Free grounding film, circuit board and method for preparing free grounding film

Abstract

An embodiment of the present invention provides a free grounding film, a circuit board and a method for preparing the free grounding film, wherein the free grounding film comprises a stacked resin film layer and an adhesive film layer, wherein the resin film layer is provided with a first through hole, and a metal protrusion is provided at the first through hole, and the metal protrusion extends into the adhesive film layer; the metal protrusion is formed by fusible metal flowing from one side of the first through hole to the other side at a preset temperature and then instantly cooling; when the free grounding film is used for grounding of a printed circuit board, the free grounding film is pressed together with the electromagnetic shielding film on the printed circuit board through its adhesive film layer, and the metal protrusion pierces the insulating layer of the adhesive film layer and the electromagnetic shielding film, and is electrically connected to the shielding layer of the electromagnetic shielding film, thereby effectively conducting out the interference charges accumulated in the shielding layer, avoiding the accumulation of interference charges to form an interference source, and thereby effectively ensuring 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] In order to solve the above technical problems, the present invention provides a free grounding film, comprising a resin film layer and an adhesive film layer stacked, wherein the resin film layer is provided with a first through hole penetrating the upper and lower surfaces thereof, and a metal protrusion is provided at the first through hole, and the metal protrusion extends into the adhesive film layer; the metal protrusion is formed by a fusible metal flowing from one side of the first through hole to the other side at a preset temperature and then cooling instantly;

[0007] 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 electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked. The free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the metal protrusions pierce the adhesive film layer and the insulating layer and are electrically connected to the shielding layer.

[0008] As an improvement of the above solution, the fusible metal is any single metal or any multiple alloys of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0009] As an improvement of the above solution, the preset temperature is 300°C to 2000°C.

[0010] As an improvement of the above solution, the surface of the metal protrusion is provided with convex conductor particles; the height of the conductor particles is 20 μm-100 μm.

[0011] 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 not containing conductive particles.

[0012] As an improvement of the above solution, the free grounding film further includes an anti-oxidation layer, and the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is arranged on a side of the resin film layer away from the adhesive film layer.

[0013] As an improvement of the above solution, the free grounding film further comprises a peelable protective film layer, and the peelable protective film layer is arranged on a side of the adhesive film layer away from the resin film layer.

[0014] As an improvement of the above solution, the free grounding film further includes a first conductor layer, which is arranged between the resin film layer and the adhesive film layer, and a protrusion is formed at a position where the first conductor layer covers the metal protrusion.

[0015] As an improvement of the above solution, the surface of the protrusion is provided with convex conductor particles.

[0016] As an improvement of the above solution, the first conductor layer includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer and a graphene conductor layer.

[0017] As an improvement of the above scheme, 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.

[0018] Compared with the prior art, the embodiment of the present invention discloses a free grounding film, which provides the metal protrusion at the first through hole of the resin film layer and extends into the adhesive film layer, so that when the free grounding film is pressed together with the electromagnetic shielding film through its adhesive film layer, the metal protrusion 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 conducting away the interference charges accumulated in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that at high temperature, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly conducted away due to the pressing of the free grounding film with the electromagnetic shielding film through the conductive adhesive layer, thereby ensuring the integrity of signal transmission.

[0019] In order to solve the same technical problem, the present invention also provides a circuit board, comprising a printed circuit board and an electromagnetic shielding film arranged on the printed circuit board, wherein the circuit board also comprises the free grounding film of any one of the above embodiments;

[0020] The electromagnetic shielding film comprises a shielding layer and an insulating layer which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer;

[0021] Alternatively, the electromagnetic shielding film comprises a stacked shielding layer and an insulating layer, the free grounding film is pressed together with the electromagnetic shielding film via the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0022] 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 a free grounding film as described in any one of the above items. When the free grounding film is pressed together with the electromagnetic shielding film through its adhesive film layer, the metal protrusion or the protrusion 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 conducting away the interference charges accumulated in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that at high temperatures, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly conducted away due to the pressing of the free grounding film with the electromagnetic shielding film through the conductive adhesive layer. Therefore, the accumulation of interference charges and the influence on the normal operation of the printed circuit board are effectively avoided.

[0023] In order to solve the same technical problem, the present invention also provides a method for preparing a free grounding film, comprising the steps of:

[0024] forming a resin film layer; wherein the resin film layer is provided with first through holes penetrating the upper and lower surfaces thereof;

[0025] forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole;

[0026] A glue film layer is formed on the side of the resin film layer where the metal protrusion is formed; 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 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the metal protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0027] As an improvement of the above solution, the forming of the metal protrusion at the first through hole is specifically:

[0028] A fusible metal is arranged at the first through hole, and the fusible metal is made to flow from one side of the first through hole to the other side at a preset temperature and then instantly cooled, thereby forming the metal protrusion at the first through hole.

