JP5494787B2 - Electroless plating apparatus and oxygen supply method to electroless plating solution - Google Patents

Description

  The present invention relates to an electroless plating apparatus and a method for supplying oxygen to an electroless plating solution. In particular, the present invention relates to an electroless plating apparatus for electroless copper plating and a method for supplying oxygen to an electroless plating solution.

  The most frequently used method for interlayer connection of multilayer printed wiring boards is the plated through hole method. The through-hole generally penetrates through the entire thickness of the printed wiring board, and some having a large number of layers use via holes that connect some layers. The plated through-hole method is a method of conducting a hole in a hole by making a hole in a wiring board with a drill in order to make a through-hole connection and applying electroless copper plating to the hole. The connection of via holes is also the same, and this is a method of making the holes conductive by making holes in the wiring board using a laser or the like and applying electroless copper plating to the holes. Electroless copper plating is also used for forming a wiring pattern in the full additive method and forming a conductive layer in the semi-additive method.

  As the electroless copper plating solution used for the production of the printed wiring board as described above, an autocatalytic electroless copper plating solution is usually used. In addition, the electroless copper plating solution contains a divalent copper salt such as copper sulfate, a complexing agent of divalent copper ions, a reducing agent such as formaldehyde and a pH adjusting agent such as sodium hydroxide as main components. In general, it further contains an additive for increasing the stability of the electroless copper plating solution, an additive for improving the physical properties of the plating film, and the like.

  However, such an electroless copper plating solution is still not sufficiently stable. Thus, attempts have been made to improve stability by dissolving oxygen in the electroless copper plating solution.

  For example, Patent Document 1 discloses supplying a gas containing oxygen such as air to an electroless copper plating solution. Patent Document 2 proposes a method of adjusting the dissolved oxygen concentration in the electroless copper plating solution to a specific concentration. Further, Patent Document 3 discloses reaction by-products such as sulfates and formates that gradually accumulate in the electroless copper plating solution as the copper ion supply source, complexing agent, or reducing agent in the electroless copper plating solution is consumed. A method for increasing the dissolved oxygen concentration of the electroless copper plating solution as the product concentration increases is described.

  Furthermore, in Patent Document 4, a fine bubble generation source that is provided on the entire bottom of the electroless copper plating tank and generates fine bubbles having a diameter of 5 to 100 μm is provided at a predetermined distance above the fine bubble generation source. A method of adjusting the dissolved oxygen concentration in an electroless copper plating solution using an electroless copper plating apparatus including a large bubble generating source that generates large bubbles having a diameter of 1 to 3 cm is disclosed.

  And in patent document 5, while supplying the bubble flow which consists of many bubbles from the lower part in this plating tank with respect to the printed circuit board suspended and arranged in the electroless copper plating tank, the said electroless copper plating The plating solution is circulated to the external circulation flow path by the overflow weir provided in the tank, air is blown into the return circulation flow path returning from the external circulation flow path to the plating tank, and the bubbles are pulverized using a pipe mixer. A method for supplying oxygen to an electroless plating solution is described, wherein fine air bubbles are generated to increase the amount of dissolved oxygen in the plating solution in the electroless plating tank.

U.S. Pat. No. 2,938,805 U.S. Pat. No. 4,152,467 Japanese Patent No. 2768408 Japanese Patent No. 2978780 Japanese Patent No. 3091583

  However, in the above conventional electroless copper plating apparatus and electroless copper plating method, the stability of the electroless copper plating solution has not been sufficiently improved in practice. According to the study by the present inventors, a precipitate is generated in the plating solution while the electroless copper plating is applied to the object to be plated, and the precipitate adheres to the object to be plated or the plating tank, or the surface of the precipitate. Thus, it has been found that a plating reaction, that is, a reduction reaction of copper ions by a reducing agent occurs, and problems such as decomposition of the plating solution may occur. Moreover, in the method described in Patent Document 4 described above, since a porous board having extremely fine holes is used as a fine bubble generation source, problems such as easy clogging and fine bubbles having a diameter of 5 to 100 μm are caused. There is a problem that the apparatus becomes large because the amount of ventilation for generating is very large.

  The present invention has been made in view of the above circumstances, and can suppress the formation of precipitates in the electroless plating solution over a long period of time, and the electroless plating solution can have practically sufficient stability. An object is to provide a plating apparatus and a method for supplying oxygen to an electroless plating solution.

  The cause of destabilizing the electroless copper plating solution is presumed to be the production of monovalent copper ions. Since the monovalent copper ions form a copper precipitate due to cuprous oxide or a disproportionation reaction, the life of the electroless copper plating solution is reduced. On the other hand, the dissolved oxygen in the electroless copper plating solution functions to oxidize the monovalent copper ions to form stable divalent copper ions, so that precipitation occurs when oxygen is dissolved in the electroless copper plating solution. It is possible to suppress the formation of objects. Therefore, it is considered that by efficiently supplying oxygen to the electroless copper plating solution, the formation of precipitates can be suppressed for a long period of time, and the electroless copper plating solution can be sufficiently stabilized practically. In addition, hereinafter, the description that the electroless copper plating solution is stable includes the meaning that the generation of precipitates in the electroless copper plating solution is small.

  As a result of intensive studies based on such estimation, the present inventors have reached the present invention shown below.

  The electroless plating apparatus of the present invention comprises an electroless plating bath for storing an electroless plating solution and a circulating flow connected to the electroless plating bath and circulating the electroless plating solution between the electroless plating bath. An external circulation means having a path, wherein the external circulation means mixes a gas containing oxygen into the electroless plating solution and pressurizes the electroless plating solution in the circulation flow path to circulate the gas. A gas mixing means for dissolving in the electroless plating solution, and a pressure reducing means for reducing the pressure of the electroless plating solution in which the gas is dissolved to generate fine bubbles.

  According to such an electroless plating apparatus, the formation of precipitates in the electroless plating solution can be suppressed over a long period of time, and the electroless plating solution can be sufficiently stabilized practically.

  The electroless plating apparatus of the present invention can make the diameter of bubbles formed of a gas containing oxygen very small by making the above-described configuration. Thereby, the residence time of bubbles in the electroless plating solution can be increased, and the area of the gas-liquid interface between the bubbles and the electroless plating solution can also be increased. For this reason, if the electroless plating apparatus of the present invention is used, oxygen can be efficiently supplied to the electroless plating solution.

  In addition, the electroless plating apparatus of the present invention includes an electroless plating bath for storing an electroless plating solution, and a circulating flow connected to the electroless plating bath and circulating the electroless plating solution between the electroless plating baths. External circulation means having a path, and the external circulation means mixes oxygen-containing gas into the electroless plating solution to form bubbles in the circulation flow path and pulverizes the bubbles to generate fine bubbles. You may have a fine bubble generation means to make.

