Electromagnetic shielding film and circuit board

Abstract

The present application belongs to the technical field of electromagnetic shielding functional materials, and specifically relates to an electromagnetic shielding film and a circuit board. The electromagnetic shielding film comprises an insulating layer and a shielding layer, which are arranged in a stacked manner, wherein after the electromagnetic shielding film is press-fitted on a circuit board body, a dyne value of a surface on the side of the insulating layer that is away from the shielding layer is greater than or equal to 30 mN / m; and a contact angle θ of a surface on the side of the insulating layer that is away from the shielding layer is less than or equal to 130 degrees. By means of numerous studies, the inventor has found that the technical problem of screen printing on a surface of an electromagnetic shielding film being unstable is accidentally solved by means of setting a corresponding contact angle (an infiltration angle) and a dyne value, the screen printing of the shielding film meeting the conditions of the technical solution in the present application has relatively high stability, and no blur is caused to the screen printing on the surface of the shielding film which has been subjected to high-temperature press fitting; and the thickness of the screen printing is relatively uniform, and the color difference deviation is relatively small. Moreover, the screen printing is firmly bonded with a bonding layer on a surface of an insulating layer and thus does not easily fall off, thereby facilitating processing in subsequent processes of a circuit board.

Description

Electromagnetic shielding film and circuit board

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 21, 2023, with application number 202311558226.9 and invention name “An electromagnetic shielding film and circuit board”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the technical field of electromagnetic shielding functional materials, and specifically relates to an electromagnetic shielding film and a circuit board. Background Art

[0004] With the increasing number of integrated components on circuit boards and the need for process traceability, screen printing is becoming necessary. This facilitates component identification and orientation, enhances brand and product recognition, and prevents misoperation or misconnection. Screen printing can also be used to trace the source of components and improve product quality control. Shielding film, as it is attached to the outer surface of the circuit board, also needs to meet the requirements for screen printing.

[0005] The existing screen printing process on the shielding film suffers from printing instability. After high-temperature lamination to the circuit board, the printed content on the shielding film becomes blurred or even disappears, defeating the purpose of screen printing. Furthermore, the screen printing on the shielding film's surface may not adhere securely to the adhesive layer and easily fall off, hindering subsequent processing and repair of the circuit board.

[0006] Although there are a large number of improved methods for overcoming the above technical problems of shielding films, it is still difficult to meet the requirements of screen printing in the market.

[0007] Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present application is to overcome the defect of relatively poor silk screen printing performance of electromagnetic shielding films in the prior art, thereby providing an electromagnetic shielding film and a circuit board.

[0009] To this end, this application provides the following technical solutions:

[0010] The present application provides an electromagnetic shielding film, comprising an insulating layer and a shielding layer arranged in a stacked manner. After the electromagnetic shielding film is pressed onto a circuit board body, the dyne value of the surface of the insulating layer away from the shielding layer is greater than or equal to 30 mN / m; the water drop angle θ of the surface of the insulating layer away from the shielding layer is less than or equal to 130°.

[0011] After extensive research, the inventors discovered that setting a corresponding water drop angle (wetting angle) and dyne value unexpectedly solved the technical problem of unstable silk screen printing on the surface of electromagnetic shielding film. The specific mechanism of action is currently unclear, but the technical effect was unexpectedly achieved. After silk screen printing on the surface of the electromagnetic shielding film, the silk screen is extremely stable, and even after high-temperature testing, the electromagnetic shielding film can still meet market requirements. The silk screen content will not fall off, or the printing will not be blurred or missing. Problems such as silk screen misalignment, uneven silk screen thickness, and color deviation are effectively solved.

[0012] The dyne value of the surface of the insulating layer away from the shielding layer is 30-44mN / m. Optionally, the dyne value can be any one value such as 30mN / m, 32mN / m, 34mN / m, 36mN / m, 38mN / m, 40mN / m, 42mN / m, 44mN / m, or an interval consisting of any two values. The size of the dyne value reflects the surface tension of the insulating layer and is an important factor affecting silk screen printing. When the dyne value does not meet the requirements, the silk screen printing will show more serious unevenness, blurring and color deviation. That is, if the dyne value is too small, it will be difficult to silk screen and the color deviation will be serious; if the dyne value is too large, the silk screen printing will be blurred and the color deviation will be serious.

[0013] The water drop angle θ on the surface of the insulating layer away from the shielding layer is less than or equal to 130°. Optionally, the water drop angle can be any value such as 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, or a range consisting of any two values. Optionally, when the water drop angle satisfies 70°≤θ≤90°, screen printing on the surface has better uniformity and stability.

