Multilayer fpc with improved step structure, method for manufacturing the same, and electronic device

Abstract

The present application relates to a multilayer FPC with improved stepped structure and a manufacturing method thereof, which comprises: manufacturing core plates of each layer of the FPC, wherein each layer of the core plates comprises a circuit layer, a flexible core layer and an adhesive layer; determining a stepped area of the FPC, manufacturing a porous hole structure at the boundary of the stepped area of the adhesive layer, processing a protective layer on the layer where the stepped surface of the stepped area of the FPC is located; injecting a liquid phase material into the hole structure; pressing the core plates of each layer of the FPC in a preset order to obtain the FPC; and using a vertical laser controlled depth milling process to subtractively manufacture the stepped area of the FPC to form the multilayer FPC with stepped structure. During the subtractive processing of the vertical laser controlled depth milling process, the function of heat absorption by gasification of the liquid phase material is used to cool and protect each core layer at the boundary of the non-stepped area, so as to avoid burning 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

TECHNICAL FIELD

[0001] The present application relates to the field of flexible circuit board manufacturing technology, in particular to an improved multi-layer FPC with stepped structure and a manufacturing method thereof, and an electronic device. BACKGROUND

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

[0003] In order to form a stepped structure on a multi-layer FPC, the FPC board needs to be subjected to controlled depth milling processing to form a stepped structure. However, in the existing method for manufacturing a multi-layer FPC board with stepped structure, the controlled depth milling process is prone to inaccurate processing due to low processing precision, which can damage the finished layers of the FPC board and affect the reliability of the product.

[0004] In the prior art, a protective layer is provided on the multi-layer FPC to protect the finished layers of the FPC, so that the laser controlled depth milling only removes 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 precision of the laser controlled depth milling is not enough, the boundary of the non-stepped area may be damaged. SUMMARY

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

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

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

[0008] determining a stepped area of the FPC, manufacturing a porous hole 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 substance into the hole structure;

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

[0011] adopting a vertical laser controlled depth milling process to subtractively manufacture the stepped area of the FPC to form a multi-layer FPC with stepped structure.

[0012] In one embodiment, the step of making a porous hole structure at the boundary of the stepped region of the adhesive layer comprises:

[0013] Ablating at the boundary of the stepped region of the adhesive layer using a femtosecond laser to form a porous hole structure.

[0014] In one embodiment, the step of ablation at the boundary of the stepped region of the adhesive layer using a femtosecond laser to form a porous hole structure further comprises:

[0015] Radiating at the boundary of the stepped region of the adhesive layer using 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 structure comprises:

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

[0018] In one embodiment, the FPC is an N-layer board, the N-layer board comprising N layers of circuit layers, N-1 layers of flexible core board layers, N-2 layers of adhesive layers, and 2 layers of solder mask layers, the layers of the N-layer board being alternately and oppositely distributed, and the solder mask layers being located at the outermost sides.

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

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

[0021] In one embodiment, the step of subtractive manufacturing the stepped region of the FPC using the vertical laser-controlled depth milling process to form the multilayer FPC with a stepped structure further comprises:

[0022] Removing the protective layer on the other core board other than the circuit layer using acid etching;

[0023] Making a cover film on the surface of the stepped region to form the multilayer 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 comprises:

[0025] If the layer where the stepped surface is located is a flexible core board layer, processing a protective layer on the side without a circuit 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 in the circuit layer;

[0027] In the present application, the cross-sectional shape of the protective layer on the side of the flexible core board layer without circuit is trapezoidal, and the thickness of the middle part of the protective layer is greater than that of the edge.

[0028] A multilayer FPC with an improved stepped structure is manufactured by the method for manufacturing a multilayer FPC with an improved stepped structure described in any of the above embodiments.

[0029] An electronic device includes the multilayer FPC with an improved stepped structure described in any of the above embodiments.

