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

Abstract

The 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, a conductive adhesive layer, a second conductor layer, a third conductor layer and an adhesive film layer which are stacked in sequence, and a protrusion is provided at the first through hole of the second conductor layer; the protrusion is formed by the conductive adhesive layer flowing from one side of the first through hole to the other side at the melting temperature and then instantly cooling; the third conductor layer covers the protrusion, thereby forming a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer; when the free grounding film is used for grounding of a printed circuit board, the free grounding film is pressed together with the electromagnetic shielding film on the printed circuit board through the adhesive film layer, the protrusion pierces the insulating layer of the adhesive film layer and the electromagnetic shielding film, and is electrically connected to the shielding layer of the electromagnetic shielding film, thereby effectively conducting out the interference charge accumulated in the shielding layer, avoiding the accumulation of interference charge to form an interference source, and thereby effectively ensuring the integrity of signal transmission.

Description

Technical Field

[0001] The present 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, lightweighting, and high-density assembly. This has greatly promoted the development of flexible circuit boards, thereby realizing the integration of component devices and wire connections. Flexible circuit boards are widely used in industries such as mobile phones, LCD displays, communications, and aerospace.

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

[0004] Currently, the free grounding film commonly used in existing circuit boards generally includes a conductor layer and a conductive adhesive layer. The conductor layer is in contact and conductive with the shielding layer of the electromagnetic shielding film through the conductive adhesive layer. This allows the printed circuit board to be electrically connected to the housing of the electronic device through the free grounding film, thereby conducting away interference charges from the electromagnetic shielding film. However, during the implementation of the present invention, the inventors discovered that the prior art has at least the following problems: at high temperatures, the conductive adhesive layer expands, causing conductive particles in the conductive adhesive layer that were originally in contact with each other to separate, or causing conductive particles that were originally in contact with the electromagnetic shielding film to separate, resulting in the failure of the connection between the free grounding film and the electromagnetic shielding film. Consequently, the interference charges accumulated on the electromagnetic shielding film cannot be effectively conducted away, thereby forming an interference source that affects signal transmission on 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-mentioned technical problems, the present invention provides a free grounding film, comprising a first conductor layer, a conductive adhesive layer, a second conductor layer, a third conductor layer, and an adhesive film layer, which are sequentially stacked. The second conductor layer is provided with a first through-hole extending through its upper and lower surfaces, and a protrusion is provided at the first through-hole; the protrusion is formed by the conductive adhesive layer flowing from one side of the first through-hole to the other side at a melting temperature and then instantaneously cooling; the third conductor layer covers the protrusion, thereby forming a protrusion on the outer surface of the third conductor layer at a position corresponding to the protrusion, and the protrusion extends into the adhesive 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, and the electromagnetic shielding film includes a shielding layer and an insulating layer arranged in a stacked manner. The free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0008] As an improvement to the above solution, the surface of the protrusion is provided with convex conductive particles; the height of the conductive particles is 20 μm-100 μm.

[0009] As an improvement to the above solution, the adhesive film layer includes an adhesive layer containing conductive particles; or the adhesive film layer includes an adhesive layer not containing conductive particles.

[0010] As an improvement of the above solution, the first conductor layer, the second conductor layer and the third conductor layer respectively include one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer and a graphene conductor layer.

[0011] As an improvement to 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.

[0012] As an improvement to the above solution, 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 -1mm 2 .

[0013] As an improvement to the above solution, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is provided on a side of the first conductor layer away from the conductive adhesive layer.

[0014] 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 provided on a side of the adhesive film layer away from the third conductor layer.

[0015] Compared with the prior art, an embodiment of the present invention discloses a free grounding film, which forms a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer by arranging a protrusion at the first through hole on the second conductor layer and making the third conductor layer cover the protrusion, and makes the protrusion extend into the adhesive film layer, so that when the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the protrusion can pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film in turn and connect with the shielding layer of the electromagnetic shielding film, thereby effectively conducting 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 against 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 the interference charges, thereby ensuring the integrity of signal transmission.

