JPH0568550B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to electroless copper plating (chemical copper plating) in which metallic copper is deposited by an autocatalytic reaction in which the deposited metal itself acts as a catalyst for the plating reaction. In particular, the present invention relates to a chemical copper plating apparatus having a suitable chemical supply structure for stably obtaining high-quality chemical copper plating with gloss and excellent mechanical properties.

[Background of the invention]

Through holes in printed circuit boards
The so-called additive process, which uses a chemical copper plating method to form holes and conductor wiring patterns, is a well-known method in the electronics industry and is used on a large scale industrially. The chemical copper plating solution used here generally contains divalent copper ions, copper ion complexing agents,
It contains a copper ion reducing agent and an alkali metal hydroxide as essential components, and the common method of use is to perform chemical copper plating while replenishing the components consumed in the plating reaction. . That is, by always controlling the concentration of essential components in the chemical copper plating solution to a constant value, plating of several μm or more is achieved. Various methods have been proposed for controlling the concentration of essential components in the plating solution, examples of which are disclosed in JP-A-54-143734 and JP-A-56-120943.

However, these methods simply replenish the chemical solution and control the concentration in order to maintain the concentration of the essential components of the plating solution at a predetermined value. Therefore, no consideration or recognition was given to the ability to provide a glossy, high-quality plating at a low cost under constant, uniform component concentrations. In other words, the chemical replenishment component for the chemical copper plating solution contains at least divalent copper (Cu ²⁺ ).
This is an aqueous solution containing an ionic salt aqueous solution, a Cu ²⁺ ion reducing agent, and an alkali metal hydroxide, but when these highly concentrated chemical components are replenished into the plating solution, Because the concentration of the components is higher than the average concentration in the plating solution, the plating solution becomes unstable, which has a significant negative effect on the chemical plating reaction and makes it impossible to provide stable, high-quality plating. There has been a strong desire to develop a method for replenishing chemical components that does not cause such problems, and a chemical copper plating apparatus having a replenishment structure.

[Purpose of the invention]

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and when replenishing a chemical copper plating solution with a highly concentrated chemical component containing essential components, it is possible to sufficiently mix and dissolve the chemical components in the plating solution to ensure uniformity. To provide a chemical copper plating apparatus which produces a plating solution with a high component concentration and has a chemical solution supply structure that does not impair the stability of the plating solution.

[Summary of the invention]

The present inventors have discovered that in chemical copper plating operations, in order to replenish the missing components consumed by the plating reaction, a rich chemical solution containing the missing components is usually replenished. If the replenished chemical solution is not sufficiently dissolved and diffused into the plating solution to form a plating solution with a uniform concentration, chemical plating will become extremely unstable, and copper will precipitate due to processes other than the original autocatalytic plating reaction. I learned that I would do it. In other words, due to the difference in component concentration between the replenishing chemical solution and the chemical copper plating solution, copper may be deposited on the walls of the plating tank, inside piping equipment, and on the inside of the piping, and when plating printed circuit boards. In this case, extremely undesirable phenomena such as copper depositing on the insulating material other than the intended through-hole portions and conductor wiring pattern portions occur, such as short circuits between circuits.

The present inventors discovered that the chemical copper plating solution is, as mentioned above, a strongly alkaline solution containing a large amount of alkali metal hydroxide, and that by adding a replenishing chemical solution for Cu ²⁺ ions, such as a copper sulfate solution, Copper hydroxide precipitates form instantaneously. This precipitate will completely dissolve if the chemical copper plating solution contains excess Cu ²⁺ ion complexing agent and is allowed to reach equilibrium for a sufficient period of time, but chemical copper plating on the production line During the operation, sufficient time cannot be taken because there is a delay in controlling the concentration of the plating solution. Therefore, if the plating operation is performed while the precipitated copper hydroxide remains undissolved, this precipitate will be adsorbed onto the insulating material other than the conductor wiring pattern of the printed circuit board, becoming the nucleus of plating and removing unnecessary copper plating. A problem arises in that a bond is formed. This problem is the same when replenishing formaldehyde, which is a reducing agent for Cu ²⁺ ions, or alkali metal hydroxide, and unlike when replenishing Cu ²⁺ ions, copper hydroxide precipitates are generated. However, if the concentrated replenishment solution reaches the plating reaction part in the plating tank without being dispersed, or
It was discovered that the stability of chemical copper plating is significantly reduced by contact with the hydroxide of Cu ²⁺ ions mentioned above, and as a result of exploring various ways to solve these problems, the present invention was completed. It came to this.

