Flexible circuit board and method of manufacturing the same

Abstract

The application relates to the technical field of circuit boards, and discloses a flexible circuit board and a manufacturing method thereof. The flexible circuit board comprises an insulating base, a conductive circuit layer located on opposite surfaces of the insulating base, a covering film covering one side of the conductive circuit layer away from the insulating base, wherein the projection of the covering film completely covers the insulating base, and the covering film comprises a protective film layer and an insulating adhesive layer, the insulating adhesive layer fills the space of the surface of the insulating base which is not covered by the conductive circuit layer, covers the conductive circuit layer, and the protective film layer covers the insulating adhesive layer; the flexible circuit board further comprises a filling heat dissipation layer, the material of the filling heat dissipation layer is mainly metal, part of the filling heat dissipation layer is in the same layer as the conductive circuit layer, and part of the filling heat dissipation layer is in the same layer as the insulating base, and the covering film also completely covers the filling heat dissipation layer; the flexible circuit board comprises an external connection area and a non-external connection area, the filling heat dissipation layer is located in the non-external connection area and is spaced from the conductive circuit in the conductive circuit layer. The application can effectively reduce the risk of local overheating and ablation damage of the flexible circuit board.

Description

Technical Field

[0001] This application relates to the field of circuit board technology, specifically to a flexible circuit board and its manufacturing method. Background Technology

[0002] Flexible printed circuit boards (FPCs) are an indispensable component of circuit systems in the modern electronics industry. Existing FPCs are typically composite structures consisting of an insulating substrate and single- or double-sided copper foil and a cover film. Their heat dissipation capacity largely depends on the area of ​​the patterned copper foil in the final product. When the circuit load is too high, a large amount of heat can easily accumulate in the circuitry. Because the copper foil is patterned and not uniformly distributed throughout the circuit board, localized overheating can occur, potentially leading to ablation damage to the cover film and substrate at the overheated locations, resulting in FPC failure. Therefore, a solution is needed to reduce the risk of ablation damage due to localized overheating when FPCs are under excessive load. Summary of the Invention

[0003] In view of this, this application provides a flexible circuit board and a method for manufacturing the same, so as to reduce the risk of burn-off damage caused by local overheating when the flexible circuit board is subjected to excessive load.

[0004] In one aspect of this application, a flexible circuit board is provided, comprising: an insulating substrate; conductive lines located on opposite sides of the insulating substrate; a cover film covering the conductive lines on the side facing away from the insulating substrate, the projection of the cover film onto the insulating substrate completely covering the substrate; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer filling the space on the surface of the insulating substrate not covered by the conductive lines and covering the conductive lines, the protective film layer covering the insulating adhesive layer; further comprising: a heat dissipation filling layer, the main material of the heat dissipation filling layer being metal, partly co-layered with the conductive lines and partly co-layered with the insulating substrate, the cover film also completely covering the heat dissipation filling layer; the conductive lines of the flexible circuit board cover an area including an external connection area and a non-external connection area; the external connection area is provided with pads for connection to external lines and connected to the conductive lines; the heat dissipation filling layer is located in the non-external connection area and connected to the conductive lines in the conductive lines.

