JPH09223858A - Manufacture of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain through hole plating excellent in adhesion and reliability and contribute to cost reduction and the preservation of the environment by applying undoped conductive polymer and making a sulfonic acid dopant react with the polymer. SOLUTION: Metal foil 2 for wiring is formed on an insulating substrate 1, and a through hole 3 is formed therein. The substrate is cleaned, and is made to react with a base treatment agent 4 to activate the inside surface of the through hole. A solution of conductive polymer is applied to the inside of the through hole to form a conductive polymer layer 5 there. Then it is doped with sulfonic dopant to become highly conductive. The substrate 1 is immersed in a plating tank. At this time, a plating liquid is used wherein metal is deposited at a current density of 1-10mA/cm<2> or so and at a plating voltage of 0.3 V or below, preferably 0.1V or below. For copper plating, a plating liquid with a pH of 2-8, preferably 3-6, is used. This obtains through hole plating 6 excellent in adhesion and reliability, and contributes to cost reduction and the preservation of the environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a method for manufacturing the same, and more particularly to a method for plating through holes.

[0002] In recent years, highly advanced highly integrated devices represented by large scale integrated circuits have been realized due to remarkable progress in microelectronics, especially in semiconductor element manufacturing technology. By adopting this in the control system of various devices, electronic devices have been dramatically miniaturized, and home appliances in general households have been miniaturized and multifunctional as well as in various industries.

The above-mentioned electronic equipment is composed of a glass epoxy resin, which is a composite material obtained by curing glass fibers with a resin,
It is configured by mounting components such as semiconductor elements, resistors, capacitors, and coils on a printed wiring board that has a specific wiring pattern formed on various insulating substrates such as paper phenolic resin and bakelite resin. This printed wiring board plays an important role in improving the packaging density, and is a key element for downsizing and multi-functionalization of devices.

[0004]

2. Description of the Related Art Recently, double-sided wiring or multi-layer laminated wiring boards have been used for printed wiring boards in order to cope with high-density mounting for miniaturization of devices. This is a copper foil pattern for wiring that connects components to each other on the front and back of the board, and there is also a wiring formed in the middle of it so that complicated wiring can be efficiently realized within a limited area. ing.

In this double-sided or multi-layer laminated wiring board,
It is important to form through-hole wiring portions for connecting both surfaces or multilayer wirings to each other and perpendicularly to the substrate. The through-hole wiring part is 0.3 to 0.3
By opening a hole of about 1 mm and plating this inner wall in the direction perpendicular to the substrate, the upper and lower wirings connected here are electrically connected.

This plating process in the through hole is called through hole plating, and various methods have been proposed and realized so far. However, the method that makes the surface of the insulative substrate material electrically conductive by some method, and uses this as an electrode for further plating is the mainstream method. For example, a fine particle catalyst using a salt of a noble metal such as palladium as a catalyst is deposited (activated) in the through holes, and this is immersed in an electroless plating bath containing a reducing agent such as formalin and copper sulfate, The so-called electroless plating method of depositing reduced copper on the surface coated with a catalyst is actually practiced.

In the conventional method for manufacturing a printed wiring board, since through-hole plating is electroless copper plating, expensive and rare precious metals such as palladium must be used, which saves resources and costs. Not desirable from a point of view. Furthermore, it is a manufacturing method that has problems in terms of ensuring safety and improving the working environment, such as the use of formaldehyde, which has teratogenicity and carcinogenicity as well as acute toxicity.

For this reason, a direct plating method called a direct plating method has recently been proposed. For example, U.S. Pat. No. 5,300,208 discloses that a conductive polymer is used, and this is applied to a portion of an insulating substrate having a through hole to be plated, and this is used as an electrode directly on the copper or the like. This is a method of applying metal plating.

[0009]

However, in the method disclosed in the present invention, when polyaniline which is a conductive polymer is applied to form a conductive layer, polyaniline is used with acetic acid having strong acidity. Since it is used as a dopant that improves the conductivity at the same time as it dissolves, polyaniline is significantly aggregated, and the pot life of the material is short and process control is difficult.

