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 method for preparing the free grounding film, wherein the free grounding film comprises a first conductor layer and a glue film layer which are stacked, a metal protrusion is provided at the first through hole of the first conductor layer, and the metal protrusion extends into the glue 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, an electromagnetic shielding film is provided on the printed circuit board, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, the metal protrusion pierces the insulating layer of the glue film layer and the electromagnetic shielding film, and is electrically connected to the shielding layer of the electromagnetic shielding film, thereby effectively conducting out interference charges accumulated on 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] To solve the above technical problems, the present invention provides a free grounding film, which includes a first conductor layer and an adhesive film layer stacked on top of each other. A first through hole penetrating the upper and lower surfaces is provided on the first conductor layer, 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 instantaneously cooling.

[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. The electromagnetic shielding film includes a shielding layer and an insulating layer stacked on top of each other. The free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0008] As an improvement of the above solution, the fusible metal is any one of single metals or any combination of 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 first conductor layer includes a first surface in contact with the adhesive film layer, and the first surface is an uneven surface with undulations.

[0011] As an improvement of the above solution, convex conductor particles are provided on the surface of the metal protrusion; the height of the conductor particles is 20μm - 100μm.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] As an improvement of the above solution, the number of the first through holes in the first conductor layer per square centimeter is 5 - 10 6 pieces; and / or, the cross-sectional area of the first through hole is 0.01μm 2 -1mm2 。

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

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

[0018] As an improvement to the above solution, the free grounding film further includes a second conductor layer, and the second conductor layer is disposed between the first conductor and the adhesive film layer, and a raised portion is formed at a position where the second conductor layer covers the metal protrusion.

[0019] As an improvement to the above solution, convex conductor particles are provided on the surface of the raised portion.

[0020] Compared with the prior art, the embodiment of the present invention discloses a free grounding film. By providing the metal protrusion at the first through hole of the first conductor layer and making the metal protrusion extend into the adhesive film layer, when the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the metal protrusion can pierce through the adhesive film layer and the insulating layer of the electromagnetic shielding film in sequence 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, due to the free grounding film being 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 as to ensure the integrity of signal transmission.

[0021] To solve the same technical problem, the present invention further provides a circuit board, including a printed circuit board and an electromagnetic shielding film disposed on the printed circuit board, and the circuit board further includes the free grounding film of any one of the above embodiments;

[0022] The electromagnetic shielding film includes a shielding layer and an insulating layer stacked, and the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer;

[0023] Or, the electromagnetic shielding film includes a shielding layer and an insulating layer stacked, and the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the raised portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0024] 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 metal protrusion or the protrusion part can pierce through the adhesive film layer and the insulating layer of the electromagnetic shielding film in sequence and be connected to the shielding layer of the electromagnetic shielding film, so as to effectively conduct the interfering charges accumulated in the electromagnetic shielding film, thereby 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 adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly conducted out, so as to effectively avoid the accumulation of interfering charges and affect the normal operation of the printed circuit board.

[0025] To solve the same technical problem, the present invention also provides a preparation method of a free grounding film, including the steps:

[0026] Form a first conductor layer; wherein, a first through hole penetrating through the upper and lower surfaces thereof is formed on the first conductor layer;

[0027] Form a metal protrusion at the first through hole; wherein, the metal protrusion extends out of the first through hole;

[0028] Form an adhesive film layer on one side of the first conductor layer where the metal protrusion is formed; when the free grounding film is used for grounding of 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 which are laminated, and the free grounding film is laminated with the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0029] As an improvement of the above solution, the forming of the metal protrusion at the first through hole specifically is:

[0030] Set a fusible metal at the first through hole, and make the fusible metal flow from one side of the first through hole to the other side and be instantaneously cooled at a preset temperature, so as to form the metal protrusion at the first through hole.

[0031] As an improvement of the above solution, before forming the adhesive film layer on one side of the first conductor layer where the metal protrusion is formed, the following steps are further included:

[0032] Form conductor particles on the outer surface of the metal protrusion through one or more of the processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating.

[0033] As an improvement of the above solution, the forming of the adhesive film layer on one side of the first conductor layer where the metal protrusion is formed specifically is:

[0034] Coat a glue film layer on the release film, and laminate and transfer the glue film layer to the side of the first conductor layer where the metal protrusions are formed; or,

[0035] Coat a glue film layer on the side of the first conductor layer where the metal protrusions are formed.

[0036] Compared with the prior art, in the method for preparing a free grounding film provided by the embodiment of the present invention, by forming the metal protrusions at the first through holes of the first conductor layer, and forming a glue film layer on the side of the first conductor layer where the metal protrusions are formed, when the free grounding film is laminated with the electromagnetic shielding film through its glue film layer, the metal protrusions can sequentially 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 adhesive 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.

