JP7569006B2 - Manufacturing method of copper clad laminate - Google Patents

Description

The present invention relates to a method for producing a copper-clad laminate. More specifically, the present invention relates to a method for producing a copper-clad laminate used in the manufacture of flexible printed circuit boards (FPCs) and the like.

Flexible printed wiring boards, in which wiring patterns are formed on the surface of a resin film, are used in electronic devices such as liquid crystal panels, notebook computers, digital cameras, and mobile phones. Flexible printed wiring boards are manufactured from copper-clad laminates, in which copper foil is laminated onto a resin film. Copper-clad laminates are also obtained by forming a base metal layer on a resin film by dry plating, and then forming a copper plating film by electrolytic plating (for example, Patent Document 1).

The amount of information processed by electronic devices is increasing year by year, and electronic devices are required to process high-frequency signals. Accordingly, flexible printed wiring boards are required to keep transmission loss low when processing high-frequency signals. For example, mobile terminals such as smartphones are required to have high-speed data communication in order to keep up with the increase in data transmission and reception in recent years. Flexible printed wiring boards used in mobile terminals are required to keep transmission loss low when performing high-frequency wireless communication.

JP 2010-205799 A

When the pulses flowing through the wiring reach a high frequency range, a large amount of current flows on the surface of the wiring due to the skin effect. Therefore, by lowering the surface resistivity of the wiring, transmission loss can be kept low. The larger the crystallites in the copper plating film that makes up the wiring, the lower the surface resistivity of the wiring. The crystallites in the copper plating film are small immediately after plating, and grow larger over time due to room-temperature recrystallization. However, it takes a long time (e.g., several weeks) for the crystallites to reach a sufficient size through room-temperature recrystallization.

In view of the above circumstances, an object of the present invention is to provide a method for producing a copper-clad laminate capable of enlarging the crystallites of a copper plating film in a short period of time.

The method for producing a copper-clad laminate of the present invention includes an electrolytic plating step of forming a copper plating film on the surface of a substrate to obtain a copper-clad laminate, and a heating step of heating the copper-clad laminate while transporting it by roll-to-roll, and is characterized in that in the heating step, the transport tension is set to 50 to 105 N/m and the heating temperature is set to 134 to 170°C, or the transport tension is set to 105 to 160 N/m and the heating temperature is set to 113 to 170°C .

According to the present invention, in the heating process carried out after the electrolytic plating process, the crystallites of the copper plating film can be enlarged by using a specific heating temperature and conveying tension. Therefore, the crystallites of the copper plating film can be enlarged in a short period of time.

1 is a cross-sectional view of a copper-clad laminate according to one embodiment of the present invention. 1 is a graph showing the relationship between the heating temperature of a heating furnace and the crystallite size of a copper plating film. 1 is a graph showing the relationship between crystallite size and surface resistivity of a copper plating film.

Next, an embodiment of the present invention will be described with reference to the drawings.
As shown in Fig. 1, a copper clad laminate 1 produced by a method according to one embodiment of the present invention comprises a substrate 10 and a copper plating film 20 formed on the surface of the substrate 10. As shown in Fig. 1, the copper plating film 20 may be formed on only one side of the substrate 10, or the copper plating film 20 may be formed on both sides of the substrate 10.

The substrate 10 is a metal layer 12 formed on the surface of an insulating base film 11. A resin film such as a polyimide film or a liquid crystal polymer (LCP) film can be used as the base film 11. The metal layer 12 is formed, for example, by a sputtering method. The metal layer 12 is made of an undercoat metal layer 13 and a copper thin film layer 14. The undercoat metal layer 13 and the copper thin film layer 14 are laminated in this order on the surface of the base film 11. In general, the undercoat metal layer 13 is made of nickel, chromium, or a nickel-chromium alloy. Although not particularly limited, the thickness of the base film 11 is generally 30 to 40 μm, the thickness of the undercoat metal layer 13 is generally 5 to 50 nm, and the thickness of the copper thin film layer 14 is generally 50 to 400 nm.

The base metal layer 13 may not be necessary. The copper thin film layer 14 may be formed on the surface of the base film 11 via the base metal layer 13, or may be formed directly on the surface of the base film 11 without the base metal layer 13.

The copper plating film 20 is formed on the surface of the copper thin film layer 14. Although not particularly limited, the thickness of the copper plating film 20 is generally 8 to 12 μm in the case of a copper clad laminate 1 processed by a subtractive method, and generally 0.1 to 5 μm in the case of a copper clad laminate 1 processed by a semi-additive method. The metal layer 12 and the copper plating film 20 are collectively referred to as the "conductor layer."

