Electromagnetic shielding film and circuit board

Abstract

The invention relates to the technical field of electronics, and discloses an electromagnetic shielding film and a circuit board. A shielding layer; a bonding layer; the substrate layer, the shielding layer and the bonding layer are stacked; the tensile strength change rate delta sigma t of the electromagnetic shielding films which are arranged in an oppositely-pasted mode before and after being soaked in saline water meets the condition that delta sigma t is smaller than or equal to 25%; wherein delta sigma < t > = sigma < 1 >-sigma < 2 > / sigma < 1 >, sigma < 1 > represents the tensile strength of the oppositely-pasted electromagnetic shielding films before soaking, and sigma < 2 > represents the tensile strength of the oppositely-pasted electromagnetic shielding films after soaking. When the tensile strength change rate delta sigma t of the oppositely-pasted electromagnetic shielding film before and after being soaked in saline water is smaller than or equal to 25%, the electromagnetic shielding film has durability and stability, is slightly influenced by external environment change, and also has a good electromagnetic shielding effect and high adaptability.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and particularly relates to an electromagnetic shielding film and a circuit board. Background Art

[0002] An electromagnetic shielding film is a key material for reducing electromagnetic interference, and is widely used in various electronic devices such as mobile phones and computers. With the rapid development of folding screens, the requirements for electromagnetic shielding films are getting higher and higher. In order to enable a folding mobile phone to operate normally and avoid electromagnetic interference generated by the outside and itself, it is necessary to apply an electromagnetic shielding film on the surface of electronic devices such as folding mobile phones to ensure good electromagnetic shielding effect even in the folded state of the electronic device.

[0003] Currently, due to the increasingly high requirements for the application environment of folding mobile phones, such as being applied in humid, high-salt and other environments, in order to ensure good electromagnetic shielding effect of folding mobile phones in humid, high-salt and other environments, it is necessary to ensure that the electromagnetic shielding film can also meet the requirements of application environments such as humidity and high salt.

[0004] However, before the current electromagnetic shielding film is applied, it is difficult to confirm whether it can still maintain good stability and electromagnetic shielding effect in a corrosive environment by other means except simulating the real application environment and then measuring its electromagnetic shielding effect. Summary of the Invention

[0005] In view of this, the present invention provides an electromagnetic shielding film and a circuit board, and the electromagnetic shielding film can meet the electromagnetic shielding effect in environments such as humidity and high salt.

[0006] In a first aspect, the present invention provides an electromagnetic shielding film, including:

[0007] A base layer;

[0008] A shielding layer;

[0009] An adhesive layer; the base layer, the shielding layer and the adhesive layer are stacked;

[0010] Two oppositely attached electromagnetic shielding films are placed in salt water with a preset concentration and soaked for a preset soaking time Δt, the unit of the preset soaking time is hour (h), and the change rate Δσt of the tensile strength of the oppositely attached electromagnetic shielding films before and after soaking in salt water satisfies: Δσt≤25%; where Δσt = |σ1 - σ2| / σ1, σ1 represents the tensile strength of the oppositely attached electromagnetic shielding film before soaking, and σ2 represents the tensile strength of the oppositely attached electromagnetic shielding film after soaking.

[0011] Among them, the base layer includes, but is not limited to, polystyrene, vinyl acetate resin, polyester, polyethylene, polyamide, rubber, acrylate resin, phenolic resin, epoxy resin, polyimide, urethane resin, melamine resin, alkyd resin, and ABF resin, all of which can meet the requirements of the carrier function within the scope of this solution, and will not be elaborated here. 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. Among them, the metal shielding layer includes a single-metal shielding layer and / or an alloy shielding layer; among them, the single-metal shielding layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy shielding layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. Among them, the shielding layer can be a single-layer structure or a multi-layer structure, and the materials between layers in the multi-layer structure can be the same or different, and can be specifically set according to actual needs. The adhesive layer includes, but is not limited to, polystyrene, vinyl acetate resin, polyester, polyethylene, polyamide, rubber, acrylate resin, phenolic resin, epoxy resin, polyimide, urethane resin, melamine resin, alkyd resin, and ABF resin. Specifically, it can be acrylate glue, silicone glue, polyurethane glue, epoxy resin glue, or it can also use the same material as the base layer. Any adhesive material that can meet the application requirements and environmental conditions is within the scope of this solution, and will not be elaborated here.

