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

Abstract

An embodiment of the present invention provides a free grounding film, a circuit board, and a preparation method of the free grounding film. The free grounding film includes a first conductor layer, a conductive adhesive layer, a second conductor layer, and a film adhesive layer that are sequentially stacked. A conductive protrusion is provided on a surface of the second conductor layer close to the film adhesive 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 free grounding film is pressed against the electromagnetic shielding film through the film adhesive layer. The conductive protrusion pierces through the insulating layers of the film adhesive layer and the electromagnetic shielding film and is electrically connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the shielding layer, avoiding the accumulation of interfering charges to form an interference source, and further 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, a conductive adhesive layer, a second conductor layer, and a film layer stacked in sequence. A conductive protrusion is provided on a surface of the second conductor layer close to the film layer;

[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. The free grounding film is pressed and bonded with the electromagnetic shielding film through the film layer, and the conductive protrusion pierces through the film layer and the insulating layer and is electrically connected to the shielding layer.

[0008] As an improvement of the above solution, a first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating the upper and lower surfaces thereof is provided on the conductive adhesive layer;

[0009] The conductive protrusion is correspondingly formed at an outer side of the second through hole; the conductive protrusion is formed by cooling and solidifying of fusible metal flowing from the first through hole through the third through hole to the outer side of the second through hole; wherein, the outer side of the second through hole is far from the conductive adhesive layer.

[0010] As an improvement of the above solution, a first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer;

[0011] The conductive protrusion is correspondingly formed at an outer side of the second through hole; the conductive protrusion is formed by cooling and solidifying of fusible metal from the first through hole and hot melt adhesive of the conductive adhesive layer flowing to the outer side of the second through hole; wherein, the outer side of the second through hole is far from the conductive adhesive layer.

[0012] As an improvement of the above solution, a convex conductor particle is provided on a surface of the conductive protrusion.

[0013] As an improvement of the above solution, the film layer includes an adhesive layer containing conductive particles; or, the film layer includes an adhesive layer not containing conductive particles.

[0014] As an improvement of the above solution, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is provided on a surface of the first conductor layer far from the conductive adhesive layer.

[0015] As an improvement of the above solution, the free grounding film further includes a peelable protective film layer, and the peelable protective film layer is provided on a surface of the film layer far from the second conductor layer.

[0016] As an improvement to the above solution, the free grounding film further includes a third conductor layer, which is disposed on the surface of the second conductor layer where the conductive protrusions are formed, and a protrusion is formed at the position where the third conductor layer covers the conductive protrusions.

[0017] As an improvement to the above solution, the surface of the protrusion is provided with convex conductor particles.

[0018] To solve the same technical problem, the present invention also 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;

[0019] 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 conductive protrusions pierce through the adhesive film layer and the insulating layer and are electrically connected to the shielding layer;

[0020] 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 protrusions pierce through the adhesive film layer and the insulating layer and are electrically connected to the shielding layer.

[0021] To solve the same technical problem, the present invention also provides a preparation method for a free grounding film, which is applicable to preparing the free grounding film of the above first embodiment, and includes the steps of:

[0022] Form a first conductor layer, form a conductive adhesive layer on one surface of the first conductor layer, and form a second conductor layer on the surface of the conductive adhesive layer away from the first conductor layer;

[0023] Form conductive protrusions on the surface of the second conductor layer away from the conductive adhesive layer;

[0024] Form an adhesive film layer on the surface of the second conductor layer where the conductive protrusions are 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 stacked, and the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the conductive protrusions pierce through the adhesive film layer and the insulating layer and are electrically connected to the shielding layer.

[0025] As an improvement to the above solution, the first conductor layer is provided with a first through hole penetrating its upper and lower surfaces, the second conductor layer is provided with a second through hole penetrating its upper and lower surfaces, and the conductive adhesive layer is provided with a third through hole penetrating its upper and lower surfaces;

[0026] Then, forming the conductive protrusions on the surface of the second conductor layer away from the conductive adhesive layer specifically includes:

[0027] After the fusible metal flows from the first through-hole to the outside of the second through-hole via the third through-hole, it is cooled and solidified, so as to form a conductive bump on the surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through-hole is away from the conductive adhesive layer.

[0028] As an improvement of the above solution, the conductive adhesive layer is a hot-melt adhesive layer; a first through-hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, and a second through-hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer;

[0029] Then, forming the conductive bump on the surface of the second conductor layer away from the conductive adhesive layer specifically includes:

[0030] A fusible metal is provided at the first through-hole, and the fusible metal is made to flow from the first through-hole to the second through-hole at a preset temperature, and the conductive adhesive layer forms a hot-melt adhesive flow to the second through-hole during the flow of the fusible metal;

[0031] The fusible metal and the hot-melt adhesive flowing to the outside of the second through-hole are cooled, so as to form a conductive bump on the surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through-hole is away from the conductive adhesive layer.

[0032] As an improvement of the above solution, before forming the adhesive film layer on the surface of the second conductor layer where the conductive bump is formed, it further includes:

[0033] Conductor particles are formed on the outer surface of the conductive bump 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.

[0034] As an improvement of the above solution, forming the adhesive film layer on the surface of the second conductor layer where the conductive bump is formed specifically includes:

[0035] Form an adhesive film layer on the release film, and then laminate and transfer the adhesive film layer to the surface of the second conductor layer where the conductive bump is formed; or,

[0036] Directly form an adhesive film layer on the surface of the second conductor layer where the conductive bump is formed.

