Metal-clad laminate

Abstract

To provide a metal-clad laminate capable of suppressing increase of a transmission loss of a high frequency signal.SOLUTION: A metal-clad laminate 100 includes a substrate 10, and a metal layer 20. The metal layer 20 has a porous first metal layer 21 provided on the substrate 10, and having multiple voids, 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.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a metal-clad laminate.

Background Art

[0002] In the manufacture of flexible printed wiring boards and the like, a metal-clad laminate in which a metal layer made of a metal such as copper is laminated on a base material is used.

[0003] As such a metal-clad laminate, for example, Patent Document 1 below discloses a substrate with a conductive film including a base material and a conductive film provided on the base material. The conductive film has a film formed by baking copper fine particles and a plating film applied to the film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in recent years, with the improvement in performance of electronic devices, a wiring board capable of passing high-frequency signals has been demanded.

[0006] However, it is known that due to the so-called skin effect, current only flows on the surface of the conductor as the frequency increases. In the conductive film described in Patent Document 1 above, there is a problem that transmission loss increases when a signal in a high-frequency band, particularly an ultra-high-frequency band of 60 GHz, is passed.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a metal-clad laminate capable of suppressing an increase in transmission loss of high-frequency signals.

Means for Solving the Problems

[0008] The inventor of the present invention studied the cause of the above problems in the conductive film described in Patent Document 1. As a result, the inventor of the present invention considered the cause of the above problems as follows. That is, the film formed by firing copper fine particles has a porous structure with voids, and high-frequency signals flow along the voids of this porous structure due to the skin effect. For this reason, the inventor considered that the signal would not be transmitted over the shortest distance, which might cause an increase in transmission loss. Therefore, as a result of further intensive studies, the inventor found that the above problems can be solved by the following invention.

[0009] That is, the present invention includes a base material and a metal layer provided on the base material, the metal layer being provided on the base material and having a porous first metal layer 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, which is a metal-clad laminate.

[0010] According to this metal-clad laminate, since the porosity of the second metal layer is smaller than the porosity of the first metal layer, the transmission loss of high-frequency signals is more likely to increase in the first metal layer than in the second metal layer. At this time, when the porosity of the first metal layer exceeds 12%, the proportion of voids in the first metal layer becomes large, and when high-frequency signals flow along the voids due to the skin effect, the high-frequency signals are more likely to be transmitted in a zigzag manner, and the transmission distance of the high-frequency signals becomes long. On the other hand, in the present invention, the porosity of the first metal layer is 12% or less. That is, in the first metal layer, the proportion of voids is sufficiently small. Therefore, even when high-frequency signals flow along the voids, the high-frequency signals are more likely to be transmitted straight, and the transmission distance of the high-frequency signals becomes shorter. Therefore, an increase in the transmission loss of high-frequency signals can be suppressed.

[0011] 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.

[0012] In this case, compared with the case where the porosity of the second metal layer is greater than 0 times the porosity of the first metal layer, in the second metal layer, the high-frequency signal is transmitted more straightly, and the transmission distance of the high-frequency signal becomes shorter. Therefore, an increase in the transmission loss of the high-frequency signal can be more effectively suppressed.

[0013] In the metal-clad laminate, it is preferable that the average diameter of the voids in the first metal layer is 100 nm or less.

[0014] In this case, the average diameter of the voids in the first metal layer becomes sufficiently small. Therefore, compared with the case where the average diameter of the voids in the first metal layer exceeds 100 nm, when the high-frequency signal flows along the voids, the high-frequency signal is transmitted more straightly, and the transmission distance of the high-frequency signal becomes shorter. Therefore, an increase in the transmission loss of the high-frequency signal can be more effectively suppressed.

[0015] In the present invention, the porosity refers to a value calculated by the following formula when the cross section of the first metal layer is observed with a scanning electron microscope (SEM). Porosity = 100 × 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.)

[0016] The average diameter d of the voids refers to 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.)

[0017] Specifically, the above S and S1 are values measured by image processing software "ImageJ".

Advantages of the Invention

[0018] According to the present invention, there is provided a metal-clad laminate capable of suppressing an increase in the transmission loss of a high-frequency signal.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the metal-clad laminate of the present invention will be described in detail.

[0021] First, the metal-clad laminate of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view showing an embodiment of the metal-clad laminate of the present invention, FIG. 2 is an enlarged view of the region surrounded by the two-dot chain line A in FIG. 1, and FIG. 3 is a view showing a state where the porosity in the first metal layer in FIG. 2 is made larger than 12%.