[0012] In the present invention, the change rate Δσt of the tensile strength of the electromagnetic shielding film disposed by laminating before and after soaking in brine can be: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or an interval composed of any two values. Among them, the tensile strength of the electromagnetic shielding film disposed by laminating before soaking in brine is 10 MPa - 60 MPa, and specifically, it can be selected from 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, or an interval composed of any two values.

[0013] Specifically, multiple electromagnetic shielding films that are placed in parallel are placed in salt water with a concentration of 5% and immersed for 24 hours. According to the test results, it can be determined that when the change rate of tensile strength Δσt of the electromagnetic shielding film before and after immersion in salt water satisfies: Δσt≤25%, that is, when the change in tensile strength of the electromagnetic shielding film before and after immersion in salt water is within the allowable range, the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film have good bending resistance and shielding performance. In addition, the electromagnetic shielding film has high adaptability and can adapt to high humidity environments. When the change rate of tensile strength of the electromagnetic shielding film exceeds the above range, the high humidity resistance of the electromagnetic shielding film is reduced, and the bending resistance of the electromagnetic shielding film and the circuit board or soft board containing the electromagnetic shielding film is reduced.

[0014] In an optional embodiment, the change rate of elastic modulus ΔEt of the electromagnetic shielding film provided for the patch before and after soaking in salt water satisfies: ΔEt≤40%; wherein ΔEt=|E1-E2| / E1, E1 represents the elastic modulus of the electromagnetic shielding film provided for the patch before soaking, and E2 represents the elastic modulus of the electromagnetic shielding film provided for the patch after soaking. The elastic modulus of the electromagnetic shielding film provided for the patch before soaking in salt water is 0.6GPa-3GPa, and can be specifically selected as 0.6GPa, 0.7GPa, 0.8GPa, 0.9GPa, 1.0GPa, 1.1GPa, 1.5GPa, 1.8GPa, 2.0GPa, 2.1GPa, 2.5GPa, 2.8GPa or an interval consisting of any two values.

[0015] The elastic modulus of the electromagnetic shielding film refers to the ability of the material to undergo elastic deformation when subjected to force. In this embodiment, the change rate of the elastic modulus ΔEt of the electromagnetic shielding film before and after soaking in salt water can be: 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40% or an interval consisting of any two values. When the change rate of the elastic modulus ΔEt of the electromagnetic shielding film before and after soaking in salt water satisfies: ΔE≤40%, the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film have high bending resistance and good electromagnetic shielding effect.

[0016] In the present invention, when the tensile strength change rate Δσt of the electromagnetic shielding film set before and after immersion in salt water satisfies Δσt≤25%, and the elastic modulus change rate ΔEt of the electromagnetic shielding film set before and after immersion in salt water satisfies ΔEt≤40%, the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film have better bending resistance and better high humidity resistance, and at the same time will not reduce the shielding effectiveness of the electromagnetic shielding film. The shielding effectiveness can be stabilized at above 60DB, can adapt to the application requirements of existing circuit boards or flexible boards, and has high adaptability.

[0017] In an alternative embodiment, the change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating before and after soaking in brine satisfies: Δσ ≤ 10 Mpa, and / or, the change in elastic modulus ΔE of the electromagnetic shielding film disposed by laminating before and after soaking in brine satisfies: ΔE ≤ 1 Gpa; wherein, Δσ = |σ1 - σ2|, ΔE = |E1 - E2|.