[0037] In order to solve the same technical problem, the present invention also provides a method for preparing a free grounding film, which is applicable to preparing the free grounding film in the above second embodiment, and includes the steps of:

[0038] Form a first conductor layer, form a conductive adhesive layer on one surface of the first conductor layer, and form a second conductor layer on the surface of the conductive adhesive layer away from the first conductor layer;

[0039] Form a conductive protrusion on the side of the second conductor layer away from the conductive adhesive layer;

[0040] Form a third conductor layer on the side of the second conductor layer where the conductive protrusion is formed, and form a protrusion portion at the position where the third conductor layer covers the conductive protrusion;

[0041] Form a glue film layer on the side of the third conductor layer away from the second conductor layer; 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 arranged in a stacked manner, the free grounding film is pressed against the electromagnetic shielding film through the glue film layer, and the protrusion portion pierces through the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0042] As an improvement of the above solution, a first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating the upper and lower surfaces thereof is provided on the conductive adhesive layer;

[0043] Then, forming the conductive protrusion on the side of the second conductor layer away from the conductive adhesive layer specifically includes:

[0044] Set a fusible metal at the first through hole, and at a preset temperature, make the fusible metal flow from the first through hole through the third through hole to the second through hole, and after the fusible metal flows to the outside of the second through hole, it cools and solidifies, so as to form a conductive protrusion on the side of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

[0045] As an improvement of the above solution, the conductive adhesive layer is a hot melt adhesive layer; a first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer;

[0046] Then, forming the conductive protrusion on the side of the second conductor layer away from the conductive adhesive layer specifically includes:

[0047] Set a fusible metal at the first through hole, and at a preset temperature, make the fusible metal flow from the first through hole to the second through hole, and the conductive adhesive layer forms a hot melt adhesive flow to the second through hole during the flow of the fusible metal;

[0048] Cool the fusible metal and the hot melt adhesive flowing to the outside of the second through hole, so as to form a conductive protrusion on the side of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

[0049] Compared with the prior art, for the free grounding film, circuit board and preparation method of the free grounding film provided by the embodiments of the present invention, by providing the conductive protrusions on the surface of the second conductor layer close to the adhesive film layer, when the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the conductive protrusions can successively pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film and be connected to the shielding layer of the electromagnetic shielding film;

[0050] Alternatively, by providing the third conductor layer on the surface of the second conductor layer where the conductive protrusions are formed, so that the position of the third conductor layer covering the conductive protrusions correspondingly forms a raised portion, and the adhesive film layer is laid on the surface of the third conductor layer away from the second conductor layer, when the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the raised portion can successively pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film and be connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, 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 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. Therefore, the integrity of signal transmission is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a schematic structural diagram of the first free grounding film provided by Embodiment 1 of the present invention;

[0052] Figure 2 is a schematic structural diagram of the second free grounding film provided by Embodiment 1 of the present invention;

[0053] Figure 3 is a schematic structural diagram of the third free grounding film provided by Embodiment 1 of the present invention;

[0054] Figure 4 is a schematic structural diagram of the first free grounding film provided by Embodiment 2 of the present invention;

[0055] Figure 5 is a schematic structural diagram of the second free grounding film provided by Embodiment 2 of the present invention;

[0056] Figure 6 is a schematic structural diagram of the third free grounding film provided by Embodiment 2 of the present invention;

[0057] Figure 7 is a schematic structural diagram of the fourth free grounding film provided by Embodiment 2 of the present invention;

[0058] Figure 8 is a cross-sectional view of a free grounding film provided by an embodiment of the present invention;

[0059] Figure 9 is a schematic structural diagram of the first circuit board provided in the third embodiment of the present invention;

[0060] Figure 10 is a schematic structural diagram of the second circuit board provided in the third embodiment of the present invention;

[0061] Figure 11 is a flowchart of the preparation method of the free grounding film provided in the fourth embodiment of the present invention;

[0062] Figure 12 is a flowchart of the preparation method of the free grounding film provided in the fourth embodiment of the present invention.

[0063] Among them, 1 is the first conductor layer; 10 is the first through hole; 2 is the conductive adhesive layer; 20 is the third through hole; 3 is the second conductor layer; 30 is the second through hole; 4 is the adhesive film layer; 5 is the conductive protrusion; 6 is the conductor particle; 7 is the third conductor layer; 70 is the protrusion part; 8 is the anti-oxidation layer; 9 is the electromagnetic shielding film; 90 is the insulating layer; 91 is the shielding layer; 11 is the printed circuit board. Detailed implementation manners

[0064] 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0065] Embodiment 1

[0066] Please refer to Figure 1 , the embodiment of the present invention provides a free grounding film, which includes a first conductor layer 1, a conductive adhesive layer 2, a second conductor layer 3 and an adhesive film layer 4 stacked in sequence; a conductive protrusion 5 is provided on the surface of the second conductor layer 3 close to the adhesive film layer 4;

[0067] Refer to Figure 9 , when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 9 is provided on the printed circuit board 11. The electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 stacked. The free grounding film is pressed together with the electromagnetic shielding film 9 through the adhesive film layer 4, and the conductive protrusion 5 pierces through the adhesive film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91. Among them, the material of the conductive protrusion 5 can be materials such as pure metal, alloy or conductive adhesive with good electrical conductivity, which is not specifically limited here.

[0068] In this embodiment, by providing the conductive protrusions 5 on the side of the second conductor layer 3 close to the adhesive film layer 4, during the lamination process of the free grounding film and the electromagnetic shielding film 9, the conductive protrusions 5 can smoothly pierce through the adhesive film layer 4 and the insulating layer 90 and contact the shielding layer 91, thereby effectively discharging the interfering charges accumulated in the electromagnetic shielding film, and further ensuring the integrity of signal transmission.

[0069] In this embodiment, preferably, the conductive protrusions 5 extend into the adhesive film layer 4, which can make it easier for the conductive protrusions 5 to pierce through the adhesive film layer 4 and the insulating layer 90 during the lamination process. Alternatively, the conductive protrusions 5 can also pierce through the adhesive film layer 4, so that during the lamination process, the conductive protrusions 5 can directly pierce through the insulating layer 90. Of course, the conductive protrusions 5 may not extend into the adhesive film layer 4 but be covered by the adhesive film layer 4.