[0029] As an improvement of the above solution, before forming the adhesive film layer on the side of the resin film layer where the metal protrusion is formed, the following steps are also included:

[0030] Conductor particles are formed on the outer surface of the metal protrusion 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.

[0031] As an improvement of the above solution, the adhesive film layer is formed on the side of the resin film layer where the metal protrusion is formed, specifically:

[0032] Coating an adhesive film layer on the release film, and transferring the adhesive film layer by lamination to the side of the resin film layer where the metal protrusions are formed; or,

[0033] A glue film layer is coated on the side of the resin film layer where the metal protrusion is formed.

[0034] Compared with the prior art, the preparation method of the free grounding film provided in the embodiment of the present invention forms the metal protrusion at the first through hole of the resin film layer, and forms an adhesive film layer on the side of the resin film layer where the metal protrusion is formed, so that when the free grounding film is pressed together with the electromagnetic shielding film through its adhesive film layer, the metal protrusion 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 conducting away the interference charges accumulated in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that at high temperature, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly conducted away due to the pressing of the free grounding film with the electromagnetic shielding film through the conductive adhesive layer, thereby effectively avoiding the accumulation of interference charges and affecting the normal operation of the printed circuit board.

[0035] In order to solve the same technical problem, the present invention also provides another method for preparing a free grounding film, comprising the steps of:

[0036] forming a resin film layer; wherein the resin film layer is provided with first through holes penetrating the upper and lower surfaces thereof;

[0037] forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole;

[0038] forming a first conductor layer on the side of the resin film layer where the metal protrusion is formed, and forming a protrusion portion so that the first conductor layer covers the position of the metal protrusion;

[0039] A glue film layer is formed on the side of the first conductor layer away from the resin film 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 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0040] Compared with the prior art, the method for preparing a free grounding film provided in an embodiment of the present invention forms the metal protrusion at the first through hole of the resin film layer, and forms a first conductor layer on the side of the resin film layer where the metal protrusion is formed, so as to form a protrusion on the outer surface of the first conductor layer at a position corresponding to the metal protrusion, and finally forms a glue film layer on the side of the first conductor layer away from the resin film layer, so that when the free grounding film is pressed together with the electromagnetic shielding film through its glue film layer, the protrusion can pierce the glue film layer and the insulating layer of the electromagnetic shielding film in turn, and connect with the shielding layer of the electromagnetic shielding film, thereby effectively conducting out the interference charge accumulated in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic structural diagram of a free grounding film in Embodiment 1 of the present invention;

[0042] Figure 2 is a cross-sectional view of the free grounding film in the first embodiment of the present invention;

[0043] Figure 3 is a schematic structural diagram of a free grounding film in a second embodiment of the present invention;

[0044] Figure 4 is a schematic structural diagram of a free grounding film in Embodiment 3 of the present invention;

[0045] Figure 5 It is a schematic diagram of the structure of a circuit board in Embodiment 4 of the present invention;

[0046] Figure 6 is a structural schematic diagram of another circuit board in the fourth embodiment of the present invention;

[0047] Figure 7 is a schematic flow chart of a method for preparing a free grounding film according to a fifth embodiment of the present invention;

[0048] Figure 8 It is a schematic flow chart of a method for preparing a free grounding film according to a sixth embodiment of the present invention.

[0049] Among them, 1. resin film layer; 11. first through hole; 12. metal protrusion; 13. conductor particles; 2. adhesive film layer; 3. peelable protective film layer; 4. first conductor layer; 41. protrusion; 5. anti-oxidation layer; 6. electromagnetic shielding film; 61. insulating layer; 62. shielding layer; 7. printed circuit board. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Embodiment 1

[0052] Combination Figure 1 and Figure 2 As shown, the free grounding film comprises a resin film layer 1 and an adhesive film layer 2 which are stacked, the resin film layer 1 is provided with a first through hole 11 which passes through the upper and lower surfaces thereof, the first through hole 11 is provided with a metal protrusion 12, the metal protrusion 12 extends into the adhesive film layer 2; the metal protrusion 12 is formed by a fusible metal flowing from one side of the first through hole 11 to the other side at a preset temperature and then cooling instantly;

[0053] When the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 6 is provided on the printed circuit board 7, and the electromagnetic shielding film 6 includes a stacked shielding layer 62 and an insulating layer 61. The free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2, and the metal protrusion 12 pierces the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0054] In an embodiment of the present invention, the metal protrusion 12 is provided at the first through hole 11 of the resin film layer 1, and the metal protrusion 12 is extended into the adhesive film layer 2, so that when the free grounding film is pressed together with the electromagnetic shielding film 6 through its adhesive film layer 2, the metal protrusion 12 can sequentially pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, and connect with the shielding layer 62 of the electromagnetic shielding film 6, so that the interference charges accumulated in the electromagnetic shielding film 6 are effectively discharged, thereby ensuring the grounding of the electromagnetic shielding film 6, and effectively avoiding the problem that at high temperature, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly discharged due to the pressing of the free grounding film with the electromagnetic shielding film through the conductive adhesive layer, thereby ensuring the integrity of signal transmission.