[0030] The multilayer FPC with an improved stepped structure and the method for manufacturing the same, and the electronic device, by making the porous hole structure at the boundary of the stepped area of the adhesive layer and injecting the liquid phase material into the hole structure, use the function of heat absorption of the gasification of the liquid phase material to protect the core layers at the boundary of the non-stepped area from burning during the subtractive processing of the vertical laser controlled depth milling process, so that the stepped structure of the FPC is more complete, thereby effectively improving the yield and quality of the FPC. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0032] Figure 1 Flowchart of the method for manufacturing the multilayer FPC with an improved stepped structure of an embodiment;

[0033] Figure 2 Structure diagram of the multilayer FPC with an improved stepped structure of an embodiment. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[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 the positions of the boundaries and edges of each layer in the non-stepped area can still be damaged by burning.

[0036] To this end, the present application provides a manufacturing method of a multi-layer FPC with an improved stepped structure.

[0037] Embodiment 1

[0038] As shown in FIG. 1, which is a manufacturing method of a multi-layer FPC with an improved stepped structure according to an embodiment of the present application, the method comprises: Figure 1

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

[0040] As shown in FIG. 2, the core board of each layer of the FPC comprises a plurality of circuit layers, a plurality of flexible core board layers, and a plurality of adhesive layers, wherein the circuit layer is of metal material and is used to bear the function of circuit, the flexible core board layer is used to support the circuit layer and provide the function of electrical insulation, in some embodiments, the material of the flexible core board layer is PI (Polyimide), and in other embodiments, the material of the flexible core board layer can also be PET (Polyethylene terephthalate) or polyethylene naphthalate. The adhesive layer, also known as the adhesive glue layer or the AD glue layer, is used to bond adjacent core boards, such as the adjacent circuit layer and the flexible core board layer. Figure 2 Step 120, determining the stepped area of the FPC, manufacturing a porous hole 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.

[0041] In this embodiment, the stepped area is determined and divided in the design stage of the FPC, and the stepped area of each layer of the FPC can be determined when manufacturing each layer. 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. The stepped area of the adhesive layer is determined, and the boundary of the stepped area of the adhesive layer is determined. The porous honeycomb hole structure is manufactured at the boundary of each stepped area of each adhesive layer, and the hole structure is used to accommodate the liquid substance.

[0042]

[0043] ​​In addition, the design stage of the FPC not only determines the stepped region, but also determines the stepped surface of the stepped region, which is the layer where the outermost plate of the stepped region is located after the stepped structure is formed. In this embodiment, while the structures of each layer are being made, a protective layer is processed on the layer corresponding to the stepped surface according to the determined stepped surface of the stepped region. The protective layer is used to protect other core plates below the protective layer from being burned by the laser-controlled deep milling.

[0044] Step 130: injecting 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 region. When laser-controlled deep milling is performed, the liquid-phase substance at the boundary vaporizes, absorbs a large amount of heat, and cools down the boundary of the stepped region, so that the temperature at the boundary is lower than that in the stepped region. As a result, the core layers at the boundary of the non-stepped region are protected from burning, and the adhesive layer is also prevented from carbonization, and the flexible core plate is also prevented from delamination. It is worth mentioning that, as the laser-controlled deep milling performs subtractive processing on each layer of the stepped region of the FPC, the liquid-phase substance at the boundary of the stepped region vaporizes, and the hole-like structure is also eliminated, finally leaving the adhesive layer of the non-stepped region or the adjacent stepped region, so that the structure of the remaining adhesive layer is more stable. In addition, in this embodiment, only the adhesive layer is made to have a hole-like structure, and the circuit layer and the flexible core plate layer are not made to have a hole-like structure. The reason is that the circuit layer and the flexible core plate layer are the main base materials of the FPC and bear the main functions of the FPC. Therefore, the circuit layer and the flexible core plate layer are not made to have a hole-like structure, but only the adhesive layer is made to have a hole-like structure, which can effectively ensure the stability of the structure of the circuit layer and the flexible core plate layer of the FPC. In addition, compared with the circuit layer and the flexible core plate layer, it is simpler and easier to make a hole-like structure and inject a liquid-phase substance in the adhesive layer, and the adhesive layer is located between the adjacent circuit layer and the flexible core plate layer, so the heat absorption effect of vaporization can act on the adjacent circuit layer and the flexible core plate layer at the same time. Therefore, the adjacent circuit layer and the flexible core plate layer can be well protected from cooling.

