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 second conductor layer, and an adhesive film layer. A resin protrusion formed by resin flowing from one side of the first through-hole to the other side and then solidifying is provided at the first through-hole of the first conductor layer; the second conductor layer is disposed on the side of the first conductor layer close to the resin protrusion to form a protrusion at a position corresponding to the resin protrusion on the outer surface of the second conductor layer; the adhesive film layer is disposed on the side of the second conductor layer away from the first conductor layer; when the free grounding film is used for grounding of a printed circuit board, it can be pressed against the electromagnetic shielding film on the printed circuit board through its adhesive film layer, and the protrusion pierces the insulating layers 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 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 circuit board. 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 second conductor layer and a film adhesive layer. A first through hole penetrating the upper and lower surfaces is provided on the first conductor layer, and a resin protrusion is provided at the first through hole. The resin protrusion is formed by resin flowing from one side of the first through hole to the other side and then solidifying; the second conductor layer is disposed on one side of the first conductor layer close to the resin protrusion and covers the resin protrusion, so as to form a protrusion portion at a position corresponding to the resin protrusion on the outer surface of the second conductor layer; the film adhesive layer is disposed on one side of the second conductor layer away from the first conductor 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 which are stacked. The free grounding film is press-fitted with the electromagnetic shielding film through the film adhesive layer, and the protrusion portion pierces through the film adhesive layer and the insulating layer and is electrically connected to the shielding layer.

[0008] As an improvement of the above solution, the resin protrusion is formed by resin flowing from one side of the first through hole to the other side at room temperature and then solidifying at a curing temperature; or,

[0009] The resin protrusion is formed by resin flowing from one side of the first through hole to the other side at a melting temperature and then instantaneously cooled.

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

[0011] As an improvement of the above solution, the film adhesive layer includes an adhesive layer containing conductive particles; or, the film adhesive layer includes an adhesive layer without conductive particles.

[0012] As an improvement of the above solution, the first conductor layer and the second 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.

[0013] As an improvement of the above solution, the metal conductor layer includes a single metal conductor layer and / or an alloy conductor layer; wherein, the single metal conductor layer is made of any one of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy conductor layer is made of any two or more of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0014] As an improvement of the above solution, the number of the first through holes in each square centimeter of the first conductor layer is 5 - 10 6 pieces; and / or, the cross-sectional area of the first through hole is 0.01μm2 -1 mm 2 。

[0015] As an improvement to the above solution, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is disposed on a surface of the first conductor layer away from the second conductor layer.

[0016] As an improvement to the above solution, the free grounding film further includes a peelable protective film layer, and the peelable protective film layer is disposed on a surface of the adhesive film layer away from the second conductor layer.

[0017] Compared with the prior art, the embodiment of the present invention discloses a free grounding film. By providing a resin protrusion at a first through hole of the first conductor layer, and disposing the second conductor layer on a side of the first conductor layer close to the resin protrusion, a protrusion portion is formed at a position corresponding to the resin protrusion on an outer surface of the second conductor layer. At the same time, an adhesive film layer is disposed on a side of the second conductor layer away from the first conductor layer. When the free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, the protrusion portion can pierce through the adhesive film layer and an insulating layer of the electromagnetic shielding film in sequence, and be connected to a shielding layer of the electromagnetic shielding film, so as to effectively conduct interference charges accumulated in the electromagnetic shielding film, thereby ensuring 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 a conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly conducted out. Therefore, the accumulation of interference charges is effectively avoided, and the normal operation of the printed circuit board is not affected.

[0018] To solve the same technical problem, the present invention further provides a circuit board, including a printed circuit board, an electromagnetic shielding film, and the above free grounding film. The electromagnetic shielding film is disposed on the printed circuit board. The electromagnetic shielding film includes a shielding layer and an insulating layer stacked. The free grounding film is pressed against the electromagnetic shielding film through the adhesive film layer, and the protrusion portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0019] Compared with the prior art, an embodiment of the present invention discloses a circuit board, which includes a printed circuit board, an electromagnetic shielding film, and the free grounding film described in any one of the above. When the free grounding film is laminated with the electromagnetic shielding film through its adhesive film layer, the convex portion can sequentially pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film and connect to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, further ensuring the grounding of the electromagnetic shielding film, and effectively avoiding the problem that when the temperature is high, since the free grounding film is laminated with the electromagnetic shielding film through the conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly led out. Therefore, the accumulation of interfering charges is effectively avoided, and the normal operation of the printed circuit board is not affected.