[0037] To solve the same technical problem, the present invention also provides another method for preparing a free grounding film, including the steps of:

[0038] Form a first conductor layer; wherein, a first through hole penetrating the upper and lower surfaces thereof is formed on the first conductor layer;

[0039] Form metal protrusions at the first through holes; wherein, the metal protrusions protrude out of the first through holes;

[0040] Form a second conductor layer on the side of the first conductor layer where the metal protrusions are formed, and make the second conductor layer cover the position of the metal protrusions to form a raised portion;

[0041] Form a glue film layer on the side of the second conductor layer away from the first conductor layer; when the free grounding film is used for grounding 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 laminated with the electromagnetic shielding film through the glue film layer, and the raised portion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0042] Compared with the prior art, the method for preparing a free grounding film provided by the embodiment of the present invention forms the metal protrusion at the first through hole of the first conductor layer, and forms a second conductor layer on one side of the first conductor layer where the metal protrusion is formed, so as to form a protrusion portion at a position corresponding to the metal protrusion on the outer surface of the second conductor layer. Finally, a glue film layer is formed on the side of the second conductor layer away from the first conductor layer, so that when the free grounding film is pressed against the electromagnetic shielding film through its glue film layer, the protrusion portion can pierce through the glue film layer and the insulating layer of the electromagnetic shielding film in sequence, and be connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interference charges accumulated in the electromagnetic shielding film, and further ensuring the grounding of the electromagnetic shielding film. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 FIG. 6 is a schematic structural diagram of a free grounding film according to Embodiment 1 of the present invention;

[0044] Figure 2 FIG. 10 is a schematic structural diagram of another free grounding film according to Embodiment 1 of the present invention;

[0045] Figure 3 FIG. 14 is a cross-sectional view of the free grounding film according to Embodiment 1 of the present invention;

[0046] Figure 4 FIG. 18 is a schematic structural diagram of the free grounding film according to Embodiment 2 of the present invention;

[0047] Figure 5 FIG. 22 is a schematic structural diagram of the free grounding film according to Embodiment 3 of the present invention;

[0048] Figure 6 FIG. 26 is a schematic structural diagram of a circuit board according to Embodiment 4 of the present invention;

[0049] Figure 7 FIG. 30 is a schematic structural diagram of another circuit board according to Embodiment 4 of the present invention;

[0050] Figure 8 FIG. 34 is a schematic flow chart of the method for preparing a free grounding film according to Embodiment 5 of the present invention;

[0051] Figure 9 FIG. 38 is a schematic flow chart of the method for preparing a free grounding film according to Embodiment 6 of the present invention.

[0052] Wherein, 1. First conductor layer; 11. First through hole; 12. Metal protrusion; 13. Conductor particle; 14. First surface; 15. Second surface; 2. Glue film layer; 3. Peelable protective film layer; 4. Second conductor layer; 41. Protrusion portion; 5. Anti-oxidation layer; 6. Electromagnetic shielding film; 61. Insulating layer; 62. Shielding layer; 7. Printed circuit board. DETAILED DESCRIPTION OF THE 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 shall fall within the protection scope of the present invention.

[0054] Embodiment 1

[0055] Combined with Figures 1 to 3 As shown, a free grounding film according to an embodiment of the present invention includes a first conductor layer 1 and an adhesive film layer 2 arranged in a stacked manner. A first through hole 11 penetrating the upper and lower surfaces is provided on the first conductor layer 1. A metal protrusion 12 is provided at the first through hole 11, and 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 instantaneously cooling.

[0056] As Figure 6 As shown, when the free grounding film is used for grounding a printed circuit board 7, an electromagnetic shielding film 6 is provided on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 arranged in a stacked manner. The free grounding film is pressed against the electromagnetic shielding film 6 through the adhesive film layer 2, and the metal protrusion 12 pierces through the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0057] In the embodiment of the present invention, by providing the metal protrusion 12 at the first through hole 11 of the first conductor layer 1 and making the metal protrusion 12 extend into the adhesive film layer 2, when the free grounding film is pressed against the electromagnetic shielding film 6 through its adhesive film layer 2, the metal protrusion 12 can successively pierce through the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 and be connected to the shielding layer 62 of the electromagnetic shielding film 6, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film 6, and further ensuring the grounding of the electromagnetic shielding film 6. It effectively avoids 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 accumulation of interfering charges affecting the normal operation of the printed circuit board is avoided.

