JP2008169413A - Method for adjusting concentration of metal ion, device for adjusting concentration of metal ion, and plating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably keeping the concentration of a metal ion in a plating solution; a device suitable for carrying out the method; and a plating method using them. <P>SOLUTION: This adjusting method includes: placing an anode 30 and a cathode 40 made from a metal material having a lower hydrogen overvoltage than that of a metal material composing the anode 30, in a plating solution 20; and applying a direct-current voltage between the anode 30 and the cathode 40 from a direct-current power supply E0. Thereby, the concentration X<SP>n+</SP>of the metal ion in the plating solution 20 is adjusted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for adjusting a metal ion concentration in an electroplating solution (metal ion concentration adjusting method), an apparatus for adjusting a metal ion concentration in a plating solution (metal ion concentration adjusting device), and a plating method.

  The electroplating technology is small, for example, from the formation of a thin film microdevice, a multilayer chip capacitor, an inductor, a chip varistor, an NCT thermistor, or a conductive film of a small electronic component such as a chip resistor (see Patent Documents 1 and 2), For large ones, they are used in a very wide range up to surface treatment of industrial machine parts.

As is well known, electroplating is a technique in which an object to be plated is immersed in an electrolyte such as an aqueous solution or molten salt, and direct current electricity is applied to deposit metal ions in the solution on the surface of the object to be plated. is there.
In the electroplating process, first, the object to be plated is washed with washing water, and then the object to be plated is immersed in a plating solution to perform the electroplating process.

  One of the problems associated with this electroplating treatment was that the object to be plated washed with washing water was immersed in the plating solution, and then the object to be plated was pulled up from the plating solution, so that it adhered to the object to be plated. While water is mixed in the plating solution, the plating solution adheres to the object to be plated and is taken out after the plating process. As the plating process is repeated, the metal ion concentration in the plating solution decreases and the plating quality is reduced. It will be reduced.

As a means for solving this problem, conventionally, there has been no choice but to rely on a passive means of periodically replenishing a new plating solution or discarding an old plating solution and replacing it with a completely new plating solution. . However, even if such measures are taken, a decrease in plating quality due to a decrease in metal ion concentration is inevitable, management of metal ion concentration, decrease in workability due to replenishment and replacement of plating solution, increase in production cost, and There are also problems such as environmental pollution.
Japanese Patent Laid-Open No. 8-126872 JP 2006-111977 A

  An object of the present invention is to provide a method capable of stably maintaining a metal ion concentration in a plating solution, an apparatus suitable for carrying out this method, and a plating method using them.

  Another subject of the present invention is a method for stably maintaining the metal ion concentration in the plating solution while reducing the amount of plating solution used and the plating cost, an apparatus suitable for carrying out this method, and It is to provide a plating method used.

  Still another object of the present invention is to provide a method capable of stably maintaining the metal ion concentration in the plating solution while ensuring high plating work efficiency, an apparatus suitable for carrying out this method, and the use of these. It is to provide a plating method.

  In order to achieve the above-described problems, the present invention first places an anode and a cathode in the plating solution when adjusting the metal ion concentration in the plating solution. The cathode is made of a metal material whose hydrogen overvoltage is lower than that of the metal material constituting the anode, and a DC voltage is applied between the anode and the cathode from a DC power source.

  As described above, when the cathode is made of a metal material whose hydrogen overvoltage is lower than the metal material constituting the anode, hydrogen ions are actively generated at the cathode having a low hydrogen overvoltage. For this reason, the generated hydrogen ions are preferentially combined with the electrons supplied from the cathode to generate hydrogen gas.

  As a result, the amount of electrons provided for bonding with the metal ions present in the plating solution is relatively decreased, and the amount of metal ions remaining in the plating solution is increased. As a result, the metal ions in the plating solution are increased. The concentration will increase.

  In the present invention, the anode and cathode are selected from the group of Pt, Pd, Ru, Rh, Au, Fe, Co, Ag, Ni, Cu, Cd, Sn, PB, Zn, Hg, and alloys thereof. It is a combination. The combination is selected such that the hydrogen overvoltage of the metal material constituting the cathode is lower than that of the metal material constituting the anode.

  The metal ion concentration adjusting method according to the present invention is performed on a plating solution that has undergone at least one plating process. Thereby, the metal ion concentration in the plating solution is increased, and the plating solution is adjusted to a predetermined metal ion concentration. Unlike the prior art, the metal ion concentration in the plating solution can be stably maintained because it is not a stepwise adjustment of the metal ion concentration such as periodic replenishment of the plating solution or replacement of the plating solution.

