CN1307327C - Electroplating method - Google Patents

Abstract

Due to environmental protection requirements, lead-free solder plating is required. In order to meet this demand, a simple lead-free solder plating method is provided. The conductive member 21 is sequentially immersed in the first electroplating solution and the second electroplating solution, and two layers of electroplating films 22 and 23 of different metal materials are applied. The first electroplating solution and the second electroplating solution, in addition to the metal material and the dissolved Except for acidic solvents for metal materials, the same liquid composition is formed. Thereby, the electroplating method which does not require the liquid bath for washing|cleaning and which can control the concentration of electroplating liquid easily is realizable.

Description

Plating method

The present invention relates to an electroplating method, in particular to an electroplating method which is lead-free and continuously forms an electroplating film of a metal material with good solderability.

The lead material formed by coating the surface of conductive parts such as Cu monomer, Cu alloy or Fe-Ni alloy with the electroplating layer of Sn monomer or Sn alloy is a high-performance conductor and has the excellent properties of Cu monomer and Cu alloy. Electrical conductivity and mechanical strength, but also has the corrosion resistance and good solderability of Sn alone or Sn alloy, and is widely used in the fields of electrical and electronic equipment such as various terminals, joints, and leads, or in the field of power cables, etc. .

In addition, when mounting a semiconductor chip on a circuit board, hot-dip plating or plating using a Sn alloy is performed on the outer lead portion of the semiconductor chip, thereby improving the solderability of the outer lead portion. A representative example of such a Sn alloy is, for example, solder (Sn-Pb alloy). Since solderability, corrosion resistance, etc. are good, it is used as industrial plating for electrical and electronic industry components such as joints and lead frames. widely used.

However, since Pb used in solder has a bad influence on the human body, its harmfulness has been pointed out, and proposals to limit the use of Pb have been made around the world. For example, if electronic devices that are discarded outdoors are exposed to acid rain, Pb will be dissolved from the solder (Sn-Pb alloy) used inside the device or the solder plating applied to the surface of electronic parts, Cause ground water or river pollution. In order to prevent environmental pollution, it is preferable to use a Pb-free Sn alloy. Therefore, a new plating solution not containing Pb is being developed to replace the conventional Sn-Pb plating solution. At present, electroplating solutions containing Sn as the main component without Pb have been developed, such as Sn-Bi-based, Sn-Ag-based, and Sn-Cu-based electroplating solutions, and are gradually replacing the original electroplating solutions.

Fig. 3 is a sectional view showing a basic configuration of a lead wire. For example, the conductive member 21 is made of Cu, a Cu-based alloy mainly composed of Cu, or an Fe-Ni-based alloy mainly composed of Fe-Ni. Furthermore, two plating films of different metal materials are plated on the surfaces of these conductive members 21 . For example, the first plating film 22 of Sn and the second plating film 23 of Sn—Bi are sequentially formed. Here, it is known that when the thickness of the first electroplated film 22 is _t1 and the thickness of the second electroplated film 23 is _t2 , if _t1 is set to about 3 to 15 μm, _t2 is set to about 1 to 15 μm. 5μm, t ₂ /t ₁ is set to about 0.1 to 0.5, no matter in terms of cost, solderability and heat resistance, or the welding strength of solder or the welding strength of the welding part with aluminum wire, etc. It has good characteristics and is suitable for improving the performance as a lead material.

Fig. 4 is a plan view of the entire automatic plating device. First, in the alkaline electrolytic cleaning solution tank 31 , organic contaminants such as fats and oils that interfere with the adhesion or solderability of the solder plating film on the surface of the conductive member 21 are removed. Next, after cleaning in the water washing liquid tank 32, a chemical etching treatment (basically a treatment utilizing an oxidation-reduction reaction) is performed in the chemical etching liquid tank 33 to make unevenness due to the presence of grain boundaries or inclusions, etc. The surface of the conductive member 21 is uniformized.