[0070] Please refer to Figure 2 , preferably, one or more conductor particles 6 are provided on the surface of the conductive protrusions 5. Among them, by providing the conductor particles 6 on the surface of the conductive protrusions 5, it is further ensured that during the lamination process, the conductive protrusions 5 can smoothly pierce through the adhesive film layer 4 and the insulating layer 90 of the electromagnetic shielding film 9, and further ensure the normal discharge of interfering charges.

[0071] In the embodiment of the present invention, the height of the conductor particles 6 is preferably 20 μm - 100 μm, the thickness of the adhesive film layer 4 is preferably 0.1 μm - 80 μm, and the thickness of the insulating layer 90 is preferably 1 μm - 20 μm. By setting the height of the conductor particles 6 to be preferably 20 μm - 100 μm and the thickness of the adhesive film layer 4 to be preferably 0.1 μm - 80 μm, it is ensured that the conductor particles 6 can pierce through the adhesive film layer 4 and the insulating layer 90 of the electromagnetic shielding film 9, thereby ensuring that the free grounding film can discharge the interfering charges accumulated on the electromagnetic shielding film 9. Preferably, the conductor particles 6 are concentratedly distributed at the outwardly protruding positions on the surface of the conductive protrusions 5, which makes it easier to pierce through the adhesive film 4. Of course, the non-convex parts on the surface of the conductive protrusions 5 can also have conductor particles 6 distributed. In addition, the conductor particles 6 can also be distributed at other positions on the side of the second conductor layer 3 close to the adhesive film layer 4.

[0072] In the embodiment of the present invention, the conductor particles 6 may have a certain distance from the inner surface of the adhesive film layer 4 (i.e., the surface close to the second conductor layer 3), may also be in contact with the inner surface of the adhesive film layer 4 or extend out of the outer surface of the adhesive film layer 4. In addition, the outer surface of the adhesive film layer 4 can be a flat surface without undulations or an uneven surface with undulations.

[0073] In the embodiments of the present invention, it should be noted that the shape of the conductor particle 6 shown in the figure is only exemplary. Due to differences in process means and parameters, the conductor particle 6 can also be in other shapes such as cluster shape, icicle shape, stalactite shape, dendritic shape, etc. In addition, the conductor particle 6 in the present invention is not limited by the illustrated and the above shapes. As long as it is a conductor particle 6 with piercing and conductive functions, it is within the protection scope of the present invention.

[0074] In the embodiments of the present invention, the conductor particle 6 includes 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; among them, 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.

[0075] In the embodiments of the present invention, the formation process of the conductive protrusion 5 is as follows: a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, and a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3. The conductive protrusion 5 is formed by the cooling and solidification of fusible metal flowing from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0076] Specifically, please refer to Figure 3 and Figure 8 , in one preferred manner, the conductive protrusion 5 is formed by the cooling and solidification of fusible metal flowing from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30, and specifically manifested as:

[0077] A third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2; the conductive protrusion 5 is correspondingly formed at the outside of each second through hole 30;

[0078] The conductive protrusion 5 is formed by the cooling and solidification of fusible metal flowing from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30, and specifically manifested as: the conductive protrusion 5 is formed by the cooling and solidification of fusible metal flowing from the first through hole 10 through the third through hole 20 of the conductive adhesive layer 2 to the outside of the second through hole 30; among them, the outside of the second through hole 30 is far from the conductive adhesive layer 2.

[0079] Preferably, the first through-hole 10, the second through-hole 30 and the third through-hole 20 are aligned with each other one by one, and the fusible metal flows from the first through-hole 10 to the outside of the corresponding second through-hole 30. In another case, the first through-hole 10, the second through-hole 30 and the third through-hole 20 may also be in a misaligned state. For example, the first through-hole 10 and the second through-hole are partially aligned, and the second through-hole and the third through-hole are partially aligned. Then, the fusible metal can also flow from the first through-hole 10 through the third through-hole 20 to the outside of the second through-hole 30 that is aligned or misaligned with it.

[0080] It should be noted that in the embodiments of the present invention, the fusible metal flowing out of the corresponding through-holes is divided into the following three cases: the first is that the fusible metal almost completely flows out of the corresponding through-hole and there is no residue in the through-hole; the second is that there is residue in the through-hole or even the through-hole is filled with metal; the third is that there is still metal residue at the edge of the outer hole opening (i.e., the hole opening facing outwards) of the first through-hole 10. Among them, Figure 3 there is no metal residue in the through-hole, but Figure 3 is only exemplary, and the above three cases are all within the protection scope of the present invention. It can be understood that the Figure 6 and Figure 7 referred to below can be referred to the relevant description here for Figure 3 .

[0081] It should be noted that the melting temperature of the fusible metal is preferably 300-2000 degrees Celsius.

[0082] In the embodiments of the present invention, the through-holes (i.e., the first through-hole 10, the second through-hole 30 and the third through-hole 20) can be distributed regularly or irregularly on the corresponding structural layers (i.e., the first conductor layer 1, the second conductor layer 3 and the conductive adhesive layer 2); among them, the through-holes are regularly distributed on the corresponding structural layer means that each through-hole has the same shape and is evenly distributed on the corresponding structural layer; the through-holes are irregularly distributed on the corresponding structural layer means that the shapes of each through-hole are different and are disorderly distributed on the corresponding structural layer. Preferably, each through-hole has the same shape and each through-hole is evenly distributed on the corresponding structural layer. In addition, the through-hole can be a circular through-hole or any other arbitrary shape through-hole. The present invention Figure 8 only takes the through-hole as a circular through-hole for illustration, but any other shape through-holes are within the protection scope of the present invention.