[0014] The dyne value reflects the surface tension of the insulation layer and is a key factor affecting screen printing. If the dyne value does not meet the required level, the screen print will be severely uneven, blurry, and have color deviations. If the dyne value is too low, screen printing will be difficult and color deviations will be severe; if the dyne value is too high, the screen print will be blurry and have color deviations.

[0015] Optionally, on a side of the insulating layer away from the shielding layer, the error between the maximum and minimum dyne values ​​within a 5 cm length is less than or equal to 4 mN / m. When the dyne value error is controlled within this range, screen printing on the surface is more uniform and stable, and the probability of expansion and contraction after screen printing is reduced.

[0016] Optionally, on a side of the insulating layer away from the shielding layer, the error rate of the water drop angle within an area of ​​4 square centimeters is less than or equal to 20%. Similarly, on the basis of meeting the above conditions, when the error range of the water drop angle is controlled within the above range, the uniformity and stability after silk screen printing are further improved.

[0017] Optionally, the surface roughness Rz of the insulating layer on a side away from the shielding layer is 1.8-7.0 μm. Optionally, the roughness value Rz can be any one of 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.8 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 6.0 μm, 7.0 μm, or a range consisting of any two values. In addition to affecting the silk screen printing effect, the appropriate roughness allows the surface of the insulating layer to evenly absorb and retain a certain amount of silk screen ink, thereby improving the silk screen printing effect and ensuring good adhesion after silk screen printing.

[0018] And / or, the error rate of surface roughness Rz within an area of ​​4 square centimeters on the side of the insulating layer away from the shielding layer is less than or equal to 15%. When the error range of the roughness is controlled within the above range, the screen printing on the surface has good uniformity and stability, and has good adhesion after screen printing.

[0019] Optionally, the adhesive force of the insulating layer on the side away from the shielding layer is 0.2-0.7 N / cm. Optionally, the adhesive force value can be any one of 0.2 N / cm, 0.3 N / cm, 0.4 N / cm, 0.5 N / cm, 0.6 N / cm, 0.7 N / cm, or an interval consisting of any two values.

[0020] Optionally, the main resin of the insulating layer includes at least one of phenolic resins, alkyd resins, amino resins, polyester resins, polyurethane resins, acrylic resins, vinyl resins, fluororesins, cyanate esters, polystyrenes, vinyl acetates, polyamides, rubbers, carbamates, melamines, BT resins, ABF resins, polypropylenes, polyphenylene sulfides, polyethylene terephthalates, epoxies or polyimides.

[0021] Optionally, the insulating layer has at least two layers.

[0022] Optionally, the outermost layer of the insulating layer is a polyimide layer.

[0023] Optionally, the weight of the polyimide layer accounts for 20%-80% of the total weight of the insulating layer. Alternatively, the weight percentage of the polyimide layer can be any one of 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range consisting of two values. A weight percentage of the polyimide layer within the aforementioned range ensures the shielding film has excellent high-temperature resistance, while also increasing the rigidity of the insulating layer, improving the stability of the silk screen printing, and reducing silk screen misalignment and deformation.

[0024] In the present application, the shielding layer includes one or more of a metal shielding layer, a carbon nanotube shielding layer, a ferrite shielding layer and a graphene shielding layer.

[0025] Optionally, the metal is selected from any one or any combination of any two or more of the following metals: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, tin, palladium, copper, silver, and gold.

[0026] The present application also provides a circuit board, the circuit board comprising a circuit board body and the electromagnetic shielding film as described above;

[0027] Optionally, the electromagnetic shielding film is pressed onto the circuit board body via an adhesive film layer.

[0028] The technical solution of this application has the following advantages:

[0029] After extensive research, the inventors of the electromagnetic shielding film provided by this application have discovered that setting a corresponding water drop angle (wetting angle) and dyne value unexpectedly solves the technical problem of unstable silk screen printing on the electromagnetic shielding film surface. The silk screen printing of the shielding film that meets the requirements of the technical solution of this application is highly stable, and the silk screen printing on the shielding film surface after high-temperature lamination will not be blurred. The silk screen printing thickness is relatively uniform, with minimal color deviation. Moreover, the adhesive layer adheres firmly to the surface of the insulating layer and is not easily detached, facilitating subsequent processing of the circuit board.

