JP2004068029A - Electroless plating method and electroless plating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless plating method which makes a complex stably exist in a plating liquid, and plates in a mild condition, and to provide an electroless plating apparatus. <P>SOLUTION: The electroless plating method is characterized by using the plating liquid which employs a liquid except water as the solvent and substitutes oxygen in the plating liquid for an inert gas. The electroless plating apparatus for electroless plating with the use of the above plating liquid, comprises at least pretreatment tanks 3A and 3B, a plating tank 5 and post-treatment tanks 3C and 3D, and has a transportation system for transporting an article to be plated, which is held with a width direction horizontal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a basic technology of plating.
[0002]
[Prior art]
Plating is currently an indispensable technology in the manufacturing industry of automobile parts, electronic parts and the like.
In particular, in electronic components, various kinds of electroless copper plating for forming a conductor layer on an insulating resin, electrolytic copper plating for forming wiring, nickel and gold plating as surface treatment in mounting after forming wiring, etc. Plating is used.
[0003]
Among them, with respect to gold plating, depending on the mounting mode, for example, in solder ball bonding, plating is performed with a thickness of about 0.03 μm to 0.2 μm for the purpose of preventing corrosion of nickel under the base, for example, wire bonding bonding For example, plating with a thickness of about 0.2 μm to 0.5 μm for gold-gold bonding, or plating with a thickness of several μm for bump bonding may be used.
[0004]
Currently, electroplating can be processed in either form. However, in the future printed wiring boards that allow higher frequency electric signals to pass through, the lead wire for electroplating has an effect as an antenna, so there is a limit to gold plating in electroplating.
[0005]
Therefore, electroless gold plating has attracted attention as a process for printed wiring boards. However, in electroless gold plating, it is practically impossible to perform plating by a thickness necessary for bump bonding.
In addition, electroless gold plating has a small tendency to ionize gold, and thus cannot stably exist a gold complex in an aqueous solution. Therefore, reverse-donable cyanide that 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, gold plating baths using a cyan-free complexing agent different from cyanide such as sulfurous acid have been developed. However, since these complexing agents have a lower ability to form a complex with gold than cyanide, the plating solution is easily decomposed.
In particular, in electroless plating, in the case of autocatalytic gold plating in which a plating thickness of 0.2 μm or more is obtained, since a reducing agent for gold ions is contained in the plating solution, the plating solution is particularly decomposed. Easy and impractical.
[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, electroless plating is performed in a state in which the surface of a plating solution is in contact with air, and is therefore performed in a system in which oxygen molecules having electrons in highly reactive π orbitals are mixed. Also, since the solvent for the plating solution is water having a high polarity, unless a complex is formed using a ligand having a high coordinating ability such as cyanide, the electron between the lone pair of water and the complex is formed. And gold is deposited in an inappropriate place other than the object to be plated.
Also, research on electroless plating has been performed on the assumption that the solvent is still water. Therefore, when a complexing agent other than cyan is used, the stability of gold ions is deteriorated.
[0008]
On the other hand, in an atmosphere of an inert gas and when the solvent does not use a highly polar solvent such as water, for example, triphenylphosphine, which is a ligand that cannot form a complex with gold stably in water, And complex formation with 1,2-bis (diphenylphosphino) ethane.
When it is desired to form a complex that is not stable in the atmosphere or in water, it is common to use a solvent that has been subjected to a dehydration treatment and to use an inert gas such as nitrogen or argon as a 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 described above, are It is already known as a known technique that a precursor can be easily obtained as a reagent and can be obtained in a simple synthesis of about one step with a high yield.
However, in studies on ordinary electroless gold plating, since water is used as a solvent, their complexes are hardly studied.
[0010]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problem by constructing a stable electroless plating process. That is, although the development of the plating solution itself based on the above idea has not been made, it is an object of the present invention to provide an electroless plating method and an electroless plating apparatus corresponding to a plating solution based on the above idea, which can be a future form. I do.
[0011]
[Means for Solving the Problems]
The present invention provides an electroless plating method, wherein a solvent of a plating solution is a liquid other than water, and electroless plating is performed using a plating solution obtained by replacing oxygen in the plating solution with an inert gas. It is.
[0012]
Further, the present invention is the electroless plating method according to the above invention, wherein the inert gas is nitrogen or argon.
[0013]
Further, the present invention is 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 solution in which the solvent of the plating solution is a liquid other than water and oxygen in the plating solution is replaced with an inert gas. The electroplating apparatus is an electroless plating apparatus including at least a pre-bath, a plating bath, and a post-bath, and a transport system for horizontally transporting an object to be plated whose width direction is horizontal.
[0015]
The present invention also provides the electroless plating apparatus according to the present invention, wherein the pre-bath, between the plating baths, and the post-bath are provided in a chamber including a first chamber, a second chamber, and a third chamber, The lower end of the partition between the first chamber and the second chamber is located above the object to be plated in the bath solution of the front tub, and the lower end of the partition between the second and third chambers is located at the rear. An electroless plating apparatus characterized by being located above an object to be plated in a bath liquid of a bathtub.
