JP7679182B2 - metal clad laminate - Google Patents

Description

The present invention relates to 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 an example of such a metal-clad laminate, the following Patent Document 1 discloses a substrate with a conductive film, which includes a base material and a conductive film provided on the base material, and the conductive film has a coating of fired copper particles and a plating film applied to the coating.

JP 2013-135089 A

In recent years, with the increasing performance of electronic devices, there is a demand for wiring boards that can transmit high-frequency signals.

However, it is known that as the frequency of a signal increases, the current flows only on the surface of the conductor due to the so-called skin effect, and the conductive film described in Patent Document 1 above has the problem that transmission loss increases when passing high-frequency signals, particularly signals in the ultra-high frequency band of 60 GHz.

The present invention was made in consideration of the above circumstances, and aims to provide a metal-clad laminate that can suppress an increase in transmission loss of high-frequency signals.

The present inventors have investigated the causes of the above-mentioned problems in the conductive film described in Patent Document 1. As a result, the present inventors have concluded that the causes of the above-mentioned problems are as follows. That is, the film formed by sintering copper fine particles has a porous structure with voids, and high-frequency signals flow along the voids in this porous structure due to the skin effect. As a result, the signals are no longer transmitted over the shortest distance, which the present inventors believe causes an increase in transmission loss. As a result of further intensive investigations, the present inventors have discovered that the above-mentioned problems can be solved by the following invention.

That is, the present invention is a metal-clad laminate comprising a substrate and a metal layer provided on the substrate, the metal layer having a porous first metal layer provided on the substrate and having a plurality of voids, and a second metal layer provided on the first metal layer, the first metal layer having a porosity of 12% or less, and the porosity of the second metal layer being smaller than the porosity of the first metal layer.

In this metal-clad laminate, the porosity of the second metal layer is smaller than that of the first metal layer, so that the transmission loss of the high-frequency signal is more likely to increase in the first metal layer than in the second metal layer. In this case, if the porosity of the first metal layer exceeds 12%, the proportion of voids in the first metal layer increases, and when the high-frequency signal flows along the voids due to the skin effect, the high-frequency signal is more likely to be transmitted in a zigzag manner, and the transmission distance of the high-frequency signal is longer. In contrast, in the present invention, the porosity of the first metal layer is 12% or less. That is, the proportion of voids in the first metal layer is sufficiently small. Therefore, even when the high-frequency signal flows along the voids, the high-frequency signal is more likely to be transmitted in a straight line, and the transmission distance of the high-frequency signal is shorter. Therefore, the increase in the transmission loss of the high-frequency signal can be suppressed.

In the above metal-clad laminate, it is preferable that the porosity of the second metal layer is 0 times the porosity of the first metal layer.

In this case, the high-frequency signal is transmitted more directly through the second metal layer, and the transmission distance of the high-frequency signal is shorter, compared to when the porosity of the second metal layer is greater than 0 times the porosity of the first metal layer. Therefore, the increase in transmission loss of the high-frequency signal can be further suppressed.

In the above metal-clad laminate, it is preferable that the average diameter of the voids in the first metal layer is 100 nm or less.

In this case, the average diameter of the voids in the first metal layer becomes sufficiently small. Therefore, when the high-frequency signal flows along the voids, it is transmitted in a straighter direction and the transmission distance of the high-frequency signal is shorter than when the average diameter of the voids in the first metal layer exceeds 100 nm. Therefore, the increase in the transmission loss of the high-frequency signal can be further suppressed.

In the present invention, the porosity refers to a value calculated by the following formula when a cross section of the first metal layer is observed with a scanning electron microscope (SEM).
Porosity = 100 x S1/S
(In the above formula, S represents the area of the first metal layer, and S1 represents the area of the voids in the first metal layer.)

The average void diameter d is a value calculated as follows.
d=2×(S1/(n×π)) ^1/2
(In the above formula, S1 represents the area of the voids in the first metal layer, and n represents the number of voids.)

The above S and S1 are values measured using the image processing software "Image J."

The present invention provides a metal-clad laminate that can suppress an increase in transmission loss of high-frequency signals.

1 is a cross-sectional view showing one embodiment of 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. FIG. 3 is a diagram showing a state in which the porosity in the first metal layer in FIG. 2 is set to be greater than 12%. FIG. 2 is a cross-sectional view showing a first metal layer precursor forming step in the method for producing the metal-clad laminate of the present invention.