  In addition, when the object to be plated washed with washing water is immersed in the plating solution, the amount of moisture brought into the plating solution, and then the plating solution taken out when the object to be plated is pulled up from the plating solution, Since it can be considered that the amount is almost the same, the replenishment of the plating solution is little even if it is necessary. For this reason, it is possible to stably maintain the metal ion concentration in the plating solution while reducing the amount of the plating solution used and reducing the plating cost.

  In addition, since there is no need to replenish the plating solution or replace the plating solution, the metal ion concentration in the plating solution can be stably maintained while ensuring high plating work efficiency.

  The present invention can be applied not only to a normal plating process, but also to a barrel plating process that is frequently used in the plating process of minute electronic components.

As described above, according to the present invention, the following operational effects can be obtained.
(A) It is possible to provide a method capable of stably maintaining the metal ion concentration in the plating solution, an apparatus suitable for carrying out this method, and a plating method using them.
(B) A method capable of stably maintaining the metal ion concentration in the plating solution while reducing the amount of plating solution used and the plating cost, an apparatus suitable for carrying out this method, and a plating method using these methods are provided. can do.
(C) To provide a method capable of stably maintaining the metal ion concentration in the plating solution, ensuring a high plating work efficiency, an apparatus suitable for carrying out this method, and a plating method using them. it can.

FIG. 1 is a diagram showing a metal ion concentration adjusting method and a metal ion concentration adjusting apparatus according to the present invention. In adjusting the concentration of the metal ion X ^{n +} of the plating solution 20 in the liquid tank 10, first, the anode 30 and the cathode 40 are placed in the plating solution 20.

  In the plating process, the object to be plated washed with washing water is immersed in the plating solution, and then the object to be plated is pulled up from the plating solution. After the plating process, the plating solution adheres to the object to be plated and is taken out. For this reason, the more the plating process is repeated, the lower the metal ion concentration in the plating solution and the lower the plating quality. The present invention intends to return the metal ion concentration to the original state in such a case. Accordingly, the plating solution 20 is usually subjected to the plating process at least once.

The metal ions ^{Xn +} in the plating solution 20 include those eluted from the metal material X constituting the anode 30 in addition to the plating solution composition. The metal material X constituting the anode 30 is made of a material to be plated.

  The cathode 40 is made of a metal material Y whose hydrogen overvoltage is lower than that of the metal material X constituting the anode 30. A DC voltage is applied between the anode 30 and the cathode 40 from the DC power supply E0.

  In the above configuration, the anodic reaction and the cathodic reaction in normal plating deposition can be expressed by the following equilibrium condition equation.

Anode reaction X → X ^{n +} + n · e ⁻ (1)
Cathode reaction X ^{n +} + n · e ⁻ → X (2)
That is, the metal ion X ^{n +} eluted from the anode 30 based on the formula (1) is combined with the electron e ⁻ according to the formula (2), and the metal X is deposited on the surface of the cathode 40.

In the present invention, the cathode 40 is made of a metal material Y whose hydrogen overvoltage is lower than that of the metal material X constituting the anode 30 in the present invention. H ⁺ is actively generated. The generated hydrogen ions H ⁺ are preferentially combined with electrons e ⁻ supplied from the cathode 40 to generate hydrogen gas H ₂ .

Of the electrons (n · e ⁻ ) generated at the anode 30, a (a is a hydrogen generation rate and takes a value of 0 to 1) is combined with hydrogen ions H ⁺ and contributes to generation of hydrogen gas H _2. Then, the following cathode reaction formula is established. Note that a (%) is a hydrogen generation rate.

a · n · H ⁺ + a · n · e ⁻ → a · n / 2 · H ₂ (3)
(1-a) · n · X ^{n +} + (1-a) · n · e ⁻ → (1-a) · X (4)

From the above formulas (1) and (4), the plating solution 20 includes
n- (1-a) .n = n.a
Of metal ions X ^{n +} remain. As a result, the concentration of the metal ion ^{Xn + in} the plating solution 20 increases. When the metal material X is plated on the surface of the metal material Y by this cathodic reaction, the hydrogen overvoltage becomes high, so that the metal material Y can be regenerated by etching with an acid to prevent this.

  The anode 30 and cathode 40 are a combination of Pt, Pd, Ru, Rh, Au, Fe, Co, Ag, Ni, Cu, Cd, Sn, PB, Zn, Hg, and combinations thereof. Become. The arrangement is arranged in the order of increasing hydrogen overvoltage from the lowest. The combination of the anode 30 and the cathode 40 is selected such that the hydrogen overvoltage of the metal material Y constituting the cathode 40 is lower than that of the metal material X constituting the anode 30. An example of the combination is as follows.

