Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board. The electromagnetic shielding film comprises an insulating layer, a shielding layer and an adhesive film layer which are sequentially stacked, the surface of one side, close to the shielding layer, of the insulating layer is a first rough surface, the first rough surface is provided with a plurality of first wave crests, the number of the first wave crests is larger than or equal to 10 within any 100-micrometer length in the slicing state in the thickness direction, the distance between every two adjacent first wave crests is 3-10 micrometers, and the height difference is smaller than or equal to 1 micrometer; the surface of one side, far away from the insulating layer, of the shielding layer is a second rough surface, the shielding layer and the first rough surface are conformal, so that the second rough surface forms a second wave crest corresponding to the first wave crest of the first rough surface, and the second wave crest is wrapped by the adhesive film layer. According to the invention, the problem of uneven grounding resistance after the electromagnetic shielding film is pressed on the circuit board substrate can be improved, and the electromagnetic shielding performance of the circuit board is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic information materials, and in particular to an electromagnetic shielding film and a circuit board. BACKGROUND

[0002] With the rapid development of electronic industry, electronic products further develop towards miniaturization, light weight and high density assembly, which greatly promotes the development of flexible circuit boards. At present, flexible circuit boards dominate the market of flexible circuit boards, and an important indicator for evaluating the performance of functional flexible circuit boards is electromagnetic shielding (EMI Shielding).

[0003] The electromagnetic shielding film commonly used in the existing circuit board includes a shielding layer and a film layer. The shielding layer is connected to the ground layer of the circuit board through the film layer, and then the interference charge is guided into the ground layer of the circuit board, so as to realize shielding. However, after the current electromagnetic shielding film is pressed on the circuit board, the problem of local uneven deviation of grounding resistance easily occurs, which affects the electromagnetic shielding effect of the circuit board. SUMMARY

[0004] The purpose of the embodiment of the present application is to provide an electromagnetic shielding film and a circuit board, which can improve the problem of uneven grounding resistance after the electromagnetic shielding film is pressed on the circuit board substrate, and effectively improve the electromagnetic shielding performance of the circuit board.

[0005] To achieve the above-mentioned purpose, the embodiment of the present application provides an electromagnetic shielding film, which comprises an insulating layer, a shielding layer and a film layer which are sequentially stacked.

[0006] The side surface of the insulating layer close to the shielding layer is a first rough surface, and the first rough surface is provided with a plurality of first peaks. In the state of a slice in the thickness direction, the number of the first peaks in any 100 μm length is greater than or equal to 10, and the distance between adjacent two first peaks is 3-10 μm, and the height difference is less than or equal to 1 μm.

[0007] The side surface of the shielding layer away from the insulating layer is a second rough surface, and the shielding layer is conformal with the first rough surface, so that the second rough surface forms second peaks corresponding to the first peaks of the first rough surface, and the second peaks are covered by the film layer.

[0008] As an improvement of the above-mentioned scheme, in the state of a slice in the thickness direction, the difference between the maximum peak height and the minimum peak height on the first rough surface in any 100 μm length is less than or equal to 1 μm; wherein the maximum peak height refers to the height value of the first peak with the maximum height, and the minimum peak height refers to the height value of the first peak with the minimum height.

[0009] As an improvement of the above-mentioned scheme, the roughness Rz of the first rough surface is 3-15 μm.

[0010] As an improvement of the above-mentioned scheme, the magnetic particles are filled in the insulating layer, and in the slicing state in the thickness direction, at least one magnetic particle is contained in each of the first wave peaks.

[0011] As an improvement of the above-mentioned scheme, the particle size of the magnetic particles is 1-10 μm.

[0012] As an improvement of the above-mentioned scheme, the particle size of 70% of the magnetic particles in the insulating layer is 2-5 μm.

[0013] As an improvement of the above-mentioned scheme, the total mass of the magnetic particles accounts for 1%-10% of the total mass of the insulating layer, and at least 70% of the magnetic particles are distributed on the side close to the first rough surface.

[0014] As an improvement of the above-mentioned scheme, the top of each of the second wave peaks is provided with a conductive protrusion.

[0015] As an improvement of the above-mentioned scheme, the conductive protrusion is formed by agglomeration of one or more conductive particles.

[0016] The embodiment of the present application also provides a circuit board comprising a circuit board substrate and the electromagnetic shielding film according to any one of the above-mentioned schemes, and the electromagnetic shielding film is pressure-bonded to the circuit board substrate through the adhesive film layer.