  Also with such an electroless plating apparatus, the formation of precipitates in the electroless plating solution can be suppressed over a long period of time, and the electroless plating solution can be sufficiently stabilized practically.

  The electroless plating solution used in the electroless plating apparatus of the present invention may be an electroless copper plating solution containing copper ions, a copper ion complexing agent, a reducing agent, and a pH adjusting agent.

  Usually, when an object to be plated such as a printed wiring board is immersed in an electroless copper plating solution, hydrogen is generated by the deposition reaction of the electroless copper plating, and the dissolved oxygen concentration of the electroless copper plating solution is lowered. In particular, when the area of the object to be plated is increased, a large amount of hydrogen is generated by the above-described precipitation reaction, and the dissolved oxygen concentration of the plating solution is rapidly decreased. Furthermore, in an electroless copper plating solution containing a large amount of reaction byproducts such as formate and sulfate accompanying the deposition reaction of electroless copper plating, it is difficult for dissolved oxygen to be present in the solution.

  However, since the electroless plating apparatus of the present invention can efficiently supply oxygen to the electroless copper plating solution even in the above-described situation, the rapid decrease in dissolved oxygen concentration accompanying the precipitation reaction is also suppressed. be able to. Therefore, when the electroless plating apparatus of the present invention is used, even when electroless copper plating is performed on an object to be plated having a large area, it can be operated in a state in which the stability of the electroless copper plating solution is ensured over a long period of time. . Furthermore, according to such an electroless plating apparatus, since the mixing ratio of gas can be reduced as compared with the case where fine bubbles are generated by ventilation, the load on the apparatus used for mixing gas can be reduced. .

  In addition, according to the electroless plating apparatus of the present invention, since the stability of the electroless copper plating solution can be improved, the area of the object to be plated immersed in the electroless copper plating solution can be increased. Improvement of work efficiency can be expected. Furthermore, when the amount of inorganic cyanide such as sodium cyanide, which has been used as a stabilizer for electroless copper plating solutions and is highly dangerous for work safety, is reduced, or when inorganic cyanide is not included Also has the effect of ensuring the stability of the electroless copper plating solution.

  The present invention provides a method for supplying oxygen to an electroless plating solution using the above-described electroless plating apparatus.

  The oxygen supply method of the present invention is an oxygen supply method to an electroless plating solution, and an extraction step of extracting a part of the electroless plating solution from an electroless plating tank storing the electroless plating solution, In addition, a gas containing oxygen is mixed in the electroless plating solution and the electroless plating solution is pressurized to dissolve the gas in the electroless plating solution, and the electroless plating solution in which the gas is dissolved is decompressed. A pressure reducing step for generating fine bubbles and a feeding step for returning the electroless plating solution to the electroless plating tank together with the fine bubbles are provided.

  Further, the oxygen supply method of the present invention is an oxygen supply method to the electroless plating solution, wherein an extraction step of extracting a part of the electroless plating solution from the electroless plating tank storing the electroless plating solution, A gas pulverization process in which oxygen-containing gas is mixed into the discharged electroless plating solution to form bubbles and pulverize the bubbles to generate fine bubbles, and the electroless plating solution together with the fine bubbles to the electroless plating tank And a feeding step for returning.

  The oxygen supply method to the electroless plating solution having such a configuration can suppress a decrease in the dissolved oxygen concentration in the electroless plating solution, and can stabilize the electroless plating solution such as an electroless copper plating solution over a long period of time. It is possible to drive in a state where the safety is secured.

  The electroless plating solution used in the oxygen supply method of the present invention may be an electroless copper plating solution containing copper ions, a copper ion complexing agent, a reducing agent, and a pH adjusting agent.

  The oxygen supply method to the electroless copper plating solution having such a configuration can suppress a rapid decrease in the dissolved oxygen concentration accompanying the electroless copper plating reaction, and can improve the stability of the electroless copper plating solution over a long period of time. It is possible to drive in a secured state.

  In the method for supplying oxygen to the electroless plating apparatus and the electroless plating solution of the present invention, the volume flow rate mixed in the electroless plating solution containing oxygen is such that the electroless plating solution is externally circulated from the electroless plating bath. It is preferable that the volume flow rate is 0.01 to 0.5 times the volume flow rate. By setting the volume flow rate mixed in the electroless plating solution containing oxygen in such a range, fine bubbles can be stably supplied.

  Moreover, in the said electroless-plating tank, it is preferable that the mixing rate of the gas containing the oxygen in an electroless-plating liquid is 0.001-10 volume%. By setting the mixing ratio of the gas containing oxygen in the electroless plating solution in such a range, the dissolved oxygen concentration necessary for ensuring the stability of the electroless plating solution can be maintained.

  Furthermore, in the electroless plating apparatus and the oxygen supply method using the same, the gas containing oxygen is preferably a gas at 5 to 90 ° C. and contains 10% by volume or more of oxygen. By using such a gas, it becomes even easier to maintain the dissolved oxygen concentration necessary to ensure the stability of an electroless plating solution such as an electroless copper plating solution.

  According to the present invention, the formation of precipitates in the electroless plating solution can be suppressed over a long period of time, and the electroless plating solution can have practically sufficient stability. An oxygen supply method can be provided.

It is a schematic diagram showing 1st Embodiment which concerns on the electroless-plating apparatus of this invention. It is a schematic diagram showing 2nd Embodiment which concerns on the electroless-plating apparatus of this invention.

  Hereinafter, a preferred embodiment when an electroless copper plating solution is used as the electroless plating solution will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  FIG. 1 is a schematic view showing a first embodiment according to the electroless plating apparatus of the present invention. An electroless plating apparatus 100 shown in FIG. 1 is connected to an electroless plating tank (hereinafter simply referred to as “plating tank” in the embodiment) 1 for storing an electroless copper plating solution 30, and the plating tank 1. And an external circulation means 2 having a circulation passage 21 for circulating an electroless copper plating solution (hereinafter simply referred to as “plating solution”) 30 between the tank 1 and the tank 1. Further, the external circulation means 2 has a pump 4 and a pressure reducing valve 8 in the circulation flow path 21.

  The plating tank 1 is, for example, a bottomed container having an open top, and the plating solution 30 is filled therein. An object 18 to be plated is immersed in the plating tank 1 and electroless copper plating is applied to the surface thereof. An external circulation means 2 is connected to the side surface of the plating tank 1.

  In the circulation channel 21 of the external circulation means 2, a pump 4, a levitation separator 6, a liquid flow meter 7, and a pressure reducing valve 8 are arranged in that order along the circulation direction D <b> 1 of the plating solution 30. The levitating / separating device 6 separates a gas not dissolved in the plating solution 30 and has a vent hole 6a. Undissolved gas is discharged from the vent hole 6a to the outside of the apparatus. The electroless plating apparatus 100 may not include the levitation separation apparatus 6 depending on the flow rate of the gas to be dissolved. The liquid flow meter 7 is for measuring the flow rate of the plating solution 30 returned from the circulation channel 21 to the plating tank 1.