The manufacturing method of the copper-clad laminate 1 according to this embodiment includes an electrolytic plating process and a heating process. A roll-to-roll plating apparatus is used. This plating apparatus performs electrolytic plating on the long strip-shaped substrate 10 while transporting the substrate 10 by roll-to-roll.

The plating equipment has a supply device that pays out the substrate 10 wound in a roll, and a winding device that winds up the substrate 10 (copper-clad laminate 1) after plating into a roll. On the transport path between the supply device and the winding device, a pre-treatment tank, a plating tank, a post-treatment tank, a liquid cutting device, and a heating furnace are preferably arranged in this order from upstream to downstream. In the pre-treatment tank, the substrate 10 is pickled. In the plating tank, an electrolytic plating process is performed. In the post-treatment tank, an anti-rust treatment is performed on the copper-clad laminate 1. The liquid that has adhered to the copper-clad laminate 1 is cut off by the liquid cutting device. The heating furnace performs a heating process.

In this way, by arranging a plating tank and a heating furnace on the transport path of the substrate 10, the electrolytic plating process and the heating process can be completed by transporting the substrate 10 once. Therefore, the manufacture of the copper-clad laminate 1, including the heating process, can be completed in a short time. It is also preferable to provide tension-cutting mechanisms before and after the heating furnace on the transport path of the substrate 10. This allows the transport tension of the copper-clad laminate 1 in the heating furnace to be set as desired.

(Electrolytic plating process)
An electrolytic plating process is carried out in the plating tank. While the substrate 10 is transported through the plating tank, a copper plating film 20 is formed on the surface of the substrate 10 by electrolytic plating. In this way, a long strip-shaped copper-clad laminate 1 is obtained.

A copper plating solution is stored in the plating tank. The copper plating solution contains a water-soluble copper salt. Any water-soluble copper salt that is generally used in copper plating solutions may be used without any particular limitation. The copper plating solution may contain sulfuric acid. The pH and sulfate ion concentration of the copper plating solution can be adjusted by adjusting the amount of sulfuric acid added. The copper plating solution may contain additives that are generally added to plating solutions. As the additive, one type selected from a brightener component, a leveler component, a polymer component, a chlorine component, etc. may be used alone, or two or more types may be used in combination.

The content of each component in the copper plating solution can be selected as desired. However, the copper plating solution preferably contains 15 to 70 g/L of copper and 20 to 250 g/L of sulfuric acid. This allows the copper plating film 20 to be formed at a sufficient speed. The copper plating solution preferably contains 1 to 50 mg/L of a brightener component. This allows the precipitated crystals to be finer and the surface of the copper plating film 20 to be smooth. The copper plating solution preferably contains 1 to 300 mg/L of a leveller component. This allows protrusions to be suppressed and a flat copper plating film 20 to be formed. The copper plating solution preferably contains 10 to 1,500 mg/L of a polymer component. This allows current concentration at the end of the substrate 10 to be alleviated and a uniform copper plating film 20 to be formed. The copper plating solution preferably contains 20 to 80 mg/L of a chlorine component. This allows abnormal precipitation to be suppressed.

The temperature of the copper plating solution is preferably 20 to 35°C. It is also preferable to stir the copper plating solution in the plating tank. For example, the copper plating solution can be stirred by spraying the copper plating solution from a nozzle onto the substrate 10.

(Heating process)
A heating step is carried out in the heating furnace. That is, after the copper plating film 20 is formed, the copper plating film 20 is heated with hot air. The heating step is carried out by blowing hot air onto the copper plating film 20 to heat it while transporting the copper-clad laminate 1 by roll-to-roll.

The purpose of the heating process is usually to dry the copper plating film 20. Therefore, the usual heating temperature (temperature of the copper-clad laminate 1) is 50 to 70°C, and the treatment time is about 1 minute.

However, when the inventors of the present application performed heating at a high temperature, which is not normally performed, it was confirmed that the higher the heating temperature, the larger the crystallites of the copper plating film 20. It was also confirmed that when heating at a high temperature, the higher the conveying tension of the copper-clad laminate 1, the larger the crystallites of the copper plating film 20. From this, the inventors of the present application came up with the idea of enlarging the crystallites of the copper plating film 20 by setting the heating temperature and conveying tension in the heating process to specific conditions. In other words, the heating process in this embodiment is intended to promote recrystallization of the copper plating film 20 and enlarge the crystallites.

Specifically, the conveying tension is set to 50-105 N/m and the heating temperature is set to 134-170°C, or the conveying tension is set to 105-160 N/m and the heating temperature is set to 113-170°C. This allows the crystallite diameter of the copper plating film 20 to be 1,500 Å or more. If the crystallite diameter of the copper plating film 20 is set to 1,500 Å or more, the surface resistivity will be 0.25 Ω/□ or less. Therefore, the transmission loss in the processing of high-frequency signals in the flexible printed wiring board manufactured from the copper-clad laminate 1 can be kept low.