Although a method of applying undoped reduced polyaniline is also disclosed, in this case, a so-called spontaneous plating method is used by reducing and depositing a noble metal such as silver or palladium. However, there is a drawback that the manufacturing cost increases due to the use of expensive silver or palladium.

Similarly, JP-A-06-220685 proposes a method using a conductive polymer. However,
In this method, the conductive polymer monomer is polymerized on the surface of the insulator, so it is also difficult to control the monomer solution.

[0012] Further, the method of conducting the conductive film by forming a thin film by casting a conductive polymer solution has the problems that the adhesion between the conductive polymer and the base is low, and the drawing stress is small.

Further, in Japanese Patent Laid-Open No. 63-311797, the wall surface of the through hole is subjected to surface treatment using a silicon coupling agent, and then through hole plating is performed. The present invention does not use precious metals or highly toxic formalin,
Realizes highly reliable through-hole plating with good adhesion.
The purpose is to contribute to cost reduction and environmental conservation.

[0014]

Means for Solving the Problems To solve the above problems, 1) form an undoped conductive polymer layer by treating a plated portion of an insulating substrate with a reagent having a plurality of reactive groups in one molecule. Then, a method of manufacturing a printed wiring board, in which a dopant is caused to act on the conductive polymer layer to render it conductive, the substrate is immersed in a plating solution in which metal ions are dissolved, and electroplating is performed on the conductive polymer layer Or 2) the method for producing a printed wiring board as described in 1 above, wherein the conductive polymer layer is made of polyaniline or a derivative thereof, and aliphatic sulfonic acid is used as the dopant, or 3) the conductive polymer layer is made of polyaniline or The method for producing a printed wiring board as described in 1 above, which is made of a derivative thereof and uses aromatic sulfonic acid as the dopant, or 4) the electroplating is performed at 0.3 V or less. The method for producing a printed wiring board as described in 1 above, which uses a plating solution for precipitating a metal by pressure, or 5) the electroplating, after the plating as described in 4), is a plating in which a metal is deposited at a voltage of 0.3 V or more. Or a method of manufacturing a printed wiring board for plating using a liquid, or 6) the above-mentioned 1 to 5 in which the plated portion is in a through hole
This is achieved by the method for manufacturing a printed wiring board described.

Next, the operation of the present invention will be described. In the present invention, the plated part of the insulating substrate is treated with a reagent having a plurality of reactive groups in one molecule, and then an undoped conductive polymer is applied, and a sulfonic acid type dopant is applied to this. Therefore, it is possible to form a stable and highly conductive conductive polymer film. At this time, by using the above-mentioned reagent, the adhesion between the base and the conductive polymer is improved, and the adhesion of the plated film in the plated parts such as through holes is improved, so that the plating reliability is improved. Further, the details of the operation of the present invention will be described. (1) Why is it possible to form a stable and highly conductive conductive polymer film by applying an undoped conductive polymer and applying a sulfonic acid-based dopant to this, which is the main point of the present invention? The reason will be explained.

The conductive polymer, particularly polyaniline, needs to be soluble in the solvent during the coating process. The doped conductive polymer is preferably poorly soluble and insoluble, and even if it is applied in this state, good conductivity cannot be expected. This is because the overlapping state of the conductive polymer main chains responsible for conductivity depends on whether the film is formed from a sufficiently dissolved solution or is formed from an aggregated state by doping.

Film formation from a complete solution, in which the main chains overlap with each other, has a conductivity of about 2 to 5 orders of magnitude higher. In this respect, the present invention uses undoped material. Also, regarding the stability of the applied solution, the undoped conductive polymer solution can maintain a uniform dissolved state for a long period of time. Due to the interaction, the free energy is smaller and the polymer can exist stably when it is in an aggregated state with a smaller average molecular chain length than it exists as a polymer chain spread in the solvent.

As a result, the agglomerates are formed as described above, and when these agglomerates grow into large particles, they precipitate and cause phase separation, impairing the homogeneity as a solution and lowering the conductivity after film formation. .

