JP7634946B2 - Manufacturing method of metal-clad laminate - Google Patents

Description

The present invention relates to a method for manufacturing a metal-clad laminate.

When manufacturing flexible printed wiring boards and the like, metal-clad laminates are used, in which a metal layer made of a metal such as copper is laminated onto a substrate.

As a method for manufacturing such a metal-clad laminate, for example, Patent Document 1 below discloses a conductive film formation method that includes a step of forming a film of fired copper fine particles on a substrate, and a step of plating the film to form a conductive film.

JP 2013-135089 A

However, the conductive film forming method described in Patent Document 1 above leaves room for improvement in terms of the adhesion of the conductive film to the substrate.

The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a metal-clad laminate that can produce a metal-clad laminate in which the decrease in adhesion of the metal layer to the substrate is suppressed.

The present inventor has studied the cause of the insufficient adhesion of the conductive film to the substrate in the conductive film forming method described in the above Patent Document 1. As a result, the present inventor has considered that the cause of the insufficient adhesion of the conductive film to the substrate is due to the following reasons. That is, in the conductive film forming method described in the above Patent Document 1, the film has a porous structure with multiple voids, and it is considered that the metal particles constituting this film are embedded in a state where they are caught in the substrate. That is, it is considered that the film adheres to the substrate due to the anchor effect of the metal particles constituting it. And since plating is applied to this porous structure film, when the metal growing by plating enters the voids in the film and grows during plating, the metal eventually enters the gap between the substrate and the film, and applies a stress between the substrate and the film that is sufficient to separate them. Alternatively, the metal growing by plating applies a stress to the metal particles constituting the film. As a result, the present inventor has considered that the metal layer may be easily peeled off from the substrate. Then, the present inventor has further studied and found that the above problem can be solved by the following invention.

That is, the present invention is a method for manufacturing a metal-clad laminate, which includes a metal layer forming step of manufacturing a metal-clad laminate by forming a metal layer on a substrate, and the metal layer forming step includes a first metal layer forming step of forming a porous first metal layer having voids on the substrate, a second metal layer forming step of forming a non-porous second metal layer on the first metal layer, and a third metal layer forming step of forming a third metal layer on the second metal layer by plating.

According to this method for manufacturing a metal-clad laminate, a porous first metal layer is formed on the substrate, a non-porous second metal layer is formed on the first metal layer, and a third metal layer is formed on the second metal layer by plating. In this way, a metal layer having a first metal layer, a second metal layer, and a third metal layer is formed on the substrate. At this time, when the third metal layer is formed on the second metal layer by plating, the second metal layer prevents the plating from penetrating into the gaps of the first metal layer. Therefore, even if the metal grows by plating, the metal is prevented from penetrating into the gap between the substrate and the first metal layer, and the application of stress that separates the substrate and the first metal layer is prevented. Therefore, according to the method for manufacturing a metal-clad laminate of the present invention, a metal-clad laminate in which the decrease in adhesion of the metal layer to the substrate is suppressed can be manufactured.

In the manufacturing method of the metal-clad laminate described above, in the second metal layer forming step, it is preferable to form the second metal layer so that the ten-point average surface roughness of the second metal layer is smaller than the ten-point average surface roughness of the first metal layer.

In this case, compared to when the second metal layer is formed so that the ten-point average surface roughness of the second metal layer is equal to or greater than the ten-point average surface roughness of the first metal layer, the surface irregularities of the second metal layer are smaller, and the current path is shorter when a high-frequency current flows. This makes it possible to further reduce the electrical resistance of the second metal layer.

In the above-mentioned method for manufacturing a metal-clad laminate, it is preferable that in the second metal layer forming step, the second metal layer is made of the same metal as the first metal layer.

In this case, compared to when the first metal layer and the second metal layer are made of different metals, metal is less likely to dissolve out of the second metal layer due to moisture or the like penetrating into the porous first metal layer. In other words, corrosion of the second metal layer is sufficiently suppressed. As a result, an increase in the resistance of the second metal layer is suppressed, and the second metal layer is sufficiently suppressed from cracking or peeling off from the first metal layer.

The present invention provides a method for producing a metal-clad laminate that can produce a metal-clad laminate in which the decrease in adhesion of the metal layer to the substrate is suppressed.