[0016]
Further, the present invention is the electroless plating apparatus according to the above invention, wherein the plating tank is provided with a separation mechanism for separating water and a solvent other than water.
[0017]
The present invention also 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 flexible printed wiring board in a reel form. It is a plating device.
[0018]
BEST MODE FOR CARRYING OUT 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 manufacture of a printed wiring board will be described.
First, as a method for replacing oxygen in the plating solution with an inert gas, for example, the oxygen gas can be easily replaced by simply blowing an inert gas into the plating solution. As an inert gas, nitrogen is particularly suitable because it is inexpensive. When there is a component that reacts with nitrogen, it is preferable to use argon.
[0019]
In addition, when heating the plating bath and maintaining the temperature of the plating solution, the amount of the inert gas to be blown is not so large, but when the temperature is lowered after plating, the pressure is reduced. It is necessary to increase the amount.
[0020]
FIG. 1 is a sectional view schematically showing one 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 horizontally conveyed. As shown in FIG. 1, the electroless plating apparatus is an example configured with two front baths (3A, 3B), one plating bath (5), and two rear baths (3C, 3D). is there. The electroless plating apparatus is provided with 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 including a first chamber (30), a second chamber (40), and a third chamber (50). The second chamber (40) is in a state where the air inside has been 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) is separated from the outside air by a partition plate (6A), and the third chamber (50) is separated from the outside air by a partition plate (6D).
[0022]
In the second chamber (40), a plating bath (5), a second half of the front bath (3B), and a first half of the rear bath (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 provided, and 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 to be plated (1) in the bath solution of the front tub (3B). The lower end of the partition plate (6C) between the chamber (40) and the third chamber (50) is located above the object to be plated in the bath liquid of the rear bathtub (3C).
[0023]
An inert gas supply device (not shown) is provided in the plating tank (5), and an end of an 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). Also, the bath liquid in the front bath (3A, 3B) and the rear bath (3C, 3D) is circulated in the same manner.
[0024]
The inert gas is blown into the plating solution to replace oxygen in the plating solution. The inert gas is blown from the surface of the plating solution to the second chamber (40), and the air in the second chamber (40) is replaced with the inert gas.
Therefore, oxygen does not exist in the plating solution, and the surface of the plating solution does not come into contact with air. Also, while the object to be plated (1) is being conveyed by the conveying roller (2), the second chamber (40) does not come into contact with air.
[0025]
For example, a state in which the object to be plated (1) is immersed in a bath solution in a bath (pre-baths (3A, 3B) in FIG. 1) in a cleaning step after a pretreatment of gold plating, generally a nickel plating treatment. Then, it passes through a partition plate (6A, 6B) which separates the atmosphere.
[0026]
The electroless plating apparatus shown in FIG. 2 is an example of an electroless plating apparatus in which an object to be plated is a reel product and is horizontally conveyed. For example, in a bath (pre-bath (3A, 3B) in FIG. 2) of a cleaning step after pre-treatment of gold plating, generally nickel plating, a state in which an object to be plated (9) is immersed in a bath solution. Then, it passes through a partition plate (6A, 6B) which separates the atmosphere.
[0027]
A gas flow indicator (8) is provided for easily observing that the inside of the chamber once in the atmosphere of the inert gas is maintained in the pressurized state. As shown in FIG. 3, a liquid paraffin (11) is placed inside a hollow glass container.
The inflow port (21A) of the gas flow indicator (8) is connected to, for example, the second chamber (40), the inert gas flows from the second chamber (40), and is discharged from the outflow port (21B) to the outside air. . By adjusting the amount of liquid paraffin (11), a pressure difference with the outside air is set.
Although not shown, when a glass ball is provided at the tip of the gas flow indicator and is used as a check valve, it is possible to prevent the backflow of air in addition to the role of the indicator.
[0028]
For example, in the case of gold plating, it is possible to replace oxygen in the plating solution with an inert gas, and the plating solution can contain a plating solution using a solvent other than water. The material of the bath for the device must be insoluble in organic solvents.
When isopropyl alcohol, which is an organic solvent, is used as the solvent for the plating solution, for example, a polypropylene bath used in a usual plating apparatus may be used.
[0029]
Further, in order for the plating solution to be an organic solvent, it is necessary to eliminate the introduction of water. Therefore, the bath solution in the cleaning step after the pretreatment of gold plating, generally after the nickel plating process, also serves as the gold plating pre-dip, and uses the same solvent as the gold plating solution or a water-soluble organic solvent. It is good to use for. Preferably, washing is performed using a water-soluble organic solvent in the bathtub two stages before the gold plating bath and the same solvent as the gold plating solution in the bath bath before the gold plating bath.