[0016] In order to solve the same technical problem, the present invention also provides a circuit board, including a printed circuit board, an electromagnetic shielding film and the above-mentioned free grounding film, the electromagnetic shielding film is arranged on the printed circuit board, the electromagnetic shielding film includes a stacked shielding layer and an insulating layer, the free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0017] Compared with the prior art, an embodiment of the present invention discloses a circuit board, which includes a printed circuit board, an electromagnetic shielding film and a free grounding film as described in any one of the above items. When the free grounding film is pressed against the electromagnetic shielding film through its adhesive film layer, the protrusion can sequentially pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film, and connect with the shielding layer of the electromagnetic shielding film, thereby effectively conducting away the interference charges in the electromagnetic shielding film, thereby ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that at high temperatures, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly conducted away due to the free grounding film being pressed against the electromagnetic shielding film through the conductive adhesive layer. Therefore, the accumulation of interference charges is avoided to affect the normal operation of the printed circuit board, and the integrity of signal transmission is ensured.

[0018] In order to solve the same technical problem, the present invention also provides a method for preparing a free grounding film, which is suitable for preparing the above-mentioned free grounding film, comprising the steps of:

[0019] forming a first conductor layer;

[0020] forming a conductive adhesive layer on one side of the first conductor layer;

[0021] A second conductor layer is formed on a side of the conductive adhesive layer away from the first conductor layer; wherein the second conductor layer is formed with a first through hole penetrating the upper and lower surfaces thereof;

[0022] At a melting temperature, the conductive adhesive layer is caused to flow from one side of the first through hole to the other side and then cooled instantly, thereby forming a protrusion on a side of the first through hole away from the conductive adhesive layer;

[0023] forming a third conductor layer on the side of the second conductor layer where the protrusion is formed, and making the third conductor layer cover the protrusion, thereby forming a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer;

[0024] A glue film layer is formed on the side of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, and the electromagnetic shielding film includes a shielding layer and an insulating layer arranged in a stacked manner. The free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

[0025] As an improvement to the above solution, before forming the adhesive film layer on the side of the third conductor layer away from the second conductor layer, the following steps are further included:

[0026] Conductive particles are formed on the outer surface of the protrusion by one or more processes selected from the group consisting of physical roughening, chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating.

[0027] As an improvement to the above solution, the adhesive film layer is formed on a side of the third conductor layer away from the second conductor layer, specifically:

[0028] coating an adhesive film layer on the release film, and laminating and transferring the adhesive film layer to a side of the third conductor layer away from the second conductor layer; or

[0029] A glue film layer is coated on a side of the third conductor layer away from the second conductor layer.

[0030] Compared with the prior art, the method for preparing the free grounding film provided in the embodiment of the present invention sequentially forms the first conductor layer, the conductive adhesive layer, and the second conductor layer, and at the melting temperature, causes the conductive adhesive layer to flow from one side of the first through hole of the second conductor layer to the other side and then instantly cools, thereby forming a bulge on the side of the first through hole away from the conductive adhesive layer, and at the same time forming a third conductor layer on the side of the second conductor layer where the bulge is formed, so as to form a bulge at a position corresponding to the bulge on the outer surface of the third conductor layer, and finally forming a bulge on the third conductor layer away from the second conductor layer. A film layer is formed on one side, so that when the free grounding film is pressed against the electromagnetic shielding film through its film layer, the protrusion can sequentially pierce the 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 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 against 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 lead out the interference charges, thereby ensuring the integrity of signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic structural diagram of a free grounding film in the first embodiment of the present invention at an angle;

[0032] Figure 2 is a schematic structural diagram of the free grounding film in the first embodiment of the present invention from another angle;

[0033] Figure 3 is a schematic structural diagram of a free grounding membrane in a second embodiment of the present invention;

[0034] Figure 4 is a schematic structural diagram of a circuit board in a third embodiment of the present invention;

[0035] Figure 5 It is a schematic flow chart of a method for preparing a free grounding film in the fourth embodiment of the present invention.

