Improved multi-layer FPC with stepped structure, manufacturing method thereof and electronic equipment

Abstract

The invention relates to an improved multi-layer FPC with a step structure and a manufacturing method thereof, and the method comprises the steps: manufacturing the core board of each layer of the FPC, and each layer of the core board comprises a circuit layer, a flexible core board layer and a bonding layer; a step area of the FPC is determined, a porous hole-shaped structure is manufactured at the boundary of the step area of the bonding layer, and a protective layer is machined on the layer where the step face of the step area of the FPC is located; injecting a liquid-phase substance into the porous structure; laminating the core plates of each layer of the FPC according to a preset sequence to obtain the FPC; and carrying out subtractive manufacturing on the stepped region of the FPC by adopting a vertical laser controlled depth milling process to form the multi-layer FPC with the stepped structure. In the material reducing treatment process of the vertical laser depth-controlled milling process, the function of gasifying and absorbing heat of the liquid-phase substance is utilized, so that each core layer at the boundary of the non-step area is cooled and protected, the boundary of the non-step area of each core layer is prevented from being burnt, the step structure of the FPC is more complete, and the yield and quality of the FPC are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible circuit board manufacturing, and particularly to an improved multi-layer FPC with a stepped structure, a manufacturing method thereof, and an electronic device. Background Art

[0002] An FPC (Flexible Printed Circuit Board) can provide excellent electrical performance, can meet the design requirements of smaller size and higher density installation, and is widely used in various electronic devices. Among them, the characteristic of a multi-layer FPC board with a stepped structure is that the number of circuit layers and the board thickness are different in different regions within a complete FPC unit, so that the FPC board can meet the requirements of different functions and sizes.

[0003] In order to form a stepped structure on a multi-layer FPC, it is necessary to perform controlled-depth milling on the FPC board to form the stepped structure. However, in the existing manufacturing methods of multi-layer FPC boards with a stepped structure, the controlled-depth milling process is prone to inaccurate processing due to low processing accuracy, and it is easy to damage the finished layer of the FPC board, affecting the reliability of the product.

[0004] In the prior art, a protective layer is provided on the multi-layer FPC to protect the finished layer of the FPC, so that the laser controlled-depth milling only reduces the material to the protective layer (stepped surface). However, since the laser controlled-depth milling will burn the entire stepped area, the boundary of the non-stepped area adjacent to the stepped area will also be burned. If the processing accuracy of the laser controlled-depth milling is insufficient, it may cause damage to the boundary of the non-stepped area. Summary of the Invention

[0005] Based on this, it is necessary to provide an improved multi-layer FPC with a stepped structure, a manufacturing method thereof, and an electronic device.

[0006] A manufacturing method of an improved multi-layer FPC with a stepped structure includes:

[0007] Manufacturing core boards for each layer of the FPC, wherein each layer of the core board includes a circuit layer, a flexible core board layer, and an adhesive layer;

[0008] Determining the stepped area of the FPC, manufacturing a porous hole-like structure at the boundary of the stepped area of the adhesive layer, and processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located;

[0009] Injecting a liquid phase substance into the hole-like structure;

[0010] Pressing the core boards of each layer of the FPC in a preset order to obtain the FPC;

[0011] Adopting a vertical laser controlled-depth milling process to perform subtractive manufacturing on the stepped area of the FPC to form a multi-layer FPC with a stepped structure.

[0012] In one embodiment, the step of fabricating a porous hole-like structure at the boundary of the stepped region of the adhesive layer includes:

[0013] Using femtosecond laser to ablate at the boundary of the stepped region of the adhesive layer to form a porous hole-like structure.

[0014] In one embodiment, after the step of using femtosecond laser to ablate at the boundary of the stepped region of the adhesive layer to form a porous hole-like structure, the following steps are further included:

[0015] Radiating the boundary of the stepped region of the adhesive layer with high-energy rays to crosslink the adhesive layer at the boundary of the stepped region.

[0016] In one embodiment, the step of injecting a liquid-phase substance into the hole-like structure includes:

[0017] Injecting the liquid-phase substance into the hole-like structure by vacuum impregnation method.

