Protective film and manufacturing method thereof

Abstract

The invention provides a protective film and a manufacturing method thereof. The protective film comprises an adhesive layer and a protective layer. The adhesive layer contains a resin having a chloride ion content of less than 50 ppm. The protective layer covers the adhesive layer. The protective layer is made of polyimide and inorganic filler. When the total weight of the protective layer is 100 parts by weight, the weight of the inorganic filler is 25-50 parts by weight. The resistance value measured by applying a voltage of 32 volts (V) to the protective film under the conditions that the temperature is 85 DEG C, the relative humidity is 85% and the time is 1000 hours is greater than 106 ohms (ohm, omega).

Description

Technical Field

[0001] The present invention relates to a sheet and a manufacturing method thereof, and particularly to a protective film and a manufacturing method thereof. Background Art

[0002] With the progress of circuit board manufacturing technology, fine pitch circuit boards with a fine line width of less than 35 micrometers or high density circuit boards with a line width / line pitch of less than 35 micrometers / 35 micrometers have been increasingly widely used. However, considering the applications of these circuit boards, how to provide a protective film that can have good insulation and appropriate concealment (e.g., it is not easy to directly observe or directly record the circuit layout of the circuit board to understand) has become a research topic. Summary of the Invention

[0003] The present invention is directed to a protective film that can be applied to electronic components.

[0004] According to an embodiment of the present invention, the protective film includes an adhesive layer and a protective layer. The adhesive layer contains a resin with a chloride ion content of less than 50 ppm. The protective layer covers the adhesive layer. The material of the protective layer includes polyimide and an inorganic filler. Based on the total weight of the protective layer being 100 parts by weight, the weight of the inorganic filler is 25 parts by weight to 50 parts by weight. The resistance value measured by applying a voltage of 32 V to the protective film under the conditions of a temperature of 85 °C, a relative humidity of 85%, and 1000 hours is greater than 10 6 ohm (Ω).

[0005] According to an embodiment of the present invention, the adhesive layer further includes an inorganic filler. Based on the total weight of the adhesive layer being 100 parts by weight, the weight of the inorganic filler is 5 parts by weight to 15 parts by weight.

[0006] According to an embodiment of the present invention, the resin includes polyester, hydrocarbon resin, polyimide, a mixture or copolymer of the above.

[0007] According to an embodiment of the present invention, the resistance value measured by applying a voltage of 32 V to the protective film under the conditions of a temperature of 85 °C, a relative humidity of 85%, and 1000 hours is greater than 10 8 Ω.

[0008] According to an embodiment of the present invention, the light transmittance of the protective film is less than or equal to 10%.

[0009] According to an embodiment of the present invention, the protective layer has a first surface in contact with the adhesive layer and a second surface opposite to the first surface, and the glossiness of the second surface is less than the glossiness of the first surface.

[0010] According to an embodiment of the present invention, the glossiness measured at a measurement angle of 60° of the second surface is less than 5 GU.

[0011] According to an embodiment of the present invention, the protective film further includes a first release layer. The adhesive layer is located between the first release layer and the protective layer.

[0012] According to an embodiment of the present invention, the protective film further includes a second release layer. The protective layer is located between the second release layer and the adhesive layer.

[0013] According to an embodiment of the present invention, a method for manufacturing a protective film includes the following steps: forming a protective layer on a release layer; and forming an adhesive layer on the protective layer. In the thickness direction of the protective layer and the adhesive layer, the light transmittance of the stacked protective layer and adhesive layer is less than or equal to 10%; and / or the material of the protective layer includes polyimide and inorganic filler, wherein based on 100 parts by weight of the total weight of the protective layer, the weight of the inorganic filler is 25 parts by weight to 50 parts by weight.

[0014] Based on the above, since the protective film can have low light transmittance or can blur the object covered by it, it can be applied to electronic components. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A AND Figure 2 A cross-sectional schematic view of a partial manufacturing method of a protective film according to an embodiment of the present invention;

[0016] Figure 1B A partial cross-sectional schematic view of a partial manufacturing method of a protective film according to an embodiment of the present invention;

[0017] Figure 3 、 Figure 4 OR Figure 5 A cross-sectional schematic view of a usage mode of a protective film according to an embodiment of the present invention.