[0036] Among them, 1. First conductor layer; 2. Conductive adhesive layer; 21. Protrusion; 3. Second conductor layer; 31. First through hole; 4. Third conductor layer; 41. Protrusion; 42. Conductor particles; 5. Adhesive film layer; 6. Peelable protective film layer; 7. Anti-oxidation layer; 8. Electromagnetic shielding film; 81. Insulation layer; 82. Shielding layer; 9. Printed circuit board. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1

[0039] Combine Figure 1 and Figure 2 As shown, the free grounding film includes a first conductor layer 1, a conductive adhesive layer 2, a second conductor layer 3, a third conductor layer 4, and an adhesive film layer 5, which are stacked in sequence. The second conductor layer 3 is provided with a first through-hole 31 extending through its upper and lower surfaces. The first through-hole 31 is provided with a protrusion 21. The protrusion 21 is formed by the conductive adhesive layer 2 flowing from one side of the first through-hole 31 to the other side at a melting temperature and then instantly cooling. The third conductor layer 4 covers the protrusion 21, thereby forming a protrusion 41 on the outer surface of the third conductor layer 4 at a position corresponding to the protrusion 21. The protrusion 41 extends into the adhesive film layer 5.

[0040] like Figure 4 As shown, when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 8 is provided on the printed circuit board 9, and the electromagnetic shielding film 8 includes a shielding layer 82 and an insulating layer 81 arranged in a stacked manner. The free grounding film is pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5, and the protrusion 41 pierces the adhesive film layer 5 and the insulating layer 81 and is electrically connected to the shielding layer 82.

[0041] In an embodiment of the present invention, a protrusion 21 is provided at the first through hole 31 on the second conductor layer 3, and the third conductor layer 4 covers the protrusion 21, so as to form a protrusion 41 at a position corresponding to the protrusion 21 on the outer surface of the third conductor layer 4, and at the same time, the protrusion 41 extends into the adhesive film layer 5, so that when the free grounding film is pressed against the electromagnetic shielding film 8 through its adhesive film layer 5, the protrusion 41 can sequentially pierce the adhesive film layer 5 and the insulating layer 81 of the electromagnetic shielding film 8, and connect with the shielding layer 82 of the electromagnetic shielding film 8, thereby effectively conducting away the interference charges accumulated in the electromagnetic shielding film 8, thereby ensuring the grounding of the electromagnetic shielding film 8, and effectively avoiding the problem that at high temperatures, the free grounding film is pressed against 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 the interference charges, thereby ensuring the integrity of signal transmission.

[0042] Specifically, in the process of forming the protrusion 21, the conductive adhesive layer 2 is melted at the melting temperature; and after the conductive adhesive layer 2 flows from one side of the first through hole 31 close to the conductive adhesive layer 2 to the other side, the conductive adhesive layer 2 is instantly cooled, thereby forming the protrusion 21 on the side of the first through hole 31 close to the adhesive film layer 5.

[0043] In the embodiment of the present invention, it should be noted that the shape of the protrusion 21 shown in the drawings is merely exemplary, and the protrusion 21 in the present invention is not limited to the shape shown in the drawings. As long as it is a protrusion with piercing ability, it is within the scope of protection of the present invention.

[0044] In the embodiment of the present invention, it should be noted that the shape of the protrusion 41 may be the same as or different from the shape of the protrusion 21 , and the shape of the protrusion 41 shown in the drawings is merely exemplary.

[0045] In the embodiment of the present invention, in order to ensure that the protrusion 21 can be formed at the first through hole 31 and at the same time ensure that the second conductor layer 3 is not easily broken, preferably, in this embodiment, the cross-sectional area of ​​the first through hole 31 is 0.01 μm 2 -1mm 2 .

