Flexible printed circuit board and preparation method thereof

Abstract

The invention belongs to the technical field of printed circuit boards, and provides a flexible printed circuit board and a preparation method thereof. A first metal organic framework layer over the substrate; a metal film layer on the first metal organic framework layer; a metal conductive layer on the metal film layer; a film layer on the metal conductive layer; a second metal organic framework layer on the film coating layer; a shielding film layer on the second metal organic framework layer; an insulating protective layer on the shielding film layer; wherein the first metal organic framework layer is used for improving the binding force between the substrate and the metal film layer, the second metal organic framework layer is used for improving the binding force between the film coating layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used for improving the flexible performance of the flexible printed circuit board; according to the flexible printed circuit board, the bonding force is improved, the falling risk is reduced, the shielding effect, the use experience and the protection effect of the flexible printed circuit board are improved, and the bending performance is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of printed circuit boards, and in particular, relates to a flexible printed circuit board and a preparation method thereof. Background Art

[0002] Flexible Printed Circuit Board (FPCB), also known as "soft board", is a flexible printed circuit board with an electromagnetic shielding layer that is widely used in consumer electronic products such as mobile phones and digital cameras. The current structure of a flexible printed circuit board mainly consists of a substrate, an adhesive layer, a metal conductive layer (such as copper foil), a covering layer, and a metal sheet shielding layer. Among them, the bonding force between the substrate and the metal conductive layer, and between the covering layer and the metal sheet shielding layer is poor, which causes the metal conductive layer and / or the metal sheet shielding layer to fall off easily, affecting the shielding effect, user experience, and protection effect of the flexible printed circuit board. If the hardness of the metal shielding layer is too high, the FPCB will be easily broken or damaged when bent, affecting the functional performance and user experience of the electronic product.

[0003] The flexible printed circuit board in the prior art has the problem of being easily detached and easily broken, which reduces the performance and use experience. Summary of the invention

[0004] The embodiments of the present application provide a flexible printed circuit board and a method for preparing the same, which are intended to solve the problem that the flexible printed circuit board is easy to fall off and break, thereby reducing the performance and use experience.

[0005] In a first aspect, an embodiment of the present application provides a flexible printed circuit board, comprising:

[0006] substrate;

[0007] a first metal organic framework layer on the substrate;

[0008] a metal film layer on the first metal organic framework layer;

[0009] a metal conductive layer on the metal film layer;

[0010] a coating layer on the metal conductive layer;

[0011] a second metal organic framework layer on the coating layer;

[0012] a shielding film layer on the second metal organic framework layer;

[0013] An insulating protective layer on the shielding film layer;

[0014] Among them, the first metal organic framework layer is used to improve the bonding strength between the substrate and the metal film layer, the second metal organic framework layer is used to improve the bonding strength between the covering layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used to improve the flexibility of the flexible printed circuit board.

[0015] In a second aspect, an embodiment of the present application provides a method for preparing a flexible printed circuit board as described in any one of the contents of the first aspect, characterized in that it comprises:

[0016] providing a substrate;

[0017] forming a first metal organic framework layer on the substrate;

[0018] forming a metal film layer on the first metal organic framework layer;

[0019] forming a metal conductive layer on the metal film layer;

[0020] forming a coating layer on the metal conductive layer;

[0021] forming a second metal organic framework layer on the coating layer;

[0022] forming a shielding film layer on the second metal organic framework layer;

[0023] forming an insulating protective layer on the shielding film layer;

[0024] Among them, the first metal organic framework layer is used to improve the bonding strength between the substrate and the metal film layer, the second metal organic framework layer is used to improve the bonding strength between the covering layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used to improve the flexibility of the flexible printed circuit board.

[0025] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0026] The present application provides a flexible printed circuit board. Compared with the prior art, a first metal-organic framework layer is provided between a substrate and a metal film layer, a metal conductive layer is provided on the metal film layer, a coating layer is provided on the metal conductive layer, a second metal-organic framework layer is provided between the coating layer and the shielding film layer, and an insulating protective layer is provided on the shielding film layer; wherein the first metal-organic framework layer is used to improve the bonding force between the substrate and the metal film layer, the second metal-organic framework layer is used to improve the bonding force between the coating layer and the shielding film layer, and the first metal-organic framework layer and the second metal-organic framework layer are also used to improve the flexibility of the flexible printed circuit board; since the nano-scale first metal-organic framework layer and the second metal-organic framework layer are provided, and the nano-scale metal film layer increases the bonding force with the metal conductive layer, the bonding force between the substrate and the metal conductive layer, the coating layer and the shielding film layer is improved, the risk of the metal conductive layer and / or the shielding film layer falling off is reduced, the shielding effect, the use experience and the protection effect of the flexible printed circuit board are improved, and the bending performance of the metal conductive layer and the shielding film layer is improved, the risk of easy breakage and damage of the FPCB when bending is avoided, and the functional performance and the use experience of the electronic product are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 is a schematic diagram of the structure of a flexible printed circuit board provided in an embodiment of the present application;

