JPH0273689A - Copper plating method for printed board - Google Patents

Abstract

PURPOSE:To prevent the exhaustion of the additive of electrolyte simply and steadily by forming a necessary covering layer at the surface of an insoluble anode which is used at copper plating. CONSTITUTION:When electrolyzing electrolyte which contains copper ions and additives using an insoluble anode so as to do copper plating to a printed board being a cathode, an electrochemically inert film such as fluoroion exchanging resin, TiO2, Ta2O5, ZrO2, SnO2, WO2, HfO2, these compound oxide, or the like is overlaid on the surface of the insoluble anode. And the consumption of the additive of electrolyte can be prevented simply and steadily without using a partition film to isolate the anode and the cathode, and the printed board can be plated with copper inclusive of a through hole.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for copper plating printed circuit boards and their through-holes using insoluble electrodes.

(Prior art and its problems) In order to connect the circuit parts on the front and back sides of a printed circuit board with copper foil layers formed on both sides, through holes, or through holes, are formed in the necessary parts, and the inner surface of the through holes is The two circuit parts are connected by copper plating. When performing through-hole plating, after forming the through-holes on the printed circuit board, activation is performed using a palladium-containing bath, and then electroless copper plating is performed on the entire printed circuit board to attach a thin plating layer. After this, electrolytic copper plating is further performed. The reason why electroless copper plating is used in conjunction with electrolytic copper plating without plating the entire body is as follows:
This is because electroless plating has a slow deposition rate and requires a long time with electroless plating alone, and secondly, electroless copper plating solution is expensive.

The electrolytic copper plating requires extremely strict control because it is necessary to uniformly perform etching and uniformly plate the inside of a through hole with a diameter of 0.3 mm or less.
Thickness must be good so that copper can be uniformly inserted into through-holes of 3 mm or less, copper plating must have appropriate hardness, no cracks, etc., and no fading due to gloss. required. In order to satisfy these various demands, a wide variety of additives are usually included in the plating solution.

The additives used include 1,3-dioxolane polymers, polyethers such as polypropylene glycol and polypropylene propanol, organic sulfur compounds, and organic nitrogen compounds, but all of them are said to be easily oxidized and decomposed by anodic polarization. The problem is that the decomposition of the additive is more likely to occur as the equilibrium potential of the anode is higher. Therefore, in conventional copper plating methods, a soluble anode of copper or a copper alloy is used as an anode to lower the equilibrium potential and prevent decomposition of the additive. In other words, when copper or copper alloy is used, the anode (Cu-
The equilibrium potential of “Cu”+’le) is 0.345V (v
sNHE), which is extremely low, whereas the anodic reaction when using an insoluble metal electrode is a normal oxygen evolution reaction (20H-
+2 e-*%O2+HzO), and its equilibrium potential is 1
．． 24V vs NHE (pH=o), which becomes nearly 1■ high.

However, when the anode is a soluble electrode made of pure copper, the additive decomposes even at such a low potential, so it is necessary to constantly replenish the additive to maintain the amount of the additive almost constant. Maintenance of the electrolyte and electrodes, such as avoiding imbalance between the amount of plating and the amount of elution of the soluble electrode, minimizing changes in the copper ion concentration in the electrolytic bath, and replacing the dissolved soluble anode, as usual for electrodes. The problem is that it requires management.

In order to solve the above-mentioned problems in copper plating using a normal copper sulfate bath, a plating method is adopted in which the cavity is housed in a bag-like body and electrolysis is carried out. In this method, a phosphate film is formed on the surface of copper, which is a soluble anode. It is believed that this suppresses excessive elution of

However, this method has problems such as the phosphorous-containing copper being expensive and the formation of sludge, and it is not completely effective in preventing additive decomposition and excessive elution of copper, so it is not directly effective in reducing maintenance work. The big problem is that it doesn't connect.

A method using a copper birophosphate bath has been proposed to overcome the problems of each of the above methods. This method has the advantages of relatively little additive decomposition and the ability to perform relatively stable electrolysis even when pure copper is used as the anode, but the cost of birophosphoric acid is extremely high and it is not economical. The problem is that it is not the target.