[0046] In addition, in order to ensure that a sufficient number of protrusions 21 can be formed to ensure that the third conductor layer 4 can sequentially pierce the adhesive film layer 5 and the insulating layer 81 of the electromagnetic shielding film 8 through the protrusions 41, thereby connecting with the shielding layer 82, and at the same time ensure that the second conductor layer 3 is not easily broken, the number of the first through holes 31 in the second conductor layer 3 per square centimeter in this embodiment is 5-10. 10 Correspondingly, the number of the protrusions 21 in the second conductor layer 3 is 5-10 per square centimeter. 10 It should be noted that, since the third conductor layer 4 covers the protrusion 21, a protrusion 41 is formed on the outer surface of the third conductor layer 4 at a position corresponding to the protrusion 31. Therefore, the number of the protrusions 41 corresponds to the number of the protrusions 21, thereby ensuring that the protrusions 41 can smoothly pierce the adhesive film layer 5 and the insulating layer 81 of the electromagnetic shielding film 8.

[0047] like Figure 2As shown, the first through holes 31 can be regularly or irregularly distributed on the second conductor layer 3; wherein, the first through holes 31 being regularly distributed on the second conductor layer 3 means that the first through holes 31 have the same shape and are evenly distributed on the second conductor layer 3; and the first through holes 31 being irregularly distributed on the second conductor layer 3 means that the first through holes 31 have different shapes and are randomly distributed on the second conductor layer 3. Preferably, the first through holes 31 have the same shape and are evenly distributed on the second conductor layer 3. In addition, the first through holes 31 can be circular through holes or any other shape. The drawings of the present invention illustrate the first through holes 31 as circular through holes, but first through holes 31 of any other shape are within the scope of protection of the present invention.

[0048] In an embodiment of the present invention, the thickness of the first conductor layer 1 is preferably 2 μm to 45 μm; the thickness of the second conductor layer 3 is preferably 2 μm to 45 μm; and the thickness of the third conductor layer 4 is preferably 2 μm to 45 μm, thereby ensuring that the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 are not easily broken and have good flexibility. Furthermore, to ensure that the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 have good conductivity, the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 each comprise one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer. The metal conductor layer comprises a single metal conductor layer and / or an alloy conductor layer; 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.

[0049] In the embodiment of the present invention, the first conductor layer 1 includes a first surface and a second surface arranged opposite to each other, the first surface is in contact with the conductive adhesive layer 2; the second surface is in contact with the anti-oxidation layer 7. It should be noted that the first surface and the second surface can be surfaces of any shape, for example, Figure 1 The flat surface shown may also be an undulating, non-flat surface or other rough surface. Furthermore, the first and second surfaces may be regular or irregular surfaces. The accompanying drawings of the present invention illustrate examples in which the first and second surfaces are both flat. First and second surfaces of any other shape are within the scope of protection of the present invention.

[0050] In the embodiment of the present invention, the second conductor layer 3 includes a third surface and a fourth surface arranged opposite to each other, wherein the third surface contacts the third conductor layer 4; and the fourth surface contacts the conductive adhesive layer 2. It should be noted that the third surface and the fourth surface can be surfaces of any shape, for example, Figure 1 The flat surface shown may also be an undulating, non-flat surface or other rough surface. Furthermore, the third and fourth surfaces may be regular or irregular surfaces. The accompanying drawings of the present invention illustrate the third and fourth surfaces as flat surfaces only. Third and fourth surfaces of any other shape are within the scope of protection of the present invention.

[0051] In the embodiments of the present invention, it should be noted that the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 shown in the drawings of this embodiment can all be single-layer structures or multi-layer structures. Furthermore, depending on actual production and application requirements, the first conductor layer 1, the second conductor layer 3, and the third conductor layer 4 shown in the drawings of this embodiment can be configured in a grid-like shape, a foamed shape, or the like.

[0052] In an embodiment of the present invention, one structure of the adhesive film layer 5 is specifically manifested as follows: the adhesive film layer 5 includes an adhesive layer containing conductive particles. By including the adhesive layer containing conductive particles, the adhesive film layer 5 not only has an adhesive function, thereby tightly bonding the electromagnetic shielding film 8 and the free grounding film, but also has a conductive function. It cooperates with the first conductor layer 1, the conductive adhesive layer 2, the second conductor layer 3, and the third conductor layer 4 to quickly remove interfering electrons. The conductive particles in the adhesive film layer 5 can be separated conductive particles or aggregated large particles. When the conductive particles are separated conductive particles, the area of ​​electrical contact can be further increased and the uniformity of electrical contact can be improved. When the conductive particles are aggregated large particles, the penetration strength can be increased.