[0058] Specifically, during the process of forming the metal bump 12, the preset temperature is 300°C to 2000°C. Therefore, the process of forming the metal bump 12 is specifically manifested as follows: at a temperature of 300°C to 2000°C, the fusible metal disposed at the first through hole 11 melts and flows from the side of the first through hole 11 away from the adhesive film layer 2 to the other side. At this time, the fusible metal is instantaneously cooled, so that the fusible metal solidifies, and then the metal bump 12 is formed on the side of the first through hole 11 close to the adhesive film layer 2. Wherein, the fusible metal is any one of single metals such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold or any combination of alloys.

[0059] In the embodiment of the present invention, it should be noted that the structure of the metal bump 12 shown in the drawings is only exemplary. Since the metal bump 12 is formed by the fusible metal flowing from one side of the first through hole 11 to the other side and then instantaneously cooled at a preset temperature, in one case, the fusible metal almost completely flows out of the first through hole 11 and there is no residue in the first through hole 11. Therefore, the formed metal bump 12 can be as shown in the drawings, that is, the metal bump 12 is formed at the boundary between the first through hole 11 and the adhesive film layer 2, and the metal bump 12 entirely extends into the adhesive film layer 2; in another case, there is residual fusible metal in the first through hole 11, and the first through hole 11 is even filled with the fusible metal. Therefore, one end of the formed metal bump 12 is located in the first through hole 11, and the other end of the metal bump 12 extends out of the first through hole 11 and extends into the adhesive film layer 2; in still another case, there is residual fusible metal on the surface of the first conductor layer 1 away from the adhesive film layer 2. Therefore, the formed metal bump 12 can penetrate through the first through hole 11, wherein one end of the metal bump 12 close to the adhesive film layer 2 extends into the adhesive film layer 2. In addition, the metal bump 12 in the present invention is not limited by the illustrated and above shapes, as long as it is a metal bump having a piercing and conductive function, it is within the protection scope of the present invention.

[0060] As Figure 3 shown, in order to ensure that the metal bump 12 can be formed at the first through hole 11 and at the same time ensure that the first conductor layer 1 is not easily broken, preferably, in this embodiment, the cross-sectional area of the first through hole 11 is 0.01μm 2 -1mm 2 。

[0061] In addition, in order to ensure that the metal protrusions 12 can smoothly pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, and at the same time ensure that the first conductor layer 1 is not easily broken, so as to ensure that the interference charges in the electromagnetic shielding film 6 can be extracted, the number of the first through holes 11 in the first conductor layer 1 per square centimeter in this embodiment is 5-10. 6 Correspondingly, the number of the metal protrusions 12 in the first conductor layer 1 is 5-10 per square centimeter. 6 It should be noted that, since the metal protrusions 12 are provided at the first through holes 11, the number of the first through holes 11 corresponds to the number of the metal protrusions 12, thereby ensuring that the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 can be smoothly pierced to connect the free grounding film with the electromagnetic shielding film 6.

[0062] In the embodiment of the present invention, the first through holes 11 may be regularly or irregularly distributed on the first conductor layer 1; wherein, the first through holes 11 being regularly distributed on the first conductor layer 1 means that the shapes of the first through holes 11 are the same and are evenly distributed on the first conductor layer 1; the first through holes 11 being irregularly distributed on the first conductor layer 1 means that the shapes of the first through holes 11 are different and are randomly distributed on the first conductor layer 1. Preferably, the shapes of the first through holes 11 are the same and are evenly distributed on the first conductor layer 1. In addition, the first through holes 11 may be circular through holes or through holes of any other shapes. The 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.

[0063] In an embodiment of the present invention, the thickness of the first conductor layer 1 is 2μm-45μm to ensure that the first conductor layer 1 is not easy to break and has good flexibility. It can be understood that in order to ensure that the first conductor layer 1 has good conductivity, 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. Among them, 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.

[0064] In the embodiment of the present invention, the first conductor layer 1 includes a first surface 14 in contact with the adhesive film layer 2. It should be noted that the first surface 14 can be a surface of any shape, for example, Figure 1 The flat surface shown can also beFigure 2 The uneven surface shown, or a rough surface; in addition, the first surface 14 may be a regular surface or an irregular surface.

[0065] As Figure 2 As shown, in order to ensure that the metal protrusion 12 can pierce the insulating layer 61 of the adhesive film layer 2 and the electromagnetic shielding film 6 to ensure reliable connection between the electromagnetic shielding film 6 and the free grounding film, preferably, the first surface 14 is an uneven surface. When the first surface 14 is an uneven surface, the first surface 14 includes several convex portions, and the first through hole 11 is preferably disposed on the convex portions. Therefore, the metal protrusions 12 are distributed on the convex portions, so that during the pressing process, the metal protrusions 12 are more likely to pierce the insulating layer 61 of the adhesive film layer 2 and the electromagnetic shielding film 6, thereby further ensuring the reliability of the connection between the electromagnetic shielding film 6 and the free grounding film.

