JP4565181B2 - Metal coating method - Google Patents

Description

  The present invention relates to a metal coating method for coating a surface of various base materials such as plastic and ceramic.

  Conventionally, the surface of various base materials such as plastics and ceramics is coated with metal. For example, in the production of a printed circuit board, copper is coated on the surface of a glass fiber reinforced epoxy plate. Moreover, in order to shield the electromagnetic waves radiated | emitted from an electronic device, copper, nickel, etc. are also coated inside the housing of an electronic device. As described above, coating a metal on the surface of various base materials is an important basic technique in various industrial fields.

  As a method for coating a metal on the substrate surface, a dry plating method in which the metal is coated in a vacuum system, such as a vacuum deposition method or a sputtering method, or a metal is deposited on the surface of the substrate in a solution. An electroless plating method or the like is performed. Among these, the metal coating by electroless plating method is simpler than the dry method, which requires a large-scale device for maintaining a vacuum system, can be continuously processed, and is relatively easy to operate. It is widely used for some reason.

  However, in the metal coating by the electroless plating method, it is necessary to apply an expensive palladium catalyst to the object to be plated in order to promote metal deposition, and there is a problem that the cost burden required for the pretreatment process is increased. . In addition, as a method for imparting a palladium catalyst to an object to be plated, the object to be plated is immersed in a hydrochloric acid solution of tin (II) chloride and then immersed in a hydrochloric acid solution of palladium chloride, or in a tin-palladium mixed colloid solution. There is a method of improving catalyst activity by immersing in an accelerator solution made of an acidic solution such as sulfuric acid after soaking to give a catalyst, and improving the catalytic activity by dissolving excess tin ions. In many cases, the management is complicated, and this also contributes to an increase in the cost of the pretreatment process.

In contrast, the inventors have developed metal coating methods that do not require the use of a catalyst such as palladium by a method different from that of conventional electroless plating solutions (Non-Patent Documents 1 and 2).
Journal of Materials Chemistry, 2004,14,976-981 Journal of Colloid and Interface Science 263 (2003) 190-195

  The metal coating method described in Non-Patent Document 1 is a method in which a silicon wafer surface is treated with 3-aminopropyltriethoxysilane to modify amino groups on the surface, and then copper coating is performed with an electroless copper plating solution. In this method, copper particles generated in the electroless copper plating solution are electrostatically adsorbed to amino groups, and copper coating can be performed without using a noble metal catalyst. In addition, a copper pattern can be selectively formed in a region by performing ultraviolet irradiation using a photomask before performing copper coating.

  Further, the metal coating method described in Non-Patent Document 2 is a method in which the surface of barium titanate is treated with 3-aminopropyltriethoxysilane to modify the amino group on the surface, and then nickel coating is performed with an electroless nickel plating solution. It is. Also by this method, it is possible to perform nickel coating by the same principle as the method of Non-Patent Document 1, and it is also possible to selectively form a nickel pattern in a region-selective manner by the same method.

  Furthermore, the inventors have developed a base material by a silicon treatment liquid in which an amino-containing organosilicon compound having an amino group and capable of polycondensation by hydrolysis is mixed with a carbonyl compound that reacts with the amino group to form an imine compound. A patent application has been filed for a method of treating a surface and then coating a metal with an electroless plating solution (Japanese Patent Application No. 2003-324238). According to this method, not only a precious metal catalyst need not be used, but also any substrate can be coated with a metal. In addition, after treating the substrate surface with a silicon treatment liquid, further forming a polysiloxane film, detaching molecular chains present on the surface by energy irradiation, and then coating the metal with an electroless plating solution, the region A selective metal coating can also be performed.

  However, the metal coating film obtained by the methods of Non-Patent Documents 1 and 2 and the above-mentioned patent application is based on the principle that it is formed by electrostatic interaction between the metal fine particles and the modified substrate surface. There was a problem that the bonding force between the fine particles was weak and the conductivity was slightly lowered. In addition, since metal coating is performed while depositing fine metal particles in an electroless plating bath that self-decomposes, there is also a problem that the bath life of the electroless plating bath is short.