  Here, since the volume flow rate of the plating solution 30 after dissolving the gas is considered to be equal to the volume flow rate of the plating solution 30 extracted from the plating tank 1, in this embodiment, the liquid flow meter 7 is used. The volume flow rate of the plating solution 30 measured in step 1 is defined as the volume flow rate of the plating solution 30 extracted from the plating tank 1.

  The pump 4 functions as gas mixing means for mixing a gas containing oxygen into the plating solution 30 and pressurizing the plating solution 30 to dissolve the gas in the plating solution 30 in the circulation flow path 21. The pump 4 is connected to an air supply pipe 11 for supplying a gas containing oxygen thereto. The air supply pipe 11 conveys the gas containing oxygen from the gas intake 10 to the pump 4. A gas flow meter 12 is provided in the air supply pipe 11 so that the amount of gas transported, in other words, the amount of gas mixed into the plating solution 30 can be grasped. The pressure reducing valve 8 functions as a pressure reducing means for reducing the pressure of the plating solution 30 in which the gas is dissolved to generate fine bubbles. Note that the bubble generating nozzle 9 may be provided with a pressure reducing part (flow passage restricting part) such as an orifice. When such a pressure reducing part is provided, the pressure reducing valve 8 can be omitted.

  The electroless plating apparatus 100 may be provided with an aeration pipe 15 as shown in FIG. The aeration pipe 15 vents air bubbles having a diameter of several millimeters to several centimeters from the inside toward the plating solution 30 in the plating tank 1. By this ventilation, the plating solution 30 can be agitated. When the aeration pipe 15 is provided, the electroless plating apparatus 100 may include an air supply pipe 14 that supplies a gas such as air to the aeration pipe 15. Further, although not shown, a stirring bar or a stirring rod for stirring the plating solution 30 may be provided in the plating tank 1.

  Further, it is preferable to provide a filter 3 on the upstream side of the pump 4 in order to filter cuprous oxide, metallic copper or other precipitates deposited in the plating solution 30 extracted from the plating tank 1. Thereby, clogging of the circulation channel 21 by the deposit can be suppressed, and re-mixing of the deposit into the plating tank 1 can be suppressed. Further, in order to confirm the degree of pressurization by the pump 4, a pressure gauge 5 may be provided on the discharge side and on the upstream side of the pressure reducing valve 8. Further, it is preferable that a bubble generating nozzle 9 is provided at a connection portion between the plating tank 1 and the external circulation means 2 in order to reliably supply the fine bubbles generated by the pressure reduction by the pressure reducing valve 8 to the plating tank 1. is there.

  Next, a method for supplying oxygen to the plating solution 30 using the electroless plating apparatus 100 shown in FIG. 1 will be described.

  The oxygen supply method described above includes a storing step of storing the plating solution 30 in the plating tank 1, a drawing step of extracting a part of the plating solution 30 from the plating tank 1, and a gas containing oxygen in the extracted plating solution 30. It comprises a dissolving step for mixing and dissolving, a depressurizing step for reducing the pressure of the plating solution 30 in which the gas is dissolved, and a feeding step for returning the plating solution 30 to the plating tank 1. Hereinafter, each process is demonstrated in order.

  In the storage step, a plating solution 30 containing copper ions, a copper ion complexing agent, a reducing agent and a pH adjusting agent is supplied to the plating tank 1.

  The plating solution 30 is generally an aqueous solution containing a copper salt as a copper ion supply source, a copper ion complexing agent, a reducing agent, and a pH adjusting agent such as an alkali hydroxide.

  The copper salt only needs to contain a divalent copper ion, and examples thereof include copper sulfate, copper nitrate, copper chloride, copper bromide, copper oxide, copper hydroxide, and copper pyrophosphate. The concentration of the copper salt is preferably in the range of 0.1 to 1000 mmol / L, and more preferably in the range of 1 to 500 mmol / L from the viewpoint of stable plating depositability. When the concentration of the copper salt is less than 0.1 mmol / L, the plating deposition efficiency tends to decrease, and when it exceeds 1000 mmol / L, the stability of the plating solution tends to decrease.

  The copper ion complexing agent only needs to form a complex with copper ions. For example, oxycarboxylic acids such as lactic acid, malic acid, tartaric acid, citric acid, and gluconic acid or salts thereof, nitrilotriacetic acid, ethylenediamine Tetraacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol etherdiaminetetraacetic acid, aspartic acid diacetic acid, methyl Examples thereof include aminocarboxylic acids such as glycine diacetic acid, glutamic acid diacetic acid, ethylenediamine disuccinic acid or salts thereof, triethanolamine, and glycerin. The concentration of the complexing agent is preferably in the range of 1 to 30 mol times relative to the concentration of the copper salt, and more preferably in the range of 1 to 20 mol times from the viewpoint of stable plating precipitation. . When the concentration of the complexing agent is less than 1 mole, the stability of the plating solution tends to be lowered, and when it exceeds 30 moles, it tends to be economically disadvantageous.

  The reducing agent may be any one that can reduce copper ions, such as formaldehyde, paraformaldehyde, dimethylamine borane, borohydride, glyoxylic acid, and reducing sugar. The concentration of the reducing agent is preferably in the range of 0.1 to 1000 mmol / L, and more preferably in the range of 1 to 500 mmol / L from the viewpoint of stable plating depositability. When the concentration of the reducing agent is less than 0.1 mmol / L, the deposition efficiency of plating tends to decrease, and when it exceeds 1000 mmol / L, the stability of the plating solution tends to decrease.

  Examples of the pH adjuster include alkali metals such as sodium hydroxide and potassium hydroxide, and hydroxides of alkaline earth metals, acidic solutions such as hydrochloric acid, nitric acid, and sulfuric acid, but are not particularly limited. The pH of the plating solution 30 is preferably in the range of 6 to 14, and more preferably in the range of pH 10 to 13 from the viewpoint of stable plating precipitation. If the pH is less than 6, the deposition efficiency of plating tends to decrease, and if it exceeds 14, the stability of the plating solution tends to decrease.