[0066] In addition, the first conductor layer 1 further includes a second surface 15 disposed opposite to the first surface 14, and the second surface 15 is in contact with the anti-oxidation layer 5. It should be noted that the second surface 15 may be a surface of any shape. For example, it may be Figure 1 The flat surface shown, or an uneven surface, or other rough surfaces; in addition, the second surface 15 may be a regular surface or an irregular surface. The accompanying drawings of the present invention only take the second surface 15 as a flat surface for illustration, and any other shaped second surface 15 is within the protection scope of the present invention.

[0067] In the embodiment of the present invention, it should be noted that the first conductor layer 1 in the accompanying drawings of this embodiment may be a single-layer structure or a multi-layer structure. In addition, according to the actual production and application needs, the first conductor layer 1 in the accompanying drawings of this embodiment may be set in a grid shape, a foam shape, etc.

[0068] In an embodiment of the present invention, one structure 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 to tightly bond the free grounding film and the electromagnetic shielding film 6, but also has a conductive function, which cooperates with the first conductor layer 1 and the metal protrusion 12 to quickly conduct interfering electrons. Among them, the conductive particles in the adhesive film layer 2 can be separated conductive particles or large particle conductive particles formed by aggregation; when the conductive particles are 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 an 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 an adhesive function to tightly bond the free grounding film and the electromagnetic shielding film 6, and at the same time, since the adhesive film layer 2 does not contain conductive particles, the insertion loss of the circuit board during use is reduced and the bendability of the circuit board is improved.

[0070] In addition, in this embodiment, the thickness of the adhesive film layer 2 is 0.1 μm - 80 μm. The materials used for the adhesive film layer 2 are selected from the following types: modified epoxy resin types, acrylic types, modified rubber types, and modified thermoplastic polyimide types. In addition, it should be noted that the outer surface of the adhesive film layer 2 can be a flat surface without undulations or a non-flat surface with gentle undulations.

[0071] Combined Figure 1 and Figure 2 As shown, in order to protect the adhesive film layer 2, in this embodiment, the free grounding film further includes a peelable protective film layer 3, and the peelable protective film layer 3 is provided on the side of the adhesive film layer 2 away from the first conductor layer 1. The peelable protective film layer 3 plays a protective role to prevent the adhesive film layer 2 from being damaged before use, so as to ensure that the free grounding film can be pressed against the electromagnetic shielding film 6 through the adhesive film layer 2. It should be noted that when the free grounding film is pressed against the electromagnetic shielding film 6, the peelable protective film layer 3 needs to be peeled off, and then the free grounding film is pressed against the electromagnetic shielding film 6 through the adhesive film layer 2.

[0072] 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.

[0073] 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 5, and the anti-oxidation layer 5 is arranged on the side of the first conductor layer 1 away from the adhesive film layer 2. By providing the anti-oxidation layer 5 on the side of the first conductor layer 1 away from the adhesive film layer 2, the first conductor layer 1 is prevented from being oxidized by contact with air, thereby ensuring that the interference charges in the electromagnetic shielding film 6 can be led out through the free grounding film.

[0074] 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.

[0075] 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.

[0076] Embodiment 2

[0077] like Figure 4 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.

[0078] Preferably, the conductor particles 13 are concentratedly distributed at the outwardly protruding positions on the surface of the metal protrusions 12, making it easier to pierce. In addition, the conductor particles 13 can also be distributed at other positions on the side of the first conductor layer 1 close to the adhesive film layer 2, not only distributed on the surface of the metal protrusions 12, such as Figure 4 as shown. Of course, the conductor particles 13 can also be only distributed on the surface of the metal protrusions 12.

[0079] In specific implementation, as Figure 4 shown, the metal protrusions 12 can be formed first, and then the conductor particles 13 can be formed on the outer surface of the metal protrusions 12 through other processes. Of course, the metal protrusions 12 and the conductor particles 13 can also be an integral structure formed by a one-step forming process.

[0080] In the embodiment of the present invention, the conductor particles 13 may have 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.

[0081] 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 be preferably 20 μm - 100 μm and the thickness of the adhesive film layer 2 to be preferably 0.1 μm - 80 μm, it is ensured that the conductor particles 13 can pierce through the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, thereby ensuring that the free grounding film can conduct the interfering charges accumulated on the electromagnetic shielding film 6.