The cause of the development of stability with respect to the sulfonic acid type dopant is as follows. That is, the conductivity stability is affected by the ionic radius and shape, and those having a larger ionic radius and ions having a larger asymmetry (anisotropic property) are less likely to move in the conductive polymer film, and thus have a conductive property. It comes from the experience of contributing to stability for sex.

Other than sulfonic acid type, perchloric acid (Cl
O ₄ ^-) system, tetrafluoroborate (BF ₄ ^-) system, hexafluorophosphate (PF ₆
^- ) System, etc., but using the sulfonic acid-based dopant rather than any of the ions, the heat treatment test shown in Fig. 3 shows that the conductivity becomes 1/2 the initial time.
A film that was 2 to 10 times more stable could be obtained.

FIG. 2 is a structural diagram of an electrode for measuring a change in resistivity during the above heat treatment test. As measuring electrodes, two transparent electrodes (ITO) with a width of 10mm and a thickness of 1000Å are formed on the quartz plate 11 with a space of 10mm as shown in the figure.
12 and 13 are formed, a conductive polymer film is formed in this space, and the surface resistivity between both electrodes is measured.

FIG. 3 is a diagram showing the relationship between the dopant and the resistance stability, showing the change in the surface resistivity of various dopants with the passage of time at a temperature of 120 ° C. The types of dopants used for the measurement are metasulfonic acid, sulfuric acid, 2-NS (2-naphthalenesulfonic acid), and PTS (p-toluenesulfonic acid).

Further, even with the same sulfonic acid system, the stability of the aromatic system having a benzene ring is improved by about one digit with respect to the minimum ion (SO ₄ ²⁻ ). This is considered to be because the introduction of an aromatic ring can realize a large anisotropy, and the sulfonic acid system is practically most suitable for giving such a degree of freedom to the anion. In addition, organic molecules modified with sulfonic acid are easier to produce than those with other ions. (2) For electroplating, use a plating solution that deposits metal at a voltage of 0.3 V or less, and perform 0.3% after performing this plating.
The principle and action of plating using a plating solution that deposits metal at a voltage of V or higher will be described.

The plating operation is essentially to reduce and deposit the metal, and an electrochemically reducing atmosphere is formed in the vicinity of the object to be plated. At this time, in the conductive polymer used in the present invention, reduction of the main chain and elimination of the dopant occur in parallel and in competition. Due to the reduction of the main chain of the conductive polymer and the removal of the dopant, the conductivity becomes 2
When the conductive polymer is plated, the important point is how to proceed with the plating without reducing the conductive polymer because the conductive polymer drops by 8 digits.

FIG. 4 is a diagram showing the redox behavior of the plating solution and polyaniline. The figure shows the relationship between the voltage and current (Current) with respect to the type of plating solution, and the voltage with respect to the type of dopant doped in the conductive polymer (polyaniline).
Shows the relationship of current (Current2).

The horizontal axis represents the voltage (mV) with respect to the Ag / AgCl reference electrode.
Then, the negative side is reduction and the positive side is oxidation. In plating solution 1, the reduction current (with deposition) begins to flow from around −0.25 V, but in plating solution 2, it begins to flow from the moment when 0 V is cut off.

On the other hand, both of PTS (p-toluenesulfonic acid; aromatic dopant) and HBF ₄ have two kinds of dopants in which a current is already flowing near 0 V, and −0.3
A peak is shown below V, indicating that the reduction reaction is proceeding.

As described above, the potential at which the metal is deposited varies depending on the type of plating solution (pH of the solution and the presence or absence of additives such as brighteners), and empirically it can be deposited at a plating voltage of about 0.1 V or less. Therefore, it is important to obtain a through-hole plating film. In this case, the plating solution 2 satisfies this condition. On the contrary, as shown in the figure, at a voltage of −0.3 V or less, the potential is sufficient to reduce the conductive polymer, and the conductivity is lost before the plating film is deposited. as a result,
Precipitation of metal becomes difficult.

The above is the reason for -0.3 V, and the plating voltage of 0.3 V or less is considered to be a necessary condition for not losing the conductivity of the conductive polymer film. Also, if a metal is deposited on the conductive polymer with a small thickness, a current will flow through it, so the plating voltage will be 0.3
It does not matter at all if the voltage is higher than V, and any plating solution can be selected.

