JP2510422B2 - Copper plating method for printed circuit boards - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for copper plating on printed circuit boards using insoluble electrodes.

(Prior art and its problems) In order to connect the circuit parts on the front and back surfaces 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 formed. Copper plating is applied to connect both circuit parts.
When performing the through-hole plating, after forming the through-hole on the printed board, activation is performed using a palladium-containing bath, and then electroless copper plating is performed on the entire printed board to deposit a thin plating layer. After this, electrolytic copper plating is further performed. The reason why electrolytic copper plating is used only without electroless copper plating is that electroless plating has a slow deposition rate and requires a long time only with electroless plating. Secondly, electroless copper plating solution. Is expensive.

The electrolytic copper plating is extremely strict control because it is necessary to perform etching uniformly and to uniformly plate the through holes having a diameter of 0.3 mm or less, that is, copper is evenly introduced into the through holes having a diameter of 0.3 mm or less. It is required that the fitting contact is good, that the copper plating has an appropriate hardness, that cracks and the like do not occur, and that it has gloss and does not cause burns and the like. In order to satisfy these various requirements, many kinds of additives are usually contained in the plating solution.

As the additive, polyethers such as 1,3-dioxolane polymer or polypropylene glycol, polypropylene propanol and organic sulfur compounds, organic nitrogen compounds and the like are used, but they are easily oxidized and decomposed by anodic polarization. There is a problem, and the decomposition of the additive easily occurs as the equilibrium potential of the anode increases. Therefore, in the conventional copper plating method, a soluble anode made of copper or a copper alloy is used as an anode to lower the equilibrium potential and prevent decomposition of the additive. That is, the anode when using copper or copper alloy (Cu → Cu
Equilibrium potential ²⁺ + 2e) whereas very low 0.345V (vsNHZ), anodic reaction in the case of using an insoluble metal electrode is normally oxygen evolution reaction ^{(2OH - + 2e → 1 /} 2O 2 + H 2 O) becomes The equilibrium potential becomes 1.24V vs NHZ (pH = 0), which is higher than 1V.

However, when the anode is a pure copper soluble electrode, decomposition of the additive occurs even at such a low potential,
It is necessary to constantly replenish the additive to maintain the additive amount substantially constant, and to avoid an imbalance between the plating amount and the elution amount of the soluble electrode, which is the usual condition for the soluble electrode, to avoid the copper ion concentration in the electrolytic bath. However, there is a problem in that the electrolytic solution and the electrode need to be maintained and managed by, for example, suppressing the change of the electrolyte to a minimum and replacing the soluble anode.

In copper plating using a normal copper sulfate bath, a plating method in which phosphorus-containing copper is contained in a bag-shaped body and electrolysis is adopted in order to solve the above problems. In the plating method, a phosphate coating is formed on the surface of copper, which is a soluble anode, and the coating reduces the degree of contact of the additive with the copper anode to suppress the decomposition of the additive and to prevent excess copper. It is believed to suppress elution. However, this method has problems that the phosphorus-containing copper is expensive and that sludge is generated, and since the prevention of additive decomposition and the prevention of excessive elution of copper are not perfect, the maintenance work is directly reduced. It has a big problem of not being connected.

In order to overcome the problems of each of the above methods, a method of using a copper pyrophosphate bath has been proposed. This method has the advantages that the decomposition of additives is relatively small and that relatively stable electrolysis can be performed even when pure copper is used as the anode, but the price of pyrophosphoric acid is extremely high, and the economy is low. There is a problem that it is not the target.

Therefore, recently, a method has been proposed in which copper ions of an electrolytic solution are supplied 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 problem in the case of using the above-mentioned soluble anode is solved, but the problem of decomposition of the additive still remains, and in order to solve this, the additive may be replaced with an oxidation resistant compound. Attempts have been made, but it is the present situation that an additive that is stable under special conditions such as the above-mentioned through-hole plating has not been found yet, and it has not been industrially used yet.

