Flexible metal-clad laminate and manufacturing method thereof

Abstract

To provide a flexible metal-clad laminate and a method for manufacturing a flexible copper-clad laminate by thermocompression molding an insulating layer made of a liquid crystal polymer and a copper foil having a surface root mean square gradient (Sdq) within a predetermined range, thereby achieving both sufficient peel strength between the liquid crystal polymer insulating layer and the copper foil, and solder heat resistance.SOLUTION: Provided is a flexible metal-clad laminate comprising an insulating layer made of a liquid crystal polymer and a metal layer laminated on one or both sides of the insulating layer, wherein the surface of the metal layer that overlaps the insulating layer has a root mean square gradient (Sdq) of 0.17 or more and 0.82 or less, measured in accordance with ISO 25178-2:2021, and a method for manufacturing the same is also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flexible metal-clad laminate and a method for manufacturing the same. [Background technology]

[0002] In recent years, amid calls for the promotion of DX (Digital Transformation), typified by the use of IoT (Internet of Things) and AI, there is a demand for the widespread adoption of 5G, which utilizes high frequency bands such as millimeter waves and sub-6, in order to utilize the vast amounts of data. For this reason, printed wiring boards used in communication devices are required to have low transmission loss even in high frequency bands, as well as the same adhesion and dimensional stability as conventional boards.

[0003] Liquid crystal polymer resins are known for their high heat resistance, low dielectric constant, and low dielectric loss tangent, and high-frequency flexible printed wiring boards using liquid crystal polymers as insulating layers have been actively used in recent years. Patent Documents 1 and 2 disclose a method of continuously thermo-compressing a liquid crystal polymer while applying surface pressure using a double-belt press equipped with a pair of endless belts. However, while these documents discuss peel strength, dimensional change rate, thickness, transmission loss, and MIT folding endurance, they do not discuss solder heat resistance, an important property required for metal-clad laminates (CCLs).

[0004] That is, in Patent Document 1, the metal foil used is copper-plated to a surface roughness (Rz) of 0.5 to 4.0 μm in order to ensure sufficient adhesion with the liquid crystal polymer insulating layer. However, in the examples of copper foil disclosed in Patent Document 1, even within the above (Rz) range, sufficient peel strength is not obtained without copper plating (Example 7, Table 1). Furthermore, no consideration is given to solder heat resistance.

[0005] Furthermore, Patent Document 2 discloses a flexible laminate having a metal layer formed on one or both sides of an insulating layer as a flexible laminate for providing a flexible laminate with a small dimensional change rate, in which the liquid crystal polymer has a melting point of more than 250°C, and in a dimensional stability test specified in JIS C 6471, the dimensional change rate is within ±0.05% when heated to a temperature of 250°C, and the standard deviation of the thickness in the width direction of the insulating layer is 1.2 μm or less. However, no consideration is given to solder heat resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5411656 [Patent Document 2] Patent No. 6518445 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present inventors have aimed to provide a flexible metal-clad laminate that has both sufficient peel strength and solder heat resistance, and have conducted extensive research into a method for producing the same. [Means for solving the problem]