  When Ni is selected as the metal material X composing the anode 30 for performing Ni plating, the metal material Y composing the cathode 40 has Pt, Pd, Ru, Rh as a hydrogen overvoltage lower than Ni. , Au, Fe, Co, or Ag.

  When Cu is selected as the metal material X composing the anode 30 for Cu plating, the metal material Y composing the cathode 40 has Pt, Pd, Ru, Rh as the hydrogen overvoltage lower than that of Cu. , Au, Fe, Co, Ag, or Ni.

  Further, when Sn is selected as the metal material X constituting the anode 30 for Sn plating, the metal material Y constituting the cathode 40 may be Pt, Pd, Ru whose hydrogen overvoltage is lower than Sn. , Rh, Au, Fe, Co, Ag, Ni or Cu.

  Next, the metal ion concentration adjusting method according to the present invention will be described together with the plating process. 2 to 7 are diagrams showing a general two-layer plating process, in which a first cleaning process A, a first plating process B, a second cleaning process C, and a second plating process D are sequentially arranged. Yes.

  First, as shown in FIG. 2, in the first cleaning step A, the object 6 to be plated supported by the conveying means 7 is cleaned with cleaning water containing water as a main component. Although the figure shows an image of immersing the object 6 to be cleaned in the cleaning water 11 circulating in the liquid tank 1, the present invention is not limited to such a cleaning method. A cleaning method by water jetting on the workpiece 6 may be used.

  Next, as shown in FIG. 3, the object to be plated 6 that has been cleaned is moved to the first plating step B, and the object 6 to be plated is subjected to the first plating in the liquid tank 2 as shown in FIG. 4. It is immersed in the liquid 21 to perform a plating process. In plating, a DC voltage from a DC power source E1 is applied to the anode 51 made of a metal material to be plated and the workpiece 6.

  Next, as shown in FIG. 5, the plated object 6 after the plating process is pulled up from the first plating solution 21 and moved to the second cleaning step C as shown in FIG. Wash with washing water.

  Thereafter, as shown in FIG. 7, the object to be plated 6 that has been cleaned is moved to the second plating step D, and the object to be plated 6 is immersed in the second plating solution 41 accommodated in the liquid tank. Then, the second plating process is performed. In plating, a DC voltage is applied from the DC power source E2 to the anode 51 made of a metal material to be plated and the object 6 to be plated to perform the plating process. Wash after plating.

  The plating process described above is repeated for each object 6 to be plated. In the plating process, the object to be plated washed with washing water is immersed in the plating solution, and then the object to be plated is lifted from the plating solution, so that the water adhering to the object to be plated is mixed into the plating solution. Then, after the plating process, the plating solution adheres to the object to be plated and is taken out. The more the plating process is repeated, the lower the metal ion concentration in the plating solution and the lower the plating quality.

  Therefore, after the plating process is repeated several times, the metal ion concentration adjusting method according to the present invention is performed on the first plating solution 21 or the second plating solution 41. FIG. 8 shows a case where the metal ion concentration adjusting method is performed on the first plating solution 21 used in the first plating process B. The adjustment mechanism of the metal ion concentration in this case is not different from that described with reference to FIG. That is, the cathode 40 is made of a metal material Y whose hydrogen overvoltage is lower than the metal material X constituting the anode 30, and a DC voltage is applied between the anode 30 and the cathode 40 from the DC power source E 0.

Then, the cathode reaction occurring at this time, electrons e to be subjected to the binding of the metal ion X ^{n + -} amount of decreases, the consumption of metal ions X ^{n +} eluted in the first plating solution 21 is reduced As a result, the concentration of the metal ions ^{Xn + in} the first plating solution 21 increases. In this way, the first plating solution 21 whose metal ion concentration has been adjusted is returned to the original plating process.

  In FIG. 8, the first plating solution 21 arranged in the process line is transferred into the liquid tank 10 prepared for adjusting the metal ion concentration, and the anode 30, the cathode 40 and the direct current prepared for adjusting the metal ion concentration. Although the power source E0 is used, in the process lines of FIGS. 2 to 7, the first plating solution 21, the anode 30, and the DC power source E0 are used as they are, but the cathode 40 is used instead of the object 6 to be plated. It is also possible to employ a technique for adjusting the metal ion concentration.

By the metal ion concentration adjustment described above, the concentration of metal ions ^{Xn +} in the first plating solution 21 is increased, and the first plating solution 21 is adjusted to a predetermined concentration of metal ions ^{Xn +} . And unconventional, recruitment and regular first plating solution 21, is not a stepwise metal ion X ^{n +} density adjustment such substitutions, stable metal ion X ^{n +} concentration of the first plating solution 21 It can be maintained.