[0018] In one embodiment, the FPC is an N-layer board, the N-layer board includes N circuit layers, N - 1 flexible core board layers, N - 2 adhesive layers, and 2 solder mask layers. The layers in the N-layer board are alternately and symmetrically distributed, and the solder mask layers are located on the outermost sides;

[0019] The FPC board includes M stepped regions, the number of layers of the stepped region is less than N, and the number of layers of adjacent stepped regions is different.

[0020] In one embodiment, the liquid-phase substance includes one of ethylene glycol, ionic liquid, and perfluoropolyether oil.

[0021] In one embodiment, after the step of using vertical laser controlled-depth milling process to perform subtractive manufacturing on the stepped region of the FPC to form a stepped multi-layer FPC, the following steps are included:

[0022] Using acid etching to remove the protective layer on the other core boards except those on the circuit layers;

[0023] Fabricating a cover film on the surface of the stepped region to form a multi-layer FPC.

[0024] In one embodiment, the step of processing a protective layer on the layer where the stepped surface of the stepped region of the FPC is located includes:

[0025] If the layer where the stepped surface is located is a flexible core board layer, then process a protective layer on the side without circuits of the flexible core board layer;

[0026] If the layer where the stepped surface is located is a circuit layer, a protective layer is processed on the circuit layer;

[0027] Among them, the cross-sectional shape of the protective layer on the side without circuits of the flexible core board layer is trapezoidal, and the thickness in the middle of the protective layer on the side without circuits of the flexible core board layer is greater than that at the edge.

[0028] An improved multi-layer FPC with a stepped structure is manufactured by using the manufacturing method of the improved multi-layer FPC with a stepped structure in any of the above embodiments.

[0029] An electronic device includes the improved multi-layer FPC with a stepped structure in any of the above embodiments.

[0030] The above-mentioned improved multi-layer FPC with a stepped structure, its manufacturing method, and electronic device make a porous hole-like structure at the boundary of the stepped area of the adhesive layer, inject a liquid-phase substance into the hole-like structure, and utilize the function of the liquid-phase substance vaporizing and absorbing heat during the subtractive process of the vertical laser controlled-depth milling process, so that the core layers at the boundary of the non-stepped area are protected from temperature reduction, avoiding burns at the boundary of the non-stepped area of each core layer, thereby making the stepped structure of the FPC more complete, and effectively improving the yield and quality of the FPC. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 It is a schematic flow chart of the manufacturing method of the improved multi-layer FPC with a stepped structure in an embodiment;

[0033] Figure 2 It is a schematic structural diagram of the improved multi-layer FPC with a stepped structure in an embodiment. Detailed Embodiments

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] In the prior art, CN118946046A processes a protective layer on the layer where the stepped surface of the stepped area of the FPC board is located, and uses the protective layer to protect the core board below the stepped surface. However, this can only protect the core board below the stepped surface, and for the boundaries and edges of each layer in the non-stepped area, they may still be burned and damaged.

[0036] Therefore, the present application provides a manufacturing method for a multi-layer FPC with an improved stepped structure.

[0037] Embodiment 1

[0038] As Figure 1 shown, it is a manufacturing method for a multi-layer FPC with an improved stepped structure according to an embodiment of the present invention, including:

[0039] Step 110, manufacturing the core boards of each layer of the FPC, wherein each of the core boards of each layer includes a circuit layer, a flexible core board layer, and an adhesive layer.

[0040] As Figure 2 shown, each core board of the FPC includes a plurality of circuit layers, a plurality of flexible core board layers, and a plurality of adhesive layers. Among them, the circuit layer is made of a metal material and is used to undertake the circuit function. The flexible core board layer is used to support the circuit layer and provide electrical insulation function. In some embodiments, the material of the flexible core board layer is PI (Polyimide), and in some other embodiments, the material of the flexible core board layer can also be polyester film (PET) or polyethylene naphthalate. The adhesive layer is also called the adhesive glue layer or the AD glue layer and is used to bond adjacent core boards, such as bonding adjacent circuit layers and flexible core board layers.

[0041] Step 120, determining the stepped area of the FPC, manufacturing a porous hole-like structure at the boundary of the stepped area of the adhesive layer, and processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located.