(Object of the Invention) The present invention solves the above-mentioned problems of the prior art, that is, the decomposition of additives, the use of expensive reagents, etc., and a plating method capable of obtaining a high-quality plated material through-hole plated. The purpose is to provide.

(Means for Solving Problems) The present invention separates an anode composed of an insoluble metal electrode coated on a titanium-based base material and a cathode composed of a material to be plated for a printed circuit board by a diaphragm to separate copper ions and an additive material. In a copper plating method for a printed circuit board, wherein a contained liquid is electrolyzed as an electrolytic solution to plate the surface of the material to be plated and through holes, the insoluble metal electrode is an electrode obtained by coating a platinum group metal oxide on a titanium-based substrate. The method is characterized in that the electrolysis is performed while applying pressure to the anode chamber side.

 The present invention will be described in detail below.

In the copper plating method according to the present invention, an anode composed of an insoluble metal electrode coated with a platinum group metal oxide on a titanium-based substrate is separated from a cathode composed of a material to be plated by a diaphragm and pressure is applied to the anode chamber side. A printed circuit board which is a material to be plated continuously, which prevents most of the electrolyte solution containing the additive from coming into contact with the anode, thereby preventing the decomposition of the additive and continuously supplying the additive. Copper plating is applied to the through holes.

In the method of the present invention, a so-called DSE electrode, which is an insoluble anode formed by coating a platinum base metal oxide on a titanium substrate, is used as the anode. The DSE electrode has an anode potential (oxygen generation potential) of about 1000 mV higher than that of a soluble anode, but the anode potential is 500 to 8 when compared with an electrode in which a platinum group metal is coated on a substrate or a lead electrode.
Since it is lower than 00 mV, the decomposition of additives can be effectively prevented. The shape of the insoluble anode may be any shape such as porous, plate-like, rod-like, and box-like with an open top. In order to install the anode in the electrolytic cell, a beam is installed between the upper edges of the electrolytic cell even if a power feeding rod is erected from the bottom and connected to the power feeding rod like a normal salt electrolytic cell. The upper end of, for example, an inverted J-shaped power supply unit connected to the beam may be suspended from the beam.

The cathode is a material to be plated for a printed circuit board, and the material to be plated is, for example, a composite plate in which a synthetic resin is thinly coated with copper foil and a large number of through holes or through holes are formed at predetermined positions. . Before the electroplating according to the method of the present invention, it is desirable that a thin copper plating layer is formed on the surface of the material to be plated by chemical plating in order to smoothly perform the electroplating. The material to be plated is usually a plate of about 30 cm × 30 cm, but in the method of the present invention, a large number of materials to be plated are arranged in the vertical and horizontal directions so that a large number of materials to be plated can be processed in one operation. It is preferable to form a large flat plate and install it in the electrolytic cell with a predetermined jig.

The septum used should be one that almost completely blocks the passage of additives. The additive often exists in a liquid in a colloidal state rather than an ion, and the additive has a particle size of agglomerated with each other or is accompanied by water molecules in the periphery of several μ to
Since it is considered to be several tens of μ, it is desirable that the opening of the diaphragm is 10 μ or less.

According to the method of the present invention, since the copper ions are sufficiently sent to the surface of the material to be plated and the air is sent to remove the gas generated in the cathode chamber to stir the liquid, the flow of the liquid becomes extremely good. The diaphragm is for preventing the contact of the circulating plating solution with the anode, and may be installed in any electrolytic cell as long as it can separate the anode chamber and the cathode chamber and prevent the penetration of the plating solution. It is preferable that the shape is close to the anode and encloses the anode, and the upper part is opened for the release of generated gas. In addition to this, a plurality of anode chambers and cathode chambers are divided by a planar diaphragm, so-called You may make it comprise a filter press type electrolytic cell.

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 convert and use the electrolytic cell that has been used for the conventional soluble anode. This can be performed by a relatively simple operation of replacing the insoluble anode with the diaphragm and partitioning the anode and the cathode, and installing a line for supplying copper ions from the outside.