[0018] The change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating before and after soaking in brine can be: 1 Mpa, 2 Mpa, 3 Mpa, 4 Mpa, 5 Mpa, 6 Mpa, 7 Mpa, 8 Mpa, 9 Mpa, 10 Mpa or an interval composed of any two numerical values. The change in elastic modulus ΔE of the electromagnetic shielding film disposed by laminating before and after soaking in brine can be: 0.1 Gpa, 0.2 Gpa, 0.3 Gpa, 0.4 Gpa, 0.5 Gpa, 0.6 Gpa, 0.7 Gpa, 0.8 Gpa, 0.9 Gpa, 1 Gpa or an interval composed of any two numerical values. When the change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating before and after soaking in brine satisfies Δσ ≤ 10 Mpa, Δσ is calculated in units of Mpa; and / or, when the change in elastic modulus ΔE of the electromagnetic shielding film disposed by laminating before and after soaking in brine satisfies ΔE ≤ 1 Gpa, it indicates that the electromagnetic shielding film can still maintain stable performance in environments such as humidity and high salt content.

[0019] In an alternative embodiment, the electromagnetic shielding film disposed by laminating is placed in brine with a preset concentration and soaked for a preset soaking time Δt. The relationship between the change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating and the preset soaking time Δt satisfies the formula: Δσ / Δt ≤ 0.3. The formula is a dimensionless calculation, that is, it does not depend on specific physical units. Δσ is calculated as a numerical value in units of Mpa, and Δt is calculated as a numerical value in units of hours.

[0020] The ratio between the change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating and the preset soaking time Δt can be: 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3 or an interval composed of any two numerical values. When the relationship between the change in tensile strength Δσ of the electromagnetic shielding film disposed by laminating and the preset soaking time Δt satisfies Δσ / Δt ≤ 0.3, the electromagnetic shielding film not only has good moisture resistance and stability, but also meets the effective electromagnetic shielding effect. According to this relationship, the stability and durability of the electromagnetic shielding film under specific environmental conditions, such as soaking in brine, can be evaluated. If the ratio of the change in tensile strength Δσ to the preset soaking time Δt is less than or equal to 0.3, it indicates that the change rate of the tensile strength of the electromagnetic shielding film is stable within the above range, has strong moisture resistance, and at the same time, the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film have stable bending resistance performance.

[0021] In an alternative embodiment, the electromagnetic shielding film provided by laminating is placed in salt water with a preset concentration and soaked for a preset soaking time Δt. The relationship between the change in elastic modulus ΔE of the electromagnetic shielding film provided by laminating and the preset soaking time Δt satisfies the formula: ΔE / Δt ≤ 0.03. The formula is a dimensionless calculation. When calculating ΔE, it is calculated as a value in GPa, and when calculating Δt, it is calculated as a value in hours.

[0022] The ratio between the change in tensile strength Δσ of the electromagnetic shielding film provided by laminating and the preset soaking time Δt can be: 0.01, 0.01, 0.03, or an interval composed of any two values. When the relationship between the change in elastic modulus ΔE of the electromagnetic shielding film provided by laminating and the preset soaking time Δt satisfies ΔE / Δt ≤ 0.03, it indicates that the rigidity change of this material is relatively slow, and it can maintain elastic properties for a long time, and it is not easy to cause excessive reduction in stiffness due to environmental factors. Therefore, at this time, the performance of the electromagnetic shielding film is more stable and can provide a lasting shielding effect; the bending resistance of the electromagnetic shielding film and the circuit board or flexible board containing this electromagnetic shielding film is also more stable.

[0023] Generally, the tensile strength and elastic modulus before soaking are greater than those after soaking.

[0024] In an alternative embodiment, the average thickness of the base layer is 3 μm - 15 μm. The average thickness of the base layer can be: 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or an interval composed of any two values.

[0025] In an alternative embodiment, the average thickness of the shielding layer is 1 μm - 9 μm. The average thickness of the shielding layer can be: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or an interval composed of any two values. The average thickness of the electromagnetic shielding film is 4 μm - 20 μm.

[0026] Of course, the average thickness of the base layer and the shielding layer is not limited to the specific values listed above, and it can be set according to actual usage requirements, and no more details will be elaborated here.

[0027] When the electromagnetic shielding film is within the range of an average thickness of 1 μm to 9 μm, the relatively thin shielding layer can provide an effective electromagnetic shielding effect within a specific frequency range.