[0083] In an embodiment of the present invention, in order to ensure that when the fusible metal flows from the first through-hole 10 through the third through-hole 20 to the outside of the second through-hole 30, it cools and solidifies to form the conductive bump 5, and at the same time ensure that the first conductor layer 1, the conductive adhesive layer 2, and the second conductor layer 3 are not easily broken. Preferably, in this embodiment, the cross-sectional areas of the first through-hole 10, the second through-hole 30, and the third through-hole 20 are 0.01μm 2 -1mm 2 。

[0084] In addition, in order to ensure that enough conductive bumps 5 can be formed to ensure that the conductive bumps 5 can pierce through the adhesive film layer 4 and the insulating layer 90 to connect with the shielding layer 91, and at the same time ensure that the first conductor layer 1, the conductive adhesive layer 2, and the second conductor layer 3 are not easily broken. Preferably, in this embodiment, the number of the first through-holes 10 in the first conductor layer 1 per square centimeter is 5-10 6 ; the number of the second through-holes 30 in the second conductor layer 3 per square centimeter is 5-10 6 ; the number of the third through-holes 20 in the conductive adhesive layer 2 per square centimeter is 5-10 6 。Correspondingly, the number of the conductive bumps 5 in the second conductor layer 3 per square centimeter is 5-10 6 。

[0085] In another preferred manner, the conductive bump 5 is formed by the fusible metal flowing from the first through-hole 10 through the conductive adhesive layer 2 to the outside of the second through-hole 30 and cooling and solidifying, specifically manifested as:

[0086] The first conductor layer 1 is provided with a first through-hole 10 penetrating through its upper and lower surfaces, and the second conductor layer 3 is provided with a second through-hole 30 penetrating through its upper and lower surfaces; a conductive bump 5 is correspondingly formed at the outside of each second through-hole 30;

[0087] The conductive bump 5 is formed by the fusible metal from the first through-hole 10 and the hot melt adhesive of the conductive adhesive layer flowing to the outside of the second through-hole 30 and cooling and solidifying; wherein, the outside of the second through-hole 30 is far from the conductive adhesive layer 2. Specifically, the conductive adhesive layer 2 is a hot melt adhesive layer. Since the fusible metal flowing from the first through-hole 10 has a very high temperature, the fusible metal will heat-melt the conductive adhesive layer 2 on the flow path, so that the conductive adhesive layer 2 on the flow path is heat-melted into a hot melt adhesive and flows to the second through-hole 30 together with the fusible metal.

[0088] Among them, the first through-hole 10 and the second through-hole 30 may be aligned one by one or in a non-aligned state. For specific details, reference may be made to the above description of the first through-hole 10 and the second through-hole 30, and no further elaboration will be provided here.

[0089] In the embodiments of the present invention, the thicknesses of the first conductor layer 1 and the second conductor layer 3 are both preferably 2 μm - 45 μm to ensure that the first conductor layer 1 and the second conductor layer 3 are not easily broken and have good flexibility. To ensure good electrical conductivity of the first conductor layer 1 and the second conductor layer 3, the first conductor layer 1 and the second conductor layer 3 respectively include one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer. Among them, the metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer; among them, the single-metal conductor layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy conductor layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0090] In the above embodiments, it should be noted that both the first conductor layer 1 and the second conductor layer 3 can be single-layer structures or multi-layer structures. In addition, according to the needs of actual production and application, the first conductor layer 1 and the second conductor layer 3 can be set in a grid shape, a foamed shape, etc.

[0091] In the above embodiments, both sides of the first conductor layer 1 can be flat or undulating, and the side of the second conductor layer 3 away from the protrusion can be flat or undulating, and no specific limitations are made here.

[0092] In the above embodiments, to protect the adhesive film layer 4, the free grounding film in this embodiment further includes a peelable protective film layer (not shown in the figure), and the peelable protective film layer is disposed on the side of the adhesive film layer 4 away from the second conductor layer 3. The peelable protective film layer plays a protective role to prevent the adhesive film layer 4 from being damaged before use, so as to ensure that the free grounding film can be pressed against the electromagnetic shielding film 9 through the adhesive film layer 4. It should be noted that when pressing the free grounding film against the electromagnetic shielding film 9, the peelable protective film layer needs to be peeled off, and then the free grounding film is pressed against the electromagnetic shielding film 9 through the adhesive film layer 4.

[0093] In addition, the peelable protective film layer includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after curing of epoxy resin ink, a film layer formed after curing of polyurethane ink, a film layer formed after curing of modified acrylic resin, or a film layer formed after curing of polyimide resin.

[0094] Combination Figures 1 to 3 As shown, in order to protect the first conductor layer 1 to ensure that the interference charge can be conducted out, the free grounding film in this embodiment further includes an anti-oxidation layer 8, and the anti-oxidation layer 8 is arranged on the side of the first conductor layer 1 away from the conductive adhesive layer 2.

[0095] In one preferred embodiment, the material of the anti-oxidation layer 8 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 8 is 0.01 μm-5 μm, and the thickness of the anti-oxidation layer 8 is preferably 0.1 μm-1 μm. In addition, the anti-oxidation layer 8 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.

[0096] In another preferred embodiment, the anti-oxidation layer 8 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 8 is preferably 0.1 μm-5 μm. In addition, the anti-oxidation layer 8 can be formed by a coating and then curing process.

[0097] In the above embodiment, one of the structures of the adhesive film layer 4 is specifically manifested as follows: the adhesive film layer 4 includes an adhesive layer containing conductive particles (not shown); therefore, the adhesive film layer 4 not only has a bonding function to make the electromagnetic shielding film 9 and the free grounding film tightly bonded, but also has a conductive function, which cooperates with the first conductor layer 1 and the second conductor layer 3 to quickly conduct the interfering electrons. Among them, the conductive particles of the adhesive film layer 4 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.

[0098] In the above embodiment, another structure of the adhesive film layer 4 is specifically manifested as follows: the adhesive film layer 4 includes an adhesive layer (not shown) that does not contain conductive particles; therefore, the adhesive film layer 4 has a bonding effect to allow the electromagnetic shielding film 9 and the free grounding film to be tightly bonded, while reducing the insertion loss of the circuit board during use and improving the bendability of the circuit board.