For example, as shown in FIG. 1, the present invention provides a plating solution circulation flow path in which a part of the chemical copper plating solution 2 is returned to the chemical copper plating tank 1 via circulation pumps 3, 3', 3''. By providing inlets for the replenishment chemicals 6, 7, 8 upstream of the circulation pumps 3, 3', 3'', the mechanical rotational force of the circulation pumps 3, 3', 3'' is utilized. By using a chemical copper plating apparatus having a replenishment structure based on such a chemical replenishment method, the first feature is that the replenishment chemical solutions 6, 7, and 8 are forcibly stirred mechanically. , it is possible to instantly mix and disperse the concentrated replenishment chemical solution to increase contact with the chemical copper plating solution, and it is possible to quickly dissolve and diffuse the replenishment chemical components.

Furthermore, the second feature of the present invention is that, as shown in FIG.
By providing the injection ports for each of the different circulation channels individually, this structure prevents high concentration replenishment chemicals from coming into contact with each other in the circulation channels, and prevents chemical copper metallization. This makes it possible to further improve the stability of the soaking liquid.

A preferable drug solution supply structure of the present invention is as follows:
An inlet for replenishing the chemical liquid is provided upstream of the circulation pump provided in the circulation flow path, and it is preferable that the inlet for the chemical liquid be placed as close to the circulation pump as possible. Further, it is preferable that the chemical solution inlet has a structure in which the replenishment solution is injected into the chemical copper plating solution having a high flow rate hydrodynamically within the piping of the plating solution circulation channel.

Further, in the present invention, there is no need to provide special stirring equipment for the replenishment chemical solution, and the object of the present invention can be achieved simply by utilizing the circulation channel for the chemical plating solution.

[Embodiments of the invention]

Examples of the present invention and comparative examples of the prior art will be given below to explain the features of the present invention in more detail. The experimental conditions common to the examples of the present invention and the comparative examples according to the prior art are as follows.

Polypropylene is used for the chemical copper plating bath, and 50
A chemical copper plating solution was heated to 70°C and tested.
A printed circuit board with a plating load of 1 dm ² / was immersed in the plating solution, and a plating operation was performed for 15 hours. A magnetic pump with a flow rate of 15/min was used as a circulation pump for the plating solution. The compositions of the chemical copper plating solution and replenishment chemical solution used are as follows.

Chemical copper plating solution CuSO ₄・5H ₂ O 12g EDTA-2Na (ethylenediaminetetraacetate) 42g NaOH Amount to make PH12.3 37% formalin 3ml α,α′-dipyridyl 30ml Polyethylene glycol stearylamine 100ml Water Amount to make 1 Cu ²⁺ ion replenishment solution CuSO ₄・5H ₂ O 200g Water 1 amount OH ^- ion replenishment solution NaOH 200g Water 1 amount Formalin replenishment solution 37% Formalin 500ml Water 1 amount Examples of the present invention In addition, the experimental printed circuit board used in the comparative example using the conventional technology was made by drilling holes in a double-sided copper-clad laminate, applying catalyst treatment to the inner surface of the hole, and then forming a circuit using the well-known tenting method. Formed.

Embodiment 1 FIG. 1 is an explanatory diagram showing the configuration of a chemical copper plating apparatus which is an embodiment of the present invention.A chemical copper plating tank 1 is provided with three circulation paths, each of which is equipped with a circulation pump 3, 3', 3'' and filters 4, 4', 4'' are provided, and the chemical copper plating solution 2 is circulated and returned to the plating tank 1.

A heat exchanger 5 is provided in one of the circulation channels for the chemical copper plating solution 2 to heat the plating solution 2. The components of the plating liquid 2 consumed by the plating reaction are Cu ²⁺
Copper sulfur which is a replenishment chemical solution 6 for ions, sodium hydroxide which is a replenishment chemical solution 7 for OH ^- ions, and a replenishment chemical solution 8 consisting of formalin which is a reducing agent are supplied from respective replenishment chemical tanks to chemical replenishment pumps 9, 9',
9'' into the circulation channel of the plating liquid 2.
One of the features of the present invention is that the inlet for the replenishment chemical solution is provided upstream of the circulation pumps 3, 3', 3'' in the circulation flow path of each plating solution 2, so that the injected high concentration The structure is such that the replenishing chemical solutions 6, 7, and 8 are rapidly mixed and dissolved by mechanical stirring of the circulation pumps 3, 3', and 3''.