[0055] Specifically, in the process of forming the metal protrusion 12, the preset temperature is 300°C to 2000°C. Therefore, the process of forming the metal protrusion 12 is specifically manifested as: melting the fusible metal at a temperature of 300°C to 2000°C; and after the fusible metal flows from one side of the first through hole 11 away from the adhesive film layer 2 to the other side, cooling the fusible metal instantly, so that the fusible metal solidifies, thereby forming the metal protrusion 12 on the side of the first through hole 11 close to the adhesive film layer 2. Wherein, the fusible metal is any single metal or any multiple alloys of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0056] In the embodiment of the present invention, it should be noted that the structure of the metal protrusion 12 shown in the drawings is only exemplary. Since the metal protrusion 12 is formed by the fusible metal flowing from one side of the first through hole 11 to the other side at a preset temperature and then cooling instantly, in one case, the resin film layer is a film layer containing conductive particles, and the fusible metal flows out of the first through hole 11 almost completely, and there is no residue in the first through hole 11. The metal protrusion 12 is formed at the boundary between the first through hole 11 and the adhesive film layer 2. At this time, the interference charge in the electromagnetic shielding film 6 is led out through the electrical connection of the metal protrusion 12, the resin film layer 1 and the anti-oxidation layer 5. In another case, there is fusible metal remaining in the first through hole 11, and the first through hole 11 is filled with fusible metal. One end of the formed metal protrusion 12 is flush with one end of the first through hole 11 and is electrically connected to the anti-oxidation layer 5. The other end of the metal protrusion 12 extends out of the first through hole 11, as shown in the drawings. In another case, fusible metal remains on the surface of the resin film layer 1 away from the adhesive film layer 2, so the formed metal protrusion 12 can penetrate the first through hole 11. In addition, the metal protrusion 12 in the present invention is not limited by the shapes shown in the figure and the above-mentioned shapes, as long as it is a metal protrusion with piercing and conductive functions, it is within the protection scope of the present invention.

[0057] In the embodiment of the present invention, in order to further ensure that the metal protrusion 12 can be formed at the first through hole 11 and at the same time ensure that the resin film layer 1 is not easily broken, preferably, in this embodiment, the cross-sectional area of ​​the first through hole 11 is 0.01 μm 2 -1mm 2 .

[0058] In addition, in order to ensure that enough metal protrusions 12 can be formed to ensure that they can pierce the adhesive film layer 2 and the insulating layer 61 and connect to the shielding layer 62, and at the same time ensure that the resin film layer 1 is not easy to break, the number of the first through holes 11 in the resin film layer 1 per square centimeter in this embodiment is 5-10. 6 Correspondingly, the number of the metal protrusions 12 in the resin film layer 1 is 5-10 per square centimeter. 6 Therefore, it is ensured that the metal protrusion 12 can pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 in sequence, so that the free grounding film is connected to the electromagnetic shielding film 6.

[0059] like Figure 2 As shown, the first through holes 11 can be regularly or irregularly distributed on the first conductor layer 1; wherein, the first through holes 11 being regularly distributed on the resin film layer 1 means that the shapes of the first through holes 11 are the same and are evenly distributed on the resin film layer 1; the first through holes 11 being irregularly distributed on the resin film layer 1 means that the shapes of the first through holes 11 are different and are randomly distributed on the resin film 1. Preferably, the shapes of the first through holes 11 are the same and are evenly distributed on the resin film 1. In addition, the first through holes 11 can be circular through holes or through holes of any other shapes. The accompanying drawings of the present invention only illustrate the first through holes 11 as circular through holes, but the first through holes 11 of any other shapes are within the protection scope of the present invention.

[0060] In the embodiment of the present invention, the resin film layer 1 includes a first surface and a second surface arranged opposite to each other, the first surface is in contact with the adhesive film layer 2; the second surface is in contact with the protective film layer 3. It should be noted that the first surface and the second surface can be surfaces of any shape, for example, Figure 1 The flat surface shown may also be an undulating non-flat surface or other rough surface; in addition, the first surface and the second surface may be regular surfaces or irregular surfaces. The drawings of the present invention only illustrate the first surface and the second surface as flat surfaces, and any other shapes of the first surface and the second surface are within the protection scope of the present invention. In addition, it should be noted that the resin film layer 1 in the drawings of this embodiment may be a single-layer structure or a multi-layer structure.