[0099] In the above embodiment, the adhesive film layer 4 is a pure adhesive film layer (i.e., a film layer formed by applying pure adhesive on the second conductor layer 3) or a conductive adhesive film layer (i.e., a film layer formed by applying conductive adhesive on the second conductor layer 3). Specifically, the material used for the adhesive film layer 4 is selected from the following: modified epoxy resin, acrylic acid, modified rubber, and modified thermoplastic polyimide.

[0100] It should be noted that the adhesive film layer 4 may be made of other materials besides a pure adhesive film layer or a conductive adhesive film layer, as long as the adhesive film layer 4 can be smoothly pierced by the conductive protrusion 5 during the lamination process.

[0101] In the above embodiment, by providing the conductive adhesive layer 2 between the first conductor layer 1 and the second conductor layer 3, the bendability of the free grounding film is further improved.

[0102] In the above embodiment, the first conductor layer 1, the conductive adhesive layer 2 and the second conductor layer 3 may be porous or non-porous.

[0103] Embodiment 2

[0104] See also Figure 4 , an embodiment of the present invention provides another free grounding film, which includes a first conductor layer 1, a conductive adhesive layer 2, a second conductor layer 3, a third conductor layer 7 and an adhesive film layer 4; the first conductor layer 1, the conductive adhesive layer 2 and the second conductor layer 3 are stacked in sequence; a conductive protrusion 5 is provided on a surface of the second conductor layer 3 away from the conductive adhesive layer 2; the third conductor layer 7 is covered on the one surface of the second conductor layer 3, and a protrusion 70 is formed at the position of the third conductor layer 7 covering the conductive protrusion 5 (the relationship between the protrusion 70 and the conductive protrusion 5 can be one-to-one correspondence, one-to-many correspondence or multiple-to-one correspondence, etc. When the relationship between the protrusion 70 and the conductive protrusion 5 is one-to-one correspondence, the shape structure of the protrusion 70 and the shape structure of the conductive protrusion 5 can correspond to or be different from each other); the adhesive film layer 4 is covered on a surface of the third conductor layer 7 away from the second conductor layer 3;

[0105] See also Figure 10 When the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 9 is provided on the printed circuit board 11, and the electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 which are stacked. The free grounding film is pressed together with the electromagnetic shielding film 9 through the adhesive film layer 4, and the protrusion 70 pierces the adhesive film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91, so that the interference charge can be normally discharged with the cooperation of the first conductor layer 1, the conductive adhesive layer 2, the second conductor layer 3 and the third conductor layer 7.

[0106] In an embodiment of the present invention, the formation process of the conductive bump 5 is as follows: a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, and a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3. The conductive bump 5 is formed by the cooling and solidification of fusible metal when it flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0107] Specifically, please refer to Figure 6 , in a preferred manner, the conductive bump 5 is formed by the cooling and solidification of fusible metal when it flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30. Specifically:

[0108] A third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2; the conductive bump 5 is correspondingly formed at the outside of the second through hole 30.

[0109] The conductive bump 5 is formed by the cooling and solidification of fusible metal when it flows from the first through hole 10 through the third through hole 20 to the outside of the second through hole 30; wherein, the outside of the second through hole 30 is far from the conductive adhesive layer 2.

[0110] Preferably, the first through hole 10, the second through hole 30 and the third through hole 20 are aligned with each other one by one, so that the fusible metal flows from the first through hole 10 to the outside of the corresponding second through hole 30. Another situation is that the first through hole 10, the second through hole 30 and the third through hole 20 may also be in a misaligned state. For example, the first through hole 10 and the second through hole are partially aligned, and the second through hole and the third through hole are partially aligned, then the fusible metal can also flow from the first through hole 10 to the outside of the second through hole 30 that is aligned or misaligned with it.

[0111] Please refer to Figure 7 , in another preferred manner, the conductive bump 5 is formed by the cooling and solidification of fusible metal when it flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30. Specifically:

[0112] A first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, and a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3; the conductive bump 5 is correspondingly formed at the outside of the second through hole 30.

[0113] The conductive protrusion 5 is formed by the fusible metal from the first through hole 10 and the hot melt adhesive of the conductive adhesive layer 2 cooling and solidifying when flowing to the outside of the second through hole 30; wherein, the outside of the second through hole 30 is far from the conductive adhesive layer. Specifically, since the fusible metal flowing from the first through hole 10 has a very high temperature, the fusible metal can heat-melt the conductive adhesive layer 2 on the flow path, so that the conductive adhesive layer 2 on the flow path is heat-melted into hot melt adhesive and flows to the second through hole 30 together with the fusible metal.

[0114] Wherein, the first through hole 10 and the second through hole 30 may be aligned one by one or in a misaligned state.

[0115] In the embodiment of the present invention, the protrusion 70 extends into the adhesive film layer 4 or pierces the adhesive film layer 4. In addition, referring to Figure 5 , in order to further ensure the piercing ability of the protrusion 70, preferably, one or more conductor particles 6 are provided on the surface of the protrusion 70.

[0116] In the above embodiment, the free grounding film in this embodiment further includes a peelable protective film layer (not shown in the figure), and the peelable protective film layer is provided on the side of the adhesive film layer 4 away from the second conductor layer 3. In addition, the free grounding film further includes an anti-oxidation layer 8, and the anti-oxidation layer 8 is provided on the side of the first conductor layer 1 away from the conductive adhesive layer 2.

[0117] As an improvement of the above embodiment, the adhesive film layer 4 includes an adhesive layer containing conductive particles; or, the adhesive film layer 4 includes an adhesive layer without conductive particles.