[0082] In the 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 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. In addition, it should be noted that the conductor particles 13 can be the same as or different from the material of the metal protrusions 12.

[0083] In the embodiment of the present invention, it should be noted that, as Figure 4The shape of the conductor particles 13 shown is merely exemplary. Due to differences in process means and parameters, the conductor particles 13 may also be in other shapes such as cluster shape, icicle shape, stalactite shape, dendritic shape, etc. In addition, the conductor particles 13 in the present invention are not limited to the shapes shown in the drawings and described above. As long as they are conductor particles with piercing and conductive functions, they are within the protection scope of the present invention.

[0084] 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.

[0085] Embodiment Three

[0086] As Figure 5 shown, the difference between the free grounding film in this embodiment and the first embodiment is that the free grounding film includes a first conductor layer 1 and a glue film layer 2 which are stacked. The first conductor layer 1 is provided with a first through hole 11 penetrating its upper and lower surfaces, and a metal protrusion 12 is provided at the first through hole 11; 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 instantaneously cooling.

[0087] The free grounding film further includes a second conductor layer 4. The second conductor layer 4 is disposed between the first conductor layer 1 and the glue film layer 2, and a protrusion 41 is formed at a position where the second conductor layer 4 covers the metal protrusion 12, and the protrusion 41 extends into the glue film layer 2. As Figure 7 shown, by disposing the second conductor layer 4 between the first conductor layer 1 and the glue film layer 2, so that a protrusion 41 is formed at a position where the second conductor layer 4 covers the metal protrusion 12, it can smoothly pierce the insulating layer 61 of the glue film layer 2 and the electromagnetic shielding film 6 during the pressing process of the free grounding film and the electromagnetic shielding film 6 in cooperation with the metal protrusion 12 and the protrusion 41, so as to ensure the normal export of interference charges.

[0088] In the embodiments 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. The shape of the protrusion 41 shown in the drawings is merely exemplary.

[0089] In an embodiment of the present invention, in order to further ensure that the convex portion 41 can smoothly pierce the adhesive film layer 2 and the insulating layer 61, conductive particles 13 in a convex shape are provided on the surface of the convex portion 41 in this embodiment. By providing the conductive particles 13 on the surface of the convex portion 41, the convex portion 41 can more easily pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6 and connect to the shielding layer 62 of the electromagnetic shielding film 6, so as to effectively conduct the interfering charges accumulated in the electromagnetic shielding film 6.

[0090] Preferably, the conductive particles 12 are concentratedly distributed at the outwardly convex positions on the surface of the convex portion 41, making it easier to pierce the adhesive film layer 2. Of course, conductive particles 2 may also be distributed on the non-convex portions of the surface of the convex portion 41. In addition, the conductive particles 7 may also be distributed at other positions on the side of the second conductor layer 4 close to the adhesive film layer 2, not only distributed on the surface of the convex portion 41, as Figure 5 shown. Of course, the conductive particles 13 may also be distributed only on the surface of the convex portion 41.

[0091] In specific implementation, the second conductor layer 4 may be formed first, and then the conductive particles 13 may be formed on the side of the second conductor layer 4 away from the first conductor layer 1 through other processes; of course, the second conductor layer 4 and the conductive particles 13 may also be an integral structure formed by a one-time molding process.

[0092] In an embodiment of the present invention, the conductive particles 13 may have 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.

[0093] In an embodiment of the present invention, the height of the conductive 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 conductive particles 3 to be preferably 20 μm - 100 μm and the thickness of the adhesive film layer 2 to be preferably 0.1 μm - 80 μm, it is ensured that the conductive particles 13 can pierce the adhesive film layer 2 and the insulating layer 61 of the electromagnetic shielding film 6, thus ensuring that the free grounding film can conduct the interfering charges accumulated on the electromagnetic shielding film 6.

[0094] 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 materials including aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy particles are made of any two or more of materials including aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. In addition, it should be noted that the material of the conductor particles 13 may be the same as or different from that of the second conductor layer 4.

[0095] In an embodiment of the present invention, it should be noted that as Figure 5 shown, the shape of the conductor particles 13 is merely exemplary. Due to differences in process means and parameters, the conductor particles 13 may also be in other shapes such as cluster shape, icicle shape, stalactite shape, dendritic shape, etc. In addition, the conductor particles 13 in the present invention are not limited by the illustrated and above-mentioned shapes, and as long as they are conductor particles with piercing and conductive functions, they are within the protection scope of the present invention.