[0029] Figure 2 It is a schematic diagram of a process of preparing a flexible printed circuit board provided in one embodiment of the present application;

[0030] Figure 3 It is a structural schematic diagram of a flexible printed circuit board with a shielding metal layer provided by the prior art.

[0031] Figure numbers:

[0032] 1. Substrate; 2. First metal organic framework layer; 3. Metal film layer; 4. Metal conductive layer; 5. Coating layer; 6. Second metal organic framework layer; 7. Shielding film layer; 8. Insulating protective layer; 9. Adhesive layer. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0035] In the present application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all mean: a, b, c, a~b (i.e. a and b), a~c, b~c, or a~b~c, where a, b, c can be single or multiple, respectively.

[0036] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. For example, without departing from the scope of the implementation regulations of this application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0037] The terms used in the embodiments of the present application are only for the purpose of describing specific implementation rules, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the implementation rules of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0038] It should be understood that in the various embodiments of the present application, the size of the serial number of each process does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0039] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0040] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0041] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0042] Flexible Printed Circuit Board (FPCB), also known as "soft board", is a flexible printed circuit board with an electromagnetic shielding layer that is widely used in electronic products such as mobile phones, digital cameras, computers, GPS, electric cars, tablet computers, smart TVs, wearable smart watches, etc. FPCB anti-electromagnetic wave and anti-static can not only protect conductors and sensors, but also more effectively prevent external environmental factors from affecting the communication of electronic products. These electronic products require small size, easy to carry, and can be used in complex electromagnetic and electrostatic environments.

[0043] The current structure of flexible printed circuit boards mainly includes a substrate, an adhesive layer on the substrate, a metal conductive layer (such as copper foil) on the adhesive layer, a covering layer on the metal conductive layer, and a metal shielding layer on the covering layer. The bonding force between the substrate and the metal conductive layer, and between the covering layer and the metal shielding layer is poor, which causes the metal conductive layer and / or the metal shielding layer to easily fall off, affecting the shielding effect, usage experience and protection effect of the flexible printed circuit board. If the hardness of the metal shielding layer is too high, the FPCB will easily break or break when bent, affecting the functional performance and usage experience of the electronic product.

[0044] In order to overcome the above problems, Figure 1As shown, the first aspect of the present application provides a flexible printed circuit board, comprising: a substrate 1; a first metal-organic framework layer 2 on the substrate 1; a metal film layer 3 on the first metal-organic framework layer 2; a metal conductive layer 4 on the metal film layer 3; a coating layer 5 on the metal conductive layer 4; a second metal-organic framework layer 6 on the coating layer 5; a shielding film layer 7 on the second metal-organic framework layer 6; and an insulating protective layer 8 on the shielding film layer 7; wherein the first metal-organic framework layer 2 is used to improve the bonding force between the substrate 1 and the metal film layer 3, the second metal-organic framework layer 6 is used to improve the bonding force between the coating layer 5 and the shielding film layer 7, and the first metal-organic framework layer 2 and the second metal-organic framework layer 6 are also used to improve the flexibility of the flexible printed circuit board.

[0045] Compared with the prior art, in the present embodiment, since a nanoscale first metal-organic framework layer and a second metal-organic framework layer are provided, the first metal-organic framework layer is used to improve the bonding force between the substrate and the metal film layer, and the second metal-organic framework layer is used to improve the bonding force between the covering layer and the shielding film layer, and the first metal-organic framework layer and the second metal-organic framework layer are also used to improve the flexibility of the flexible printed circuit board; and the nanoscale metal film layer increases the bonding force with the metal conductive layer, thereby improving the bonding force between the substrate and the metal conductive layer, and between the covering layer and the shielding film layer, reducing the risk of the metal conductive layer and / or the shielding film layer falling off, improving the shielding effect, usage experience and protection effect of the flexible printed circuit board, and improving the bending performance of the metal conductive layer and the shielding film layer, avoiding the risk of easy breakage or damage of the FPCB when bending, thereby improving the functional performance and usage experience of the electronic product.