[0017] Compared with the prior art, the electromagnetic shielding film and the circuit board disclosed by the present application, the electromagnetic shielding film comprises an insulating layer, a shielding layer and an adhesive film layer which are sequentially stacked, by limiting the number, interval and height difference of the wave peaks of the first rough surface of the insulating layer, the wave peaks of the first rough surface are uniformly distributed and have consistent height, so that the second rough surface of the shielding layer which is conformally generated on the first rough surface also has uniformly distributed and consistent height wave peak topography, which ensures that the rough surface of the shielding film pierces the adhesive film layer for grounding more uniformly and consistently during the pressure bonding process, effectively improves the uniformity of the grounding resistance when the entire electromagnetic shielding film is grounded, and thus improves the grounding performance and shielding effect of the electromagnetic shielding film. Moreover, by clearly defining the wave peak parameters of the first rough surface of the insulating layer, the present application provides a quantitative standard for the processing of the insulating layer, which is conducive to the standardized production of the rough surface, effectively reduces the product failure rate of the electromagnetic shielding film, and improves the product quality of the electromagnetic shielding film. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic diagram of the first electromagnetic shielding film provided by the embodiment of the present application;

[0019] Figure 2 is a schematic diagram of the wave peak distance and wave peak height in the embodiment of the present application;

[0020] Figure 3 is a structural schematic diagram of a second electromagnetic shielding film provided by the embodiment of the present application;

[0021] Figure 4 is a structural schematic diagram of a third electromagnetic shielding film provided by the embodiment of the present application;

[0022] Figure 5 is a structural schematic diagram of a fourth electromagnetic shielding film provided by the embodiment of the present application;

[0023] Figure 6 is a structural schematic diagram of a fifth electromagnetic shielding film provided by the embodiment of the present application;

[0024] Figure 7 is a structural schematic diagram of a circuit board provided by the embodiment of the present application;

[0025] In the figure, 10, electromagnetic shielding film; 11, insulating layer; 111, first rough surface; 112, first wave peak; 113, magnetic particles; 12, shielding layer; 121, second rough surface; 122, second wave peak; 123, conductive protrusion; 124, conductive particles; 13, adhesive film layer; 131, conductive particles; 20, circuit board; 21, circuit board substrate. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] In the description of the present application, it should be understood that the terms “center”, “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0028] The terms "first", "second", "third", etc. are used only for descriptive purposes and should not be construed as implying or suggesting relative importance or an indicated number of technical features. Thus, features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise stated.

[0029] Referring to Figure 1 FIG. 1 is a structural schematic diagram of a first electromagnetic shielding film according to an embodiment of the present application. The electromagnetic shielding film 10 includes an insulating layer 11, a shielding layer 12 and a film layer 13 which are sequentially stacked. That is, the shielding layer 12 is provided on the insulating layer 11, and the film layer 13 is provided on the shielding layer 12. When the electromagnetic shielding film is applied to a printed circuit board, the film layer 13 is pressure-bonded to the circuit board substrate, and the rough surface of the shielding layer 12 penetrates the film layer 13 to connect to the circuit board substrate, thereby achieving grounding.

[0030] The side surface of the insulating layer 11 close to the shielding layer 12 is a first rough surface 111, and the first rough surface is provided with a plurality of first peaks 112. In the state of a slice along the thickness direction, the number of the first peaks 112 in any 100 μm length is greater than or equal to 10, and the distance between adjacent two first peaks 112 is 3-10 μm, and the height difference is less than or equal to 1 μm.

[0031] The side surface of the shielding layer 12 away from the insulating layer 11 is a second rough surface 121, and the shielding layer 12 is conformal with the first rough surface 111, so that the second rough surface 121 forms a second peak 122 corresponding to the first peak 112 of the first rough surface, and the second peak is covered by the film layer.

[0032] In the embodiment of the present application, the first rough surface of the insulating layer close to the shielding layer is the core of the entire structure design. In the production process of the electromagnetic shielding film, the shielding layer material will conformally grow along the profile of the surface of the insulating layer, that is, the morphology of the shielding layer will copy the relief features of the first rough surface.

[0033] In the embodiment of the present application, a plurality of first peaks 112 are formed on the rough surface of the insulating layer 11, so that when the shielding layer 12 is generated on the first rough surface of the insulating layer 11, the shielding layer 12 copies the relief features of the first rough surface, thereby forming a plurality of second peaks 122 on the second rough surface 121, and the second peaks 122 correspond to the first peaks 112.

[0034] The embodiment of the present application limits the number, interval and height difference of the first wave peaks on the first rough surface. In the slicing state along the thickness direction of the insulating layer, the number of the first wave peaks 112 of the first rough surface is greater than or equal to 10, for example, 10, 11, 12, 13, 15, 17, 18 or 20, etc., the interval between the adjacent two first wave peaks 112 is in the range of 3-10 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc., and the height difference between the adjacent two first wave peaks 112 is less than or equal to 1 μm, for example, 1 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm or 0 μm, etc. Of course, the above number, interval and height difference can be set to other values meeting the conditions according to the actual situation, which is not limited here.

[0035] It should be noted that the definition of the wave peak is that the profile of the protrusion is formed by observing the fluctuation in the slicing state along the thickness direction of the electromagnetic shielding film by using the electron microscope.

[0036] Referring to Figure 2 , which is a schematic diagram of the wave peak interval and the wave peak height in the embodiment of the present application.

