Free grounding film, circuit board and preparation method of free grounding film

Abstract

An embodiment of the present invention provides a free grounding film, a circuit board, and a preparation method of the free grounding film. The free grounding film includes a third conductor layer, a film adhesive layer, and a first conductor layer, a conductive adhesive layer, and a second conductor layer that are sequentially stacked. A convex portion is provided on a surface of the second conductor layer away from the conductive adhesive layer; the third conductor layer is disposed on the surface of the second conductor layer where the convex portion is formed, and a convex portion is formed at a position where the third conductor layer covers the convex portion; the film adhesive layer is disposed on a surface of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, and the free grounding film is pressed against the electromagnetic shielding film through the film adhesive layer. The convex portion pierces through the insulating layers of the film adhesive layer and the electromagnetic shielding film and is electrically connected to the shielding layer of the electromagnetic shielding film, so as to effectively lead out the interfering charges accumulated on the shielding layer, avoid the accumulation of interfering charges to form an interference source, and further effectively ensure the integrity of signal transmission.

Description

Technical Field

[0001] The invention relates to the field of electronics, and in particular to a free grounding film, a circuit board and a method for preparing the free grounding film. Background Art

[0002] With the rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightness, and high-density assembly, which greatly promotes the development of flexible circuit boards, thereby realizing the integration of component devices and wire connections. Flexible circuit boards can be widely used in industries such as mobile phones, LCD displays, communications, and aerospace.

[0003] Driven by the international market, functional flexible circuit boards dominate the flexible circuit board market, and an important indicator for evaluating the performance of functional flexible circuit boards is electromagnetic interference shielding (EMI shielding). With the integration of functions of mobile phones and other communication devices, their internal components are rapidly becoming high-frequency and high-speed. For example, in addition to the original audio transmission function, the camera function has become a necessary function of mobile phones, and WLAN (Wireless Local Area Networks), GPS (Global Positioning System) and Internet access functions have become popular. Coupled with the integration of future sensing components, the trend of rapid high-frequency and high-speed components is even more inevitable. Driven by high frequency and high speed, the electromagnetic interference inside and outside the components, signal attenuation during transmission, insertion loss and jitter problems are becoming increasingly serious.

[0004] At present, the commonly used free grounding film of the existing circuit board generally includes a conductor layer and a conductive adhesive layer. The conductor layer is in contact and connected with the shielding layer of the electromagnetic shielding film through the conductive adhesive layer, so that when the printed circuit board is applied to an electronic device, it can be electrically connected to the shell of the electronic device through the free grounding film, thereby extracting the interference charge of the electromagnetic shielding film. However, in the process of implementing the present invention, the inventor found that there are at least the following problems in the prior art: at high temperature, due to the expansion of the conductive adhesive layer, the conductive particles that were originally in contact with each other in the conductive adhesive layer are pulled apart, or the conductive particles that were originally in contact with the electromagnetic shielding film are pulled apart, resulting in the failure of the connection between the free grounding film and the electromagnetic shielding film, so that the interference charge accumulated on the electromagnetic shielding film cannot be effectively extracted, thereby forming an interference source, affecting the signal transmission of the circuit board. Summary of the invention

[0005] The purpose of the present invention is to provide a free grounding film, a circuit board and a method for preparing the free grounding film, which can achieve reliable connection between the free grounding film and the electromagnetic shielding film to ensure that the interference charges in the electromagnetic shielding film can be extracted, thereby ensuring the integrity of signal transmission.

[0006] To solve the above technical problems, the present invention provides a free grounding film, which includes a first conductor layer, a conductive adhesive layer, and a second conductor layer that are sequentially stacked. A protrusion is provided on a surface of the second conductor layer away from the conductive adhesive layer.

[0007] The free grounding film further includes a third conductor layer and a film adhesive layer. The third conductor layer is provided on a surface of the second conductor layer where the protrusion is formed, and a protrusion portion is formed at a position where the third conductor layer covers the protrusion. The film adhesive layer is provided on a surface of the third conductor layer away from the second conductor layer.

[0008] When the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board. The electromagnetic shielding film includes a shielding layer and an insulating layer that are stacked. The free grounding film is pressed and bonded to the electromagnetic shielding film through the film adhesive layer, and the protrusion portion pierces through the film adhesive layer and the insulating layer and is electrically connected to the shielding layer.

[0009] As an improvement of the above solution, a first through hole penetrating through upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating through upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating through upper and lower surfaces thereof is provided on the conductive adhesive layer.

[0010] A corresponding protrusion is formed at an outer side of each second through hole. The protrusion is formed by curing of a resin having fluidity when flowing from the first through hole through the third through hole to the outer side of the second through hole. Among them, the outer side of the second through hole is away from the conductive adhesive layer.

[0011] As an improvement of the above solution, a first through hole penetrating through upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating through upper and lower surfaces thereof is provided on the second conductor layer.

[0012] A corresponding protrusion is formed at an outer side of each second through hole. The protrusion is formed by cooling and solidifying of the resin provided in the first through hole and the conductive adhesive layer when flowing to the outer side of the second through hole after being heated and melted. Among them, the outer side of the second through hole is away from the conductive adhesive layer.

[0013] As an improvement of the above solution, convex conductor particles are provided on a surface of the protrusion portion. The height of the conductor particles is 20μm - 100μm.

[0014] As an improvement of the above solution, the first conductor layer, the second conductor layer, and the third conductor layer respectively include one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer.

[0015] As an improvement of the above solution, the metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer; wherein, the single-metal conductor layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy conductor layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0016] As an improvement of the above solution, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is disposed on a surface of the first conductor layer away from the conductive adhesive layer.

[0017] As an improvement of the above solution, the free grounding film further includes a peelable protective film layer, and the peelable protective film layer is disposed on a surface of the adhesive film layer away from the third conductor layer.

[0018] As an improvement of the above solution, the adhesive film layer includes an adhesive layer containing conductive particles; or, the adhesive film layer includes an adhesive layer without conductive particles.

[0019] Compared with the prior art, the embodiment of the present invention discloses a free grounding film. By providing the protrusion on a surface of the second conductor layer away from the conductive adhesive layer, and disposing the third conductor layer on the surface of the second conductor layer where the protrusion is formed, a protrusion portion is formed at a position where the third conductor layer covers the protrusion. At the same time, the adhesive film layer is disposed on a surface of the third conductor layer away from the second conductor layer, so that when the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the protrusion portion can sequentially pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film, and be connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, and further ensuring the grounding of the electromagnetic shielding film, effectively avoiding the problem that when the temperature is high, the connection between the free grounding film and the electromagnetic shielding film fails due to the free grounding film being pressed against the electromagnetic shielding film through the conductive adhesive layer and the interfering charges cannot be quickly led out, so as to ensure the integrity of signal transmission.