[0042] In this embodiment, the stepped area is determined and divided during the FPC design stage. When manufacturing each layer of the FPC, the stepped area of this layer can be determined. In this embodiment, the boundary of the stepped area is the junction between the stepped area and the non-stepped area, or the junction between one stepped area and another stepped area. By determining the stepped area of the adhesive layer, the boundary of the stepped area of the adhesive layer can be determined, and a porous honeycomb hole-like structure is manufactured at the boundary of each stepped area of each adhesive layer. This hole-like structure is used to accommodate liquid-phase substances.

[0043] In addition, in the design stage of the FPC, not only the stepped area is determined, but also the stepped surface of the stepped area is determined. This stepped surface is the layer where the outermost plate of the stepped area is located after the formation of the stepped structure. In this embodiment, while manufacturing each layer structure, according to the determined stepped surface of the stepped area, a protective layer is processed on the layer where the corresponding stepped surface is located. This protective layer is used to protect other core boards below the protective layer, preventing the core boards below the protective layer from being burned out by laser controlled-depth milling.

[0044] Step 130, inject a liquid-phase substance into the hole-like structure.

[0045] In this embodiment, the liquid-phase substance is located at the boundary of the stepped area. When laser controlled-depth milling is performed, the liquid-phase substance located at the boundary vaporizes, absorbing a large amount of heat, cooling the boundary of the stepped area, making the temperature at the boundary lower than that inside the stepped area, so that the core layers at the boundary of the non-stepped area are cooled and protected, preventing the core layers at the boundary of the non-stepped area from being burned, and also preventing the adhesive layer from carbonizing and the flexible core board from delaminating. It is worth mentioning that as laser controlled-depth milling performs subtractive processing on each layer of the stepped area of the FPC, the liquid-phase substance at the boundary of the stepped area vaporizes, and the hole-like structure is also eliminated, finally leaving the adhesive layer of the non-stepped area or adjacent stepped areas, making the structure of the remaining adhesive layer more stable. In addition, in this embodiment, hole-like structures are only made in the adhesive layer, and not in the circuit layer and the flexible core board layer. The reason is that the circuit layer and the flexible core board layer, as the main substrates of the FPC, undertake the main functional roles of the FPC. Therefore, not making hole-like structures in the circuit layer and the flexible core board layer, but only in the adhesive layer, can effectively ensure the stability of the structures of the circuit layer and the flexible core board layer of the FPC. In addition, compared with the circuit layer and the flexible core board layer, making porous structures and injecting liquid-phase substances in the adhesive layer is simpler and easier. And the adhesive layer is located between the adjacent circuit layer and the flexible core board layer, and its vaporization and heat absorption effect can act on the adjacent circuit layer and the flexible core board layer at the same time. Therefore, it can achieve a good cooling and protection effect on the adjacent circuit layer and the flexible core board layer.

[0046] Step 140, press the core boards of each layer of the FPC in a preset order to obtain the FPC.

[0047] In this embodiment, since hole-like structures are provided at the boundaries of the stepped areas of each adhesive layer, the hole-like structures can absorb the flow of excess adhesive (AD glue) during the pressing process, further effectively preventing glue overflow, thereby making the structures of each layer of the FPC more stable and the pressing effect better.

[0048] Step 150, use the vertical laser controlled-depth milling process to perform subtractive manufacturing on the stepped area of the FPC to form a multi-layer FPC with a stepped structure.

[0049] In this embodiment, the vertical laser controlled-depth milling process is used to perform material removal on the layers above the stepped surface in the stepped area of the FPC to form a stepped structure. Since a protective layer is provided on the stepped surface, it can effectively protect the core board below the stepped surface from being burned or damaged.

[0050] It is worth mentioning that the porous honeycomb-like pore structure is located in the part removed by the laser in the stepped area. In this way, the liquid-phase substances can be fully removed to avoid remaining on the FPC.

[0051] In this embodiment, by fabricating a porous pore structure at the boundary of the stepped area of the adhesive layer and injecting a liquid-phase substance into the pore structure, during the material removal process of the vertical laser controlled-depth milling process, by utilizing the function of the liquid-phase substance vaporizing and absorbing heat, the core layers at the boundary of the non-stepped area are cooled and protected, avoiding burns at the boundary of the non-stepped area of each core layer, so that the stepped structure of the FPC is more complete, thereby effectively improving the yield and quality of the FPC.