[0037] The interval D of the adjacent two first wave peaks refers to that a central axis parallel to the thickness direction of the electromagnetic shielding film is made at the highest point of the first wave peak, and the straight line distance between the central axes of the adjacent two first wave peaks is the interval.

[0038] The height difference of the adjacent two first wave peaks refers to that a parallel line is made at the highest point and the lowest point on one side of the first wave peak, respectively, and the vertical height between the two horizontal lines is the height H of the first wave peak, and the difference between the heights of the adjacent two first wave peaks is the height difference.

[0039] In the embodiment of the present application, the number of the first wave peaks 112 is limited to at least 10 in a certain range, which ensures that the first rough surface 111 has a high enough distribution density. The high-density wave peak distribution provides uniform growth anchor points for the shielding layer, avoiding the problem of local thinning or uneven growth of the shielding layer due to the sparse local wave peaks. If the number of wave peaks is too small, the area between the wave peaks is prone to planar growth, resulting in sparse distribution of conductive protrusions during subsequent roughening.

[0040] The interval of the adjacent first wave peak 112 is limited to 3-10 μm, which balances the roughness and uniformity of the first rough surface. If the interval is too small, such as less than 3 μm, the gap between the first wave peaks is too narrow, and the material is easy to accumulate in the gap during sputtering, causing local thickness abnormalities. If the interval is too large, such as greater than 10 μm, the surface of the shielding layer will be too undulating, and the height difference of the protrusions will be difficult to control during subsequent roughening. By controlling the interval between the first wave peaks on the first rough surface of the insulating layer to be within the range of 3-10 μm, the first wave peaks are uniformly distributed within a certain range while avoiding being too dense, so that during the subsequent generation of the shielding layer on the first rough surface of the insulating layer, the stress can be uniformly released during the growth of the shielding layer, and a foundation is laid for the uniform distribution of the conductive protrusions.

[0041] The height difference between the adjacent first wave peaks 112 is limited to be less than or equal to 1 μm, that is, the height difference is small, so that the overall undulation degree is similar. If the height difference of the wave peaks is too large, such as more than 1 μm, the surface of the shielding layer after growth will form a high-low undulating surface morphology, and the conductive protrusions in the high wave peak area will be significantly higher than those in the low wave peak area during roughening, resulting in uneven contact pressure distribution during subsequent grounding. By controlling the height difference within 1 μm, the undulation amplitude of the surface of the shielding layer tends to be consistent, providing a prerequisite for the isohypse of the conductive protrusions.

[0042] In traditional designs, since the rough surface of the insulating layer is not parameter-limited, the number, interval, and height difference of the wave peaks are randomly distributed, resulting in problems such as local density, local sparsity, and high-low inconsistency of the conductive protrusions of the shielding layer. During compression grounding, local conductive protrusions with large height difference or uneven distribution may cause grounding resistance deviation, thereby affecting the grounding performance and shielding effect of the electromagnetic shielding film.

[0043] The embodiments of the present application limit the number, interval, and height difference of the wave peaks on one side of the insulating layer, which forms a first rough surface with uniform wave peak distribution and consistent undulation height from different dimensions, lays a foundation for the subsequent conformal shielding layer on the first rough surface, and makes the shielding layer generated on the first rough surface reproduce the undulating morphology of the first rough surface, so that the second rough surface on the other side of the shielding layer is also a uniform wave peak morphology. When the electromagnetic shielding film is compressed on the circuit board, the second rough surface on the shielding layer can pierce the adhesive film layer and the ground layer of the circuit board to form a window contact, and the second wave peaks with uniform distribution and small height difference on the second rough surface can ensure more uniform grounding during the compression process, avoiding the problem of uneven distribution of local wave peaks causing grounding resistance deviation, thereby effectively ensuring the uniformity of the grounding resistance of the entire electromagnetic shielding film during grounding, and improving the grounding performance and shielding effect of the electromagnetic shielding film.

[0044] In the embodiment of the present application, the insulating layer 11 comprises a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after curing of epoxy resin ink, a film layer formed after curing of polyurethane ink, a film layer formed after curing of modified acrylic resin, or a film layer formed after curing of polyimide resin.

[0045] The shielding layer 12 is single-layer or multi-layer structure, and the shielding layer 12 is single metal shielding layer and / or alloy shielding layer. 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.

[0046] The material of the adhesive film layer 13 can be selected from modified epoxy resin, acrylic, modified rubber, and modified thermoplastic polyimide.

[0047] The preparation process of the electromagnetic shielding film of the embodiment of the present application is as follows:

[0048] First, an insulating layer is formed on a carrier film by coating; wherein the insulating layer is formed on the carrier film by multi-layer coating, and a modifier or a dispersant is added to form a rough surface on one side of the insulating layer to obtain a first rough surface, and a plurality of first wave peaks satisfying the above-mentioned number, spacing and height difference are protruded on the first rough surface.

[0049] Then, a shielding layer is formed on the rough surface of the insulating layer; wherein the shielding layer is formed on the first rough surface by one or more processes of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and hybrid plating, so that the shielding layer is conformal to obtain a second rough surface with a plurality of second wave peaks;

[0050] Finally, an adhesive film layer is formed on the second rough surface of the shielding layer by coating.