[0018] DESCRIPTION OF REFERENCE NUMERALS:

[0019] 100: Protective film;

[0020] 110: Protective layer;

[0021] 111: First surface;

[0022] 112: Second surface;

[0023] 110T: Thickness;

[0024] 130: Adhesive layer;

[0025] 130T: Thickness;

[0026] 510: First release layer;

[0027] 520: The second release layer;

[0028] 521: Surface;

[0029] 800: Circuit board;

[0030] 810: Core layer;

[0031] 820: Circuit layer;

[0032] 830: Conductive via;

[0033] R1: Region. Detailed implementation manner

[0034] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0035] In the accompanying drawings, for clarity, the thickness of some components or film layers may be exaggerated. Throughout the specification, the same reference numerals denote the same components.

[0036] In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe the relationship of one component to another, as shown in the figures. It should be understood that the relative terms are intended to include different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one figure is flipped, the component described as on the "lower" side of other components will be oriented on the "upper" side of other components.

[0037] Figure 1A With Figure 2 A cross-sectional schematic view of a partial manufacturing method of a protective film according to an embodiment of the present invention. Figure 1B A partial cross-sectional schematic view of a partial manufacturing method of a protective film according to an embodiment of the present invention. Specifically, Figure 1B It may correspond to Figure 1A An enlarged view of the region R1 in.

[0038] Please refer to Figure 1A And Figure 1B to provide the second release layer 520.

[0039] In one embodiment, the second release layer 520 may have a rough surface, and the protective layer 110 formed thereon may have a corresponding roughness. For example, the surface 521 of the second release layer 520 may have a corresponding roughness by means of imprinting, scratching, grinding, etching or other suitable methods.

[0040] Please continue to refer to Figure 1A And Figure 1B, a protective layer 110 is formed on the second release layer 520.

[0041] In one embodiment, the protective layer 110 can be formed on the second release layer 520 by coating or other suitable means. For example, an appropriate resin composition can be coated on the second release layer 520; then, by appropriate means (such as heating, light irradiation, drying or standing), semi-curing or curing can be carried out to form the corresponding protective layer 110.

[0042] In one embodiment, the above coating methods can include but are not limited to: dipping coating, roll coating, blade coating, bar coating, slot-die coating or spraying coating.

[0043] In one embodiment, the thickness 110T of the protective layer 110 can be between about 3 micrometers (μm) and about 7 micrometers; for example, about 5 micrometers.

[0044] In one embodiment, since the protective layer 110 is formed by coating. Therefore, the outer surface of the protective layer 110 can have a corresponding smooth surface. For example, the first surface 111 of the protective layer 110 can be a smooth surface.

[0045] In one embodiment, since the protective layer 110 can be directly formed on the rough surface of the second release layer 520. Therefore, the protective layer 110 can have a corresponding rough surface. For example, the second surface 112 of the protective layer 110 can be a rough surface.

[0046] In one embodiment, taking the arithmetic mean deviation (Ra) of the corresponding surface as the comparison benchmark for roughness, the roughness of the second surface 112 is greater than that of the first surface 111.

[0047] In one embodiment, the roughness of the corresponding surface can be defined by glossiness. And, if the protective layer 110 is formed by a second release layer 520 (which can be referred to as: rough release film) having a corresponding rough surface, the glossiness of the second surface 112 of the protective layer 110 can correspond to the glossiness of the rough surface of the second release layer 520. In one embodiment, the glossiness of the second surface 112 of the protective layer 110 may be slightly less than the glossiness of the rough surface of the second release layer 520, and the possible reason is that subsequent processing may be required during the formation of the protective layer 110 and / or the protective layer 110 may not be in complete contact with the rough surface of the second release layer 520 at the microscopic level during the formation process. Taking the second release layer 520 having a rough surface with a glossiness of 5 GU (gloss unit) as an example, the glossiness of the corresponding formed protective layer 110 may be 2 GU. The foregoing glossiness can be measured at a measurement angle of 60°.

[0048] In one embodiment, the glossiness of the second surface 112 is less than the glossiness of the first surface 111.