[0030] The electromagnetic shielding film provided in this application can further improve the adhesion between the silk screen and the insulating layer and prevent it from falling off by limiting the roughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] FIG1 is a schematic structural diagram of the electromagnetic shielding film provided in Example 1 of the present application;

[0033] Reference numerals: 1. polyimide layer; 2. insulating layer; 3. shielding layer; 4. adhesive film layer. DETAILED DESCRIPTION

[0034] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0035] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0036] In the following embodiments, the performance parameter layer testing method is:

[0037] The dyne value test method is: wipe the surface of the insulating layer of the shielding film clean, and draw lines on its surface with different types of dyne pens, and determine the dyne value according to the changes in the drawing results.

[0038] The test method for the water drop angle is: drop 3 microliters of water on the surface of the insulating layer of the shielding film and measure the angle with an instrument (see the test standard GB / T30693-2014).

[0039] The roughness test method is: use an instrument to measure the roughness on the surface of the insulating layer of the shielding film (see the test standard GB / T10610-2009).

[0040] The bonding strength test method is to use 3M tape for bonding and use a tensile testing machine to test in a 90° direction.

[0041] The error rate value (water drop angle or roughness) is calculated as W = ((θmax-θmin) / θmin) × 100%.

[0042] Example 1

[0043] This embodiment provides an electromagnetic shielding film, the structural diagram of which is shown in FIG1 , comprising an insulating layer 2 , a shielding layer 3 and an adhesive film layer 4 arranged in layers, wherein the outermost layer of the insulating layer is a polyimide layer 1 .

[0044] The dyne value of the insulating layer's surface away from the shielding layer is 44 mN / m, with a 3 mN / m error between the maximum and minimum dyne values ​​within a 5 cm length. The water drop angle is 72°, with a 10% error rate within a 4 square centimeter area. The roughness Rz is 2.0 μm, with a 10% error rate within a 4 square centimeter area. The adhesive strength is 0.4 N / cm. The main resin material of the insulating layer is polyimide and polyester resin, with the weight of the polyimide accounting for 20% of the total weight of the insulating layer. The shielding layer is made of copper and has a thickness of 3 μm. The adhesive film layer is made of acrylic resin and has a thickness of 5 μm.

[0045] Example 2

[0046] This embodiment provides an electromagnetic shielding film, the structural diagram of which is shown in FIG1 , comprising an insulating layer 2 , a shielding layer 3 and an adhesive film layer 4 arranged in layers, wherein the outermost layer of the insulating layer is a polyimide layer 1 .

[0047] The dyne value of the insulating layer's surface away from the shielding layer is 30 mN / m, with a 4 mN / m error between the maximum and minimum dyne values ​​within a 5 cm length. The water drop angle is 130°, with a 10% error rate within a 4 square centimeter area. The roughness Rz is 5.0 μm, with a 10% error rate within a 4 square centimeter area. The adhesive strength is 0.5 N / cm. The insulating layer is made of polyimide and polyester resin, with the polyimide layer accounting for 30% of the total weight of the insulating layer. The shielding layer is made of copper and has a thickness of 3 μm. The adhesive film layer is made of polyurethane resin and has a thickness of 5 μm.

[0048] Example 3

[0049] This embodiment provides an electromagnetic shielding film, the structural diagram of which is shown in FIG1 , comprising an insulating layer 2 , a shielding layer 3 and an adhesive film layer 4 arranged in layers, wherein the outermost layer of the insulating layer is a polyimide layer 1 .

[0050] The dyne value of the insulating layer's surface away from the shielding layer is 36 mN / m, with a 4 mN / m error between the maximum and minimum dyne values ​​within a 5 cm length. The water drop angle is 81°, with a 10% error rate within a 4 square centimeter area. The roughness Rz is 4.3 μm, with a 10% error rate within a 4 square centimeter area. The adhesive strength is 0.6 N / cm. The insulating layer is made of polyimide and alkyd resin, with the polyimide layer accounting for 20% of the total weight of the insulating layer. The shielding layer is made of copper and is 3 μm thick. The adhesive film layer is made of acrylic resin and is 5 μm thick.

[0051] Example 4

[0052] This embodiment provides an electromagnetic shielding film, the structural diagram of which is shown in FIG1 , comprising an insulating layer 2 , a shielding layer 3 and an adhesive film layer 4 arranged in layers, wherein the outermost layer of the insulating layer is a polyimide layer 1 .

[0053] The dyne value of the insulating layer's surface away from the shielding layer is 34 mN / m, with a 3 mN / m error between the maximum and minimum dyne values ​​within a 5 cm length. The water drop angle is 90°, with a 10% error rate within a 4 square centimeter area. The roughness Rz is 6.5 μm, with a 10% error rate within a 4 square centimeter area. The adhesive strength is 0.6 N / cm. The insulating layer is made of polyimide and alkyd resin, with the polyimide layer accounting for 30% of the total weight of the insulating layer. The shielding layer is made of copper-nickel alloy and is 3 μm thick. The adhesive film layer is made of polyurethane resin and is 5 μm thick.