[0022] As shown in FIGS. 1 and 2, the metal-clad laminate 100 includes a base material 10 and a metal layer 20 provided on the main surface 10a of the base material 10. The metal layer 20 has a porous first metal layer 21 provided on the base material 10 and having a plurality of voids V, and a second metal layer 22 provided on the first metal layer 21. And 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.

[0023] According to this metal-clad laminate 100, since the porosity of the second metal layer 22 is smaller than that of the first metal layer 21, the transmission loss of high-frequency signals 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 becomes larger than 12%, the proportion of the voids V in the first metal layer 21 increases. When high-frequency signals flow along the voids V, the high-frequency signals are more likely to be transmitted in a zigzag manner, and the transmission distance of the high-frequency signals becomes longer (see Fig. 3). On the contrary, in the metal-clad laminate 100, the porosity of the first metal layer is 12% or less. That is, in the first metal layer 21, the proportion of the voids V is sufficiently small. Therefore, when high-frequency signals flow along the voids V, the high-frequency signals are more likely to be transmitted straight, and the transmission distance of the high-frequency signals becomes shorter (see Fig. 2). Therefore, an increase in the transmission loss of high-frequency signals can be suppressed. In Figs. 2 and 3, the two-dot chain line indicates the boundary between the first metal layer 21 and the second metal layer 22.

[0024] Next, the base material 10, the first metal layer 21, and the second metal layer 22 will be described in detail.

[0025] <Base material> The material constituting the base material 10 is not particularly limited. Examples of the material constituting the base material 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 ethylene tetrafluoride-perfluoroalkoxyethylene copolymer (PFA).

[0026] 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 part 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 fluorine-based resins.

[0027] When particularly emphasizing the reflow soldering process, as the material constituting the base material 10, a resin with a continuous use temperature of 200°C or higher is preferable. Examples of such resins include LCP, COP, and fluorine-based resins.

[0028] Also, when emphasizing the suppression of warping due to temperature changes, as the material constituting the base material 10, a resin having a coefficient of linear expansion close to that of the first metal layer 21 is preferable. For example, when the first metal layer 21 is made of copper, an LCP or polyimide resin having a coefficient of linear expansion close to that of copper (16 ppm / K) is preferably used.

[0029] The average thickness of the base material 10 cannot be generally stated as it depends on the application, but it is usually 25 to 100 μm. The average thickness of the base material 10 can be measured by the method described in, for example, JIS K7130:1999 "Plastics - Films and Sheets - Method for Measuring Thickness".

[0030] <First Metal Layer> The porosity of the first metal layer 21 may be 12% or less, but preferably 10% or less.

[0031] 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 more. In this case, a decrease in the adhesion of the first metal layer 21 to the base material 10 can be more sufficiently suppressed.

[0032] 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, when a high-frequency signal flows along the voids V in the first metal layer 21, compared to the case where the average diameter d of the voids V in the first metal layer 21 exceeds 100 nm, the high-frequency signal is transmitted more straightly and the transmission distance of the high-frequency signal becomes shorter. Thus, an increase in the transmission loss of the high-frequency signal can be more suppressed.

[0033] The average diameter d of the voids V in the first metal layer 21 is more preferably 50 nm or less from the viewpoint of further suppressing an increase in transmission loss of high-frequency signals.

[0034] However, the average diameter d of the voids V in the first metal layer 21 is preferably 10 nm or more. In this case, a decrease in the adhesion of the first metal layer 21 to the base material 10 can be more sufficiently suppressed.

[0035] The average thickness of the first metal layer 21 is preferably at least twice the average particle diameter of the metal particles constituting the first metal layer 21. In this case, in terms of calculation, there are two or more metal particles on the base material 10, and the second metal layer 22 is not directly formed on the metal particles directly adhering to the base material 10. For this reason, it becomes difficult for the stress due to the second metal layer 22 to be applied to the metal particles directly adhering to the base material 10, and a decrease in the adhesion of the first metal layer 21 to the base material 10 can be sufficiently suppressed.

[0036] 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. As a method for obtaining a cross section of the first metal layer 21, there is a method of embedding the metal-clad laminate 100 in resin and then polishing it.

[0037] Examples of the metal constituting the metal particles include gold, silver, and copper. Among them, copper is preferable because it is inexpensive.

[0038] <Second Metal Layer> The porosity of the second metal layer 22 may be smaller than the porosity of the first metal layer 21, but the porosity of the second metal layer 22 is preferably 0.1 times or less the porosity of the first metal layer 21.