[0028] In an alternative embodiment, a bonding layer is further laminated on the surface of the shielding layer away from the base layer.

[0029] In an alternative embodiment, the adhesive layer contains conductive particles. In this embodiment, the adhesive layer containing conductive particles can effectively enhance the conduction path and improve the conductivity and shielding effectiveness of the shielding layer.

[0030] In an alternative embodiment, protrusions are provided on the surface of the shielding layer away from the base layer to form an uneven surface. Due to differences in process means and parameters, the protrusions can also be of other shapes. Such a setting has better bending performance and high-step difference resistance performance.

[0031] In a second aspect, the circuit board includes the electromagnetic shielding film in any of the above embodiments.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] When the tensile strength change rate Δσt of the electromagnetic shielding film before and after soaking in brine satisfies Δσt ≤ 25%, the performance stability of the electromagnetic shielding film is good, it is less affected by changes in the external environment, the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film have good bending resistance and also have good electromagnetic shielding effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a schematic structural diagram of another electromagnetic shielding film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0037] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Embodiment 1

[0039] See Figure 1As shown in the figure, it is a schematic structural diagram of an electromagnetic shielding film provided by an embodiment of the present invention.

[0040] In this embodiment, an electromagnetic shielding film is provided, including: a base layer, a shielding layer and an adhesive layer, and the base layer, the shielding layer and the adhesive layer are stacked; wherein, the average thickness of the base layer is 5 μm, and the materials used are epoxy resin and polyester; the average thickness of the shielding layer is 3 μm, and the material used is a copper shielding layer; the material used for the adhesive layer is acrylate resin, and the overall average thickness of the electromagnetic shielding film is 10 μm.

[0041] The electromagnetic shielding films arranged in a face-to-face manner are placed in a salt water with a concentration of 5% and soaked for a preset soaking time of 24 h. The change rate Δσt of the tensile strength of the electromagnetic shielding film before and after soaking is ≤ 25%.

[0042] Example 2

[0043] Other technical features of this embodiment are the same as those of Example 1, except that: the change rate ΔEt of the elastic modulus of the electromagnetic shielding film before and after soaking is ≤ 40%.

[0044] Example 3

[0045] Other technical features of this embodiment are the same as those of Example 2, except that: Δσ ≤ 10 Mpa and ΔE ≤ 1 Gpa before and after soaking the electromagnetic shielding film.

[0046] Example 4

[0047] Other technical features of this embodiment are the same as those of Example 3, except that: Δσ / Δt ≤ 0.3 and ΔE / Δt ≤ 0.03.

[0048] Comparative Example 1

[0049] This comparative example provides an electromagnetic shielding film, whose structure and the materials of each structure are the same as those of Example 1, except that: the change rate Δσt of the tensile strength of the electromagnetic shielding film before and after soaking is 28% ≥ 25%.

[0050] Comparative Example 2

[0051] This comparative example provides an electromagnetic shielding film, whose structure and the materials of each structure are the same as those of Comparative Example 1, except that: the change rate ΔEt of the tensile strength of the electromagnetic shielding film before and after soaking is 45% ≥ 40%, Δσ = 15 Mpa > 10 Mpa, and Δσ / Δt > 0.3.

[0052] Test Example

[0053] In this test example, multiple electromagnetic shielding film samples of different batches can be placed in a saline solution with a preset concentration for a preset soaking time of 24 hours. Before and after soaking the electromagnetic shielding film, the performance of the electromagnetic shielding film is tested respectively, and the change rates of tensile strength, elastic modulus, etc. are calculated. At the same time, the electromagnetic shielding films of the same batch are subjected to a bending resistance performance test and a shielding effectiveness test. The test method for the bending resistance of the electromagnetic shielding film is as follows: for bending resistance, two electromagnetic shielding films to be tested of the same model are attached to the two surfaces of a bending plate (the bending plate contains a circuit) and pressed (pre-pressing time: 10 seconds, forming time: 180 seconds, forming pressure: 120 kg, pressing temperature: 185 °C); after pressing, it is baked and cured (baking temperature: 160 °C, baking time: 90 min); the width of the sample strip is 1.5 cm, and the bending conditions are: R angle: 0.8 mm, speed: 60 revolutions / min, angle: ±135 degrees, load: 500 g. When the change in the resistance of the bent circuit exceeds 10%, the test is stopped. The shielding effectiveness of the electromagnetic shielding film is detected in accordance with GB / T 30142-2013. Among them, in the test results, the test results in Comparative Example 1 are used as the reference (poor), and the test results are divided into poor, good, and excellent according to the test results.