[0020] 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 above free grounding film, and includes the steps of:

[0021] Form a first conductor layer; wherein, the first conductor layer is formed with a first through hole penetrating its upper and lower surfaces;

[0022] Form a resin protrusion at the first through hole; wherein, the resin protrusion protrudes from the first through hole;

[0023] Form a second conductor layer on one side of the first conductor layer where the resin protrusion is formed, and make the second conductor layer cover the resin protrusion, so as to form a convex portion at a position corresponding to the resin protrusion on the outer surface of the second conductor layer;

[0024] Form an adhesive film layer on the side of the second conductor layer away from the first conductor layer; when the free grounding film is used for grounding the 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 laminated with the electromagnetic shielding film through the adhesive film layer, and the convex portion pierces the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0025] As an improvement of the above solution, forming the resin protrusion at the first through hole specifically includes:

[0026] Set resin at the first through hole, and make the resin flow from one side of the first through hole to the other side at room temperature and then solidify at the curing temperature, so as to form a resin protrusion at the first through hole; or,

[0027] Set resin at the first through hole, and make the resin flow from one side of the first through hole to the other side at the melting temperature and then be instantaneously cooled, so as to form a resin protrusion at the first through hole.

[0028] As an improvement of the above solution, before forming the adhesive film layer on the side of the second conductor layer away from the first conductor layer, the following steps are further included:

[0029] Conductor particles are formed on the outer surface of the raised portion by one or more processes among physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating.

[0030] As an improvement of the above solution, forming the adhesive film layer on the side of the second conductor layer away from the first conductor layer specifically includes:

[0031] Coating the adhesive film layer on the release film and laminating and transferring the adhesive film layer to the side of the second conductor layer away from the first conductor layer; or

[0032] Coating the adhesive film layer on the side of the second conductor layer away from the first conductor layer.

[0033] Compared with the prior art, the method for preparing the free grounding film provided by the embodiment of the present invention forms the resin raised portion at the first through hole of the first conductor layer, and forms the second conductor layer on the side of the first conductor layer where the resin raised portion is formed, so as to form a raised portion at the position corresponding to the resin raised portion on the outer surface of the second conductor layer. Finally, an adhesive film layer is formed on the side of the second conductor layer away from the first conductor layer, so that when the free grounding film is laminated with the electromagnetic shielding film through its adhesive film layer, the raised portion can sequentially pierce the adhesive film layer and the insulating layer of the electromagnetic shielding film and be connected to the shielding layer of the electromagnetic shielding film, thereby effectively leading out the interfering charges accumulated in the electromagnetic shielding film, and further ensuring the grounding of the electromagnetic shielding film, effectively avoiding the problem that when the temperature is high, since the free grounding film is laminated with the electromagnetic shielding film through the conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interfering charges cannot be quickly led out, so the accumulation of interfering charges is effectively avoided and the normal operation of the printed circuit board is affected. Description of the Drawings

[0034] Figure 1 is a schematic structural diagram of the free grounding film in Embodiment 1 of the present invention;

[0035] Figure 2 is a cross-sectional view of the free grounding film in Embodiment 1 of the present invention;

[0036] Figure 3 is a schematic structural diagram of the free grounding film in Embodiment 2 of the present invention;

[0037] Figure 4 is a schematic structural diagram of the circuit board in Embodiment 3 of the present invention;

[0038] Figure 5It is a schematic flow chart of the preparation method of the free grounding film in the fourth embodiment of the present invention.

[0039] Among them, 1 is the first conductor layer; 11 is the first through hole; 12 is the resin protrusion; 13 is the first surface; 14 is the second surface; 2 is the second conductor layer; 21 is the protrusion part; 22 is the conductor particle; 3 is the adhesive film layer; 4 is the peelable protective film layer; 5 is the anti-oxidation layer; 6 is the electromagnetic shielding film; 61 is the insulating layer; 62 is the shielding layer; 7 is the printed circuit board. Specific embodiments

[0040] 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 creative efforts shall fall within the protection scope of the present invention.