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

First, the metal-clad laminate of the present invention will be described with reference to Figures 1 to 3. Figure 1 is a cross-sectional view showing one embodiment of the metal-clad laminate of the present invention, Figure 2 is an enlarged view of the area surrounded by the two-dot chain line A in Figure 1, and Figure 3 is a view showing the state in Figure 2 where the porosity in the first metal layer is greater than 12%.

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 a plurality of voids V, and a second metal layer 22 provided on the first metal layer 21. The first metal layer 21 has a porosity of 12% or less, and the porosity of the second metal layer 22 is smaller than the porosity of the first metal layer 21.

According to this metal-clad laminate 100, the porosity of the second metal layer 22 is smaller than that of the first metal layer 21, so that the transmission loss of the high-frequency signal is more likely to increase in the first metal layer 21 than in the second metal layer 22. At this time, when the porosity of the first metal layer 21 is greater than 12%, the proportion of the voids V in the first metal layer 21 becomes larger, and when the high-frequency signal flows along the voids V, the high-frequency signal is more likely to be transmitted in a zigzag manner, and the transmission distance of the high-frequency signal becomes longer (see FIG. 3). In contrast, in the metal-clad laminate 100, the porosity of the first metal layer is 12% or less. That is, the proportion of the voids V in the first metal layer 21 is sufficiently small. Therefore, when the high-frequency signal flows along the voids V, the high-frequency signal is more likely to be transmitted in a straight line, and the transmission distance of the high-frequency signal becomes shorter (see FIG. 2). Therefore, the increase in the transmission loss of the high-frequency signal can be suppressed. In addition, in Figures 2 and 3, the two-dot chain line indicates the boundary between the first metal layer 21 and the second metal layer 22.

Next, the substrate 10, the first metal layer 21, and the second metal layer 22 will be described in detail.

<Base material>
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 small dielectric constant is preferred. In this case, a portion of the electrical energy of the high frequency signal is less likely to become heat and is less likely to be lost. Examples of such resins with a small 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 21 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 porosity of the first metal layer 21 may be 12% or less, and is preferably 10% or less.

However, since the first metal layer 21 has voids V, the porosity of the first metal layer 21 is greater than 0%. The porosity of the first metal layer 21 is preferably 1% or greater. In this case, the decrease in adhesion of the first metal layer 21 to the substrate 10 can be more sufficiently suppressed.

The average diameter d of the voids V in the first metal layer 21 is not particularly limited, but is preferably 100 nm or less. In this case, the average diameter d of the voids V in the first metal layer 21 becomes sufficiently small. Therefore, compared to when the average diameter d of the voids V in the first metal layer 21 exceeds 100 nm, when the high-frequency signal flows along the voids V, the high-frequency signal is transmitted more directly and the transmission distance of the high-frequency signal is shorter. Therefore, the increase in transmission loss of the high-frequency signal can be further suppressed.

The average diameter d of the voids V in the first metal layer 21 is preferably 50 nm or less in order to further suppress an increase in transmission loss of high-frequency signals.

However, it is preferable that the average diameter d of the voids V in the first metal layer 21 is 10 nm or more. In this case, the decrease in adhesion of the first metal layer 21 to the substrate 10 can be more sufficiently suppressed.

The average thickness of the first metal layer 21 is preferably at least twice the average particle size of the metal particles that make up the first metal layer 21. In this case, mathematically there will be two or more metal particles on the substrate 10, and the second metal layer 22 will not be 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 can be sufficiently suppressed.

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.

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

<Second metal layer>
The porosity of the second metal layer 22 may be smaller than the porosity of the first metal layer 21 , but it is preferable that the porosity of the second metal layer 22 is 0.1 times or less the porosity of the first metal layer 21 .

It is more preferable that the porosity of the second metal layer 22 is 0 times the porosity of the first metal layer 21, i.e., the second metal layer 22 is non-porous. In this case, the high-frequency signal is more likely to be transmitted straighter in the second metal layer 22 than when the second metal layer 22 is not non-porous, and the transmission distance of the high-frequency signal is shorter. Therefore, the increase in transmission loss of the high-frequency signal can be further suppressed.