[0046] like Figure 2 As shown, the second aspect of the present application provides a method for preparing a flexible printed circuit board as described in any one of the first aspect, comprising:

[0047] S10, providing a substrate 1;

[0048] S20, forming a first metal organic framework layer 2 on the substrate 1;

[0049] S30, forming a metal film layer 3 on the first metal organic framework layer 2;

[0050] S40, forming a metal conductive layer 4 on the metal film layer 3;

[0051] S50, forming a coating layer 5 on the metal conductive layer 4;

[0052] S60, forming a second metal organic framework layer 6 on the coating layer 5;

[0053] S70, forming a shielding film layer 7 on the second metal organic framework layer 6;

[0054] S80, forming an insulating protection layer 8 on the shielding film layer 7.

[0055] In this embodiment, the first metal organic framework layer is used to improve the bonding force between the substrate and the metal film layer, the second metal organic framework layer is used to improve the bonding force between the covering film layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used to improve the flexibility of the flexible printed circuit board. Compared with the prior art, since the nano-scale first metal organic framework layer and the second metal organic framework layer are formed, and the nano-scale metal film layer increases the bonding force with the metal conductive layer, the bonding force between the substrate and the metal conductive layer, the covering layer and the shielding film layer is improved, the risk of the metal conductive layer and / or the shielding film layer falling off is reduced, the shielding effect, use experience and protection effect of the flexible printed circuit board are improved, and the bending performance of the metal conductive layer and the shielding film layer is improved, avoiding the risk of easy breakage and damage of the FPCB when bending, thereby improving the functional performance and use experience of the electronic product.

[0056] It should be noted that, except for the contents in this application, all steps in the preparation method of the flexible printed circuit board are prepared using existing technologies, and the specific preparation process will not be described one by one. For example, the surface of the metal conductive layer of the circuit exposed to the outside that needs to be welded or connected is first covered with photoresist or other materials before the subsequent steps, and then processed after completing other steps.

[0057] In some embodiments, the first metal-organic framework layer is a complex of a first metal salt and a first flexible carboxylic acid ligand; the second metal-organic framework layer is a complex of a second metal salt and a second flexible carboxylic acid ligand; since the metal-organic framework layer includes a flexible carboxylic acid ligand and a metal salt to form a metal-organic framework (MOF), the metal-organic framework layers are all nanoscale composite structures, and the first metal-organic framework layer chemically reacts with the polymer compound of the substrate to form chemical crosslinks, thereby improving the bonding force between the first metal-organic framework layer and the substrate, and the first metal-organic framework layer also has a metal with similar material properties to the metal conductive layer, so that the first metal-organic framework layer and the metal film layer are more tightly bonded, thereby improving the bonding force between the substrate and the metal conductive layer; the second metal-organic framework layer and the compound of the covering layer also chemically react to form chemical crosslinks, thereby improving the bonding force between the second metal-organic framework layer and the covering layer, and the second metal-organic framework layer also has a material property similar to that of the shielding film layer. The metal makes the second metal-organic framework layer and the shielding film layer more tightly bonded, thereby improving the bonding force between the covering layer and the shielding film layer; therefore, the risk of the metal conductive layer and / or the shielding film layer falling off is reduced, and the shielding effect, usage experience and protection effect of the flexible printed circuit board are improved; in addition, since the metal-organic framework layer includes flexible carboxylic acid ligands, the flexible carboxylic acid ligands react and coordinate with the metal salt to form chemical bonds that can rotate freely, and then form configurations that match the substrate and the metal film layer, and the covering layer and the shielding film layer, respectively, thereby improving the bending performance of the metal conductive layer and the shielding film layer, avoiding the risk of easy breakage or damage when the FPCB is bent, thereby improving the functional performance and usage experience of electronic products.