[0061] In the embodiment of the present invention, one of the structures of the adhesive film layer 2 is specifically manifested as follows: the adhesive film layer 2 includes an adhesive layer containing conductive particles. By making the adhesive film layer 2 include an adhesive layer containing conductive particles, the adhesive film layer 2 not only has an adhesive function, so that the free grounding film and the electromagnetic shielding film 6 are tightly bonded, but also has a conductive function, which cooperates with the metal protrusion 12 to quickly conduct the interference electrons. Among them, the conductive particles in the adhesive film layer 2 can be conductive particles separated from each other, or they can be large-particle conductive particles formed by aggregation; when the conductive particles are conductive particles separated from each other, the area of ​​electrical contact can be further increased, and the uniformity of electrical contact can be improved; and when the conductive particles are large-particle conductive particles formed by aggregation, the puncture strength can be increased.

[0062] In the embodiment of the present invention, another structure of the adhesive film layer 2 is specifically manifested as follows: the adhesive film layer 2 includes an adhesive layer without conductive particles. By making the adhesive film layer 2 include an adhesive layer without conductive particles, the adhesive film layer 2 has a bonding effect, so that the free grounding film and the electromagnetic shielding film 6 are tightly bonded. At the same time, because the adhesive film layer 2 includes no conductive particles, the insertion loss of the circuit board during use is reduced, and the bendability of the circuit board is improved.

[0063] In addition, the thickness of the adhesive film layer 2 in this embodiment is 0.1 μm-80 μm. The material used for the adhesive film layer 2 is selected from the following: modified epoxy resin, acrylic acid, modified rubber, and modified thermoplastic polyimide. The outer surface of the adhesive film layer 2 can be a flat surface without undulations, or a non-flat surface with gentle undulations.

[0064] like Figure 1 As shown, in order to protect the adhesive film layer 2, the free grounding film in this embodiment further includes a peelable protective film layer 3, and the peelable protective film layer 3 is arranged on the side of the adhesive film layer 2 away from the resin film layer 1. The peelable protective film layer 3 plays a protective role to prevent the adhesive film layer 2 from being damaged before use, thereby ensuring that the free grounding film can be pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2. It should be noted that when the free grounding film is pressed together with the electromagnetic shielding film 6, the peelable protective film layer 3 needs to be peeled off, and then the free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2.

[0065] In addition, the peelable protective film layer 3 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.

[0066] In the embodiment of the present invention, in order to protect the resin film layer 1, the free grounding film in this embodiment further includes an anti-oxidation layer 5, and the anti-oxidation layer 5 is arranged on the side of the resin film layer 1 away from the adhesive film layer 2. By arranging the anti-oxidation layer 5 on the side of the resin film layer 1 away from the adhesive film layer 2, the resin film layer 1 is prevented from being oxidized, thereby ensuring that the interference charges in the electromagnetic shielding film 6 can be led out through the free grounding film.

[0067] In one preferred embodiment, the material of the anti-oxidation layer 5 is one of metal material, ferrite, graphite, carbon nanotube, 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 5 is 0.01 μm-5 μm, and the thickness of the anti-oxidation layer 5 is preferably 0.1 μm-1 μm. In addition, the anti-oxidation layer 5 can be formed by a composite process of at least two of the processes of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, and electroplating.

[0068] In another preferred embodiment, the anti-oxidation layer 5 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 5 is preferably 0.1 μm-5 μm. In addition, the anti-oxidation layer 5 can be formed by a coating and then curing process.

[0069] Embodiment 2

[0070] like Figure 3 As shown, the free grounding film in this embodiment is different from the embodiment 1 in that convex conductor particles 13 are provided on the surface of the metal protrusion 12. By providing the conductor particles 13 on the surface of the metal protrusion 12, it is further ensured that during the pressing process, the metal protrusion 12 can smoothly pierce the insulating layer 61 of the adhesive film layer 2 and the electromagnetic shielding film 6, thereby ensuring the normal extraction of interference charges.

[0071] Preferably, the conductor particles 13 are concentrated on the outwardly protruding position of the surface of the metal protrusion 12, so that it is easier to pierce the adhesive film layer 2. Of course, the conductor particles 13 can also be distributed on the non-convex part of the surface of the metal protrusion 12. In addition, the conductor particles 13 can also be distributed on other positions of the side of the resin film layer 1 close to the adhesive film layer 2, rather than only on the surface of the metal protrusion 12. Figure 3 Of course, the conductor particles 22 may also be distributed only on the metal protrusions 12 .

[0072] In the specific implementation, Figure 3 As shown, the metal protrusion 12 may be formed first, and then the conductor particles 13 may be formed on the outer surface of the metal protrusion 12 through other processes. Of course, the metal protrusion 12 and the conductor particles 13 may also be an integral structure formed through a one-time molding process.