[0039] It is more preferable that the porosity of the second metal layer 22 is 0 times that of the first metal layer 21, that is, the second metal layer 22 is non-porous. In this case, compared with the case where the second metal layer 22 is not non-porous, in the second metal layer 22, high-frequency signals are more likely to be transmitted straight, and the transmission distance of the high-frequency signals becomes shorter. Therefore, an increase in the transmission loss of the high-frequency signals can be more suppressed.

[0040] Examples of the metal constituting the second metal layer 22 include gold, silver, and copper. Among them, copper is preferable because it is inexpensive.

[0041] The second metal layer 22 is preferably made of the same metal as the first metal layer 21.

[0042] In this case, compared with the case where the first metal layer 21 and the second metal layer 22 are made of different metals, it becomes difficult for the metal to dissolve out from the second metal layer 22 due to moisture or the like that penetrates into the porous first metal layer 21. That is, 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 the second metal layer 22 being cracked or peeled off from the first metal layer 21 is sufficiently suppressed.

[0043] The average thickness of the second metal layer 22 is not particularly limited, and for example, it may be 1 to 20 μm.

[0044] The average thickness of the second metal layer 22 can be measured in the same manner as the first metal layer 21.

[0045] Next, a method for manufacturing the metal-clad laminate 100 will be described with reference to FIGS. 1 and 4. FIG. 4 is a cross-sectional view showing a first metal layer precursor formation step in the method for manufacturing the metal-clad laminate of the present invention.

[0046] As shown in FIGS. 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 a base material 10, and an electroplating step on 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 growing by electroplating enters the gaps between the metal particles in the first metal layer precursor 21A, 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.

[0047] According to this manufacturing method of the metal-clad laminate 100, a metal-clad laminate 100 capable of suppressing an increase in transmission loss of high-frequency signals is manufactured.

[0048] Hereinafter, the above-described first metal layer precursor forming step and metal layer forming step will be described in detail.

[0049] <First Metal Layer Precursor Forming Step> The first metal layer precursor forming step is a step of forming a porous first metal layer precursor 21A on the base material 10 (see FIG. 4).

[0050] (First Metal Layer Precursor) The first metal layer precursor 21A can be obtained by coating a first metal layer precursor forming paste containing, for example, metal particles and a solvent on the main surface 10a of the base material 10 and subjecting it to light baking.

[0051] Here, the metal particles preferably include nanoparticles having an average particle diameter of 1 to 100 nm. The metal particles may be composed only of nanoparticles, or may be composed of a mixture of nanoparticles and coarse particles. As the coarse particles, for example, disk particles having a diameter of 1 μm and a thickness of 200 nm can be used. Note that only the nanoparticles are dissolved by light baking, and the coarse particles are not dissolved.

[0052] From the viewpoint of making the volume resistivity of the first metal layer 21 smaller, it is preferable that the metal particles are composed only of nanoparticles. This is presumably because when the metal particles are composed only of nanoparticles, all the metal particles are melted by photo-firing and welded to each other, so that the contact area between the metal particles becomes large.

[0053] However, the metal particles may be composed of a mixture of nanoparticles and coarse particles. In this case, since the coarse particles are not melted by photo-firing, the shrinkage of the metal film during photo-firing can be reduced, and it is possible to suppress the substrate 10 from warping or the first metal layer 21 from peeling off from the substrate 10.

[0054] As the solvent, for example, 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, propylene carbonate, 1,3-dimethyl-2-imidazolidinone, etc. can be used.

[0055] The paste for forming the first metal layer precursor may further contain a dispersant. Examples of the dispersant include polyethylene glycol and polyvinylpyrrolidone.

[0056] The coating of the paste for forming the first metal layer precursor can be performed using, for example, a microgravure coater or a spin coater.

[0057] It is preferable to perform a drying treatment on the paste for forming the first metal layer precursor before photo-firing. Further, when the paste for forming the first metal layer precursor contains a large amount of organic components such as a binder, it is preferable to further perform a treatment for removing the organic components. In this case, it is possible to suppress the voids from becoming large due to the gas generated by the decomposition of the organic components during photo-firing.

[0058] Examples of the drying treatment method include heat treatment at 50 to 100°C. Examples of the treatment method for removing organic components include, for example, heat-treating the paste for forming the first metal layer precursor at about 150°C, then immersing it in dilute sulfuric acid to remove the oxide film, washing it with water, and then immersing it in isopropyl alcohol.