[0058] In some embodiments, the first flexible carboxylic acid ligand comprises any one or more of maleic acid and fumaric acid, and the second flexible carboxylic acid ligand comprises any one or more of terephthalic acid and isophthalic acid. The maleic acid and fumaric acid of the first flexible carboxylic acid ligand are isomers of succinic acid, and the chemical formulas of maleic acid and fumaric acid are C 4 H 4 O 4 , have different double bond positions, and both include two carboxyl groups, so that they can combine with the first metal salt and the polymer in the substrate to form the first metal framework layer; while the second flexible carboxylic acid ligands of terephthalic acid and isophthalic acid have carboxyl groups (-COOH) and methoxy groups (-OCH 2 ), the chemical formula of terephthalic acid and isophthalic acid is C 10 H 10 O 6, both of which can combine with the second metal salt and the chemical molecules in the coating layer to form a second metal frame layer with more chelating or bridging coordination; and then form a first metal frame layer matching the substrate and the metal film layer, and a second metal frame layer matching the covering layer and the shielding film layer, respectively, thereby improving the bending performance of the metal conductive layer and the shielding film layer, avoiding the risk of easy breakage or damage when the FPCB is bent, thereby improving the functional performance and usage experience of electronic products.

[0059] In some embodiments, the first metal salt includes any one or more combinations of gold, silver, copper, nickel, palladium, and aluminum, and the metal in the metal film layer includes any one or more combinations of gold, silver, copper, and aluminum; since the metal film layer is mainly used to more closely combine with the conductive metal conductive layer of the conductive line, and the thickness of the metal conductive layer is reduced, the flexibility of the FPCB board is improved. The second metal salt includes any one or more combinations of gold, silver, copper, iron, aluminum, and nickel, and the metal in the shielding film layer includes any one or more combinations of gold, silver, copper, iron, aluminum, nickel, and stainless steel; since the shielding film layer is mainly used to more closely combine with the shielding film layer of the shielding, and the thickness of the shielding film layer is reduced, the flexibility of the FPCB board is improved.

[0060] In some embodiments, the substrate is made of a combination of any one or more of polyethylene terephthalate, polyimide, polyethylene naphthalate, polycarbonate, and polyamide; the coating layer is made of a combination of any one or more of polyacrylic resin, epoxy resin, phenolic resin, polyester resin, and polyurethane resin; a variety of materials allow the substrate and coating layer to be selected according to needs, thereby improving the use scenarios of the FPCB board.

[0061] In some embodiments, both the first metal organic framework layer and the second metal organic framework layer are subjected to surface treatment by vacuum plasma cleaning and then metal sputtering deposition is performed, thereby further improving the bonding strength between the metal organic framework layer and the sputtering layer.

[0062] In some embodiments, a first metal-organic framework layer is formed on a substrate, comprising: subjecting the substrate to chemical plating under first preset conditions to form the first metal-organic framework layer, the chemical plating solution comprising a first metal salt, a first flexible carboxylic acid ligand, a chelating agent and a reducing agent; in this embodiment, the chelating agent forms a complex with some metal ions (e.g., gold, silver, copper, nickel, palladium, aluminum) in the first metal salt to prevent the metal ions from precipitating in the plating solution, and increases the contact area between the first metal salt and the first flexible carboxylic acid ligand, and between the first flexible carboxylic acid ligand and the surface of the substrate, thereby accelerating the reaction rate, thereby forming a first metal-organic framework layer having a nanoscale two-dimensional structure, wherein the metal ions in the first metal salt react with the carboxyl groups in the first flexible carboxylic acid ligands to form stable coordination bonds, and the double bonds in the first flexible carboxylic acid ligands react with the polymers in the substrate to form chemical crosslinks; the reducing agent is used to prevent the components in the plating solution from being oxidized.

[0063] In some embodiments, the first preset condition is: the pH value of the chemical plating solution is 7.0~8.5, and the temperature of the chemical plating is 65℃~85℃; the dosage ratio of the first metal salt, the first flexible carboxylic acid ligand, the complexing agent and the reducing agent is (0.1mol~0.3mol):(0.2mol~0.9mol):(5g~50g):(0.2mol~0.5mol); under the preset conditions of this embodiment, the carboxylic acid group in the flexible carboxylic acid ligand can form a more stable coordination bond with the metal ion in the first metal salt under alkaline conditions. At the temperature of this embodiment, the first flexible carboxylic acid ligand reacts with the polymer in the substrate to form chemical crosslinks, thereby forming a first metal organic framework layer, connecting the substrate and the metal film layer.