[0051] By limiting the number, spacing and height difference of the wave peaks of the first rough surface of the insulating layer, the wave peaks of the first rough surface are uniformly distributed and have consistent height, so that the second rough surface of the shielding layer conformally generated on the first rough surface also has uniformly distributed and consistent height wave peak topography, which ensures that the rough surface of the shielding film pierces the adhesive film layer for grounding during the pressing process, effectively improves the uniformity of the grounding resistance when the entire electromagnetic shielding film is grounded, and improves the grounding performance and shielding effect of the electromagnetic shielding film. Moreover, by specifying the wave peak parameters of the first rough surface of the insulating layer, the present application provides a quantitative standard for the processing of the insulating layer, which is conducive to the standardized production of the rough surface, effectively reduces the product failure rate of the electromagnetic shielding film, and improves the product quality of the electromagnetic shielding film.

[0052] As a preferred embodiment, the embodiment of the present application is further implemented on the basis of the above-mentioned embodiment, referring to Figure 3 Fig. 2 is a structural schematic diagram of a second electromagnetic shielding film provided by the embodiment of the present application, wherein the top of each second wave crest 122 is provided with a conductive protrusion 123.

[0053] In the embodiment of the present application, the conductive protrusions 123 in convex shape are formed on the second rough surface 121 of the shielding layer 12, and the conductive protrusions 123 are specifically distributed on the outer top of the second wave crest 122, and the adhesive film layer 13 is arranged outside the second rough surface to completely cover the conductive protrusions 123.

[0054] In the embodiment of the present application, the conductive protrusions 123 in convex shape with a certain height are arranged on the top of each second wave crest 122 of the second rough surface 121 of the shielding layer, so that when the electromagnetic shielding film is pressed on the circuit board substrate, the adhesive on the conductive protrusions 123 on the second wave crest of the second rough surface will be squeezed into the concave part between the second wave crest 122 of the second rough surface 121 during the pressing process, thereby avoiding the small adhesive capacity which easily causes the board explosion phenomenon and further leads to the grounding failure phenomenon. At the same time, the conductive protrusions 123 on the second wave crest 122 of the shielding layer can more effectively pierce the adhesive film layer 13 for grounding. Since the number, spacing and height difference of the first wave crest 112 on the first rough surface 111 of the insulating layer within a certain range are optimized in the embodiment of the present application, the second wave crest 122 on the second rough surface 121 of the shielding layer is also uniformly and consistently distributed, so that the distribution position, density and height of the conductive protrusions 123 formed by roughening at the second wave crest 122 are more consistent, so that the conductive protrusions 123 pierce the adhesive film layer for grounding during pressing are more uniform and consistent, thereby effectively improving the grounding resistance uniformity of the electromagnetic shielding film, avoiding the problem of large height difference or uneven distribution density of local conductive protrusions which leads to the deviation of grounding resistance, and improving the grounding performance and shielding effect of the electromagnetic shielding film.

[0055] Preferably, the conductive protrusions 123 can be at a certain distance from the outer surface of the adhesive film layer 13, or can be in contact with the outer surface of the adhesive film layer 13, so as to ensure that the conductive protrusions 123 can effectively pierce the adhesive film layer 13 for grounding. In addition, the outer surface of the adhesive film layer 13 can be a flat surface without undulations, or a gently undulating uneven surface.

[0056] The preparation process of the electromagnetic shielding film of the embodiment of the present application is as follows:

[0057] First, an insulating layer is formed on a carrier film; wherein the insulating layer is formed on the carrier film by multi-layer coating, and a modifier or dispersant is added to coat the rough side of the insulating layer to obtain a first rough side, and the first rough side has a plurality of first wave peaks satisfying the above-mentioned quantity, spacing and height difference.

[0058] Next, a shielding layer is formed on the rough side of the insulating layer; wherein the shielding layer is formed on the first rough side by one or more processes selected from the group consisting of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and hybrid plating, so that the shielding layer is conformal to obtain a second rough side having a plurality of second wave peaks;

[0059] Next, the second wave peaks on the side of the shielding layer away from the insulating layer are roughened to form conductive protrusions on the top of the second wave peaks, which can be formed by chemical plating, PVD, CVD, evaporation plating, sputtering plating, electroplating or a combination thereof.

[0060] Finally, a glue film layer is formed on the second rough side of the shielding layer.

[0061] Of course, in specific implementations, a material layer of the shielding foil can be formed first, and then conductive protrusions 123 are formed on the shielding layer by other processes. Alternatively, the shielding layer and the conductive protrusions 123 can also be an integral structure formed by one-step forming process, which does not affect the beneficial effects of the present application.

[0062] It should be noted that, Figure 3 The shape of the conductive protrusions 123 is only exemplary, and due to differences in process means and parameters, the conductive protrusions 123 can also be in the shape of clusters, icicles, stalactites, branches, etc. In addition, the conductive protrusions 123 in the embodiments of the present application are not limited by the illustrations and the above-mentioned shapes, as long as they are conductive protrusions 123 that provide the shielding layer with surface roughness, they are within the scope of the present application.