Examples of metals that can be used to form the second metal layer 22 include gold, silver, and copper. Of these, copper is preferred 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 21, 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 average thickness of the second metal layer 22 is not particularly limited and may be, for example, 1 to 20 μm.

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

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

1 and 4, the manufacturing method of the metal-clad laminate 100 includes a first metal layer precursor forming step of forming a porous first metal layer precursor 21A on the substrate 10, and a metal layer forming step of electroplating the first metal layer precursor 21A to form a metal layer 20 including a porous first metal layer 21 having a plurality of voids V and a second metal layer 22. In the metal layer forming step, the metal grown by plating penetrates into the gaps between the metal particles in the first metal layer precursor 21A, and the first metal layer 21 is formed to have a porosity of 12% or less, and the second metal layer 22 is formed so that the porosity of the second metal layer 22 is smaller than the porosity of the first metal layer 21.

This manufacturing method for the metal-clad laminate 100 produces a metal-clad laminate 100 that can suppress an increase in transmission loss of high-frequency signals.

The first metal layer precursor forming process and the metal layer forming process are described in detail below.

<First metal layer precursor formation step>
The first metal layer precursor forming step is a step of forming a porous first metal layer precursor 21A on the substrate 10 (see FIG. 4).

(First metal layer precursor)
The first metal layer precursor 21A can be obtained by applying a paste for forming a first metal layer precursor, which contains, for example, metal particles and a solvent, onto the main surface 10a of the substrate 10, and then baking it 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 are dissolved by light sintering, and the coarse particles are not dissolved.

From the viewpoint of reducing the volume resistivity of the first metal layer 21, it is preferable that the metal particles are composed of nanoparticles only. This is because, if the metal particles are composed of nanoparticles only, 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, the shrinkage of the metal film during light sintering can be reduced, and warping of the substrate 10 and peeling of the first metal layer 21 from the substrate 10 can be suppressed.

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 precursor may further contain a dispersant. Examples of dispersants include polyethylene glycol and polyvinylpyrrolidone.

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

It is preferable to perform a drying process on the paste for forming the first metal layer precursor before light sintering. Furthermore, if the paste for forming the first metal layer precursor 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 50 to 100°C can be mentioned. As a method of removing organic components, for example, a method of heat treating the paste for forming the first metal layer precursor 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 mentioned.

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 precursor 21A is preferably 5 μm or less. In this case, compared to when the average thickness of the first metal layer precursor 21A exceeds 5 μm, the formation of voids due to gas generated in the paste for forming the first metal layer precursor when the paste for forming the first metal layer precursor is optically fired is sufficiently suppressed. It is more preferable that the average thickness of the first metal layer precursor 21A is 1 μm or less.

<Metal layer formation process>
The metal layer forming step is a step of electroplating the first metal layer precursor 21A to form the metal layer 20 including the porous first metal layer 21 having a plurality of voids V and the second metal layer 22 .

The plating solution used for plating is not particularly limited, but if the second metal layer 22 is made of copper, it is preferably a copper sulfate solution. The copper sulfate solution mainly contains copper sulfate and sulfuric acid. In this case, the second metal layer 22, which has a smooth surface, is uniformly attached to the surface of the first metal layer 21. A brightener may be added to the plating solution.

Plating is performed by electroplating. The reason is as follows. That is, during plating, hydrogen gas is generated when metal is deposited. If electroless plating is performed at this time, hydrogen gas does not escape from the porous first metal layer precursor 21A, hindering plating, and plating proceeds on the surface of the first metal layer precursor 21A before the gaps between the metal particles are sufficiently filled with the metal grown by plating. If plating proceeds first on the surface of the first metal layer precursor 21A, the first metal layer precursor 21A becomes in a state in which it is capped, and metal ions are not supplied into the first metal layer precursor 21A. Therefore, the metal by plating does not grow any further in the porous first metal layer precursor 21A. In contrast, electroplating allows plating to proceed in a short time. Therefore, the gaps between the metal particles of the first metal layer precursor 21A can be sufficiently filled with the metal grown by plating. That is, the porosity of the first metal layer 21 can be easily adjusted.