[0118] In the above embodiment, by providing the conductive adhesive layer 2 between the first conductor layer 1 and the second conductor layer 3, the bendability of the free grounding film is further improved. It should be noted that the specific setting methods, specific shapes and sizes, specific positions and specific functions of the structures such as the first conductor layer 1, the conductive adhesive layer 2, the second conductor layer 3, the conductive protrusion 5, the conductive adhesive layer 2, the adhesive film layer 4, the conductor particles 6, the anti-oxidation layer 8 and the peelable protective film layer in this embodiment can all refer to the relevant content in Embodiment 1, and will not be elaborated here.

[0119] Embodiment 3

[0120] Referring to Figure 9 And Figure 10 , the embodiment of the present invention provides a circuit board, including a printed circuit board 11 and an electromagnetic shielding film 9 provided on the printed circuit board 11.

[0121] Referring to Figure 9The circuit board also includes the free grounding film of any one of the schemes in the first embodiment; the electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film 9 through the adhesive film layer 4, and the conductive protrusion 5 pierces the adhesive film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91.

[0122] or, see Figure 10 The circuit board also includes the free grounding film of any one of the schemes in the second embodiment; the electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 which are stacked, the free grounding film is pressed together with the electromagnetic shielding film 9 through the adhesive film layer 4, and the protrusion 70 pierces the adhesive film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91.

[0123] 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.

[0124] Preferably, the printed circuit board 11 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0125] In a specific implementation, when the circuit board is applied to an electronic device, the interference charges accumulated in the electromagnetic shielding film 9 can be led out by electrically connecting the free grounding film to the housing of the electronic device.

[0126] In an embodiment of the present invention, through the above-mentioned structure, during the pressing of the free grounding film and the electromagnetic shielding film 9, the conductive protrusion 5 on the second conductor layer 3 is used to pierce the adhesive film layer 4 and the insulating layer 90 in turn and connect with the shielding layer 91; or the protrusion 70 on the third conductor layer 7 is used to pierce the adhesive film layer 4 and the insulating layer 90 in turn and connect with the shielding layer 91, 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 effectively avoiding the accumulation of interference charges and affecting the normal operation of the printed circuit board.

[0127] Embodiment 4

[0128] See also Figure 11 The embodiment of the present invention provides a method for preparing a free grounding film, which is suitable for preparing the free grounding film described in the first embodiment, and includes steps S11 to S13:

[0129] S11. Form a first conductor layer 1, form a conductive adhesive layer 2 on one surface of the first conductor layer 1, and form a second conductor layer 3 on a surface of the conductive adhesive layer 2 away from the first conductor layer 1.

[0130] S12. Form a conductive protrusion 5 on a surface of the second conductor layer 3 away from the conductive adhesive layer 2.

[0131] S13. Form a glue film layer 4 on the surface of the second conductor layer 3 where the conductive protrusion 5 is formed; when the free grounding film is used for grounding of the printed circuit board, an electromagnetic shielding film 9 is provided on the printed circuit board 11. The electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 arranged in a stacked manner. The free grounding film is pressed against the electromagnetic shielding film 9 through the glue film layer 4, and the conductive protrusion 5 pierces through the glue film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91.

[0132] In this embodiment, the formation method of the conductive protrusion 5 is preferably: a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3, and the conductive protrusion 5 is formed by cooling and solidifying when the fusible metal flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0133] Specifically, refer to Figure 3 , a third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2;

[0134] Then the step S12 is specifically:

[0135] Flow the fusible metal from the first through hole 10 through the third through hole 20 of the conductive adhesive layer 2 to the outside of the second through hole 30 and cool and solidify it, so as to form a conductive protrusion 5 on a surface of the second conductor layer 3 away from the conductive adhesive layer 2; wherein, the outside of the second through hole 30 is away from the conductive adhesive layer 2.

[0136] Alternatively, the conductive adhesive layer 2 is a hot-melt adhesive layer;

[0137] Then the step S12 is specifically:

[0138] Set the fusible metal at the first through hole 10, and at a preset temperature, make the fusible metal flow from the first through hole 10 to the second through hole 30, and the conductive adhesive layer 2 forms a hot-melt adhesive flow to the second through hole 30 during the flow of the fusible metal;

[0139] Cool the fusible metal and the hot-melt adhesive flowing to the outside of the second through hole 30, so as to form a conductive protrusion 5 on a surface of the second conductor layer 3 away from the conductive adhesive layer 2.

[0140] It should be noted that the melting temperature of the fusible metal is preferably 300 - 2000 degrees Celsius. In addition, the conductive protrusion 5 can be formed by directly applying a conductive adhesive bump on the side of the second conductor layer 3 away from the conductive adhesive layer 2 and solidifying it to form the conductive protrusion 5, or by directly electroplating a metal point on the side of the second conductor layer 3 away from the conductive adhesive layer 2 to form the conductive protrusion 5, etc. Specific limitations are not made here.

[0141] In the above embodiment, preferably, after the step S12 and before the step S13, the preparation method further includes:

[0142] Forming a plurality of conductor particles 6 on the outer surface of the conductive protrusion 5 by one or more processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating. See Figure 2 .

[0143] In the above embodiment, specifically, the step S13 is specifically:

[0144] Forming a glue film layer 4 on the release film, and then laminating and transferring the glue film layer 4 to the side of the second conductor layer 3 where the conductive protrusion 5 is formed; or,

[0145] Directly forming a glue film layer 4 on the side of the second conductor layer 3 where the conductive protrusion 5 is formed.

[0146] It should be noted that the preparation method of the free grounding film provided in this embodiment is only an example of preparing the free grounding film described in Embodiment 1. The free grounding film described in Embodiment 1 can also be manufactured by other preparation methods. For example, a conductive protrusion 5 can be formed on one side of the second conductor layer 3 first, and then the first conductor layer 1 and the conductive adhesive layer 2 are formed.