[0020] To solve the same technical problem, the present invention further provides a circuit board, which includes a printed circuit board, an electromagnetic shielding film, and the above free grounding film. The electromagnetic shielding film is disposed on the printed circuit board. The electromagnetic shielding film includes a shielding layer and an insulating layer stacked. The free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the protrusion portion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0021] Compared with the prior art, an embodiment of the present invention discloses a circuit board, which includes a printed circuit board, an electromagnetic shielding film, and the free grounding film described in any one of the above. When the free grounding film is laminated with the electromagnetic shielding film through its adhesive film layer, the convex portion can sequentially pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film and connect with the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, further ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that when the temperature is high, due to the free grounding film being laminated with the electromagnetic shielding film through the conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly led out, so as to effectively avoid the accumulation of interfering charges and affect the normal operation of the printed circuit board.

[0022] To solve the same technical problem, the present invention also provides a preparation method of a free grounding film, which is applicable to preparing the above-mentioned free grounding film, and includes the steps:

[0023] Form a first conductor layer, form a conductive adhesive layer on one surface of the first conductor layer, and form a second conductor layer on the surface of the conductive adhesive layer away from the first conductor layer;

[0024] Form a convex on the surface of the second conductor layer away from the conductive adhesive layer;

[0025] Form a third conductor layer on the surface of the second conductor layer where the convex is formed, and form a convex at the position where the third conductor layer covers the convex;

[0026] Form an adhesive film layer on the surface of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding the printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer stacked, and the free grounding film is laminated with the electromagnetic shielding film through the adhesive film layer, and the convex portion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0027] As an improvement of the above solution, a first through hole penetrating the upper and lower surfaces is provided on the first conductor layer, a second through hole penetrating the upper and lower surfaces is provided on the second conductor layer, and a third through hole penetrating the upper and lower surfaces is provided on the conductive adhesive layer;

[0028] Then, forming a convex on the surface of the second conductor layer away from the conductive adhesive layer specifically is:

[0029] A resin with fluidity is disposed at the first through hole, such that the resin with fluidity flows from the first through hole through the third through hole to the outside of the second through hole and is cured, thereby forming a protrusion on a surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

[0030] As an improvement to the above solution, the flowing of the resin with fluidity from the first through hole through the third through hole to the outside of the second through hole and curing specifically includes:

[0031] A resin that is uncured or semi-cured at room temperature is disposed at the first through hole, such that the resin that is uncured or semi-cured at room temperature flows from the first through hole through the third through hole to the second through hole, and the resin that is uncured or semi-cured at room temperature flowing to the outside of the second through hole is thermally cured;

[0032] Or, specifically includes:

[0033] A resin is disposed at the first through hole, the resin is heated and melted, and the resin flowing to the outside of the second through hole is cooled and solidified.

[0034] As an improvement to the above solution, a resin is provided on a surface of the first conductor layer away from the conductive adhesive layer, and the conductive adhesive layer is a hot melt adhesive layer;

[0035] A first through hole penetrating through the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating through the upper and lower surfaces thereof is provided on the second conductor layer;

[0036] Then, the forming of the protrusion on a surface of the second conductor layer away from the conductive adhesive layer specifically includes:

[0037] At a preset temperature, the resin is caused to flow from the first through hole to the second through hole, and the conductive adhesive layer forms a hot melt adhesive flow to the second through hole during the flowing of the resin;

[0038] The resin and the hot melt adhesive flowing to the outside of the second through hole are cooled and solidified, thereby forming the protrusion on a surface of the second conductor layer away from the conductive adhesive layer.

[0039] As an improvement to the above solution, before forming a glue film layer on a surface of the third conductor layer away from the second conductor layer, further included is:

[0040] By one or more processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating, a plurality of conductor particles are formed on an outer surface of the protrusion portion.

[0041] As an improvement of the above solution, forming a glue film layer on the side of the third conductor layer away from the second conductor layer specifically includes:

[0042] Coating a glue film layer on a release film, and then laminating and transferring the glue film layer to the side of the third conductor layer away from the second conductor layer; or,

[0043] Directly forming a glue film layer on the side of the third conductor layer away from the second conductor layer.

[0044] Compared with the prior art, in the method for preparing a free grounding film provided by the embodiment of the present invention, a protrusion is formed on the side of the second conductor layer away from the conductive glue layer, and then a third conductor layer is formed on the side of the second conductor layer where the protrusion is formed, so as to form a protrusion part at the position where the third conductor layer covers the protrusion. Finally, a glue film layer is formed on the side of the third conductor layer away from the second conductor layer. When the free grounding film is laminated with the electromagnetic shielding film through its glue film layer, the protrusion part can successively pierce the glue film layer and the insulating layer of the electromagnetic shielding film, and be connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, further ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that when the temperature is high, since the free grounding film is laminated with the electromagnetic shielding film through the conductive glue layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly led out. Therefore, the accumulation of interfering charges is effectively avoided, and the normal operation of the printed circuit board is not affected. Description of the Drawings

[0045] Figure 1 is a schematic structural diagram of a free grounding film provided by Embodiment 1 of the present invention;

[0046] Figure 2 is a schematic structural diagram of a free grounding film provided by Embodiment 2 of the present invention;

[0047] Figure 3 is a schematic structural diagram of a free grounding film provided by Embodiment 3 of the present invention;

[0048] Figure 4 is a schematic structural diagram of a free grounding film provided by Embodiment 4 of the present invention;

[0049] Figure 5 is a cross-sectional view of a free grounding film provided by an embodiment of the present invention;

[0050] Figure 6 is a schematic structural diagram of a circuit board provided by Embodiment 5 of the present invention;

[0051] Figure 7 is a flowchart of a method for preparing a free grounding film provided by Embodiment 6 of the present invention.