  The present invention has been made in view of the above-described conventional situation, and it is not necessary to use a noble metal catalyst, the number of pretreatment steps is small, the coating film has excellent conductivity, and a pattern can be formed. Therefore, it is an object to be solved to provide a metal coating method having a long service life for the treatment liquid.

  The inventors paid attention to a thiol group having a high affinity with a metal such as copper in order to solve the above problem. As a result of intensive studies, it was found that the above problems can be solved by coating a metal after the thiol group is modified on the surface of the substrate, and the present invention has been completed.

That is, the metal coating method of the present invention is modified by a thiol group-modifying compound capable of modifying a thiol group on the surface of a substance and a thiol group-modifying compound on the surface of the base material. The substrate is brought into contact with an electroless plating solution containing a metal ion and a reducing agent capable of reducing the metal ion, and the metal is deposited on a portion of the surface of the substrate modified with the thiol group modifying compound. A metal deposition step.

In the metal coating method of the present invention, first, in the modification step, a thiol group is modified on the surface of the substrate with a thiol group modifying compound. Next, as a metal deposition step, the base material modified with a thiol group is brought into contact with the metal deposition solution, thereby precipitating a metal on the portion modified with the thiol group modifying compound on the surface of the base material. According to the test results of the inventors, the deposited metal was excellent in electrical conductivity and good adhesion. In addition, this metal coating method does not require a precious metal catalyst to be applied to the substrate surface, and the number of processing steps is small. For this reason, the processing cost is low. Furthermore, since metal coating can be performed without depositing metal fine particles in an electroless plating solution in a self-decomposing manner, there is an advantage that the bath life is long.

  As the thiol group-modifying compound that can be used in the modification step of the present invention, any compound that can modify the thiol group on the surface of the substance can be used. Examples of such a compound include a thiol-containing organosilicon compound that can be polycondensed by hydrolysis (for example, a silicon trialkoxide having a thiol group, a silicon dialkoxide having a thiol group, a silicon monoalkoxide having a thiol group, and a thiol group. Silicon trihalide, silicon dihalide having a thiol group, silicon monohalide having a thiol group), titanium alkoxide having a thiol group, zirconium alkoxide having a thiol group, tantalum alkoxide having a thiol group, germanium alkoxide having a thiol group , A carboxylic acid having a thiol group, an amine having a thiol group, and the like can be used. The inventors confirmed that by using a thiol-containing organosilicon compound that can be polycondensed by hydrolysis as a thiol group-modifying compound, it is possible to reliably coat a substrate surface with a metal having excellent conductivity and good adhesion. is doing.

  The modification of the thiol group on the surface of the substrate by the thiol group-modifying compound may be either a chemical bond modification or a physical adsorption modification. The number of thiol groups in the thiol group-modified compound may be plural. Furthermore, two or more thiol group-modified compounds can be used in combination.

  In addition, examples of metal ions contained in the electroless plating solution used in the metal deposition step include copper ions and nickel ions. Among these, copper ions are particularly preferable. According to the test results of the inventors, when the metal ion is a copper ion, copper having excellent conductivity and adhesion can be deposited on the surface of the substrate. This reason is presumed to be due to the particularly high affinity between copper and thiol groups.

  Examples of the reducing agent added to the electroless plating solution include dimethylamine borane and hypophosphite. In addition to these components, it is of course possible to add a complexing agent such as EDTA or a pH adjusting agent such as boric acid in order to adjust the redox potential.

  In the metal coating method of the present invention, after the modification step and before the metal deposition step, it is possible to deposit metal selectively in a region by providing a pattern formation step of irradiating a part of the surface of the substrate with energy. Become. This principle is explained as follows. That is, the thiol group modified on the surface of the base material in the modification step is desorbed together with the thiol group due to the elimination reaction of the molecular chain by energy irradiation. For this reason, in the next metal deposition step, metal deposition does not occur and a pattern is formed at a place where energy irradiation has been performed. In this way, a metal plating pattern can be formed by full additive.