[0147] Embodiment Five

[0148] See Figure 12 , the embodiment of the present invention provides a preparation method of a free grounding film, which is applicable to preparing the free grounding film described in Embodiment 2, including steps S21 to S24:

[0149] S21. Form a first conductor layer 1, form a conductive adhesive layer 2 on one side of the first conductor layer 1, and form a second conductor layer 3 on the side of the conductive adhesive layer 2 away from the first conductor layer 1.

[0150] S22. Form a conductive protrusion 5 on the side of the second conductor layer 3 away from the conductive adhesive layer 2.

[0151] S23. A third conductor layer 7 is formed on the surface of the second conductor layer 3 where the conductive protrusion 5 is formed, and a protrusion 70 is formed on the third conductor layer 7 to cover the position of the conductive protrusion 5 (the relationship between the protrusion 70 and the conductive protrusion 5 can be one-to-one, one-to-many, many-to-one, etc.).

[0152] S24. An adhesive film layer 4 is formed on the surface of the third conductor layer 7 away from the second conductor layer 3; when the free grounding film is used for grounding of the printed circuit board, an electromagnetic shielding film 9 is provided on the printed circuit board 11. The electromagnetic shielding film 9 includes a shielding layer 91 and an insulating layer 90 arranged in a stacked manner. The free grounding film is pressed and bonded to the electromagnetic shielding film 9 through the adhesive film layer 4, and the protrusion 70 pierces through the adhesive film layer 4 and the insulating layer 90 and is electrically connected to the shielding layer 91.

[0153] In this embodiment, the preferred formation method of the conductive protrusion 5 is as follows: a first through hole 10 penetrating the upper and lower surfaces is provided on the first conductor layer 1, and a second through hole 30 penetrating the upper and lower surfaces is provided on the second conductor layer 3. The conductive protrusion 5 is formed by the cooling and solidification of fusible metal when it flows from the first through hole 10 through the conductive adhesive layer 2 to the outside of the second through hole 30.

[0154] Specifically, referring to Figure 6 , a third through hole 20 penetrating the upper and lower surfaces is provided on the conductive adhesive layer 2;

[0155] Then the step S22 is specifically:

[0156] Fusible metal is provided at the first through hole 10, and at a preset temperature, the fusible metal flows from the first through hole 10 through the third through hole 20 of the conductive adhesive layer 2 to the corresponding second through hole 30. After the fusible metal flows to the outside of the second through hole 30, it cools and solidifies, so as to form a conductive protrusion 5 on the surface of the second conductor layer 3 away from the conductive adhesive layer 2; wherein, the outside of the second through hole 30 is away from the conductive adhesive layer 2.

[0157] Or, referring to Figure 7 , the conductive adhesive layer 2 is a hot melt adhesive layer;

[0158] Then the step S22 is specifically:

[0159] Fusible metal is provided at the first through hole 10, and at a preset temperature, the fusible metal flows from the first through hole 10 to the second through hole 30, and the conductive adhesive layer 2 forms a hot melt adhesive flow to the second through hole 30 during the flow of the fusible metal;

[0160] Cool the fusible metal and hot melt adhesive flowing to the outside of the second through hole 30, so as to form a conductive bump 5 on the side of the second conductor layer 3 away from the conductive adhesive layer 2.

[0161] It should be noted that the melting temperature of the fusible metal is preferably 300 - 2000 degrees Celsius. In addition, the formation method of the conductive bump 5 can also be to directly apply a conductive adhesive bump on the side of the second conductor layer 3 away from the conductive adhesive layer 2 and solidify it to form the conductive bump 5, or it can be to directly electroplate a metal point on the side of the second conductor layer 3 away from the conductive adhesive layer 2 to form the conductive bump 5, etc., which will not be specifically limited here.

[0162] As an improvement to the above solution, after the step S23 and before the step S24, it further includes:

[0163] Form a plurality of conductor particles 6 on the outer surface of the convex portion 70 through one or more processes of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating. See Figure 5 .

[0164] It should be noted that the manufacturing method of the conductor particles 6 can also be: when manufacturing the third conductor layer 7, the conductor particles 6 and the third conductor layer 7 can be an integral structure formed by a one - step forming process. In addition, when the third conductor layer 7 is a multi - layer structure, the manufacturing method of the conductor particles 6 can also be: the third conductor layer 7 is manufactured layer by layer in sequence, and when manufacturing each layer, the conductor particles 6 are formed at the corresponding positions of this layer, so as to form the third conductor layer 7 with conductor particles 6 on each layer.

[0165] In the embodiment of the present invention, the step S24 is specifically:

[0166] Form a glue film layer 4 on the release film, and then press and transfer the glue film layer 4 to the side of the third conductor layer 7 away from the second conductor layer 3; or

[0167] Directly form a glue film layer 4 on the side of the third conductor layer 7 away from the second conductor layer 3.

[0168] It should be noted that the preparation method of the free grounding film provided in this embodiment is only an example of preparing the free grounding film described in Embodiment 2. The free grounding film described in Embodiment 2 can also be manufactured by other preparation methods. For example, a conductive bump 5 can be formed on one side of the second conductor layer 3 first, and then the first conductor layer 1 and the conductive adhesive layer 2 are stacked.

[0169] 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, a conductive adhesive layer, a second conductor layer and a film adhesive layer which are sequentially stacked. A conductive protrusion is provided on a surface of the second conductor layer close to the film adhesive layer; the thickness of the film adhesive layer is 0.1μm - 80μm; 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 with the electromagnetic shielding film through the film adhesive layer. The conductive protrusion pierces through the film adhesive layer and the insulating layer and is electrically connected to the shielding layer; a first through hole penetrating through the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating through the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating through the upper and lower surfaces thereof is provided on the conductive adhesive layer; the conductive protrusion is correspondingly formed at an outer side of the second through hole; the conductive protrusion is formed by cooling and solidifying of fusible metal flowing from the first through hole through the third through hole to the outer side of the second through hole; wherein, the outer side of the second through hole is far from the conductive adhesive layer; alternatively, a first through hole penetrating through the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating through the upper and lower surfaces thereof is provided on the second conductor layer; the conductive protrusion is correspondingly formed at an outer side of the second through hole; the conductive protrusion is formed by cooling and solidifying of fusible metal from the first through hole and hot melt adhesive of the conductive adhesive layer flowing to the outer side of the second through hole; wherein, the outer side of the second through hole is far from the conductive adhesive layer.