[0096] In an embodiment of the present invention, the thickness of the second conductor layer 4 is 2 μm - 45 μm to ensure that the second conductor layer 4 is not easily broken and has good flexibility. It can be understood that in order to ensure that the second conductor layer 4 has good conductivity, the second conductor layer 4 includes one or more of a metal shielding layer, a carbon nanotube shielding layer, a ferrite shielding layer, and a graphene shielding layer. In addition, the metal shielding layer includes a single-metal shielding layer and / or an alloy shielding layer; wherein, the single-metal shielding layer is made of any one of materials including aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy shielding layer is made of any two or more of materials including aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0097] In an embodiment of the present invention, it should be noted that the second conductor layer 4 in the drawings of this embodiment may be a single-layer structure or a multi-layer structure. In addition, according to the needs of actual production and application, the second conductor layer 4 in the drawings of this embodiment may be set in a grid shape, a foamed shape, etc. 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.

[0098] Embodiment 4

[0099] See Figure 6 And Figure 7 In an embodiment of the present invention, a circuit board is further provided, including a printed circuit board 7 and an electromagnetic shielding film 6 provided on the printed circuit board 7;

[0100] See Figure 6, the circuit board further includes the free grounding film described in Embodiment 1 or 2. The electromagnetic shielding film 6 is disposed on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 which are stacked. The free grounding film is pressed with the electromagnetic shielding film 6 through the adhesive film layer 2. The metal protrusion 12 pierces through the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62;

[0101] Or, refer to Figure 7 , the circuit board further includes the free grounding film described in Embodiment 3. The electromagnetic shielding film 6 is disposed on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 which are stacked. The free grounding film is pressed with the electromagnetic shielding film 6 through the adhesive film layer 2. The protrusion 41 pierces through the adhesive film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0102] In the embodiments of the present invention, it should be noted that the metal protrusion 12 or the protrusion 41 on the free grounding film may all be in contact with the shielding layer 62 of the electromagnetic shielding film 6, or part of them may be in contact with the shielding layer 62 of the electromagnetic shielding film 6.

[0103] In this embodiment, the implementation manner of the free grounding film can refer to the description of the above embodiments and will not be elaborated here.

[0104] 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-flex board.

[0105] In specific implementation, when the circuit board is applied to an electronic device, the free grounding film can be electrically connected to the housing of the electronic device, so as to export the interfering charges accumulated in the electromagnetic shielding film 6.

[0106] In the embodiments of the present invention, through the above structure, 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 are pierced by the metal protrusion 12 or the protrusion 41, so that at least a part of the outer surface of the first conductor layer 1 is connected to the shielding layer 62 of the electromagnetic shielding film 6, thereby realizing the export of the interfering charges in the electromagnetic shielding film 6, avoiding the accumulation of interfering charges to form an interference source and affecting the normal operation of the circuit board.

[0107] Embodiment 5

[0108] As Figure 8 shown, the embodiments of the present invention provide a preparation method of a free grounding film. This method is applicable to preparing the free grounding film described in Embodiment 1, and includes steps S11 to S13:

[0109] S11. Form a first conductor layer; wherein, a first via hole penetrating through the upper and lower surfaces of the first conductor layer is formed.

[0110] In step S11, the first conductor layer can be formed in the following manner:

[0111] Form an anti-oxidation layer on the carrier film;

[0112] Form the first conductor layer on the side of the anti-oxidation layer away from the carrier film.

[0113] Or, form a peelable layer on the carrier film;

[0114] Form the first conductor layer on the side of the peelable layer away from the carrier film;

[0115] After forming an anti-oxidation layer on the side of the first conductor layer away from the peelable layer, peel off the peelable layer.

[0116] In an embodiment of the present invention, preferably, the cross-sectional area of the first via hole is 0.01 μm 2 -1 mm 2 ; the number of the first via holes in each square centimeter of the first conductor layer is 5 - 10 6 pieces.

[0117] S12. Form a metal protrusion at the first via hole; wherein, the metal protrusion protrudes out of the first via hole.

[0118] In step S12, the forming of the metal protrusion at the first via hole specifically is:

[0119] Set a fusible metal at the first via hole, and make the fusible metal flow from one side of the first via hole to the other side and then instantaneously cool at a preset temperature, so as to form the metal protrusion at the first via hole. Wherein, the fusible metal is any one of single metals such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold or any alloy of any plurality of them; the preset temperature is 300 °C to 2000 °C.