[0052] Among them, 1 is the first conductor layer; 10 is the first through hole; 2 is the conductive adhesive layer; 20 is the third through hole; 3 is the second conductor layer; 30 is the second through hole; 4 is the third conductor layer; 40 is the raised portion; 41 is the conductor particle; 5 is the adhesive film layer; 6 is the protrusion; 7 is the anti-oxidation layer; 8 is the electromagnetic shielding film; 80 is the insulating layer; 81 is the shielding layer; 9 is the printed circuit board; 11 is the resin. Specific embodiments

[0053] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0054] Embodiment 1

[0055] Please refer to Figure 1 , the embodiment of the present invention provides a free grounding film, which includes a first conductor layer 1, a conductive adhesive layer 2 and a second conductor layer 3 that are sequentially stacked. A protrusion 6 is provided on the surface of the second conductor layer 3 away from the conductive adhesive layer 2;

[0056] The free grounding film further includes a third conductor layer 4 and an adhesive film layer 5. The third conductor layer 4 is provided on the surface of the second conductor layer 3 where the protrusion 6 is formed, and a raised portion 40 is formed at the position where the third conductor layer 4 covers the protrusion 6 (the relationship between the raised portion 40 and the protrusion 6 can be one-to-one, one-to-many or many-to-one, etc. When the relationship between the raised portion 40 and the protrusion 6 is one-to-one, the shape structure of the raised portion 40 and the shape structure of the protrusion 6 can correspond to each other or be different from each other); the adhesive film layer 5 is provided on the surface of the third conductor layer 4 away from the second conductor layer 3.

[0057] In an embodiment of the present invention, a protrusion 6 is provided on a surface of the second conductor layer 3 away from the conductive adhesive layer 2, and the third conductor layer 4 is disposed on a surface of the second conductor layer 3 where the protrusion 6 is formed, so that a protrusion portion 40 is formed at a position where the third conductor layer 4 covers the protrusion 6. At the same time, the adhesive film layer 5 is disposed on a surface of the third conductor layer 4 away from the second conductor layer 3. When the free grounding film is pressed against the electromagnetic shielding film 8 through its adhesive film layer 5, the protrusion portion 40 can successively pierce the adhesive film layer 5 and the insulating layer 80 of the electromagnetic shielding film 8 and connect to the shielding layer 81 of the electromagnetic shielding film 8, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film 8, further ensuring the grounding of the electromagnetic shielding film 8, and effectively avoiding the problem that when the temperature is high, since the free grounding film is pressed against the electromagnetic shielding film through the conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly led out, so the integrity of signal transmission is ensured.

[0058] In an embodiment of the present invention, preferably, refer to Figure 1 , the protrusion portion 40 extends into the adhesive film layer 5, which can make the protrusion portion 40 more easily pierce the adhesive film layer 5 and the insulating layer 80 of the electromagnetic shielding film 8 during the pressing process. Alternatively, the protrusion portion 40 can also pierce the adhesive film layer 5. In this way, during the pressing process of the electromagnetic shielding film 8 and the free grounding film, the protrusion portion 40 can directly pierce the insulating layer 80 of the electromagnetic shielding film 8 and connect to the shielding layer 81 of the electromagnetic shielding film 8. Of course, the protrusion portion 40 may not extend into the adhesive film layer 5 but be covered by the adhesive film layer 5.

[0059] In the above embodiment, in order to ensure good electrical conductivity of the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4, preferably, the first conductor layer 1 includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer; the second conductor layer 3 includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer; the third conductor layer 4 includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer. Among them, the metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer; among them, the single-metal conductor layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy conductor layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0060] Specifically, the thickness of the first conductor layer 1, the thickness of the second conductor layer 3 and the thickness of the third conductor layer 4 are preferably 2 μm-45 μm, so as to ensure that the first conductor layer, the second conductor layer and the third conductor layer are not easy to break and have good flexibility.

[0061] In the above embodiment, it should be noted that the first conductor layer 1, the second conductor layer 3 and the third conductor layer 4 can all be single-layer structures or multi-layer structures. In addition, according to the needs of actual production and application, the first conductor layer 1, the second conductor layer 3 and the third conductor layer 4 can be arranged in a grid shape, a foam shape, etc.

[0062] In the above embodiment, the two sides of the first conductor layer 1 can be flat or undulating; the side of the second conductor layer 3 away from the protrusion can be flat or undulating; the side of the third conductor layer 4 close to the protrusion can be flat or undulating, and no specific limitation is made here.

[0063] In the above embodiment, preferably, in order to protect the adhesive film layer 5, the free grounding film in this embodiment also includes a peelable protective film layer (not shown), and the peelable protective film layer is arranged on the side of the adhesive film layer 5 away from the third conductor layer 4. The peelable protective film layer plays a protective role to prevent the adhesive film layer 5 from being damaged before use, thereby ensuring that the free grounding film can be pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5. It should be noted that when the free grounding film is pressed together with the electromagnetic shielding film 8, the peelable protective film layer needs to be peeled off, and then the free grounding film is pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5.

[0064] In addition, the peelable protective film layer includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after epoxy resin ink is cured, a film layer formed after polyurethane ink is cured, a film layer formed after modified acrylic resin is cured, or a film layer formed after polyimide resin is cured.

[0065] In the embodiment of the present invention, in order to protect the first conductor layer 1 and ensure that the interference charges can be led out, the free grounding film in this embodiment further includes an anti-oxidation layer 7, and the anti-oxidation layer 7 is provided on the side of the first conductor layer 1 away from the conductive adhesive layer 2. By providing the anti-oxidation layer 7 on the side of the first conductor layer 1 away from the conductive adhesive layer 2, the first conductor layer 1 is prevented from being oxidized by contact with air, thereby ensuring that the interference charges accumulated in the electromagnetic shielding film 8 can be led out through the free grounding film.

[0066] In one preferred embodiment, the material of the anti-oxidation layer 7 is one of a metal material, ferrite, graphite, carbon nanotubes, graphene, and silver paste; wherein, the metal material is any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; or the metal material is an alloy formed by two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; at this time, the thickness of the anti-oxidation layer 7 is 0.01 μm - 5 μm, and the thickness of the anti-oxidation layer 7 is preferably 0.1 μm - 1 μm. Additionally, the anti-oxidation layer 7 can be formed by one of electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, or a composite process of at least two of the above processes.

[0067] In another preferred embodiment, the anti-oxidation layer 7 is made of a mixture of glue and conductive particles; wherein, the volume ratio of the conductive particles to the glue is 5% - 80%; at this time, the thickness of the anti-oxidation layer 7 is preferably 0.1 μm - 5 μm. Additionally, the anti-oxidation layer 7 can be formed by a process of coating and then curing.