[0059] As an apparatus for performing photo-firing, for example, "Pulsforge 1300" manufactured by Novacentrix can be used. As a light source used in this apparatus, for example, a xenon lamp or the like can be used.

[0060] The irradiation energy of light may be, for example, 0.1 to 100 J / cm 2 That's all right. The irradiation time of light may be 0.1 to 100 ms. The number of irradiations may be once or multiple multi-stage irradiations.

[0061] The average thickness of the first metal layer precursor 21A is preferably 5 μm or less. In this case, compared with the case where the average thickness of the first metal layer precursor 21A exceeds 5 μm, when the paste for forming the first metal layer precursor is photo-fired, the formation of voids due to the gas generated in the paste for forming the first metal layer precursor is sufficiently suppressed. The average thickness of the first metal layer precursor 21A is more preferably 1 μm or less.

[0062] <Metal layer forming step> The metal layer forming step is a step of performing electroplating on 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.

[0063] The plating solution used for plating is not particularly limited, but when 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 with a smooth surface is uniformly attached to the surface of the first metal layer 21. A brightener may be added to the plating solution.

[0064] Plating is performed by electroplating. The reasons are as follows. That is, during plating, hydrogen gas is generated when metal is deposited. At this time, if electroless plating is performed, in the porous first metal layer precursor 21A, hydrogen gas cannot escape and plating is inhibited, 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 that grows by plating. And when plating proceeds first on the surface of the first metal layer precursor 21A, the first metal layer precursor 21A becomes in a state like being covered, and metal ions are no longer supplied into the first metal layer precursor 21A. For this reason, the metal by plating no longer grows in the porous first metal layer precursor 21A. On the other hand, in electroplating, plating can be made to proceed in a short time. For this reason, the gaps between the metal particles in the first metal layer precursor 21A can be sufficiently filled with the metal that grows by plating. That is, the porosity of the first metal layer 21 can be easily adjusted.

[0065] When the plating is electroplating, the current density is not particularly limited, but it is preferably 2 as follows. The reasons are as follows. First, the current density is usually preferably made 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. And when plating proceeds first on the surface of the first metal layer precursor 21A, the first metal layer precursor 21A becomes in a state like being covered, and metal ions are no longer supplied into the first metal layer precursor 21A. For this reason, the metal by plating no longer grows in the porous first metal layer precursor 21A. On the other hand, when the current density is 2 as follows, the gaps between the metal particles in the first metal layer precursor 21A can be more sufficiently filled with the metal that grows by plating.

[0066] After the gaps between the metal particles in the first metal layer precursor 21A are more sufficiently filled with the metal that grows by plating, the current density is 2It may exceed this. For example, when the thickness of the plating film on the first metal layer precursor 21A is up to 1 μm, plating is performed at 2 A / dm 2 and thereafter, plating may be performed at 4 A / dm 2 In this case, the plating time is shortened and productivity is improved.

[0067] The present invention is not limited to the above-described embodiments. For example, in the above-described embodiments, the metal layer 20 is formed only on the main surface 10a of the base material 10, but the metal layer 20 may be formed on the main surface opposite to the main surface 10a of the base material 10.

[0068] Further, in the above-described embodiment, the first metal layer precursor 21A is formed by light baking of 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 baking of the paste for forming the first metal layer precursor. For example, the first metal layer precursor 21A can also be formed by thermal baking.

Example

[0069] Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

[0070] (Example 1) First, a base material with an average thickness of 25 μm was prepared. As the base material, an LCP film (trade name “Vectra”, manufactured by Kuraray Co., Ltd.) was used.

[0071] Next, a paste containing metal particles composed only of copper nanoparticles with an average particle size of 70 nm, a solvent composed of hexylene glycol, and a dispersant composed of polyethylene glycol was prepared, the paste was applied onto the main surface of the base material with a spin coater, and dried at 50° C. for 10 minutes.

[0072] Next, the paste was subjected to light firing using an optical firing apparatus (product name: "PulsForge 1300", manufactured by Novacentrix) with a xenon flash lamp as the light source, and a first metal layer precursor made of copper was obtained. Thus, a structure was obtained. The average thickness of the first metal layer precursor obtained after light firing was 1 μm.