In addition, the plating solution 30 improves the properties of the electroless copper plating film, improves the liquid stability accompanying continuous use of the electroless copper plating solution, improves the plating deposition rate, or suppresses fluctuations in the plating deposition rate. Depending on the purpose, additives can be further included. Examples of the additive include 2,2′-bipyridyl, orthophenanthrin, potassium ferrocyanide, benzothiazole, thiazole, nicotinic acid, benzotriazole, potassium polysulfide, 8-azaguanine, 8-azaxanthine, and 8-aza. Hypoxanthine, adenine, 8-azaadenine, guanine, hypoxanthine, sodium cyanide, cupron, potassium sulfide, sodium sulfide, sodium metasilicate, sodium germanate, germanium dioxide, sodium stannate, sodium molybdate, sodium metavanadate, five Vanadium oxide, polyethylene glycol, polypropylene glycol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, sodium sulfate, potassium sulfate, Examples include, but are not limited to, nickel sulfate, boric acid, potassium oxalate, thiourea, allyl thiourea, thiomalic acid, thioglycolic acid, thiocyanic acid, glycolic acid, sodium carbonate, potassium nitrate, and lead salts.
Each component of the above-mentioned plating solution 30 is used individually by 1 type or in combination of 2 or more types.

  The temperature of the plating solution 30 is generally in the range of 5 to 90 ° C, and preferably in the range of 10 to 80 ° C. If the temperature of the plating solution 30 is less than 5 ° C., the deposition efficiency of the plating tends to be reduced. Tend to decrease.

  In the extraction step, a part of the plating solution 30 in the plating tank 1 is extracted to the external circulation means 2 and circulated in the circulation flow path 21. The plating solution 30 extracted from the plating tank 1 is preferably filtered through the filter 3 with cuprous oxide, metallic copper, or other precipitates.

  The volume flow rate of the plating solution 30 withdrawn from the plating tank 1 per minute is preferably 0.01 times or more with respect to the total amount of the plating solution 30 stored in the plating tank 1, and 0.05 times or more. More preferably. If it is less than 0.01 times, it tends to be difficult to supply dissolved oxygen necessary for stabilizing the plating solution.

  In the melting step, the pump 4 is used to mix a gas containing oxygen into the plating solution 30 extracted in the extraction step and pressurize the plating solution 30 to dissolve the gas in the plating solution 30. At this time, you may isolate | separate undissolved gas with the floating separation apparatus 6 as needed.

  The gas containing oxygen is preferably oxygen or a gas containing 5% by volume or more of oxygen in the range of 5 to 90 ° C. Examples of the gas that is a gas in the range of 5 to 90 ° C. and contains 10% or more by volume of oxygen include a mixed gas of oxygen and a gas that is a gas in the range of 5 to 90 ° C. And a mixed gas of oxygen and nitrogen, air, and the like.

  Further, in the melting step, it is preferable to appropriately adjust the gas mixing amount and pressure depending on the oxygen supply state to the plating solution 30 in the plating tank 1. Examples of the evaluation index of the oxygen supply state include the dissolved oxygen concentration in the plating solution 30 in the plating tank 1, the diameter of the fine bubbles, and the mixing ratio (void ratio) of the gas containing oxygen.

  The dissolved oxygen concentration in the plating solution 30 in the plating tank 1 is preferably in the range of 0.5 to 35 mg / L at a plating solution temperature of 5 to 90 ° C., and in the range of 1.5 to 20 mg / L. More preferably. Moreover, in order to drive | operate stably over a long period of time, it is still more preferable that it is 2.0-15 mg / L. When the dissolved oxygen concentration is less than 0.5 mg / L, monovalent copper ions increase in the plating solution, and the plating solution tends to decompose. On the other hand, if it exceeds 35 mg / L, the plating film is oxidized to form a passive state and the deposition reaction of electroless copper plating tends to be suppressed.

  Here, the measurement of the dissolved oxygen concentration in the plating solution 30 in the plating tank 1 may be performed by, for example, a method of installing a commercially available dissolved oxygen meter in the plating tank 1 or “high temperature absence” described in Japanese Patent No. 2622268. It can be performed by a known method such as “Method for measuring dissolved oxygen concentration in electrolytic copper plating solution”. However, in the method using a commercially available dissolved oxygen meter, in addition to the dissolved oxygen in the plating solution 30, it may be influenced by oxygen in fine bubbles that stay in the plating solution 30. For this reason, if fine bubbles are excessively attached to the sensor electrode during measurement, it is necessary to remove them. In addition, the measurement temperature range of a commercially available diaphragm electrode type dissolved oxygen meter is limited by the temperature compensation range based on the temperature change of the oxygen permeation characteristic of the diaphragm and the heat resistance of the sensor electrode, and is usually 5 to 40 ° C. Therefore, when a high-temperature plating solution is used, it is preferable to use the method described in Japanese Patent No. 262268.

  The dissolved oxygen concentration in the plating solution 30 in the plating tank 1 is preferably 3.0 mg / L or more within 5 minutes, and more preferably 3.0 mg / L within 3 minutes. Moreover, in order to drive | operate stably over a long period of time, it is still more preferable that it can be 3.0 mg / L or more within 2 minutes. If the dissolved oxygen concentration exceeds 3.0 mg / L for more than 5 minutes, the decrease in dissolved oxygen concentration accompanying the electroless copper plating precipitation reaction is not sufficiently suppressed, and monovalent copper ions in the plating solution Tends to increase and decomposition of the plating solution tends to occur.

  The diameter of the fine bubbles in the plating solution 30 in the plating tank 1 is preferably less than 300 μm, and more preferably less than 100 μm. When the diameter of the fine bubbles is 300 μm or more, the residence time of the fine bubbles in the plating solution is shortened, and there is a tendency that it is difficult to supply the amount of dissolved oxygen necessary for stabilizing the plating solution.

  The mixing ratio of the gas containing oxygen in the plating solution 30 in the plating tank 1 (hereinafter sometimes referred to as “void ratio”) is the ratio of the gas that is constantly present in the plating solution 30 by the generated fine bubbles. That is, the volume ratio of the gas phase to the liquid phase is shown. For example, the void ratio can be estimated from a change in a measured value obtained by a buoyancy type hydrometer before and after generating fine bubbles. When fine bubbles stay in the plating solution 30, the apparent specific gravity of the plating solution 30 containing fine bubbles is reduced. That is, the mixing ratio of the gas containing oxygen in the plating solution 30 has a larger value as the apparent specific gravity of the plating solution 30 containing fine bubbles decreases.

  The mixing ratio of the gas containing oxygen is preferably 0.001 to 10% by volume, more preferably 0.003 to 7% by volume, and 0.005 to 5% by volume. Is particularly preferred. Moreover, in order to drive | operate stably over a long term, it is most preferable that it is the range of 0.01-3 volume%. When the mixing ratio of the gas containing oxygen in the plating solution 30 is less than 0.001% by volume, it tends to be difficult to supply the dissolved oxygen in an amount necessary for stabilizing the plating solution. When the mixing ratio of the gas containing oxygen in the plating solution 30 exceeds 10% by volume, the deposition reaction of the electroless copper plating tends to be inhibited.