[0064] In some embodiments, a second metal-organic framework layer is formed on the coating layer, comprising: subjecting the substrate to chemical plating under second preset conditions to form the second metal-organic framework layer, the chemical plating solution comprising a second metal salt, a second flexible carboxylic acid ligand, a chelating agent and a reducing agent; in this embodiment, the chelating agent forms a complex with some metal ions (e.g., gold, silver, copper, iron, aluminum, nickel) in the second metal salt to prevent the metal ions from precipitating in the plating solution, and increases the contact area between the second metal salt and the second flexible carboxylic acid ligand, and between the second flexible carboxylic acid ligand and the surface of the coating layer, thereby accelerating the reaction rate, thereby forming a second metal-organic framework layer having a nanoscale two-dimensional structure, wherein the metal ions in the second metal salt react with the carboxyl groups in the second flexible carboxylic acid ligands to form stable coordination bonds, and the double bonds in the second flexible carboxylic acid ligands react with the polymers in the substrate to form chemical crosslinks; the reducing agent is used to prevent the components in the plating solution from being oxidized.

[0065] In some embodiments, the second preset condition is: the pH value of the electroless plating solution is 8.0-10.0, the temperature of the electroless plating is 75°C-95°C; the amount ratio of the second metal salt, the second flexible carboxylic acid ligand, the complexing agent and the reducing agent is (0.1mol-0.3mol):(0.2mol-0.9mol):(5g-50g):(0.2mol-0.5mol); under the preset conditions of this embodiment, the carboxylic acid group (-COOH) in the second flexible carboxylic acid ligand can form a more stable coordination bond with the metal ion in the second metal salt under the strong alkaline condition, and the carboxylic acid group (-COOH) and / or methoxy group (-OCH 2 ) reacts with the polymer in the coating layer to form chemical crosslinks, thereby forming a second metal organic framework layer, connecting the coating layer and the shielding film layer.

[0066] In some embodiments, the complexing agent includes any one or more combinations of sodium citrate, ammonium citrate, EDTA (ethylenediaminetetraacetic acid), lactic acid, glycolic acid, succinic acid, and sodium pyrophosphate; the reducing agent includes any one or more combinations of sodium hypophosphite, ferrous sulfate, ascorbic acid, and soluble ascorbate; the pH adjuster includes any one or more combinations of ammonia water, sodium hydroxide, and potassium hydroxide; multiple choices are conducive to selecting the complexing agent, reducing agent, and pH adjuster according to the needs of the FPCB.

[0067] In some embodiments, the thickness of the first metal organic framework layer and the second metal organic framework layer are both 2μm to 20μm, the thickness of the metal film layer is 10μm to 45μm, and the thickness of the shielding film layer is 5μm to 100μm; each layer does not increase the thickness of the FPCB, and the transmission loss rate is minimized without affecting the electromagnetic wave shielding performance, and the flexibility is also improved, further improving the use experience of the FPCB. Among them, if the thickness of the metal film layer is ≧30μm, the flexible printed circuit board does not include a metal conductor layer, and the unidirectional flexible printed circuit board includes a substrate, a first metal organic framework layer, a metal film layer, a coating layer, a second metal organic framework layer, a shielding film layer, and an insulating protective layer from bottom to top.

[0068] like Figure 3 As shown in FIG. 1 , the flexible printed circuit board and film shielding structure of the prior art are: a substrate, an adhesive layer, a metal conductive layer (such as copper foil), a cover layer and a metal sheet shielding layer. Figure 1 As shown, in some embodiments, the widths of the first metal-organic framework layer, the metal film layer, the metal conductive layer, the coating layer, the second metal-organic framework layer, and the shielding film layer are all smaller than the width of the insulating protective layer, that is, the insulating protective layer not only covers the surface of the shielding film layer, but also covers the sides of the first metal-organic framework layer, the metal film layer, the metal conductive layer, the coating layer, the second metal-organic framework layer, and the shielding film layer on the substrate. Compared with the Film shielding method of the prior art, the shielding metal and the metal conductive layer are avoided from being exposed on the sides, the insulating protective layer can completely cover the shielding film layer, the impact of the environment on the shielding film layer is reduced, and the shielding performance and service life of the FPCB are improved.

[0069] It can be understood that the metal film layer and the shielding film layer in the present application are prepared by a vacuum coating process, and the sputtering process is a type of vacuum physical vapor deposition (PVD) coating process, including DC sputtering, AC sputtering, reactive sputtering and magnetron sputtering.

[0070] In some embodiments, the metal film layer and the shielding film layer are prepared by a vacuum PVD coating process other than a sputtering process. The material of the metal film layer is a combination of any one or more of aluminum, copper, iron, and silver. The material of the shielding film layer is a combination of any one or more of aluminum, copper, iron, nickel, silver, and carbon nanotubes.