From the viewpoint of manufacturing costs, a lower heating temperature is preferable. Therefore, within the above range, it is preferable to increase the conveying tension while decreasing the heating temperature. In this way, it is possible to suppress the increase in costs due to heating while achieving the desired crystallite size of the copper plating film 20.

As described above, the crystallites of the copper plating film 20 can be enlarged by using a specific heating temperature and conveying tension in the heating process carried out after the electrolytic plating process. The processing time for the heating process can be 1 to 2 minutes. It takes several weeks to make the crystallites large enough by room temperature recrystallization. In comparison, the crystallites of the copper plating film 20 can be enlarged in an extremely short time.

The electrolytic plating process and the heating process may be performed in separate devices. That is, the copper-clad laminate 1 may be produced in a plating device and wound into a roll by a winding device, and then the copper-clad laminate 1 may be heated in a separate heating device while being transported in a roll-to-roll manner. In this case, however, the substrate 10 (copper-clad laminate 1) must be unwound and wound twice, making the process more complicated and lengthening the processing time.

In addition, if the copper-clad laminate 1 wound in a roll is heated in that state, a temperature difference occurs between the outside and inside of the roll, and the copper plating film 20 cannot be heated uniformly. Moreover, if the inside of the roll is heated, a long time (e.g., several hours) is required. In contrast, if the copper plating film 20 is heated while being transported by roll-to-roll, the copper plating film 20 can be heated uniformly and the process can be completed in a short time (1 to 2 minutes).

(Common conditions)
A long strip-shaped polyimide film (Upilex-35SGAV1 manufactured by Ube Industries, Ltd.) having a thickness of 35 μm was prepared as the base film. The base film was set in a magnetron sputtering device. A nickel-chromium alloy target and a copper target were installed in the magnetron sputtering device. The composition of the nickel-chromium alloy target was 20 mass % Cr and 80 mass % Ni. Under a vacuum atmosphere, a base metal layer made of a nickel-chromium alloy having a thickness of 25 nm was formed on both sides of the base film, and a copper thin film layer having a thickness of 100 nm was formed thereon.

A copper-plated laminate was obtained by forming a copper plating film on both sides of the substrate using a roll-to-roll plating device. A plating tank and a circulating hot air heating furnace were placed on the substrate transport path, so that electrolytic plating and heating were performed in a single transport of the substrate.

The copper plating solution stored in the plating tank contains 120 g/L copper sulfate, 70 g/L sulfuric acid, 16 mg/L brightener, 20 mg/L leveler, 1,100 mg/L polymer, and 50 mg/L chlorine. Bis(3-sulfopropyl) disulfide (a reagent manufactured by RASCHIG GmbH) was used as the brightener. Diallyldimethylammonium chloride-sulfur dioxide copolymer (PAS-A-5 manufactured by Nittobo Medical Co., Ltd.) was used as the leveler. Polyethylene glycol-polypropylene glycol copolymer (UNILUBE 50MB-11 manufactured by NOF Corporation) was used as the polymer. Hydrochloric acid (35% hydrochloric acid manufactured by Wako Pure Chemical Industries, Ltd.) was used as the chlorine component.

The substrate was fed into the plating tank, and a copper plating film having a thickness of 2.0 μm was formed on both sides of the substrate by electrolytic plating. The current conditions in the electrolytic plating were a current density of 1.0 A/dm ² for 1 minute, 3.0 A/dm ² for 1 minute, and 5.0 A/dm ² for 1 minute. The temperature of the copper plating solution was set to 31° C. During the electrolytic plating, the copper plating solution was agitated by spraying the copper plating solution ejected from the nozzle substantially perpendicularly to the surface of the substrate. The conveying tension during the electrolytic plating was set to 105 N/m.

The heating process was carried out in a circulating hot air heating furnace. Suction rollers that can cut the conveying tension are installed before and after the heating furnace, allowing the conveying tension inside the furnace to be set as desired. The heating process time was 1 minute.

The crystallite diameter of the copper plating film of the obtained copper-clad laminate was measured. The measurement was performed using a fully automated multipurpose X-ray diffraction device SmartLab manufactured by Rigaku Corporation, and the crystallite diameter was calculated from the half-width of the (200) plane peak using the Scherrer formula. The measurement was performed 18 hours after the completion of electrolytic plating.

(Test 1)
The conveying tension in the heating step was set to 50 N/m.
The temperature was either 0, 130, 150 or 170° C. The crystallite sizes of the copper-clad laminates produced under each condition are shown in Table 1 and FIG.