[0073] In the embodiment of the present invention, the conductor particles 13 may be at a certain distance from the outer surface of the adhesive film layer 2 , or may be in contact with the outer surface of the adhesive film layer 2 or extend out of the outer surface of the adhesive film layer 2 .

[0074] In the embodiment of the present invention, the height of the conductor particles 13 is preferably 20 μm-100 μm, the thickness of the adhesive film layer 2 is preferably 0.1 μm-80 μm, and the thickness of the insulating layer 61 is preferably 1 μm-20 μm. By setting the height of the conductor particles 13 to preferably 20 μm-100 μm and the thickness of the adhesive film layer 2 to preferably 0.1 μm-80 μm, it is ensured that the conductor particles 13 can pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, thereby ensuring that the free grounding film can lead out the interference charges accumulated on the electromagnetic shielding film 6.

[0075] In an embodiment of the present invention, the conductor particles 13 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 conductor particles 13 may be the same material as the metal protrusions 12, or they may be different.

[0076] In the embodiment of the present invention, it should be noted that, Figure 3 The shape of the conductor particles 13 shown is only exemplary. Due to differences in process means and parameters, the conductor particles 13 may also be in other shapes such as clusters, hanging ice, stalactites, and dendrites. In addition, the conductor particles 13 in the present invention are not limited to the shapes shown in the figure and described above. As long as the conductor particles have piercing and conductive functions, they are within the protection scope of the present invention.

[0077] In addition, other structures and working principles of the free grounding film of this embodiment are the same as those of the first embodiment, and are not further described here.

[0078] Embodiment 3

[0079] like Figure 4As shown, the free grounding film in this embodiment is different from that in the first embodiment in that the free grounding film comprises a resin film layer 1 and an adhesive film layer 2 which are stacked, the resin film layer 1 is provided with a first through hole 11 which passes through the upper and lower surfaces thereof, and the first through hole 11 is provided with a metal protrusion 12; the metal protrusion 12 is formed by a fusible metal flowing from one side of the first through hole 11 to the other side at a preset temperature and then cooling instantly;

[0080] The free grounding film also includes a first conductor layer 4, which is arranged between the resin film layer 1 and the adhesive film layer 2, and a protrusion 41 is formed at a position of the first conductor layer 4 covering the metal protrusion 12, and the protrusion 41 extends into the adhesive film layer 2; specifically, the first conductor layer 4 is arranged on a surface of the resin film layer 1 close to the adhesive film layer 2, and covers the metal protrusion 12, so that the protrusion 41 is formed at a position corresponding to the metal protrusion 12 on the outer surface of the first conductor layer 4. By arranging the first conductor layer 4 between the resin film layer 1 and the adhesive film layer 2, so that the protrusion 41 is formed at a position corresponding to the metal protrusion 12 on the outer surface of the first conductor layer 4, it is ensured that during the pressing process of the free grounding film and the electromagnetic shielding film 6, the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 can be smoothly pierced with the cooperation of the metal protrusion 12 and the protrusion 41, so as to ensure the normal extraction of interference charges.

[0081] In the embodiment of the present invention, it should be noted that the shape of the protrusion 41 may be the same as or different from the shape of the metal protrusion 12 , and the shape of the protrusion 41 shown in the drawings is merely exemplary.

[0082] In the embodiment of the present invention, in order to further ensure that the protrusion 41 can pierce the adhesive film layer 2 and the insulating layer 61 , convex conductive particles 13 are provided on the surface of the protrusion 41 in this embodiment.

[0083] Preferably, the conductor particles 13 are concentrated on the outwardly protruding position of the surface of the protruding portion 41, so that it is easier to pierce the adhesive film layer 2 and the insulating layer 61. Of course, the conductor particles 13 can also be distributed on the non-convex portion of the surface of the protruding portion 41. In addition, the conductor particles 13 can also be distributed on other positions of the first conductor layer 4 close to the adhesive film layer 2, rather than only on the surface of the protruding portion 41. Figure 4 Of course, the conductor particles 22 may also be distributed only on the protrusions 41 .

[0084] In the specific implementation, Figure 4As shown, the first conductor layer 4 can be formed first, and then the conductor particles 13 can be formed on the side of the first conductor layer 4 away from the resin film layer 1 through other processes. Of course, the first conductor layer 4 and the conductor particles 13 can be an integral structure formed through a one-time molding process.

[0085] In the embodiment of the present invention, the conductor particles 13 may be at a certain distance from the outer surface of the adhesive film layer 2 , or may be in contact with the outer surface of the adhesive film layer 2 or extend out of the outer surface of the adhesive film layer 2 .

[0086] In the embodiment of the present invention, the height of the conductor particles 13 is preferably 20 μm-100 μm, the thickness of the adhesive film layer 2 is preferably 0.1 μm-80 μm, and the thickness of the insulating layer 61 is preferably 1 μm-20 μm. By setting the height of the conductor particles 13 to preferably 20 μm-100 μm and the thickness of the adhesive film layer 2 to preferably 0.1 μm-80 μm, it is ensured that the conductor particles 13 can pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, thereby ensuring that the free grounding film can lead out the interference charges accumulated on the electromagnetic shielding film 6.

