JP4078915B2 - Electroless plating equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a basic technology for plating.
[0002]
[Prior art]
Plating is an indispensable technology in the manufacturing industry for automobile parts, electronic parts and the like.
Especially in electronic parts, there are various types such as electroless copper plating for forming a conductor layer on insulating resin, electrolytic copper plating for wiring formation, nickel and gold plating as surface treatment in mounting after wiring formation. Plating is used.
[0003]
Among them, for gold plating, depending on the mounting form, for example, in solder ball bonding, plating with a thickness of about 0.03 μm to 0.2 μm performed for the purpose of preventing corrosion of the underlying nickel, for example, wire bonding bonding There are plating for the gold-gold bonding used in the plating of about 0.2 μm to 0.5 μm or plating for the bump bonding of several μm.
[0004]
Currently, electroplating can be processed in either form. However, in future printed wiring boards that pass electric signals of higher frequency, the lead wire for electroplating has an effect as an antenna, and therefore there is a limit to the gold plating process by electroplating.
[0005]
Therefore, electroless gold plating is currently attracting attention as a process for printed wiring boards. However, in electroless gold plating, it is practically impossible to plate the thickness necessary for bump bonding.
Further, electroless gold plating has a small ionization tendency of gold, and a gold complex cannot exist stably in an aqueous solution. Therefore, cyan capable of reverse donation, which can stably form a complex with gold, is used. However, cyanide is highly toxic and dangerous.
[0006]
In order to avoid this, in recent years, a gold plating bath using a complexing agent different from cyan, such as sulfurous acid, has been developed. However, since these complexing agents have a lower ability to form a complex with gold than cyan, the plating solution is easily decomposed.
In particular, in the electrocatalytic gold plating in which a plating thickness of 0.2 μm or more is obtained in electroless plating, the plating solution is particularly decomposed because a reducing agent of gold ions is contained in the plating solution. Easy to use and not practical.
[0007]
In order for the complex to exist stably, it is desirable to construct a system that does not transfer electrons when the complex approaches another molecule.
However, since electroless plating is performed in a state where the surface of the plating treatment solution is in contact with air, it is performed in a system in which oxygen molecules having electrons are mixed in a highly reactive π orbit. In addition, since the plating solution is water with a high polarity, if a complex is not formed using a ligand having a high coordination ability such as cyan, an electron between the lone pair of water and the complex Then, gold is deposited at an inappropriate place other than the object to be plated.
In addition, research on electroless plating is still performed on the assumption that the solvent is water. Therefore, when a complexing agent other than cyan is used, the stability of the gold ion is deteriorated.
[0008]
On the other hand, when an inert gas atmosphere and a highly polar solvent such as water are not used, for example, triphenylphosphine, which is a ligand that cannot be stably complexed with gold in water, 1,2-bis (diphenylphosphino) ethane and a complex can be formed.
In general, when it is desired to form a complex that is not stable in the air or in water, it is common to use a dehydrated solvent as the solvent and an inert gas such as nitrogen or argon as the gas.
[0009]
Note that chloro (triphenylphosphine) gold (I) and bis [1,2-bis (diphenylphosphino) ethane] gold (I) chloride, which are gold complexes complexed with the ligands shown above, are It is already known as a known technique that a precursor can be easily obtained as a reagent and can be obtained with a simple synthesis of about one step in a high yield.
However, since ordinary electroless gold plating studies use water as a solvent, these complexes have hardly been studied.
[0010]
[Problems to be solved by the invention]
The present invention constructs an electroless plating process that can be stably performed in order to solve the above problems. That is, although development of the plating solution itself based on the above idea has not been made, it is an object to provide an electroless plating method and an electroless plating apparatus corresponding to a plating treatment solution based on the above idea that can be a future form. To do.
[0011]
[Means for Solving the Problems]
The present invention relates to an electroless plating method characterized in that electroless plating is performed using a plating treatment solution in which the solvent of the plating treatment solution is a liquid other than water and oxygen in the plating treatment solution is replaced with an inert gas. It is.
[0012]
Moreover, the present invention is the electroless plating method according to the above invention, wherein the inert gas is nitrogen or argon.
[0013]
The present invention is also the electroless plating method according to the above invention, wherein the electroless plating is electroless gold plating.