1 is a cross-sectional view showing a metal-clad laminate produced by the method for producing a metal-clad laminate of the present invention. FIG. 2 is an enlarged view of a region surrounded by a two-dot chain line A in FIG. 2 is a cross-sectional view showing a first metal layer forming step in the manufacturing method of the metal-clad laminate of the present invention. FIG. 3 is a cross-sectional view showing a second metal layer forming step in the manufacturing method of the metal-clad laminate of the present invention. FIG.

The following describes in detail an embodiment of the method for manufacturing a metal-clad laminate of the present invention.

First, the metal-clad laminate produced by the method for producing a metal-clad laminate of the present invention will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing the metal-clad laminate produced by the method for producing a metal-clad laminate of the present invention, and FIG. 2 is an enlarged view of the area surrounded by the two-dot chain line A in FIG. 1.

As shown in Figures 1 and 2, the metal-clad laminate 100 includes a substrate 10 and a metal layer 20 provided on the main surface 10a of the substrate 10. The metal layer 20 includes a porous first metal layer 21 provided on the substrate 10 and having voids V, a non-porous second metal layer 22 provided on the first metal layer 21, and a third metal layer 23 provided on the second metal layer 22.

Next, the manufacturing method of the metal-clad laminate 100 will be described with reference to Figures 1 to 4. Figure 3 is a cross-sectional view showing the first metal layer forming step in the manufacturing method of the metal-clad laminate of the present invention, and Figure 4 is a cross-sectional view showing the second metal layer forming step in the manufacturing method of the metal-clad laminate of the present invention.

As shown in Figures 1 to 4, the manufacturing method of the metal-clad laminate 100 includes a metal layer forming process for manufacturing the metal-clad laminate 100 by forming a metal layer 20 on the substrate 10. The metal layer forming process includes a first metal layer forming process for forming a porous first metal layer 21 having voids V on the substrate 10, a second metal layer forming process for forming a non-porous second metal layer 22 on the first metal layer 21, and a third metal layer forming process for forming a third metal layer 33 on the second metal layer 22 by plating.

According to the manufacturing method of the metal-clad laminate 100, a porous first metal layer 21 is formed on the substrate 10, a non-porous second metal layer 22 is formed on the first metal layer 21, and a third metal layer 23 is formed on the second metal layer 22 by plating. In this way, a metal layer 20 having the first metal layer 21, the second metal layer 22, and the third metal layer 23 is formed on the substrate 10. At this time, when the third metal layer 23 is formed on the second metal layer 22 by plating, the second metal layer 22 suppresses the metal grown by plating from entering the gap V of the first metal layer 21. Therefore, even if the metal grows by plating, the metal is suppressed from entering the gap between the substrate 10 and the first metal layer 21, and the application of stress between the substrate 10 and the first metal layer 21 that separates them is suppressed. Therefore, a metal-clad laminate 100 in which peeling of the metal layer 20 from the substrate 10 is sufficiently suppressed can be manufactured.

The first metal layer forming process, the second metal layer forming process, and the third metal layer forming process are described in detail below.

<First metal layer forming step>
The first metal layer forming step is a step of forming a porous first metal layer 21 having voids V on the substrate 10 (see FIG. 3).

(Substrate)
The material constituting the substrate 10 is not particularly limited, but examples of the material constituting the substrate 10 include non-thermoplastic polyimide resins; thermoplastic polyethylene terephthalate (PET), liquid crystal polymer (LCP), cycloolefin polymer (COP); and fluorine-based resins such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA).

When the metal clad laminate 100 is used for high frequency applications, a resin with a low dielectric constant is preferred. In this case, a portion of the electrical energy is less likely to become heat and is less likely to be lost. Examples of such resins with a low dielectric constant include LCP, COP, and fluororesins.

When solder reflow is of particular importance, the material constituting the substrate 10 is preferably a resin with a continuous use temperature of 200°C or higher. Examples of such resins include LCP, COP, and fluorine-based resins.

In addition, when emphasis is placed on suppressing warping due to temperature changes, the material constituting the substrate 10 is preferably a resin having a linear expansion coefficient close to that of the first metal layer 21. For example, when the first metal layer is made of copper, it is preferable to use an LCP or polyimide resin having a linear expansion coefficient close to that of copper (16 ppm/K).

