Manufacturing method of metal-clad laminate

Abstract

To provide a manufacturing method for a metal-clad laminate capable of producing a metal-clad laminate in which adhesion of a metal layer to a base material is suppressed.SOLUTION: A manufacturing method for a metal-clad laminate includes a metal layer forming step for forming a metal layer on a base material to manufacture the metal-clad laminate. The metal layer forming step includes a first metal layer forming step, in which a porous first metal layer with voids is formed on the base material, a second metal layer forming step, in which a non-porous second metal layer is formed on the first metal layer, and a third metal layer forming step, in which a third metal layer is formed on the second metal layer by plating.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a metal-clad laminate. [Background technology]

[0002] 2. Description of the Related Art When manufacturing 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 substrate is used.

[0003] As a method for manufacturing such a metal-clad laminate, for example, Patent Document 1 listed below discloses a conductive film formation method having a step of forming a coating of fired copper fine particles on a substrate, and a step of plating the coating to form a conductive film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-135089 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conductive film forming method described in Patent Document 1 above has room for improvement in terms of the adhesion of the conductive film to the substrate.

[0006] 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 a decrease in adhesion of the metal layer to the substrate is suppressed. [Means for solving the problem]

[0007] 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 having a plurality of voids, and it is considered that the metal particles constituting this film are embedded in a state of being 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, the metal eventually enters the gap between the substrate and the film, and applies a stress between the substrate and the film that is enough 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.

[0008] That is, the present invention is a method for manufacturing a metal-clad laminate, which includes a metal layer formation step of forming a metal layer on a substrate to produce a metal-clad laminate, the metal layer formation step including a first metal layer formation step of forming a porous first metal layer having voids on the substrate, a second metal layer formation step of forming a non-porous second metal layer on the first metal layer, and a third metal layer formation step of forming a third metal layer on the second metal layer by plating.

[0009] According to this method for producing 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. Thus, 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 between the substrate and the first metal layer to separate them is prevented. Therefore, according to the method for producing 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 produced.

[0010] In the above-mentioned method for manufacturing a metal-clad laminate, in the second metal layer forming process, 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.

[0011] 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, which makes it possible to further reduce the electrical resistance of the second metal layer.

[0012] In the above-mentioned method for producing a metal-clad laminate, in the second metal layer forming step, the second metal layer is preferably made of the same metal as the first metal layer.

[0013] In this case, compared to when the first metal layer and the second metal layer are made of different metals, the metal is less likely to be dissolved from the second metal layer by moisture or the like that penetrates 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. Effect of the Invention

[0014] According to the present invention, there is provided a method for producing a metal-clad laminate, which can produce a metal-clad laminate in which a decrease in adhesion of the metal layer to the substrate is suppressed. [Brief description of the drawings]

[0015] [Figure 1] 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. [Diagram 2] 2 is an enlarged view of the area surrounded by the two-dot chain line A in FIG. [Diagram 3] 2 is a cross-sectional view showing a first metal layer forming step in the manufacturing method for the metal-clad laminate of the present invention. FIG. [Figure 4] 3 is a cross-sectional view showing a second metal layer forming step in the manufacturing method for the metal-clad laminate of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the method for producing a metal-clad laminate of the present invention will be described in detail.

[0017] First, a 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 a 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.

[0018] 1 and 2, a metal-clad laminate 100 includes a substrate 10 and a metal layer 20 provided on a 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.

[0019] Next, a method for producing the metal-clad laminate 100 will be described with reference to Fig. 1 to Fig. 4. Fig. 3 is a cross-sectional view showing a first metal layer forming step in the method for producing the metal-clad laminate of the present invention, and Fig. 4 is a cross-sectional view showing a second metal layer forming step in the method for producing the metal-clad laminate of the present invention.

[0020] 1 to 4, the manufacturing method of the metal-clad laminate 100 includes a metal layer forming step of forming a metal layer 20 on a substrate 10 to manufacture the metal-clad laminate 100. The metal layer forming step includes a first metal layer forming step of forming a porous first metal layer 21 having voids V on the substrate 10, a second metal layer forming step of forming a non-porous second metal layer 22 on the first metal layer 21, and a third metal layer forming step of forming a third metal layer 33 on the second metal layer 22 by plating.

[0021] 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 to separate them is suppressed. Therefore, a metal-clad laminate 100 in which the peeling of the metal layer 20 from the substrate 10 is sufficiently suppressed can be manufactured.