The electrolytic solution used is such that the catholyte contains copper ions and the aforementioned additives such as 1,3-dioxolane polymer or polypropylene glycol, polyethers such as polypropylene propanol and organic sulfur compounds, nitrogen compounds (phenazine dyes, etc.). The contained electrolyte solution is used, and the anolyte solution is an electrolyte solution containing an arbitrary conductive substance.

Electrolysis conditions such as current concentration, applied voltage, current density, and liquid temperature may be the same as the conventional copper plating method using a soluble anode, for example, current concentration is 0.5 to 10.0 A /, applied voltage is 2.5 to
3.5V, anode current density is 1-10A / dm ² , cathode current density is 1
〜6A / dm ² , liquid temperature is about 15〜35 ℃.

Copper ions are supplied by dissolving an appropriate copper compound in an electrolytic solution, for example, copper carbonate, and adding it to the cathode chamber of the electrolytic cell, and circulating the electrolytic solution to reduce the amount of copper that has been reduced by plating the material to be plated. It is preferable to redissolve it in the electrolytic solution so that the copper ion concentration in the cathode chamber is maintained substantially constant.

During electrolysis, if the anode chamber side is slightly pressurized,
Penetration of the additive into the anode chamber due to liquid diffusion of the catholyte through the diaphragm is reduced, and the decomposition of the additive can be prevented more effectively. The pressurization can be performed, for example, by providing a valve for discharging waste gas on the anode chamber side and adjusting the amount of waste gas discharged by the valve, or by keeping the water level in the anode chamber always higher than the water level in the cathode chamber. it can.

According to the method of the present invention, a composite board having a copper plating layer having a substantially uniform thickness formed on the surface and in the through holes is manufactured, and the composite board is subjected to a process such as cleaning and then subjected to a subsequent step for manufacturing a printed circuit board. Sent.

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

Examples 1-2 Commercially available CuSO ₄ .5H ₂ O 70 g /, H ₂ SO ₄ 10% by volume, Cl ^- 50 ppm
A continuous Hull cell test was carried out by adding a Cubleite TH (trade name, manufactured by EBARA Eugelite Co., Ltd.) as an additive to the copper sulfate type plating bath consisting of 5 ml /.

The test was conducted with a Hull cell capacity of 267 ml, a current value of 2 A (average cathode current density of 4 A / dm ² ), a temperature of 25 ° C., an electrolytic time of 10 minutes / time while stirring the liquid with air, and 12 times while exchanging with the cathode. I went over again. Using a pure copper plate as the cathode,
As the ion exchange membrane, a cation exchange membrane, trade name Nafion # 117 (manufactured by DuPont, Example 1) and a neutral diaphragm, trade name Yumicron Y9025 (manufactured by Yuasa Battery Co., Example 2), are used. The periphery of an anode, which is a titanium electrode (hereinafter referred to as an iridium oxide electrode) coated with a complex oxide whose component is iridium oxide, was covered. As a comparative example, copper plating of the same cathode was performed using the same electrode not covered with a diaphragm, a phosphorus-containing copper-soluble anode and a platinum-plated titanium electrode. During the test, no additive was added to the plating bath, and copper ions were supplemented by adding a copper carbonate solution corresponding to the plating amount. The results are shown in Table 1.

As can be seen from Table 1, if a diaphragm is not used, no matter whether the platinum-plated titanium electrode (Comparative Example 1) or the iridium oxide electrode (Comparative Example 2) is used, clouding will occur after the second time. This indicates that decomposition of the additive has occurred. On the other hand, when a platinum-plated titanium electrode was used as the anode and the anode was covered with Nafion (Comparative Example 4) or Yumicron (Comparative Example 5), both were compared with the case of using the phosphorus-containing copper-soluble anode (Comparative Example 3). The characteristics are equivalent or close to it. Decomposition of the additive was less with the iridium oxide electrode than with the platinum-plated titanium electrode. It is speculated that this is because the oxygen overvoltage of the iridium oxide electrode is lower than that of the platinum-plated titanium electrode by 300 to 400 mV. Further, the roughness of the plating surface due to the excessive copper concentration in the latter half, which was observed in the phosphorus-containing copper-soluble anode, was not seen at all in this example.