  Examples of the energy irradiation method include ultraviolet irradiation, electron beam irradiation, X-ray irradiation, light irradiation, and ion beam irradiation. Among these, ultraviolet irradiation is preferable because the apparatus is simple and molecular chains can be detached quickly.

  Moreover, before the modification step in the metal coating method of the present invention, a hydrophilic treatment step for hydrophilic treatment of the surface of the substrate can be provided. In this way, the thiol group can be reliably modified on the surface of the substrate by the thiol group modifying compound in the modification step, and the metal coating according to the present invention is applied to various types of substrates such as plastics. It becomes possible.

  As a method of hydrophilic treatment, for example, after the surface of the substrate is treated with a silane coupling agent, the substrate is placed in a solution obtained by hydrolyzing tetraalkoxysilane, by applying energy irradiation with ultraviolet rays or the like. Examples thereof include a sol-gel method in which a silica film is formed on the surface by dipping and drying, and a plasma treatment method in which the surface of a plastic such as PET is made hydrophilic by plasma treatment. The inventors of the present invention, as a hydrophilization treatment using a silane coupling agent, include an amino-containing organosilicon compound having an amino group and capable of polycondensation by hydrolysis, and a carbonyl compound that reacts with the amino group to produce an imine compound. Mixing step to form a silicon treatment solution, a silicon treatment step for treating the surface of the substrate with the silicon treatment solution, and an irradiation step for irradiating the surface of the substrate treated with the silicon treatment step with energy. It has been confirmed that a copper coating excellent in electrical conductivity and adhesion can be reliably performed by the hydrophilization process comprising: In this hydrophilization process, the surface of the substrate is coated by a polycondensation reaction of the silicon treatment liquid in the silicon treatment process, and the molecular chain in the coating is cleaved with Si by the energy irradiation in the irradiation process to form silanol groups. As a result, the surface has hydrophilicity. Examples of the energy irradiation method include ultraviolet irradiation, electron beam irradiation, X-ray irradiation, light irradiation, and ion beam irradiation. Among these, ultraviolet irradiation is preferable because the apparatus is simple and molecular chains can be detached quickly.

  Hereinafter, examples embodying the present invention will be described in detail.

Example 1
In Example 1, a polyethylene phthalate (hereinafter abbreviated as “PET”) film (Yunitika emblet thickness 50 μm) was used as a substrate, and the steps (S1 to S6) shown in FIG. 1 were performed. These steps are described in detail below.

<Mixing step S1>
3-aminopropyltrimethoxysilane (hereinafter abbreviated as “APTMS”) was prepared as an amino-containing organosilicon compound, and this was added to acetone so as to be 1% by volume, and the mixture was allowed to stand at room temperature for 2 weeks. A silicon treatment liquid is used.

<Silicon processing step S2>
Next, after the PET film ultrasonically washed in order of acetone and ethanol for 5 minutes is dried in a dryer at 50 ° C., it is gently put into the silicon treatment liquid obtained in the mixing step S1 from the direction perpendicular to the liquid surface. After being soaked in, the operation of gently pulling it up is repeated three times, followed by natural drying.

<Irradiation process S3>
The PET film that has undergone the silicon treatment step S2 is irradiated with ultraviolet rays (200 W low-pressure mercury lamp) for 5 minutes. The mixing step S1, the silicon treatment step S2, and the irradiation step S3 so far are hydrophilic steps.

<Modification step S4>
Mercaptopropyltrimethoxysilane (hereinafter abbreviated as “MPTS”) as a thiol group modifying compound is prepared and added to 1% by volume in toluene in a glove box to obtain an MPTS solution. Then, after the PET film after the irradiation step S3 is gently dipped from the direction perpendicular to the liquid surface of the MPTS solution, the PET film is gently lifted as it is and then dried at 50 ° C. with a dryer.