Next, after washing in the liquid tank 34 for water washing, the oxide film adhering to the liquid tank 34 for water washing is removed in the acid activation liquid tank 35 . Subsequently, after washing in the liquid tank 36 for washing|cleaning, electroplating is performed in the solder plating apparatus 37. The solder plating solution is strongly acidic, so the surface after plating becomes acidic. On such a surface, the film discolors with time, and the solderability deteriorates. For this reason, in the liquid tank 38 for washing and the neutralization treatment tank 39, the acid remaining on the surface of the electroplating layer is neutralized, and the adsorbed organic matter is removed. Thereafter, washing is performed in the liquid tank 40 for washing with water and the liquid tank 41 for hot water washing, and the plated conductive member is dried in the drying device 42 .

FIG. 5 is a detailed plan view of a portion where electroplating is performed in a conventional electroplating apparatus 37 . In this electroplating method, the conductive member 21 is dipped in the pre-dipping tank 371, the hydroxide film on the surface is removed, immersed in the electroplating solution in the first electroplating solution tank 372, and after the first electroplating film 22 is applied, the conductive member 21 is Immerse in the pure water of the washing solution tank 373 provided between the plating solution in the first plating solution tank 372 and the plating solution in the second plating solution tank 374, remove the first plating solution, and then immerse the conductive member 21 in the second plating solution tank 374. 2. In the plating solution in the plating solution tank 374, the second plating film 23 is applied. Finally, the plated surface is washed in the washing liquid tank 375 .

In the above-mentioned electroplating method, the electroplating solution of the first electroplating solution tank 372 for applying the first electroplating film 22 and the electroplating solution of the second electroplating solution tank 374 for applying the second electroplating film, except for the metal materials and Except for the acidic solvent that dissolves these metal materials, it is not the same liquid composition. For example, when the first electroplating film 22 is composed of Sn alone and the second electroplating film 23 is composed of a Sn-Bi alloy, in the configuration of the electroplating solutions in the first electroplating solution tank 372 and the second electroplating solution tank 374, regarding the organic Acids, solvents, and pure water use materials composed of the same liquid. However, as for the additives, additives for solder plating solutions are generally used for the former, and additives for Sn—Bi plating solutions are generally used for the latter.

In addition, the first plating solution tank 372 and the second plating solution tank 374 often use the same shape of the plating solution tank.

Such a plating method is described in JP-A-10-229152.

First, the plating solution of the first plating solution tank 372 for applying the above-mentioned first plating film 22 and the plating solution of the second plating solution tank 374 for applying the second plating film 23, if the metal materials and the dissolved metal materials constituting the respective plating solutions are removed Except for the acidic solvent of these metal materials, it is not the same liquid composition. Therefore, the electroplating solution of the first electroplating solution tank 372 adheres on the conductive member 21, and the electroplating solution of the first electroplating solution tank 372 and the electroplating solution of the second electroplating solution tank 374 are provided with a washing liquid tank 373, so that the first The plating solution in the first plating solution tank 372 is not directly brought into the plating solution in the second plating solution tank 374. And it is necessary to remove the plating solution in the first plating solution tank 372 using the pure water in the washing liquid tank 373 . Therefore, in the conventional electroplating method, it is indispensable to use the liquid tank 373 for washing, which has a problem of requiring redundant steps.

In addition, in the plating solution of the second plating solution tank 374 where the second plating film 23 is applied, the conductive member 21 to which the first plating film 22 has been applied is washed in the washing liquid tank 373, and then immersed in the second plating solution tank. 374 in the plating solution. At this time, the pure water in the washing liquid tank 373 is mixed into the plating solution in the second plating solution tank 374 , so that the plating solution in the second plating solution tank 374 is diluted. Therefore, it is necessary to control the composition and concentration of the plating solution in the second plating solution tank 374, which complicates the management of the process.

Furthermore, the metal material contained in the plating solution in the first plating solution tank 372 and the plating solution in the second plating solution tank 374 is not only plated on the conductive member 21, but also substituted and deposited on the anode. However, since Bi, Ag, and Cu constituting the second electroplating solution are significantly substituted and precipitated on the anode, the amount of replenishment of the above-mentioned metals also increases significantly. On the other hand, metal materials (particularly Bi, Ag, and Cu) are very expensive, thus leading to an increase in production cost.