[0046] Step 140: pressing the core plates of each layer of the FPC in a predetermined order to obtain the FPC.

[0047] In this embodiment, since each adhesive layer is provided with a hole-like structure at the boundary of the stepped region, the hole-like structure can absorb the excess adhesive (AD glue) flowing during the pressing process, further effectively preventing glue overflow, so that the structure of each layer of the FPC is more stable, and the pressing effect is better.

[0048] Step 150: using a vertical laser-controlled deep milling process to perform subtractive manufacturing on the stepped region 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 subtractively process each layer above the stepped surface in the stepped region of the FPC to form a stepped structure. Since the stepped surface is provided with a protective layer, the core board below the stepped surface can be effectively protected from being burned out or damaged.

[0050] It is worth mentioning that the porous honeycomb-like hole structure is located in the part cut by laser in the stepped region, so that the liquid phase material can be fully cleared, and residual on the FPC is avoided.

[0051] In this embodiment, by making a porous hole structure at the boundary of the stepped region of the adhesive layer and injecting a liquid phase material into the hole structure, the liquid phase material is used to absorb heat during the subtractive processing of the vertical laser controlled depth milling process, so that each core layer at the boundary of the non-stepped region is cooled and protected from being burned, thereby making the stepped structure of the FPC more complete, and effectively improving the yield and quality of the FPC.

[0052] It is worth mentioning that in some scenarios, in order to avoid the burn of the laser controlled depth milling process at the boundary of the non-stepped region, it is considered to use the laser controlled depth milling process in a low temperature environment or use liquid nitrogen to cooperate with the laser controlled depth milling process, but this is easy to cause the temperature of the FPC to be unstable, and the adhesive layer is easy to shrink due to thermal expansion and contraction, and then the adhesive layer and the flexible core layer are separated, resulting in unstable bonding results of the FPC. Therefore, in this embodiment, the liquid phase material is used to absorb heat, which can effectively avoid the structural instability caused by thermal expansion and contraction of the FPC.

[0053] In one embodiment, the step of making a porous hole structure at the boundary of the stepped region of the adhesive layer includes ablating the boundary of the stepped region of the adhesive layer with a femtosecond laser to form a porous hole structure.

[0054] In this embodiment, a femtosecond laser is used to directionally ablate micropores at the boundary of the stepped region of the adhesive layer to form a porous honeycomb hole structure. The femtosecond laser has the characteristics of high precision and high efficiency, and can accurately directionally ablate micropores at the boundary of the stepped region to form a honeycomb hole with a hole diameter of 3-12 μm. It is worth mentioning that the diameter of the hole of the hole structure is controlled within 3-12 μm, and when the contact angle θ of the liquid phase material and the AD glue is greater than 90°, the capillary pressure generated by the surface tension (γ) forms a negative pressure, which can effectively prevent the liquid phase material from flowing out.

[0055] In one embodiment, after the step of using a femtosecond laser to ablate at the boundary of the stepped region of the adhesive layer to form a porous structure, the method further includes: radiating the boundary of the stepped region of the adhesive layer with high-energy rays to cause the adhesive layer to crosslink at the boundary of the stepped region.

[0056] In this embodiment, high-energy rays include ultraviolet rays, X-rays, etc. High-energy rays are used to irradiate the boundary of the stepped area of ​​the adhesive layer to cross-link it, retain and solidify the honeycomb pore structure, so that the pore structure is shaped and can better inject and accommodate liquid phase substances.

[0057] In one embodiment, after the step of using a femtosecond laser to ablate at the boundary of the stepped region of the adhesive layer to form a porous structure, the method further includes: injecting a liquid phase substance into the porous structure and radiating the boundary of the stepped region of the adhesive layer with high-energy rays to cause the adhesive layer to crosslink at the boundary of the stepped region.