[0063] It should be noted that the material of the conductive protrusions 123 can be the same as that of the metal foil, or different, which is not limited here.

[0064] As a preferred embodiment, the embodiments of the present application are further implemented on the basis of the above-mentioned embodiments, and in the sliced state in the thickness direction, the difference between the maximum wave height and the minimum wave height on the first rough side 111 within any 100 μm length is less than or equal to 1 μm. Wherein, the maximum wave height refers to the height value of the first wave peak with the maximum height, and the minimum wave height refers to the height value of the first wave peak with the minimum height.

[0065] In the embodiment of the present application, the difference between the maximum peak height and the minimum peak height on the first rough surface of the insulating layer is further limited to be less than or equal to 1 μm, for example, 1 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm or 0 μm, etc. Of course, other values meeting the conditions can also be set according to actual conditions, which are not limited here.

[0066] In the embodiment of the present application, the difference between the maximum peak height and the minimum peak height on the first rough surface 111 is less than or equal to 1 μm, so that the first peak 112 is more uniform in the first rough surface 111 as a whole, the second peak 122 formed on the other side of the shielding layer is also similar in the fluctuation degree, and the protruding height of the conductive protrusion 123 formed by roughening at the second peak 122 of the shielding layer is also more uniform, thereby further improving the grounding uniformity of the electromagnetic shielding film.

[0067] As a preferred embodiment, the roughness Rz of the first rough surface 111 is 3-15 μm in the embodiment based on the above embodiment.

[0068] It should be noted that the roughness Rz is the sum of the average value of n maximum profile peak heights and the average value of n maximum profile valley depths in the sampling length, and n≥1; preferably, n=5. The roughness Rz can fully reflect the profile peak height.

[0069] In the embodiment of the present application, the roughness Rz of the first rough surface 111 of the insulating layer 11 is further limited to be within a reasonable range of 3-15 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc. Of course, other values meeting the conditions can also be set according to actual conditions, which are not limited here.

[0070] The roughness Rz of the first rough surface 111 is limited, so that the roughness of the first rough surface is within a reasonable range, which is beneficial to improve the stability of the bonding force between the insulating layer 11 and the shielding layer 12, and prevents the insulating layer 11 and the shielding layer 12 from being separated. When the roughness Rz of the first rough surface 111 is within the range of 3-15 μm, the height of the first wave peak 112 on the first rough surface 111 is moderate, and after the shielding layer 12 is conformally grown along the first rough surface 111, a fluctuation structure matching the first rough surface 111 is formed, a plurality of second wave peaks 122 are formed, and the second wave peaks 122 or the conductive protrusions 123 on the second wave peaks are used to pierce the adhesive film layer to ground, so that the grounding effect is ensured. If the roughness Rz of the first rough surface is less than 3 μm, the rough surface of the shielding layer may not be able to completely penetrate the adhesive film layer, resulting in a virtual connection problem and a sharp increase in grounding resistance; if the roughness Rz of the first rough surface is greater than 15 μm, the fluctuation of the shielding layer may be too large, resulting in a large insertion loss of the circuit board after pressing.

[0071] As a preferred embodiment, the embodiment of the present application is further implemented on the basis of the above-mentioned embodiment, and the structure of the third electromagnetic shielding film provided by the embodiment of the present application is shown in FIG. 3. Figure 4 , the insulating layer 11 is filled with magnetic particles 113, and in the thickness direction slice state, each first wave peak 112 contains at least one magnetic particle 113.

[0072] Preferably, the magnetic particles 113 can be single soft magnetic material particles, composite structure magnetic particles or functionalized modified magnetic particles. The single soft magnetic material can include ferrite particles, nanocrystalline alloy particles, metal soft magnetic powder particles, etc., wherein the ferrite particles can be manganese-zinc ferrite or nickel-zinc ferrite, the nanocrystalline alloy particles can be iron-based nanocrystalline particles or cobalt-based nanocrystalline particles, and the metal soft magnetic powder particles can be carbonyl iron powder or atomized iron powder, etc. The composite structure magnetic particles can be magnetic particles formed by combining carbonyl iron powder with surface SiO2 coating, etc.

[0073] Traditional metal shielding layers, such as copper, aluminum, nickel, conductive silver paste, etc., mainly shield high-frequency electromagnetic fields through eddy current effect, and the skin effect of low-frequency magnetic fields, especially magnetic fields with a frequency less than 100 kHz, is very shallow, and the shielding effect is poor.

[0074] In the embodiment of the present application, the magnetic particles 113 are filled in the insulating layer 11, so that the insulating layer 11 becomes a magnetic shielding layer, which can effectively absorb and guide low-frequency magnetic lines, greatly improving the overall shielding effectiveness of the electromagnetic shielding film in the low-frequency band, which is crucial for suppressing the low-frequency magnetic field interference generated by power transformers, motors, inductors and the like. Moreover, each of the first wave crests 112 contains at least one magnetic particle 113, which can effectively ensure the uniformity of the dispersion of the magnetic particles, so as to better exert the shielding effect on the low-frequency magnetic field.