[0120] S13. Form a glue film layer on the side of the first conductor 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 arranged in a stacked manner, the free grounding film is press-fitted with the electromagnetic shielding film through the glue film layer, and the metal protrusion pierces through the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0121] Wherein, the forming of the glue film layer on the side of the first conductor layer where the metal protrusion is formed specifically is:

[0122] Coat a glue film layer on the release film, and then laminate and transfer the glue film layer to the side of the first conductor layer where the metal protrusions are formed, so as to form a glue film layer on the side of the first conductor layer where the metal protrusions are formed; or,

[0123] Directly coat a glue film layer on the side of the first conductor layer where the metal protrusions are formed, so as to form a glue film layer on the side of the first conductor layer where the metal protrusions are formed.

[0124] In another preferred embodiment applicable to preparing the free grounding film described in Embodiment 2, after step S12 and before step S13, the method further includes the step of:

[0125] Form conductor particles on the outer surface of the metal protrusions by one or more of the processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating.

[0126] In the embodiment of the present invention, the preparation method of the free grounding film forms the metal protrusions at the first through holes of the first conductor layer, and forms a glue film layer on the side of the first conductor layer where the metal protrusions are formed, so that when the free grounding film is pressed against the electromagnetic shielding film through its glue film layer, the metal protrusions can sequentially pierce the glue 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 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, 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 as to avoid the accumulation of interfering charges and affect the normal operation of the printed circuit board.

[0127] Embodiment Six

[0128] See Figure 9 , the embodiment of the present invention provides another preparation method of the free grounding film, which is applicable to preparing the free grounding film described in Embodiment 3, and includes steps S21 to S24:

[0129] S21. Form a first conductor layer; wherein, a first through hole penetrating the upper and lower surfaces thereof is formed on the first conductor layer;

[0130] Wherein, the first conductor layer can be formed in the following manner:

[0131] Form an anti-oxidation layer on the carrier film;

[0132] Form the first conductor layer on the side of the anti-oxidation layer away from the carrier film.

[0133] Or, form a peelable layer on the carrier film;

[0134] The first conductor layer is formed on a side of the peelable layer away from the carrier film;

[0135] After an anti-oxidation layer is formed on a side of the first conductor layer away from the peelable layer, the peelable layer is peeled off.

[0136] In an embodiment of the present invention, preferably, a cross-sectional area of the first through hole is 0.01 μm 2 -1 mm 2 ; and the number of the first through holes in each square centimeter of the first conductor layer is 5-10 6 pieces.

[0137] S22. A metal protrusion is formed at the first through hole; wherein, the metal protrusion protrudes out of the first through hole;

[0138] In step S22, the forming of the metal protrusion at the first through hole specifically is:

[0139] A fusible metal is disposed at the first through hole, and the fusible metal is caused to flow from one side of the first through hole to the other side and then instantaneously cooled at a preset temperature, so as to form the metal protrusion at the first through hole. Wherein, the fusible metal is any one of single metals such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold or any alloy of a plurality of them; the preset temperature is 300 °C to 2000 °C.

[0140] S23. A second conductor layer is formed on a side of the first conductor layer where the metal protrusion is formed, and a raised portion is formed at a position where the second conductor layer covers the metal protrusion;

[0141] Preferably, after step S23 is implemented, conductor particles can be formed on an outer surface of the raised portion by one or more processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating.

[0142] S24. An adhesive film layer is formed on a side of the second conductor layer away from the first 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 which are stacked, and the free grounding film is press-fitted with the electromagnetic shielding film through the adhesive film layer, and the raised portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0143] Wherein, the forming of the adhesive film layer on the side of the second conductor layer away from the first conductor layer specifically is:

[0144] Coat a glue film layer on the release film, and then laminate and transfer the glue film layer to the side of the second conductor layer away from the first conductor layer, so as to form a glue film layer on the side of the second conductor layer away from the first conductor layer; or,

[0145] Directly coat a glue film layer on the side of the second conductor layer away from the first conductor layer, so as to form a glue film layer on the side of the second conductor layer away from the first conductor layer.

[0146] In summary, the 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 first conductor layer 1 and a glue film layer 2 which are stacked. A first through hole 11 penetrating the upper and lower surfaces is provided on the first conductor layer 1. A metal protrusion 12 is provided at the first through hole 11, and the metal protrusion 12 extends into the glue 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 instantaneously cooling; when the free grounding film is used for grounding of a printed circuit board 7, an electromagnetic shielding film 6 is provided on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 which are stacked. The free grounding film is pressed and bonded with the electromagnetic shielding film 6 through the glue film layer 2. The metal protrusion 12 pierces through the glue film layer 2 and the insulating layer 61 and is electrically connected to the shielding layer 62, so as to effectively lead out the interfering charges in the electromagnetic shielding film 6, and further ensure the grounding of the electromagnetic shielding film 6, effectively avoiding the problem that when the temperature is high, since the free grounding film is pressed and bonded with the electromagnetic shielding film through a 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 avoid the accumulation of interfering charges and affect the normal operation of the printed circuit board.