[0058] In this embodiment, after the porous structure is formed, the boundary of the stepped area of ​​the adhesive layer is not directly radiated. Instead, liquid phase material is injected first, followed by high-energy radiation. This allows the porous structure to cross-link and solidify, and forms a nanoscale dense layer at the pore entrance, which restricts the liquid phase material and effectively prevents the liquid phase material in the porous structure from detaching.

[0059] In one embodiment, the step of injecting liquid phase material into the porous structure includes: injecting the liquid phase material into the porous structure by vacuum impregnation.

[0060] In this embodiment, the vacuum impregnation method can effectively inject liquid phase material into the pores of the porous structure, thus fully filling the porous structure.

[0061] In one embodiment, the FPC is an N-layer board, which includes N circuit layers, N-1 flexible core board layers, N-2 adhesive layers, and 2 solder resist layers. The layers in the N-layer board are alternate and distributed in pairs, and the solder resist layers are located on the outermost side. The FPC board includes M stepped regions, the number of layers in each stepped region is less than N, and the number of layers in adjacent stepped regions is different.

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

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

[0064] The second area A2 includes the first anti-solder layer 510, the first circuit layer 210, and the first flexible core layer 310.

[0065] The third area A3 includes the first anti-solder layer 510, the first circuit layer 210, the second circuit layer 220, the third circuit layer 240, the first flexible core layer 310, the second flexible core layer 320, the third flexible core layer 330, the first adhesive layer 410, and the 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-adhesive layer is injected with the liquid phase substance, the FPC needs to be pressed. The pressing temperature is 150-180°C. If the boiling point of the liquid phase substance is too low, it will vaporize during the pressing process, causing air holes in the adhesive layer, which is not conducive to the full bonding of the adhesive 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 ionic liquid is greater than 250°C, and the boiling point of perfluoropolyether oil is greater than 200°C, which can effectively avoid vaporization during the pressing process, and the thermal stability of the liquid phase substance is high, effectively avoiding unstable conditions during the pressing process. During the laser-controlled deep milling process, it can quickly vaporize and cool the step boundary. After vaporization, no impurities are left to avoid pollution of subsequent processes.

[0068] In one embodiment, the step of using a vertical laser-controlled deep milling process to subtractively manufacture the step area of the FPC to form the multi-layer FPC with a step structure includes:

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

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

[0071] In this embodiment, the protective layer is made of copper. Copper effectively protects each core board layer from laser ablation. Furthermore, at the location where the stepped surface is the circuit layer, copper can serve as both a protective layer and a circuit layer. Specifically, in the process of fabricating the core boards of each layer of the FPC, the protective layer pattern is designed in the inner layer patterning layer where the stepped surface is located; in the process of creating the exposure data, the protective layer pattern and the circuit pattern have the same exposure polarity. Thus, since the protective layer pattern and the circuit pattern have the same exposure polarity and the same processing steps, the protective layer pattern and the circuit pattern can be exposed together, simplifying the manufacturing process. This protective layer can both protect the underlying core boards and serve as a circuit layer. This improves production efficiency and reduces production costs.

[0072] After subtractive processing of the stepped areas of each core board, acid etching is used to remove the protective layers except those used as circuit layers, leaving only the stepped structure of the FPC. A cover film is then made to cover the stepped structure, isolating it from air and moisture, preventing copper foil oxidation or chemical corrosion, and serving as an insulating layer. The cover film can prevent short circuits between lines and ensure the stability of signal transmission.

[0073] In one embodiment, the step of processing a protective layer on the layer containing the stepped surface of the stepped region of the FPC includes:

[0074] If the layer containing the stepped surface is a flexible core board layer, a protective layer is processed on the non-wire side of the flexible core board layer.

[0075] If the layer containing the stepped surface is a circuit layer, then a protective layer is fabricated on the circuit layer.