[0052] It is worth mentioning that in some scenarios, in order to avoid burns at the boundary of the non-stepped area during the laser controlled-depth milling process, it is considered to perform the laser controlled-depth milling process in a low-temperature environment or use liquid nitrogen in cooperation with the laser controlled-depth milling process. However, this is likely to cause unstable temperature of the FPC, and the adhesive layer is likely to shrink due to thermal expansion and contraction, and then the adhesive layer is separated from the flexible core board layer, resulting in unstable bonding results of the FPC. Therefore, in this embodiment, by utilizing the heat absorption of the liquid-phase substance vaporization, it can effectively avoid the structural instability caused by the thermal expansion and contraction of the FPC.

[0053] In one embodiment, the step of fabricating a porous pore structure at the boundary of the stepped area of the adhesive layer includes: using femtosecond laser to ablate at the boundary of the stepped area of the adhesive layer to form a porous pore structure.

[0054] In this embodiment, femtosecond laser is used to perform directional ablation of microholes at the boundary of the stepped area of the adhesive layer, thereby forming a porous honeycomb-like pore structure. Using femtosecond laser for ablation has the characteristics of high precision and high efficiency, and can accurately perform directional ablation of microholes at the boundary of the stepped area, and can form honeycomb-like holes with a pore diameter of 3 - 12 μm. It is worth mentioning that the diameter of the holes in the pore structure is controlled within 3 - 12 μm. When the contact angle θ between the liquid-phase substance and the AD glue > 90°, the capillary pressure generated by the surface tension (γ) forms a negative pressure, which can effectively prevent the liquid-phase substance from flowing out.

[0055] In one embodiment, after the step of using femtosecond laser to ablate at the boundary of the stepped area of the adhesive layer to form a porous hole-like structure, the method further includes: irradiating the boundary of the stepped area of the adhesive layer with high-energy rays so that the adhesive layer crosslinks at the boundary of the stepped area.

[0056] In this embodiment, the high-energy rays include ultraviolet rays, X-rays, etc. By irradiating the boundary of the stepped area of the adhesive layer with high-energy rays, crosslinking is carried out to retain and solidify the honeycomb hole-like structure, so that the hole-like structure is shaped, and liquid-phase substances can be better injected and accommodated.

[0057] In one embodiment, after the step of using femtosecond laser to ablate at the boundary of the stepped area of the adhesive layer to form a porous hole-like structure, the method further includes: injecting a liquid-phase substance into the hole-like structure and irradiating the boundary of the stepped area of the adhesive layer with high-energy rays so that the adhesive layer crosslinks at the boundary of the stepped area.

[0058] In this embodiment, after the hole-like structure is formed, the boundary of the stepped area of the adhesive layer is not directly irradiated. Instead, a liquid-phase substance is first injected, and then high-energy ray irradiation is carried out. In this way, the hole-like structure is crosslinked and shaped, and a nano-level dense layer is formed at the hole entrance to restrict the liquid-phase substance, effectively preventing the liquid-phase substance in the hole-like structure from detaching.

[0059] In one embodiment, the step of injecting the liquid-phase substance into the hole-like structure includes: injecting the liquid-phase substance into the hole-like structure by vacuum impregnation.

[0060] In this embodiment, the vacuum impregnation method can effectively allow the liquid-phase substance to be fully injected into the holes of the hole-like structure and fully fill the hole-like structure.

[0061] In one embodiment, the FPC is an N-layer board, the N-layer board includes N circuit layers, N - 1 flexible core board layers, N - 2 adhesive layers, and 2 solder mask layers. The layers in the N-layer board are alternately and oppositely distributed, and the solder mask layers are located on the outermost sides; the FPC board includes M stepped areas, the number of layers of the stepped area is less than N, and the number of layers of adjacent stepped areas is different.

[0062] In this embodiment, as Figure 2 shown, the stepped areas of the FPC are the second area A2 and the third area A3 in the figure, and the non-stepped area is the first area A1 in the figure. The number of layers of the second area A2 and the third area A3 is different.