[0008] The inventors discovered that it is possible to manufacture a flexible metal-clad laminate that combines sufficient peel strength and solder heat resistance by thermocompressing an insulating layer made of a liquid crystal polymer with a metal foil having a root-mean-square gradient (Sdq) of 0.17 or more and 0.82 or less on the surface to be bonded to the insulating layer, and thus completed the present invention. That is, the present invention provides the following inventions [1] to [7]. [1] A flexible metal-clad laminate comprising an insulating layer made of a liquid crystal polymer and a metal layer laminated on one or both sides of the insulating layer, wherein the surface of the metal layer that overlaps the insulating layer has a root-mean-square gradient (Sdq) of 0.17 or more and 0.82 or less, measured in accordance with ISO 25178-2:2021. [2] In accordance with JIS C6471:1995, the peel strength between the metal layer and the insulating layer measured by Method A is 0.60 N / mm or more, and after pre-treatment at 105 ° C for 1 hour, the number of bubbles generated when floated in a solder bath at 288 ° C for 1 minute is 15,000 mm 2 The flexible metal-clad laminate according to [1], wherein the number of the metal-clad particles is 10 or less within an area of ​​10. [3] The flexible metal-clad laminate according to [1] or [2], wherein the metal layer is copper foil. [4] A method for manufacturing a flexible metal-clad laminate, which comprises an insulating layer formed of a liquid crystal polymer, and a metal layer superimposed on one or both sides of the insulating layer and thermocompressing the layer, wherein the root mean square gradient (Sdq) of the surface of the metal layer overlapping the insulating layer, measured in accordance with ISO 25178-2:2021, is in the range of 0.17 to 0.82. [5] The method for producing a flexible metal-clad laminate according to [4], wherein the heating temperature during the thermocompression molding is in the range of 15°C higher than the melting point of the liquid crystal polymer forming the insulating layer and 30°C higher than the melting point. [6] The method for producing a flexible metal-clad laminate according to [4] or [5], wherein the thermo-compression molding is performed using a double belt press, the pressure during the thermo-compression molding is in the range of 0.5 to 5.5 MPa, and the heating and pressing time is in the range of 70 to 280 seconds. [7] The method for producing a flexible metal-clad laminate according to any one of [4] to [6] above, wherein the metal layer is a copper foil. [Effects of the Invention]

[0009] According to the present invention, by thermocompressing a liquid crystal polymer insulating layer and a metal foil having a root mean square gradient (Sdq) of the surface to be bonded to the insulating layer in the range of 0.17 to 0.82, a flexible metal-clad laminate having excellent adhesion to the liquid crystal polymer insulating layer and excellent solder heat resistance, and a method for manufacturing the same, can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a schematic configuration of an example of a thermocompression bonding step in a manufacturing method for a flexible metal-clad laminate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will now be described.

[0012] The flexible metal-clad laminate of the present invention is a flexible metal-clad laminate comprising an insulating layer made of a liquid crystal polymer and a metal layer laminated on one or both sides of the insulating layer, characterized in that the surface of the metal layer that overlaps the insulating layer has a root-mean-square gradient (Sdq) of 0.17 or more and 0.82 or less, measured in accordance with ISO 25178-2:2021.

[0013] <Insulating layer> In the flexible metal-clad laminate of the present invention, the insulating layer is formed of a liquid crystal polymer. The type of liquid crystal polymer is not particularly limited, and examples include liquid crystal polymers having ethylene terephthalate and parahydroxybenzoic acid as structural units, liquid crystal polymers having phenol, phthalic acid, and parahydroxybenzoic acid as structural units, and liquid crystal polymers having 6-hydroxy-2-naphthoic acid and parahydroxybenzoic acid as structural units. Preferably, liquid crystal polymers having 6-hydroxy-2-naphthoic acid and parahydroxybenzoic acid as structural units and liquid crystal polymers having 6-hydroxy-2-naphthoic acid and terephthalic acid as structural units are recommended. In the present invention, the insulating layer may be in the form of either a film or a sheet. In the present invention, the difference between "film-like" and "sheet-like" conforms to the classification by thickness in the JIS "Packaging Terminology" standard, where a film is "a plastic membrane with a thickness of less than 250 μm" and a sheet is "a thin plastic plate with a thickness of 250 μm or more." Methods for forming a film-like or sheet-like insulating layer include the T-die method and the inflation method. Among these, the inflation method is preferred from the viewpoints of dimensional stability and production costs.

[0014] The thickness of the insulating layer is not particularly limited, and is preferably in the range of, for example, 6 to 300 μm. When an insulating film is used, the thickness is preferably in the range of, for example, 6 to less than 250 μm, more preferably in the range of 12 to 150 μm, and even more preferably in the range of 25 to 100 μm.

[0015] <Metal layer> The material of the metal layer constituting the flexible metal-clad laminate of the present invention is not particularly limited as long as it is a metal, and copper, copper alloy, aluminum, stainless steel, etc. are used. Copper and copper alloy are preferred, and copper is more preferred. When metal layers are provided on both sides of the insulating layer, the materials of the respective metal layers may be the same or different. The metal layer is preferably in the form of a metal foil, which can be selected from the metal foils made of the above-mentioned materials, and is particularly preferably a copper foil. As the copper foil, either an electrolytic copper foil or a rolled copper foil is preferably used.