[0068] In the above embodiment, one structure of the adhesive film layer 5 is specifically as follows: the adhesive film layer 5 includes an adhesive layer containing conductive particles (not shown in the figure). By making the adhesive film layer 5 include an adhesive layer containing conductive particles, the adhesive film layer 5 not only has an adhesive function to tightly bond the free grounding film and the electromagnetic shielding film 8, but also has a conductive function, which cooperates with the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 to quickly conduct interfering electrons. Among them, the conductive particles of the adhesive film layer 5 can be mutually separated conductive particles or large particle conductive particles formed by aggregation; when the conductive particles are mutually separated conductive particles, the electrical contact area can be further increased and the uniformity of electrical contact can be improved; while when the conductive particles are large particle conductive particles formed by aggregation, the piercing strength can be increased.

[0069] In the above embodiment, another structure of the adhesive film layer 5 is specifically as follows: the adhesive film layer 5 includes an adhesive layer without conductive particles (not shown in the figure). By making the adhesive film layer 5 include an adhesive layer without conductive particles, the adhesive film layer 5 has an adhesive function to tightly bond the free grounding film and the electromagnetic shielding film 8, and at the same time reduces the insertion loss of the circuit board during use and improves the bendability of the circuit board.

[0070] In the above embodiment, specifically, the outer surface of the adhesive film layer 5 can be flat or uneven, and no specific limitation is made on the shape structure of the outer surface of the adhesive film layer 5.

[0071] In the above embodiments, specifically, the thickness of the adhesive film layer 5 is 0.1 μm - 80 μm.

[0072] In the above embodiments, the adhesive film layer 5 is a pure adhesive film layer (i.e., a film layer formed by applying pure adhesive on the third conductor layer 4) or a conductive adhesive film layer (i.e., a film layer formed by applying conductive adhesive on the third conductor layer 4). Specifically, the materials used for the adhesive film layer 5 are selected from the following: modified epoxy resins, acrylics, modified rubbers, modified thermoplastic polyimides.

[0073] In the above embodiments, the outer surface of the adhesive film layer 5 can be flat or undulating.

[0074] It should be noted that the adhesive film layer 5 can be made of other materials in addition to being a pure adhesive film layer or a conductive adhesive film layer, as long as it can be smoothly pierced by the convex portion 40 during the pressing process.

[0075] In the above embodiments, by providing the conductive adhesive layer 2 between the first conductor layer 1 and the second conductor layer 3, the bendability of the free grounding film is effectively improved. In the above embodiments, the first conductor layer 1, the conductive adhesive layer 2, and the second conductor layer 3 can be porous or non-porous.

[0076] In the above embodiments, the convex 6 can be made of materials such as resin, conductive adhesive, or metal, that is, the convex 6 can be a resin convex 6, a conductive adhesive convex 6, or a metal convex 6, etc., which are not specifically limited herein.

[0077] Embodiment 2

[0078] Please refer to Figure 2 , this embodiment provides another free grounding film, the main difference from Embodiment 1 being that: the surface of the convex portion 40 is provided with convex conductor particles 41. Among them, by providing the conductor particles 41 on the surface of the convex portion 40, it is further ensured that during the pressing process, the convex portion 40 can smoothly pierce the adhesive film layer 5 and the insulating layer 80 of the electromagnetic shielding film 8, thereby ensuring the normal export of interfering charges.

[0079] In an embodiment of the present invention, the height of the conductor particles 41 is preferably 20 μm - 100 μm, the thickness of the adhesive film layer 5 is preferably 0.1 μm - 80 μm, and the thickness of the insulating layer 80 is preferably 1 μm - 20 μm. By setting the height of the conductor particles 41 to be preferably 20 μm - 100 μm and the thickness of the adhesive film layer 5 to be preferably 0.1 μm - 80 μm, it is ensured that the conductor particles 41 can pierce through the adhesive film layer 5 and the insulating layer 80 of the electromagnetic shielding film 8, thereby ensuring that the free grounding film can conduct out the interfering charges accumulated on the electromagnetic shielding film 8.

[0080] Preferably, the conductor particles 41 are concentratedly distributed at the outwardly protruding positions on the surface of the convex portion 40, making it easier to pierce through the adhesive film layer 5 and the insulating layer 80. Of course, the conductor particles 41 can also be distributed on the non-convex portions of the surface of the convex portion 40. In addition, the conductor particles 41 can also be distributed at other positions on the side of the third conductor layer 4 close to the adhesive film layer 5, not only distributed on the surface of the convex portion 40, as Figure 2 shown. Of course, the conductor particles 41 can also be distributed only on the surface of the convex portion 40.

[0081] In an embodiment of the present invention, the conductor particles 41 may have a certain distance from the inner surface of the adhesive film layer 5 (i.e., the surface facing the third conductor layer 4), may be in contact with the inner surface of the adhesive film layer 5, or may extend out of the outer surface of the adhesive film layer 5. In addition, the outer surface of the adhesive film layer 5 can be a flat surface without undulations or an uneven surface with undulations.

[0082] In an embodiment of the present invention, it should be noted that, as Figure 2 shown, the shape of the conductor particles 41 is only exemplary. Due to differences in process means and parameters, the conductor particles 41 can also be in other shapes such as cluster shape, icicle shape, stalactite shape, dendritic shape, etc. In addition, the conductor particles 41 in the present invention are not limited by the illustrated and above-mentioned shapes. As long as the conductor particles 41 have the functions of piercing and conducting electricity, they are within the protection scope of the present invention.

[0083] In an embodiment of the present invention, the conductor particles 41 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 the materials of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy particles are made of any two or more of the materials of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. It should be noted that the conductor particles 41 may be the same as or different from the material of the third conductor layer 4. In addition, the other structures and working principles of the free grounding film in this embodiment are the same as those in the first embodiment, and will not be elaborated here.

[0084] Embodiment Three

[0085] Please refer to Figure 3 and Figure 5 , this embodiment provides another free grounding film, and the main differences from the first and second embodiments are as follows: The formation process of the protrusion 6 is as follows: A first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, and a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3. The protrusion 6 is formed by the solidification of a resin with fluidity when flowing from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0086] Specifically, as Figure 3 shown, the protrusion 6 is formed by the solidification of a resin with fluidity when flowing from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30, and is specifically manifested as: A third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2;

[0087] A protrusion 6 is correspondingly formed at the outside of each second through hole 30; the protrusion 6 is formed by the solidification of a resin with fluidity when flowing from the first through hole 10 through the third through hole 20 to the outside of the second through hole 30; wherein, the outside of the second through hole 30 is far from the conductive adhesive layer 2.