[0030]
Further, when the plating solution is composed of a solvent that is insoluble in water, an organic solvent that can be separated from water by two layers is preferably used so as to cope with a 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, when the solvent is a liquid such as chloroform having a higher specific gravity than water, as shown in FIG. 4, the liquid is once overflowed from a bath, and after the liquid is separated by an elongated cylindrical separation device (12), the liquid is separated from the liquid. What is necessary is just to remove the water (13) which accumulates in the water.
On the other hand, when the solvent having a lower specific gravity than water such as benzene is the solvent of the gold plating solution, as shown in FIG. 5, a slope is provided at the bottom of the plating tank, and after removing the solution from the bottom, an elongated cylindrical shape is formed. The separation device (12) may be provided to remove the water (15) collected at the bottom.
[0031]
【Example】
Hereinafter, a specific example will be described in detail.
<Example 1>
As the treatment tanks, tanks each having a volume of 10 liters were used. The size of the tank is 50 cm in the transport direction × 10 cm in depth × 20 cm in depth. The flow was as shown in FIG. 6 for the plating bath and the flow as shown in FIG. 7 for the bathtub.
As shown in FIG. 8, the lid was of a type that could be opened and closed from above, and the lid was kept confidential by rubber packing.
First, it was confirmed that a printed circuit board could be plated with a normal electroless gold plating solution using this apparatus. The thickness was 0.05 μm at 90 ° C. for 15 minutes.
[0032]
Next, it was confirmed that the inside of the plating solution could be replaced with nitrogen by nitrogen bubbling to confirm whether or not it could be used for a gold plating solution using a liquid other than water as a solvent, which would be developed in the future.
In the method, xylene as a solvent was added to the treatment tank, and nitrogen bubbling was performed for 6 hours. Then, 500 ml of iron pentacarbonyl (manufactured by Aldrich) was charged, 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, since the solvent of the plating solution is a liquid other than water, and the electroless plating is performed using a plating solution obtained by replacing oxygen in the plating solution with an inert gas, a ligand other than cyan, for example, A complex can be prepared using a ligand such as triphenylphosphine or diphenylphosphinoethane, which has a weaker coordination ability than cyanide. Therefore, it is possible to handle a compound having a lower stability than in the past, and to achieve electroless plating that can be plated under milder conditions than the current plating conditions.
Further, gold plating with a thickness of several μm or more, which is impractical at present, becomes possible. Further, by developing a process for plating in an organic solvent, a milder process can be constructed for other metals.
[Brief description of the drawings]
FIG. 1 is a 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 a workpiece is a reel product and is horizontally transported.
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 a solvent is a liquid having a specific gravity larger than that of water.
FIG. 5 is an explanatory diagram of a plating tank and a separation device when a solvent is a liquid having a specific gravity smaller than that of water.
FIG. 6 is an explanatory diagram of a flow of a plating tank in Example 1.
FIG. 7 is an explanatory diagram of a flow of a bathtub in the first embodiment.
FIG. 8 is an explanatory view of a lid of a plating tank in Example 1.
[Explanation of symbols]
1, 9: Plated object 2: Transport rollers 3A, 3B: Front bath 3C, 3D: Rear bath 4: Pump 5: Plating baths 6A, 6B, 6C, 6D: Partition plate for separating chambers 7: Piping 8: Gas Flow indicator 10 ... Inert gas supply pipe 11 ... Liquid paraffin 12 ... Elongated tubular separating device 13 ... Water collected at the top after being separated 14 ... Water collected at the bottom 15 ... Valve 16 ... Storage tank 17 ... Rubber packing 18 ... Screw 19 ... Lid of processing tank 20 ... Upper lid 21A of processing tank ... Inlet 21B ... Outlet 30 ... First chamber 40 ... Second chamber 50 ... Third chamber

Claims (7)

An electroless plating method, wherein a solvent of the plating solution is a liquid other than water, and electroless plating is performed using a plating solution obtained by replacing oxygen in the plating solution with an inert gas. 2. The electroless plating method according to claim 1, wherein the inert gas is nitrogen or argon. The electroless plating method according to claim 1, wherein the electroless plating is electroless gold plating. The solvent of the plating solution is a liquid other than water, and in an electroless plating apparatus for electroless plating using a plating solution obtained by replacing oxygen in the plating solution with an inert gas, the electroless plating apparatus is at least An electroless plating apparatus comprising a front bath, a plating bath, and a rear bath, and having a transport system for horizontally transporting an object to be plated whose width direction is horizontal. The front bath, between the plating baths, the rear bath, the first chamber, the second chamber, is provided in the chamber configured by the third chamber, the lower end of the partition plate between the first chamber and the second chamber. , That the lower end of the partition plate between the second chamber and the third chamber is located above the object to be plated in the bath solution of the front tub. The electroless plating apparatus according to claim 4, wherein The electroless plating apparatus according to claim 4, wherein the plating treatment tank includes a separation mechanism that separates water and a solvent other than water. 7. The electroless plating apparatus according to claim 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. apparatus.

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