JP2013204107A - Electroless plating method and wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless plating method capable of forming high density copper wiring without using a resin pattern mask.SOLUTION: An electroless plating method of the embodiment includes: a UV irradiation step of irradiating a partial region of a resin substrate 10 of cycloolefin polymer with an ultraviolet light; a catalyst application step of applying a catalyst of an electroless plating reaction to a surface of the resin substrate; and a plating step of selectively forming a wiring pattern of a copper plating film in the ultraviolet light irradiation region by using an electroless copper plating bath. In the electroless copper plating bath, 2-mercapto benzotriazole is included as an inhibitor, and a pattern size of the copper plating film is less than a size of the ultraviolet light irradiation region.

Description

  The present invention relates to an electroless plating method for producing a copper plating wiring without using a resin pattern mask by an ultraviolet irradiation method and a wiring board manufactured using the electroless plating method.

  The printed wiring board is manufactured by forming a copper wiring pattern on a resin substrate. As a resin for a substrate, a cycloolefin polymer, a polyimide film, a liquid crystal polymer film or the like having excellent electrical characteristics has attracted attention. Conventionally, an additive method or a subtractive method is used to form a wiring pattern. However, in any method, in order to form a wiring pattern, a resin pattern mask is indispensable and a complicated process is required.

  For example, in the subtractive method, an etching resin pattern mask that covers a wiring pattern is formed on a substrate covered with a copper film having the same thickness as the wiring pattern to be formed using, for example, a photoresist, and the mask is used. After the copper film in the uncovered region is dissolved, the mask is removed. On the other hand, in the semi-additive method, a resin pattern mask having an opening of a wiring pattern is formed on a thin conductive layer covering a substrate, and an electroplating film is formed in the opening, and then the mask and the conductive layer are removed. .

  In contrast, Japanese Patent Laid-Open No. 10-88361 discloses an electroless nickel plating method that can omit the resin pattern mask formation / removal step and the etching step. That is, in the above publication, the pattern of the electroless nickel plating film can be selectively formed only in the ultraviolet irradiation region by partially irradiating the resin substrate with ultraviolet rays before the electroless nickel plating catalyst application step. It is disclosed.

  However, the electroless plating film grows at the same speed not only in the vertical direction but also in the horizontal direction with respect to the main surface of the substrate. The plating film in the region grown in the horizontal direction not only has low adhesion to the substrate, but also has a possibility that the pattern width is increased and a short circuit occurs between the patterns. Moreover, there is a possibility that the plating film is deposited also in the region not irradiated with ultraviolet rays. Furthermore, copper having a lower resistance than nickel and used as a wiring material is less susceptible to electroless plating reaction than nickel.

  For this reason, it is not easy to apply the electroless nickel plating method that does not use a resin pattern mask by the conventional ultraviolet irradiation method to the production of high-density copper wiring.

JP-A-10-88361

  An embodiment of the present invention aims to provide an electroless plating method capable of producing a high-density copper wiring without using a resin pattern mask and a wiring board manufactured using the electroless plating method.

  An electroless plating method according to an embodiment of the present invention includes: a UV irradiation step of irradiating a partial region of a resin substrate with ultraviolet rays; a catalyst application step of applying a catalyst for an electroless plating reaction to the surface of the resin substrate; A plating step of selectively forming a wiring pattern of a copper plating film in the ultraviolet irradiation region using a copper plating bath, and an inhibitor that suppresses an electroless plating reaction in the electroless copper plating bath. The pattern size of the copper plating film is smaller than the size of the ultraviolet irradiation region.

  According to the embodiment of the present invention, it is possible to provide an electroless plating method capable of producing a high-density copper wiring without using a resin pattern mask and a wiring board manufactured using the electroless plating method.

It is a flowchart of the electroless-plating method of 1st Embodiment. It is a cross-sectional schematic diagram for demonstrating the electroless-plating method of 1st Embodiment. It is an anodic polarization curve of an electroless plating bath. It is a cathode polarization curve of an electroless plating bath. It is a flowchart of the electroless-plating method of 3rd Embodiment.

<First Embodiment>
Hereinafter, the electroless plating method of the first embodiment and the wiring board 40 of the first embodiment will be described along the flowchart shown in FIG.