[0014]
Further, the present invention provides an electroless plating apparatus for electroless plating using a plating treatment solution in which the solvent of the plating treatment solution is a liquid other than water and oxygen in the plating treatment solution is replaced with an inert gas. The electroplating apparatus comprises at least a front tub, a plating bath, and a rear tub, and includes a transport system that horizontally transports an object to be plated whose width direction is horizontal.
[0015]
Further, the present invention is the electroless plating apparatus according to the above invention, wherein the front tub, between the plating baths, the rear tub is provided in a chamber constituted by a first chamber, a second chamber, and a third chamber, The lower end of the partition plate between the first chamber and the second chamber is positioned above the object to be plated in the bath liquid of the front tub, and the lower end of the partition plate between the second chamber and the third chamber is An electroless plating apparatus, which is located above an object to be plated in a bath liquid of a bathtub.
[0016]
Moreover, the present invention is the electroless plating apparatus according to the above invention, wherein the plating tank comprises a separation mechanism for separating water and a solvent other than water.
[0017]
Further, the present invention provides the electroless plating apparatus according to the above invention, wherein the electroless plating apparatus is for electroless gold plating, and the object to be plated is a reel-shaped flexible printed wiring board. It is a plating device.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
Here, the case of electroless nickel-electroless gold plating as a surface treatment in the production of a printed wiring board will be described.
First, as a method of substituting oxygen in the plating treatment solution with an inert gas, for example, it can be easily replaced by simply blowing an inert gas into the plating treatment solution. As the inert gas, nitrogen is particularly suitable because it is inexpensive. Further, argon is preferably used when there is a component that reacts with nitrogen.
[0019]
Note that when the plating bath is heated and the temperature of the plating solution is maintained, the amount of inert gas blown does not have to be so large, but since the pressure is reduced when the temperature is lowered after plating, the nitrogen gas must be reduced. It is necessary to increase the amount.
[0020]
FIG. 1 is a cross-sectional view schematically showing an embodiment of the electroless plating apparatus of the present invention.
The electroless plating apparatus shown in FIG. 1 is an electroless plating apparatus in which an object to be plated is a single wafer and is transported horizontally. As shown in FIG. 1, the electroless plating apparatus is an example configured with two front tubs (3A, 3B), one plating bath (5), and two rear tubs (3C, 3D). is there. The electroless plating apparatus includes a transport system including a transport roller (2) for horizontally transporting an object to be plated whose width direction is horizontal.
[0021]
The electroless plating apparatus is provided in a chamber constituted by a first chamber (30), a second chamber (40), and a third chamber (50). The second chamber (40) is in a state where the internal air is replaced with an inert gas. The first chamber and the third chamber have a buffer function between the second chamber (40) and the outside air.
The first chamber (30) and the second chamber (40) are partitioned by a partition plate (6B), and the second chamber (40) and the third chamber (50) are partitioned by a partition plate (6C). The first chamber (30) and the outside air are partitioned by a partition plate (6A), and the third chamber (50) and the outside air are partitioned by a partition plate (6D).
[0022]
In the second chamber (40), a plating tank (5), the latter half of the front tub (3B), and the first half of the rear tub (3C) are provided. In the first chamber (30), the first half of the front tub (3B) and the second half of the front tub (3A) are included. In the third chamber (50), the second half of the rear tub (3C) and the rear tub ( The first half of 3D) is provided.
The lower end of the partition plate (6B) between the first chamber (30) and the second chamber (40) is located above the object (1) to be plated in the bath liquid of the front tub (3B), and the second The lower end of the partition plate (6C) between the chamber (40) and the third chamber (50) is positioned above the object to be plated in the bath liquid of the rear tub (3C).
[0023]
The plating tank (5) is provided with an inert gas supply device (not shown), and the end of the inert gas supply pipe (10) connected to the inert gas supply device is placed in the plating solution. Has reached.
The plating solution in the plating tank (5) overflows and is circulated by the pump (4). Moreover, the bath liquid of a front bathtub (3A, 3B) and a rear bathtub (3C, 3D) is circulated similarly.
[0024]
The inert gas blows out into the plating solution and replaces oxygen in the plating solution.
Moreover, an inert gas blows off from the surface of a plating process liquid to a 2nd chamber (40), and replaces the air in a 2nd chamber (40) with an inert gas.
Therefore, oxygen does not exist in the plating processing solution, and the surface of the plating processing solution is not in contact with air. In addition, while the object to be plated (1) is transported by the transport roller (2), it is not exposed to air in the second chamber (40).
