JPH01297884A - Copper plating of printed board - Google Patents

Abstract

PURPOSE:To apply high quality plating to a surface of a plating object and a through hole by separating an anode consisting of insoluble metal electrode from a cathode consisting of a plating object for a printed board by a barrier and by making electrolytic solution of copper ion and additive-containing solution. CONSTITUTION:When applying copper plating to a printed substrate by using an insoluble electrode, an anode consisting of an insoluble metal electrode is covered with a bag-like barrier whose upper section is open to separate the anode from a cathode consisting of a plating object for a printed board. Copper ion and additive-containing solution is used as electrolytic solution to apply plating to a surface of the plating object and a through hole. Electrolytic plating is applied while pressurizing an anode room side. High quality copper plating of the printed board is applied by making an ion exchanging film of the barrier to separate the anode from the cathode and by making an electrode which is made by coating titanium base with platinum group metallic oxide, of the cathode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for copper plating printed circuit boards 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.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.
The copper plating must have a good throwing power so that the copper can be uniformly inserted into the through hole of 3 mm or less, the copper plating must have appropriate hardness, no cracks will occur, and it will be shiny and will not cause fading. required. In order to satisfy these various demands, a wide variety of additives are usually included in the plating solution.

As the additive, 1,3-dioxolane polymer, polypropylene glycol, polyethers such as polypropylene glycol, organic sulfur compounds, organic nitrogen compounds, etc. are used, but all of them are oxidatively decomposed by anodic polarization. The higher the equilibrium potential of the anode, the more easily the additive decomposes. 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 the additive from decomposing. In other words, when copper or copper alloy is used, the anode (Cu-+
The equilibrium potential of Cu”+2 e) is 0.345V (vsNH
2), which is extremely low, whereas the anodic reaction when using an insoluble metal electrode is a normal oxygen evolution reaction (20H-+2
e='AOz+HzO), and the equilibrium potential is 1.24
V vs NH2 (pH=o), which becomes high near IV.

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 problems in copper plating using a normal copper sulfate bath, a plating method is adopted in which phosphorous-containing copper is contained in a bag-like body and electrolyzed. In this plating method, a phosphate film is formed on the surface of copper, which is a soluble anode. It is thought to suppress elution.

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.

In order to overcome the problems of each of the above methods, a method using a copper pyrophosphate bath has been proposed. This method has the advantage of relatively little decomposition of additives and the ability to perform relatively stable electrolysis even when pure copper is used as the anode, but the cost of pyrophosphoric 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.

(Object of the Invention) The present invention solves the problems of the prior art described above, such as the decomposition of additives and the use of expensive reagents, and provides a plating method that can obtain high-quality through-hole plated materials. The purpose is to provide

(Means for Solving the Problems) The present invention separates an anode made of an insoluble metal electrode and a cathode made of a material to be plated on a printed circuit board by a diaphragm, and electrolyzes the solution using a solution containing copper ions and additives as an electrolyte. This copper plating method is characterized in that the surface of the material to be plated and the through holes are plated.

The present invention will be explained in detail below.

In the copper plating method according to the present invention, the anode made of an insoluble metal electrode is separated from the cathode made of the material to be plated by a diaphragm, thereby preventing most of the electrolyte containing additives from coming into contact with the anode. This prevents the additive from decomposing and allows copper plating to be continuously applied to the through-holes of the printed circuit board, which is the material to be plated, without replenishing the additive.

In the method of the present invention, an insoluble anode consisting of a titanium base coated with a platinum group metal oxide, for example, a so-called DSE electrode, is used as the anode. The DSE electrode has an anode potential (oxygen evolution potential) about 10,100 O higher than that of a soluble anode, but the anode potential is 500 to 800 mV lower than that of an electrode coated with a platinum group metal or a lead electrode, so the additive decomposes. can be effectively prevented. However, the platinum group metal coated electrodes and lead electrodes may be used in the method of the present invention. The shape of the insoluble anode can be arbitrary, such as a porous shape, a plate shape, a rod shape, or a box shape with an open top. In order to install the anode in the 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 rod as in a normal salt electrolytic cell. The upper end of, for example, an inverted J-shaped power supply body connected to the anode may be suspended from the beam.

The cathode is a plated material for a printed circuit board to be plated, and the plated material is, for example, a composite board in which a synthetic resin is thinly coated with copper foil and a large number of through holes are bored at predetermined positions. . 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 30c+n
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.

The diaphragm used should almost completely prevent 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 thought to be from several microns to several tens of microns when they aggregate with each other or are surrounded by water molecules. Therefore, it is desirable that the opening of the diaphragm be 10 μm or less.

In the method of the present invention, the liquid is stirred by sending air to sufficiently feed copper ions to the surface of the material to be plated and to remove gas generated in the cathode chamber, so that the liquid can flow very well.