When the plating is electroplating, the current density is not particularly limited, but is preferably 2 A/dm ² or less. The reason is as follows. First, it is usually preferable to make the current density as large as possible in order to shorten the plating time. This is because the growth rate of the plating film is proportional to the current density. However, if the current density is too large, plating will proceed first on the surface of the first metal layer precursor 21A, which is easily plated. Then, if plating proceeds first on the surface of the first metal layer precursor 21A, the first metal layer precursor 21A will be in a state where it is capped, and metal ions will not be supplied into the first metal layer precursor 21A. For this reason, the metal by plating will not grow any more in the porous first metal layer precursor 21A. On the other hand, if the current density is 2 A/dm ² or less, the gaps between the metal particles in the first metal layer precursor 21A can be more sufficiently filled with the metal grown by plating.

After the gaps between the metal particles in the first metal layer precursor 21A are more sufficiently filled with the metal grown by plating, the current density may exceed 2 A/dm ^2. For example, plating can be performed at 2 A/dm ² until the thickness of the plating film on the first metal layer precursor 21A reaches 1 μm, and thereafter at 4 A/dm ^2. In this case, the plating time is shortened, and productivity is improved.

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 main surface opposite to the main surface 10a of the substrate 10.

In addition, in the above embodiment, the first metal layer precursor 21A is formed by light-firing the paste for forming the first metal layer precursor, but the first metal layer precursor 21A does not necessarily have to be formed by light-firing the paste for forming the first metal layer precursor. For example, the first metal layer precursor 21A 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, an LCP film (product name "Vextar", manufactured by Kuraray Co., Ltd.) 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.

The paste was then photo-fired using a photo-firing device (product name "PulsForge 1300", manufactured by Novacentrix) with a xenon flash lamp as the light source to obtain a first metal layer precursor made of copper. In this way, a structure was obtained. The average thickness of the first metal layer precursor obtained after photo-firing was 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 first metal layer precursor 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 copper sulfate pentahydrate, 180 g/L sulfuric acid, 0.12 mL/L hydrochloric acid, and distilled water (remainder). The liquid temperature of the plating solution was 25°C, and the current density was 2.0 A/ ^dm2 . In this way, a metal layer composed of a first metal layer and a second metal layer was formed on the substrate, and a metal-clad laminate was produced. At this time, the metal-clad laminate was embedded in an epoxy resin (product name "CY-230", manufactured by Nagase Chemtex Corporation) and then cut, and the cross section was polished with waterproof abrasive paper (product name "Carbomac Paper", manufactured by Refine Tech Co., Ltd.), diamond paste abrasive (product name "DP-Paste P", manufactured by Struers Co., Ltd.), and an ion milling device (product name "IM4000PLUS", manufactured by Hitachi High-Technologies Corporation). The cross section of the metal-clad laminate was observed with an SEM, and the porosity of the first metal layer and the second metal layer was measured using the image processing software "Image J". The porosity R1 of the first metal layer was 11.1%, and the porosity R2 of the second metal layer was 0%. The average thickness of the second metal layer was 12 μm.

Example 2
A metal-clad laminate was produced in the same manner as in Example 1, except that the current density when forming the second metal layer by electroplating was changed to 1.5 A/ ^dm2 , thereby making the porosity R1 of the first metal layer 10%.

Example 3
A metal-clad laminate was produced in the same manner as in Example 1, except that the current density when forming the second metal layer by electroplating was changed to 1.0 A/ ^dm2 , thereby making the porosity R1 of the first metal layer 9.1%.

Example 4
The structure obtained in the same manner as in Example 1 was pretreated with 10% by mass sulfuric acid and distilled water in sequence, and then the first metal layer precursor of the structure was copper plated to form a first metal layer. The copper plating was performed by immersing the structure in a plating solution having the same composition as the plating solution in Example 1 and electroplating. At this time, the temperature of the plating solution was 25°C, and the current density was 2.0 A/ ^dm2 . The copper plating was performed until the porous portion in the first metal layer precursor was filled with plating.

Next, 0.5 ml/L of hydrobromic acid and 0.3 ml/L of glycerin were added to the plating solution, and electroplating was performed at a current density of 2.0 A/ ^dm2 to form a second metal layer. At this time, electroplating was performed until the second metal layer had the same thickness as the second metal layer in Example 1.

In this way, a metal layer consisting of a first metal layer and a second metal layer was formed on the substrate, and a metal-clad laminate was produced.

When the porosity of the first metal layer and the second metal layer of the obtained metal-clad laminate was measured in the same manner as in Example 1, the porosity R1 of the first metal layer was 11.0%, and the porosity R2 of the second metal layer was 1.0%.