  The volume flow rate of the gas containing oxygen mixed into the plating solution 30 from the pump 4, that is, the gas flow rate measured by the gas flow meter 12 is 0.01 of the volume flow rate of the electroless copper plating solution 30 extracted from the plating tank 1. The volume flow rate is preferably -0.5 times, more preferably 0.02-0.3 times. When the volume flow rate of the gas containing oxygen is less than 0.01 times, it tends to be difficult to supply dissolved oxygen necessary for stabilizing the plating solution, and when it exceeds 0.5 times, fine bubbles are efficiently formed. It tends to be difficult.

  The pressure for dissolving the oxygen-containing gas in the plating solution 30, that is, the pressure measured by the pressure gauge 5, is preferably 0.1 MPa or more, more preferably 0.2 MPa or more in terms of gauge pressure. . If it is less than 0.1 MPa, there is a tendency that the gas necessary for efficiently generating fine bubbles cannot be dissolved.

  Next, in the decompression step, the plating solution 30 in which the gas is dissolved in the dissolution step is decompressed by the decompression valve 8 to generate fine bubbles. Next, in the feeding process, the plating solution 30 in which fine bubbles are generated in the decompression process is returned to the plating tank 1.

  Next, a method for applying electroless copper plating to the workpiece 18 will be described.

  A printed wiring board is suitable as the object to be plated 18 when performing electroless copper plating, but is not limited thereto. Examples of objects to be plated other than printed wiring boards include, for example, metals such as iron, copper, nickel, cobalt, and chromium, alloys containing these metals, plastics such as PET resin, epoxy resin, and polyimide resin, glass, ceramics, Other composite materials may be mentioned.

Area of the object to be plated 18 is immersed in the plating solution 30, i.e., load factor, preferably the plating solution 1L per 0.001~0.3m ^2, 0.003~0.1m ² is more preferable. If the load factor is less than 0.001 m ² / L, the production efficiency tends to decrease, and if it exceeds 0.3 m ² / L, the dissolved oxygen concentration in the plating solution decreases and the plating solution is unstable. Tend to be.

  The object to be plated 18 may be pretreated before being immersed in the plating solution 30. Examples of the pretreatment include (A) a process for degreasing and cleaning the object 18 to be plated, (B) a process for applying a catalyst to the object 18 to be plated, and (C) a process for activating the catalyst applied to the object 18 to be plated. Can be mentioned. In particular, when conducting through holes and via holes in a printed wiring board, it is preferable to perform all of the pretreatments (A) to (C) in this order.

  The pretreatment (A) is performed to clean the surface of the object 18 to be plated. The surface of the object 18 is cleaned with a solvent, an acidic aqueous solution, an alkaline aqueous solution, or the like. Moreover, it is preferable that acidic aqueous solution or alkaline aqueous solution contains 1 or more types of surfactant. When such a solvent and aqueous solution are used, the metal which becomes a catalyst of the precipitation reaction of electroless copper plating can be efficiently provided in the pretreatment of (B).

  The surfactant is not particularly limited, but a nonionic surfactant is preferable. Examples of nonionic surfactants include fatty acid monoglycerin esters, fatty acid polyglycol esters, fatty acid sorbitan esters, fatty acid monoethanolamides, fatty acid diethanolamides, fatty acid polyethylene glycol condensates, fatty acid amide / polyethylene glycol condensates, fats Aromatic alcohol / polyethylene glycol condensate, aliphatic amine / polyethylene glycol condensate, aliphatic mercaptan / polyethylene glycol condensate, alkylphenol / polyethylene glycol condensate and polypropylene glycol / polyethylene glycol condensate. These are used singly or in combination of two or more.

  The pretreatment of (B) includes a noble metal or noble metal that serves as a catalyst for the deposition reaction of electroless copper plating on the surface of the object to be plated 18 using an acidic or alkaline aqueous solution or colloidal liquid containing a noble metal. Performed to provide alloy or noble metal ions. Examples of the noble metal include palladium, rhodium, platinum, gold, silver and the like, but palladium is preferable. As the aqueous solution or colloidal liquid, known ones can be used.

  The pretreatment (C) is performed in order to activate the noble metal, the alloy containing the noble metal, or the noble metal ion applied to the surface of the workpiece 18 in the pretreatment (B). In other words, it is a process for developing a function as a catalyst for the deposition reaction of electroless copper plating. This pretreatment is usually performed by immersing the workpiece 18 in an acidic aqueous solution or an alkaline aqueous solution. The acidic aqueous solution or alkaline aqueous solution used for this pretreatment may contain a reducing agent such as formaldehyde, paraformaldehyde, dimethylamine borane, borohydride, glyoxylic acid, and reducing sugar. In particular, when the precious metal provided in the pretreatment of (B) is a precious metal ion, it is preferable to include the reducing agent.

  Plating on the object 18 is performed by immersing the object 18 in the plating solution 30. The time for immersing the workpiece 18 in the plating solution 30 is preferably 30 seconds or longer, and more preferably 1 minute or longer. If it is less than 30 seconds, the plating tends to be difficult to deposit.

  When the object 18 is plated using the electroless plating apparatus 100 and the method for supplying oxygen to the plating solution 30 as described above, the dissolved oxygen concentration in the plating solution can be quickly improved. Therefore, it is possible to suppress a rapid decrease in the dissolved oxygen concentration accompanying the deposition reaction of the electroless copper plating on the surface of the object to be plated. As a result, the electroless plating apparatus can be operated in a state where the stability of the plating solution is ensured over a long period of time.

  FIG. 2 is a schematic view showing a second embodiment according to the electroless plating apparatus of the present invention. An electroless plating apparatus 200 shown in FIG. 2 includes a plating tank 1 that stores a plating solution 30, and an external circuit that is connected to the plating tank 1 and has a circulation channel 21 that circulates the plating solution 30 between the plating tank 1. And circulation means 2. Further, the external circulation means 2 has a pump 4 and fine bubble generation means 19 in the circulation flow path 21.

  The plating tank 1 is, for example, a bottomed container having an open top, and the plating solution 30 is filled therein. An object 18 to be plated is immersed in the plating tank 1 and electroless copper plating is applied to the surface thereof. An external circulation means 2 is connected to the side surface of the plating tank 1.

  In the circulation channel 21 of the external circulation means 2, the pump 4, the liquid flow meter 7, and the fine bubble generation means 19 are arranged in that order along the circulation direction D <b> 1 of the plating solution 30. The liquid flow meter 7 is for measuring the flow rate of the plating solution 30 returned from the circulation channel 21 to the plating tank 1.

  Here, since the volume flow rate of the plating solution 30 after passing through the pump 4 is considered to be equal to the volume flow rate of the plating solution 30 extracted from the plating tank 1, in this embodiment, the liquid flow meter 7 is used. The measured volume flow rate of the plating solution 30 is defined as the volume flow rate of the plating solution 30 withdrawn from the plating tank 1.