Therefore, recently, a method has been proposed in which copper ions in an electrolytic solution are replenished using a separate copper dissolving tank, and the electrolytic solution is supplied to a copper plating tank in which an insoluble anode is installed. According to this method, the problems described above when using a soluble anode are solved, but the problem of decomposition of the additive still remains, and in order to solve this problem, it is necessary to replace the additive with an oxidation-resistant compound. Although attempts have been made, no additive has yet been found that is stable under special conditions such as through-hole plating, and has not yet been used industrially.

The present inventors have realized that by separating an anode made of an insoluble metal electrode from a cathode made of a material to be plated by a diaphragm, most of the electrolyte containing the additive is prevented from coming into contact with the anode. We have proposed a method of preventing the additive from decomposing and continuously applying copper plating to the through-holes of the printed circuit board, which is the material to be plated, with a very small amount of replenishment of the additive (Japanese Patent Application No. 128078/1983). ).

The present inventors have arrived at the present invention as a result of further improving this method and investigating various methods that can almost completely suppress the consumption of the additive without using the diaphragm.

(Object of the Invention) The object of the present invention is to provide a method for copper plating a printed circuit board or the like having a through hole that has an effect of suppressing additive decomposition that is equal to or greater than that of the diaphragm. shall be.

(Means for Solving the Problems) The present invention provides a method for plating a printed circuit board by electrolyzing an electrolytic solution containing copper ions and additives using an insoluble anode. This method is characterized by using an anode on which a coating layer that is inert is formed.

The present invention will be explained in detail below.

By using the method of the present invention to plate through-holes in printed circuit boards using an anode with a coating layer formed on its surface, it is possible to obtain effects equal to or greater than the above-mentioned method in which the anode and cathode are separated by a diaphragm. .

When electrolysis is performed using the anode of the method of the present invention, the coating layer formed on the anode surface suppresses the diffusion of the electrolytic solution containing additives into the electrode active material on the anode surface through the coating layer. By preventing the additive from coming into contact with the anode, decomposition of the additive is suppressed. However, as will be described later, the thickness of the coating layer is about 0.5 to 10 μm, which is extremely thin compared to the thickness of a normal diaphragm, which is several hundred μ to several hundred μ, and is simply due to the diffusion of the electrolyte. It is impossible to explain the suppression of additive decomposition by the method of the present invention solely by a decrease in speed. It is thought that the diffusion suppressing effect and the barrier effect of the stable gas layer formed on the anode surface contribute synergistically to suppress the decomposition of the additive, and the formation and function of the gas layer are as follows. can be understood as such. The coating layer of the anode is considered to be easily attached to the generated gas, and promotes the recombination of the generated gas on its surface to form a considerably thick gas layer on the anode surface, and the gas adheres to the anode surface. When it leaves the anode, the bubble size becomes quite large, and the gas rises quickly due to the added buoyancy, which causes clouding of the electrolyte due to fine bubbles generated from the anode, which is a problem when electrolysis is performed using a normal insoluble anode. Object to be plated (
The occurrence of plating defects due to the adhesion of air bubbles to the surface of the cathode,
This eliminates the problem of severe deterioration of the working environment due to the generation of intense mist from the surface of the electrolytic bath. It is presumed that this behavior is similar to that of using a diaphragm to separate the gas generated from the anode, and that the consumption of additives in the electrolyte is suppressed.

Of course, in order to completely prevent the separation of the gas generated from the anode and the consumption of additives in the electrolyte, the anode on which the coating layer is formed may be separated from the negative bottle using a diaphragm.

In the copper plating method according to the present invention, an insoluble anode, so-called DSE electrode, which is formed by coating a titanium base material with, for example, a platinum group metal oxide, is used as the anode.

The DSE electrode has an anode potential (oxygen evolution potential) approximately 10,100 O higher than a soluble anode, but an anode potential of 300 O higher than an electrode whose base material is coated with a platinum group metal or a lead electrode.
Since the voltage is low by ~600 mV, additive decomposition can be effectively prevented. However, the platinum group metal coated electrode or the lead electrode may be used in the method of the present invention, and the shape of the insoluble anode may be any shape such as porous, plate, rod, or box shape with an open top. .