Example 5
A metal-clad laminate was produced in the same manner as in Example 1, except that the porosity R1 of the first metal layer was set to 2.0% by adding a via-fill additive (product name "Thru-Cup EVF", manufactured by Uemura Kogyo Co., Ltd.) to the plating solution.

(Comparative Example 1)
A metal-clad laminate was produced in the same manner as in Example 1, except that the current density when forming the second metal layer by electroplating was changed to 2.5 A/ ^dm2 , thereby making the porosity R1 of the first metal layer 12.5%.

(Comparative Example 2)
A metal-clad laminate was produced in the same manner as in Example 1, except that the current density when forming the second metal layer by electroplating was changed to 3.0 A/ ^dm2 , thereby making the porosity R1 of the first metal layer 14.3%.

(Comparative Example 3)
A metal-clad laminate was produced in the same manner as in Example 1, except that the current density when forming the second metal layer by electroplating was changed to 4.0 A/ ^dm2 , thereby making the porosity R1 of the first metal layer 16.7%.

(Comparative Example 4)
A metal-clad laminate was produced in the same manner as in Example 1, except that the second metal layer was formed by electroless plating instead of electroplating, thereby making the porosity R1 of the first metal layer 16.7%.

(Comparative Example 5)
The structure obtained in the same manner as in Example 1 was pretreated with 10% by mass sulfuric acid and distilled water in sequence, and then the first metal layer precursor of the structure was copper plated to form a first metal layer. The copper plating was performed by immersing the structure in a plating solution having the same composition as the plating solution in Example 1 and electroplating. At this time, the temperature of the plating solution was 25°C, and the current density was 2.0 A/ ^dm2 . The copper plating was performed until the porous portion in the first metal layer precursor was filled with plating.

Next, 2.0 ml/L of hydrobromic acid and 1.0 ml/L of glycerin were added to the plating solution, and electroplating was performed at a current density of 2.0 A/ ^dm2 to form a second metal layer. At this time, electroplating was performed until the second metal layer had the same thickness as the second metal layer in Example 1.

In this way, a metal layer consisting of a first metal layer and a second metal layer was formed on the substrate, and a metal-clad laminate was produced.

When the porosity of the first metal layer and the second metal layer of the obtained metal-clad laminate was measured in the same manner as in Example 1, the porosity R1 of the first metal layer was 11.0%, and the porosity R2 of the second metal layer was 11.0%.

[Evaluation of Transmission Loss]
The metal-clad laminates obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were evaluated for transmission loss at high frequencies. Specifically, the transmission loss values were measured at 10 GHz, 30 GHz, and 60 GHz. The results are shown in Table 1.

The results shown in Table 1 show that the metal-clad laminates of Examples 1 to 5 significantly suppress the increase in transmission loss at a high frequency of 60 GHz compared to the metal-clad laminates of Comparative Examples 1 to 5.

From the above, it has been confirmed that the metal-clad laminate of the present invention can suppress an increase in transmission loss of high-frequency signals.

DESCRIPTION OF SYMBOLS 10... Base material 20... Metal layer 21... First metal layer 22... Second metal layer 100... Metal-clad laminate V... Void

Claims (3)

A substrate;
A metal layer provided on the substrate,
The metal layer is
A porous first metal layer provided on the substrate and having a plurality of voids (excluding a first metal layer having a substrate-derived component-containing region that contains a component derived from the substrate in at least a portion of the voids);
a second metal layer provided on the first metal layer;
The metal layer is
a first metal layer precursor formed by light- sintering a paste containing metal particles , and a first metal layer formed by a metal filling gaps between the metal particles;
the second metal layer being a plating film on the first metal layer ;
the metal layer is a metal layer having no electroless plating layer,
the first metal layer and the second metal layer are made of copper;
the first metal layer (excluding the first metal layer having a porosity of 2% or less) has a porosity of 12% or less;
A metal-clad laminate, wherein the second metal layer has a porosity smaller than the porosity of the first metal layer. The metal-clad laminate according to claim 1, wherein the porosity of the second metal layer is 0 times the porosity of the first metal layer. The metal-clad laminate according to claim 1 or 2, wherein the average diameter of the voids in the first metal layer is 100 nm or less.

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