<Step S11> Substrate Preparation A substrate made of 30 mm × 50 mm × 0.188 mm cycloolefin polymer (COP) was prepared. The substrate may be a liquid crystal polymer film or the like as long as it is a resin that can be surface-modified by ultraviolet rays.

<Step S12> Pretreatment The substrate 10 is removed with an alkaline solution containing a surfactant. If the substrate is clean, this pretreatment is not necessary.

<Step S13> Ultraviolet Irradiation As shown in FIG. 2A, the surface of the substrate 10 is selectively irradiated with ultraviolet rays (UV light) for 10 minutes through a photomask 20, for example. Irradiation is performed in an air atmosphere by arranging a light source 30 having a high-power low-pressure mercury lamp (main wavelength: 253.7 nm, sub-wavelength: 184.9 nm) at a distance of, for example, 30 mm from the substrate 10.

In the photomask 20, a chromium vapor deposition film 20B having an opening in a wiring pattern is formed on a synthetic quartz glass 20A. For this reason, the substrate 10 is irradiated with UV light only in a region (width W0) corresponding to the wiring pattern. The intensity of the UV light after passing through the quartz glass 20A is 60.0mW / cm ² at a main wavelength was in secondary wavelength at 7.8 mW / cm ^2.

  In addition, since the effect of ultraviolet irradiation at reduced pressure is small, oxygen in the air between the substrate 10 and the photomask 20 is ozonized by UV light greatly contributes to the surface modification of the resin substrate. It is thought that.

<Step S14> Alkali Treatment The substrate 10 is immersed in a NaOH solution of 60 ° C. and 50 g / dm ³ for 5 minutes.

After alkali treatment, according to the infrared absorption spectrum observed in the UV radiation region 11 of the substrate ^10, 3600 cm -1, around 3300 cm ^-1 and 1750 cm ^-1, respectively, intermolecular hydrogen bonds of hydroxyl groups, hydroxyl groups and Absorption due to the carbonyl group was confirmed. That is, a hydroxyl group and a carbonyl group are introduced into the UV irradiation region 11 of the substrate 10.

  By the alkali treatment, a hydrophilic group is introduced into the polymer cleaved by UV irradiation, whereby a highly hydrophilic modified layer is formed in the UV irradiation region 11.

<Step S15> Conditioning treatment One or two types selected from four types of surfactants roughly classified into cationic, anionic, amphoteric and nonionic for the purpose of making the surface wettability uniform. A conditioning treatment using a conditioning agent solution containing the above surfactant is performed.

  A surfactant, for example, CC-231 manufactured by Rohm and Haas Electronic Materials Co., Ltd., was immersed in a conditioning solution (25 ° C. to 60 ° C.) containing 0.01 g / L to 10 g / L for 1 minute to 20 minutes. .

<Step S16> Catalyst Application Substrate 10 is immersed in a 0.3 mg / dm ³ PdCl ₂ containing solution (45 ° C.) for 120 seconds, and then added to a 0.25 mol / dm ³ NaH ₂ PO ₂ containing solution (60 ° C.). It was immersed for 30 seconds, Pd ions were reduced, and used as a catalyst for electroless plating reaction.

In the ultraviolet irradiation region where the modified layer having high hydrophilicity was formed, the palladium adsorption amount was 1.82 μg / cm ² , whereas in the unirradiated region where the ultraviolet ray was not irradiated by the chromium mask. The amount of palladium adsorbed was 0.36 μg / cm ² . In addition, from the experiment conducted separately, the electroless copper plating reaction did not occur when the palladium adsorption amount was 0.7 μg / cm ² or less.

  In addition, you may use various well-known processing methods for catalyst provision.

<Step S17> Electroless Copper Plating For comparison, a wiring board of a comparative example in which an electroless copper plating pattern is formed on a substrate by immersing in the electroless copper plating bath (basic bath) shown in Table 1 below for 1 hour. Was made.