In the present invention, an anode having an electrochemically inactive coating layer formed on the anode surface is used. The material forming the coating layer is selected from materials having a certain degree of electrical conductivity and liquid permeability, and examples of organic materials include ion exchange functional groups such as sulfonic acid groups, carboxylic acid groups, and quaternary ammonium bases. Examples of polymer resins in which ion exchange resins are introduced include so-called ion exchange resins. Considering that the anode surface is electrochemically exposed to a high oxidation potential, it is recommended to use fluorocarbon resins as the pace polymer in order to improve durability. Desirable from all aspects. Furthermore, as an inorganic material, Ti0, which is chemically and electrochemically stable and has electrically insulating semiconductor properties, is used.
z, Ta2es, ZrO2,5n02, WO', ,
Examples include HfO□ or composite oxides thereof,
The inorganic material can also be used in combination with the organic material.

As a method for attaching these materials to the anode surface, for example, firstly, material powder is dispersed in an organic solvent or water to form an emulsion liquid, an acid solution is applied to the anode surface and dried, and an appropriate heat treatment is applied to the anode surface. How to combine, 2nd
For inorganic materials, starting materials that can be converted into oxides, such as chlorides, nitric acid compounds, alkoxide compounds, etc., are made into a hydrochloric acid solution, nitric acid solution, alcohol solution, etc., and then applied to the anode surface and dried, and then heated in an electric furnace. There is a method in which a thermal decomposition reaction is carried out to simultaneously synthesize the target compound and the bonding of the compound to the anode surface, and a third method is a dry method such as a chemical vapor deposition method.

The coating thickness of these materials on the anode surface is preferably in the range of 0.5 to 10μ; if it is less than 0.5μ, the effect of forming the coating layer will be insufficient, and if it exceeds 10μ, the properties of the materials , the disadvantage is that electrical resistance increases and continuous operation becomes difficult.

In order to install such an anode in an electrolytic cell, it is necessary to install a beam between the upper edges of the electrolytic cell, even if a power supply rod is erected from the bottom and connected to the power supply as in a normal salt electrolytic cell. erected,
For example, the upper end of an inverted J-shaped power supply body connected to the anode may be suspended from the beam.

The cathode is a material to be plated such as a printed circuit board, and the material to be plated is, for example, a composite plate in which a synthetic resin is coated with a thin layer of copper foil and a large number of through holes are bored at predetermined positions. be. Before the material to be plated is electroplated by the method of the present invention, it is desirable to form a thin copper plating layer on the surface of the material by chemical plating in order to perform the electroplating smoothly.The material to be plated is usually 30 cm thick. X
Although the plate is approximately 30 cm long, in the method of the present invention, in order to process a large number of plated materials in one operation, a large number of plated materials are arranged vertically and horizontally to form one large flat plate, and a predetermined jig is used. It is preferable to install it in an electrolytic cell.

When a diaphragm is used to separate the anode and cathode, it is desirable that the diaphragm substantially completely prevents the passage of additives. The additives often exist in a colloidal state rather than ions in the liquid, and the particle size of the additives is from several microns to several tens of microns when they aggregate with each other or are surrounded by water molecules.
Therefore, the opening of the diaphragm is 1
It is desirable that it be 0μ or less.

Particularly when using the diaphragm, if the liquid is stirred by sending air to sufficiently feed copper ions to the surface of the material to be plated and remove gas generated in the cathode chamber, the flow of the liquid will be extremely good. The diaphragm is intended to almost completely prevent the flowing plating solution from coming into contact with the anode, and can be installed in any way in the electrolytic cell as long as it can separate the anode chamber and the cathode chamber and prevent the plating solution from penetrating. However, it is preferable that the bag-like shape is placed close to the anode and encloses the anode, and that the upper part is open for releasing the generated gas.In addition, a planar diaphragm partitions the plurality of anode chambers and cathode chambers. A so-called filter press type electrolytic cell may be configured.

The material of the diaphragm is not particularly limited, but an ion exchange membrane is most suitable from the viewpoint of liquid impermeability and resistance loss.

The electrolytic cell used in the method of the present invention may be a new one, but it is preferable to use a converted electrolytic cell that has been used for a conventional soluble anode. This can be carried out by a relatively simple process of replacing the insoluble anode on which the surface coating layer has been formed, dividing the anode and cathode with a diaphragm as necessary, and installing a line to supply copper ions from the outside. can.