Moreover, when the to-be-plated to-be-plated object 6 is immersed in the 1st plating solution 21, the quantity of the moisture brought in in the 1st plating solution 21, and then pulls up the to-be-plated object 6 from the 1st plating solution 21. In this case, since the amount of the first plating solution 21 taken out can be regarded as almost the same amount, even if it is necessary to replenish the first plating solution 21, only a small amount is required. For this reason, the usage-amount of the 1st plating solution 21 can be reduced, and the density | concentration of the metal ion ^{Xn +} in the 1st plating solution 21 can be maintained stably, reducing plating cost.

In addition, since the replenishment or replacement process of the first plating solution 21 is unnecessary, the concentration of the metal ions ^{Xn +} in the first plating solution 21 can be stably maintained while ensuring high plating work efficiency. Although explanation is omitted, the metal ion concentration of the second plating solution 41 can be adjusted in the same manner. Further, this method may be carried out in a replenishing tank, a spare tank, etc. connected to the plating tank by a pipe or the like. Furthermore, this method may be carried out simultaneously with production.

  The present invention can be applied not only to a normal plating process but also to a barrel plating method that is frequently used in the plating process of minute electronic components. Next, this point will be described with reference to FIGS. 9 to 11 are based on the premise that the series of plating steps shown in FIGS. 2 to 8 are executed, and the first cleaning step A (FIG. 9) and the first plating step B ( FIG. 10 and FIG. 11) are extracted and shown individually. As for the second cleaning step C and the second plating step D, only the materials to be plated are different, and the first plating solution 21 itself is a repetition of the first cleaning step A and the first plating step B. Description is omitted.

  First, in the cleaning step of FIG. 9, the barrel plating apparatus 8 is rinsed with the cleaning water 11 inside the liquid tank 1. The barrel plating apparatus 8 has a barrel 81 that is at least large enough to be immersed in the liquid tank 1, and the barrel 81 is conveyed by the conveying means 7.

  The barrel 81 has a cylindrical drum shape, and an object to be processed 6 that is an electronic component such as a multilayer ceramic capacitor and a spherical medium 83 are placed therein. Also, the surface of the barrel 81 has a large number of holes having a diameter smaller than that of the object to be plated 6, and when the barrel 81 is immersed in the cleaning water, the cleaning is efficiently performed inside and outside the barrel 81. . As the material of the barrel 81, polypropylene (PP), acrylic resin, or the like is generally used from the viewpoint of ensuring corrosion resistance against the plating solution.

  An electrode mounting shaft 84 that rotatably supports the barrel 81 is provided in the center of the barrel 81 so as to pass therethrough. In the central portion of the electrode mounting shaft 84, the workpiece 6 and the spherical media in the barrel 81 are provided. A cathode 82 is provided to come into contact with 83 and to connect the spherical media 83 to the workpiece 6.

  Further, side end plates 85 are provided at both end portions of the electrode mounting shaft 84, and the electrode mounting shaft 84 is supported by one end portion of the side end plate 85, and at the other end portion of the side end plate 85. Then, the edge of the liquid tank 1 is hooked. The side end plate 24 is set to such a length that the barrel 81 is completely immersed in the cleaning water when the end of the side end plate 24 is hooked on the edge of the liquid tank 1.

  The spherical media 83 may have any structure as long as the conductivity is ensured. That is, it is not limited to a metal sphere, and for example, a ceramic sphere or a plastic sphere whose surface is treated with electroless plating may be used, and these may be used depending on conditions of an electronic component to be plated. What is necessary is just to select suitably.

  In the cleaning step shown in FIG. 9, desirably, the barrel plating apparatus 8 is rotated in the direction of arrow R1 in the cleaning water. Thereby, the whole barrel plating apparatus 8 including the workpiece 6 is cleaned.

  After the cleaning process, the barrel plating apparatus 8 is subjected to a plating process as shown in FIG. In the plating step shown in FIG. 10, the barrel 81 is rotated in the direction of the arrow R <b> 1 in the first plating solution 21. In the rotation operation, the conductive portion of the object to be plated 6 is electrically connected to the cathode 82 via the spherical medium 83, and the metal ions eluted from the anode 51 and the metal dissolved in the first plating solution 21. Ions adhere to the surface of the workpiece 6 and barrel plating is performed.

Thereafter, as shown in FIG. 11, the barrel plating apparatus 8 is pulled up from the first plating solution 21 as indicated by the arrow F <b> 2, and further moved to the cleaning process C and the plating process D (see FIGS. 2 to 7).
As described above, as the plating process described above is repeated, the metal ion concentration in the plating solution decreases and the plating quality decreases.