[0147] 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 substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A free grounding film, characterized in that, it includes a first conductor layer and an adhesive film layer which are stacked. A first through hole penetrating the upper and lower surfaces is provided on the first conductor layer. 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 instantaneously cooling; 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 press-fitted with the electromagnetic shielding film through the adhesive film layer, and the metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer; the first conductor layer includes a metal conductor layer, and the metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer.

2. The free grounding film according to claim 1, characterized in that, the fusible metal is any one of single metals such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold or any alloy of any combination thereof.

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

4. The free grounding film according to claim 1, characterized in that, the first conductor layer includes a first surface in contact with the adhesive film layer, and the first surface is an undulating and non-planar surface.

5. The free grounding film 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 20μm - 100μm.

6. The free grounding film 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 without conductive particles.

7. The free grounding film according to any one of claims 1 - 6, characterized in that, the first conductor layer further includes one or more of a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer.

8. The free grounding film according to claim 7, 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.

9. The free grounding film according to any one of claims 1 - 6, characterized in that, The number of the first through-holes in the first conductor layer per square centimeter is 5 - 10 6 ; and / or, the cross-sectional area of the first through-hole is 0.01 μm 2 - 1 mm 2 .

10. The free grounding film according to any one of claims 1 - 6, characterized in that, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is provided on the surface of the first conductor layer away from the adhesive film layer.

11. The free grounding film according to any one of claims 1 - 6, characterized in that, the free grounding film further includes a peelable protective film layer, and the peelable protective film layer is provided on the surface of the adhesive film layer away from the first conductor layer.

12. The free grounding film according to any one of claims 1 - 6, characterized in that, The free grounding film further includes a second conductor layer, which is disposed between the first conductor layer and the adhesive film layer, and a raised portion is formed at a position where the second conductor layer covers the metal protrusion.

13. The free grounding film according to claim 12, wherein, conductor particles in a convex shape are provided on the surface of the raised portion.

14. A circuit board includes a printed circuit board and an electromagnetic shielding film disposed on the printed circuit board, wherein, the circuit board further includes the free grounding film according to any one of claims 1-11. The electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked. The free grounding film is pressed and bonded to the electromagnetic shielding film through the adhesive film layer. The metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer; or, the circuit board further includes the free grounding film according to claim 12 or 13. The electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked. The free grounding film is pressed and bonded to the electromagnetic shielding film through the adhesive film layer. The raised portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

15. A preparation method of a free grounding film, wherein, it is applicable to prepare the free grounding film according to any one of claims 1-11, and includes the steps of: forming a first conductor layer; wherein, a first through hole penetrating through the upper and lower surfaces thereof is formed on the first conductor layer; forming a metal protrusion at the first through hole; wherein, the metal protrusion extends out of the first through hole; forming an adhesive film layer on one side of the first conductor 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 and bonded to the electromagnetic shielding film through the adhesive film layer. The metal protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

16. The preparation method of the free grounding film according to claim 15, wherein, the forming of the metal protrusion at the first through hole specifically is: disposing fusible metal at the first through hole, and making the fusible metal flow from one side of the first through hole to the other side and instantaneously cool at a preset temperature, so as to form the metal protrusion at the first through hole.

17. The preparation method of the free grounding film according to claim 15, wherein, before forming the adhesive film layer on one side of the first conductor layer where the metal protrusion is formed, the following steps are further included: forming conductor particles on the outer surface of the metal protrusion through one or more of the processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating.

18. The preparation method of the free grounding film according to claim 15, wherein, the forming of the adhesive film layer on one side of the first conductor layer where the metal protrusion is formed specifically is: coating the adhesive film layer on a release film, and pressing and transferring the adhesive film layer to one side of the first conductor layer where the metal protrusion is formed; or, A glue film layer is coated on the side of the first conductor layer where the metal protrusion is formed.

19. A method for preparing a free grounding film, characterized in that it is applicable to preparing the free grounding film described in claim 12 or 13, and includes the steps of: forming a first conductor layer; wherein, a first through hole penetrating the upper and lower surfaces thereof is formed on the first conductor layer; forming a metal protrusion at the first through hole; wherein, the metal protrusion protrudes out of the first through hole; forming a second conductor layer on the side of the first conductor layer where the metal protrusion is formed, and forming a protrusion at the position where the second conductor layer covers the metal protrusion; forming a glue film layer on the side of the second conductor layer away from the first 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 which are stacked, and the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces through the glue film layer and the insulating layer and is electrically connected to the shielding layer.

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