[0071] In some embodiments, the coating conditions of the metal film layer and the shielding film layer are as follows: the coating temperature is 20°C to 50°C, the flow rate of the inert gas is 200 Sccm to 500 Sccm, and the vacuum degree is 1.0×10 -2 Pa~9.0×10 -4 Pa, the ambient air pressure is 0.3Pa-0.5Pa, and the inert gas includes at least one of helium, neon, argon and krypton.

[0072] The technical solution of the present application is illustrated below through specific embodiments and comparative examples.

[0073] Example 1

[0074] A method for preparing a flexible printed circuit board comprises the following steps:

[0075] Step 1: providing a substrate, wherein the substrate is made of polyimide.

[0076] Step 2, forming a first metal organic framework layer on the substrate, specifically, chemically plating the substrate under first preset conditions to form the first metal organic framework layer, the chemical plating solution includes a first metal salt, a first flexible carboxylic acid ligand, a chelating agent and a reducing agent, wherein the first preset condition is: the pH value of the chemical plating solution is 7.5, and the chemical plating temperature is 75°C; the thickness of the first metal organic framework layer is 8μm, the first metal salt is copper sulfate, the first flexible carboxylic acid ligand is maleic acid, the chelating agent is sodium citrate, the reducing agent is ascorbic acid, and the amount ratio of copper sulfate: maleic acid: sodium citrate: ascorbic acid is 0.2mol:0.6mol:30g:0.3mol.

[0077] Step 3: A metal film layer is formed on the first metal organic framework layer after vacuum plasma cleaning by a vacuum coating process. The metal of the metal film layer is copper, the thickness of the metal film layer is 10 μm, and the coating conditions of the vacuum coating are: the coating temperature is 35° C., the flow rate of the inert gas is 350 Sccm, and the vacuum degree is 5.0×10 -4 Pa, the ambient pressure is 0.4 Pa, and the inert gas is argon.

[0078] Step 4: forming a metal conductive layer on the metal film layer, wherein the metal of the metal conductive layer is copper.

[0079] Step 5: forming a coating layer on the metal conductive layer, wherein the coating layer is polyacrylic acid resin.

[0080] Step 6, forming a second metal organic framework layer on the coating layer, specifically, performing chemical plating on the substrate under second preset conditions to form the second metal organic framework layer, the chemical plating solution includes a second metal salt, a second flexible carboxylic acid ligand, a chelating agent and a reducing agent, wherein the second preset conditions are: the pH value of the chemical plating solution is 8.5, and the chemical plating temperature is 80°C; the thickness of the second metal organic framework layer is 8μm, the second metal salt is aluminum sulfate, the second flexible carboxylic acid ligand is terephthalic acid, the chelating agent is sodium citrate, the reducing agent is ascorbic acid, and the amount ratio of aluminum sulfate, terephthalic acid, sodium citrate and ascorbic acid is 0.2mol:0.6mol:25g:0.3mol.

[0081] Step 7: A shielding film layer is formed on the second metal organic framework layer after vacuum plasma cleaning by a vacuum coating process. The metal of the shielding film layer is aluminum, the thickness of the shielding film layer is 8 μm, and the coating conditions of the vacuum coating are: the coating temperature is 35° C., the flow rate of the inert gas is 350 Sccm, and the vacuum degree is 5.0×10 -4 Pa, the ambient pressure is 0.4 Pa, and the inert gas is argon.

[0082] Step 8: Silk-screen the shielding film layer to form an insulating protective layer.

[0083] Example 2

[0084] The difference between this embodiment and embodiment 1 is that: the pH value of the first preset condition and the second preset condition is increased, and the amount of the first metal salt, the second metal salt, the first flexible carboxylic acid ligand, and the second flexible carboxylic acid ligand is increased;

[0085] The first preset condition in step 2 is: the pH value of the chemical plating solution is 8.5, the temperature of the chemical plating is 85°C; the first metal salt is copper sulfate, and the first flexible carboxylic acid ligand is fumaric acid; the dosage ratio of copper sulfate: fumaric acid: sodium citrate: ascorbic acid is 0.3 mol: 0.9 mol: 30 g: 0.3 mol.

[0086] The second preset condition in step 7 is: the pH value of the chemical plating solution is 10.0, the temperature of the chemical plating is 95°C; the second metal salt is copper sulfate, the second flexible carboxylic acid ligand is isophthalic acid, the dosage ratio of copper sulfate, isophthalic acid, sodium citrate and ascorbic acid is 0.3 mol: 0.9 mol: 25 g: 0.3 mol, and the metal of the shielding film layer is copper.