[0087] In an embodiment of the present invention, the conductor particles 13 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 conductor particles 13 may be the same as the material of the first conductor layer 4, or may be different.

[0088] In the embodiment of the present invention, it should be noted that, Figure 4 The shape of the conductor particles 13 shown is only exemplary. Due to differences in process means and parameters, the conductor particles 13 may also be in other shapes such as clusters, hanging ice, stalactites, and dendrites. In addition, the conductor particles 13 in the present invention are not limited to the shapes shown in the figure and described above. As long as the conductor particles have piercing and conductive functions, they are within the protection scope of the present invention.

[0089] In an embodiment of the present invention, the thickness of the first conductor layer 4 is 2μm-45μm to ensure that the first conductor layer 4 is not easy to break and has good flexibility. It can be understood that in order to ensure that the first conductor layer 4 has good conductivity, the first 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. In addition, 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.

[0090] In the embodiment of the present invention, it should be noted that the first conductor layer 4 in the drawings of this embodiment can be a single-layer structure or a multi-layer structure. In addition, according to the needs of actual production and application, the first conductor layer 4 in the drawings of this embodiment can be set to a grid shape, a foam shape, etc.

[0091] In addition, other structures and working principles of the free grounding film of this embodiment are the same as those of the first embodiment, and are not further described here.

[0092] Embodiment 4

[0093] Combination Figure 5 and Figure 6 As shown, an embodiment of the present invention further provides a circuit board, comprising a printed circuit board 7 and an electromagnetic shielding film 6 arranged on the printed circuit board 7.

[0094] like Figure 5 As shown, the circuit board also includes the free grounding film described in Embodiment 1 or 2, the electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 stacked, the free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2, and the metal protrusion 12 pierces the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62;

[0095] or, as Figure 6 As shown, the circuit board also includes the free grounding film described in Example 3, the electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 that are stacked, the free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2, and the protrusion 41 pierces the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0096] 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.

[0097] In the embodiment of the present invention, it should be noted that the metal protrusion 12 or the protrusion 41 on the free grounding film may all contact with the shielding layer 62 of the electromagnetic shielding film 6 or may partially contact with the shielding layer 62 of the electromagnetic shielding film 6 .

[0098] Preferably, the printed circuit board 7 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0099] In a specific implementation, when the circuit board is applied to an electronic device, the interference charges accumulated in the electromagnetic shielding film 6 can be led out by electrically connecting the free grounding film to the housing of the electronic device.

[0100] In an embodiment of the present invention, through the above-mentioned structure, during the pressing process of the free grounding film and the electromagnetic shielding film 6, the metal protrusion 12 or the protrusion 41 is used to pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 in turn, thereby connecting with the shielding layer 62 of the electromagnetic shielding film 6, thereby realizing the extraction of interference charges in the electromagnetic shielding film 6, avoiding the accumulation of interference charges to form an interference source, and affecting the normal operation of the circuit board.

[0101] Embodiment 5

[0102] like Figure 7 As shown, an embodiment of the present invention provides a method for preparing a free grounding film, which is applicable to the preparation of the free grounding film described in Example 1, and includes steps S11 to S13:

[0103] S11, forming a resin film layer; wherein the resin film layer is formed with first through holes penetrating the upper and lower surfaces thereof;

[0104] In step S11, the resin film layer may be formed by:

[0105] forming an anti-oxidation layer on the carrier film;

[0106] The resin film layer is formed on a side of the anti-oxidation layer away from the carrier film.

[0107] or, forming a peelable layer on a carrier film;

[0108] forming the resin film layer on a side of the peelable layer away from the carrier film;

[0109] After forming an anti-oxidation layer on a side of the resin film layer away from the peelable layer, the peelable layer is peeled off.

[0110] The resin film layer has a first through hole penetrating the upper and lower surfaces thereof. The cross-sectional area of ​​the first through hole is 0.01 μm 2 -1mm2 The number of the first through holes in the resin film layer per square centimeter is 5-10 6 indivual.

[0111] S12, forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole;

[0112] The forming of the metal protrusion at the first through hole is specifically:

[0113] A fusible metal is arranged at the first through hole, and the fusible metal is allowed to flow from one side of the first through hole to the other side at a preset temperature and then instantly cooled, thereby forming the metal protrusion at the first through hole. The fusible metal is any single metal or any multiple alloys of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold; and the preset temperature is 300°C to 2000°C.