The chemical copper plating liquid automatic management device 10 in this embodiment uses Cu ²⁺ ions in the chemical copper plating liquid 2,
The pH and formal concentration are automatically detected, and the components of the depleted pampering liquid 2 are supplied to the chemical replenishment pumps 9, 9',
It may be of any type or format as long as it has the function of outputting a 9'' drive signal, and it is also possible to have such a function performed manually.

By the chemical copper plating apparatus in this example,
As a result of chemical copper plating on printed circuit boards,
No unnecessary copper deposits were observed in the plating bath 1, piping, filters 4, 4', 4'', circulation pumps 3, 3', 3'', or between the circuits on the printed circuit board. . The deposited copper coating has metallic luster and good mechanical properties,
It was confirmed that the effects of the present invention were significantly superior.

Example 2 This example shows an example in which the effects of the present invention can be obtained with a simpler chemical copper plating apparatus, and the configuration of the chemical copper plating apparatus is shown in FIG. . In this example, chemical copper plating solution 2
This is an example in which the number of circulation pumps 3, 3' can be reduced by providing two circulation channels. In the two-path chemical copper plating solution 2 circulation flow path, there is a pump upstream of the circulation pump 3 in one flow path.
A replenishing chemical solution 6 for Cu ²⁺ ions is injected, and a replenishing chemical solution 7 for OH ^- ions is injected upstream of the circulation pump 3' in the other channel, but the replenishing chemical solution 8 for formalin remains.
This is a method in which the water is injected downstream of the circulation pump 3'.
In this case, Cu ²⁺ ions and OH ^- ions are sufficiently mixed and stirred into the chemical copper plating solution 2 by the respective circulation pumps 3 and 3', so that the chemical copper plating solution 8 is mixed with the formalin replenishment chemical solution 8. The safety of the plating solution was not compromised.

In this example, as well as in Example 1 above,
No unnecessary copper deposits were observed on the printed circuit board. In order to obtain the effects of the present invention, the injection positions of at least three component replenishment chemicals should be separated, and at least two component replenishment chemicals should be forcibly stirred and dissolved by their respective circulation pumps. I confirmed that it was necessary to do so.

Example 3 As shown in FIG. 3, this example is an example of a chemical copper plating apparatus according to the present invention in which the forced stirring function of the replenishment chemical solution circulation pump is strengthened, and the plating liquid has three routes. Two of the circulation channels are equipped with stirring pumps 11 and 11' for forcibly mixing replenishment chemicals, and the mixing and dissolving capabilities are further increased than in the chemical copper plating apparatus of the present invention shown in Example 1. It is a case. As a result of chemical copper plating using the plating apparatus in this example,
As in Examples 1 and 2 described above, no copper precipitation was observed between the printed circuits, and the object of the present invention could be fully achieved. What is also noteworthy is that when the chemical copper plating speed is more than twice the normal rate, even though the amount of replenishment chemicals for the missing components of the plating solution is more than doubled, there is still no damage between the printed circuits. No copper precipitation was observed at all. As described above, it has been confirmed that the present invention can sufficiently exhibit its effects even when chemical copper plating is performed particularly at high speed.

Comparative Example 1 In this comparative example, which is a conventional technique, as shown in FIG. 4, the chemical solution replenishment structure of the present invention was not adopted in the circulation flow path of the chemical copper plating solution 2, but instead the chemical solution replenishment structure of the present invention was used, as shown in FIG. This is an example of chemical copper plating applied to a printed circuit board using the mixer 12, which is a chemical solution replenishing unit. In this case, the three-component replenishment chemical solution is injected into a mixer 12 provided in a part of the circulation flow path, and the replenishment tank is replenished. This mixer 1
2 may simply be a pipe, or may include a static mixer for mixing fluids to mix chemical liquids; in this comparative example, the latter mixer 12 is used.
was used. When this chemical copper plating apparatus was used to plate a printed circuit board, copper was deposited between the circuits and on a part of the inner wall of the plating bath. Further, the deposited copper film lacked luster and was a rough copper plating film. As mentioned above, the cause of this is thought to be insufficient mixing of the replenishment chemical components. It was confirmed that even if higher-grade mixer parts were used, it was not possible to obtain a mixing and dissolving ability equal to or greater than that of the present invention.