[0087] Example 3

[0088] The difference between this embodiment and embodiment 1 is that: the pH value of the first preset condition and the second preset condition is reduced, and the amount of the first metal salt, the second metal salt, the first flexible carboxylic acid ligand, and the second flexible carboxylic acid ligand is reduced;

[0089] The first preset condition in step 2 is: the pH value of the chemical plating solution is 7.0, the temperature of the chemical plating is 85°C; the first metal salt is copper sulfate, and the first flexible carboxylic acid ligand is fumaric acid; the dosage ratio of copper sulfate: fumaric acid: sodium citrate: ascorbic acid is 0.1 mol: 0.3 mol: 30 g: 0.3 mol.

[0090] The second preset condition in step 7 is: the pH value of the chemical plating solution is 8.0, the temperature of the chemical plating is 95°C; the second metal salt is copper sulfate, the second flexible carboxylic acid ligand is isophthalic acid, the dosage ratio of copper sulfate, isophthalic acid, sodium citrate and ascorbic acid is 0.1 mol: 0.3 mol: 25 g: 0.3 mol, and the metal of the shielding film layer is copper.

[0091] Example 4

[0092] The difference between this embodiment and embodiment 1 is that: the thickness of the first metal organic framework layer and the second metal organic framework layer is increased;

[0093] The thickness of the first metal organic framework layer in step 2 is 5 μm.

[0094] In step 6, the thickness of the second metal organic framework layer is 5 μm; the second metal salt is ferric sulfate, and the metal of the shielding film layer is iron.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that the second metal salt is nickel sulfate, and the metal of the shielding film layer is nickel.

[0097] Example 6

[0098] The difference between this embodiment and embodiment 1 is that the second metal salt is ferric sulfate, and the metal of the shielding film layer is stainless steel.

[0099] Comparative Example 1

[0100] The difference between this embodiment and embodiment 1 is that: the first metal organic framework layer, the metal film layer and the second metal organic framework layer are not provided, and the shielding film layer is a metal sheet shielding film layer;

[0101] A method for preparing a flexible printed circuit board comprises the following steps:

[0102] Step 1: providing a substrate, wherein the substrate is made of polyimide.

[0103] Step 2, forming an adhesive layer on the substrate using an adhesive;

[0104] Step 3: forming a metal conductive layer on the adhesive layer, wherein the metal of the metal conductive layer is copper.

[0105] Step 4: forming a coating layer on the metal conductive layer, wherein the coating layer is polyacrylic acid resin.

[0106] Step 5, forming a metal sheet shielding film layer on the coating layer, wherein the metal of the shielding film layer is aluminum.

[0107] Step 6: Silk-screen the shielding film layer to form an insulating protective layer.

[0108] It should be understood that the order of execution of the steps in the above embodiments does not necessarily mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application. The metal conductive layer, coating layer, and insulating protective layer in the above embodiments and comparative examples are all formed by existing technologies and will not be described in detail.

[0109] The corresponding flexible printed circuit boards prepared in Examples 1 to 5 and Comparative Example 1 were subjected to performance tests under the same conditions, and the film surface performance, electromagnetic shielding performance, adhesion of the first metal organic framework layer and adhesion of the second metal organic framework layer after bending 500 times were tested. The test results are shown in Table 1.

[0110] Table 1 Performance test data of corresponding flexible printed circuit boards prepared in Examples 1 to 5 and Comparative Example 1

[0111]

[0112] According to the test data in Table 1, it is shown that the preparation method of the present application increases the adhesion of the flexible printed circuit board by adding a first metal organic framework layer between the substrate and the metal film layer and adding a second metal organic framework layer between the substrate and the shielding film layer. At the same time, since the shielding film layer is formed on the second metal organic framework layer after vacuum plasma cleaning by a vacuum coating process, the electromagnetic shielding performance is improved, and the bending performance of the flexible printed circuit board is improved.

[0113] It can be understood that the beneficial effects of the second to fifth aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0114] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0115] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A flexible printed circuit board, characterized in that: include: substrate; a first metal organic framework layer on the substrate; a metal film layer on the first metal organic framework layer; a metal conductive layer on the metal film layer; a coating layer on the metal conductive layer; a second metal organic framework layer on the coating layer; a shielding film layer on the second metal organic framework layer; An insulating protective layer on the shielding film layer; Among them, the first metal organic framework layer is used to improve the bonding strength between the substrate and the metal film layer, the second metal organic framework layer is used to improve the bonding strength between the covering layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used to improve the flexibility of the flexible printed circuit board.