The present invention was made in view of the above-mentioned conventional problems, and the object is to apply different metal materials or the same metal material on the surface of a conductive member, but the first plating film of a two-layer plating film with a different metal material composition ratio In the electroplating method of the second electroplated film, an electroplating method capable of shortening the work process and simplifying concentration control is provided.

In order to achieve the above-mentioned purpose, in the present invention, except for the metal material composition and the acidic solvent for dissolving the metal material contained in the first electroplating solution and the second electroplating solution, the composition of the electroplating solutions is basically the same. Specifically, organic acids, solvents, additives, and pure water other than the metal material contained in the first plating solution and the second plating solution and the acidic solvent for dissolving the metal material are basically the same liquid composition.

FIG. 1 is a diagram illustrating a solder plating apparatus used in the plating method of the present invention.

Fig. 2 is a diagram illustrating a first plating solution tank and a second plating solution tank used in the plating method of the present invention.

Fig. 3 is a diagram illustrating the present invention and a conventional electroconductive member to which two layers of plating have been applied.

Fig. 4 is a plan view illustrating the entirety of the present invention and a conventional automatic plating apparatus.

Fig. 5 is a plan view illustrating part of a conventional solder plating apparatus.

FIG. 1 is a plan view showing the plating part in an automatic plating apparatus for carrying out the plating method of the present invention, and corresponds to a solder plating apparatus 37 of the entire plating apparatus shown in FIG. 4 .

In FIG. 1 , the automatic plating apparatus is composed of a pre-dipping solution tank 1 , a first plating solution tank 2 , a second plating solution tank 3 , and a washing solution tank 4 . The oxide film adhering to the conductive member 21 (see FIG. 3 ) during washing in the preceding washing liquid tank 36 (see FIG. 4 ) is removed in the prepreg tank 1 to make the surface of the conductive member 21 active. In the first plating solution tank 2 , the first plating film 22 is applied to the conductive member 21 , and then the second plating film 23 is applied to the conductive member 21 in the second plating solution tank 3 . Here, regarding the thickness of the plated film, when the thickness of the first plated film 22 is conventionally defined as t ₁ and the thickness of the second plated film 23 is defined as t ₂ , t ₁ becomes about 3 to 15 μm and t ₂ becomes about 1. Electroplating is performed so that t ₂ /t ₁ becomes about 0.1 to 0.5. The structure of the lead wire is the same as that in Figure 3, so the symbols are the same.

In the present invention, the solutions other than the first and second metal materials contained in the electroplating solution of the first electroplating solution tank 2 and the electroplating solution of the second electroplating solution tank 3 and the acidic solvent for dissolving these metal materials are formed into the same liquid composition. Thus, it has the following features, that is, after immersing the conductive member 21 in the electroplating solution of the first electroplating solution tank 2 and applying the first electroplating film 22, it can be subsequently immersed in the electroplating solution of the second electroplating solution tank 3 to apply the second plating film 23 .

That is, as the composition of the electroplating solution of the first electroplating solution tank 2, Sn is used as all or almost all of the first metal material, except for the solution of the metal material and an acidic solvent that dissolves the metal material, an organic acid, a solvent, an additive and pure water. For example, the organic acid includes methanesulfonic acid or propanolsulfonic acid, and the solvent includes isopropanol. And, as the composition of the plating solution of the 2nd plating solution tank 3, the 2nd metal material of at least one kind selected from Bi, Ag and Cu and the metal material including Sn which is the 1st metal material are used as the metal material, except A solution of these metal materials and an acidic solvent in which these metal materials are dissolved consists of an organic acid, a solvent, and pure water. For example, like the first plating solution tank 2, the organic acid includes methanesulfonic acid or propanolsulfonic acid, and the solvent includes isopropanol.

Therefore, in this electroplating method, the electroplating solution of the first electroplating solution tank 2 is attached to the conductive member 21, and is brought into the electroplating solution of the second electroplating solution tank 3. Even if two kinds of electroplating solutions are mixed, except for the first and second Except for the metal material and the acidic solvent in which these metal materials are dissolved, since the same solution composition is formed, the composition of the plating solution in the second plating solution tank 3 will not be disturbed.