Comparative Example 2 In this comparative example, the chemical replenishment structure according to the present invention was not adopted, and the replenishment chemical components 6, 7, and 8 were directly injected into the chemical copper plating tank 1 as shown in FIG. This is an example of a case where a test is performed. In this case, it is not limited to the circuit on the printed circuit board.
Wall surface of plating tank 1, circulation pump 3, filter 4,
A large amount of copper was observed to be deposited inside the heat exchanger 5 and the piping, and the chemical copper plating solution was virtually decomposed.

〔Effect of the invention〕

As explained in detail above, in the chemical copper plating apparatus equipped with the chemical supply structure according to the present invention,
With a simple structure and inexpensive device, it is possible to efficiently and sufficiently mix and dissolve the replenishment chemical solution, which is a missing ingredient in the plating solution, and to stably produce high-quality chemical copper plating with glossy and excellent mechanical properties. Therefore, it is possible to significantly improve the productivity of printed circuit boards, printed wiring boards, etc., and the technical and economic effects of the present invention in industrial applications are extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of the chemical copper plating apparatus used in Example 1 of the present invention, FIG. 2 is an explanatory diagram showing the configuration of the chemical copper plating apparatus used in Example 2 of the present invention, 3 is an explanatory diagram showing the configuration of the chemical copper plating apparatus used in Example 3 of the present invention, FIG. 4 is an explanatory diagram showing the configuration of the conventional chemical copper plating apparatus used in Comparative Example 1, FIG. 5 is an explanatory diagram showing the configuration of a conventional chemical copper plating apparatus used in Comparative Example 2. 1...Chemical copper plating tank, 2...Chemical copper plating solution, 3, 3', 3''...Circulation pump, 4, 4',
4″...Filter, 5...Heat exchanger, 6...Cu ²⁺
Ion replenishment chemical solution, 7...OH ^- ion replenishment chemical solution, 8...Formalin replenishment chemical solution, 9,9',
9''... Chemical solution supply pump, 10... Plating liquid automatic management device, 11, 11'... Stirring pump, 12...
...Mixer.

Claims (1)

[Scope of Claims] 1. A chemical copper plating tank, a circulation flow path for the chemical copper plating solution in which the chemical copper plating solution in the chemical copper plating tank is refluxed by a circulation pump, and a chemical copper plating solution circulating in the chemical copper plating tank. In a chemical copper plating apparatus comprising a chemical solution replenishing section that supplies plating solution components consumed by plating reactions to the plating solution, at least two circulation channels for the chemical copper plating solution are provided.
There is a route, and the chemical solution replenishing section has at least two routes, and the chemical solution supplying structure has a chemical solution supply structure in which the chemical solution is individually injected into the upstream side of the circulation pump or stirring pump provided in each of the circulation channels. Characteristic chemical copper plating equipment. 2. There are at least two circulation channels for the chemical copper plating solution, and at least three chemical solution replenishment sections.
Regarding the route, the chemical solution supplied from the chemical solution supply section is individually injected into the upstream side of the circulation pump or stirring pump provided in each of the circulation flow paths, and is discharged from the remaining chemical solution supply section. The chemical solution supplied is
Claim 1, characterized in that the chemical liquid is individually injected into the downstream side of the circulation pump or stirring pump provided in each of the circulation channels, and has a chemical liquid supply structure in which the chemical liquids to be replenished do not come into contact with each other.
Chemical copper plating equipment as described in section. 3. There are at least two circulation channels having circulation pumps for the chemical copper plating solution, and at least two routes for the chemical solution replenishment section, and at least one of the plurality of circulation channels includes:
3. The chemical copper plating apparatus according to claim 1, further comprising at least one stirring pump for mixing the supplied chemical solution. 4 There are two circulation channels for the chemical copper plating solution, and Cu ²⁺ ions are supplied from the chemical supply section.
Claim 1, characterized by having a chemical solution supply structure for individually injecting any two types of chemical solutions selected from OH ^- ions and formalin into the upstream side of the circulation pump or the stirring pump.
2. The chemical copper plating apparatus according to item 2, item 3, or item 3. 5 There are three circulation channels for the chemical copper plating solution, and Cu ²⁺ ions are supplied from the chemical supply section.
Claims 1, 2, 3 or 3, characterized by having a chemical solution supply structure for individually injecting OH ^- ion and formalin chemical solutions into the upstream side of the circulation pump or stirring pump, respectively. Fourth
Chemical copper plating equipment as described in section.