[0063] The first region A1 includes a first solder mask layer 510, a first circuit layer 210, a second circuit layer 220, a third circuit layer 240, a fifth circuit layer 250, a sixth circuit layer 260, a first flexible core board layer 310, a second flexible core board layer 320, a third flexible core board layer 330, a fourth flexible core board layer 340, a fifth flexible core board layer 350, a first adhesive layer 410, a second adhesive layer 420, a third adhesive layer 430, a fourth adhesive layer 440, and a first solder mask layer 520.

[0064] The second region A2 includes a first solder mask layer 510, a first circuit layer 210, and a first flexible core board layer 310.

[0065] The third region A3 includes a first solder mask layer 510, a first circuit layer 210, a second circuit layer 220, a third circuit layer 240, a first flexible core board layer 310, a second flexible core board layer 320, a third flexible core board layer 330, a first adhesive layer 410, and a second adhesive layer 420.

[0066] In one embodiment, the liquid phase substance includes one of ethylene glycol, ionic liquid, and perfluoropolyether oil.

[0067] It is worth mentioning that after the porous structure of the re-bonding layer is injected with the liquid phase substance, the FPC needs to be pressed. The pressing temperature is between 150°C and 180°C. If the boiling point of the liquid phase substance is too low, it will vaporize during the pressing process, resulting in pores in the bonding layer, which is not conducive to the full bonding of the bonding layer. Therefore, in this embodiment, the boiling point of the liquid phase substance is greater than 180°C. For example, the boiling point of ethylene glycol is 197°C, the boiling point of the ionic liquid is greater than 250°C, and the boiling point of the perfluoropolyether oil is greater than 200°C, which can effectively avoid vaporization during the pressing process, and the liquid phase substance has high thermal stability, effectively avoiding unstable situations during the pressing process. During the laser-controlled depth milling process, it can quickly vaporize, cool down the stepped boundary, and leave no impurities after vaporization, avoiding contamination of subsequent processes.

[0068] In one embodiment, after the step of forming a multi-layer FPC with a stepped structure by using the vertical laser-controlled depth milling process to perform subtractive manufacturing on the stepped area of the FPC, it includes:

[0069] Using acid etching to remove the protective layer on other core boards located outside the circuit layer;

[0070] Making a cover film on the surface of the stepped area to form a multi-layer FPC.

[0071] In this embodiment, the material of the protective layer is copper. Copper can effectively protect each layer of the core board from being ablated by laser. In addition, at the position where the stepped surface is the circuit layer, copper can serve as both the protective layer and the circuit layer. Specifically, in the step of manufacturing each layer of the core board of the FPC, in the inner layer graphic design, a protective layer graphic is designed on the layer where the stepped surface is located; in the production of exposure materials, the exposure polarity of the protective layer graphic is the same as that of the circuit graphic. In this way, since the exposure polarity of the protective layer graphic is the same as that of the circuit graphic and the processing steps are the same, the protective layer graphic and the circuit graphic can be exposed together, simplifying the production process. For this part of the protective layer, it can protect the lower-layer core boards and also serve as the circuit layer. In this way, both the production efficiency is improved and the production cost is reduced.

[0072] After performing subtractive processing on the stepped areas of each layer of the core board, acid etching is used to remove the protective layer except for the one used as the circuit layer, and only the stepped structure of the FPC is retained. Then a cover film is made to cover the stepped structure to isolate air and moisture, prevent oxidation or chemical corrosion of the copper foil, and serve as an insulating layer. The cover film can prevent short circuits between circuits and ensure the stability of signal transmission.

[0073] In one embodiment, the step of processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located includes:

[0074] If the layer where the stepped surface is located is a flexible core board layer, a protective layer is processed on the side of the flexible core board layer without circuits;

[0075] If the layer where the stepped surface is located is a circuit layer, a protective layer is processed on the circuit layer;

[0076] Among them, the cross-sectional shape of the protective layer on the side of the flexible core board layer without circuits is trapezoidal, and the thickness in the middle of the protective layer on the side of the flexible core board layer without circuits is greater than that at the edge.