[0053] In an embodiment of the present invention, another structure of the adhesive film layer 5 is specifically characterized by including an adhesive layer that does not contain conductive particles. By including an adhesive layer that does not contain conductive particles, the adhesive film layer 5 has an adhesive function, thereby tightly adhering the electromagnetic shielding film 8 and the free grounding film. Furthermore, since the adhesive film layer 5 does not contain conductive particles, the insertion loss of the circuit board during use is reduced, and the flexibility of the circuit board is improved.

[0054] In an embodiment of the present invention, the thickness of the adhesive film layer 5 is 0.1 μm to 80 μm. The material used for the adhesive film layer 5 is selected from the following: modified epoxy resins, acrylic resins, modified rubbers, and modified thermoplastic polyimides. Furthermore, the outer surface of the adhesive film layer 2 can be a smooth surface with no undulations, or a non-flat surface with gently undulating surfaces.

[0055] Combine Figure 1 and Figure 2 As shown, to protect the adhesive film layer 5, the free grounding film in this embodiment further includes a peelable protective film layer 6, which is disposed on the surface of the adhesive film layer 5 facing away from the third conductor layer 4. The peelable protective film layer 6 protects the adhesive film layer 5 from damage before use, thereby ensuring that the free grounding film can be pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5. It should be noted that when pressing the free grounding film onto the electromagnetic shielding film 8, the peelable protective film layer 6 needs to be peeled off, and then the free grounding film can be pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5.

[0056] In addition, the peelable protective film layer 6 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.

[0057] In this embodiment of the present invention, to protect the first conductor layer 1 and ensure that interfering charges can be discharged, the free grounding film in this embodiment further includes an anti-oxidation layer 7, which is disposed on the side of the first conductor layer 1 remote from the conductive adhesive layer 2. Providing the anti-oxidation layer 7 on the side of the first conductor layer 1 remote from the conductive adhesive layer 2 prevents oxidation of the first conductor layer 1 due to contact with air, thereby ensuring that interfering charges in the electromagnetic shielding film 8 can be discharged through the free grounding film.

[0058] In one preferred embodiment, the material of the anti-oxidation layer 7 is one of a metal material, ferrite, graphite, carbon nanotubes, graphene, and silver paste; wherein the metal material is any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; or the metal material is an alloy formed by two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; in this case, the thickness of the anti-oxidation layer 7 is 0.01 μm-5 μm, and the thickness of the anti-oxidation layer 7 is preferably 0.1 μm-1 μm. In addition, the anti-oxidation layer 7 can be formed by one of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, and electroplating, or a composite process of at least two of the above processes.

[0059] In another preferred embodiment, the anti-oxidation layer 7 is made of a mixture of glue and conductive particles, wherein the volume ratio of the conductive particles to the glue is 5%-80%. In this case, the thickness of the anti-oxidation layer 7 is preferably 0.1 μm-5 μm. Alternatively, the anti-oxidation layer 7 can be formed by a coating and then curing process.

[0060] Example 2

[0061] like Figure 3 As shown, the free grounding film in this embodiment differs from that in the first embodiment in that the surface of the protrusion 41 is provided with convex conductive particles 42. Providing the conductive particles 42 on the surface of the protrusion 41 further ensures that the protrusion 41 can smoothly pierce the adhesive film layer 5 and the insulating layer 81 during the pressing process, thereby ensuring the normal discharge of interference charges.

[0062] Preferably, the conductive particles 42 are concentrated on the outwardly protruding portion of the surface of the protrusion 41, so that it is easier to pierce the adhesive film layer 5. Of course, the conductive particles 42 can also be distributed on the non-convex portion of the surface of the protrusion 41. In addition, the conductive particles 42 can also be distributed on other positions of the side of the third conductive layer 4 close to the adhesive film layer 5, rather than only on the surface of the protrusion 41. Figure 3 Of course, the conductive particles 42 may also be distributed only on the protrusions 41 .