[0075] Preferably, the particle size of the magnetic particles is 1-10 μm.

[0076] Preferably, the particle size of 70% of the magnetic particles in the insulating layer is 2-5 μm.

[0077] In the embodiment of the present application, the particle size of the magnetic particles 113 in the insulating layer 11 is further optimized, and the particle size of the magnetic particles is controlled to be within the range of 1-10 μm, for example, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc. Of course, other values meeting the conditions can also be set according to the actual situation, which is not limited specifically herein. Moreover, the particle size of 70% of the magnetic particles is controlled to be within the preferred range of 2-5 μm.

[0078] When the particle size of the magnetic particles 113 is too small, for example, less than 1 μm, the magnetic performance of the magnetic particles 113 will be attenuated, the magnetic permeability will be too low, and the proportion of the surface oxidation layer will be too large, which will result in a decrease in the effective magnetic volume and a superposition of the strong Brownian motion and magnetic attraction, which will easily cause serious re-agglomeration phenomenon and destroy the uniformity of the coating. When the particle size of the magnetic particles 113 is too large, for example, greater than 10 μm, the eddy current loss will increase dramatically, the magnetic permeability will drop sharply in the high-frequency band, the high-frequency shielding effect will be poor, and meanwhile, a through conductive path will be easily formed, which will cause a breakdown of the insulating layer and result in a leakage failure. Moreover, the stress is relatively concentrated, which will easily make the insulating coating brittle.

[0079] Therefore, the embodiment of the present application limits the particle size of the magnetic particles 113 to be within the relatively moderate range of 1-10 μm, and most of the particle sizes are within the relatively small range of 2-5 μm, which can effectively optimize the magnetic performance, realize wide-frequency magnetic permeability, suppress magnetic loss, weaken eddy current loss, avoid the superparamagnetic critical point, and control the dispersion stability and insulation, so as to meet the requirements of wide-frequency shielding, high insulation and coating toughness.

[0080] For example, the spherical carbonyl iron powder with a particle size of 2-3 μm and coated with SiO2 is filled in the insulating layer 11 to form the magnetic particles, which can effectively meet the shielding effect of high and low frequencies, and meanwhile, the coating of the insulating layer is uniform and controllable, the dispersion is stable, and the brittle failure of the insulating layer caused by excessive concentrated stress can be avoided.

[0081] As a preferred embodiment, the total mass of the magnetic particles accounts for 1% to 10% of the total mass of the insulating layer, and at least 70% of the magnetic particles are distributed on the side close to the first rough surface.

[0082] In the embodiment of the present application, the total mass of the magnetic particles 113 accounts for 1% to 10% of the total mass of the insulating layer 11, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, and of course, other values meeting the conditions can also be set according to actual conditions, which are not limited here.

[0083] In the embodiment of the present application, the mass proportion of the magnetic particles 113 in the insulating layer 11 is optimized, so that the total mass proportion of the magnetic particles 113 in the insulating layer 11 is within a reasonable range, which can avoid the shielding effect being not obvious due to too few magnetic particles, and at the same time, avoid the dielectric constant and loss of the insulating layer fluctuating too much due to too many magnetic particles. Therefore, the present application limits the mass proportion within the range of 1% to 10%, which can effectively improve the shielding effect while not greatly affecting the dielectric properties of the insulating layer.

[0084] Moreover, at least 70% of the magnetic particles 113 are distributed on the side of the first rough surface 111. The insulating layer is divided into two regions, one close to the rough surface and the other away from the rough surface, with the first rough surface as the reference surface. For example, if the overall thickness of the insulating layer is 20 μm and the first rough surface is the surface at 0 μm, the side of the first rough surface can refer to the region from 0 μm to a target depth, such as 10 μm, and the remaining region from 10 μm to 20 μm is the side away from the rough surface. Among all the magnetic particles in the insulating layer, 70% or more of the particles are concentrated in the region close to the first rough surface, and only 30% or less of the particles are distributed on the other side away from the rough surface.

[0085] In the electromagnetic shielding film, the first rough surface is the interface between the insulating layer and the shielding layer, and the shielding layer needs to be conformally grown through the rough structure of the interface, that is, the morphology of the shielding layer is copied with the rough surface, and finally the wave peak or the conductive protrusion of the shielding layer is grounded with the circuit board. The core role of the magnetic particles is to enhance the low-frequency magnetic field shielding effect by absorbing and guiding low-frequency magnetic lines, and the shielding demand of the low-frequency magnetic field is more focused on the coupling area of the shielding layer and the circuit board, that is, the position close to the grounding interface, because this area is the key path for the magnetic field to pass through the shielding film. In the embodiment of the present application, more than 70% of the magnetic particles are concentrated on the side of the first rough surface, so that the magnetic particles are closer to the core action area of the magnetic field shielding, and the waste of efficiency caused by the particles being dispersed in the position away from the functional area is avoided.