[0054] As shown in Table 1, the performance parameters between the examples and the comparative examples are presented.

[0055] Table 1

[0056] Flexural resistance Electromagnetic shielding effectiveness Example 1 Good Good Example 2 Good Good Example 3 Excellent Excellent Example 4 Excellent Excellent Comparative example 1 Poor Poor Comparative example 2 Poor Poor

[0057] It can be seen that when the change rate of tensile strength Δσt of the electromagnetic shielding film arranged in a facing manner before and after soaking in saline solution satisfies Δσt ≤ 25%, the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film have bending resistance, and also the electromagnetic shielding film is less affected by the external environment, has weather resistance, and has a good electromagnetic shielding effect.

[0058] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. An electromagnetic shielding film, characterized in that: include: Basal layer; Shielding layer; Adhesive layer; the base layer, the shielding layer and the adhesive layer are stacked; The tensile strength change rate Δσt of the electromagnetic shielding membrane set on the patch before and after immersion in salt water satisfies: Δσt≤25%; wherein, Δσt=|σ1-σ2| / σ1, σ1 represents the tensile strength of the electromagnetic shielding membrane set on the patch before immersion, and σ2 represents the tensile strength of the electromagnetic shielding membrane set on the patch after immersion.

2. The electromagnetic shielding film according to claim 1, characterized in that The elastic modulus change rate ΔEt of the electromagnetic shielding film set on the patch before and after immersion in salt water satisfies: ΔEt≤40%; wherein, ΔEt=|E1-E2| / E1, E1 represents the elastic modulus of the electromagnetic shielding film set on the patch before immersion, and E2 represents the elastic modulus of the electromagnetic shielding film set on the patch after immersion.

3. The electromagnetic shielding film according to claim 1, characterized in that The change Δσ in tensile strength of the electromagnetic shielding film arranged on the patch before and after being immersed in salt water satisfies: Δσ≤10Mpa, and / or the change ΔE in elastic modulus of the electromagnetic shielding film arranged on the patch before and after being immersed in salt water satisfies: ΔE≤1Gpa; wherein, Δσ=|σ1-σ2|, ΔE=|E1-E2|.

4. The electromagnetic shielding film according to claim 3, characterized in that The electromagnetic shielding film set on the patch is placed in salt water of preset concentration and immersed for a preset immersion time Δt. The tensile strength change Δσ of the electromagnetic shielding film set on the patch and the preset immersion time Δt satisfy the relationship: Δσ / Δt≤0.3, and the formula is a dimensionless calculation.

5. The electromagnetic shielding film according to claim 2, characterized in that The electromagnetic shielding film set on the patch is placed in salt water of preset concentration and immersed for a preset immersion time Δt. The elastic modulus change ΔE of the electromagnetic shielding film set on the patch and the preset immersion time Δt satisfy the relationship: ΔE / Δt≤0.03, and the formula is a dimensionless calculation.

6. The electromagnetic shielding film according to claim 1, characterized in that The average thickness of the base layer is 3 μm-15 μm.

7. The electromagnetic shielding film according to claim 1, characterized in that The average thickness of the shielding layer is 1 μm-9 μm.

8. The electromagnetic shielding film according to claim 1, characterized in that The adhesive layer contains conductive particles.

9. The electromagnetic shielding film according to claim 1, characterized in that A surface of the shielding layer away from the base layer is provided with a protrusion.

10. A circuit board, characterized in that: The circuit board comprises the electromagnetic shielding film as described in any one of claims 1 to 9.

Images