adhering to a tin or tin alloy plating film deposited from the tin or tin alloy plating solution, The method for preventing adhesion of particles to a tin or tin alloy plating film is characterized in that the chelating resin has an N-methylglucamine group as a functional group.

2. 2. The method for preventing adhesion of particles to a tin or tin alloy plating film according to claim 1, wherein the chelating resin is a resin having a cellulose fiber as a base material.

3. 3. The method for preventing adhesion of particles to a tin or tin alloy plating film according to claim 1, further comprising circulating the tin or tin alloy plating solution from a plating tank containing the tin or tin alloy plating solution and bringing the chelate resin into contact with the tin or tin alloy plating solution, thereby preventing the particles from adhering to the tin or tin alloy plating film.

4. 4. The method for preventing adhesion of particles to a tin or tin alloy plating film according to claim 3, wherein the chelating resin is contained in a cartridge filter arranged in a circulation path of the tin or tin alloy plating solution.

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