[0005] The flexible circuit board provided in this application adds a metal-filled heat dissipation layer to the non-external connection area of ​​the circuit board. This heat dissipation layer is located in the non-external connection area and does not directly connect to external circuits via pads, but it is physically connected (in direct contact) to the conductive lines in the external connection area. Typically, in a double-sided flexible circuit board, the conductive lines on one side are concentrated in the external connection area to connect to external circuit devices (hereinafter referred to as the front side), while the conductive lines on the other side are mainly connected to the conductive lines on the front side through vias in the external connection area, and do not (or rarely) directly connect to external circuit devices via pads (hereinafter referred to as the back side). This results in the back side conductive line layer primarily passively receiving the current transmitted from external circuit devices by the conductive lines on the front side. This portion of the current, relying solely on vias in the external connection area for current transmission, has relatively small via diameters. While the current can pass smoothly to meet the requirements, the heat generated by the current is difficult to conduct quickly from the front conductive layer to the back conductive layer through these vias. This results in a significant accumulation of heat in the front conductive layer. Furthermore, since the conductive layer itself is a patterned metal layer, heat tends to accumulate locally, especially on the front side, leading to localized overheating. The flexible circuit board provided in this application directly connects the conductive lines in the external connection area to the filling heat dissipation layer in the non-external connection area, establishing a new connection channel from the front conductive layer to the back conductive layer in the non-external connection area. On the one hand, this new connection channel provides more pathways for heat transfer, allowing more heat to be transferred from the front conductive layer to the filling heat dissipation layer and then to the back conductive layer. This facilitates more heat transfer from the front to the back, preventing localized heat accumulation and overheating. On the other hand, since the area where the heat dissipation layer is located is not used for external connections, the heat dissipation layer can occupy a large area without considering the placement of pads for external connections. Therefore, it can form a channel area much larger than the vias in the external connection area (depending on the circuit design, it can even be larger than the total area of ​​all vias). This allows heat to be transferred more quickly from the conductive layers on the front to the back, resulting in a more uniform heat distribution across the flexible circuit board and preventing localized overheating. Furthermore, because the heat dissipation layer replaces part of the insulating substrate, it increases the metal volume of the conductive layers in the thickness direction. The metal in the heat dissipation layer has a higher thermal conductivity and thermal capacity than the insulating substrate. Therefore, this increased metal volume improves the overall thermal capacity of the flexible circuit board, allowing it to hold more heat and further preventing overall or localized overheating. In addition, since the heat dissipation layer is a metal conductor integrated into the conductive lines, acting as an extension of the original conductive lines and replacing part of the insulating substrate, it increases the metal volume of the conductive lines in the thickness direction, thus improving the current-carrying capacity of the conductive lines.

[0006] In some embodiments of this application, the external connection area includes a first external connection area and a second external connection area, which are insulated from each other; the non-external connection area includes a first non-external connection area and a second non-external connection area; the first non-external connection area is provided with a first heat dissipation filling layer, the second non-external connection area is provided with a second heat dissipation filling layer, the first heat dissipation filling layer and the second heat dissipation filling layer are insulated from each other, the first heat dissipation filling layer is connected to the conductive line layer of the first external connection area, and the second heat dissipation filling layer is connected to the conductive line layer of the second external connection area.

[0007] The flexible circuit board provided in this application is, in some cases, divided into multiple interconnected external connection areas that are not interconnected with each other. In this case, by connecting the different interconnected external connection areas with non-external connection areas filled with heat dissipation layers, the heat distribution can be further balanced, local heat accumulation can be avoided, the overall heat dissipation capacity of the flexible circuit board can be improved, and the risk of burn-off damage caused by local overheating can be further reduced.

[0008] In some embodiments of this application, the first external connection area includes a plurality of first sub-line areas, and a first non-external connection area is provided between adjacent first sub-line areas, and a first heat dissipation filling layer is provided in the first non-external connection area; the second external connection area includes a plurality of second sub-line areas, and a second non-external connection area is provided between adjacent second sub-line areas, and a second heat dissipation filling layer is provided in the second non-external connection area.

[0009] In some cases, the flexible circuit board provided in this application has first and second external connection areas that are internally connected, and each of them contains sub-circuit areas. Some sub-circuit areas are far apart. The wiring design can set up non-external connection areas, and the heat dissipation filling layer can be set in these non-external connection areas to adapt to the circuit layout.

[0010] In some embodiments of this application, a portion of the first sub-line area extends along a first direction, and a portion of the first sub-line area extends along a second direction; a first heat-dissipating filling layer is located between the first sub-line area extending along the first direction and the first sub-line area extending along the second direction, and the first heat-dissipating filling layer itself extends partly along the first direction and partly along the second direction; a portion of the second sub-line area extends along the first direction, and a portion of the second sub-line area extends along the second direction; a second heat-dissipating filling layer is located between the second sub-line area extending along the first direction and the second sub-line area extending along the second direction, and the second heat-dissipating filling layer itself extends partly along the first direction and partly along the second direction; the first direction and the second direction have an angle greater than 0.

[0011] In some cases, the flexible circuit board provided in this application does not extend in a single direction but has a second extension direction with a certain angle to the first direction. In this case, an external connection area is usually not set at the corner. Therefore, a heat dissipation filling layer can be set at the corner position, covering both extension directions, thereby further balancing the heat distribution, avoiding local heat accumulation, improving the overall heat dissipation capacity of the flexible circuit board, and further reducing the risk of burn-off damage caused by local overheating.