The electrolyte used includes a catholyte containing copper ions, and the above-mentioned additives, such as 1,3-dioxolane polymer or polyethers such as polypropylene glycol and polypropylene propanol, and N [sulfur compounds, nitrogen compounds (phenazine dyes, etc.)]. The anolyte is an electrolytic solution containing an arbitrary conductive substance.

Electrolytic conditions such as current concentration, applied voltage, current density, and liquid temperature may be the same as those for conventional copper plating methods using soluble anodes; for example, the current concentration is 0.5 to 10.0 A/1, and the applied voltage is 2. .5-3.5V, anode current density 1-10A/dI
II! , cathode current density 1~6A/d111! The liquid temperature is 1
The temperature should be about 5-35°C.

Copper ions are supplied by dissolving an appropriate copper compound, such as copper carbonate, in an electrolytic solution and adding it to the cathode chamber of the electrolytic cell, and circulating the electrolytic solution to remove the amount of copper that has been reduced by plating the material to be plated. Preferably, the copper ion concentration in the cathode chamber is maintained approximately constant by redissolving it in the electrolyte.

When using a diaphragm, slightly pressurizing the anode chamber side will completely prevent the additive from penetrating into the anode chamber due to catholyte diffusion through the diaphragm, thereby preventing decomposition of the additive. This can be more effectively prevented. The pressurization can be performed, for example, by providing a valve for dissipating waste gas on the anode chamber side and adjusting the amount of dissipated gas using the valve.

According to the method of the present invention, a composite board is manufactured in which a copper plating layer of approximately uniform thickness is formed on the surface and in the through holes, and after processing such as cleaning, the composite board is processed in subsequent steps for manufacturing printed circuit boards, etc. sent to.

Further, the present invention can also be applied to electronic materials other than printed circuit boards such as copper metal and 7 metal.

(Example) Examples of the method of the present invention will be described below, but the examples do not limit the present invention.

Example 1 Commercially available Cu5O<, 5t[zo 70g/l, II
A copper sulfate type plating bath consisting of 10% by volume of ZSO4 and 50ppm of CI was added with 5a+I/j of Cubrite TH (trade name, manufactured by Ebara Nishilight Co., Ltd.) as an additive. In addition, a continuous Hull cell test was conducted so that

The test was conducted using a Hull cell capacity of 1267 m1 and a current value of 2 A.
(average cathode current density 4A/d+n2), temperature 25℃, electrolysis time 10 minutes/while stirring the liquid with air.
The test was repeated 12 times while changing the cathode. A pure copper plate was used as the cathode, and Nafion liquid (manufactured by Altrift Chemical Co., USA) was selected as the liquid-permeable and electrochemically inert anode surface treatment material, which was repeatedly applied and dried on the surface of the platinum-plated titanium anode substrate. and finally 230℃
A coating layer having a thickness of 7.50 μm was formed on the surface of the anode by heat treatment for 10 minutes.

During the test, no additives were added to the plating bath, but by adding and dissolving copper carbonate powder equivalent to the plating bath,
Copper ions were replenished. Table 1 shows the results regarding the sliding voltage and plating condition.

Example 2 A pure copper plate was plated with copper under the same conditions as in Example 1, except that the anode base material was a titanium material (iridium oxide bridge) coated with a composite oxide whose main component was iridium oxide. The results are shown in Table 1.

8. A mixed alcohol solution of titanium alkoxide, tank alkoxide, and Nafion was used as a material for surface treatment of the anode of the large scale anode, and after coating the solution on the anode surface and drying, thermal decomposition treatment was repeatedly performed at 300° C. for 15 minutes. Copper plating was carried out on a pure copper plate under the same conditions as in Example 2, except that a coating layer consisting of a titanium oxide-tank Lunafion thin film having a thickness of 0 μm was formed.

The results are shown in Table 1.

Odomemasu ↓ The coating layer thickness is 3.0μ, and the diaphragm is Nafion #11.
Copper plating was performed on a pure copper plate under the same conditions as in Example 1, except that Copper Plating No. 7 (manufactured by DuPont) was used. The results are shown in Table 1.

Flame-stopping comparison 21 In all cases, no coating layer was formed, and an iridium oxide electrode (comparative example 1), a phosphorus-containing copper electrode (comparative example 2), and an iridium oxide electrode (comparative example 3) were used as anodes, respectively. Furthermore, Nafion #117 was used as a diaphragm (Comparative Example 3).
Only) Copper plating was performed on a pure copper plate under the same conditions as in the example.