[0016] In the present invention, the surface of the metal layer overlapping the insulating layer must have a root mean square gradient (Sdq) of 0.17 or more and 0.82 or less, measured in accordance with ISO 25178-2:2021.

[0017] In the present invention, the root-mean-square gradient (Sdq) of the surface of the metal layer overlapping the insulating layer, measured in accordance with ISO 25178-2:2021, is 0.17 to 0.82, preferably 0.28 to 0.70, and more preferably 0.45 to 0.65. If the root-mean-square gradient (Sdq) is less than 0.17, the surface of the metal layer becomes nearly flat, resulting in insufficient penetration into the insulating layer surface (anchor effect), and the peel strength of the resulting flexible metal-clad laminate is reduced. If the Sdq exceeds 0.82, the surface of the metal layer becomes too steep, making it difficult for the insulating layer to penetrate fully into the deepest recesses. This makes it more likely that microvoids will form between the metal layer and the insulating layer, resulting in poor solder heat resistance. In other words, by setting the root mean square gradient (Sdq) within this range, it is possible to maintain a sufficiently high peel strength between the insulating layer and the metal layer while exhibiting excellent solder heat resistance. If it is outside this range, the peel strength will be weak or the solder heat resistance will be poor, and there is a concern that peeling will occur between the metal foil and the insulating layer in practical use.

[0018] The root mean square gradient (Sdq) is one of the surface roughness parameters determined by measurements in accordance with ISO 25178, and is expressed by the following formula (1). The root mean square gradient (Sdq) represents the average magnitude of the local gradient of the uneven shape of the metal layer surface, and a larger value indicates a steeper metal layer surface.

[0019]

number

[0020] In the present invention, the surface roughness (ten-point average roughness) (Rz) of the metal layer on the surface overlapping the insulating layer is preferably in the range of 0.7 to 2.0 μm as defined in JIS B0601:1994. A surface roughness (Rz) in this range, combined with the surface characteristic of the root-mean-square gradient (Sdq) described above, is preferable from the viewpoint of ensuring adhesion (adhesion) with a sufficiently high peel strength between the insulating layer and the metal layer.

[0021] The flexible metal-clad laminate of the present invention has a metal layer on one or both sides of an insulating layer. That is, either embodiment 1, in which the layer structure is metal layer / insulating layer / metal layer, or embodiment 2, in which the layer structure is two layers, metal layer / insulating layer, can be selected depending on the application.

[0022] The flexible metal-clad laminate of the present invention preferably has a peel strength (peel strength) between the metal layer and the insulating layer measured by Method A in accordance with JIS C6471:1995 of 0.60 N / mm or more, more preferably 0.70 N / mm or more, and even more preferably 0.80 N / mm or more. If the peel strength between the metal layer and the insulating layer is 0.60 N / mm or more, the peel resistance required when processing the flexible metal-clad laminate into a flexible circuit board can be ensured.

[0023] Furthermore, the flexible metal-clad laminate of the present invention is required to have excellent solder heat resistance. In the present invention, the solder heat resistance is evaluated by the method described below. From the continuously wound, long flexible metal-clad laminate of the present invention, a sheet having dimensions of 500 mm in the transverse direction (TD) perpendicular to the longitudinal direction, 30 mm in the longitudinal direction (MD), and an area of ​​TD 500 mm × MD 30 mm = 15,000 mm 2 This test piece (sample) is dried at 105°C for 1 hour, then floated on the top surface of a solder bath set at a specified temperature for 1 minute, then pulled out and cooled to room temperature, after which the solder heat resistance is evaluated based on the number of bubbles that form in the sample. The flexible metal-clad laminate of the present invention has a bubble count as an evaluation of solder heat resistance of 10 or less, preferably 5 or less, and more preferably 2 or less. By keeping the bubble count within this range, the possibility of circuit peeling occurring during solder reflow mounting can be reduced.