[0076] The protective layer on the non-wire side of the flexible core board layer has a trapezoidal cross-sectional shape, and the thickness of the protective layer on the non-wire side of the flexible core board layer is greater in the middle than at the edge.

[0077] In this embodiment, the protective layer, which is not used as a circuit layer, has a trapezoidal cross-sectional shape. The thickness of the protective layer is greater in the middle and less at the edges, with the thickness gradually decreasing from the middle to the edges. 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 edges. During the pressing process, the stress experienced during pressing decreases from the middle to the edges, corresponding to the pressure distribution of the adhesive layer. This allows the porous structure at the boundary of the stepped area of ​​the adhesive layer to reduce stress, avoid excessive compression of the porous structure, prevent liquid substances from flowing out of the porous structure, and reduce stress on the adhesive layer to prevent adhesive overflow. In addition, during vertical laser controlled deep milling, the cut adhesive layer tends to shrink towards the inside of the stepped area, facilitating the separation of the stepped and non-stepped areas of the adhesive layer, thereby improving the separation efficiency.

[0078] Embodiment 2

[0079] In this embodiment, as shown in FIG. 2, each layer of the FPC includes a stepped region and a non-stepped region. The stepped region of the FPC is the second region A2 and the third region A3 in the figure, and the non-stepped region is the first region Al in the figure. Figure 2 The first region Al includes the first solder resist layer 510, the first circuit layer 210, the second circuit layer 220, the third circuit layer 240, the fifth circuit layer 250, the sixth circuit layer 260, the first flexible core layer 310, the second flexible core layer 320, the third flexible core layer 330, the fourth flexible core layer 340, the fifth flexible core layer 350, the first adhesive layer 410, the second adhesive layer 420, the third adhesive layer 430, the fourth adhesive layer 440, and the first solder resist layer 520.

[0080] The second region A2 includes the first solder resist layer 510, the first circuit layer 210, and the first flexible core layer 310.

[0081] The third region A3 includes the first solder resist layer 510, the first circuit layer 210, the second circuit layer 220, the third circuit layer 240, the first flexible core layer 310, the second flexible core layer 320, the third flexible core layer 330, the first adhesive layer 410, and the second adhesive layer 420.

[0082] In this embodiment, the stepped surface of the second region A2 is the side of the first flexible core layer 310 facing away from the first circuit layer 210, and a protective layer is formed on the stepped surface of the second region A2; the stepped surface of the third region A3 is the side of the third circuit layer 240 facing away from the first circuit layer 210, and a protective layer is formed on the third circuit layer 240 of the third region A3 by retaining the copper skin. In this way, during the vertical laser controlled depth milling process, the layers above the first flexible core layer 310 in the second region A2 and the layers above the third circuit layer 240 in the third region A3 will be removed. Subsequently, the first cover film 320 and the second cover film 630 are respectively made on the surfaces of the second region A2 and the third region A3.

[0083]

[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 the hole-shaped structure at the boundary of the abutting region, and the liquid-phase substance is injected into the hole-shaped structure, 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 gasified at the boundary in the vertical laser controlled-depth milling process, 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, and 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 the hole-shaped structure at the boundary of the other abutting region, which can also play a gasification cooling protection role.

[0085] In the embodiment, the FPC is divided into a stepped region and a non-stepped region, wherein the stepped region is 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. Through the hole-shaped structure with multiple holes made at the boundary of the stepped region of the adhesive layer and the liquid-phase substance injected into the hole-shaped structure, the vertical stepped surface between the second region A2 and the third region A3 and the vertical stepped surface between the first region A1 and the second region A2 can be effectively protected in the subtractive processing process of the vertical laser controlled-depth milling process by using the heat absorption function of the gasification of the liquid-phase substance, thereby effectively avoiding burning.