[0114] S13. Form a glue film layer on the side of the resin film layer where the metal protrusion is formed; 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 electromagnetic shielding film includes a shielding layer and an insulating layer that are stacked, and the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the metal protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0115] The step of forming the adhesive film layer on the side of the first conductor layer where the metal protrusion is formed is specifically:

[0116] Coating an adhesive film layer on the release film, and then laminating and transferring the adhesive film layer to the side of the resin film layer where the metal protrusion is formed, thereby forming an adhesive film layer on the side of the resin film layer where the metal protrusion is formed; or,

[0117] The adhesive film layer is directly coated on the side of the resin film layer where the metal protrusion is formed, so that the adhesive film layer is formed on the side of the resin film layer where the metal protrusion is formed.

[0118] In another preferred embodiment suitable for preparing the free grounding film described in the second embodiment, after step S12 and before step S13, the following steps are further included:

[0119] Conductor particles are formed on the outer surface of the metal protrusion 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.

[0120] In an embodiment of the present invention, the preparation method of the free grounding film forms the metal protrusion at the first through hole of the resin film layer, and forms an adhesive film layer on the side of the resin film layer where the metal protrusion is formed, so that when the free grounding film is pressed together with the electromagnetic shielding film through its adhesive film layer, the metal protrusion 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 conducting away the interference charges accumulated in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that at high temperatures, the free grounding film is pressed together with the electromagnetic shielding film through the conductive adhesive layer, resulting in failure of the connection between the free grounding film and the electromagnetic shielding film and the inability to quickly conduct away the interference charges, thereby avoiding the accumulation of interference charges and affecting the normal operation of the printed circuit board.

[0121] Embodiment 6

[0122] like Figure 8 As shown, the embodiment of the present invention provides another method for preparing a free grounding film, which is applicable to the preparation of the free grounding film described in the third embodiment, and includes steps S21 to S24:

[0123] S21, forming a resin film layer; wherein the resin film layer is formed with first through holes penetrating the upper and lower surfaces thereof;

[0124] In step S21, the resin film layer may be formed in the following manner:

[0125] forming an anti-oxidation layer on the carrier film;

[0126] The resin film layer is formed on a side of the anti-oxidation layer away from the carrier film.

[0127] or, forming a peelable layer on a carrier film;

[0128] forming the resin film layer on a side of the peelable layer away from the carrier film;

[0129] After forming an anti-oxidation layer on a side of the resin film layer away from the peelable layer, the peelable layer is peeled off.

[0130] The resin film layer has a first through hole penetrating the upper and lower surfaces thereof. The cross-sectional area of ​​the first through hole is 0.01 μm 2 -1mm 2 The number of the first through holes in the resin film layer per square centimeter is 5-10 6 indivual.

[0131] S22, forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole;

[0132] The forming of the metal protrusion at the first through hole is specifically:

[0133] A fusible metal is arranged at the first through hole, and the fusible metal is allowed to flow from one side of the first through hole to the other side at a preset temperature and then instantly cooled, thereby forming the metal protrusion at the first through hole. The fusible metal is any single metal or any multiple alloys of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold; and the preset temperature is 300°C to 2000°C.

[0134] S23, forming a first conductor layer on the side of the resin film layer where the metal protrusion is formed, and making the first conductor layer cover the position of the metal protrusion to form a protrusion;

[0135] Preferably, after implementing step S23, conductor particles may be formed on the outer surface of the protrusion 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.

[0136] S24. A glue film layer is formed on a side of the first conductor layer away from the resin film 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 electromagnetic shielding film includes a shielding layer and an insulating layer stacked in layers. The free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0137] The step of forming a glue film layer on a side of the first conductor layer away from the resin film layer is specifically:

[0138] Coating an adhesive film layer on the release film, and then laminating and transferring the adhesive film layer to the side of the first conductor layer away from the resin film layer, thereby forming an adhesive film layer on the side of the first conductor layer away from the resin film layer; or,

[0139] A glue film layer is directly coated on a side of the first conductor layer away from the resin film layer, so that a glue film layer is formed on a side of the first conductor layer away from the resin film layer.

[0140] In summary, the embodiments of the present invention provide a free grounding film, a circuit board and a method for preparing the free grounding film, wherein the free grounding film comprises a resin film layer 1 and an adhesive film layer 2 which are stacked, wherein the resin film layer 1 is provided with a first through hole 11 which passes through the upper and lower surfaces thereof, and the first through hole 11 is provided with a metal protrusion 12, and the metal protrusion 12 extends into the adhesive film layer 2; the metal protrusion 12 is formed by fusible metal flowing from one side of the first through hole 11 to the other side at a preset temperature and then instantly cooling; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 6 is provided on the printed circuit board 7, and the electromagnetic shielding The membrane 6 includes a shielding layer 62 and an insulating layer 61 which are stacked together. The free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 2. The metal protrusion 12 pierces the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62, thereby effectively conducting away the interference charges accumulated in the electromagnetic shielding film 6, thereby ensuring the grounding of the electromagnetic shielding film 6, and effectively avoiding the problem that at high temperatures, the free grounding film is pressed together with the electromagnetic shielding film through the conductive adhesive layer, resulting in failure of the connection between the free grounding film and the electromagnetic shielding film and the inability to quickly conduct away the interference charges, thereby ensuring the integrity of the signal transmission.