[0086] The preparation process of the electromagnetic shielding film of the embodiment of the present application is as follows:

[0087] First, an insulating layer is formed on the carrier film by coating; wherein the insulating layer is formed on the carrier film by multi-layer coating, magnetic particles are mixed in the last coating layer, and a modifier or a dispersant is added to form a rough side of the insulating layer to obtain a first rough surface, and a plurality of first wave peaks satisfying the above-mentioned quantity, spacing and height difference are protruded on the first rough surface, and at least one magnetic particle exists in each wave peak.

[0088] Then, a shielding layer is formed on the rough surface of the insulating layer; wherein the shielding layer is formed on the first rough surface by one or more processes of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating, so that the shielding layer is conformal to obtain a second rough surface with a plurality of second wave peaks;

[0089] Then, roughening is performed on the side of the shielding layer away from the insulating layer to form conductive protrusions on the top of the second wave peaks on that side; specifically, a plurality of conductive protrusions can be formed on the top of the second wave peaks of the shielding layer by chemical plating, PVD, CVD, evaporation plating, sputtering plating, electroplating or a composite process thereof.

[0090] Finally, a glue film layer is formed on the second rough surface of the shielding layer.

[0091] As a preferred embodiment, the embodiment of the present application is further implemented on the basis of any of the above embodiments, referring to Figure 5 FIG. 4 is a structural schematic diagram of a fourth electromagnetic shielding film provided by the embodiment of the present application, and the conductive protrusion 123 is formed by agglomeration of one or more conductive particles 124.

[0092] In the present application, the conductive protrusion 123 includes at least one conductive particle 124. The conductive protrusion 123 can be formed by agglomeration of one or more conductive particles 124, and the conductive particles 124 are used to pierce the glue film layer and the ground layer of the circuit board to make contact.

[0093] The conductive particles 124 include one or more of metal particles, carbon nanotube particles and ferrite particles. In addition, the metal particles include single metal particles and / or alloy particles; wherein the single metal particles are made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy particles are made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. It should be noted that the conductive particles 124 can be the same as or different from the material of the shielding layer 12.

[0094] In the roughening process of the shielding layer, the conductive protrusions formed by the simple metal plating layer are prone to deformation due to mechanical stress or pressing pressure, and the addition of the conductive particles can enhance the structural strength of the protrusions through mechanical engagement between the particles, and the conductive protrusions formed by the agglomeration of the conductive particles maintain a sharp form at the top of the protrusions, which can effectively pierce the adhesive film layer to achieve reliable grounding.

[0095] As a preferred embodiment, the present application limits the composition structure of the adhesive film layer 13.

[0096] In one embodiment, the adhesive film layer 13 includes an adhesive layer without conductive particles.

[0097] The present application can reduce the insertion loss of the circuit board during use by setting the adhesive film layer 13 as an adhesive layer without conductive particles, improve the shielding effectiveness, and improve the bending property of the circuit board.

[0098] In another embodiment, referring to Figure 6 is a structural schematic diagram of a fifth electromagnetic shielding film provided by the present application, and the adhesive film layer 13 includes an adhesive layer containing conductive particles 131.

[0099] By controlling the adhesive film layer 13 to be an adhesive layer containing conductive particles 131, the conductive particles 131 and the conductive protrusions 123 provided on the second peak top of the second rough surface of the shielding layer 12 cooperate to pierce the adhesive film layer 13, and the conductive particles 131 cooperate with the shielding layer 12 to achieve more reliable piercing grounding and rapidly guide the interference charge into the ground layer of the circuit board.

[0100] In specific embodiments, the structure of the electromagnetic shielding film of the present application is compared with that of a conventional electromagnetic shielding film. The electromagnetic shielding film S of the present application includes samples S1 to S5, and each of the samples S1 to S5 includes an insulating layer, a shielding layer, and an adhesive film layer which are sequentially stacked. The comparative electromagnetic shielding film R includes comparisons R1 to R3, and each of the comparisons R1 to R3 includes an insulating layer, a shielding layer, and an adhesive film layer which are sequentially stacked. The electromagnetic shielding films are sliced along the thickness direction, the structural parameters of the insulating layer within any 100 μm length are tested, and the electromagnetic shielding films are pressed on the circuit board substrate to form a circuit board, the grounding resistance of multiple openings of the circuit board is tested, and the extreme difference of the grounding resistance is calculated. The test data of the electromagnetic shielding film S of the present application and the comparative electromagnetic shielding film R are shown in Tables 1 and 2:

[0101] Table 1

[0102]

[0103] According to the data analysis of Table 1, in the samples S1-S5 of the embodiment of the application, the number of first wave peaks is in the range of 11-31, meeting the requirement of being greater than or equal to 10, the interval is controlled in 3-10 μm, the height difference is controlled in 0.3-0.8 μm, meeting the requirement of being less than 1 μm, and the corresponding ground resistance difference value is only 52-88 mΩ, the numerical fluctuation is small and the overall level is low. This shows that in this number interval, the wave peak distribution can provide a uniform adhesion basis for the shielding layer, at the same time, the number, interval and height difference of the wave peaks formed by the shielding layer replication also meet the requirement of uniform distribution, all the wave peaks can be pierced through the adhesive film layer synchronously and uniformly during pressing, the ground resistance consistency is excellent, the grounding instability problem caused by local over-dense or over-sparse is avoided, and then the stability of current conduction during grounding is ensured, and the resistance difference is reduced.