[0025]
For example, in a pre-treatment of gold plating, generally a nickel plating treatment, in a washing step bath (the pre-tubs (3A, 3B) in FIG. 1), the object to be plated (1) is immersed in a bath solution. Thus, it passes through partition plates (6A, 6B) that separate the atmosphere.
[0026]
The electroless plating apparatus shown in FIG. 2 is an example of an electroless plating apparatus in which the object to be plated is a reel product and is transported horizontally. For example, in the pretreatment of gold plating, generally after the nickel plating treatment, in the washing step bath (the pretubs (3A, 3B) in FIG. 2), the object to be plated (9) is immersed in the bath liquid. Thus, it passes through partition plates (6A, 6B) that separate the atmosphere.
[0027]
A gas flow indicator (8) is provided for easily observing that the inside of the chamber once set to an inert gas atmosphere maintains the pressurized state. As shown in FIG. 3, liquid paraffin (11) is put inside a hollow glass container.
The inlet (21A) of the gas flow indicator (8) is connected to, for example, the second chamber (40), an inert gas is allowed to flow from the second chamber (40), and the air is discharged from the outlet (21B) to the outside air. . The pressure difference from the outside air is set by adjusting the amount of liquid paraffin (11).
Although not shown, if a glass ball is provided at the tip of the gas flow indicator and used as a check valve, it can prevent the backflow of air in addition to the role as an indicator.
[0028]
For example, in the case of gold plating, electroless gold plating in which oxygen in the plating treatment solution can be replaced with an inert gas and the plating treatment solution can contain a plating treatment solution using a solvent other than water. The material for the bathtub for the apparatus needs to be insoluble in an organic solvent.
For example, when isopropyl alcohol, which is an organic solvent, is used as a solvent for the plating treatment solution, a polypropylene bath used in a normal plating apparatus may be used.
[0029]
Further, since the plating solution is an organic solvent, it is necessary to eliminate the introduction of water. Therefore, the pretreatment of gold plating, generally the nickel plating treatment, the bath solution in the cleaning process also serves as a gold plating pre-dip, and the same solution as the gold plating solution or a water-soluble organic solvent is used as the bath solution. It is good to use for. Preferably, washing is performed using a water-soluble organic solvent in the two-stage bath in the gold plating tank and the same solvent as the gold plating solution in the first-stage bath.
[0030]
Furthermore, when the plating solution is made of a solvent insoluble in water, an organic solvent that can be separated into two layers from water should be used so that it can cope with the case where water is mixed into the plating solution. This is because separation is easy even when water is mixed in the plating solution. For example, in the case where the solvent is a liquid having a specific gravity greater than that of water, such as chloroform, as shown in FIG. 4, the liquid is once overflowed from the bath and separated after being separated by an elongated cylindrical separation device (12). What is necessary is just to remove the water (13) which collects in the.
On the other hand, when the solvent having a specific gravity lower than that of water such as benzene is the solvent of the gold plating solution, as shown in FIG. 5, the bottom of the plating treatment tank is inclined, and after the liquid is drained from the bottom, an elongated cylindrical shape is formed. The separation device (12) may be provided to remove the water (15) accumulated at the bottom.
[0031]
【Example】
Hereinafter, the present invention will be described in detail with specific examples.
<Example 1>
As processing tanks, tanks each having a volume of 10 liters were used. The size of the tank is 50 cm in the conveyance direction × 10 cm in depth × 20 cm in depth. The flow was as shown in FIG. 6 for the plating tank and as shown in FIG. 7 for the bathtub.
As shown in FIG. 8, the lid can be opened and closed from the upper side, and the lid is kept confidential by rubber packing.
First, it was confirmed that a printed circuit board can be plated with a normal electroless gold plating solution using this apparatus. The thickness was 0.05 μm after treatment at 90 ° C. for 15 minutes.
[0032]
Next, as a confirmation of whether or not a gold plating solution using a liquid other than water, which will be developed in the future, can be used, it was confirmed that the inside of the plating treatment solution could be replaced with nitrogen by nitrogen bubbling.
In the method, xylene as a solvent was added to the previous treatment tank, and after bubbling with nitrogen for 6 hours, 500 ml of iron pentacarbonyl (manufactured by Aldrich) was added and the change with time was captured. When every absorption by the stretching vibration of the carbonyl hours was examined by IR, about 2000 cm ^-1 derived from [nu _CO iron pentacarbonyl as the raw material, only absorption of 1900 cm ^-1 is observed, decomposition products obtained Not confirmed.