The average thickness of the substrate 10 depends on the application and cannot be generally determined, but is usually 25 to 100 μm. The average thickness of the substrate 10 can be measured, for example, by the method described in JIS K7130:1999 "Plastics - Films and sheets - Thickness measurement method."

(First Metal Layer)
The first metal layer 21 can be obtained by applying a paste for forming the first metal layer, which paste contains, for example, metal particles and a solvent, onto the main surface 10a of the base material 10, and then firing the paste with light.

Here, the metal particles preferably include nanoparticles with an average particle size of 1 to 100 nm. The metal particles may be composed of only nanoparticles, or may be composed of a mixture of nanoparticles and coarse particles. As the coarse particles, for example, disk particles with a diameter of 1 μm and a thickness of 200 nm can be used. Note that only the nanoparticles dissolve when irradiated with light, and the coarse particles do not dissolve.

It is preferable that the metal particles are composed only of nanoparticles. In this case, the volume resistivity of the first metal layer 21 can be made smaller. This is thought to be because when the metal particles are composed only of nanoparticles, all the metal particles melt and are fused together by light sintering, which increases the contact area between the metal particles.

However, the metal particles may be composed of a mixture of nanoparticles and coarse particles. In this case, since the coarse particles do not dissolve by light sintering, it is possible to reduce the shrinkage of the metal film during light sintering, and it is possible to prevent the substrate 10 from warping and the first metal layer 21 from peeling off from the substrate 10.

Metals that make up the metal particles include, for example, gold, silver, and copper. Among these, copper is preferred because it is inexpensive.

Examples of solvents that can be used include 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, propylene carbonate, and 1,3-dimethyl-2-imidazolidinone.

The paste for forming the first metal layer may further contain a dispersant. Examples of dispersants include polyethylene glycol and polyvinylpyrrolidone.

The paste for forming the first metal layer can be applied, for example, using a microgravure coater or a spin coater.

It is preferable to perform a drying process on the paste for forming the first metal layer before light sintering. Furthermore, if the paste for forming the first metal layer contains a large amount of organic components such as binders, it is preferable to further perform a process to remove the organic components. In this case, it is possible to prevent the voids from becoming larger due to gas generated by decomposition of the organic components during light sintering.

As a drying method, a method of heat treatment at about 50 to 100°C can be used. As a method of removing organic components, for example, a method of heat treating the paste for forming the first metal layer at about 150°C, immersing it in dilute sulfuric acid to remove the oxide film, rinsing with water, and then immersing it in isopropyl alcohol can be used.

As an apparatus for performing light sintering, for example, the "Pulsforge 1300" manufactured by Novacentrix can be used. As a light source for this apparatus, for example, a xenon lamp can be used.

The light irradiation energy may be, for example, 0.1 to 100 J/cm ^2. The light irradiation time may be 0.1 to 100 ms. The number of irradiations may be one or multiple.

The average thickness of the first metal layer 21 is preferably 2x or more, where x is the average particle size of the metal particles that make up the first metal layer 21. In this case, two or more metal particles are mathematically present on the substrate 10, and the second metal layer 22 is not formed directly on the metal particles that are in direct contact with the substrate 10. As a result, stress from the second metal layer 22 is less likely to be applied to the metal particles that are in direct contact with the substrate 10, and a decrease in the adhesion of the first metal layer 21 to the substrate 10 is sufficiently suppressed.

The average thickness of the first metal layer 21 is preferably 5 μm or less. In this case, the voids V are sufficiently prevented from becoming large due to gas generated in the paste for forming the first metal layer when the paste for forming the first metal layer is optically fired, compared to when the average thickness of the first metal layer 21 exceeds 5 μm. It is more preferable that the average thickness of the first metal layer 21 is 1 μm or less.

The average thickness of the first metal layer 21 can be measured, for example, by observing a cross section of the first metal layer 21 with a scanning electron microscope. One method for exposing the cross section of the first metal layer 21 is to embed the metal-clad laminate 100 in resin and then polish it.