一方、基本浴に、２−メルカプトベンゾトリアゾール（２−ＭＢＴ）を、０．５ｍｇ／ｄｍ^３（ｐｐｍ）加えた異方性浴を用いて、同様に基板１０上に無電解銅めっきパターン４１を形成し、実施形態の配線板４０を作製した（図２（Ｂ）参照）。

On the other hand, an electroless copper plating pattern 41 is similarly formed on the substrate 10 using an anisotropic bath obtained by adding 0.5 mg / dm ³ (ppm) of 2-mercaptobenzotriazole (2-MBT) to the basic bath. Then, the wiring board 40 according to the embodiment was manufactured (see FIG. 2B).

  “2-MBT” is an inhibitor that suppresses the progress of the electroless plating reaction. That is, as shown in FIGS. 3 and 4, 2-MBT is a water-soluble additive that shifts the cathode polarization curve to the base and has an inhibitory effect on the reduction reaction in the anodic polarization curve. The polarization curve was measured at a sweep rate of 2.0 mV / sec using an Ag / AgCl electrode as a reference power, using platinum as the counter electrode and a copper plate as the working electrode.

The value of the hybrid potential calculated from the anodic polarization and the cathodic polarization was −650 mV in the 2-MBT non-added bath (basic bath) and i ₀ = 0.2 mA / cm ² , whereas In the MBT addition bath (anisotropic bath), it was −818 mV and i ₀ = 0.14 mA / cm ² . That is, since 2-MBT has a high inhibitory effect on anodic polarization, it can be seen that it is a reduction inhibitor.

  As the electroless plating basic bath, paraformaldehyde or glyoxylic acid can be used as a reducing agent. Glyoxylic acid is similar in structure to formaldehyde and has a small reducing power, but has little effect on the human body.

  In order to accelerate the deposition reaction of electroless copper plating, a thin electroless nickel film may be deposited first, and then the electroless copper plating film may be grown. It may be added.

<Step S18> Heat treatment The wiring board 40 was heat-treated in the air atmosphere at 80 ° C. for 1 hour. This heat treatment is intended to reduce the electrical resistance by measuring the particle growth of the plating film.

<Evaluation>
When the width W0 of the ultraviolet irradiation region is 75 μm and the thickness W1 of the copper plating film is 3 μm, the pattern width W1 exceeds, for example, 81 μm and W0 in the comparative wiring board that is copper-plated using the basic bath, and In addition, slight precipitation also occurred in the UV light non-irradiated region.

  On the other hand, in the wiring board 40 manufactured using the anisotropic bath. The pattern width W1 was 74.3 μm, which was less than W0, and there was no deposition on the UV light non-irradiated region. That is, the pattern size (W1) of the copper plating film 41 is smaller than the size (W0) of the ultraviolet irradiation region.

  In addition, in the surface observation with an electron microscope, the copper plating pattern formed from the anisotropic bath had a smoother side portion than the top portion where the deposition rate was slow due to the action of the inhibitor.

  As the inhibitor, for example, a compound comprising triazole, tetrazole, imidazole or pyrazole, sodium thiosulfate, thioglycol, thiourea or potassium thiocyanate can be used. However, thiourea had a pattern width W1 of less than W0 in the 0.5 ppm addition bath, but precipitation may occur in the unirradiated region of UV light, and no precipitation reaction occurred in the 1 pmm addition bath. In addition, for example, in the 1 ppm addition bath, the pattern width W1 is less than W0, but the thickness of the plating film is 0.5 μm or less, and the potassium thiocyanate has a strong suppression effect, and precise control of the addition amount is necessary. there were.

  For this reason, 2-MBT is particularly preferable as the inhibitor because of its effect and ease of management. The amount of 2-MBT added is preferably 0.3 ppm or more and less than 10 ppm. If it is not less than the above range, there is an effect of suppressing the expansion of the pattern width (W1).

  As described above, since the electroless plating method of the embodiment forms a film using an electroless plating copper bath containing an inhibitor, it is a partial plating deposition method by ultraviolet exposure, but with a desired pattern width. A wiring board 40 having high-density copper wiring can be produced.

Second Embodiment
Next, the electroless plating method of the second embodiment will be described.

  The electroless plating method of the first embodiment using an electroless plating copper bath containing an inhibitor can produce high-density wiring. However, when an inhibitor is added, the plating deposition rate decreases.