[0086] Embodiment 3

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

[0088] In the embodiment, through the hole-shaped structure with multiple holes made at the boundary of the stepped region of the adhesive layer and the liquid-phase substance injected into the hole-shaped structure, the core layers at the boundary of the non-stepped region are cooled and protected in the subtractive processing process of the vertical laser controlled-depth milling process by using the heat absorption function of the gasification of the liquid-phase substance, thereby avoiding burning at the boundary of the non-stepped region of the core layers, 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 the embodiment, an electronic device is provided, which includes the multi-layer FPC with an improved stepped structure in any of the above embodiments.

[0091] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, as long as the combination of the technical features does not exist in contradiction, it shall be considered within the scope of the present disclosure.

[0092] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the patent scope of the present application. It shall be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method of manufacturing a multilayer FPC of an improved stepped structure, characterized by, The method comprises the following steps: manufacturing core plates of each layer of the FPC, wherein the core plates of each layer of the FPC comprise a circuit layer, a flexible core plate layer and an adhesive layer; determining a step region of the FPC, manufacturing a porous hole structure at the boundary of the step region of the adhesive layer, and processing a protective layer on the layer where the step surface of the step region of the FPC is located; injecting a liquid phase substance into the hole structure; pressing the core plates of each layer of the FPC in a preset order to obtain the FPC; adopting a vertical laser depth control milling process to subtractively manufacture the step region of the FPC to form a multi-layer FPC with a step structure.

2. The manufacturing method of the multi-layer FPC of the improved step structure according to claim 1, characterized in that, The step of manufacturing a porous hole structure at the boundary of the step region of the adhesive layer comprises: adopting a femtosecond laser to ablate at the boundary of the step region of the adhesive layer to form a porous hole structure.

3. The manufacturing method of multi-layer FPC of improved step structure according to claim 2, wherein, The step of adopting a femtosecond laser to ablate at the boundary of the step region of the adhesive layer to form a porous hole structure is further followed by: irradiating the boundary of the step region of the adhesive layer with high-energy rays to cross-link the adhesive layer at the boundary of the step region.

4. The manufacturing method of multi-layer FPC of improved step structure according to claim 2, wherein, The step of injecting a liquid phase substance into the hole structure comprises: injecting the liquid phase substance into the hole structure by a vacuum impregnation method.

5. The manufacturing method of multi-layer FPC of improved step structure according to claim 1, wherein, The FPC is an N-layer plate, which comprises N layers of circuit layers, N-1 layers of flexible core plate layers, N-2 layers of adhesive layers and 2 layers of anti-solder layers, the layers of the N-layer plate are alternately and oppositely distributed, and the anti-solder layers are located at the outermost sides. The FPC plate comprises M step regions, the number of layers of the step regions is less than N, and the number of layers of adjacent step regions is different.

6. The manufacturing method of multi-layer FPC of improved step structure according to claim 1, wherein, The liquid phase substance comprises one of ethylene glycol, ionic liquid and perfluoropolyether oil.

7. The manufacturing method of multi-layer FPC of improved step structure according to claim 1, wherein, The step of adopting a vertical laser depth control milling process to subtractively manufacture the step region of the FPC to form a multi-layer FPC with a step structure is further followed by: adopting an acid etching to remove the protective layer on the other core plates except the circuit layer; manufacturing a cover film on the surface of the step region to form a multi-layer FPC.

8. The manufacturing method of the multi-layer FPC of the improved step structure according to any one of claims 1 to 7, characterized by, The step of processing a protective layer on the layer where the step surface of the step region of the FPC is located comprises: if the layer where the step surface is located is a flexible core plate layer, processing a protective layer on the side without a circuit of the flexible core plate layer; if the layer where the step surface is located is a circuit layer, processing a protective layer on the circuit layer; wherein the cross-sectional shape of the protective layer on the side without a circuit of the flexible core plate layer is trapezoidal, and the thickness of the middle part of the protective layer on the side without a circuit of the flexible core plate layer is greater than the thickness of the edge.

9. A multilayer FPC of an improved step structure, characterized by, The improved multi-layer FPC with a step structure is manufactured by the method.

10. An electronic device, comprising: The improved multi-layer FPC with a step structure is manufactured by the method.

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