  The fine bubble generating unit 19 functions as a unit that mixes a gas containing oxygen into the plating solution 30 to form bubbles and pulverizes the bubbles to generate fine bubbles. The fine bubble generating means 19 is connected to an air supply pipe 11 for supplying a gas containing oxygen thereto. The air supply pipe 11 conveys a gas containing oxygen from the gas intake 10 to the fine bubble generating means 19. A gas flow meter 12 is provided in the air supply pipe 11 so that the amount of gas transported, in other words, the amount of gas mixed into the plating solution 30 can be grasped.

  The electroless plating apparatus 200 may be provided with an aeration pipe 15 as shown in FIG. The aeration pipe 15 vents air bubbles having a diameter of several millimeters to several centimeters from the inside toward the plating solution 30 in the plating tank 1. By this ventilation, the plating solution 30 can be agitated. When the aeration pipe 15 is provided, the electroless plating apparatus 200 may include an air supply pipe 14 that supplies a gas such as air to the aeration pipe 15. Further, although not shown, a stirring bar or a stirring rod for stirring the plating solution 30 may be provided in the plating tank 1.

  Further, it is preferable to provide a filter 3 on the upstream side of the pump 4 in order to filter cuprous oxide, metallic copper or other precipitates deposited in the plating solution 30 extracted from the plating tank 1. Thereby, clogging of the circulation channel 21 by the deposit can be suppressed, and re-mixing of the deposit into the plating tank 1 can be suppressed.

  Here, as the fine bubble generating means 19, for example, a swirl type fine bubble generating device described in Japanese Patent No. 3397154 is preferably used. The swirling fine bubble generator sucks gas by a pressure drop caused by forming a swirling liquid flow, and pulverizes bubbles by the swirling liquid flow. When such an apparatus is used, fine bubbles having a desired diameter can be generated.

  Further, as the fine bubble generating means 19, a combination of the swirling fine bubble generating device described in Japanese Patent No. 3397154 and other methods can also be used. By combining other methods, the bubble diameter can be further reduced.

  Examples of other methods include an ejector method, a venturi tube method, and an ultrasonic method.

  The ejector method is a method in which gas is sucked using a negative pressure generated by a liquid flow passing through a narrow flow path at high speed, and bubbles are finely crushed by cavitation generated by expansion of a downstream pipe line.

  The Venturi tube system allows a bubble-containing liquid to pass through a flow path having a portion where the cross-sectional area expands and a portion where the cross-sectional area expands. In this method, fine bubbles are formed by collapsing bubbles by a sudden pressure increase in the portion.

The ultrasonic method is a method of forming fine bubbles by applying ultrasonic vibration to a gas-liquid mixed phase mixed with gas and crushing the gas phase.
Note that members other than the above-described members in the electroless plating apparatus 200 may be the same as those in the electroless plating apparatus 100 according to the first embodiment, and thus detailed description thereof is omitted here.

  Subsequently, a method for supplying oxygen to the plating solution 30 using the electroless plating apparatus shown in FIG. 2 will be described.

  The oxygen supply method described above includes a storage step of storing the plating solution 30 in the plating tank 1, an extraction step of extracting a part of the plating solution 30 from the plating tank 1, and a gas containing oxygen in the extracted plating solution 30. A bubble crushing step of mixing and forming bubbles and crushing the bubbles, and a feeding step of returning the plating solution 30 to the plating tank 1 are provided.

  In the storage step, a plating solution 30 containing copper ions, a copper ion complexing agent, a reducing agent and a pH adjusting agent is supplied to the plating tank 1. As the plating solution 30, the same one as in the first embodiment is used.

  In the extraction step, a part of the plating solution 30 in the plating tank 1 is extracted to the external circulation means 2 and circulated in the circulation flow path 21. The plating solution 30 extracted from the plating tank 1 is preferably filtered through the filter 3 to deposit precipitated cuprous oxide, metallic copper or other precipitates.

  The volume flow rate of the plating solution 30 withdrawn from the plating tank 1 per minute is preferably 0.05 times or more, more than 0.1 times the total amount of the plating solution 30 stored in the plating tank 1. More preferably. If it is less than 0.05 times, it tends to be difficult to supply dissolved oxygen necessary for stabilizing the plating solution 30.

  In the bubble crushing step, the fine bubble generating means 19 is used to mix the oxygen-containing gas into the extracted plating solution 30 to form bubbles, and the bubbles are crushed to generate fine bubbles.

  As the gas containing oxygen, the same gas as that in the first embodiment is used. Further, in the bubble crushing step, it is preferable to appropriately adjust the gas mixing amount depending on the oxygen supply state to the plating solution 30 in the plating tank 1. A preferable oxygen supply state is the same as the state in the first embodiment.

  The volume flow rate at which the gas containing oxygen is mixed into the plating solution 30 by the fine bubble generating means 19, that is, the gas flow rate measured by the gas flow meter 12, is 0.01 to It is preferably 0.5 times, and more preferably 0.02 to 0.3 times the volume flow rate. When the supply amount of gas containing oxygen is less than 0.01 times, it tends to be difficult to supply dissolved oxygen necessary for stabilizing the plating solution, and the supply amount of gas containing oxygen exceeds 0.5 times. And, it tends to be difficult to form fine bubbles efficiently.

  In the feeding step, the plating solution 30 in which fine bubbles are generated in the bubble crushing step is returned to the plating tank 1.

  Moreover, the method of performing electroless copper plating to the to-be-plated object 18 is performed by the method similar to 1st Embodiment.

  Even when electroless copper plating is applied to the object 18 using such an electroless plating apparatus 200 and an oxygen supply method to the plating solution 30, the deposition reaction of the electroless copper plating on the surface of the object to be plated It is possible to suppress a rapid decrease in the dissolved oxygen concentration associated with. As a result, the electroless plating apparatus can be operated while ensuring the stability of the electroless copper plating solution over a long period of time.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment. For example, instead of the electroless copper plating solution, other electroless plating solutions can be used.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited thereto.

  In Examples and Comparative Examples of the present invention, the dissolved oxygen concentration of the electroless copper plating solution is measured by using “OM-51” (trade name, manufactured by Horiba, Ltd.), which is a diaphragm-type electrode dissolved oxygen meter. Using. The dissolved oxygen concentration was measured by pumping the electroless copper plating solution from the electroless plating tank and allowing it to stand for 30 seconds, and then measuring the dissolved oxygen concentration of the pumped electroless copper plating solution. In addition, for measuring the specific gravity, a floating standard hydrometer (manufactured by Yokota Keiki Seisakusho Co., Ltd.) was used. The temperature at the time of measurement was adjusted to 25 ° C.