  In contrast, in the electroless plating method of the second embodiment, the electroless copper plating bath used in the first embodiment further promotes the electroless plating reaction and has an effect of increasing the deposition rate. Is added. In the electroless plating method of this embodiment, an accelerator combined with a basic bath shown in Table 1 in which, for example, tetraethylenepentamine (hereinafter referred to as “pentamine”) is added in addition to 0.5 ppm of 2-MBT. Use an isotropic bath.

As the pentamine concentration increases, the deposition rate increases, but the pattern width W1 tends to increase. For example, the precipitation rate is doubled when the pentamine concentration (addition amount) is 0.5 × 10 ⁻³ g / dm ³ (0.5 ppm), and the concentration is 1.0 × 10 ⁻³ g / dm ³ ( 1 ppm), it was 2.9 times higher. On the other hand, the pattern width W1 was 199.3 μm in the 0.5 ppm addition bath and 199.2 μm in the 1 ppm addition bath at W0 (200 μm).

On the other hand, when the pentamine concentration was 10 × 10 ⁻³ g / dm ³ (10 ppm), the deposition rate further increased, but it sometimes peeled off from the substrate. Further, when the concentration was 100 × 10 ⁻³ g / dm ³ (100 ppm), the deposition rate increased 3.7 times, but the pattern width W1 was 203.3 μm, which exceeded W0.

  As a result of further experiments, it was found that the pentamine concentration (addition amount) is preferably 0.1 ppm to 4 ppm, particularly preferably 0.3 ppm to 1 ppm.

  Since the electroless plating method of this embodiment forms a film using an electroless plating copper bath containing an inhibitor and an accelerator, it has the effect of the electroless plating method of the first embodiment, and is further faster. A wiring board can be produced.

<Third Embodiment>
Next, the electroless plating method of the third embodiment will be described.

  As already explained, since the electroless plating method of the embodiment does not use a resin pattern mask at the time of plating film formation, there is a possibility that the plating is deposited even in an ultraviolet-irradiated region.

  In the electroless plating method of this embodiment, as shown in FIG. 5, the preliminary immersion step (step S17P) is further provided before the electroless copper plating step (S16). The purpose of the pre-immersion step is to remove or inactivate palladium adsorbed on the UV non-irradiated region.

  The pre-soaking solution can be roughly classified into a method using a complexing agent-containing solution such as glycine or 2,2′-pibilidyl, and a method using an inhibitor-containing solution such as thiourea. If the effect of the pre-immersion step is too strong, the electroless copper plating film will not be deposited in the UV irradiation region. For this reason, the pre-immersion process in which the precipitation prevention to the UV non-irradiated region and the deposition of the UV irradiated region are balanced is preferable.

From this point of view, as a result of various experiments, it was most preferable to immerse in a solution of thiourea 0.2 mg / dm ^{3 to} 0.8 mg / dm ³ , for example, 0.5 mg / dm ³ for 30 seconds to 120 seconds. It turned out to be preferable.

  The electroless plating method of the present embodiment has the effect of the electroless plating method of the first embodiment, and can more reliably prevent plating deposition on the ultraviolet unirradiated region.

  The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 11 ... UV irradiation area | region 20 ... Photomask 20A ... Quartz glass 20B ... Chrome vapor deposition film 30 ... Light source 40 ... Wiring board 41 ... Copper pattern film

Claims (5)

A UV irradiation step of irradiating a partial region of the resin substrate with ultraviolet rays;
A catalyst applying step for applying a catalyst for electroless plating reaction to the surface of the resin substrate;
A plating step of selectively forming a wiring pattern of a copper plating film in the ultraviolet irradiation region using an electroless copper plating bath; and
The electroless copper plating bath contains an inhibitor that suppresses the electroless plating reaction,
The electroless plating method, wherein a pattern size of the copper plating film is less than a size of the ultraviolet irradiation region.   The electroless plating method according to claim 1, wherein the inhibitor is 2-mercaptobenzotriazole.   The electroless plating method according to claim 2, wherein the electroless copper plating bath contains tetraethylenepentamine.   The electroless plating method according to claim 3, further comprising a preliminary immersion step of immersing in a solution containing thiourea before the plating step.   A wiring board manufactured using the electroless plating method according to any one of claims 1 to 4.

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