[0049] In one embodiment, the material for forming the protective layer 110 may include polyimide (PI) resin and inorganic filler. Based on the total weight of the protective layer 110 being 100 parts by weight, the weight of the inorganic filler for the protective layer 110 is about 25 parts by weight to about 50 parts by weight. The inorganic filler can improve the light scattering chromaticity of the protective layer 110 or reduce the visible light transmittance of the protective layer 110 at least in the range of visible light.

[0050] In one embodiment, the inorganic filler for the protective layer 110 may include titanium oxide particles, carbon black particles, iron oxide particles or a mixture of the above. In one embodiment, based on the total weight of the protective layer 110 being 100 parts by weight, the weight of the inorganic filler for the protective layer 110 is about 25 parts by weight to about 50 parts by weight.

[0051] In one embodiment, compared with the method of reducing light transmittance with organic pigments, the method of adding inorganic fillers can improve the hardness or wear resistance of the protective layer 110, and thus can improve the protective power of the protective layer 110. However, it should be noted that the present invention does not completely exclude the possibility of adding organic pigments.

[0052] Please refer to Figure 2 , an adhesive layer 130 is formed on the first surface 111 of the protective layer 110. The adhesive layer 130 can be formed by an appropriate method (detailed as follows).

[0053] In one embodiment, the thickness 130T of the adhesive layer 130 can be between about 5 microns and about 25 microns; for example: about 20 microns.

[0054] In one embodiment, the resin composition for forming the adhesive layer 130 may include a high molecular polymer. The aforementioned high molecular polymer may include polyester, hydrocarbon resin, polyimide (PI), mixtures or copolymers thereof.

[0055] In one embodiment, the resin composition for forming the adhesive layer 130 may further include an inorganic filler. Based on 100 parts by weight of the total weight of the adhesive layer 130, the weight of the inorganic filler for the adhesive layer 130 is 5 to 15 parts by weight; for example: about 5 parts by weight, about 10 parts by weight, about 15 parts by weight, or between the two values mentioned above. If the proportion of the inorganic filler is too high (such as: greater than 15 parts by weight; even, greater than or equal to 20 parts by weight), the adhesiveness may be reduced.

[0056] In one embodiment, the inorganic filler for the adhesive layer 130 may include titanium oxide particles, carbon black particles, iron oxide particles, or mixtures thereof.

[0057] In one embodiment, the material for forming the adhesive layer 130 basically does not include epoxy resin or its derivatives. Because halogen ions (such as chloride ions) cannot be completely removed during the synthesis process of epoxy resin, the resin itself contains a relatively high concentration of halogen ions, which may have an electrical impact on the manufactured protective film 100 and affect the applicability of the protective film 100. For example, epoxy resin may have a relatively low ability to resist ion migration, resulting in a relatively low resistance value and relatively low insulation.

[0058] In one embodiment, by mass, the concentration of halogen ions (such as chloride ions) in the adhesive layer 130 may be less than 300 ppm; for example: less than 50 ppm.

[0059] In one embodiment, the adhesive layer 130 can be directly formed on the protective layer 110 by coating or other suitable methods.

[0060] In one embodiment, the adhesive layer 130 can be first formed on the protective layer 110; then, the release layer 510 can be formed or covered on the adhesive layer 130 formed on the protective layer 110.

[0061] In one embodiment, the adhesive layer 130 can be first formed on the release layer 510; then, with the adhesive layer 130 facing the protective layer 110, the adhesive layer 130 is sandwiched and bonded between the protective layer 110 and the release layer 510.

[0062] Through the above method, the manufacturing of the protective film 100 of this embodiment can be generally completed, but the manufacturing method of the protective film 100 of this embodiment is not limited to the above method.

[0063] Please refer to Figure 2 , the protective film 100 includes an adhesive layer 130 and a protective layer 110. The protective layer 110 covers the adhesive layer 130.

[0064] In one embodiment, the light transmittance of the stacked adhesive layer 130 and protective layer 110 in the protective film 100 is less than or equal to 10%.

[0065] In one embodiment, the material of the protective layer 110 includes polyimide and inorganic filler. Based on the total weight of the protective layer 110 being 100 parts by weight, the weight of the inorganic filler is 25 to 50 parts by weight; for example: about 25 parts by weight, about 35 parts by weight, about 50 parts by weight, or between the two values mentioned above.