[0012] In some embodiments of this application, the material filling the heat dissipation layer includes a mixture of metal paste, metal powder, resin powder and glass powder; the metal paste includes silver paste or copper paste; the metal powder includes silver powder or copper powder; the metal powder, resin powder and glass powder are all micron- to nano-sized powders.

[0013] In some embodiments of this application, the flexible circuit board further includes: a supplementary metal layer located between the conductive line layer and the cover film, and between the heat dissipation filling layer and the cover film; the supplementary metal layer is a patterned metal layer structure, the patterned shape being the same as the overall pattern of the conductive line layer and the heat dissipation filling layer; the insulating adhesive layer further fills the gaps between the patterned structures of the supplementary metal layer.

[0014] The flexible circuit board provided in this application typically requires a thinning and grinding process during the formation of the heat-dissipating fill layer to ensure it is flush with the surface of the conductive circuit layer. This may result in the overall copper thickness on that side being lower than the design value. Therefore, by adding a metal layer, the copper thickness on the side where the heat-dissipating fill layer is formed can be compensated for to meet the design value.

[0015] In another aspect of this application, a method for manufacturing a flexible circuit board is also provided, comprising the following steps: providing a processing substrate, wherein the processing substrate is a flexible substrate with copper foil adhered to both sides of an insulating substrate; patterning the copper foil to form a conductive circuit layer; the conductive circuit in the conductive circuit layer covers an area including an external connection area and a non-external connection area; opening a window in the non-external connection area, removing part of the copper foil located in the non-external connection area to expose the underlying insulating substrate; expanding the window, removing part or all of the exposed insulating substrate, the space after removal and the space after copper foil removal together constitute a filling window; forming a filling heat dissipation layer, wherein a filling heat dissipation layer is formed in the filling window, and the main material of the filling heat dissipation layer is metal.

[0016] The flexible circuit board manufacturing method provided in this application is used to manufacture the flexible circuit board provided in this application. A heat-dissipating layer filled with metal material is added to the non-external connection area of ​​the circuit board. This heat-dissipating layer is located in the non-external connection area and does not directly connect to external circuits via pads, but it is physically connected (in direct contact) to the conductive lines in the external connection area. Typically, in a double-sided flexible circuit board, the conductive lines on one side are concentrated in the external connection area to connect to external circuit devices (hereinafter referred to as the front side), while the conductive lines on the other side are mainly connected to the conductive lines on the front side through vias in the external connection area, and do not (or rarely) directly connect to external circuit devices via pads (hereinafter referred to as the back side). This results in the back side conductive line layer primarily passively receiving the current transmitted from external circuit devices by the conductive lines on the front side. This portion of the current, relying solely on vias in the external connection area for current transmission, has relatively small via diameters. While the current can pass smoothly to meet the requirements, the heat generated by the current is difficult to conduct quickly from the front conductive layer to the back conductive layer through these vias. This results in a significant accumulation of heat in the front conductive layer. Furthermore, since the conductive layer itself is a patterned metal layer, heat tends to accumulate locally, especially on the front side, leading to localized overheating. The flexible circuit board provided in this application directly connects the conductive lines in the external connection area to the filling heat dissipation layer in the non-external connection area, establishing a new connection channel from the front conductive layer to the back conductive layer in the non-external connection area. On the one hand, this new connection channel provides more pathways for heat transfer, allowing more heat to be transferred from the front conductive layer to the filling heat dissipation layer and then to the back conductive layer. This facilitates more heat transfer from the front to the back, preventing localized heat accumulation and overheating. On the other hand, since the area where the heat dissipation layer is located is not used for external connections, the heat dissipation layer can occupy a large area without considering the placement of pads for external connections. Therefore, it can form a channel area much larger than the vias in the external connection area (depending on the circuit design, it can even be larger than the total area of ​​all vias). This allows heat to be transferred more quickly from the conductive layers on the front to the back, resulting in a more uniform heat distribution across the flexible circuit board and preventing localized overheating. Furthermore, because the heat dissipation layer replaces part of the insulating substrate, it increases the metal volume of the conductive layers in the thickness direction. The metal in the heat dissipation layer has a higher thermal conductivity and thermal capacity than the insulating substrate. Therefore, this increased metal volume improves the overall thermal capacity of the flexible circuit board, allowing it to hold a higher total amount of heat, further preventing overall or localized overheating.Furthermore, since the heat dissipation filling layer is a metal conductor, it is connected to the conductive line and serves as an extension of the original conductive line to replace part of the insulating substrate. This increases the metal volume of the conductive line in the thickness direction, thus improving the current carrying capacity of the conductive line.