[0041] Embodiment 1

[0042] Combined with Figure 1 and Figure 2 As shown, it includes a first conductor layer 1, a second conductor layer 2 and an adhesive film layer 3. A first through hole 11 penetrating the upper and lower surfaces is provided on the first conductor layer 1. A resin protrusion 12 is provided at the first through hole 11. The resin protrusion 12 is formed by resin flowing from one side of the first through hole 11 to the other side and then solidifying; the second conductor layer 2 is provided on the side of the first conductor layer 1 close to the resin protrusion 12 and covers the resin protrusion 12, so as to form a protrusion part 21 at a position corresponding to the resin protrusion 12 on the outer surface of the second conductor layer 2; the adhesive film layer 3 is provided on the side of the second conductor layer 2 away from the first conductor layer 1;

[0043] As Figure 4 shown, when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film 6 is provided on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 arranged in a stacked manner. The free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 3. The protrusion part 21 pierces the adhesive film layer 3 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0044] In an embodiment of the present invention, a resin protrusion 12 is provided at a first through hole 11 of the first conductor layer 1, and the second conductor layer 2 is disposed on a side of the first conductor layer 1 close to the resin protrusion 12, so as to form a protrusion 21 at a position corresponding to the resin protrusion 12 on an outer surface of the second conductor layer 2. Meanwhile, an adhesive film layer 3 is disposed on a side of the second conductor layer 2 away from the first conductor layer 1. When the free ground film is pressed against the electromagnetic shielding film 6 through the adhesive film layer 3 thereof, the protrusion 21 can pierce through the adhesive film layer 3 and an insulating layer 61 of the electromagnetic shielding film 6 in sequence and be connected to a shielding layer 62 of the electromagnetic shielding film 6, thereby effectively leading out interference charges accumulated in the electromagnetic shielding film 6, further ensuring the grounding of the electromagnetic shielding film 6, and effectively avoiding the problem that when the temperature is high, since the free ground film is pressed against the electromagnetic shielding film through a conductive adhesive layer, the connection between the free ground film and the electromagnetic shielding film fails and the interference charges cannot be quickly led out. Therefore, the accumulation of interference charges is effectively avoided from affecting the normal operation of the printed circuit board, and the integrity of signal transmission is ensured.

[0045] In an embodiment of the present invention, in one preferred manner, the process of forming the resin protrusion 12 is specifically as follows: the resin protrusion 12 is formed after the resin flows from one side of the first through hole 11 to the other side at a melting temperature and then is instantaneously cooled. In another preferred embodiment, the resin is a cured adhesive, and the process of forming the resin protrusion 12 is specifically as follows: at room temperature, the liquefied resin flows from one side of the first through hole 11 to the other side and then solidifies at a curing temperature. Wherein, the resin for forming the resin protrusion 12 can be disposed at one end of the first through hole 11 away from the second conductor layer 2, or can be disposed on a surface of the first conductor layer 1 away from the second conductor layer 2; in addition, the resin can be a thermoplastic resin or a thermosetting resin.

[0046] In the embodiments of the present invention, it should be noted that the structure of the resin protrusion 12 shown in the drawings is only exemplary. Since the resin protrusion 12 is formed by the resin flowing from one side of the first through-hole 11 to the other side and then solidifying, in one case, the resin almost completely flows out of the first through-hole 11 without residue in the first through-hole 11. Therefore, the formed resin protrusion 12 can be as shown in the drawings, and the resin protrusion 12 is formed at the boundary between the first through-hole 11 and the second conductor layer 2; in another case, there is residual resin in the first through-hole 11, and the first through-hole 11 is even filled with resin. Therefore, one end of the formed resin protrusion 12 is located in the first through-hole 11, and the other end of the resin protrusion 12 extends out of the first through-hole 11; in still another case, there is residual resin on the surface of the first conductor layer 1 away from the second conductor layer 2. Therefore, the formed resin protrusion 12 can penetrate through the first through-hole 11. In addition, the resin protrusion 12 in the present invention is not limited by the illustrated and above shapes, as long as it is a resin protrusion with piercing ability, it is within the protection scope of the present invention.