[0024] The method for producing a flexible metal-clad laminate of the present invention will now be described. The method for manufacturing a flexible metal-clad laminate of the present invention is a method for manufacturing a flexible metal-clad laminate, which comprises an insulating layer formed of a liquid crystal polymer, and a metal layer superimposed on one or both sides of the insulating layer and thermocompressing the laminate, and is characterized in that the root-mean-square gradient (Sdq) of the surface of the metal layer overlapping the insulating layer, measured in accordance with ISO 25178-2:2021, is in the range of 0.17 to 0.82.

[0025] The liquid crystal polymer and metal layer forming the insulating layer used in the manufacturing method of the present invention are those already described. The root mean square gradient (Sdq) of the metal layer overlapping the insulating layer, measured by a specific method, also satisfies the above-described value, and is selected and used from the viewpoint of providing a flexible metal-clad laminate having an insulating layer formed from a liquid crystal polymer with excellent solder heat resistance while maintaining a sufficiently high peel strength between the insulating layer and the metal layer. Furthermore, the heating temperature during thermocompression molding is preferably in the range of at least 15°C higher than the melting point of the liquid crystal polymer forming the insulating layer and not higher than 30°C higher than the melting point, from the viewpoints of improving the adhesion (adhesion) between the metal layer and the insulating layer, ensuring sufficient peel strength, and ensuring solder heat resistance. It is more preferably at least 17°C higher than the melting point and not higher than 27°C higher than the melting point. If the heating temperature is lower than the melting point, the peel strength between the metal layer and the insulating layer will be weak, and there is a concern that the circuit may peel off when the flexible metal-clad laminate is processed into a flexible circuit board.

[0026] In the manufacturing method of the flexible metal-clad laminate of the present invention, the method of thermo-pressing may be either a method using a thermo-press roll or a method using a double belt press device for thermo-pressing between endless belts, as long as the method ensures the adhesion (tightness) between the metal layer and the insulating layer and the functionality of the metal-clad laminate. However, it is particularly preferable to perform the thermo-pressing using a double belt press device, from the viewpoint of being able to ensure continuous heating and pressing time while suppressing misalignment between the metal layer and the insulating layer when they are overlapped.

[0027] In the case of embodiment 2, in which the thermo-compression molding is performed using a double belt press device and the flexible metal-clad laminate has a metal layer on only one side of the insulating layer, in order to prevent the steel belt from being transferred to the softened insulating layer (film) during the thermo-compression molding process, the laminate may be manufactured by overlapping a release film, and provided as a release film / insulating layer / metal layer. The release film may be a known release film used in the production of flexible metal-clad laminates. In particular, it is preferable to use a release film made of a flexible material that has high heat resistance and good releasability, such as at least one material selected from non-thermocompression-bondable heat-resistant aromatic polyimide, fluororesin, and silicone resin. The release film is appropriately peeled off when the flexible metal-clad laminate is used. In addition, in Figure 1, the metal foil 12 on the upper side can be replaced with a release film (not shown), and after running it through the double belt press device 20, a recovery roll for recovering the release film can be separately provided in the winding section 40, and the release film can be peeled off from the flexible metal-clad laminate 10 at the time it is transported out of the double belt press device 20, and the flexible metal-clad laminate 10 and the release film can be recovered separately.

[0028] In the manufacturing method of the present invention, the pressure during thermocompression molding may be appropriately set, but is preferably in the range of 0.5 to 5.5 MPa, more preferably 2.0 to 5.0 MPa, and even more preferably 3.0 to 4.5 MPa. If the pressure during thermocompression molding is set within these ranges, high peel strength can be maintained. In the manufacturing method of the present invention, the heating and pressing time during thermocompression molding may be appropriately set, but is preferably in the range of 70 to 280 seconds, more preferably 80 to 240 seconds, and even more preferably 90 to 180 seconds. Within these ranges, peel strength and solder heat resistance can be improved. [Example]

[0029] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0030] The following materials were prepared and used in the examples and comparative examples. Liquid crystal polymer film for insulating layers LCP: Manufactured by Okura Kogyo Co., Ltd., melting point 318°C Copper foil was used as the metal layer, and Table 1 shows the manufacturer name, grade name, type, and thickness of the copper foil. The metal foil column in Table 2 shows the type, thickness, surface roughness (Rz) (μm), and root mean square gradient (Sdq).