[0088] Preferably, the first through hole 10, the second through hole 30, and the third through hole 20 are aligned with each other in a one-to-one correspondence, so that the resin with fluidity flows from the first through hole 10 to the outside of the corresponding second through hole 30. In another case, the first through hole 10, the second through hole 30, and the third through hole 20 may also be in a misaligned state. For example, the first through hole 10 and the second through hole 30 are partially aligned, and the second through hole 30 and the third through hole 20 are partially aligned, then the resin with fluidity can also flow from the first through hole 10 through the third through hole 20 to the outside of the second through hole 30 that is aligned or misaligned with it.

[0089] In an embodiment of the present invention, by solidifying the resin flowing from the first through-hole 10 on the first conductor layer 1 through the third through-hole 20 to the outside of the second through-hole 30 on the second conductor layer 3, the protrusion 6 is correspondingly formed. At the same time, the third conductor layer 4 is disposed on the surface of the second conductor layer 3 where the protrusion 6 is formed, so that a protrusion portion 40 is formed at a position corresponding to the protrusion 6 on the outer surface of the third conductor layer 4, and the adhesive film layer 5 is disposed on the surface of the third conductor layer 4 away from the second conductor layer 3, so that during the pressing process, it can be ensured that the protrusion portion 40 smoothly pierces through the adhesive film layer 5 and the insulating layer 80, thereby ensuring the normal export of interfering charges.

[0090] Specifically, the process of forming the protrusion 6 can be specifically as follows: The resin is a thermosetting resin, and uncured or semi-cured resin is coated at a position on the outer surface of the first conductor layer 1 (i.e., the surface away from the conductive adhesive layer 2) close to the first through-hole 10, and the uncured or semi-cured resin is made to flow from the first through-hole 10 through the third through-hole 20 to the corresponding third through-hole 20, and is thermoset when the liquid resin flows to the outside of the corresponding second through-hole 30. In addition, the process of forming the protrusion 6 can also be specifically as follows: The resin is a thermoplastic resin, and the heated resin is made to flow from the first through-hole 10 through the third through-hole 20 to the outside of the corresponding second through-hole 30 and is cold-set.

[0091] It should be noted that in an embodiment of the present invention, the resin flowing out of the corresponding through-hole is divided into the following three cases: The first is that the resin almost completely flows out of the corresponding through-hole and there is no residue in the through-hole; the second is that there is residual resin or even the through-hole is filled with resin; the third is that there is still resin residue at the edge of the outer orifice (i.e., the orifice facing outward) of the first through-hole 10. Among them, Figure 3 there is no resin residue in the through-hole, but Figure 3 is only exemplary, and the above three cases are all within the protection scope of the present invention. It can be understood that the Figure 4 mentioned below can refer to the relevant description here for Figure 3 .

[0092] In the embodiments of the present invention, the through holes (i.e., the first through hole 10, the second through hole 30, and the third through hole 20) can be distributed regularly or irregularly on the corresponding structural layers (i.e., the first conductor layer 1, the second conductor layer 3, and the conductive adhesive layer 2); wherein, the through holes being regularly distributed on the corresponding structural layer means that each through hole has the same shape and is evenly distributed on the corresponding structural layer; the through holes being irregularly distributed on the corresponding structural layer means that each through hole has different shapes and is disorderly distributed on the corresponding structural layer. Preferably, each through hole has the same shape and is evenly distributed on the corresponding structural layer. In addition, the through hole can be a circular through hole or any other shape of through hole. The present invention attaches Figure 5 Only taking the through hole as a circular through hole as an example for illustration, but any other shape of through hole is within the protection scope of the present invention.

[0093] In the embodiments of the present invention, the preparation method of the first conductor layer 1 having the first through hole 10 is specifically shown as: the first conductor layer 1 is formed by impregnating a metal sheet composed of a poorly soluble component with low solubility in a solvent and a readily soluble component with higher solubility in the solvent than the poorly soluble component in the solvent; wherein, the readily soluble component is a plurality of granular bodies dispersedly arranged in the metal sheet; by dissolving the granular bodies in the solvent, a plurality of first through holes 10 are formed on the first conductor layer 1. The preparation method of the second conductor layer 3 having the second through hole 30 is the same as that of the first conductor layer 1.

[0094] Specifically, one setting method of the poorly soluble component and the readily soluble component is specifically as follows: the poorly soluble component is a metal with copper as the main component, and the readily soluble component is copper oxide.

[0095] In addition, another setting method of the poorly soluble component and the readily soluble component is specifically as follows: the poorly soluble component is a metal with copper as the main component, and the readily soluble component is cuprous oxide.

[0096] In the embodiments of the present invention, in order to ensure that the resin protrusion 6 can be formed at the second through hole 30 and at the same time ensure that the second conductor layer 3 is not easily broken, preferably, in this embodiment, the cross-sectional area of the first through hole 10, the cross-section of the second through hole 30, and the cross-sectional area of the third through hole 20 are 0.01μm 2 -1mm 2 。

[0097] In addition, to ensure that sufficient said protrusions 6 can be formed to ensure that the third conductor layer 4 can pierce through the adhesive film layer 5 and the insulating layer 80 through the protrusion portions 40 formed thereon and thus be connected to the shielding layer 81, while ensuring that the second conductor layer 3 is not easily broken, in this embodiment, the number of the first through-holes 10 in the first conductor layer 1 per square centimeter is 5 - 10 6 , the number of the second through-holes 30 in the second conductor layer 3 per square centimeter is 5 - 10 6 , the number of the third through-holes 20 in the conductive adhesive layer 2 per square centimeter is 5 - 10 6 . Correspondingly, the number of the protrusions 6 in the second conductor layer 3 per square centimeter is 5 - 10 6 ; it should be noted that since the third conductor layer 4 wraps the protrusions 6, protrusion portions 40 are formed at positions corresponding to the protrusions 6 on the outer surface of the third conductor layer 4. Therefore, the number of the protrusion portions 40 corresponds to the number of the protrusions 6, ensuring that the third conductor layer 4 can smoothly pierce through the adhesive film layer 5 and the insulating layer 80. In addition, the other structures and working principles of the free grounding film in this embodiment are the same as those in Embodiment 1, and will not be elaborated here more