[0047] In the embodiments of the present invention, in order to ensure that the resin protrusion 12 can be formed at the first through-hole 11 and at the same time ensure that the first conductor layer 1 is not easily broken, preferably, the cross-sectional area of the first through-hole 11 in this embodiment is 0.01 μm 2 -1 mm 2 。

[0048] In addition, in order to ensure that enough resin protrusions 12 can be formed on the first conductor layer 1 to ensure that the protrusion 21 formed on the second conductor layer 2 can smoothly pierce the insulating layer 61 of the adhesive film layer 3 and the electromagnetic shielding film 6 and be connected to the shielding layer 62, and at the same time ensure that the first conductor layer 1 is not easily broken, the number of the first through-holes 11 in each square centimeter of the first conductor layer 1 in this embodiment is 5 - 10 10 pieces. Correspondingly, the number of the resin protrusions 12 in each square centimeter of the first conductor layer film 1 is 5 - 10 10 pieces; it should be noted that since the second conductor layer 2 covers the resin protrusion 12, a protrusion 21 is formed at the position corresponding to the resin protrusion 12 on the outer surface of the second conductor layer 2. Therefore, the number of the protrusions 21 corresponds to the number of the resin protrusions 12, thus ensuring that the insulating layer 61 of the adhesive film layer 3 and the electromagnetic shielding film 6 can be smoothly pierced.

[0049] In an embodiment of the present invention, the first through holes 11 may be distributed regularly or irregularly on the first shielding layer 1 of the screen; wherein, the regular distribution of the first through holes 11 on the first conductor layer 1 means that the shapes of the first through holes 11 are the same, and they are evenly distributed on the first conductor layer 1; the irregular distribution of the first through holes 11 on the first conductor layer 1 means that the shapes of the first through holes 11 are different, and they are disorderly distributed on the first conductor layer 1. Preferably, the shapes of the first through holes 11 are the same, and the first through holes 11 are evenly distributed on the first conductor layer 1, as Figure 2 shown. In addition, the first through holes 11 may be circular through holes, or through holes of any other shape. The drawings of the present invention only take the first through holes 11 being circular through holes as an example, but the first through holes 11 of any other shape are within the protection scope of the present invention.

[0050] In an embodiment of the present invention, it should be noted that the shape of the protrusion 21 may be the same as or different from the shape of the resin protrusion 12. The shape of the protrusion 21 shown in the drawings is only exemplary.

[0051] In an embodiment of the present invention, the thickness of the first conductor layer 1 is preferably 2 μm - 45 μm; the thickness of the second conductor layer 2 is preferably 2 μm - 45 μm, so as to ensure that the first conductor layer 1 and the second conductor layer 2 are not easily broken and have good flexibility. In order to ensure that the first conductor layer 1 and the second conductor layer 2 have good electrical conductivity, the first conductor layer 1 includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer; the second conductor layer 2 includes one or more of a metal conductor layer, a carbon nanotube conductor layer, a ferrite conductor layer, and a graphene conductor layer. Among them, the metal conductor layer includes a single metal conductor layer and / or an alloy conductor layer; wherein, the single metal conductor layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy conductor layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0052] In an embodiment of the present invention, the first conductor layer 1 includes a first surface 13 and a second surface 14 arranged opposite to each other. The first surface 13 is in contact with the second conductor layer 2; the second surface 14 is in contact with the protective film layer 4. It should be noted that the first surface 13 and the second surface 14 may be surfaces of any shape. For example, they may be as Figure 1The flat surface shown can also be an uneven surface with undulations or other rough surfaces; in addition, the first surface 13 and the second surface 14 can be regular surfaces or irregular surfaces. The accompanying drawings of the present invention only illustrate the case where both the first surface 13 and the second surface 14 are flat surfaces, and the first surface 13 and the second surface 14 of any other shape are within the protection scope of the present invention. In addition, the surface of the second conductor layer 2 in contact with the first surface 13 can also be a surface of any shape. For example, it can be a flat surface as shown in Figure 1 a flat surface, or an uneven surface with undulations, or other rough surfaces, and no more details will be elaborated here.

[0053] In the embodiment of the present invention, it should be noted that both the first conductor layer 1 and the second conductor layer 2 in the accompanying drawings of this embodiment 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 2 in the accompanying drawings of this embodiment can be set in a grid shape, a foam shape, etc.

[0054] In the embodiment of the present invention, one structure of the adhesive film layer 3 is specifically shown as: the adhesive film layer 3 includes an adhesive layer containing conductive particles. By making the adhesive film layer 3 include an adhesive layer containing conductive particles, the adhesive film layer 3 has an adhesive function to tightly bond the free grounding film and the electromagnetic shielding film 6. At the same time, the adhesive film layer 3 also has a conductive function, which cooperates with the second conductor layer 2 and the first conductor layer 1 to quickly conduct interfering electrons. Among them, the conductive particles can be separated conductive particles or large particle conductive particles formed by aggregation; when the conductive particles are separated conductive particles, the electrical contact area can be further increased and the uniformity of electrical contact can be improved; while when the conductive particles are large particle conductive particles formed by aggregation, the piercing strength can be increased.