[0031] [Table 1]

[0032] The surface properties of the copper foil used as the metal layer, and the peel strength and solder heat resistance of the obtained flexible metal-clad laminate were evaluated by the methods described below. Surface analysis of the copper foil insulation layer and overlapping surface <Root Mean Square Gradient (Sdq)> Measurements were performed at four random points on an A4-sized copper foil cut using a laser microscope (Keyence Model VK-X210). Measurements were performed in accordance with ISO 25178-2:2021, with an S filter of 1 μm, F-operation plane tilt correction automatic, and an L filter of 0.1 mm. The values ​​used in Table 2 are the average values ​​of the four measurement points. <Surface roughness (Rz)> The values ​​published by each copper foil manufacturer were used. Evaluation of flexible metal-clad (copper-clad) laminates <Peel strength> In accordance with JIS C 6471:1955, the peel strength under normal conditions was measured with a measurement width of 3 mm, using Method A as reference. All measurements were performed by peeling in the TD direction. <Solder heat resistance> Based on the solder heat resistance test specified in JIS C 6471, the sample obtained by the above method was dried at 105°C for 1 hour, then floated on a solder bath set at 288°C for 1 minute, pulled out, cooled to room temperature, and then printed on a 15,000mm square meter sheet. 2 The solder heat resistance was evaluated based on the number of bubbles that appeared on the sample surface. A number of bubbles of 11 or more was expressed as "numerous." <Performance evaluation> When the number of bubbles was 10 or less during the solder heat resistance test at 288°C and the peel strength was 0.60 N / mm or more, the test was evaluated as good (○), and when the number of bubbles was more than 10 or the peel strength was less than 0.60 N / mm, the test was evaluated as poor (×).

[0033] Example 1 Using a double belt press device 20 having the configuration shown in FIG. 1, a liquid crystal polymer film 11 [manufactured by Okura Kogyo Co., Ltd., melting point 318°C, thickness 50 μm] was used as an insulating film roll 31 suspended in a feeding section 30, and an electrolytic copper foil (CF-H9A-DS-HD2R, thickness 12 μm) manufactured by Fukuda Metal Foil and Powder Co., Ltd. was used as a metal layer roll 32. The copper foil 12 had surface properties of a surface roughness (Rz) of 1.5 μm and a root mean square gradient (Sdq) of 0.493 on the surface to be laminated with the insulating layer, and these were stacked to form a three-layer structure. The film was fed into a double belt press 20, and sandwiched between an endless belt 23 stretched between upper drums 21 and an endless belt 24 stretched between lower drums 22. The film was then passed through the zones of upper and lower heat presses 25, where it was subjected to heat and pressure molding (lamination) under conditions of a heating temperature of 335°C (17°C higher than the melting point of the liquid crystal polymer film), a pressure of 4.0 MPa, and a heating and pressure time of 93 seconds to produce a metal (copper) clad laminate 10, which was then wound into a roll by a winding section 40. The resulting flexible copper clad laminate 10 had a three-layer structure in which metal layers made of copper foils 12 were laminated on top and bottom of an insulating layer made of liquid crystal polymer film 11. The peel strength was evaluated using the method described above and found to be 0.91 (N / mm). Furthermore, the solder heat resistance at 288°C showed a bubble count of 0. Based on these results, the performance of the flexible copper-clad laminate was evaluated as good (○). The configuration of the insulating layer and metal foil (copper foil), the thermo-compression molding (heat and pressure) conditions, and the performance evaluation results are summarized in Table 2.

[0034] (Examples 2 to 5, Comparative Examples 1 to 5) The same insulating film LCP as in Example 1 was used as the liquid crystal polymer film for the insulating layer, and copper foils with the manufacturer names and grade names shown in Table 1 were used as the metal layers in Examples 2 to 5 and Comparative Examples 1 to 5. Flexible copper-clad laminates were produced under the same heating and pressing (thermocompression forming) conditions as in Example 1, except that the copper foil type, thickness (μm), surface roughness (Rz), and root-mean-square gradient (Sdq) were different. Table 2 summarizes the configurations of the insulating layer and metal (copper) foil, the thermocompression forming (heating and pressing) conditions, and the performance evaluation results of the obtained flexible metal-clad laminates.