Of the two insoluble anodes used, the iridium oxide electrode decomposed less additive than the platinum-plated titanium electrode. It is speculated that this is because the oxygen overvoltage of the iridium oxide electrode is lower than that of the platinum-plated titanium electrode by 300 to 400 mV.

Examples 3-4 Example 1 except that iridium oxide was used as the anode.
In the same manner as 2 and 2, copper plating was performed while covering the anode with a diaphragm, and the number of repetitions was increased to 20 times to compare the conditions around the diaphragm. In Examples 3 and 4, the diaphragm was formed into a bag shape, and a gas vent pipe was attached to the anode side so that the pipe was adjusted so that a positive pressure of about 0.5 to 1 cm of water column was applied to the bag-like diaphragm in the plating bath. In Comparative Examples 6 and 7, the upper surface of the diaphragm was opened so that no pressure difference was generated. Table 2 shows the results.

From Table 2, it was found that the decomposition of the additive was further suppressed by making the diaphragm into a bag shape and applying a slight pressure to the anode side.

Example 5 Copper plating scaled up to an industrial scale was performed based on Examples 1 to 4.

 The structure of the electrolytic cell was as follows.

Cathode: Copper foil-clad laminate (glass epoxy substrate)
Through holes are drilled in this board (length 330 mm ×
Twelve sheets (height 250 mm x thickness 1.6 mm) are placed in four inverted J-shaped rod-shaped jigs (cathode racks) that face up and down so that one plate cathode is formed by one substrate. The cathode was set, and the cathode was suspended by the dedicated jig from a cathode beam laid horizontally. Avoiding abnormal plating thickness due to edge current on the outer periphery of the substrate Therefore, a copper plate with a width of 5 cm in a window frame shape is so-called "bait" in that part.
It was installed as an electrode. The total cathode projected area was about 1.2 m ² .

Anode: Titanium lath, length 1420 mm x height 850 mm x thickness 7
A box with an open upper part (5 mm) is made, two inverted J-shaped titanium rods facing up and down are connected to the inside of the box as a power feeding body, and the tip of the power feeding body is laid horizontally in the anode. I hung it on the beam. The electrode portion of this structure was coated with iridium oxide to serve as an anode. Two anodes were prepared for supplying power from both sides of the cathode.

Diaphragm: Nafion # 117 manufactured by DuPont was molded by a thermocompression bonding method into a bag shape having an open top so that the anode could be completely covered. The anode was covered with the diaphragm and placed in an electrolytic cell.

Electrolyzer: Effective volume is 1800mm × 1200mm × 420mm = 0.91m
^An electrolytic cell of ³ was used. The cathode beam receiver was connected to a cathode rocker rod and added with a mechanism capable of reciprocating motion. The anode beam receivers were fixed at two positions sandwiching the cathode. An air diffuser for air bubbling was installed at the bottom. Further, a nozzle was installed so that it could be continuously circulated between the filter outside the tank and the copper ion supply tower.

Copper ion supply tower: A cylindrical body provided with a hopper capable of continuously supplying basic copper carbonate to the upper part thereof, and a stirring device was incorporated in the cylindrical body. The electrolytic solution was introduced from the lower part, the supernatant liquid after dissolution was allowed to overflow, and the electrolytic cell was returned after passing through the filter.