[0063] In a specific implementation, the third conductor layer 4 can be formed first, and then the conductor particles 42 can be formed on the side of the third conductor layer 4 away from the second conductor layer 3 through other processes. Of course, the third conductor layer 4 and the conductor particles 42 can also be an integral structure formed through a one-time molding process.

[0064] In the embodiment of the present invention, the conductive particles 42 may be at a certain distance from the outer surface of the adhesive film layer 5 , or may be in contact with the outer surface of the adhesive film layer 5 or extend out of the outer surface of the adhesive film layer 5 .

[0065] In the embodiment of the present invention, the height of the conductive particles 42 is preferably 20 μm to 100 μm, the thickness of the adhesive film layer 5 is preferably 0.1 μm to 80 μm, and the thickness of the insulating layer 81 is preferably 1 μm to 20 μm. By setting the height of the conductive particles 42 to preferably 20 μm to 100 μm and the thickness of the adhesive film layer 5 to preferably 0.1 μm to 80 μm, the conductive particles 42 are ensured to be able to pierce the adhesive film layer 5 and the insulating layer 81 of the electromagnetic shielding film 8, thereby ensuring that the free grounding film can conduct away interference charges accumulated on the electromagnetic shielding film 8.

[0066] In an embodiment of the present invention, the conductive particles 42 include one or more of metal particles, carbon nanotube particles, and ferrite particles. Furthermore, the metal particles include single metal particles and / or alloy particles. The single metal particles are made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy particles are made of any two or more of the following materials: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. It should be noted that the conductive particles 42 may or may not be made of the same material as the third conductive layer 4.

[0067] In the embodiment of the present invention, it should be noted that, Figure 3 The shape of the conductive particles 42 shown is merely exemplary. Due to differences in process methods and parameters, the conductive particles 42 may also have other shapes, such as clusters, ice floes, stalactites, and dendrites. Furthermore, the conductive particles 42 of the present invention are not limited to the shapes shown and described above. Any conductive particles that have piercing and conductive properties are within the scope of protection of the present invention.

[0068] In addition, other structures and working principles of the free grounding film in this embodiment are the same as those in the first embodiment, and are not described in detail here.

[0069] Example 3

[0070] like Figure 4 As shown, an embodiment of the present invention further provides a circuit board, including a printed circuit board 9, an electromagnetic shielding film 8 and the free grounding film described in embodiment one or two, wherein the electromagnetic shielding film 8 is arranged on the printed circuit board 9, and the electromagnetic shielding film 8 includes a stacked shielding layer 82 and an insulating layer 81, and the free grounding film is pressed together with the electromagnetic shielding film 8 through the adhesive film layer 5, and the protrusion 41 pierces the adhesive film layer 5 and the insulating layer 81 and is electrically connected to the shielding layer 82.

[0071] 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.

[0072] Preferably, the printed circuit board 9 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0073] In a specific implementation, when the circuit board is applied to an electronic device, the interference charges accumulated in the electromagnetic shielding film 8 can be conducted out by electrically connecting the free grounding film to the housing of the electronic device.

[0074] In an embodiment of the present invention, through the above-mentioned structure, during the process of pressing the free grounding film with the electromagnetic shielding film 8 through its adhesive film layer 5, the protrusion 41 on the third conductor layer 4 can be used to pierce the adhesive film layer 5 and the insulating layer 81 of the electromagnetic shielding film 8 in turn, so that at least a part of the outer surface of the third conductor layer 4 is connected to the shielding layer 82 of the electromagnetic shielding film 8, thereby realizing the extraction of interference charges in the electromagnetic shielding film 8 to ensure the grounding of the electromagnetic shielding film 8.

[0075] Example 4

[0076] like Figure 5 As shown, the method is applicable to the preparation of the free grounding film described in Example 1, comprising the steps of:

[0077] S1, forming a first conductor layer;

[0078] In step S1, in one preferred embodiment, the first conductor layer may be formed by:

[0079] forming an anti-oxidation layer on the carrier film;

[0080] The first conductor layer is formed on a side of the anti-oxidation layer away from the carrier film.