  Therefore, after the plating process is repeated several times, the metal ion concentration adjusting method according to the present invention is performed on the first plating solution 21 or the second plating solution 41. FIG. 12 shows a case where the metal ion concentration adjusting method is performed on the first plating solution 21. The adjustment mechanism of the metal ion concentration in this case is not different from that described with reference to FIG. Here, a case will be described in which the object to be plated 6 is a multilayer ceramic capacitor, and the metal ion concentration adjusting method according to the present invention is used for forming the terminal electrode.

  In the terminal electrode formation step, a Ni film is formed by barrel plating on the Cu base film already attached in the first plating step B, and the Sn film is barrel plated in the second plating step D thereon. Often formed by law. Among these, the adjustment of the metal ion concentration of the plating solution used for forming the Ni film will be described as follows with reference to FIG.

  In adjusting the metal ion concentration of the plating solution used for forming the Ni film, Ni is used as the constituent metal material of the anode 30. The cathode 40 is made of a metal material, for example, Pt, whose hydrogen overvoltage is lower than the metal material Ni constituting the anode 30, and a DC voltage is applied between the anode 30 and the cathode 40 from the DC power supply E 0.

Then, due to the cathode reaction that occurs at this time, the electron e ⁻ bonded to the metal ion Ni ²⁺ relatively decreases on the surface of the cathode 40, and as a result, the concentration of the metal ion Ni ²⁺ in the first plating solution 21. Will rise.

  In this way, the plating solution with the adjusted metal ion concentration is returned to the original plating process.

It is a figure which shows the metal ion concentration adjustment method and metal ion concentration adjustment apparatus which concern on this invention. It is a figure explaining the process in the 1st washing | cleaning process A in a two-layer plating process. It is a figure which shows the process after the process shown in FIG. FIG. 4 is a diagram showing a step after the step shown in FIG. 3. It is a figure which shows the process after the process shown in FIG. FIG. 6 is a diagram showing a step after the step shown in FIG. 5. It is a figure which shows the process after the process shown in FIG. It is a figure which shows the metal ion concentration adjustment method which concerns on this invention in a plating process. It is a figure which shows the washing | cleaning process in barrel plating. FIG. 10 is a diagram showing a step after the step shown in FIG. 9. It is a figure which shows the process after the process shown in FIG. It is a figure explaining the case where the metal ion concentration adjustment method which concerns on this invention is applied to the barrel-plating method shown in FIGS.

Explanation of symbols

10 Liquid bath 20 Plating solution 30 Anode 40 Cathode

Claims (9)

A method for adjusting a metal ion concentration in a plating solution,
Place the anode and cathode in the plating solution,
The cathode is made of a metal material whose hydrogen overvoltage is lower than the metal material constituting the anode,
DC power is applied between the anode and the cathode,
A method comprising the steps.   The method of claim 1, wherein the anode and the cathode are Pt, Pd, Ru, Rh, Au, Fe, Co, Ag, Ni, Cu, Cd, Sn, PB, Zn, Hg, and A method comprising a combination of those selected from the group of alloys. An apparatus that includes an anode, a cathode, and a DC power source, and adjusts the metal ion concentration in the plating solution,
The cathode is made of a metal material whose hydrogen overvoltage is lower than the metal material constituting the anode,
A DC voltage is applied from the DC power source between the anode and the cathode;
apparatus. 4. The apparatus of claim 3, wherein the anode and the cathode are Pt, Pd, Ru, Rh, Au, Fe, Co, Ag, Ni, Cu, Cd, Sn, PB, Zn, Hg, and Consisting of a group of its alloys,
apparatus. A plating method including a step of adjusting a metal ion concentration in a plating solution,
The step includes
An anode and a cathode are present in the plating solution;
The cathode is made of a metal material whose hydrogen overvoltage is lower than the metal material constituting the anode,
A DC voltage is applied from a DC power source between the anode and the cathode.
A plating method including a process.   6. The plating method according to claim 5, wherein the anode and the cathode are Pt, Pd, Ru, Rh, Au, Fe, Co, Ag, Ni, Cu, Cd, Sn, PB, Zn, Hg, And a plating method comprising a group selected from the group of the alloys.   The plating method according to claim 5 or 6, wherein the step is performed on a plating solution that has undergone at least one plating process.   It is a plating method described in Claim 7, Comprising: The said plating process process is a plating method performed after a water-washing process is performed.   The plating method according to claim 5, wherein the plating method is a barrel plating step.

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