[0077] In this embodiment, the protective layer that is not used as the circuit layer has a trapezoidal cross-sectional shape. The thickness in the middle of this protective layer is relatively large, while the thickness at the edge is relatively small. The thickness of the protective layer gradually decreases from the middle to the edge. The position of the edge of the protective layer corresponds to the boundary of the stepped area of the adhesive layer. In this way, the strength of the protective layer decreases from the middle to the edge. During the lamination process, the stress received during lamination decreases from the middle to the edge, corresponding to the pressure distribution of the adhesive layer. This enables the porous structure at the boundary of the stepped area of the adhesive layer to reduce stress, avoid excessive extrusion of the porous structure, prevent the liquid phase material from flowing out of the porous structure, and enable the adhesive layer to reduce stress and avoid glue overflow. In addition, during vertical laser controlled depth milling, it can make the cut adhesive layer form a tendency to shrink inward towards the stepped area, facilitating the separation of the stepped area and the non-stepped area of the adhesive layer, thereby improving the separation efficiency.

[0078] Example 2

[0079] In this embodiment, as Figure 2 shown, each layer of the FPC includes a stepped area and a non-stepped area. The stepped areas of the FPC are the second area A2 and the third area A3 in the figure, and the non-stepped area is the first area A1 in the figure.

[0080] The first area A1 includes a first solder mask layer 510, a first circuit layer 210, a second circuit layer 220, a third circuit layer 240, a fifth circuit layer 250, a sixth circuit layer 260, a first flexible core board layer 310, a second flexible core board layer 320, a third flexible core board layer 330, a fourth flexible core board layer 340, a fifth flexible core board layer 350, a first adhesive layer 410, a second adhesive layer 420, a third adhesive layer 430, a fourth adhesive layer 440, and a first solder mask layer 520.

[0081] The second area A2 includes a first solder mask layer 510, a first circuit layer 210, and a first flexible core board layer 310.

[0082] The third area A3 includes a first solder mask layer 510, a first circuit layer 210, a second circuit layer 220, a third circuit layer 240, a first flexible core board layer 310, a second flexible core board layer 320, a third flexible core board layer 330, a first adhesive layer 410, and a second adhesive layer 420.

[0083] In this embodiment, the stepped surface of the second area A2 is the side of the first flexible core board layer 310 facing away from the first circuit layer 210, and a protective layer is formed by processing on the stepped surface of the second area A2; the stepped surface of the third area A3 is the side of the third circuit layer 240 facing away from the first circuit layer 210, and the copper foil is reserved on the third circuit layer 240 of the third area A3 to form a protective layer. In this way, during the vertical laser controlled depth milling process, the layers above the first flexible core board layer 310 in the second area A2 will be removed, and the layers above the third circuit layer 240 in the third area A3 will be removed. Subsequently, a first cover film 320 and a second cover film 630 are respectively made on the surfaces of the second area A2 and the third area A3.

[0084] Since the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, and the fourth adhesive layer 440 located in the second region A2 are respectively provided with hole-like structures at the boundaries adjacent to the first region A1 and the third region A3, and a liquid-phase substance is injected into the hole-like structures, during the vertical laser controlled-depth milling process, the boundaries of the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, and the fourth adhesive layer 440 in the second region A2 are vaporized, which can effectively protect the edges of the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, and the fourth adhesive layer 440 in the first region A1, while the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, and the fourth adhesive layer 440 in the second region A2 are eliminated. Similarly, the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, and the fourth adhesive layer 440 located in the third region A3 are respectively provided with hole-like structures at the boundaries of other adjacent regions, and can also play a role in protecting by vaporization and cooling.

[0085] In this embodiment, the FPC is divided into a stepped region and a non-stepped region. Among them, the stepped regions are the second region A2 and the third region A3 in the figure, and the non-stepped region is the first region A1 in the figure. By making a porous hole-like structure at the boundary of the stepped region of the adhesive layer and injecting a liquid-phase substance into the hole-like structure, during the subtractive process of the vertical laser controlled-depth milling process, by using the function of the liquid-phase substance vaporizing and absorbing heat, the vertical stepped surfaces between the second region A2 and the third region A3 and between the first region A1 and the second region A2 in the figure can be effectively protected, and burns can be effectively avoided.

[0086] Embodiment 3

[0087] In this embodiment, an improved stepped structure multi-layer FPC is provided, which is manufactured by using the manufacturing method of the improved stepped structure multi-layer FPC described in any one of the above embodiments.