[0017] In some embodiments of this application, the step of forming a heat dissipation filling layer includes: filling a filling window with a corresponding material and curing and smoothing it, wherein the cured and smoothed metal top surface is flush with the surface of the conductive circuit layer on the side opposite to the insulating substrate, thereby forming a heat dissipation filling layer; wherein the curing step is achieved by a sintering process to cure the material of the heat dissipation filling layer.

[0018] In some embodiments of this application, the steps of opening and expanding windows in non-external connection areas are performed before the step of patterning copper foil. Alternatively, the steps of opening and expanding windows in non-external connection areas are performed simultaneously with the step of patterning copper foil.

[0019] In some embodiments of this application, the step of providing the processing substrate includes: cutting the roll of flexible substrate with copper foil adhered to both sides of the insulating substrate according to the process design dimensions to form a processing substrate of a preset size; patterning the copper foil, before forming the conductive lines, further includes: drilling holes in the substrate to form through holes penetrating the processing substrate; copper plating, plating copper on the inner wall of the through holes to make the upper and lower surfaces of the through holes electrically connected; the steps of drilling holes in the substrate and copper plating are performed in the external connection area; after forming the heat dissipation filling layer, further includes: laying a cover film, the cover film covering the surface of the conductive line layer facing away from the insulating substrate, the surface of the insulating adhesive layer facing away from the insulating substrate, and the top surface of the heat dissipation filling layer; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer filling the space of the insulating substrate surface not covered by the conductive line layer and covering the conductive line layer, and the protective film layer covering the insulating adhesive layer. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic cross-sectional view of a flexible circuit board in the prior art. Figure 2 This is a partial cross-sectional structural diagram of a flexible circuit board according to an embodiment of this application; Figure 3 This is a top view of a flexible circuit board according to an embodiment of this application; Figure 4A schematic diagram of a flexible circuit board with a supplementary metal layer according to another embodiment of this application; Figure 5 This is a schematic flowchart of a method for manufacturing a flexible circuit board according to an embodiment of this application; Figure 6 This is a schematic diagram of the structure of the substrate after it has been cut during the manufacturing process of a flexible circuit board according to an embodiment of this application. Figure 7 This is a schematic diagram of the dry film lamination step in a method for manufacturing a flexible circuit board according to an embodiment of this application. Figure 8 This is a schematic diagram of the exposure and development step in a method for manufacturing a flexible circuit board according to an embodiment of this application. Figure 9 This is a schematic diagram illustrating the etching process to remove a portion of the copper foil to create a window during the manufacturing method of a flexible circuit board according to an embodiment of this application. Figure 10 This is a schematic diagram of the ablation removal of the insulating substrate at the opening during the manufacturing process of a flexible circuit board according to an embodiment of this application. Figure 11 This is a schematic diagram showing the metal paste filling window positions during the manufacturing process of a flexible circuit board according to an embodiment of this application. Figure 12 This is a schematic diagram of applying a cover film during the manufacturing process of a flexible circuit board according to an embodiment of this application.