Generally, when constituting a plating solution, a metal material is dissolved in an acidic solvent and used. However, since this acidic solvent is extremely small compared to the amount of the plating solution, no matter how much it contains, it does not have any influence on the composition of the plating solution.

Therefore, after immersing the conductive member 21 in the electroplating solution of the first electroplating solution tank 2 and applying the first electroplating film 22, the conductive member 21 can be continuously immersed in the electroplating solution of the second electroplating solution tank 3 to apply the second electroplating film. Coating 23. Therefore, it is possible to omit the conventional washing with the liquid bath for washing after the application of the first plating film 22 , thereby shortening the working process and working time.

Next, regarding the electroplating solution of the second electroplating solution tank 3, as mentioned above, in the electroplating operation process, the electroplating solution of the first electroplating solution tank 2 is adhered on the conductive member 21, and the electroplating solution of the second electroplating solution tank 3 is mixed. middle. At this time, in the plating solution in the second plating solution tank 3 , Sn, which is the first metal material and adhered to the conductive member 21 , is brought in. However, the second metal material among Bi, Ag, and Cu is not used. In addition, the second metal material among Bi, Ag, and Cu is deposited on the conductive member 21 as an alloy with Sn, and in addition, is deposited on the anode by substitution. In addition, since the second metal material among these Bi, Ag, and Cu is attached to the conductive member 21 and carried away, the amount is significantly reduced compared with the first metal material Sn.

On the other hand, generally in electroplating, the thickness of the electroplating film and the composition of the electroplating film are controlled by the current density, electroplating time and concentration of the electroplating solution. Management of plating film composition. Thereby, the amount of the metal material deposited on the electroplating film or the concentration of the plating solution can be managed, and when the reduction of the metal material due to the deposition is observed, replenishment can be performed. As described above, the metal material in the plating solution of the first plating solution tank 2 and the second plating solution tank 3 also decreases due to substitution and precipitation on the anode and being carried away by the conductive member 21 . However, the anodes of the first electroplating solution tank 2 and the second electroplating solution tank 3 are formed with Sn with a purity of, for example, 99.9% or more, so the first metal material Sn of the electroplating solution is replenished mainly through the dissolution of the anode, and is periodically Analyze and make up solution as needed.

For example, when carrying out the concentration management of the electroplating solution with Sn being 100 (weight %), as various solution concentrations, the concentration of the electroplating solution is maintained at a Sn ²⁺ concentration of 30 to 60 (g/L), a free acid concentration of 120 -160 (g/L), and the additive concentration is 20-50 (ml/L) to manage Sn. However, as described above, in the management of the first plating solution tank 2 , there is anodic dissolution of Sn, so it is not necessary to be as frequent as the management of the second plating solution tank 3 .

In the electroplating solution of the second electroplating solution tank 3, as mentioned above, the first metal material Sn is supplemented by the dissolution of the anode, therefore, the first metal material selected from Bi, Ag and Cu, which is significantly reduced compared with Sn, is mainly controlled. 2 Concentration of metallic materials.

For example, when carrying out the concentration management of the electroplating solution of Sn: Bi=97 (weight %): 3 (weight %), as each liquid concentration, the concentration of electroplating solution is maintained at Sn ²⁺ concentration and is 50～60 (g/ L), the Bi ³⁺ concentration is 3.0-4.2 (g/L), the free acid concentration is 120-160 (g/L), and the additive concentration is 20-40 (ml/L).

As mentioned above, the constant operation speed generated by the production line operation can be used, and the current density in the first electroplating bath 2 and the second electroplating bath 3 can be kept constant, so the second metal material in the second electroplating bath 3 Concentration management of Bi, Ag, and Cu also becomes easy. That is, in the second plating solution tank 3, concentration control can be easily performed by regularly replenishing the second metal material such as Bi, Ag, and Cu. As a result, the metal material concentration of the plating solution in the second plating solution tank 3 can be kept constant, and the film thickness and plating film composition of the second plating film 23 can be made uniform.