[0066] In one embodiment, the protective layer 110 has a first surface 111 and a second surface 112. The second surface 112 is opposite to the first surface 111. The first surface 111 directly contacts the adhesive layer 130. In one embodiment, the glossiness of the second surface 112 is less than that of the first surface 111.

[0067] In one embodiment, the material of the adhesive layer 130 includes polyester, hydrocarbon resin, polyimide, the above mixtures or copolymers. In one embodiment, the material of the adhesive layer 130 may further include inorganic filler, and based on the total weight of the adhesive layer 130 being 100 parts by weight, the weight of the inorganic filler is 5 to 15 parts by weight.

[0068] In one embodiment, at a measurement angle of 60°, the second surface 112 of the protective layer 110 in the protective film 100 is measured, and its glossiness is less than 5 GU; for example: even less than or equal to about 2 GU.

[0069] In one embodiment, the adhesive layer 130 (with a thickness of about 20 microns) and the protective layer 110 (with a thickness of about 5 microns) are measured integrally as a sheet (i.e., not including any release layer mentioned later). Under the conditions of a temperature of 85 °C and a relative humidity of 85 RH for 1000 hours (which can be counted as: 85 / 85 1000 hr), the corresponding resistance is measured with a bias voltage of 32 volts for a temperature and humidity bias test, and the resistance value is greater than one million ohms (10 6 Ω).

[0070] In one embodiment, on the premise that the resin contained in the adhesive layer 130 is polyester, hydrocarbon resin, polyimide, a mixture or copolymer thereof, the adhesive layer 130 (with a thickness of about 20 microns) and the protective layer 110 (with a thickness of about 5 microns) are measured integrally as a sheet (i.e., not including any release layers described later). Under the conditions of a temperature of 85 °C and a relative humidity of 85RH for 1000 hours (which can be denoted as: 85 / 85 1000hr), a temperature and humidity bias test is conducted by measuring the corresponding resistance with a bias voltage of 32 volts (volt, V), and the resistance value is greater than one hundred million ohms (10 8 Ω).

[0071] In one embodiment, the adhesive layer 130 (with a thickness of about 20 microns) and the protective layer 110 (with a thickness of about 5 microns) are measured integrally as a sheet (i.e., not including any release layers described later), and its visible light transmittance is less than or equal to about 10%; for example: even less than or equal to about 9%; for example: even less than or equal to about 7%; for example: even less than or equal to about 5%; for example: even less than or equal to about 3%; for example: even less than or equal to about 0.5%; for example: even less than or equal to about 0.1%.

[0072] In one embodiment, the protective film 100 may further include a first release layer 510. The adhesive layer 130 is located between the first release layer 510 and the protective layer 110. In an exemplary usage mode, the first release layer 510 of the protective film 100 can be torn off for use. That is to say, the protective film 100 including the first release layer 510 can be one product state, and the protective film 100 without the first release layer 510 can be one usage state.

[0073] In one embodiment, the protective film 100 may further include a second release layer 520. The protective layer 110 is located between the second release layer 520 and the adhesive layer 130. In an exemplary usage mode, the second release layer 520 of the protective film 100 can be torn off for use. That is to say, the protective film 100 including the second release layer 520 can be one product state, and the protective film 100 without the second release layer 520 can be one usage state.

[0074] Figure 3 、 Figure 4 or Figure 5 A cross-sectional schematic diagram of a usage mode of a protective film 100 according to an embodiment of the present invention. It should be noted that the following description and the corresponding drawings are only for an exemplary description of the usage mode of the protective film 100, and the usage mode of the protective film 100 is not limited thereto.

[0075] Please refer to Figure 3, in one embodiment, the first release layer 510 (if any) can be separated from the adhesive layer 130 first to expose the outer surface of the adhesive layer 130 to the outside for use.

[0076] Please refer to Figure 4 , in one embodiment, the adhesive layer 130 with one surface exposed to the outside can be attached to a suitable object.

[0077] In one embodiment, the adhesive layer 130 of the protective film 100 can be attached to an electronic component.