[0141] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A free grounding membrane, characterized in that: The invention comprises a resin film layer and an adhesive film layer which are stacked, wherein the resin film layer is provided with a first through hole which penetrates the upper and lower surfaces thereof, and the first through hole is provided with a metal protrusion which extends into the adhesive film layer; the metal protrusion is formed by a fusible metal flowing from one side of the first through hole to the other side at a preset temperature and then cooling instantly; 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 electromagnetic shielding film includes an insulating layer and a shielding layer which are stacked. The free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

2. The free grounding membrane according to claim 1, characterized in that: The fusible metal is any single metal or any multiple alloys of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

3. The free grounding membrane according to claim 1, characterized in that: The preset temperature is 300°C to 2000°C.

4. The free grounding membrane according to claim 1, characterized in that: The surface of the metal protrusion is provided with convex conductor particles; the height of the conductor particles is 20 μm-100 μm.

5. The free grounding membrane according to claim 1, characterized in that: The adhesive film layer includes an adhesive layer containing conductive particles; or, the adhesive film layer includes an adhesive layer not containing conductive particles.

6. The free grounding membrane according to any one of claims 1 to 5, characterized in that: The free grounding film further comprises an anti-oxidation layer, and the anti-oxidation layer is arranged on a side of the resin film layer away from the adhesive film layer.

7. The free grounding membrane according to any one of claims 1 to 5, characterized in that: The free grounding film further comprises a strippable protective film layer, and the strippable protective film layer is arranged on a side of the adhesive film layer away from the resin film layer.

8. The free grounding membrane according to any one of claims 1 to 5, characterized in that: The free ground film further includes a first conductor layer, which is disposed between the resin film layer and the adhesive film layer, and a protrusion is formed at a position where the first conductor layer covers the metal protrusion.

9. The free grounding membrane according to claim 8, characterized in that: The surface of the protrusion is provided with protruding conductive particles.

10. The free grounding membrane according to claim 8, characterized in that: The first conductor layer includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer and a graphene conductor layer.

11. The free grounding membrane according to claim 10, characterized in that: 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.

12. A circuit board, comprising a printed circuit board and an electromagnetic shielding film arranged on the printed circuit board, characterized in that: The circuit board further comprises the free grounding film as claimed in any one of claims 1 to 7, the electromagnetic shielding film comprises a shielding layer and an insulating layer stacked in layers, the free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer; Or, the circuit board also includes a free grounding film as described in any one of claims 8-11, the electromagnetic shielding film includes a shielding layer and an insulating layer stacked together, the free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

13. A method for preparing a free grounding film, characterized in that: Suitable for preparing the free grounding film according to any one of claims 1 to 7, comprising the steps of: forming a resin film layer; wherein the resin film layer is provided with first through holes penetrating the upper and lower surfaces thereof; forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole; A glue film layer is formed on the side of the resin film layer where the metal protrusion is formed; 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 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the metal protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

14. The method for preparing a free grounding film according to claim 13, characterized in that: The forming of the metal protrusion at the first through hole is specifically: A fusible metal is arranged at the first through hole, and the fusible metal is made to flow from one side of the first through hole to the other side at a preset temperature and then instantly cooled, thereby forming the metal protrusion at the first through hole.

15. The method for preparing a free grounding film according to claim 13, characterized in that: Before forming the adhesive film layer on the side of the resin film layer where the metal protrusion is formed, the following steps are also included: Conductor particles are formed on the outer surface of the metal protrusion 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.

16. The method for preparing a free grounding film according to claim 13, characterized in that: The adhesive film layer is formed on the side of the resin film layer where the metal protrusion is formed, specifically: Coating an adhesive film layer on the release film, and transferring the adhesive film layer by lamination to the side of the resin film layer where the metal protrusions are formed; or, A glue film layer is coated on the side of the resin film layer where the metal protrusion is formed.

17. A method for preparing a free grounding film, characterized in that: Suitable for preparing the free grounding film according to any one of claims 8 to 11, comprising the steps of: forming a resin film layer; wherein the resin film layer is provided with first through holes penetrating the upper and lower surfaces thereof; forming a metal protrusion at the first through hole; wherein the metal protrusion extends out of the first through hole; forming a first conductor layer on the side of the resin film layer where the metal protrusion is formed, and forming a protrusion portion so that the first conductor layer covers the position of the metal protrusion; A glue film layer is formed on the side of the first conductor layer away from the resin film 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 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

Images