[0098] Embodiment 4

[0099] Please refer to Figure 4 , this embodiment provides another free grounding film, and the main difference from Embodiment 3 is that: the formation process of the protrusions 6 is as follows: the first through-holes 10 penetrating through the upper and lower surfaces are provided on the first conductor layer 1, the second through-holes 30 penetrating through the upper and lower surfaces are provided on the second conductor layer 3, and the protrusions 6 are formed by solidification when the resin with fluidity flows from the first through-holes 10 through the conductive adhesive layer 2 to the outside of the second through-holes 30

[0100] Specifically, as Figure 4 shown, the protrusions 6 are formed by solidification when the resin with fluidity flows from the first through-holes 10 through the conductive adhesive layer 2 to the outside of the second through-holes 30, and specifically manifested as: resin 11 is provided on the surface of the first conductor layer 1 away from the conductive adhesive layer 2, and the conductive adhesive layer 2 is a hot-melt adhesive layer

[0101] The protrusion 6 is formed correspondingly at the outer side of each second through hole 30; the protrusion 6 is formed by cooling and solidifying when the hot melt flows to the outer side of the second through hole 30; wherein the outer side of the second through hole 30 is far away from the conductive adhesive layer 2; the hot melt includes: the hot melt adhesive flowing from the first through hole 10 after the resin 11 is hot-melted, and the hot melt adhesive formed by the conductive adhesive layer 2 during the resin flow. It can be understood that the protrusion 6 is formed by cooling and solidifying when the resin provided in the first through hole 10 and the conductive adhesive layer 2 are melted by heat and flow to the outer side of the second through hole 30.

[0102] Preferably, the first through hole 10 and the second through hole 30 are aligned one by one, and the fluid resin flows from the first through hole 10 to the outside of the corresponding second through hole 30. In another case, the first through hole 10 and the second through hole 30 may also be in a non-aligned state, and the fluid hot melt may also flow from the first through hole 10 to the outside of the second through hole 30. In addition, the other structures and working principles of the free grounding film of this embodiment are the same as those of the third embodiment, and no further description is given here.

[0103] Embodiment 5

[0104] See also Figure 6 An embodiment of the present invention provides a circuit board, which includes a printed circuit board 9, an electromagnetic shielding film 8 and the free grounding film described in any one of embodiments one to four, wherein the electromagnetic shielding film 8 is arranged on the printed circuit board 9, and the electromagnetic shielding film 8 includes a stacked shielding layer 81 and an insulating layer 80, and the free grounding film is pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5, and the protrusion 40 pierces the adhesive film layer 5 and the insulating layer 80 and is electrically connected to the shielding layer 81.

[0105] In this embodiment, the implementation of the free grounding film can refer to the description of the above embodiment, which will not be repeated here.

[0106] Preferably, the printed circuit board 9 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0107] In a specific implementation, when the circuit board is applied to an electronic device, the interference charges accumulated in the electromagnetic shielding film 8 can be led out by electrically connecting the free grounding film to the housing of the electronic device.

[0108] In an embodiment of the present invention, through the above structure, during the lamination process of the free grounding film and the electromagnetic shielding film 6, the protrusions 40 on the third conductor layer 4 sequentially pierce the adhesive film layer 5 and the insulating layer 80 of the electromagnetic shielding film 8, and are connected to the shielding layer 81 of the electromagnetic shielding film 8, realizing the export of interfering charges in the electromagnetic shielding film 8, avoiding the accumulation of interfering charges to form an interference source, and affecting the normal operation of the circuit board.

[0109] Embodiment Six

[0110] See Figure 7 , an embodiment of the present invention provides a method for preparing a free grounding film, which is applicable to preparing the free grounding film described in Embodiment One. The structural diagram of the free grounding film can be referred to Figure 1 . Among them, the method for preparing the free grounding film includes steps S1 to S4:

[0111] S1. Form a first conductor layer 1, form a conductive adhesive layer 2 on one surface of the first conductor layer 1, and form a second conductor layer 3 on the surface of the conductive adhesive layer 2 away from the first conductor layer 1.

[0112] S2. Form a protrusion 6 on the surface of the second conductor layer 3 away from the conductive adhesive layer 2.

[0113] Specifically, the method of forming the protrusion 6 can be to directly apply a resin bump on the surface of the second conductor layer 3 away from the conductive adhesive layer 2 and thermoset or cold set to form the protrusion 6, or to directly spot weld a metal protrusion 6 on the surface of the second conductor layer 3 away from the conductive adhesive layer 2, etc., which is not specifically limited here.

[0114] S3. Form a third conductor layer 4 on the surface of the second conductor layer 3 where the protrusion 6 is formed, and form a protrusion 40 at the position where the third conductor layer 4 covers the protrusion 6 (the relationship between the protrusion 40 and the protrusion 6 can be one-to-one correspondence, one-to-many correspondence or many-to-one correspondence, etc.).

[0115] S4. Form an adhesive film layer 5 on the surface of the third conductor layer 4 away from the second conductor layer 3; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 8 is provided on the printed circuit board 9. The electromagnetic shielding film 8 includes a shielding layer 81 and an insulating layer 80 arranged in a stacked manner. The free grounding film is laminated with the electromagnetic shielding film 8 through the adhesive film layer 5, and the protrusion 40 pierces the adhesive film layer 5 and the insulating layer 80 and is electrically connected to the shielding layer 81.

[0116] In this embodiment, preferably, step S4 is specifically:

[0117] forming an adhesive film layer 5 on the release film, and then transferring the adhesive film layer 5 to the side of the third conductor layer 4 away from the second conductor layer 3 by pressing; or

[0118] An adhesive film layer 5 is directly formed on a surface of the third conductor layer 4 away from the second conductor layer 3 .

[0119] In this embodiment, the protrusion 6 is formed on the side of the second conductor layer 3 away from the conductive adhesive layer 2, and then the third conductor layer 4 is formed on the side of the second conductor layer 3 where the protrusion 6 is formed, so that the third conductor layer 4 covers the protrusion 6, thereby forming a protrusion 40 at the position of the third conductor layer 4 covering the protrusion 6, and finally the adhesive film layer 5 is formed on the side of the third conductor layer 4 away from the second conductor layer 3, so that the adhesive film layer 5 covers the protrusion 40. In this way, during the process of pressing the free grounding film and the electromagnetic shielding film 8, the protrusion 40 can sequentially pierce the adhesive film layer 5 and the insulating layer 80, and connect with the shielding layer 81, so that the interference charge can be smoothly discharged.