[0078] In one embodiment, the aforementioned electronic component is, for example, a circuit board 800. The circuit board 800 may include a corresponding core layer 810 and a circuit layer 820 located on the core layer 810. The circuit layout of the circuit layer 820 can be adjusted according to design requirements and is not limited in the present invention.

[0079] In one embodiment, corresponding circuit layers 820 can be provided on opposite sides of the core layer 810. Corresponding circuits in the circuit layers 820 on the opposite sides can be electrically connected by conductive vias 830 penetrating the core layer 810.

[0080] In one embodiment, since the protective film 100 has the characteristic of low light transmittance, the possibility of directly observing or directly recording and understanding the circuit layout of the circuit layer 820 can be reduced.

[0081] Please refer to Figure 5 , in one embodiment, after the adhesive layer 130 is attached to a suitable object, the second release layer 520 (if any) can be separated from the protective layer 110 to expose the second surface 112 of the protective layer 110 to the outside for use.

[0082] In one embodiment, since the second surface 112 of the protective film 100 is a rough surface, the pattern of the covered object can be blurred. For example, due to the aforementioned blurring, the possibility of directly observing or directly recording and understanding the circuit layout of the circuit layer 820 can be reduced.

[0083] [Application Examples of Protective Film]

[0084] In the following examples, the present invention will be specifically described, but the present invention is not limited by the following examples at all.

[0085] The protective films in the following examples were measured for optical activity (such as light transmittance or glossiness) in a state including a stacked adhesive layer and a protective layer (i.e., without corresponding release layers). And the protective films were pasted on the same or similar circuit boards (the same or similar to Figure 5Perform corresponding electrical measurements as shown. The aforementioned circuit board is at least a high density circuit board or a fine pitch circuit board with a line width of about 20 microns and a line pitch of about 20 microns (which can be denoted as: L / S = 20 / 20).

[0086] The structures (such as thickness) of the protective films of each example are basically the same or similar, with the difference being the material composition. Specifically, the thickness of the adhesive layer in the protective film of each example is basically 20 microns, and the thickness of the protective layer in the protective film of each example is basically 5 microns. Moreover, the adhesive layer and the protective layer in the protective film of each example may differ in material composition. Taking Example 8 as an example, the resin composition of its adhesive layer is polyester. Based on the total weight of the adhesive layer being 100 parts by weight, the weight of the inorganic filler used in the adhesive layer is 5 parts by weight, and the resin composition of its protective layer is polyimide (PI). Based on the total weight of the protective layer being 100 parts by weight, the weight of the inorganic filler used in the protective layer is 25 parts by weight. Taking Example 19 as an example, the resin composition of its adhesive layer is hydrocarbon resin. Based on the total weight of the adhesive layer being 100 parts by weight, the weight of the inorganic filler used in the adhesive layer is 5 parts by weight; the resin composition of its protective layer is polyimide (PI). Based on the total weight of the protective layer being 100 parts by weight, the weight of the inorganic filler used in the protective layer is 35 parts by weight.

[0087] The materials of the protective films of each example and the corresponding measurement results are shown in [Table 1]. Moreover, the corresponding inorganic filler in [Table 1] is titanium oxide particles, and its unit is parts by weight (wt%).

[0088] [Table 1]

[0089]

[0090] Electrical measurement: Conduct a Temperature Humidity Bias Test (THB) by measuring the corresponding resistance with a bias voltage of 32 volts for 1000 hours under the conditions of a temperature of 85°C and a relative humidity of 85RH (which can be denoted as: 85 / 85 1000hr). If the resistance value is greater than one million ohms (10 6 Ω), then the electrical test is passed (which can be denoted as: pass). On the contrary, if the resistance value is less than or equal to one million ohms (10 6 Ω), then the electrical test is not passed (which can be denoted as: NG).

[0091] Optical rotation measurement: Using a commercial gloss meter, measure the gloss of the adhesive layer and the protective layer of the stack at a measurement angle of about 60° on the outer surface of the protective layer (e.g., the aforementioned second surface).

[0092] Optical rotation measurement: Using a commercial optical transmittance meter, measure the transmittance of the adhesive layer and the protective layer of the stack in the visible light range.