That is, in this electroplating method, by setting the current density in the first electroplating solution tank 2 and the second electroplating solution tank 3 at the optimum current density, it is possible to suppress the uniformity of the metal precipitation particle size and the uniformity of the two layers. Fluctuation in film thickness ratio. Thus, in the electroplating method with a constant operating speed generated by production line operations and a constant current density, when the electroplating film thicknesses _t1 and _t2 satisfy _t1 > _t2 , the conductive member 21 is set in the first electroplating solution D ₁ is the distance that the conductive member 21 moves in the second electroplating solution, and D ₂ is the distance that the conductive member 21 moves in the second plating solution. D ₁ and D ₂ clearly establish the relationship of D ₁ >D ₂ .

FIG. 2 shows the relationship between the first plating solution tank 2 and the second plating solution tank 3 . As mentioned above, when the electroplating film thickness t ₁ and t ₂ satisfy t ₁ > t ₂ , the length in the working direction of the first electroplating bath is Z ₁ , and the length in the working direction of the second electroplating bath is Z ₂ , If the cross-sectional area is the same (X ₁ ×Y ₁ =X ₂ ×Y ₂ ), Z ₁ and Z ₂ hold the relationship of Z ₁ >Z ₂ . Therefore, as clearly shown in Figure 2, the volume of the first electroplating solution is V ₁ (=X ₁ ×Y ₁ ×Z ₁ ), and the volume of the second electroplating solution is V ₂ (=X ₂ ×Y ₂ × Z ₂ ), V ₁ and V ₂ clearly establish the relationship of V ₁ >V ₂ .

That is, the volume of the plating solution in the second plating solution tank 3 can be significantly reduced in the volume of the plating solution in the second plating solution tank 3 . That is, in the plating solution of the second plating solution tank 3, the amount of second metal materials such as Bi, Ag, and Cu, which are more expensive than the first metal material Sn, can be greatly reduced, thereby reducing costs.

Other embodiments of the present invention will be described below.

In the present invention, the plating solution in the first plating solution tank 2 and the plating solution in the second plating solution tank 3 have the same composition ratio of the respective metal materials, but have the same solution composition. Therefore, it has the following features, that is, the conductive member 21 is immersed in the electroplating solution of the first electroplating solution tank 2, and after the first electroplating film 22 is applied, it can be continuously immersed in the electroplating solution of the second electroplating solution tank 3, A second plating film 23 is applied. Furthermore, the embodiment is the same as the method described above.

For example, there is a Sn-Bi liquid in the present invention. Here, what percentage of Bi is contained in the plating solution in the first plating solution tank 2 . This significantly suppresses whiskers (needle crystals) on the surface of the first plating film 22 . In addition, as the method for controlling the concentration of the plating solution, Bi is managed in the same manner as the above-mentioned method.

That is, in the electroplating solution of the first electroplating solution tank 2, metal materials other than Sn used in the electroplating solution of the second electroplating solution tank 3 contain at least a few percent selected from Bi, Ag and Cu. A metallic material. Thereby, whiskers (needle crystals) on the surface of the first plating film 22 can be significantly suppressed.

As indicated in the above description, the electroplating method of the present invention can achieve the following effects.

First, the composition of the first plating solution and the second plating solution is substantially the same except for the first and second metal materials constituting the respective plating solutions and the acidic solvent for dissolving these metal materials. Therefore, even if the first electroplating solution is mixed into the second electroplating solution, the liquid composition is not disturbed, and different metal materials or two layers of the same metal material but different composition ratios of the metal materials can be continuously applied to the conductive member. coating. As a result, it is possible to omit cleaning between the first plated film and the second plated film with a liquid bath for rinsing, thereby shortening the working process and working time.

Second, in the management of the first and second metal materials contained in the first electroplating solution and the second electroplating solution, first, the composition of the first electroplating solution and the second electroplating solution, in addition to the first It is the same liquid composition as the second metal material and the acidic solvent which dissolves these metal materials. The concentration of the first metal material Sn in each plating solution can be adjusted mainly by the dissolution of the anode. Therefore, in the second plating solution, the concentration control using the second metal material among Bi, Ag, and Cu can be regularly performed, and the concentration control of the plating solution becomes easy.