[0088] In this embodiment, by making a porous hole-like structure at the boundary of the stepped region of the adhesive layer and injecting a liquid-phase substance into the hole-like structure, during the subtractive process of the vertical laser controlled-depth milling process, by using the function of the liquid-phase substance vaporizing and absorbing heat, the core layers at the boundary of the non-stepped region are cooled and protected, and burns at the boundary of the non-stepped region of each core layer are avoided, so that the stepped structure of the FPC is more complete, thereby effectively improving the yield and quality of the FPC.

[0089] Embodiment 4

[0090] In this embodiment, an electronic device is provided, including the improved stepped structure multi-layer FPC described in any one of the above embodiments.

[0091] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0092] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A manufacturing method of a multi-layer FPC with an improved stepped structure, characterized in that, Including: Manufacturing the core boards of each layer of the FPC, wherein each layer of the core board includes a circuit layer, a flexible core board layer, and an adhesive layer; Determining the stepped area of the FPC, manufacturing a porous hole-like structure at the boundary of the stepped area of the adhesive layer, and processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located; Injecting a liquid phase substance into the hole-like structure; Pressing the core boards of each layer of the FPC in a preset order to obtain the FPC; Adopting a vertical laser controlled depth milling process to perform subtractive manufacturing on the stepped area of the FPC to form a multi-layer FPC with a stepped structure.

2. The manufacturing method of the multi-layer FPC with an improved stepped structure according to claim 1, characterized in that, The step of manufacturing a porous hole-like structure at the boundary of the stepped area of the adhesive layer includes: Using femtosecond laser to ablate at the boundary of the stepped area of the adhesive layer to form a porous hole-like structure.

3. The manufacturing method of the multi-layer FPC with the improved stepped structure according to claim 2, characterized in that, After the step of using femtosecond laser to ablate at the boundary of the stepped area of the adhesive layer to form a porous hole-like structure, the following steps are further included: Irradiating the boundary of the stepped area of the adhesive layer with high-energy rays so that the adhesive layer crosslinks at the boundary of the stepped area.

4. The manufacturing method of the multi-layer FPC with the improved stepped structure according to claim 2, characterized in that, The step of injecting a liquid phase substance into the hole-like structure includes: Injecting the liquid phase substance into the hole-like structure by vacuum impregnation method.

5. The manufacturing method of the multi-layer FPC with an improved stepped structure according to claim 1, characterized in that, The FPC is an N-layer board, the N-layer board includes N circuit layers, N-1 flexible core board layers, N-2 adhesive layers, and 2 solder mask layers. The layers in the N-layer board are alternately and oppositely distributed, and the solder mask layers are located on the outermost sides; The FPC board includes M stepped areas, the number of layers of the stepped area is less than N, and the number of layers of adjacent stepped areas is different.

6. The manufacturing method of the multi-layer FPC with an improved stepped structure according to claim 1, characterized in that, The liquid phase substance includes one of ethylene glycol, ionic liquid, and perfluoropolyether oil.

7. The manufacturing method of the multi-layer FPC with an improved stepped structure according to claim 1, characterized in that, After the step of adopting a vertical laser controlled depth milling process to perform subtractive manufacturing on the stepped area of the FPC to form a multi-layer FPC with a stepped structure, the following steps are included: Adopting acid etching to remove the protective layer on other core boards except those on the circuit layer; Manufacturing a cover film on the surface of the stepped area to form a multi-layer FPC.

8. The manufacturing method of the improved stepped structure multi-layer FPC according to any one of claims 1-7, characterized in that, The step of processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located includes: If the layer where the stepped surface is located is a flexible core board layer, a protective layer is processed on the side without circuits of the flexible core board layer; If the layer where the stepped surface is located is a circuit layer, a protective layer is processed on the circuit layer; Wherein, the cross-sectional shape of the protective layer on the side without circuits of the flexible core board layer is trapezoidal, and the thickness in the middle of the protective layer on the side without circuits of the flexible core board layer is greater than that at the edge.

9. An improved multi-layer FPC with a stepped structure, characterized in that, Manufactured by using the manufacturing method of the improved multi-layer FPC with a stepped structure described in any one of claims 1-8.

10. An electronic device, characterized in that, Including the improved multi-layer FPC with a stepped structure described in claim 9.

Images