[0055] In the embodiment of the present invention, another structure of the adhesive film layer 3 is specifically shown as: the adhesive film layer 3 includes an adhesive layer without conductive particles. By making the adhesive film layer 3 include an adhesive layer without conductive particles, the adhesive film layer 3 has an adhesive function to tightly bond the free grounding film and the electromagnetic shielding film 6. At the same time, since the adhesive film layer 3 does not contain conductive particles, the insertion loss of the circuit board during use is reduced and the bendability of the circuit board is improved.

[0056] In the embodiment of the present invention, the thickness of the adhesive film layer 3 is 0.1 μm - 80 μm. The materials used for the adhesive film layer 3 are selected from the following types: modified epoxy resin types, acrylic types, modified rubber types, modified thermoplastic polyimide types. In addition, the outer surface of the adhesive film layer 3 can be a flat surface without undulations or a gently undulating uneven surface.

[0057] like Figure 1 As shown, in order to protect the adhesive film layer 3, the free grounding film in this embodiment further includes a peelable protective film layer 4, and the peelable protective film layer 4 is arranged on the side of the adhesive film layer 3 away from the second conductor layer 2. The peelable protective film layer 4 plays a protective role to prevent the adhesive film layer 3 from being damaged before use, thereby ensuring that the free grounding film can be pressed together with the electromagnetic shielding film 6 through the adhesive film layer 3. It should be noted that when the free grounding film is pressed together with the electromagnetic shielding film 6, the peelable protective film layer 4 needs to be peeled off, and then the free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 3.

[0058] In addition, the peelable protective film layer 4 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.

[0059] In the embodiment of the present invention, in order to protect the first conductor layer 1 and ensure that the interference charges can be led out, the free grounding film in this embodiment further includes an anti-oxidation layer 5, and the anti-oxidation layer 5 is provided on the side of the first conductor layer 1 away from the second conductor layer 2. By providing the anti-oxidation layer 5 on the side of the first conductor layer 1 away from the second conductor layer 2, the first conductor layer 1 is prevented from being oxidized by contact with air, thereby ensuring that the interference charges in the electromagnetic shielding film 6 can be led out through the free grounding film.

[0060] In one preferred embodiment, the material of the anti-oxidation layer 5 is one of metal material, ferrite, graphite, carbon nanotube, graphene, and silver paste; wherein the metal material is any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; or the metal material is an alloy formed by two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, gold, and molybdenum; at this time, the thickness of the anti-oxidation layer 5 is 0.01 μm-5 μm, and the thickness of the anti-oxidation layer 5 is preferably 0.1 μm-1 μm. In addition, the anti-oxidation layer 5 can be formed by a composite process of at least two of the processes of chemical plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, and electroplating.

[0061] In another preferred embodiment, the anti-oxidation layer 5 is made of a mixture of glue and conductive particles; wherein the volume ratio of the conductive particles to the glue is 5%-80%; at this time, the thickness of the anti-oxidation layer 5 is preferably 0.1 μm-5 μm. In addition, the anti-oxidation layer 5 can be formed by a coating and then curing process.

[0062] Example 2

[0063] As Figure 3 shown, the difference between the free grounding film in this embodiment and that in Example 1 is that the surface of the convex portion 21 is provided with convex conductor particles 22. By providing the conductor particles 22 on the surface of the convex portion 21, it is made easier for the convex portion 21 to pierce the insulating layer 61 of the adhesive film layer 3 and the electromagnetic shielding film 6, thereby ensuring that interfering charges can be conducted out.

[0064] Preferably, the conductor particles 22 are concentratedly distributed at the outwardly convex positions on the surface of the convex portion 21, which makes it easier to pierce the adhesive film layer 3. Of course, the non-convex portions on the surface of the convex portion 21 can also have conductor particles 22 distributed thereon. In addition, the conductor particles 22 can also be distributed at other positions on the side of the second conductor layer 2 close to the adhesive film layer 3, not only distributed on the surface of the convex portion 21, as Figure 3 shown. Of course, the conductor particles 22 can also be distributed only on the convex portion 21.