[0093] For Examples 2 to 10, Examples 12 to 15, and Examples 17 to 23 in [Table 1], due to the addition of inorganic fillers in the material of the protective layer and / or the material of the adhesive layer, the protective film can have a lower light transmittance (e.g., the light transmittance is less than or equal to about 10%).

[0094] As shown in Examples 1 to 20 in [Table 1], since the adhesive layer in the protective film uses polyester, hydrocarbon resin, or polyimide (PI) as the main material of the corresponding adhesive layer, and the ion content (e.g., chloride ion content) is less than 50 ppm. Therefore, the protective film can have electrical properties suitable for insulation (e.g., the resistance value is greater than 10 6 Ω).

[0095] As shown in Examples 1 to 4, Examples 8 to 14, Examples 16 to 19, and Examples 21 to 22 in [Table 1], due to the use of the corresponding rough release layer (e.g., a rough release layer with a gloss less than or equal to 5 GU) in the manufacturing process of the protective film. Therefore, the protective film can have a lower gloss (e.g., the gloss is less than 5 GU).

[0096] As shown in Examples 2 to 4, Examples 8 to 10, Examples 12 to 14, and Examples 17 to 19 in [Table 1], since the adhesive layer in the protective film uses polyester, hydrocarbon resin, or polyimide (PI) as the main material of the corresponding adhesive layer, inorganic fillers are added to the material of the protective layer and / or the material of the adhesive layer, and the corresponding rough release layer (e.g., a rough release layer with a gloss less than or equal to about 5 GU) is used. Therefore, the protective film can have a lower light transmittance (e.g., the light transmittance is less than or equal to about 10%), a lower gloss (e.g., the gloss is less than or equal to about 5 GU), and electrical properties suitable for insulation (e.g., the resistance value is greater than 10 6 Ω).

[0097] In summary, the protective film of the present invention can have a low light transmittance or can obscure the object covered by it, and thus can be applied to electronic components.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A protective film, characterized in that: include: An adhesive layer comprising a resin having a chloride ion content of less than 50 ppm; as well as A protective layer is covered on the adhesive layer, and the material of the protective layer includes: Polyimide; as well as A first inorganic filler, wherein the weight of the first inorganic filler is 25 parts by weight to 50 parts by weight based on 100 parts by weight of the total weight of the protective layer; The protective film has a resistance value greater than 10 when a voltage of 32 volts is applied under the conditions of 85°C, 85% relative humidity, and 1000 hours. 6 ohm.

2. The protective film according to claim 1, characterized in that: The adhesive layer further comprises a second inorganic filler. Based on 100 parts by weight of the total weight of the adhesive layer, the weight of the second inorganic filler is 5 parts by weight to 15 parts by weight.

3. The protective film according to claim 1, characterized in that: The resin includes polyester, hydrocarbon resin, polyimide, or a mixture or copolymer thereof.

4. The protective film according to claim 3, characterized in that: The protective film has a resistance value greater than 10 when a voltage of 32 volts is applied under the conditions of 85°C, 85% relative humidity, and 1000 hours. 8 ohm.

5. The protective film according to claim 1 or 2, characterized in that: The light transmittance of the protective film is less than or equal to 10%.

6. The protective film according to claim 1, characterized in that: The protection layer has a first surface contacting the adhesive layer and a second surface opposite to the first surface, and the glossiness of the second surface is lower than that of the first surface.

7. The protective film according to claim 6, characterized in that: The glossiness of the second surface measured at a measuring angle of 60° is less than 5GU.

8. The protective film according to claim 1, characterized in that: Also includes: A first release layer, wherein the adhesive layer is located between the first release layer and the protective layer.

9. The protective film according to claim 1, characterized in that: Also includes: A second release layer, wherein the protective layer is located between the second release layer and the adhesive layer.

10. A method for manufacturing a protective film, characterized in that: include: forming a protective layer on the release layer; as well as An adhesive layer is formed on the protective layer, wherein: In the thickness direction of the protective layer and the adhesive layer, the light transmittance of the stacked protective layer and the adhesive layer is less than or equal to 10%; and / or The material of the protective layer includes polyimide and inorganic filler, wherein the weight of the inorganic filler is 25 parts by weight to 50 parts by weight based on 100 parts by weight of the total weight of the protective layer.

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