<Second metal layer forming step>
The second metal layer forming step is a step of forming a non-porous second metal layer 22 on the first metal layer 21 (see FIG. 4 ). In other words, the second metal layer forming step is a step of forming the second metal layer 22 on the first metal layer 21 so that plating does not pass through when the third metal layer 23 is formed on the second metal layer by plating.

In the second metal layer formation process, the ten-point average surface roughness (R2) of the second metal layer 22 is not particularly limited, but it is preferable to form the second metal layer 22 so that it is smaller than the ten-point average surface roughness (R1) of the first metal layer 21.

In this case, compared to when the second metal layer 22 is formed so that R2 is equal to or greater than R1, the surface irregularities of the second metal layer 22 are smaller, and the current path is shorter when a high-frequency current flows, so the electrical resistance of the second metal layer 22 can be further reduced.

There are no particular limitations on R1-R2, but it is preferable that it is 0.03 μm or more. In this case, the electrical resistance of the second metal layer 22 can be further reduced. However, it is preferable that R1-R2 is 0.1 μm or less.

Specifically, R2 is preferably 0.01 μm or more. However, R2 is preferably 0.2 μm or less.

The second metal layer 22 may be formed so as to cover only the principal surface of the first metal layer 21 opposite the substrate 10 (hereinafter referred to as the "opposite principal surface"), but it is preferable that the second metal layer 22 is formed so as to cover not only the opposite principal surface but also the side surface connecting the opposite principal surface to the interface between the substrate 10 and the first metal layer 21. In this case, the second metal layer 22 fills the voids in the first metal layer 21, so that when the third metal layer 23 is formed on the second metal layer 22, the metal grown by plating can be prevented from entering the voids in the first metal layer 21.

The metal constituting the second metal layer 22 is not particularly limited, but when the metal-clad laminate 100 is used for high-frequency applications, it is preferable that the metal be a non-magnetic metal. In this case, the skin effect prevents the thickness of the portion of the second metal layer 22 through which current flows from becoming smaller, thereby reducing the electrical resistance of the second metal layer 22. Examples of non-magnetic metals include gold, silver, and copper. Of these, copper is preferable because it is inexpensive.

It is preferable that the second metal layer 22 is made of the same metal as the first metal layer 21.

In this case, metal is less likely to be dissolved from the second metal layer 22 by moisture or the like that penetrates into the porous first metal layer, compared to when the first metal layer 21 and the second metal layer 22 are made of different metals. In other words, corrosion of the second metal layer 22 is sufficiently suppressed. As a result, an increase in the resistance of the second metal layer 22 is suppressed, and cracking or peeling of the second metal layer 22 from the first metal layer 21 is sufficiently suppressed.

The non-porous second metal layer 22 is preferably formed by sputtering. In this case, when the second metal layer 22 is formed by sputtering, unlike when the second metal layer 22 is formed by plating, it is possible to sufficiently prevent the metal formed by sputtering from penetrating the voids in the porous first metal layer 21.

The average thickness of the second metal layer 22 is not particularly limited, but is preferably at least one time the average particle size of the metal particles that make up the first metal layer 21.

Specifically, the average thickness of the second metal layer 22 may be 1 to 20 μm.

The average thickness of the second metal layer 22 can be adjusted by the sputtering time.

The average thickness of the second metal layer 22 can be measured in the same manner as the first metal layer 21.

<Third metal layer forming step>
The third metal layer forming step is a step of forming a third metal layer 33 on the second metal layer 22 by plating (see FIG. 1).

There are no particular limitations on the metal that constitutes the third metal layer 23. Examples of such metals include gold, silver, and copper. Among these, copper is preferred because it is inexpensive.

The plating solution used for plating is not particularly limited, but is preferably a copper sulfate solution. In this case, the third metal layer 23, which has a smooth surface, is uniformly attached to the surface of the second metal layer 22. A brightener may be added to the plating solution.

Examples of plating include electroplating and electroless plating. Among these, electroplating is preferred from the viewpoint of increasing the thickness of the third metal layer 23 in a short period of time.

When the plating is electroplating, the current density is not particularly limited, but is usually 1 to 4 A/ ^dm2 .

The present invention is not limited to the above embodiment. For example, in the above embodiment, the metal layer 20 is formed only on the main surface 10a of the substrate 10, but the metal layer 20 may be formed on the opposite main surface of the substrate 10 opposite the main surface 10a.