First, after the end face polishing of the substrate after the through hole drilling process, degreasing and cleaning, and exposed to about 0.5 on the exposed front surface with a chemical copper plating bath
Copper plating of μ thickness was applied. Next, the cathode jig (rack) to which the substrate was fixed was hung down to a predetermined position in the electrolytic cell, the cathode lock was operated while air bubbling was performed, and electroplating was started while supplying copper ions. Electrolysis was carried out for 48 minutes at a current of 600 A and a cathode current density of 2.5 A / dm ² . The dissolution rate of copper carbonate depends on the current efficiency of copper deposition of 96.
21.4 g / min (CuCO ₃ · Cu (O
H) ₂ · H ₂ O). The brightener was Cublite TH manufactured by Ebara-Udylite Co., Ltd., which was injected at 2.25 ml / min. Almost no change was observed in the concentration of copper ions in the bath. The substrate after electroplating had a glossy and normal appearance, and the plating thickness (copper foil thickness + chemical plating thickness + electroplating thickness) was 41 μ, which was a substantially uniform thickness.

By the destructive inspection, the throwing power of the through hole portion and the presence or absence of a conner crack were examined, but there was no problem. The tensile strength, elongation, and hardness were normal, and there were no abnormalities in the etching property, solder wettability, heat cycle test, and heat interference test, and the plating quality was sufficient for use as a printed circuit board.

The above operation was repeated, and the plating was repeated 500 times while correcting the copper ion concentration in the electrolytic solution based on the chemical analysis value, but the appearance and physical properties of the plating could be maintained as well as during the construction. No abnormalities such as discoloration and deformation were observed in both the anode and the diaphragm.

(Effect of the invention) The copper plating method according to the present invention, an anode composed of an insoluble metal electrode coated with a platinum group metal oxide on a titanium-based substrate and a cathode composed of a material to be plated for a printed circuit board are separated by a diaphragm, Electrolysis is performed while applying pressure to the anode chamber side using a liquid containing copper ions and an additive as an electrolytic solution to plate the surface of the material to be plated and the through holes.

Therefore, firstly, since the additive in the cathode chamber hardly permeates to the anode chamber side through the diaphragm and contacts the anode to be decomposed, the expensive additive is scarcely consumed to operate economically. And because the anode chamber is pressurized,
Permeation of the additive through the diaphragm to the side of the anode chamber is further prevented. Moreover, since the platinum group metal oxide electrode having an overvoltage smaller than that of the platinum group metal electrode is used as the electrode, the consumption of the additive is almost completely avoided. Thereby, the consumption of the additive in the method of the present invention can be suppressed to be smaller than the consumption of the additive in the copper plating method using the conventional soluble anode or the platinum group metal electrode whose anode potential is lower than the potential of the method of the present invention. If possible, and if a dense membrane such as an ion exchange membrane is used as the diaphragm, the decomposition of the additive can be completely prevented.

Secondly, since the anode is insoluble, it takes time and skill to stop the operation and replace the exhausted soluble anode from the irritating electrolytic solution to replace the exhausted soluble anode. Since it is unnecessary, work efficiency is greatly improved.

Thirdly, since the anode chamber is partitioned from the material to be plated by the diaphragm, even if sludge or the like is generated in the anode chamber, the sludge or the like does not deposit on the material to be plated, and the surface A plated material in good condition can be obtained.

Fourthly, if the diaphragm is formed in a bag shape, the conventional soluble anode is replaced with an insoluble anode, the insoluble anode is housed in the bag-shaped diaphragm, and a copper supply line is externally provided. The electrolytic cell used can be easily converted into the electrolytic cell used in the method of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-26689 (JP, A) JP-A-59-193295 (JP, A) Practical application Sho-62-166265 (JP, U)

Claims (3)

(57) [Claims] 1. An anode composed of an insoluble metal electrode coated on a titanium base material and a cathode composed of a material to be plated for a printed circuit board are separated by a diaphragm and electrolyzed using a solution containing copper ions and an additive as an electrolytic solution, In the copper plating method of a printed circuit board for plating the surface of the material to be plated and through holes, the insoluble metal electrode is an electrode in which iridium oxide is coated on a titanium-based substrate, and the electrolysis is pressurized from the anode chamber side. A method characterized by doing while. 2. The method according to claim 1, wherein the diaphragm is in the shape of a bag having an open top, and the diaphragm covers the anode to separate the anode and the cathode. 3. The method according to claim 1, wherein the diaphragm is an ion exchange membrane.