[0104] The wave peak number of the controls R1 and R3 is relatively large, and the wave peak interval is relatively small, and the height difference exceeds 1 μm, resulting in that the roughness uniformity of the shielding layer replication is insufficient, the wave peaks are excessively dense, the shielding layer replication is prone to local stacking, the adhesive film layer is not uniformly pierced during pressing, and the resistance difference is significantly increased.

[0105] The wave peak number of the control R2 is less than 10, and the wave peak interval is excessively large, and the height difference exceeds 1 μm, resulting in that the roughness of the shielding layer replication is insufficient, the local wave peak-free area cannot effectively pierce the adhesive film layer for grounding, the local contact is poor during pressing and grounding, and the resistance difference is also large.

[0106] Compared with the control electromagnetic shielding film R, the ground resistance difference of the circuit board is small after the electromagnetic shielding film S of the embodiment of the application is pressed to the circuit board, and the ground resistance uniformity is more excellent, thereby reflecting that the grounding performance and shielding effect of the electromagnetic shielding film are more excellent.

[0107] Referring to Figure 7 is a structural schematic diagram of a circuit board provided by the embodiment of the application, and the embodiment of the application further provides a circuit board 20, which comprises a circuit board substrate 21 and the electromagnetic shielding film 10 described in any one of the embodiments.

[0108] The circuit board substrate 21 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board and a rigid-flexible combination board.

[0109] It should be noted that the structure, working principle and beneficial effects of the electromagnetic shielding film correspond one-to-one to the electromagnetic shielding film 10 described in any one of the embodiments, and thus will not be described again.

[0110] Through the above structure, in the process of pressing the electromagnetic shielding film on the circuit board substrate, the adhesive film layer 13 is pierced by the second wave crest 122 of the shielding layer 12 or the conductive protrusion 123 arranged thereon, so that at least a part of the shielding layer is connected with the ground layer of the circuit board substrate 21, thereby realizing the introduction of interference charges in the shielding layer 12 into the ground, avoiding the accumulation of interference charges to form interference sources, and affecting the normal work of the circuit board.

[0111] The above is the preferred embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements are also considered to be within the scope of the present application.

Claims

1. An electromagnetic shielding film, characterized by, The insulating layer, the shielding layer and the adhesive film layer are sequentially stacked. The side surface of the insulating layer close to the shielding layer is a first rough surface, and the first rough surface is provided with a plurality of first peaks, and in the state of a slice along the thickness direction, the number of the first peaks in any 100 μm length is greater than or equal to 10, and the distance between adjacent two first peaks is 3-10 μm, and the height difference is less than or equal to 1 μm. The side surface of the shielding layer away from the insulating layer is a second rough surface, and the shielding layer is conformal with the first rough surface, so that the second rough surface forms second peaks corresponding to the first peaks of the first rough surface, and the second peaks are covered by the adhesive film layer.

2. The electromagnetic shielding film according to claim 1, wherein In the state of a slice along the thickness direction, the difference between the maximum peak height and the minimum peak height on the first rough surface in any 100 μm length is less than or equal to 1 μm; wherein the maximum peak height refers to the height value of the first peak with the maximum height, and the minimum peak height refers to the height value of the first peak with the minimum height.

3. The electromagnetic shielding film according to claim 1, wherein The roughness Rz of the first rough surface is 3-15 μm.

4. The electromagnetic shielding film according to claim 1, wherein The insulating layer is filled with magnetic particles, and in the state of a slice along the thickness direction, each first peak contains at least one magnetic particle.

5. The electromagnetic shielding film according to claim 4, wherein The particle size of the magnetic particles is 1-10 μm.

6. The electromagnetic shielding film according to claim 5, wherein 70% of the magnetic particles in the insulating layer have a particle size of 2-5 μm.

7. The electromagnetic shielding film according to claim 4, wherein The total mass of the magnetic particles accounts for 1%-10% of the total mass of the insulating layer, and at least 70% of the magnetic particles are distributed on the side close to the first rough surface.

8. The electromagnetic shielding film according to any one of claims 1 to 7, wherein The top of each second peak is provided with a conductive protrusion.

9. The electromagnetic shielding film according to claim 8, wherein The conductive protrusion is formed by agglomeration of one or more conductive particles.

10. A wiring board, characterized by The electromagnetic shielding film as claimed in any one of claims 1-9 is pressure-bonded to the circuit board substrate through the adhesive film layer.

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