[0120] It should be noted that the preparation method of the free grounding film provided in this embodiment is only an example of preparing the free grounding film described in Embodiment 1. The free grounding film described in Embodiment 1 can also be made by other preparation methods. For example, a protrusion 6 can be first formed on one surface of the second conductor layer 3, and then the first conductor layer 1 and the conductive adhesive layer 2 are formed.

[0121] Embodiment 7

[0122] The embodiment of the present invention provides a method for preparing a free grounding film, which is suitable for preparing the free grounding film described in the second embodiment. The difference between the method and the sixth embodiment is that after the step S3 and before the step S4, the method further includes:

[0123] A plurality of conductive particles 41 are formed on the outer surface of the protrusion 40 by one or more processes selected from the group consisting of physical roughening, chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating. Figure 2 .

[0124] In this embodiment, by forming the conductor particles 41 on the surface of the protrusion 40 , it is further ensured that during the pressing process, the protrusion 40 can smoothly pierce the adhesive film layer 5 and the insulating layer 80 , thereby ensuring that the interference charges are normally discharged.

[0125] It should be noted that the manufacturing method of the conductor particles 41 can also be as follows: when manufacturing the third conductor layer 4, the conductor particles 41 and the third conductor layer 4 can be an integral structure formed by a one-step forming process, so that the conductor particles 41 are formed at corresponding positions on the side of the third conductor layer 4 away from the second conductor layer 3.

[0126] It can be understood that when the third conductor layer 4 is a multi-layer structure, the manufacturing method of the conductor particles 41 can also be as follows: the third conductor layer 4 is manufactured layer by layer in sequence, and when manufacturing each layer, the conductor particles 41 are formed at corresponding positions on this layer, so as to form the third conductor layer 4 with conductor particles 41 on each layer.

[0127] Embodiment VIII

[0128] The embodiment of the present invention provides a preparation method of a free grounding film, which is applicable to preparing the free grounding film described in Embodiment III. The main differences from Embodiment VI and Embodiment VII are as follows: the formation process of the protrusion 6 is as follows: a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3, and the protrusion 6 is formed by solidification when a resin with fluidity flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0129] Specifically, please refer to Figure 3 , a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3, and a third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2;

[0130] Then step S2 is specifically as follows:

[0131] Set a resin with fluidity at the first through hole 10, so that the resin with fluidity flows from the first through hole 10 through the third through hole 20 of the conductive adhesive layer 2 to the outside of the second through hole 30 and is cured, thereby forming a protrusion 6 on the side of the second conductor layer 3 away from the conductive adhesive layer 2; wherein, the outside of the second through hole 30 is far from the conductive adhesive layer 2.

[0132] In this embodiment, preferably, the step of flowing the resin with fluidity from the first through hole 10 through the third through hole 20 to the outside of the corresponding second through hole 30 and curing it specifically is:

[0133] A resin that is not cured or semi-cured at room temperature is provided at the first through hole 10, so that the resin that is not cured or semi-cured at room temperature flows from the first through hole 10 to the second through hole 30 via the third through hole 20, and the resin that is not cured or semi-cured at room temperature flowing to the outside of the second through hole 30 is thermoset;

[0134] Or, specifically:

[0135] A resin is provided at the first through hole 10, the resin is heated and melted, and the resin flowing to the outside of the second through hole 30 is cooled and solidified.

[0136] Preferably, the first through hole 10, the second through hole 30, and the third through hole 20 are aligned with each other one by one, so that the resin with fluidity flows from the first through hole 10 to the outside of the corresponding second through hole 30. Another situation is that the first through hole 10, the second through hole 30, and the third through hole 20 may also be in a misaligned state. For example, the first through hole 10 and the second through hole are partially aligned, and the second through hole and the third through hole are partially aligned, then the resin with fluidity can also flow from the first through hole 10 to the outside of the second through hole 30.

[0137] In the embodiment of the present invention, by solidifying the resin flowing from the first through hole 10 on the first conductor layer 1 to the outside of the second through hole 30 on the second conductor layer 3, a bump 6 is correspondingly formed, and at the same time, the third conductor layer 4 is provided on the surface of the second conductor layer 3 protruding with the bump 6 and covers the bump 6, so that a protruding portion 40 is formed at a position corresponding to the bump 6 on the outer surface of the third conductor layer 4, and the adhesive film layer 5 is provided on the surface of the third conductor layer 4 away from the second conductor layer 3, so that during the lamination process, the protruding portion 40 can smoothly pierce the adhesive film layer 5 and the insulating layer 80, thereby ensuring the normal export of interference charges.

[0138] Embodiment Nine

[0139] The embodiment of the present invention provides a method for preparing a free grounding film, which is applicable to preparing the free grounding film described in Embodiment Four. The main difference from Embodiment Eight is that the formation process of the bump 6 is as follows: a first through hole 10 penetrating the upper and lower surfaces thereof is provided on the first conductor layer 1, a second through hole 30 penetrating the upper and lower surfaces thereof is provided on the second conductor layer 3, and the bump 6 is formed by solidifying when the resin with fluidity flows from the first through hole 10 to the outside of the second through hole 30 via the conductive adhesive layer 2.

[0140] Specifically, please refer to Figure 4, a resin 5 is provided on a side of the first conductor layer 1 away from the conductive adhesive layer 2, and the conductive adhesive layer 2 is a hot-melt adhesive layer; a first through-hole 10 penetrating the upper and lower surfaces of the first conductor layer 1 is provided on the first conductor layer 1, and a second through-hole 30 penetrating the upper and lower surfaces of the second conductor layer 3 is provided on the second conductor layer 3;

[0141] Then the step S2 is specifically:

[0142] At a preset temperature, the resin flows from the first through-hole 10 to the second through-hole 30, and the conductive adhesive layer forms a hot-melt adhesive flow to the second through-hole 30 during the flow of the resin;

[0143] The resin and the hot-melt adhesive flowing to the outside of the second through-hole 30 are cooled and solidified, so as to form the protrusion 6 on a side of the second conductor layer 3 away from the conductive adhesive layer 2.

[0144] Preferably, the first through-holes 10 and the second through-holes 30 are aligned one by one, and the resin with fluidity flows from the first through-hole 10 to the outside of the corresponding second through-hole 30. Another situation is that the first through-holes 10 and the second through-holes 30 may also be in a non-aligned state, and the hot-melt material with fluidity can also flow from the first through-hole 10 to the outside of the second through-hole 30.