[0022] The above-mentioned first metal layer forming step, second metal layer forming step, and third metal layer forming step will be described in detail below.

[0023] <First metal layer formation process> 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).

[0024] (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).

[0025] When the metal clad laminate 100 is used for high frequency applications, a resin with a small dielectric constant is preferable. In this case, a part of the electric energy is less likely to be converted into heat and lost. Examples of such resins with a small dielectric constant include LCP, COP, and fluororesin.

[0026] When solder reflow is particularly important, the material constituting the base material 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.

[0027] Furthermore, when emphasis is placed on suppressing warping due to temperature changes, the material constituting the base material 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, an LCP or polyimide resin having a linear expansion coefficient close to that of copper (16 ppm / K) is preferably used.

[0028] 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."

[0029] (1st metal layer) The first metal layer 21 can be obtained by applying a paste for forming the first metal layer, which 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.

[0030] Here, the metal particles preferably include nanoparticles having 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 having 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.

[0031] It is preferable that the metal particles are composed of nanoparticles only. In this case, the volume resistivity of the first metal layer 21 can be made smaller. This is because, when the metal particles are composed of nanoparticles only, all the metal particles melt and fuse together by light sintering, so that the contact area between the metal particles becomes large.

[0032] However, the metal particles may be 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.

[0033] Examples of metals constituting the metal particles include gold, silver and copper, with copper being preferred because it is inexpensive.

[0034] As the solvent, for example, 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, propylene carbonate, 1,3-dimethyl-2-imidazolidinone, or the like can be used.

[0035] The paste for forming the first metal layer may further contain a dispersant, such as polyethylene glycol or polyvinylpyrrolidone.

[0036] The first metal layer forming paste can be applied using, for example, a microgravure type coater or a spin coater.

[0037] The paste for forming the first metal layer is preferably subjected to a drying process before the light firing. In addition, when 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 for removing the organic components. In this case, it is possible to suppress the enlargement of voids due to gas generated by decomposition of the organic components during the light firing.

[0038] An example of a drying method is a method of performing a heat treatment at about 50 to 100° C. An example of a method of removing organic components is a method of performing a heat treatment on the paste for forming the first metal layer at about 150° C., followed by immersion in dilute sulfuric acid to remove the oxide film, washing with water, and then immersion in isopropyl alcohol.

[0039] As an apparatus for performing light baking, for example, "Pulsforge1300" manufactured by Novacentrix can be used. As a light source used in this apparatus, for example, a xenon lamp can be used.

[0040] The light irradiation energy is, for example, 0.1 to 100 J / cm 2 The light irradiation time may be set to 0.1 to 100 ms. The number of irradiations may be one or multiple.

[0041] 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 constituting 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.

[0042] The average thickness of the first metal layer 21 is preferably 5 μm or less. In this case, the gaps 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, as compared with the case where the average thickness of the first metal layer 21 exceeds 5 μm. The average thickness of the first metal layer 21 is more preferably 1 μm or less.

[0043] 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. A method for exposing the cross section of the first metal layer 21 includes a method of embedding the metal-clad laminate 100 in a resin and then polishing it.

[0044] <Second metal layer formation process> 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.

[0045] 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.

[0046] In this case, compared to when second metal layer 22 is formed so that R2 is greater than or equal to R1, the surface irregularities of second metal layer 22 are smaller and the current path is shorter when a high-frequency current flows, thereby making it possible to further reduce the electrical resistance of second metal layer 22.

[0047] Although there are no particular limitations on R1-R2, it is preferable that it is 0.03 μm or more. In this case, it is possible to further reduce the electrical resistance of the second metal layer 22. However, it is preferable that R1-R2 is 0.1 μm or less.

[0048] Specifically, R2 is preferably 0.01 μm or more, but is preferably 0.2 μm or less.

[0049] The second metal layer 22 may be formed so as to cover only the main surface of the first metal layer 21 opposite the substrate 10 (hereinafter referred to as the "opposite main surface"), but is preferably formed so as to cover not only the opposite main surface but also the side surface connecting the opposite main surface to the interface between the substrate 10 and the first metal layer 21. In this case, the second metal layer 22 closes the voids in the first metal layer 21, so that when the third metal layer 23 is formed on the second metal layer 22, it is possible to prevent the metal grown by plating from entering the voids in the first metal layer 21.