[0065] In specific implementation, as Figure 3 shown, the second conductor layer 2 can be first formed, and then the conductor particles 22 can be formed on the side of the second conductor layer 2 away from the first conductor layer 1 through other processes. Of course, the second conductor layer 2 and the conductor particles 22 can also be an integral structure formed by a one-step forming process.

[0066] In the embodiment of the present invention, the conductor particles 22 can have a certain distance from the outer surface of the adhesive film layer 3, or can be in contact with the outer surface of the adhesive film layer 3 or extend out of the outer surface of the adhesive film layer 3.

[0067] In the embodiment of the present invention, the height of the conductor particles 22 is preferably 20 μm - 100 μm, the thickness of the adhesive film layer 3 is preferably 0.1 μm - 80 μm, and the thickness of the insulating layer 61 is preferably 1 μm - 20 μm. By setting the height of the conductor particles 22 to be preferably 20 μm - 100 μm and the thickness of the adhesive film layer 3 to be preferably 0.1 μm - 80 μm, it is ensured that the conductor particles 22 can pierce the adhesive film layer 3 and the insulating layer 61 of the electromagnetic shielding film 6, thereby ensuring that the free grounding film can conduct out the interfering charges accumulated on the electromagnetic shielding film 6.

[0068] In an embodiment of the present invention, the conductor particles 22 include one or more of metal particles, carbon nanotube particles and ferrite particles. In addition, the metal particles include single metal particles and / or alloy particles; wherein the single metal particles are made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy particles are made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. In addition, it should be noted that the conductor particles 22 may be the same as the material of the second conductor layer 2, or may be different.

[0069] In the embodiment of the present invention, it should be noted that, Figure 3 The shape of the conductor particles 22 shown is only exemplary. Due to differences in process means and parameters, the conductor particles 22 may also be in other shapes such as clusters, hanging ice, stalactites, and dendrites. In addition, the conductor particles 22 in the present invention are not limited to the shapes shown in the figure and described above. As long as the conductor particles have piercing and conductive functions, they are within the protection scope of the present invention.

[0070] In addition, other structures and working principles of the free grounding film of this embodiment are the same as those of the first embodiment, and are not further described here.

[0071] Embodiment 3

[0072] like Figure 4 As shown, an embodiment of the present invention further provides a circuit board, comprising a printed circuit board 7, an electromagnetic shielding film 6 and the free grounding film described in embodiment one or two, wherein the electromagnetic shielding film 6 is arranged on the printed circuit board 7, and the electromagnetic shielding film 6 comprises a shielding layer 62 and an insulating layer 61 which are stacked, and the free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 3, and the protrusion 21 pierces the adhesive film layer 3 and the insulating layer 61 and is electrically connected to the shielding layer 62.

[0073] 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.

[0074] Preferably, the printed circuit board 7 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0075] In a specific implementation, when the circuit board is applied to an electronic device, the interference charges accumulated in the electromagnetic shielding film 6 can be led out by electrically connecting the free grounding film to the housing of the electronic device.

[0076] In an embodiment of the present invention, through the above-mentioned structure, during the pressing process of the free grounding film and the electromagnetic shielding film 6, the protrusion 21 on the second conductor layer 2 is used to pierce the adhesive film layer 3 and the insulating layer 61 in turn, so that at least a part of the outer surface of the second conductor layer 2 is connected to the shielding layer 62 of the electromagnetic shielding film 6, so that with the cooperation of the first conductor layer 1 and the second conductor layer 2, the interference charge is extracted, avoiding the accumulation of interference charges to form an interference source, thereby affecting the normal operation of the circuit board.

[0077] Embodiment 4

[0078] like Figure 5 As shown, the method is applicable to the preparation of the free grounding film described in Example 1, and includes steps S1 to S4:

[0079] S1. forming a first conductor layer; wherein the first conductor layer has a first through hole penetrating the upper and lower surfaces thereof;

[0080] Wherein, in step S1, the first conductor layer is formed by the following method:

[0081] An anti-oxidation layer is formed on the carrier film, and the first conductor layer is formed on one side of the anti-oxidation layer.

[0082] Alternatively, a strippable layer is formed on a carrier film, the first conductor layer is formed on the surface of the strippable layer, an anti-oxidation layer is formed on a side of the first conductor layer away from the strippable layer, and then the carrier film layer is stripped.