[0073] Next, the structure obtained as described above was sequentially pretreated with 10 mass% sulfuric acid and distilled water, and then copper plating was performed on the first metal layer precursor of the structure. The copper plating was carried out by immersing the structure in a plating solution and performing 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 (the remainder). Also, the liquid temperature of the plating solution was 25°C, and the current density was 2.0 A / dm 2 Thus, 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, after embedding the metal-clad laminate in an epoxy resin (product name: "CY-230", manufactured by Nagase ChemteX), it was cut, and the cross-section was polished with a waterproof abrasive paper (product name: "Carbomac Paper", manufactured by Refine Tech), a diamond paste abrasive (product name: "DP-Paste P", manufactured by Struers), and an ion milling apparatus (product name: "IM4000PLUS", manufactured by Hitachi High-Technologies). The cross-section of the metal-clad laminate was observed by SEM, and when the porosity of the first metal layer and the second metal layer was measured using image processing software "ImageJ", the porosity R1 of the first metal layer was 11.1%, and the porosity R2 of the second metal layer was 0%. Also, the average thickness of the second metal layer was 12 μm.

[0074] (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 / dm 2 to make the porosity R1 of the first metal layer 10%.

[0075] (Example 3) The current density when forming the second metal layer by electroplating was 1.0 A / dm 2A 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 9.1% by making a change thereto.

[0076] (Example 4) The structure obtained in the same manner as in Example 1 was pretreated successively with 10 mass% sulfuric acid and distilled water, and then copper plating was performed on the first metal layer precursor of the structure to form the first metal layer. The copper plating was carried out by immersing the above structure in a plating solution having the same composition as the plating solution of Example 1 and performing electroplating. At this time, the liquid temperature of the plating solution was 25°C, and the current density was 2.0 A / dm 2 ². The copper plating was carried out until the porous portion in the first metal layer precursor was filled with the plating.

[0077] 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 / dm 2 ² to form the second metal layer. At this time, the electroplating was carried out until the second metal layer had the same thickness as the second metal layer of Example 1.

[0078] In this way, a metal layer composed of a first metal layer and a second metal layer was formed on the base material to produce a metal-clad laminate.

[0079] Regarding the obtained metal-clad laminate, when the porosities of the first metal layer and the second metal layer were 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%.

[0080] (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 an additive for via filling (product name: "Sulcup EVF", manufactured by Kamamura Kogyo Co., Ltd.) to the plating solution.

[0081] (Comparative Example 1) The current density during the formation of the second metal layer by electroplating was 2.5 A / dm 2A 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 12.5% by changing to

[0082] (Comparative Example 2) The current density during the formation of the second metal layer by electroplating was changed to 3.0 A / dm 2 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 14.3% by changing to

[0083] (Comparative Example 3) The current density during the formation of the second metal layer by electroplating was changed to 4.0 A / dm 2 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 16.7% by changing to

[0084] (Comparative Example 4) 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 16.7% by performing electroless plating instead of electroplating for the second metal layer.

[0085] (Comparative Example 5) The structure obtained in the same manner as in Example 1 was pretreated successively with 10% by mass sulfuric acid and distilled water, and then copper plating was performed on the first metal layer precursor of the structure to form the first metal layer. The copper plating was carried out by immersing the above structure in a plating solution having the same composition as the plating solution of Example 1 and performing electroplating. At this time, the liquid temperature of the plating solution was 25°C, and the current density was 2.0 A / dm 2 And the copper plating was carried out until the porous portion in the first metal layer precursor was filled with the plating.

[0086] 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 / dm 2 to form the second metal layer. At this time, the electroplating was carried out until the second metal layer had the same thickness as the second metal layer of Example 1.

[0087] Thus, a metal layer composed of a first metal layer and a second metal layer was formed on the base material to produce a metal-clad laminate.

[0088] Regarding the obtained metal-clad laminate, the porosity of the first metal layer and the second metal layer was measured in the same manner as in Example 1. As a result, the porosity R1 of the first metal layer was 11.0%, and the porosity R2 of the second metal layer was 11.0%.

[0089] [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 at 10 GHz, 30 GHz, and 60 GHz were measured. The results are shown in Table 1.

Table 1

[0090] From the results shown in Table 1, it was found that the increase in transmission loss at a high frequency of 60 GHz was significantly suppressed in the metal-clad laminates of Examples 1 to 5 compared to those of Comparative Examples 1 to 5.

[0091] From the above, it was confirmed that the metal-clad laminate of the present invention can suppress an increase in transmission loss of a high-frequency signal.

Explanation of Reference Signs

[0092] 10... Base material 20... Metal layer 21... First metal layer 22... Second metal layer 100... Metal-clad laminate V... Void

Claims

1. 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 that does not have an 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.

2. 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.

3. 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.

Images