[0054] Comparative Example 1

[0055] This comparative example provides an electromagnetic shielding film, the structural diagram of which is shown in FIG1 , comprising an insulating layer 2 , a shielding layer 3 and an adhesive film layer 4 arranged in layers, wherein the outermost layer of the insulating layer is a polyimide layer 1 .

[0056] The dyne value of the insulating layer's surface away from the shielding layer is 28 mN / m, with a 10 mN / m error between the maximum and minimum dyne values ​​within a 5 cm length. The water drop angle is 140°, with a 10% error rate within a 4 square centimeter area. The surface roughness Rz is 8.3 μm, with a 10% error rate within a 4 square centimeter area. The adhesive strength is 0.9 N / cm. The insulating layer is made of polyimide and polyester resin, with the polyimide layer accounting for 10% of the total weight of the insulating layer. The shielding layer is made of copper and has a thickness of 3 μm. The adhesive film layer is made of acrylic resin and has a thickness of 5 μm.

[0057] Test Case

[0058] The electromagnetic shielding films provided in each embodiment and comparative example were tested for performance, and a circuit board was made with a circuit board substrate. The specific steps were as follows: the shielding film was pressed under a certain pressure and temperature (the pressure was set to 120 kg / cm 2 , press at 185℃ for 3 minutes) on the surface of the circuit substrate (i.e. the circuit board body) and screen print; test the screen printing adhesion of the shielding film (rub 50 times with an eraser after screen printing), screen printing stability (put it at high temperature (66℃) for 48 hours and then cool it to room temperature after screen printing), clarity, etc. The specific test results are shown in the table below:

[0059] Table 1

[0060] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications derived therefrom remain within the scope of protection of this application.

Claims

1. An electromagnetic shielding film, characterized in that: It comprises an insulating layer and a shielding layer which are stacked. After the electromagnetic shielding film is pressed onto the circuit board body, the dyne value of the surface of the insulating layer away from the shielding layer is greater than or equal to 30mN / m; and the water drop angle θ of the surface of the insulating layer away from the shielding layer is less than or equal to 130°.

2. The electromagnetic shielding film according to claim 1, characterized in that The dyne value of the surface of the insulating layer away from the shielding layer is 30-44 mN / m.

3. The electromagnetic shielding film according to claim 1 or 2, characterized in that: On the side of the insulating layer away from the shielding layer, an error between a maximum dyne value and a minimum dyne value within a length range of 5 cm is less than or equal to 4 mN / m.

4. The electromagnetic shielding film according to claim 1 or 2, characterized in that: On the side of the insulating layer away from the shielding layer, the error rate of the water drop angle within an area of ​​4 square centimeters is less than or equal to 20%.

5. The electromagnetic shielding film according to claim 1 or 2, characterized in that: The roughness Rz of the surface of the insulating layer away from the shielding layer is 1.8-7.0 μm; And / or, the error rate of the surface roughness Rz within an area of ​​4 square centimeters on the side of the insulating layer away from the shielding layer is less than or equal to 15%.

6. The electromagnetic shielding film according to claim 1 or 2, characterized in that: The bonding force of the insulating layer on the side away from the shielding layer is 0.2-0.7 N / cm.

7. The electromagnetic shielding film according to claim 1 or 2, characterized in that: The main resin of the insulating layer includes at least one of phenolic resins, alkyd resins, amino resins, polyester resins, polyurethane resins, acrylic resins, vinyl resins, fluororesins, cyanate esters, polystyrenes, vinyl acetates, polyamides, rubbers, carbamates, melamines, BT resins, ABF resins, polypropylenes, polyphenylene sulfides, polyethylene terephthalates, epoxies or polyimides.

8. The electromagnetic shielding film according to claim 1 or 2, characterized in that: The insulating layer has at least two layers.

9. The electromagnetic shielding film according to claim 8, characterized in that The outermost layer of the insulating layer is a polyimide layer; Optionally, the weight of the polyimide layer accounts for 20%-80% of the total weight of the entire insulating layer.

10. A circuit board, characterized in that: The circuit board comprises a circuit board body and an electromagnetic shielding film as claimed in any one of claims 1 to 9; Optionally, the electromagnetic shielding film is pressed onto the circuit board body via an adhesive film layer.

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