[0083] 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 first conductor layer per square centimeter is 5-10 6 indivual.

[0084] S2, forming a resin protrusion at the first through hole; wherein the resin protrusion extends out of the first through hole;

[0085] The forming of the resin protrusion at the first through hole is specifically:

[0086] Resin is disposed at the first through hole, and the resin flows from one side of the first through hole to the other side and then solidifies, thereby forming a resin protrusion at the first through hole.

[0087] Specifically, in one preferred embodiment, resin is provided at the first through hole, and the resin flows from one side of the first through hole to the other side at room temperature and then solidifies at the curing temperature, thereby forming a resin protrusion at the first through hole; in another preferred embodiment, resin is provided at the first through hole, and the resin flows from one side of the first through hole to the other side at the melting temperature and then undergoes instant cooling, thereby forming a resin protrusion at the first through hole.

[0088] S3. A second conductor layer is formed on the side of the first conductor layer where the resin protrusion is formed, and the second conductor layer covers the resin protrusion, thereby forming a protrusion on the outer surface of the second conductor layer corresponding to the resin protrusion;

[0089] S4. An adhesive film layer is formed on the side of the second conductor layer away from the first 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 stacked, and the free grounding film is pressed and bonded to the electromagnetic shielding film through the adhesive film layer, and the protrusion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

[0090] Among them, forming the adhesive film layer on the side of the second conductor layer away from the first conductor layer specifically includes:

[0091] Coating an adhesive film layer on a release film, and then pressing and transferring the adhesive film layer to the side of the second conductor layer away from the first conductor layer, thereby forming an adhesive film layer on the side of the second conductor layer away from the first conductor layer; or

[0092] Directly coating an adhesive film layer on the side of the second conductor layer away from the first conductor layer, thereby forming an adhesive film layer on the side of the second conductor layer away from the first conductor layer.

[0093] In another preferred embodiment applicable to preparing the electromagnetic shielding film described in Embodiment 2, after step S3 and before step S4, the following step is further included:

[0094] Conductor particles are formed on the outer surface of the protrusion 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.

[0095] In summary, the embodiments of the present invention provide a free grounding film, a printed circuit board, and a method for preparing the free grounding film. The free grounding film includes a first conductor layer 1, a second conductor layer 2, and an adhesive film layer 3. A first through hole 11 penetrating the upper and lower surfaces is provided on the first conductor layer 1. A resin protrusion 12 is provided at the first through hole 11. The resin protrusion 12 is formed by resin flowing from one side of the first through hole 11 to the other side and then solidifying. The second conductor layer 2 is provided on one side of the first conductor layer 1 close to the resin protrusion 12 and covers the resin protrusion 12, so that a protrusion 21 is formed at a position corresponding to the resin protrusion 12 on the outer surface of the second conductor layer 2. The adhesive film layer 3 is provided on one side of the second conductor layer 2 away from the first conductor layer 1. When the free grounding film is used for grounding a printed circuit board, an electromagnetic shielding film 6 is provided on the printed circuit board 7. The electromagnetic shielding film 6 includes a shielding layer 62 and an insulating layer 61 which are stacked. The free grounding film is pressed together with the electromagnetic shielding film 6 through the adhesive film layer 3. The protrusion 21 pierces through the adhesive film layer 3 and the insulating layer 61 and is electrically connected to the shielding layer 62, so as to effectively export the interference charges accumulated in the electromagnetic shielding film 6, and further ensure the grounding of the electromagnetic shielding film 6. It effectively avoids the problem that when the temperature is high, since the free grounding film is pressed together with the electromagnetic shielding film through a conductive adhesive layer, the connection between the free grounding film and the electromagnetic shielding film fails and the interference charges cannot be quickly exported. Therefore, it effectively avoids the accumulation of interference charges and affects the normal operation of the printed circuit board.

[0096] 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 second conductor layer and a glue film layer. A first through hole penetrating the upper and lower surfaces is provided on the first conductor layer. A resin protrusion is provided at the first through hole, and the resin protrusion is formed by resin flowing from one side of the first through hole to the other side and then solidifying; the second conductor layer is arranged on the side of the first conductor layer close to the resin protrusion and covers the resin protrusion, so as to form a protrusion at a position corresponding to the resin protrusion on the outer surface of the second conductor layer; the glue film layer is arranged on the side of the second conductor layer away from the first conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board. The electromagnetic shielding film includes a shielding layer and an insulating layer arranged in a stacked manner. The free grounding film is pressed against the electromagnetic shielding film through the glue film layer, and the protrusion pierces through the glue film layer and the insulating layer and is electrically connected to the shielding layer; the first conductor layer and / or the second conductor layer includes a metal conductor layer, and the metal conductor layer includes a single-metal conductor layer and / or an alloy conductor layer.