The diaphragm is intended to prevent the circulating 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. It is preferable that the shape is close to the anode and wraps around the anode, and that the upper part is open for releasing the generated gas.In addition, a plurality of anode chambers and cathode chambers are partitioned by a planar diaphragm, so-called. A 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 the conventional soluble anode. This can be accomplished by a relatively simple operation of replacing the anode with an insoluble anode, separating the anode and cathode with a diaphragm, and installing a line to supply copper ions from the outside.

The electrolyte used includes a catholyte containing copper ions and the aforementioned additives such as 1,3-dioxolane polymer or polyethers such as polypropylene glycol and polypropylene propanol, organic sulfur compounds, and nitrogen compounds (phenazine dye, 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/l, and the applied voltage is 2. .5~3.5■, anode current density is 1~10A/d1
, cathode current density is 1~6 A/dm'', liquid temperature is 15~
The temperature should be around 35℃.

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.

In addition, during electrolysis, if the anode chamber side is slightly pressurized, the penetration of the additive into the anode chamber due to the diffusion of the catholyte through the diaphragm is reduced, and decomposition of the additive can be more effectively prevented. I can do it. 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 subjected to subsequent steps for manufacturing printed circuit boards. Sent.

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

Tip 2↓ Commercially available CuSO4,5Hz070g/A, HzS
A continuous Hull cell test was carried out by adding Cubrite TH (trade name, manufactured by Ebara Nishilight Co., Ltd.) as an additive to a copper sulfate type plating bath consisting of 10% by volume of Oa and 50 ppm of CI-5 at a concentration of 5 ml/β.

The test was conducted using a Hull cell capacity of 267n+] and a current value of 2 people (
The average cathode current density was 4 A/dm2), the temperature was 25°C, and the electrolysis time was 10 min/dm while stirring the liquid with air.
The test was repeated 12 times while changing the cathode. A pure copper plate was used as a cathode, and as a diaphragm, a cation exchange membrane (trade name: Nafion #117 (manufactured by DuPont, Examples 1 and 3) and a neutral diaphragm (trade name: Yumicron Y9025, manufactured by Yuasa Battery Co., Ltd., Examples 2 and 3) were used. 4), and using the diaphragm, platinum-plated titanium electrodes (Examples 1 and 2) and titanium electrodes coated with a composite oxide whose main component is iridium oxide (hereinafter referred to as iridium oxide electrodes, Examples 3 and 4). It covered the area around the anode. As a comparative example, the same electrode was not covered with a diaphragm, and the same cathode plate was plated with copper using a phosphorus-containing copper-soluble anode. During the test, no additives were added to the plating bath, and copper ions were replenished by adding a copper carbonate solution equivalent to the amount of plating.

The results are shown in Table 1.

As can be seen from Table 1, simply using an insoluble anode as an anode results in clouding after the second use, which indicates that the additive has decomposed. On the other hand, when an insoluble anode is used as the anode and the anode is covered with a diaphragm,
In both cases, the properties were equivalent to or close to those obtained when a phosphorus-containing copper-soluble anode was used. Furthermore, 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.

Of the two-year soluble anodes used, the iridium oxide electrode caused less additive decomposition than the platinum-plated 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.

Examples 5-8 Examples 1-8 except that iridium oxide was used as the anode.
Copper plating was performed while covering the anode with a diaphragm in the same manner as in 4, the repetition was increased to 20 times, and the conditions around the diaphragm were compared. In Examples 5 and 6, the diaphragm was shaped like a bag, and a gas vent pipe was attached to the anode side, and the pipe was adjusted so that a positive pressure of about 0.5 to 1 cm of water column was applied to the bag-shaped diaphragm in the plating bath. did. Examples 7 and 8 are Examples 1-
Similarly to 4, the upper surface of the diaphragm was opened to prevent pressure difference from occurring. The results are shown in Table 2.

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

Based on Examples 1 to 8, copper plating was carried out on an industrial scale.

The configuration of the electrolytic cell was as follows.

■ Cathode: Laminated board covered with copper foil (glass epoxy board)
This board (length 330m) was
One flat cathode was formed by the 12 substrates in four inverted U-shaped rod-shaped dedicated jigs (cathode racks) that faced up and down. The cathode was suspended from a cathode beam installed in the horizontal direction using the dedicated jig.

In order to avoid plating thickness abnormalities caused by edge current on the outer periphery of the substrate, a 5 cm wide steel plate was installed in the shape of a window frame as a so-called "decoy" electrode. The total cathode projected area was approximately 1.2M.

■ Anode: Titanium lath length 1420n+m x height 8
A box with an open top (50 mm x 75 mm thick) was made, and two inverted U-shaped boxes facing up and down were placed inside the box.
A titanium rod was connected as a power supply, and the tip of the power supply was suspended from an anode beam installed laterally. The electrode portion of this structure was coated with iridium oxide to serve as an anode. Two anodes were prepared to supply power from both sides of the cathode.