[0030]

FIG. 1 is an explanatory diagram of an embodiment of the present invention. In FIG. 1 (A), first, a substrate on which a circuit is manufactured is prepared. Here, 1 is an insulating substrate, and 2 is a metal foil for wiring.

In FIG. 1B, the through hole 3 is drilled. This diameter is usually 0.3 to 1 mm, and is appropriately determined according to the properties and mounting density of the printed board. After that, the substrate is cleaned with an alkaline cleaner or the like.

In FIG. 1 (C), in order to improve the adhesion of the through hole plating, the surface treatment agent 4 is reacted to activate the surface inside the through hole as the surface treatment. As the treating agent, generally, a molecule having reactivity at both ends of the molecule,
For example, a metal coupling agent such as a silane coupling agent or a titanium coupling agent, or a bifunctional molecule such as divinylbenzene or N, N'-bisacrylamide can be used.

In FIG. 1D, a conductive polymer solution is applied in the through holes to form a conductive polymer layer 5. The conductive polymer is a solvent-soluble conductive polymer such as polyaniline, and its conductivity is preferably 0.01 S / cm or more. The thickness of the conductive polymer layer 5 is 0.1 to 10μ
m.

In FIG. 1 (E), since the conductivity is generally poor in the state of being soluble in the solvent, the doping process is performed.
It is desirable to use a sulfone-based dopant as the dopant. Specifically, aliphatic sulfonic acids such as methanesulfonic acid and vinylsulfonic acid, and aromatic sulfonic acids such as p-toluenesulfonic acid, naphthalenesulfonic acid and anthraquinonesulfonic acid can be used. The doping process makes the inside of the through hole highly conductive.

In FIG. 1 (F), the substrate is dipped in a plating bath and plated at a current density of about 1 to 10 mA / cm ² . The thickness of the plating film can be selected to be an appropriate value between 5 and 50 μm. Metals such as copper, silver, nickel and palladium are used for plating.

In this case, it is necessary to use a plating solution that deposits metal at a plating voltage of 0.3 V or less, preferably 0.1 V or less. For example, in the case of copper plating, the pH of the plating solution is
It should be 2 to 8, preferably 3 to 6.

The reason for this is that the conductive polymer film formed in the through holes has a high pH, which promotes dedopant and lowers the conductivity. On the other hand, when the pH is low, a large plating overvoltage is required.Before copper is deposited on the surface of the conductive polymer film, the conductive polymer undergoes an electrochemical reduction action, reducing the main chain and simultaneously reducing the dopant. The reason for this is that the electroconductivity also drops due to the separation of

After the above-described plating treatment is performed, the plating treatment may be performed again in a plating solution having a high plating voltage. For example, it is possible to use a plating solution containing a surface brightener or a strongly acidic plating solution adjusted to a sufficiently low pH of zero or less. This makes it possible to perform plating with a uniform surface gloss and uniform film thickness.

Next, some embodiments according to the above steps will be described. Embodiment 1: To a 0.2 M aniline aqueous solution that is acidic with 1 N hydrochloric acid, ammonium persulfate that is equimolar to aniline is added,
Solvent-soluble polyaniline was obtained by chemical polymerization at -5 ° C. This polyaniline is boiled under reflux in an aqueous ammonia solution, then reduced with hydrazine, washed with pure water, and dried by heating to obtain the dedoped dope.

Next, a substrate having a through hole with a diameter of 0.5 mm opened in a four-layer substrate made of glass epoxy with a thickness of 1.6 mm was prepared, and the inside of the through hole was ultrasonically cleaned with an alkaline cleaning agent for 10 minutes. Rinse with acetone for 30 seconds at 100 ° C
Heat dry for 10 minutes.

After dipping this substrate in a 3% toluene solution of a silane coupling agent (Shin-Etsu Chemical: KBM-403) for 5 minutes,
Rinse with clean toluene and dry at 100 ° C for 10 minutes. A solution obtained by dissolving 1 part of the above polyaniline in 99 parts of N-methyl-2-pyrrolidone is applied to this substrate by a dip coating method, and dried by heating at 100 ° C. for 30 minutes.
After drying, the polyaniline applied to the flat surface of the copper foil is removed by polishing.