[0081] In another preferred embodiment, the first conductor layer may be formed by:

[0082] forming a peelable layer on the carrier film;

[0083] forming the first conductor layer on a side of the peelable layer away from the carrier film;

[0084] After forming an anti-oxidation layer on a side of the first conductor layer away from the strippable layer, the strippable layer is stripped.

[0085] S2. forming a conductive adhesive layer on one side of the first conductor layer;

[0086] S3, forming a second conductor layer on a side of the conductive adhesive layer away from the first conductor layer; wherein the second conductor layer has first through holes extending through the upper and lower surfaces thereof;

[0087] In the embodiment of the present invention, the cross-sectional area of ​​the first through hole is 0.01 μm 2 -1mm 2 The number of the first through holes in the second conductor layer per square centimeter is 5-10 6 indivual.

[0088] S4, at the melting temperature, causing the conductive adhesive layer to flow from one side of the first through hole to the other side and then instantaneously cool, thereby forming a protrusion on a side of the first through hole away from the conductive adhesive layer;

[0089] S5. Forming a third conductor layer on the side of the second conductor layer where the protrusion is formed, and making the third conductor layer cover the protrusion, thereby forming a protrusion on the outer surface of the third conductor layer at a position corresponding to the protrusion;

[0090] S6. A glue film layer is formed on the side of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, and the electromagnetic shielding film includes a shielding layer and an insulating layer that are stacked, and the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the metal protrusions pierce the glue film layer and the insulating layer and are electrically connected to the shielding layer.

[0091] Specifically, the step of forming the adhesive film layer on the side of the first conductor layer where the metal protrusion is formed is as follows:

[0092] Coating an adhesive film layer on a release film, and then laminating and transferring the adhesive film layer to a side of the third conductor layer away from the second conductor layer, thereby forming an adhesive film layer on a side of the third conductor layer away from the second conductor layer; or

[0093] A glue film layer is directly coated on the side of the third conductor layer away from the second conductor layer, thereby forming a glue film layer on the side of the third conductor layer away from the second conductor layer.

[0094] In another preferred embodiment suitable for preparing the free grounding film described in the second embodiment, after step S5 and before step S6, the following steps are further included:

[0095] Conductive particles are formed on the outer surface of the protrusion by one or more processes selected from the group consisting of physical roughening, chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating.

[0096] In an embodiment of the present invention, the preparation method of the free grounding film is to form the first conductor layer, the conductive adhesive layer and the second conductor layer in sequence, and at the melting temperature, make the conductive adhesive layer flow from one side of the first through hole on the second conductor film to the other side and then cool instantly, thereby forming a protrusion on the side of the first through hole away from the conductive adhesive layer, and at the same time forming a third conductor layer on the side of the second conductor layer where the protrusion is formed, so as to form a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer, and finally form a glue film layer on the side of the third conductor layer away from the second conductor layer, so that when the free grounding film is pressed against the electromagnetic shielding film through its glue film layer, the protrusion 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 realizing the extraction of interference charges in the electromagnetic shielding film.

[0097] In summary, the embodiments of the present invention provide a free grounding film, a circuit board, and a method for preparing a free grounding film, wherein the free grounding film comprises a first conductor layer 1, a conductive adhesive layer 2, a second conductor layer 3, a third conductor layer 4, and an adhesive film layer 5 stacked in sequence, wherein the second conductor layer 3 is provided with a first through hole 31 penetrating the upper and lower surfaces thereof, and a protrusion 21 is provided at the first through hole 31; the protrusion 21 is formed by the conductive adhesive layer 2 flowing from one side of the first through hole 31 to the other side at the melting temperature and then instantly cooling; the third conductor layer 4 covers the protrusion 21, thereby forming a protrusion 41 at a position corresponding to the protrusion 21 on the outer surface of the third conductor layer 4, and the protrusion 41 extends into the adhesive film layer 5; the free grounding film When the membrane is used for grounding a printed circuit board, an electromagnetic shielding membrane 8 is provided on the printed circuit board 9, and the electromagnetic shielding membrane 8 includes a stacked shielding layer 82 and an insulating layer 81, and the free grounding membrane is pressed together with the electromagnetic shielding membrane 8 through the adhesive film layer 5, and the protrusion 41 pierces the adhesive film layer 5 and the insulating layer 81 and is electrically connected to the shielding layer 82, thereby effectively conducting away the interference charges accumulated in the electromagnetic shielding membrane 8, thereby ensuring the grounding of the electromagnetic shielding membrane 8, and effectively avoiding the problem that at high temperatures, the free grounding membrane is pressed together with the electromagnetic shielding membrane through the conductive adhesive layer, resulting in failure of the connection between the free grounding membrane and the electromagnetic shielding membrane and the inability to quickly conduct the interference charges, thereby ensuring the integrity of the signal transmission.