<Pattern forming step S5>
A photomask having a predetermined pattern is placed on the PET film after the modification step S4, and ultraviolet irradiation (200 W low-pressure mercury lamp) is performed for 5 minutes.

<Metal deposition step S6>
The following electroless copper plating solution is prepared.
CuCl ₂・ ・ ・ ・ ・ ・ 0.05mol / L
EDTA · 2Na ··· 0.05 mol / L
Boric acid ... 0.1 mol / L
Dimethylamine borane ・ 0.1mol / L
pH: 7.0
The electroless copper plating solution is heated to 50 ° C., and the PET film after finishing the pattern forming step S5 is dipped in it for 3 hours, then pulled up, washed with water, and dried. A film was obtained.

(Comparative Example 1)
In Comparative Example 1, the irradiation step S3 and the modification step S4 were omitted in order to confirm the effect of thiol group modification by MPTS in Example 1 above. That is, in Comparative Example 1, after performing the mixing step S1 and the silicon treatment step S2, the pattern formation step S5 and the metal deposition step S6 were performed.

<Evaluation>
The following tests were conducted on the surface-treated PET films of Example 1 and Comparative Example 1 obtained by the above steps.

(1) Optical microscope observation As a result of observation using an optical microscope, in the surface-treated PET film of Example 1, as shown in FIG. 2, copper was deposited on the portion irradiated with ultraviolet rays in the pattern forming step S5. Copper was not deposited on the portion that was not irradiated with ultraviolet rays. Moreover, the resolution was also high. On the other hand, in Comparative Example 1 in which the surface modification with the thiol group was not performed, copper deposition did not occur regardless of the presence or absence of ultraviolet irradiation as shown in FIG.

(2) X-ray diffraction measurement FIG. 4 shows the results of X-ray diffraction measurement of the surfaces of the surface-treated PET film of Example 1, the surface-treated PET film of Comparative Example 1, and the untreated PET film. As can be seen from this figure, in the surface-treated PET film of Example 1, a peak based on Cu metal was observed only in the part not irradiated with ultraviolet light in the pattern forming step S5, and was not detected from the part irradiated with ultraviolet light. On the other hand, in the surface-treated PET film of Comparative Example 1, no peak based on Cu metal was observed regardless of the presence or absence of ultraviolet irradiation. These results support the results of the optical microscope observation.

(3) XPS measurement The result of having performed the XPS measurement of the surface immediately after performing pattern formation process S5 in Example 1 is shown in FIG. As can be seen from this figure, a peak based on S2p3 / 2 was detected only from the portion that was not irradiated with ultraviolet rays in the pattern forming step S5. From this, it was found that the thiol group modified on the surface was eliminated by irradiation with ultraviolet rays.

(4) Measurement of contact angle The result of having measured the contact angle with respect to untreated PET in Example 1 and the water after each process is shown in FIG. From this figure, it can be seen that the contact angle is significantly reduced and the hydrophilicity is increased by performing the irradiation step S3. This is explained by the fact that the alkoxy group on the surface modified with APTMS was removed in the silicon treatment step S2 and changed to a silanol group. Moreover, it is explained that the large contact angle is obtained again by the modification step S4 due to the modification of thiol. Further, it is explained that the contact angle of the portion irradiated with ultraviolet rays in the pattern forming step S5 is reduced because the alkoxythiol chain is eliminated to form a silanol group.

(5) Measurement of conductivity As a result of measuring the conductivity of the copper-coated portion by the four-single-needle method for the surface-treated PET film of Example 1, a high value of 7.8 × 10 ⁴ (S / cm) was obtained. Obtained.

(6) Film thickness measurement by atomic force microscope (AFM) As a result of measuring the thickness of the copper-coated portion of the surface-treated PET film of Example 1 by AFM, it was 60 to 100 nm.