Example 1
As the electroless copper plating solution, 20 L of “CUST-201” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an autocatalytic electroless copper plating solution, was prepared. Next, the electroless plating apparatus 100 of the embodiment shown in FIG. 1 was installed, and the electroless copper plating solution was filled in the electroless plating tank 1. The gas forming the fine bubbles can be sucked into the pump 4, and air is used as the gas. Further, undissolved gas is discharged from the floating separation device 6. Further, an aeration pipe 15 having a plurality of pores having a diameter of 500 μm is provided so that air and nitrogen can be vented.

First, nitrogen was passed through the electroless copper plating solution 30 at 25 ° C. stored in the electroless plating tank 1 using the aeration pipe 15. When the dissolved oxygen concentration in the electroless copper plating solution was less than 10% of the saturation concentration by air (8.1 mg / L), the dissolved oxygen concentration and specific gravity were measured. Thereafter, the ventilation through the aeration pipe 15 is stopped, the pump 4 is operated, the volume flow rate of the electroless copper plating solution 30 withdrawn from the electroless plating tank 1 is 4.0 L / min, and the amount of air mixed into the pump 4 is 0. It was operated under the condition of 3 L / min. When 5 minutes passed after the pump 4 was operated, the dissolved oxygen concentration and specific gravity were measured. Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of gas containing oxygen in the electroless copper plating solution (volume%, the same applies hereinafter). If the apparent specific gravity before the generation of fine bubbles is a, and the apparent specific gravity after the generation of fine bubbles is b, the void ratio v can be approximately calculated by the following equation.
v [%] = (1- (b / a)) × 100

(Example 2)
As in Example 1, 20 L of “CUST-201” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an electroless copper plating solution, was prepared. Next, the electroless plating apparatus of the embodiment shown in FIG. 2 was installed, and the electroless copper plating solution was filled in the electroless plating tank 1. Here, as the fine bubble generating means 19, “Awataro” (trade name, manufactured by Nitta Moore Co., Ltd.), which is a swivel type fine bubble generator, was used. The gas forming the fine bubbles can be sucked into the fine bubble generating means 19, and air is used as the gas. In addition, as in Example 1, air and nitrogen can be vented from the aeration pipe 15.

  First, nitrogen was passed through the electroless copper plating solution 30 at 25 ° C. stored in the electroless plating tank 1 using the aeration pipe 15. When the dissolved oxygen concentration in the electroless copper plating solution was less than 10% of the saturation concentration by air (8.1 mg / L), the dissolved oxygen concentration and specific gravity were measured. Thereafter, the ventilation by the aeration pipe 15 is stopped, the pump 4 is operated, and the volume flow rate of the electroless copper plating solution 30 extracted from the electroless plating tank 1 and supplied to the fine bubble generating means 19 is 6.0 L / min. The operation was performed under the condition that the amount of air mixed into the generating means 19 was 0.2 L / min. When 5 minutes passed after the pump 4 was operated, the dissolved oxygen concentration and specific gravity were measured. Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution.

(Comparative Example 1)
As in Example 1, 20 L of “CUST-201”, which is an electroless copper plating solution, was prepared. Further, nitrogen was passed through the electroless copper plating solution 30 at 25 ° C. stored in the electroless plating tank 1 using the aeration pipe 15. When the dissolved oxygen concentration in the electroless copper plating solution was less than 10% of the saturation concentration by air (8.1 mg / L), the dissolved oxygen concentration and specific gravity were measured. Next, air was aerated from the aeration pipe 15 into the electroless copper plating solution. Note that the electroless copper plating solution 30 was not circulated by the external circulation means 2. After adjusting the air flow rate to 1.0 L / min and continuously venting for 5 minutes, the dissolved oxygen concentration and specific gravity were measured. Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution.

(Example 3)
As an electroless copper plating solution, 20 L of “CUST-201” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an autocatalytic electroless copper plating solution, was prepared, and the electroless copper was used continuously in a pseudo manner. In order to obtain a plating solution, fine bubbles were generated under the same conditions as in Example 1, except that 10 mol (1.42 kg) of sodium sulfate and 20 mol (1.46 kg) of sodium formate were added as reaction byproducts. Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution.

(Example 4)
20 L of “CUST-201” which is an electroless copper plating solution was prepared, and the same as Example 2 except that 10 mol (1.42 kg) of sodium sulfate and 20 mol (1.46 kg) of sodium formate were added as reaction byproducts. Fine bubbles were generated under the following conditions. Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution.

(Comparative Example 2)
20 liters of “CUST-201” which is an electroless copper plating solution was prepared, and the same as Comparative Example 1 except that 10 mol of sodium sulfate (1.42 kg) and 20 mol of sodium formate (1.46 kg) were added as reaction byproducts. Aeration was performed under the conditions of Table 1 shows the measurement results of the dissolved oxygen concentration, specific gravity, and the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution.

  As shown in Table 1, in the oxygen supply method according to the present invention, the dissolved oxygen concentration can be increased more rapidly than in the conventional method. In particular, it can be seen that the effect of the present invention is more remarkable in an electroless copper plating solution containing a large amount of by-products.

(Example 5)
As an electroless copper plating solution, 20 L of “CUST-201” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an autocatalytic electroless copper plating solution, was prepared, and the electroless copper was used continuously in a pseudo manner. In order to obtain a plating solution, 10 mol (1.42 kg) of sodium sulfate and 20 mol (1.46 kg) of sodium formate were added as reaction byproducts. Here, the temperature of the electroless copper plating solution was adjusted to 25 ° C.

Epoxy resin from which copper foil of “MCL-E-679” (trade name, thickness 0.2 mm, manufactured by Hitachi Chemical Co., Ltd.), which is an epoxy double-sided copper-clad laminate, is etched and removed as an object to be plated. A substrate was prepared. Here, the plating area was set to 1.2 m ² , that is, the load factor was set to 0.06 m ² / L.

  Before the electroless copper plating was applied to the above-mentioned object to be plated, the above pretreatments (A) to (C) were performed.

  In the pretreatment of (A), the object to be plated is immersed in “CLC-601” (trade name, manufactured by Hitachi Chemical Co., Ltd.), a cleaner conditioner, at 60 ° C. for 5 minutes to clean and condition the object to be plated. went. Next, it was washed with water at room temperature (20 to 25 ° C.) for 2 minutes.

  Next, in the pretreatment of (B), the obtained object to be plated is added to “PD-301” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is a pretreatment liquid of a palladium-tin catalyst, at 25 ° C. Immerse for a minute. Next, the obtained object to be plated was immersed in “HS-202B” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is a palladium-tin catalyst solution, at 25 ° C. for 5 minutes. Next, the obtained object to be plated was washed with water at room temperature (20 to 25 ° C.) for 2 minutes.