2. The flexible printed circuit board according to claim 1, wherein: The first metal organic framework layer is a complex of a first metal salt and a first flexible carboxylic acid ligand; the second metal organic framework layer is a complex of a second metal salt and a second flexible carboxylic acid ligand.

3. The flexible printed circuit board according to claim 2, characterized in that: The first flexible carboxylic acid ligand comprises any one or more combinations of maleic acid and fumaric acid, and the second flexible carboxylic acid ligand comprises any one or more combinations of terephthalic acid and isophthalic acid.

4. The flexible printed circuit board according to claim 2, wherein: The first metal salt includes any one or more combinations of gold, silver, copper, aluminum, nickel, and palladium, and the metal in the metal film layer includes any one or more combinations of gold, silver, copper, and aluminum; The second metal salt includes any one or more combinations of gold, silver, copper, iron, aluminum, and nickel, and the metal in the shielding film layer includes any one or more combinations of gold, silver, copper, iron, aluminum, nickel, and stainless steel.

5. A method for preparing a flexible printed circuit board according to any one of claims 1 to 4, characterized in that: include: providing a substrate; forming a first metal organic framework layer on the substrate; forming a metal film layer on the first metal organic framework layer; forming a metal conductive layer on the metal film layer after the first surface treatment; forming a coating layer on the metal conductive layer subjected to the second surface treatment; forming a second metal organic framework layer on the coating layer; forming a shielding film layer on the second metal organic framework layer; forming an insulating protective layer on the shielding film layer; Among them, the first metal organic framework layer is used to improve the bonding strength between the substrate and the metal film layer, the second metal organic framework layer is used to improve the bonding strength between the covering layer and the shielding film layer, and the first metal organic framework layer and the second metal organic framework layer are also used to improve the flexibility of the flexible printed circuit board.

6. The method for preparing a flexible printed circuit board according to claim 5, characterized in that: Forming a first metal organic framework layer on the substrate, comprising: The substrate is subjected to chemical plating under first preset conditions to form the first metal organic framework layer, and the plating solution of the chemical plating includes a first metal salt, a first flexible carboxylic acid ligand, a complexing agent and a reducing agent.

7. The method for preparing a flexible printed circuit board according to claim 6, characterized in that: The first preset condition is: the pH value of the electroless plating solution is 7.0-8.5, and the temperature of the electroless plating is 65° C.-85° C.; The usage ratio of the first metal salt, the first flexible carboxylic acid ligand, the complexing agent and the reducing agent is (0.1 mol to 0.3 mol):(0.2 mol to 0.9 mol):(5 g to 50 g):(0.2 mol to 0.5 mol).

8. The method for preparing a flexible printed circuit board according to claim 5, characterized in that: Forming a second metal organic framework layer on the coating layer, comprising: The substrate is subjected to chemical plating under second preset conditions to form the second metal organic framework layer, and the plating solution of the chemical plating comprises a second metal salt, a second flexible carboxylic acid ligand, a complexing agent and a reducing agent.

9. The method for preparing a flexible printed circuit board according to claim 8, characterized in that: The second preset condition is: the pH value of the electroless plating solution is 8.0-10.0, and the temperature of the electroless plating is 75° C.-95° C.; The usage ratio of the second metal salt, the second flexible carboxylic acid ligand, the complexing agent and the reducing agent is (0.1 mol to 0.3 mol):(0.2 mol to 0.9 mol):(5 g to 50 g):(0.2 mol to 0.5 mol).

10. The method for preparing a flexible printed circuit board according to any one of claims 6 to 9, characterized in that: The substrate is made of any one or more combinations of polyethylene terephthalate, polyimide, polyethylene naphthalate, polycarbonate, and polyamide; The coating layer is made of any one or more combinations of polyacrylic resin, epoxy resin, phenolic resin, polyester resin, and polyurethane resin; The complexing agent includes any one or more combinations of sodium citrate, ammonium citrate, EDTA, lactic acid, glycolic acid, succinic acid, and sodium pyrophosphate; The reducing agent includes any one or more combinations of sodium hypophosphite, ferrous sulfate, ascorbic acid, and soluble ascorbate; The pH adjuster includes any one or more combinations of ammonia water, sodium hydroxide, and potassium hydroxide.

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