[0022] Explanation of reference numerals in the attached figures: 100 - Substrate; 110 - Insulating substrate; 120 - Copper foil; 121a, 121b, 122a, 122b - Pads; 130, 130a, 130b - Filler heat dissipation layer; 140 - Supplementary metal layer; 200 - Cover film; 300 - Photosensitive film; A - First external connection area; A1, A2 - First sub-circuit area; B - Second external connection area; B1, B2 - Second sub-circuit area. Detailed Implementation

[0023] As mentioned above, existing flexible circuit boards may pose a risk of heat buildup at the conductive lines due to current during use, leading to localized overheating and potential ablation. Taking a flexible circuit board with double-sided conductive lines as an example, refer to... Figure 1This is a schematic diagram of an existing flexible circuit board. Typically, a flexible circuit board consists of an insulating substrate 110 (usually PI, polyimide), conductive circuit layers (originally full-surface copper foil) on both sides of the insulating substrate 110, and a cover film 200 covering the top and bottom surfaces (serving as a protective film). While the copper foil is a full-surface structure before processing, in the final product, the copper foil is processed into patterned conductive circuit layers, which do not completely cover the insulating substrate 110. Due to circuit design, the external connections of the conductive circuits (or conductive patterns) in the conductive circuit layers, especially the external connection pads, are usually relatively concentrated in a certain area (hereinafter referred to as the external connection area); however, on the overall surface of the flexible circuit board, there are areas with concentrated conductive circuits that do not connect to external pads (hereinafter referred to as the non-external connection area). When powered on, the non-external connection area, lacking external pad connections, passively receives heat conduction, resulting in uneven heat distribution across the flexible circuit board. Higher heat accumulation occurs in the external connection area, easily leading to heat buildup and subsequent ablation damage. In double-sided flexible circuit boards, one side typically has more external circuitry connected (hereinafter referred to as the entire side), while the other side has fewer or no external circuitry connected (hereinafter referred to as the back side). Therefore, the conductive layer on the back side primarily passively receives current and heat from the conductive layer on the front side through vias. Due to the small size of the vias, heat cannot be quickly and significantly transferred to the conductive layer on the back side, further contributing to heat accumulation on the conductive layer on the front side. This can easily lead to localized overheating and potentially cause ablation damage.

[0024] In view of this, this application proposes a flexible circuit board and a method for manufacturing the same, in order to reduce the risk of burn-off damage caused by local overheating when the flexible circuit board is subjected to excessive load.

[0025] This application provides a flexible circuit board, comprising: an insulating substrate; conductive circuit layers located on opposite sides of the insulating substrate; a cover film covering the conductive circuit layers on the side facing away from the insulating substrate, the projection of the cover film onto the insulating substrate completely covering the insulating substrate; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer filling the space on the surface of the insulating substrate not covered by the conductive circuit layers and covering the conductive circuit layers; the protective film layer covers the insulating adhesive layer; further comprising: a heat dissipation filling layer, the main material of the heat dissipation filling layer being metal, partly being in the same layer as the conductive circuit layers and partly being in the same layer as the insulating substrate, the cover film also completely covering the heat dissipation filling layer; the area covered by the conductive circuit layers of the flexible circuit board includes an external connection area and a non-external connection area; the external connection area is provided with pads for connection to external circuits and is connected to the conductive circuit layers; the heat dissipation filling layer is located in the non-external connection area and is connected to the conductive circuits in the conductive circuit layers.

[0026] This application also provides a method for manufacturing a flexible circuit board, which includes the following steps: providing a processing substrate, wherein the processing substrate is a flexible substrate with copper foil pasted on both sides of an insulating substrate; patterning the copper foil to form a conductive circuit layer; the conductive circuit in the conductive circuit layer covers an area including an external connection area and a non-external connection area; opening a window in the non-external connection area, removing part of the copper foil located in the non-external connection area to expose the insulating substrate underneath; expanding the window, removing part or all of the exposed insulating substrate, the space after removal and the space after copper foil removal together constitute a filling window; forming a filling heat dissipation layer, wherein a filling heat dissipation layer is formed in the filling window, and the main material of the filling heat dissipation layer is metal.