[0050] The metal constituting the second metal layer 22 is not particularly limited, but is preferably a non-magnetic metal when the metal-clad laminate 100 is used for high frequency applications. In this case, the skin effect prevents the thickness of the portion of the second metal layer 22 through which current flows from becoming thin, thereby reducing the electrical resistance of the second metal layer 22. Examples of non-magnetic metals include gold, silver, and copper. Among these, copper is preferred because it is inexpensive.

[0051] The second metal layer 22 is preferably made of the same metal as the first metal layer 21 .

[0052] In this case, metal is less likely to be dissolved from second metal layer 22 by moisture or the like that penetrates into the porous first metal layer, compared to when first metal layer 21 and second metal layer 22 are made of different metals. That is, corrosion of second metal layer 22 is sufficiently suppressed. As a result, an increase in the resistance of second metal layer 22 is suppressed, and cracking and peeling of second metal layer 22 from first metal layer 21 are sufficiently suppressed.

[0053] 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 entering the voids of the porous first metal layer 21.

[0054] The average thickness of 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 first metal layer 21.

[0055] Specifically, the average thickness of the second metal layer 22 may be 1 to 20 μm.

[0056] The average thickness of the second metal layer 22 can be adjusted by the sputtering time.

[0057] The average thickness of the second metal layer 22 can be measured in the same manner as that of the first metal layer 21.

[0058] <Third metal layer formation process> 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).

[0059] There is no particular limitation on the metal constituting the third metal layer 23. Examples of such metals include gold, silver, and copper. Among them, copper is preferable because it is inexpensive.

[0060] 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 having a smooth surface is uniformly attached to the surface of the second metal layer 22. A brightener may be added to the plating solution.

[0061] Examples of plating include electroplating and electroless plating. Among them, electroplating is preferable from the viewpoint of increasing the thickness of the third metal layer 23 in a short period of time.

[0062] When the plating is electroplating, the current density is not particularly limited, but is usually 1 to 4 A / dm 2 It is.

[0063] 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 base material 10, but the metal layer 20 may be formed on the opposite main surface of the base material 10 opposite to the main surface 10a.

[0064] 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. EXAMPLES

[0065] 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.

[0066] Example 1 First, a substrate having an average thickness of 25 μm was prepared. A polyimide film (trade name "Apical 25NPI", manufactured by Kaneka Corporation) was used as the substrate.

[0067] 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.

[0068] Next, the paste was photo-fired using a photo-fired device (product name "PulsForge1300", 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-fired was 1 μm.

[0069] Next, using a vacuum deposition apparatus (product name "JEOL JFC-1200" manufactured by JEOL Ltd.), copper was sputtered to cover the surface of the first metal layer, forming a second metal layer to obtain a structure. The average thickness of the second metal layer was 0.1 μm.

[0070] Next, the structure obtained as described above was pretreated with 10% by mass sulfuric acid and distilled water in that order, 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. The plating solution had a composition of 100 g / L copper sulfate pentahydrate, 180 g / L sulfuric acid, 0.12 mL / L hydrochloric acid, and distilled water (balance). The temperature of the plating solution was 25° C., and the current density was 4.0 A / dm 2 In this manner, a third metal layer was formed on the second metal layer to produce a metal-clad laminate.

[0071] 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.

[0072] [Evaluation of adhesion of metal layer to substrate] The metal-clad laminates obtained in Example 1 and Comparative Example 1 were subjected to a test of the adhesion of the metal layer to the substrate 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 peeled squares on the adhesive tape was then counted. The results are shown in Table 1. [Table 1]

[0073] As shown in Table 1, for the metal-clad laminate obtained in Example 1, the number of peeled off masses in the adhesion test was 0, whereas for the metal-clad laminate obtained in Comparative Example 1, the number of peeled off masses in the adhesion test was 100 (all).

[0074] From the above, it was confirmed that the method for producing a metal-clad laminate of the present invention can produce a metal-clad laminate in which a decrease in adhesion of the metal layer to the substrate is suppressed. [Explanation of symbols]

[0075] 10...Base material 20…metal layer 21...First metal layer 22…Second metal layer 23…Third metal layer 100...Metal clad laminate V...Void

Claims

1. 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.

2. The method for manufacturing a metal-clad laminate according to claim 1 , wherein in the second metal layer forming process, 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.

3. The method for producing 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.

Images