2. The free grounding film according to claim 1, characterized in that, the resin protrusion is formed by resin flowing from one side of the first through hole to the other side at normal temperature and then solidifying at a curing temperature; or, the resin protrusion is formed by resin flowing from one side of the first through hole to the other side at a melting temperature and then instantaneously cooled.

3. The free grounding film according to claim 1, characterized in that, convex conductor particles are provided on the surface of the protrusion; the height of the conductor particles is 20μm - 100μm.

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

5. The free grounding film according to any one of claims 1 - 4, characterized in that, the first conductor layer and the second conductor layer respectively further include one or more of a carbon nanotube conductor layer, a ferrite conductor layer and a graphene conductor layer.

6. The free grounding film according to claim 5, characterized in that, the single-metal conductor layer is made of any one of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy conductor layer is made of any two or more of materials such as aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

7. The free grounding film according to any one of claims 1 - 4, characterized in that, The number of the first through holes in the first conductor layer per square centimeter is 5 - 10 6 ; and / or, the cross-sectional area of the first through hole is 0.01 μm 2 - 1 mm 2 .

8. The free grounding film according to any one of claims 1 - 4, characterized in that, the free grounding film further includes an anti-oxidation layer, and the anti-oxidation layer is arranged on the surface of the first conductor layer away from the second conductor layer.

9. The free grounding film according to any one of claims 1 - 4, characterized in that, the free grounding film further includes a peelable protective film layer, and the peelable protective film layer is arranged on the surface of the glue film layer away from the second conductor layer.

10. A circuit board, characterized in that, Comprising a printed circuit board, an electromagnetic shielding film, and a free grounding film according to any one of claims 1-9, wherein the electromagnetic shielding film is disposed on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked, the free grounding film is press-fitted with the electromagnetic shielding film through the adhesive film layer, and the protruding portion pierces through the adhesive film layer and the insulating layer and is electrically connected to the shielding layer.

11. 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 1-9, and includes the steps of: forming a first conductor layer; wherein, a first through hole penetrating the upper and lower surfaces thereof is formed in the first conductor layer; forming a resin protrusion at the first through hole; wherein, the resin protrusion extends out of the first through hole; forming a second conductor layer on one side of the first conductor layer where the resin protrusion is formed, and covering the resin protrusion with the second conductor layer, so as to form a protruding portion at a position corresponding to the resin protrusion on the outer surface of the second conductor layer; forming an adhesive film layer on one side of the second conductor layer away from the first conductor layer; when the free grounding film is used for grounding of a printed circuit board, an electromagnetic shielding film is provided on the printed circuit board, the electromagnetic shielding film includes a shielding layer and an insulating layer which are stacked, the free grounding film is press-fitted with 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.

12. The method for preparing a free grounding film according to claim 11, characterized in that the forming a resin protrusion at the first through hole specifically is: providing resin at the first through hole, and allowing the resin to flow from one side of the first through hole to the other side at normal temperature and then solidify at a curing temperature, so as to form a resin protrusion at the first through hole; or, providing resin at the first through hole, and allowing the resin to flow from one side of the first through hole to the other side at a melting temperature and then instantaneously cooled, so as to form a resin protrusion at the first through hole.

13. The method for preparing a free grounding film according to claim 11, characterized in that before forming the adhesive film layer on one side of the second conductor layer away from the first conductor layer, the following steps are further included: forming conductor particles on the outer surface of the protruding portion by one or more of physical roughening, electroless plating, physical vapor deposition, chemical vapor deposition, evaporation plating, sputtering plating, electroplating, and mixed plating processes.

14. The method for preparing a free grounding film according to claim 11, characterized in that the forming an adhesive film layer on one side of the second conductor layer away from the first conductor layer specifically is: coating an adhesive film layer on a release film, and pressing and transferring the adhesive film layer to one side of the second conductor layer away from the first conductor layer; or, coating an adhesive film layer on one side of the second conductor layer away from the first conductor layer.

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