Next, the substrate was immersed in a doping solution prepared by dissolving 1 part of methanesulfonic acid and 2 parts of hydrogen peroxide in 20 parts of propylene carbonate and left for 10 minutes. Then, wash with isopropyl alcohol and dry at 80 ° C for 10 minutes.

In the next plating step, 25 parts of copper sulfate was mixed with 100 parts of water.
A plating solution is prepared by preparing an aqueous solution dissolved in the part. The substrate whose inside of the through-hole has been made conductive in the above process is immersed in this solution, and plating is performed for 30 minutes at a current density of 10 mA / cm ² .

Embodiment 2: A substrate after cleaning is treated with a 5% toluene solution of a bis-epoxy primer for a curing agent. In the other steps, the conductive polymer layer is formed and plated in the same manner as in Embodiment 1, and a through-hole plated substrate is manufactured.

Embodiment 3: A 10% aqueous solution of 2-naphthalenesulfonic acid is used as a doping treatment agent for the conductive polymer layer produced in the same manner as in Embodiment 1. Other steps are the same as those in the first embodiment.

Fourth Embodiment: A plating solution is prepared by preparing an aqueous solution prepared by dissolving 25 parts of copper sulfate in 100 parts of water on the conductive polymer layer prepared in the same manner as in the first embodiment. In this solution, the substrate whose inside of the through-hole has been made conductive in the above step is immersed, and plating is performed for 10 minutes at a current density of 10 mA / cm ² .

Next, 25 parts of copper sulfate and 20 parts of sulfuric acid were dissolved in 100 parts of water, and paratoluenesulfonamide 1 was added as a brightener.
And 0.5 parts of 2-butyne-1,4 diol are added to the plating solution for 30 minutes at a current density of 10 mA / cm ² .

In each of the above-mentioned embodiments, the copper foil of about 5 μm was uniformly and surely deposited in the through hole after the plating treatment. As a result of examining the pull-out strength of this through hole, the pull-out strength was 5
Although it was kgf, in any of the above embodiments,
The adhesion was improved to 15 kgf and the plating adhesion was improved.

[0049]

EFFECTS OF THE INVENTION According to the present invention, through-hole plating with good adhesion and high reliability can be realized without using precious metals, formalin, which has a strong volatility and toxicity, which are required for conventional through-hole plating processing. it can. As a result, it can contribute to cost reduction and environmental protection.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a schematic diagram of electrodes for measuring changes in resistivity.

FIG. 3 is a diagram showing a relationship between a dopant and resistance stability.

FIG. 4 is a diagram showing the redox behavior of a plating solution and polyaniline.

[Explanation of symbols]

 1 Insulating substrate 2 Copper foil for wiring 3 Through hole 4 Base treatment agent 5 Conductive polymer layer 6 Electroplated metal layer 11 Quartz plate 12, 13 Electrode

Claims (5)

[Claims] 1. A plating part of an insulating substrate is treated with a reagent having a plurality of reactive groups in one molecule to form an undoped conductive polymer layer, and a dopant acts on the conductive polymer layer. A method for producing a printed wiring board, characterized in that the substrate is immersed in a plating solution in which it is made conductive and the metal ions are dissolved, and electroplating is performed on the conductive polymer layer. 2. The method for manufacturing a printed wiring board according to claim 1, wherein the conductive polymer layer is made of polyaniline or a derivative thereof, and aliphatic sulfonic acid or aromatic sulfonic acid is used as the dopant. 3. The method for producing a printed wiring board according to claim 1, wherein the electroplating uses a plating solution in which a metal is deposited at a voltage of 0.3 V or less. 4. The method of manufacturing a printed wiring board, comprising: performing the electroplating according to claim 4 and then using a plating solution in which a metal is deposited at a voltage of 0.3 V or more. . 5. The method for manufacturing a printed wiring board according to claim 1, wherein the plated portion is in a through hole.