The results are shown in Table 1.

As can be seen from Table 1, if the anode is simply used as an insoluble anode, cloudiness will appear after the second use, which indicates that the additive has decomposed.9On the other hand, as an anode, liquid penetration When all insoluble anodes with electrochemically inert and electrochemically inert surface treatment are used, the properties are the same as or close to those when using phosphorus-containing copper-soluble anodes or when separation is performed using only a diaphragm. Ta. Further, the roughness of the plating surface due to the excessive copper concentration in the latter half, which is observed in the phosphorus-containing copper-soluble anode, was not observed at all in this example.

Furthermore, in the case of an insoluble anode that has undergone surface treatment, the anode surface is covered with a fairly thick gas layer, and the gas bubbles that leave the surface are large in size and rise along the anode surface, making it possible to eliminate the use of a diaphragm. Gas-liquid separation was performed smoothly, and the electrolyte did not become cloudy due to fine dispersed bubbles. After the test, no abnormalities such as peeling or discoloration of the anode coating layer were observed.

Of the two soluble anodes used, the iridium oxide electrode caused less decomposition of the additive than the platinum titanium electrode. This is presumably because the oxygen overvoltage of the iridium oxide electrode is 300 to 400 mV lower than that of the platinum-plated titanium electrode.

(Effects of the Invention) The copper plating method according to the present invention includes separating an anode on which an electrochemically inert coating layer is formed and a cathode made of a material to be plated such as a printed circuit board by a diaphragm as necessary. Electrolysis is performed using a solution containing copper ions and additives as an electrolytic solution, and the surface of the material to be plated and, if necessary, the through holes thereof are plated.

Therefore, first, the additive in the electrolyte permeates through the surface coating layer of the anode and the gas layer formed by the generated gas, and comes into direct contact with the electrode active material on the anode surface, causing the additive to be decomposed. Since there is almost no consumption of expensive additives, the operation can be carried out economically. Furthermore, if necessary, by separating the two electrodes with a diaphragm or pressurizing the anode chamber side separated by the diaphragm, the permeation of the anode active substance through the diaphragm of the additive can be more reliably prevented. , additive wastage is almost completely avoided. This makes it possible to suppress the consumption of the additive in the method of the present invention to the same level as or less than the consumption of the additive in the conventional copper plating method using a soluble anode whose anode potential is lower than that in the method of the present invention. Furthermore, when a dense thin film such as an ion exchange resin is used as the material for forming the coating layer, the thin film is essentially impermeable to additives and the formation of a gas layer on its surface when gas is generated. Coupled with the secondary barrier effect, decomposition and consumption of the additives is even more completely prevented.

Second, because the anode is essentially insoluble, replacing a worn-out soluble anode requires the traditional effort and skill of shutting down operations and removing the soluble anode from the irritating electrolyte. This eliminates the need for additional work, greatly improving work efficiency.

Third, since the anode is essentially insoluble and the consumption of additives can be completely suppressed, there is no sludge generation that normally occurs when using soluble anodes such as phosphorus-containing copper, and the surface condition is good. A plated material can be obtained.

Fourth, all that is required is to replace the conventional soluble anode with an insoluble anode on which a coating layer is formed, install an external copper ion supply line, and, if necessary, house the insoluble anode in a bag-like diaphragm. Since an electrolytic cell using a conventional soluble anode can be easily converted into an electrolytic cell for use in the method of the present invention, an electrolytic apparatus for use in the method of the present invention can be prepared relatively easily.

Claims (4)

[Claims] (1) In a method of electrolyzing an electrolytic solution containing copper ions and additives using an insoluble anode to copper plate a printed circuit board serving as a cathode, an electrochemically inactive coating layer is formed on the surface of the insoluble anode. A method characterized by using an anode formed with. (2) The method according to claim 1, wherein the plating is performed by separating the insoluble anode and the cathode by a diaphragm. (3) The method according to claim 1, wherein the coating layer is a thin film of a fluorine-based ion exchange resin. (4) The coating layer is TiO_2, Ta_2O_5, ZrO
2. The method according to claim 1, wherein the thin film is selected from the group consisting of _2, SnO_2, WO_3, HfO_2, and composite oxides thereof.