  Next, in the pretreatment of (C), the obtained object to be plated was immersed in “ADP-601” (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an acidic treatment solution, at 25 ° C. for 5 minutes. In this way, a palladium catalyst for the deposition reaction of electroless copper plating was deposited on the surface of the object to be plated. Next, the obtained object to be plated was washed with water at room temperature (20 to 25 ° C.) for 2 minutes.

  Next, the obtained object to be plated is immersed in the electroless plating tank 1 of the electroless plating apparatus shown in FIG. After 4 seconds, the pump 4 was turned on. However, the aeration pipe 15 was not used. Here, the volume flow rate of the electroless copper plating solution 30 extracted from the electroless plating tank 1 was adjusted to 4.0 L / min, and the amount of air mixed into the pump 4 was adjusted to 0.3 L / min. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

  Regarding the stability of the electroless copper plating solution, the presence or absence of the formation of precipitate after the end of electroless copper plating was used as an evaluation index. That is, the case where the precipitate was visually confirmed in the electroless copper plating solution after the end of the electroless copper plating was unstable, and the case where the precipitate was not visually confirmed even after the end of the electroless copper plating was stabilized.

(Example 6)
Electroless copper plating was performed under the same conditions as in Example 5 except that air was continuously ventilated using the aeration pipe 15 when the object to be plated was immersed. Here, the volume flow rate of air from the aeration pipe 15 was adjusted to 1.0 L / min. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

(Example 7)
Pre-plating treatment was performed under the same conditions as in Example 5, and immersed in an electroless plating bath of an electroless plating apparatus shown in FIG. 2 at an electroless copper plating solution temperature of 25 ° C. for 20 minutes. However, as the fine bubble generating means 19, “Awataro” (trade name, manufactured by Nitta Moore Co., Ltd.), which is a swivel type fine bubble generator, was used. Moreover, the aeration pipe 15 was not used. 30 seconds after dipping the object to be plated, the fine bubble generating means 19 was activated. Here, the volume flow rate of the electroless copper plating solution 30 extracted from the electroless plating tank 1 was adjusted to 6.0 L / min, and the amount of air mixed into the fine bubble generating means 19 was adjusted to 0.2 L / min. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

(Example 8)
Electroless copper plating was performed under the same conditions as in Example 7 except that air was continuously ventilated using the aeration pipe 15 when the object to be plated was immersed. Here, the volume flow rate of air from the aeration pipe 15 was adjusted to 1.0 L / min. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

(Comparative Example 3)
Electroless copper plating was performed under the same conditions as in Example 5 except that the pump 4 was always stopped when the object to be plated was immersed. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

(Comparative Example 4)
Electroless copper plating was performed under the same conditions as in Comparative Example 3 except that air was continuously ventilated using the aeration pipe 15 when the workpiece was immersed. Here, the volume flow rate of air from the aeration pipe 15 was adjusted to 1.0 L / min. Table 2 shows the measurement results of the dissolved oxygen concentration, the mixing ratio (void ratio) of the gas containing oxygen in the electroless copper plating solution, and the stability of the electroless copper plating solution.

  As shown in Table 2, in Examples 5 to 8, the electroless copper plating solution was stable. On the other hand, in Comparative Examples 3 and 4, the electroless copper plating solution became unstable, and precipitates were confirmed in the electroless copper plating solution by visual observation.

DESCRIPTION OF SYMBOLS 1 ... Electroless plating tank, 2 ... External circulation means, 3 ... Filter, 4 ... Pump, 5 ... Pressure gauge, 6 ... Floating separation device, 7 ... Liquid flow meter, 8 ... Pressure reducing valve, 9 ... Bubble generating nozzle, 10 DESCRIPTION OF SYMBOLS ... Gas inlet, 11, 14 ... Air supply pipe, 12 ... Gas flow meter, 15 ... Aeration pipe, 18 ... To-be-plated object, 19 ... Fine bubble generation means, 21 ... Circulation flow path, 30 ... Electroless copper plating solution , 100, 200... Electroless plating apparatus.

Claims (10)

An electroless plating tank for storing an electroless plating solution;
External circulation means connected to the electroless plating tank and having a circulation channel for circulating the electroless plating solution between the electroless plating tank,
With
The external circulation means mixes oxygen-containing gas into the electroless plating solution to form bubbles in the circulation flow path and pulverizes the bubbles to generate fine bubbles having a diameter of less than 300 μm. Generating means,
An electroless plating apparatus, which is a swirling fine bubble generating device, wherein the fine bubble generating means sucks gas by a pressure drop caused by forming a swirling liquid flow and pulverizes bubbles by the swirling liquid flow.   The electroless plating apparatus according to claim 1, wherein the electroless plating solution is an electroless copper plating solution containing copper ions, a complexing agent of the copper ions, a reducing agent, and a pH adjusting agent.   The volume flow rate mixed in the electroless plating solution of the gas containing oxygen is 0.01 to 0.5 times the volume flow rate of the electroless plating solution withdrawn from the electroless plating tank. The electroless plating apparatus described.   The electroless plating according to any one of claims 1 to 3, wherein a mixing ratio of the gas containing oxygen in the electroless plating solution is 0.001 to 10% by volume in the electroless plating tank. apparatus.   The electroless plating apparatus according to claim 1, wherein the gas containing oxygen is a gas at 5 to 90 ° C. and contains 10% by volume or more of oxygen. A method for supplying oxygen to an electroless plating solution,
An extraction step of extracting a part of the electroless plating solution from the electroless plating tank for storing the electroless plating solution;
A bubble crushing step of mixing the gas containing oxygen into the extracted electroless plating solution to form bubbles and crushing the bubbles to generate fine bubbles having a diameter of less than 300 μm ;
A feeding step of returning the electroless plating solution to the electroless plating tank together with the fine bubbles;
With
In the bubble crushing step, an oxygen supply method in which gas is sucked by a pressure drop caused by forming a swirl liquid flow and the bubbles are crushed by the swirl liquid flow.   The oxygen supply method according to claim 6, wherein the electroless plating solution is an electroless copper plating solution containing copper ions, a complexing agent of the copper ions, a reducing agent, and a pH adjusting agent.   The volume flow mixed into the electroless plating solution of the gas containing oxygen is 0.01 to 0.5 times the volume flow of the electroless plating solution withdrawn from the electroless plating bath. The oxygen supply method according to the description.   The oxygen supply method according to any one of claims 6 to 8, wherein a mixing ratio of the gas containing oxygen in the electroless plating solution is 0.001 to 10% by volume in the electroless plating tank. .   The oxygen supply method according to claim 6, wherein the gas containing oxygen is a gas at 5 to 90 ° C. and contains 10% by volume or more of oxygen.

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