In addition, in the above embodiment, the first metal layer 21 is formed by light-firing the paste for forming the first metal layer, but the first metal layer 21 does not necessarily have to be formed by light-firing the paste for forming the first metal layer. For example, the first metal layer 21 can also be formed by thermal firing.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

Example 1
First, a substrate having an average thickness of 25 μm was prepared. As the substrate, a polyimide film (trade name "Apical 25NPI", manufactured by Kaneka Corporation) was used.

Next, a paste containing metal particles consisting only of copper nanoparticles with an average particle size of 70 nm, a solvent consisting of hexylene glycol, and a dispersant consisting of polyethylene glycol was prepared, and the paste was applied onto the main surface of the substrate using a spin coater and dried at 50°C for 10 minutes.

Next, the paste was photo-sintered using a photo-sintering device (product name "PulsForge 1300", manufactured by Novacentrix) that used a xenon flash lamp as a light source, to obtain a first metal layer made of copper. The average thickness of the first metal layer obtained after photo-sintering was 1 μm.

Next, a vacuum deposition apparatus (product name "JEOL JFC-1200", manufactured by JEOL Ltd.) was used to sputter copper so as to cover the surface of the first metal layer, forming a second metal layer and obtaining a structure. The average thickness of the second metal layer was 0.1 μm.

Next, the structure obtained as described above was pretreated with 10% by mass sulfuric acid and distilled water in sequence, and then copper plating was performed on the second metal layer of the structure. Copper plating was performed by immersing the structure in a plating solution and electroplating. At this time, the composition of the plating solution was 100 g/L of copper sulfate pentahydrate, 180 g/L of sulfuric acid, 0.12 mL/L of hydrochloric acid, and distilled water (remainder). The liquid temperature of the plating solution was 25°C, and the current density was 4.0 A/ ^dm2 . In this way, a third metal layer was formed on the second metal layer, and a metal-clad laminate was produced.

(Comparative Example 1)
A metal-clad laminate was produced in the same manner as in Example 1, except that the second metal layer was not formed on the first metal layer.

[Evaluation of Adhesion of Metal Layer to Substrate]
For the metal-clad laminates obtained in Example 1 and Comparative Example 1, a test of the adhesion of the metal layer to the substrate was performed by the cross-cut method (JIS-5600-5-6). Specifically, a checkerboard pattern was cut into the metal layer to form 100 squares of 1 mm x 1 mm, and an adhesive tape was applied to the metal layer and then peeled off to observe the surface of the metal layer. The number of squares that peeled off from the adhesive tape was then counted. The results are shown in Table 1.

The results shown in Table 1 show that for the metal-clad laminate obtained in Example 1, the number of squares that peeled off in the adhesion test was 0, whereas for the metal-clad laminate obtained in Comparative Example 1, the number of squares that peeled off in the adhesion test was 100 (all).

From the above, it was confirmed that the method for manufacturing a metal-clad laminate of the present invention can produce a metal-clad laminate in which the decrease in adhesion of the metal layer to the substrate is suppressed.

DESCRIPTION OF SYMBOLS 10...Base material 20...Metal layer 21...1st metal layer 22...2nd metal layer 23...3rd metal layer 100...Metal-clad laminate V...Void

Claims (3)

A method for producing a metal-clad laminate, comprising a metal layer forming step of forming a metal layer on a substrate (excluding substrates containing an elastomer),
The metal layer forming step includes:
a first metal layer forming step of forming a porous first metal layer having voids (excluding a first metal layer containing nitrogen atoms) on the substrate;
a second metal layer forming step of forming a non-porous second metal layer on the first metal layer by sputtering ;
and forming a third metal layer on the second metal layer by plating.
The method for producing a metal-clad laminate , wherein the substrate consists of a single layer . The method for manufacturing a metal-clad laminate according to claim 1, wherein in the second metal layer forming step, the second metal layer is formed so that the ten-point average surface roughness of the second metal layer is smaller than the ten-point average surface roughness of the first metal layer. The method for manufacturing a metal-clad laminate according to claim 1 or 2, wherein in the second metal layer forming step, the second metal layer is made of the same metal as the first metal layer.

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