[0145] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and replacements can be made, and these improvements and replacements should also be regarded as the protection scope of the present invention.

Claims

1. A free grounding membrane, characterized in that: It includes a first conductor layer, a conductive adhesive layer, and a second conductor layer that are sequentially stacked, and a protrusion is provided on a surface of the second conductor layer away from the conductive adhesive layer; The free grounding film further includes a third conductor layer and a film adhesive layer. The third conductor layer is provided on a surface of the second conductor layer where the protrusion is formed, and a protrusion portion is formed at a position where the third conductor layer covers the protrusion; the film adhesive layer is provided on a surface of the third conductor layer away from the second conductor layer; When the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board. The electromagnetic shielding film includes a shielding layer and an insulating layer that are stacked. The free grounding film is pressed against the electromagnetic shielding film through the film adhesive layer, and the protrusion portion pierces through the film adhesive layer and the insulating layer and is electrically connected to the shielding layer; The first conductor layer, the second conductor layer, and the third conductor layer each include one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer; The metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer; A first through hole penetrating through its upper and lower surfaces is provided on the first conductor layer, a second through hole penetrating through its upper and lower surfaces is provided on the second conductor layer, and a third through hole penetrating through its upper and lower surfaces is provided on the conductive adhesive layer; A protrusion is correspondingly formed at an outer side of each of the second through holes; the protrusion is formed by curing when a resin with fluidity flows from the first through hole through the third through hole to the outer side of the second through hole; wherein, the outer side of the second through hole is away from the conductive adhesive layer; Alternatively, a first through hole penetrating through its upper and lower surfaces is provided on the first conductor layer, and a second through hole penetrating through its upper and lower surfaces is provided on the second conductor layer; a protrusion is correspondingly formed at an outer side of each of the second through holes; the protrusion is formed by cooling and solidifying when the resin provided in the first through hole and the conductive adhesive layer are heated and melted and flow to the outer side of the second through hole; wherein, the outer side of the second through hole is away from the conductive adhesive layer.

2. The free grounding membrane according to claim 1, characterized in that: Convex conductor particles are provided on a surface of the protrusion portion; the height of the conductor particles is 20 μm - 100 μm.

3. The free grounding membrane according to claim 2, characterized in that: The single-metal conductor layer is made of any one of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy conductor layer is made of any two or more of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

4. The free grounding membrane according to any one of claims 1 to 3, characterized in that: The free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is provided on a surface of the first conductor layer away from the conductive adhesive layer.

5. The freely grounded film according to any one of claims 1 to 3, characterized in that, The free grounding film further includes a peelable protective film layer, and the peelable protective film layer is provided on a surface of the film adhesive layer away from the third conductor layer.

6. The free grounding film according to any one of claims 1 to 3, characterized in that, The film adhesive layer includes an adhesive layer containing conductive particles; or, the film adhesive layer includes an adhesive layer not containing conductive particles.

7. A circuit board, characterized in that, Comprising a printed circuit board, an electromagnetic shielding film, and a free grounding film as described in any one of claims 1-6, the electromagnetic shielding film is disposed on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer stacked, the free grounding film is pressed and bonded with the electromagnetic shielding film through the adhesive film layer, and the convex portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

8. A method for preparing a free-grounding film, characterized in that, Suitable for preparing the free grounding film as described in any one of claims 1-6, including the steps of: Forming a first conductor layer, forming a conductive adhesive layer on one surface of the first conductor layer, and forming a second conductor layer on a surface of the conductive adhesive layer away from the first conductor layer; Forming a protrusion on a surface of the second conductor layer away from the conductive adhesive layer; Forming a third conductor layer on a surface of the second conductor layer where the protrusion is formed, and forming a convex portion at a position where the third conductor layer covers the protrusion; Forming an adhesive film layer on a surface of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer stacked, the free grounding film is pressed and bonded with the electromagnetic shielding film through the adhesive film layer, and the convex portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

9. The preparation method of the freely grounded film according to claim 8, characterized in that, A first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating the upper and lower surfaces thereof is provided on the conductive adhesive layer; Then, forming the protrusion on a surface of the second conductor layer away from the conductive adhesive layer specifically is: Providing a resin with fluidity at the first through hole, such that the resin with fluidity flows from the first through hole through the third through hole to the outside of the second through hole and is cured, thereby forming a protrusion on a surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

10. The method for preparing a freely grounded film according to claim 9, characterized in that, Specifically, flowing the resin with fluidity from the first through hole through the third through hole to the outside of the second through hole and curing it is: Providing a resin that is uncured or semi-cured at normal temperature at the first through hole, making the resin that is uncured or semi-cured at normal temperature flow from the first through hole through the third through hole to the second through hole, and thermally curing the resin that is uncured or semi-cured at normal temperature flowing to the outside of the second through hole; Or, specifically is: Providing a resin at the first through hole, heating and melting the resin, and cooling and solidifying the resin flowing to the outside of the second through hole.

11. The method for preparing a freely grounded film according to claim 8, characterized in that, A resin is provided on a surface of the first conductor layer away from the conductive adhesive layer, and the conductive adhesive layer is a hot melt adhesive layer; A first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer; Then, forming the protrusion on a surface of the second conductor layer away from the conductive adhesive layer specifically is: The resin is caused to flow from the first through-hole to the second through-hole at a preset temperature, and the conductive adhesive layer forms a hot melt adhesive that flows to the second through-hole during the resin flow; The resin and the hot melt adhesive flowing to the outside of the second through-hole are cooled and solidified, so as to form the protrusion on the surface of the second conductor layer away from the conductive adhesive layer.

12. The method for preparing a free-grounding film according to claim 8, characterized in that, Before forming the adhesive film layer on the surface of the third conductor layer away from the second conductor layer, it further includes: Forming a plurality of conductor particles on the outer surface of the protrusion part by one or more processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and hybrid plating.

13. The preparation method of the freely grounded film according to claim 8, characterized in that, The forming of the adhesive film layer on the surface of the third conductor layer away from the second conductor layer specifically includes: Coating the adhesive film layer on the release film and laminating and transferring the adhesive film layer to the surface of the third conductor layer away from the second conductor layer; or, Forming the adhesive film layer on the surface of the third conductor layer away from the second conductor layer.

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