  From the results of the tests (1) to (6), the principle of copper pattern formation according to Example 1 can be described as follows. That is, as shown in FIG. 7, the imine-containing organosilicon compound condensation film 2 is formed by performing the silicon treatment step S2 on the PET film 1. In the irradiation step S3, the surface of the imine-containing organosilicon compound condensation film 2 is irradiated with ultraviolet rays, whereby the molecular chain is detached and becomes a silanol group. Further, in the modification step S4, hydrogen of the silanol group is modified to a mercaptopropyl group by MPTS. And as pattern formation process S5, by irradiating with an ultraviolet-ray partially using a photomask, the mercaptopropyl group of an ultraviolet irradiation part will detach | desorb and it will return to a silanol group. Finally, as a metal deposition step S6, by treating with an electroless copper plating solution, copper is deposited on an unirradiated portion where an SH group having high affinity with copper remains. Thus, a copper pattern can be formed on the surface of PET.

  As described above, in the copper pattern formation of Example 1, it is only necessary to irradiate ultraviolet rays after being dipped in a silicon treatment solution and dried as a pretreatment step, so that it is not necessary to use a noble metal catalyst and the number of steps is also increased. Few. Further, the conductivity of the deposited copper is excellent, and a pattern with high resolution can be formed. Further, the electroless copper plating solution in the metal deposition step S6 is also in the neutral region, and there is an advantage that the bath self-decomposition hardly occurs and the bath life is very long.

  INDUSTRIAL APPLICABILITY The present invention can coat various substrates such as plastics and ceramics with metal, and can be used in various industrial fields such as printed wiring boards and electromagnetic wave shields for housings of electronic devices.

2 is a process diagram of Example 1. FIG. 2 is an optical micrograph of the copper pattern-formed PET film surface of Example 1. FIG. 2 is an optical micrograph of the surface-treated PET film surface of Comparative Example 1. It is an X-ray-diffraction spectrum of the surface of Example 1, the comparative example 1, and an untreated PET film. It is a measurement result of the narrow scan of XPS after pattern formation process S5 in Example 1. FIG. It is a measurement result of untreated PET in Example 1, and a contact angle after each process. 2 is a schematic diagram illustrating each process in Example 1. FIG.

Explanation of symbols

S4 ... Modification step S5 ... Pattern formation step S6 ... Metal deposition step S1, S2, S3 ... Hydrophilization step (S1 ... Mixing step, S2 ... Silicon treatment step, S3 ... Irradiation step)
1 ... Base material (PET film)

Claims (7)

A modification step of modifying the surface of the substrate with a thiol group-modifying compound capable of modifying a thiol group on the surface of the substance,
The substrate modified with the thiol group modifying compound is contacted with an electroless plating solution containing a metal ion and a reducing agent capable of reducing the metal ion, and modified with the thiol group modifying compound on the surface of the substrate. And a metal deposition step of depositing a metal on the formed portion .   The metal coating method according to claim 1, wherein the thiol group-modifying compound is a thiol-containing organosilicon compound capable of polycondensation by hydrolysis.   The metal coating method according to claim 1 or 2, wherein the metal ions contained in the electroless plating solution are copper ions.   4. The metal is selectively deposited in a region by providing a pattern forming step of irradiating a part of the surface of the substrate with energy after the modification step and before the metal deposition step. The metal coating method according to claim 1.   The metal coating method according to claim 4, wherein the energy irradiation is performed by ultraviolet irradiation.   The metal coating method according to any one of claims 1 to 5, further comprising a hydrophilization step of hydrophilizing the surface of the substrate before the modification step. The hydrophilization process
A mixing step of mixing an amino-containing organosilicon compound having an amino group and capable of polycondensation by hydrolysis with a carbonyl compound that reacts with the amino group to form an imine compound, to obtain a silicon treatment liquid;
A silicon treatment step of treating the surface of the substrate with the silicon treatment liquid;
The metal coating method according to claim 6, further comprising an irradiation step of irradiating energy on the surface of the substrate processed by the silicon processing step.