Third, the constant operation speed and the constant current density generated by the use of automatic electroplating equipment and the use of the first and second metal materials in addition to the first electroplating solution and the second electroplating solution and the acidic solvent for dissolving these metal materials The solution forms the same liquid composition. Therefore, since the thickness of the second plating film is considerably thinner than that of the first plating film, the time during which the conductive member is immersed in the second plating solution can be shortened. As a result, the liquid volume of the second plating liquid tank can be significantly reduced. Thereby, the usage-amount of the 2nd metal material Bi, Ag, and Cu used for a 2nd electroplating liquid can also be reduced significantly, As a result, cost reduction can be aimed at.

Fourth, in the electroplating solution of the first electroplating solution tank, in addition to the first metal material Sn used in the electroplating solution of the second electroplating solution tank, contain at least a few percent selected from Bi, Ag and Cu A second metal material. Thereby, whiskers (needle crystals) on the surface of the first plating film can be significantly suppressed.

Fifth, in lead wires and semiconductor devices using the above plating method, since the plating solution used does not contain lead, there is no adverse effect on the human body or the environment. In addition, the solutions other than the metal material of the first electroplating solution and the second electroplating solution and the acidic solvent for dissolving these metal materials are formed into the same liquid composition, or the metal material composition ratio of the first electroplating solution and the second electroplating solution Different but the same metal material, so as to improve the quality of electroplating.

Claims (4)

1. electro-plating method, conductive component is immersed in the 1st electroplate liquid, the 2nd electroplate liquid successively, the 2nd electroplating film that on the surface of above-mentioned conductive component, overlaps to form the 1st electroplating film that constitutes by the Sn metal and constitute by the alloy of the alloy of the alloy of above-mentioned Sn metal and Bi metal, above-mentioned Sn metal and Ag metal or above-mentioned Sn metal and Cu metal, it is characterized in that

Above-mentioned the 1st electroplate liquid is by the Sn material, dissolve the solvent of this Sn material, organic acid, additive and pure water constitute, above-mentioned the 2nd electroplate liquid by with the Sn material of the same kind of above-mentioned the 1st electroplate liquid, dissolve this Sn material and the solvent same kind of above-mentioned the 1st electroplate liquid, from the Bi material, a kind of metallic substance of selecting in Ag material or the Cu material, dissolve the solvent of this metallic substance, organic acid with the same kind of above-mentioned the 1st electroplate liquid, constitute with the additive and the pure water of the same kind of above-mentioned the 1st electroplate liquid

Above-mentioned conductive component is immersed in above-mentioned the 1st electroplate liquid, form above-mentioned the 1st electroplating film, then, above-mentioned conductive component need not be washed, and with above-mentioned the 1st electroplate liquid attached to the state on the above-mentioned conductive component, above-mentioned conductive component is immersed in above-mentioned the 2nd electroplate liquid, forms above-mentioned the 2nd electroplating film;

In above-mentioned the 2nd electroplate liquid, carry out the concentration management of a kind of metallic substance of from above-mentioned Bi material, Ag material or Cu material, selecting.

2. the described electro-plating method of claim 1 is characterized in that, in above-mentioned the 2nd electroplate liquid, by being arranged on the dissolving of Sn solvability electrode and the bringing into of above-mentioned the 1st electroplate liquid in above-mentioned the 2nd electroplate liquid, carries out replenishing of above-mentioned Sn material.

3. the described electro-plating method of claim 1 is characterized in that, in above-mentioned the 1st electroplate liquid, by being arranged on the dissolving of the Sn solvability electrode in above-mentioned the 1st electroplate liquid, carries out replenishing of above-mentioned Sn material.

4. the described electro-plating method of claim 1 is characterized in that, in the above-mentioned organic acid, comprises methylsulfonic acid or propyl alcohol sulfonic acid, in above-mentioned solvent, comprises Virahol.

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