[0035] [Table 2]

[0036] As can be seen from Table 2, in Examples 1 to 5, high peel strength values ​​of 0.75 to 0.91 N / mm were obtained. In addition, the solder heat resistance at 288°C was also 15,000 mm. 2 The number of bubbles within the area is 0 to 6. In contrast, Comparative Example 4, in which the root mean square gradient (Sdq) is 0.059 (less than 0.17), has a peel strength of 0.53 N / mm, and Comparative Example 5, in which (Sdq) is 0.024, has a peel strength as low as 0.13 N / mm. None of these examples satisfy the peel strength performance requirements, and the performance evaluation is poor (×). On the other hand, Comparative Example 1, in which the root mean square gradient (Sdq) is 1.001 (greater than 0.82), Comparative Example 2, in which it is 0.991, and Comparative Example 3, in which it is 1.738), all have higher peel strengths than the Examples, but in the solder heat resistance evaluation at 288°C, there are many bubbles, and they are poor in practical use, and the performance evaluation is poor (×). Therefore, it has been demonstrated that the present invention can provide a highly practical flexible copper-clad laminate that has excellent adhesion (peel resistance) between the insulating layer and the metal layer, and shows extremely few bubbles even in a solder heat resistance test at 288°C. [Industrial Applicability]

[0037] The flexible metal-clad laminate of the present invention has a root-mean-square gradient (Sdq) of 0.17 or more and 0.82 or less at the surface where the metal layer overlaps the insulating layer, resulting in a flexible metal-clad (copper-clad) laminate with improved peel strength between the metal layer and the insulating layer and improved solder heat resistance, and can be used to suitably produce flexible printed wiring boards that can operate in high frequency bands. Furthermore, the method for producing a flexible metal-clad laminate of the present invention can be used as a method for producing the flexible metal-clad laminate with good reproducibility, stability, and economy. [Explanation of symbols]

[0038] 10: Flexible metal-clad laminate (flexible copper-clad laminate) 11: Insulating film (liquid crystal polymer film) 12: Metal foil (copper foil) 20: Double belt press device 21: Upper drum 22: Lower drum 23,24: Endless Belt 25: Heat pressing (molding) equipment 30: Feeding section 31: Insulating film roll 32: Metal layer (metal foil) roll 40: Winding section

Claims

1. A flexible metal-clad laminate comprising an insulating layer made of a liquid crystal polymer and a metal layer laminated on one or both sides of the insulating layer, A flexible metal-clad laminate, wherein the surface of the metal layer overlapping the insulating layer has a root mean square gradient (Sdq) of 0.17 or more and 0.82 or less, as measured in accordance with ISO 25178-2:2021.

2. the peel strength between the metal layer and the insulating layer measured by Method A in accordance with JIS C6471:1995 is 0.60 N / mm or more; After pre-treatment at 105°C for 1 hour, the number of bubbles generated when the sample was floated in a solder bath at 288°C for 1 minute was 15,000 mm ２ There are 10 or fewer within an area of The flexible metal-clad laminate of claim 1 .

3. 3. The flexible metal-clad laminate of claim 1, wherein the metal layer is a copper foil.

4. A method for manufacturing a flexible metal-clad laminate, comprising: laminating an insulating layer made of a liquid crystal polymer and a metal layer on one or both sides of the insulating layer; and thermocompression molding the resulting laminate. A method for producing a flexible metal-clad laminate, wherein the root mean square gradient (Sdq) of the surface of the metal layer overlapping the insulating layer, measured in accordance with ISO 25178-2:2021, is 0.17 or more and 0.82 or less.

5. 5. The method for producing a flexible metal-clad laminate according to claim 4, wherein the heating temperature during the thermocompression molding is in the range of 15°C higher than the melting point of the liquid crystal polymer of the insulating layer to 30°C higher than the melting point.

6. The thermo-compression molding is performed by a double belt press device, The method for producing a flexible metal-clad laminate according to claim 4 or 5, wherein the pressure during the thermocompression molding is in the range of 0.5 to 5.5 MPa, and the heating and pressing time is in the range of 70 to 280 seconds.

7. The method for producing a flexible metal-clad laminate according to claim 4 or 5, wherein the metal layer is a copper foil.

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