[0033]
【The invention's effect】
In the present invention, the solvent of the plating treatment liquid is a liquid other than water, and electroless plating is performed using a plating treatment liquid in which oxygen in the plating treatment liquid is replaced with an inert gas. A complex can be prepared using a ligand such as triphenylphosphine and diphenylphosphinoethane, which has a lower coordination ability than cyan. Therefore, it is possible to handle a compound that is less stable than the conventional one, and it is an electroless plating that can be plated under milder conditions than the current plating conditions.
Also, thick gold plating of several μm or more, which is not practical at present, becomes possible. Furthermore, by developing a process for plating in an organic solvent, it is possible to construct a milder process for other metals.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing one embodiment of an electroless plating apparatus of the present invention.
FIG. 2 is an example of an electroless plating apparatus in which the object to be plated is a reel product and is transported horizontally.
FIG. 3 is an explanatory diagram of a gas flow indicator.
FIG. 4 is an explanatory diagram of a plating tank and a separation device when the solvent is a liquid having a specific gravity greater than that of water.
FIG. 5 is an explanatory diagram of a plating tank and a separation device when the solvent is a liquid having a specific gravity smaller than that of water.
6 is an explanatory diagram of a flow of a plating tank in Example 1. FIG.
FIG. 7 is an explanatory diagram of a bathtub flow in the first embodiment.
8 is an explanatory diagram of a lid of a plating tank in Example 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 9 ... To-be-plated object 2 ... Conveyance roller 3A, 3B ... Front bathtub 3C, 3D ... Rear bathtub 4 ... Pump 5 ... Plating tank 6A, 6B, 6C, 6D ... Partition plate 7 which divides a chamber ... Piping 8 ... Gas Flow indicator 10 ... Inert gas supply pipe 11 ... Liquid paraffin 12 ... Elongated cylindrical separator 13 ... Water accumulated on the top after separation 14 ... Water accumulated on the bottom 15 ... Valve 16 ... Storage tank 17 ... Rubber packing 18 ... Screw 19 ... Process tank lid 20 ... Process tank top 21A ... Inlet 21B ... Outlet 30 ... First chamber 40 ... Second chamber 50 ... Third chamber

Claims (6)

In the electroless plating apparatus for electroless plating using a plating treatment liquid in which the solvent of the plating treatment liquid is a liquid other than water and oxygen in the plating treatment liquid is replaced with an inert gas, the electroless plating apparatus includes at least It consists of a first front tub, a second front tub, a plating bath, a first rear tub, a second rear tub,
The electroless plating apparatus is provided in a chamber composed of a first chamber, a second chamber, and a third chamber,
The first half of the first tub and the first half of the second tub are provided in the first chamber,
The second half of the second front tub, the plating layer, and the first half of the first rear tub are provided in the second chamber,
The second half of the first rear tub and the first half of the second rear tub are provided in the third chamber,
The chamber includes a plurality of partition plates,
The first partition plate that partitions the first chamber and the second chamber has a lower end located in the solution of the second front tub and located above the object to be plated,
An electroless plating apparatus characterized in that the second partition plate that partitions the second chamber and the third chamber has a lower end portion located in the solution of the first rear bathtub and above the object to be plated.   Furthermore, the lower end of the third partition plate that partitions the first chamber and the outside air is in the solution of the first front tub and located above the object to be plated,
  The electroless plating apparatus according to claim 1, wherein a lower end portion of a fourth partition plate that partitions the third chamber and the outside air is located in the solution of the second rear bathtub and above the object to be plated. 3. The electroless plating according to claim 1, further comprising an inert gas supply device, wherein an end portion of the inert gas supply pipe connected to the inert gas supply device reaches the plating solution. Equipment . The electroless plating apparatus according to any one of claims 1 to 3, wherein the plating tank includes a separation mechanism that separates water and a solvent other than water.   The electroless plating apparatus according to any one of claims 1 to 3, further comprising a transport system for horizontally transporting an object to be plated whose width direction is horizontal. The electroless plating apparatus according to any one of claims 1 to 4, wherein the electroless plating apparatus is for electroless gold plating, and the object to be plated is a reel-shaped flexible printed wiring board.

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