(Test 2)
The conveying tension in the heating step was 105 N/m, and the heating temperature was 50, 60, 70, 80, 100, 110, 130, 150, or 170° C. The crystallite diameters of the copper-clad laminates produced under each condition are shown in Table 1 and FIG.

(Test 3)
The conveying tension in the heating step was 160 N/m, and the heating temperature was either 80, 100, 110, 130, 150, or 170° C. The crystallite diameters of the copper plating films produced under each condition are shown in Table 1 and FIG.

As can be seen from Table 1 and the graph in Figure 2, when the heating temperature is in the range of 50 to 70°C, the crystallite diameter of the copper plating film hardly changes with the heating temperature. In contrast, when the heating temperature is 80°C or higher, the crystallite diameter of the copper plating film increases as the heating temperature is increased. In addition, when the heating temperature is 80°C or higher, the crystallite diameter of the copper plating film increases as the conveying tension is increased.

The larger the crystallite diameter of the copper plating film, the lower the surface resistivity and the less transmission loss of high-frequency pulses. Therefore, the larger the crystallite diameter of the copper plating film, the more preferable it is.

To achieve a crystallite diameter of 1,500 Å or more in the copper plating film, the conveying tension should be 50 to 105 N/m and the heating temperature should be 134 to 170°C, or the conveying tension should be 105 to 160 N/m and the heating temperature should be 113 to 170°C.

To achieve a crystallite diameter of 2,000 Å or more in the copper plating film, the conveying tension should be 50 to 105 N/m and the heating temperature should be 152 to 170°C, or the conveying tension should be 105 to 160 N/m and the heating temperature should be 125 to 170°C.

To achieve a crystallite diameter of 2,500 Å or more in the copper plating film, the conveying tension should be 50 to 105 N/m and the heating temperature should be 162 to 170°C, or the conveying tension should be 105 to 160 N/m and the heating temperature should be 140 to 170°C.

Figure 3 shows the relationship between the crystallite size and surface resistivity of the copper plating film. The graph in Figure 3 was obtained from a test carried out using the following procedure. A substrate was prepared using the procedure and conditions described under common conditions, and a copper plating film was formed on both sides of the substrate. The heating temperature in the circulating hot air heating furnace was 50°C, and the conveying tension was 105 N/m. The crystallite size and surface resistivity of the resulting copper-clad laminate were measured 2 hours, 40 hours, 85 hours, and 229 hours after the completion of electrolytic plating. A Mitsubishi Chemical Analytical Loresta AX MCP-T370 was used to measure the surface resistivity.

The graph in Figure 3 shows that the larger the crystallite diameter of the copper plating film, the lower the surface resistivity. If the crystallite diameter of the copper plating film is 1,500 Å or more, the surface resistivity can be reduced to 0.25 Ω/□ or less. If the crystallite diameter of the copper plating film is 2,000 Å or more, the surface resistivity can be reduced to 0.23 Ω/□ or less. If the crystallite diameter of the copper plating film is 2,500 Å or more, the surface resistivity can be reduced to 0.22 Ω/□ or less.

It takes about one week for the crystallite diameter of the copper plating film to reach 1,500 Å by room temperature recrystallization, and about two weeks for it to reach 3,000 Å. In comparison, this embodiment makes it possible to enlarge the crystallites of the copper plating film in an extremely short time.

REFERENCE SIGNS LIST 1 copper-clad laminate 10 substrate 11 base film 12 metal layer 13 undercoat metal layer 14 thin copper layer 20 copper plating film

Claims (4)

an electrolytic plating step of forming a copper plating film on the surface of the substrate to obtain a copper-clad laminate;
a liquid draining step of draining the liquid adhering to the copper-clad laminate after the electrolytic plating step;
A heating step of heating the copper-clad laminate while transporting it by roll-to-roll after the liquid-draining step,
In the heating step, the conveying tension is set to 50 to 105 N/m and the heating temperature is set to 134 to 170°C, or the conveying tension is set to 105 to 160 N/m and the heating temperature is set to 113 to 170°C. The method for manufacturing a copper-clad laminate according to claim 1, characterized in that a plating tank for performing the electrolytic plating process, a liquid draining device for performing the liquid draining process, and a heating furnace for performing the heating process are arranged on a roll-to-roll transport path of the substrate. The method for producing a copper-clad laminate according to claim 1 or 2, characterized in that in the heating step, the conveying tension is 50 to 105 N/m and the heating temperature is 152 to 170 ° C., or the conveying tension is 105 to 160 N/m and the heating temperature is 125 to 170 ° C. The method for producing a copper-clad laminate according to claim 1 or 2, characterized in that in the heating step, the conveying tension is 50 to 105 N/m and the heating temperature is 162 to 170 ° C., or the conveying tension is 105 to 160 N/m and the heating temperature is 140 to 170 ° C.