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Example 1 This embodiment provides a flexible circuit board, referenced... Figure 2 ,include: Insulating substrate 110; The conductive circuit layer is located on opposite sides of the insulating substrate 110; in other words, the flexible circuit board is a double-sided circuit board; the conductive circuit layer is located at the position of copper foil 120 in the figure; copper foil 120 is an unpatterned conductive circuit layer. A cover film 200 covers the conductive circuit layer on the side facing away from the insulating substrate 110, and the projection of the cover film onto the insulating substrate completely covers the insulating substrate; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer filling the space on the surface of the insulating substrate not covered by the conductive circuit layer. Figure 2 The insulating adhesive layer filling the space is shielded by the conductive circuit layer and covers the conductive circuit layer; the protective film layer covers the insulating adhesive layer (for simplicity, ...). Figure 2 The image only shows the cover film 200, without clearly distinguishing between the protective film layer and the insulating adhesive layer. Also includes: The heat dissipation layer 130 is filled with metal as its main material. Part of the heat dissipation layer 130 is in the same layer as the conductive circuit layer and part is in the same layer as the insulating substrate 110. The cover film 200 completely covers the heat dissipation layer 130. The conductive circuit layer of the flexible circuit board covers an area including an external connection area and a non-external connection area; the external connection area is provided with pads for connecting to external circuits and is connected to the conductive circuit layer; the heat dissipation layer 130 is located in the non-external connection area and is connected to the conductive circuits in the conductive circuit layer.

[0029] The flexible circuit board provided in this embodiment adds a metal-filled heat dissipation layer 130 to the non-external connection area of ​​the circuit board. The heat dissipation layer 130 is located in the non-external connection area and does not directly connect to the external circuit through the pads, but it is connected (physically in direct contact) to the conductive lines in the external connection area. As mentioned above, in a typical double-sided circuit board, the conductive lines on one side are concentrated in the external connection area to connect to external circuit devices (hereinafter referred to as the front side), while the conductive lines on the other side are mainly connected to the conductive lines on the front side through vias in the external connection area, and do not (or rarely) directly connect to external circuit devices through the pads (hereinafter referred to as the back side). This results in the conductive line layer on the back side mainly passively receiving the current transmitted from the external circuit devices by the conductive lines on the front side. This portion of the current, relying solely on vias in the external connection area for current transmission, has relatively small via diameters. While the current can pass smoothly to meet the requirements, the heat generated by the current is difficult to conduct quickly from the front conductive layer to the back conductive layer through these vias. This results in a significant accumulation of heat in the front conductive layer. Furthermore, since the conductive layer itself is a patterned metal layer, heat tends to accumulate locally, especially on the front side, leading to localized overheating. The flexible circuit board provided in this application directly connects the conductive lines in the external connection area to the filling heat dissipation layer 130 in the non-external connection area, establishing a new connection channel from the front conductive layer to the back conductive layer in the non-external connection area. This new connection channel provides more pathways for heat transfer, allowing more heat to be transferred from the front conductive layer to the filling heat dissipation layer and then to the back conductive layer, thus preventing localized heat accumulation and overheating. On the other hand, since the area where the heat dissipation layer is located is not used for external connections, the heat dissipation layer can occupy a large area without considering the placement of the pads for external connections. Therefore, it can form a channel area much larger than the vias in the external connection area (depending on the circuit design, it can even be larger than the total area of ​​all vias). This allows heat to be transferred more quickly from the conductive layers on the front to the conductive layers on the back, enabling the overall heat distribution of the flexible circuit board to reach a more balanced state more quickly, thus preventing heat accumulation in localized areas and avoiding localized overheating. Furthermore, since the heat dissipation layer 130 replaces part of the volume of the insulating substrate 110, it increases the metal volume of the conductive layers in the thickness direction. The metal of the heat dissipation layer 130 has a higher thermal conductivity and heat capacity than the insulating substrate. Therefore, this increased metal volume can improve the overall heat capacity of the flexible circuit board, meaning the flexible circuit board can hold a higher total amount of heat, further preventing overall or localized overheating of the flexible circuit board.Furthermore, since the heat dissipation layer 130 is a metal conductor connected to the conductive line, and serves as an extension replacement of the original conductive line's insulating substrate 110, the metal volume of the conductive line is increased in the thickness direction, thus enhancing the current carrying capacity of the conductive line.

[0030] Further reference Figure 3 In some embodiments of this application, the external connection area includes a first external connection area A and a second external connection area B, which are insulated from each other; the non-external connection area includes a first non-external connection area and a second non-external connection area; the first non-external connection area is provided with a first heat dissipation filling layer 130a, and the second non-external connection area is provided with a second heat dissipation filling layer 130b, which are insulated from each other.