(2) Diaphragm: Nafion #117 manufactured by DuPont was molded by thermocompression into a bag with an open top so that it could completely cover the anode. The anode was covered with the diaphragm and placed in an electrolytic cell.

■ Electrolytic cell: effective volume 1800mm x 1200m
An electrolytic cell with m x 420 mm = 0.91 rrr was used. The cathode beam receiver is connected to the cathode rocker rod and has a mechanism that allows it to reciprocate. The anode beam receivers were fixed at two locations sandwiching the cathode. A diffuser pipe was installed at the bottom for air bubbling. A nozzle was also installed to allow continuous circulation between the filter outside the tank and the copper ion supply tower.

(2) Copper ion supply tower: It was a cylindrical body equipped with a hopper at the top to which basic copper carbonate could be continuously introduced, and a stirring device was built into the cylindrical body. An electrolyte solution was introduced from the bottom, and the supernatant solution after dissolution overflowed and was returned to the electrolytic cell after passing through a filter.

First, to drill through holes, after polishing the end surface of the substrate after the process, degrease and clean it, and apply a chemical copper plating bath to the exposed front surface with a thickness of about 0.5 mm.
Copper plating with a thickness of μ is applied. Next, the cathode jig (rank) to which the substrate was fixed was hung at a predetermined position in the electrolytic bath, 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. The dissolution rate of copper carbonate was calculated assuming that the current efficiency of copper deposition was 96%.
4 g/min (CuCOz ・Cu(OR)z ・82
0)). The brightener was Cubrite TH manufactured by Ebara Nishilight Co., Ltd., and was injected at a rate of 2.25 ml/min. Almost no change in the concentration of copper ions in the bath was observed. The board after electroplating had a glossy and normal appearance, and the plating thickness (thickness of copper foil, thickness of chemical plating, and thickness of electroplating) was 41 μm, which was almost uniform.

Destructive testing was conducted to check the throwing power of the through-hole section and the occurrence of corner cranks, but no problems were found.

In addition, the tensile strength, elongation, and hardness are normal, and the etching property and
There were no abnormalities in solder wettability, thermal cycle tests, and thermal interference tests, and the plating quality was sufficient to be used for printed circuit boards.

The above operation was repeated and plating was performed 500 times while correcting the copper ion concentration in the electrolyte based on chemical analysis values, and the plating appearance and physical properties were maintained as good as when the bath was prepared. Further, no abnormality such as discoloration or deformation was observed in either the anode or the diaphragm.

(Effects of the Invention) The copper plating method according to the present invention separates an insoluble anode and a cathode made of a printed circuit board material to be plated by a diaphragm, electrolyzes the copper ion and additive-containing solution as an electrolytic solution, and then The surface and through holes are plated.

Therefore, firstly, the additives in the cathode chamber permeate through the diaphragm to the anode chamber side, come into contact with the anode, and are hardly decomposed, so the operation can be carried out economically without wasting most of the expensive additives. I can do it. Furthermore, if the anode chamber side is pressurized, the permeation of the additive through the diaphragm into the anode chamber side is further prevented, and consumption of the additive 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, if a dense membrane such as an ion exchange membrane is used as the diaphragm, the decomposition of the additive can be more completely prevented.

Second, because the anode is insoluble, it is no longer necessary to stop the operation to replace a worn-out soluble anode, and to remove the soluble anode from the irritating electrolyte and replace it, which requires time and skill. Since this is no longer necessary, work efficiency is greatly improved.

Thirdly, since the anode chamber is separated from the material to be plated by a diaphragm, even if sludge or the like occurs in the anode chamber, the sludge or the like will not be deposited on the material to be plated, and the surface A plated material in good condition can be obtained.

Fourth, if the diaphragm is bag-shaped, the conventional soluble anode can be replaced by an insoluble anode by simply housing the insoluble anode in the bag-shaped diaphragm and installing an external copper supply line. The electrolytic cell used can be easily converted into an electrolytic cell used in the method of the present invention.

Claims (4)

[Claims] (1) An anode consisting of an insoluble metal electrode and a cathode consisting of a material to be plated for a printed circuit board are separated by a diaphragm, and a solution containing copper ions and additives is electrolyzed as an electrolyte to form a surface of the material to be plated and a through hole. A copper plating method characterized by plating. (2) Claim 1, wherein the diaphragm is shaped like a bag with an open top, and the diaphragm covers the anode to separate the anode and the cathode.
The method described in. (3) The method according to claim 1 or 2, wherein the electrolysis is performed while pressurizing the anode chamber side. (4) The method according to any one of claims 1 to 3, wherein the diaphragm is an ion exchange membrane, and the anode is an electrode in which a platinum group metal oxide is coated on a titanium base material.