2. The free grounding film according to claim 1, characterized in that, convex conductor particles are provided on a surface of the conductive protrusion.

3. The free grounding film according to claim 1, characterized in that, the film adhesive layer includes an adhesive layer containing conductive particles; or, the film adhesive layer includes an adhesive layer without conductive particles.

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

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

6. The free grounding film according to any one of claims 1 - 3, characterized in that, the free grounding film further includes a third conductor layer, the third conductor layer is covered on a surface of the second conductor layer where the conductive protrusion is formed, and a protrusion part is formed at a position where the third conductor layer covers the conductive protrusion.

7. The free grounding film according to claim 6, characterized in that, convex conductor particles are provided on a surface of the protrusion part.

8. A circuit board, including a printed circuit board and an electromagnetic shielding film provided on the printed circuit board, characterized in that, The circuit board further includes the free grounding film according to any one of claims 1-5; the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked, and the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the conductive protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer; Alternatively, the circuit board further includes the free grounding film according to claim 6 or 7; the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked, and the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the protruding portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

9. A method for preparing a free grounding film, characterized in that, it is applicable to preparing the free grounding film according to any one of claims 1-5, and includes the steps of: forming a first conductor layer, forming a conductive adhesive layer on one surface of the first conductor layer, and forming a second conductor layer on a surface of the conductive adhesive layer away from the first conductor layer; forming a conductive protrusion on a surface of the second conductor layer away from the conductive adhesive layer; forming an adhesive film layer on a surface of the second conductor layer where the conductive 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 against the electromagnetic shielding film through the adhesive film layer, and the conductive protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer; a first through hole penetrating through the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating through the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating through the upper and lower surfaces thereof is provided on the conductive adhesive layer; then forming the conductive protrusion on a surface of the second conductor layer away from the conductive adhesive layer specifically includes: after the fusible metal flows from the first through hole through the third through hole to the outside of the second through hole, cooling and solidifying it, so as to form a conductive protrusion on a surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer; Alternatively, the conductive adhesive layer is a hot-melt adhesive layer; a first through hole penetrating through the upper and lower surfaces thereof is provided on the first conductor layer, and a second through hole penetrating through the upper and lower surfaces thereof is provided on the second conductor layer; then forming the conductive protrusion on a surface of the second conductor layer away from the conductive adhesive layer specifically includes: arranging the fusible metal at the first through hole, and at a preset temperature, enabling the fusible metal to flow from the first through hole to the second through hole, and the conductive adhesive layer forms a hot-melt adhesive flow to the second through hole during the flowing process of the fusible metal; cooling the fusible metal and the hot-melt adhesive flowing to the outside of the second through hole, so as to form a conductive protrusion on a surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

10. The method for preparing a free grounding film according to claim 9, characterized in that, before forming the adhesive film layer on a surface of the second conductor layer where the conductive protrusion is formed, it further includes: Conductor particles are formed on the outer surface of the conductive protrusions by one or more processes among physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating.

11. The method for preparing a free grounding film according to claim 9, characterized in that forming a glue film layer on the surface of the second conductor layer where the conductive protrusions are formed, specifically: forming a glue film layer on a release film and laminating and transferring the glue film layer to the surface of the second conductor layer where the conductive protrusions are formed; or, forming a glue film layer on the surface of the second conductor layer where the conductive protrusions are formed.

12. A method for preparing a free grounding film, characterized in that suitable for preparing the free grounding film according to claim 6 or 7, comprising the steps of: forming a first conductor layer, forming a conductive adhesive layer on one surface of the first conductor layer, and forming a second conductor layer on the surface of the conductive adhesive layer away from the first conductor layer; forming conductive protrusions on the surface of the second conductor layer away from the conductive adhesive layer; forming a third conductor layer on the surface of the second conductor layer where the conductive protrusions are formed, and making the third conductor layer cover the position of the conductive protrusions to form a raised portion; forming a glue film layer on the surface of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding 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 pressed and bonded to the electromagnetic shielding film through the glue film layer, and the raised portion pierces through the glue film layer and the insulating layer and is electrically connected to the shielding layer; a first through hole penetrating the upper and lower surfaces thereof is provided on the first conductor layer, a second through hole penetrating the upper and lower surfaces thereof is provided on the second conductor layer, and a third through hole penetrating the upper and lower surfaces thereof is provided on the conductive adhesive layer; then forming the conductive protrusions on the surface of the second conductor layer away from the conductive adhesive layer, specifically: arranging a fusible metal at the first through hole, and at a preset temperature, allowing the fusible metal to flow from the first through hole through the third through hole to the second through hole, and after the fusible metal flows to the outside of the second through hole, cooling and solidifying, so as to form conductive protrusions on the surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer; Alternatively, the conductive adhesive layer is a hot melt adhesive layer; a first through hole penetrating the upper and lower surfaces is provided on the first conductor layer, and a second through hole penetrating the upper and lower surfaces is provided on the second conductor layer; then a conductive protrusion is formed on the surface of the second conductor layer away from the conductive adhesive layer, specifically: a fusible metal is provided at the first through hole, and at a preset temperature, the fusible metal flows from the first through hole to the second through hole, and the conductive adhesive layer forms a hot melt adhesive flow to the second through hole during the flow of the fusible metal; the fusible metal and the hot melt adhesive flowing to the outside of the second through hole are cooled, so as to form a conductive protrusion on the surface of the second conductor layer away from the conductive adhesive layer; wherein, the outside of the second through hole is away from the conductive adhesive layer.

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