[0098] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A free grounding membrane, characterized in that: The invention comprises a first conductor layer, a conductive adhesive layer, a second conductor layer, a third conductor layer and an adhesive film layer which are stacked in sequence, wherein the second conductor layer is provided with a first through hole penetrating the upper and lower surfaces thereof, and a protrusion is provided at the first through hole; the protrusion is formed by the conductive adhesive layer flowing from one side of the first through hole to the other side at a melting temperature and then cooling instantly; the third conductor layer covers the protrusion, thereby forming a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer, and the protrusion extends into the adhesive film layer; When the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, and the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked. The free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

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

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

4. The free grounding membrane according to any one of claims 1 to 3, characterized in that: The first conductor layer, the second conductor layer and the third conductor layer respectively include one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer and a graphene conductor layer.

5. The free grounding membrane according to claim 4, characterized in that: The metal conductor layer includes a single metal conductor layer and / or an alloy conductor layer; wherein the single metal conductor layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy conductor layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

6. The free grounding membrane according to any one of claims 1 to 3, 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 -1mm 2 .

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

8. The free grounding membrane according to any one of claims 1 to 3, characterized in that: The free grounding film further comprises a strippable protective film layer, and the strippable protective film layer is arranged on a side of the adhesive film layer away from the third conductor layer.

9. A circuit board, characterized in that: It comprises a printed circuit board, an electromagnetic shielding film and the free grounding film as described in any one of claims 1 to 8, wherein the electromagnetic shielding film is arranged on the printed circuit board, the electromagnetic shielding film comprises a shielding layer and an insulating layer which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

10. A method for preparing a free grounding film, characterized in that: Suitable for preparing the free grounding film according to any one of claims 1 to 8, comprising the steps of: forming a first conductor layer; forming a conductive adhesive layer on one side of the first conductor layer; A second conductor layer is formed on a side of the conductive adhesive layer away from the first conductor layer; wherein the second conductor layer is formed with a first through hole penetrating the upper and lower surfaces thereof; At a melting temperature, the conductive adhesive layer is made to flow from one side of the first through hole to the other side and then instantly cooled, so as to form a protrusion on a side of the first through hole away from the conductive adhesive layer; forming a third conductor layer on the side of the second conductor layer where the protrusion is formed, and making the third conductor layer cover the protrusion, so as to form a protrusion at a position corresponding to the protrusion on the outer surface of the third conductor layer; A glue film layer is formed on the side of the third conductor layer away from the second conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked, the free grounding film is pressed together with the electromagnetic shielding film through the glue film layer, and the protrusion pierces the glue film layer and the insulating layer and is electrically connected to the shielding layer.

11. The method for preparing a free grounding film according to claim 10, characterized in that: Before forming the adhesive film layer on the side of the third conductor layer away from the second conductor layer, the following steps are also included: Conductor particles are formed on the outer surface of the protrusion by one or more processes selected from the group consisting of physical roughening, chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating and mixed plating.

12. The method for preparing a free grounding film according to claim 10, characterized in that: The step of forming a glue film layer on a side of the third conductor layer away from the second conductor layer is specifically: Coating an adhesive film layer on the release film, and transferring the adhesive film layer by lamination to a side of the third conductor layer away from the second conductor layer; or A glue film layer is coated on a side of the third conductor layer away from the second conductor layer.

Images