[0031] The flexible circuit board provided in this embodiment is, in some cases, divided into multiple external connection areas that are internally connected but not interconnected (e.g., Figure 3 (As shown in the first external connection area A and the second external connection area B). In this case, non-external connection areas filled with heat dissipation layers 130a and 130b are respectively set in the first external connection area A and the second external connection area B, which are connected internally. This can further balance the heat distribution, avoid local heat accumulation, improve the overall heat dissipation capacity of the flexible circuit board, and further reduce the risk of burn-off damage caused by local overheating.

[0032] Furthermore, in some embodiments of this application, the first external connection area A includes multiple first sub-line areas A1 and A2, and a first non-external connection area is provided between adjacent first sub-line areas A1 and A2, and the first heat dissipation layer 130a is provided in the first non-external connection area; the second external connection area B includes multiple second sub-line areas B1 and B2, and a second non-external connection area is provided between adjacent second sub-line areas B1 and B2, and the second heat dissipation layer 130b is provided in the second non-external connection area.

[0033] For details, please refer to the following: Figure 3 It should be noted beforehand that, for simplicity, the diagram only shows the location of the pads and does not display the corresponding conductive lines. Furthermore, in the actual top view, the pads are exposed by the cover film 200, while the heat dissipation filling layer is covered by the cover film 200; the two will not appear in the same view. Figure 3 The display has been simplified only to make it easier to show the relative positional relationship between the two.

[0034] refer to Figure 3The first external connection area A includes two first sub-line areas A1 and A2, each equipped with pads 121a and 122a for connecting to devices. A non-external connection area (the boundary is not clearly defined in the figure) is located between the two first sub-line areas A1 and A2, and a heat dissipation layer 130a is provided in this non-external connection area. The two first sub-line areas A1 and A2 are both located within the first external connection area A. They are not completely separated by the non-external connection area; rather, due to circuit design, they form two relatively concentrated areas of lines. They are connected by bypassing the non-external connection area (not specifically shown in the figure). In other words, the connecting lines between two relatively far concentrated areas of lines do not evenly cover the unoccupied space between them; therefore, this unoccupied space forms the non-external connection area. Similarly, the second external connection area B includes two second sub-circuit areas B1 and B2, which are respectively provided with pads 121b and 122b for connecting to devices. A non-external connection area (the boundary is not clearly defined in the figure) is provided between the two second sub-circuit areas B1 and B2, and a heat dissipation layer 130b is provided in the non-external connection area.

[0035] In some cases, the flexible circuit board provided in this embodiment has first and second external connection areas that are internally connected, and each of them also contains sub-circuit areas. Some sub-circuit areas are far apart, and the wiring design can set up non-external connection areas. The heat dissipation filling layer can be set in these non-external connection areas to adapt to the circuit layout.

[0036] Furthermore, such as Figure 3 As shown, in some embodiments of this application, a portion of the first sub-line region A1 extends along the first direction X, and a portion of the first sub-line region A2 extends along the second direction Y; the first heat-dissipating filling layer 130a is located between the first sub-line region A1 extending along the first direction X and the first sub-line region A2 extending along the second direction Y, and the first heat-dissipating filling layer 130a itself extends partly along the first direction X and partly along the second direction Y; similarly, a portion of the second sub-line region B1 extends along the first direction X, and a portion of the second sub-line region B2 extends along the second direction Y; the second heat-dissipating filling layer 130b is located between the second sub-line region B1 extending along the first direction X and the second sub-line region B2 extending along the second direction Y, and the second heat-dissipating filling layer 130b itself extends partly along the first direction X and partly along the second direction Y; the first direction X and the second direction Y have an angle greater than 0.

[0037] In some cases, the flexible circuit board provided in this embodiment does not extend in a single direction but has a second direction Y with a certain angle to the first direction X. The flexible circuit board extends in both directions simultaneously. In this case, the corner (i.e., the angle between the two extension directions) is usually not provided with an external connection area, that is, this is a non-external connection area. Therefore, the heat dissipation filling layer (130a, 130b) can be set at the corner position to cover the two extension directions, thereby further balancing the heat distribution, avoiding local heat accumulation, improving the overall heat dissipation capacity of the flexible circuit board, and further reducing the risk of burn-off damage caused by local overheating.

[0038] Furthermore, in some embodiments of this application, the material filling the heat dissipation layer 130 includes a mixture of metal paste, metal powder, resin powder, and glass powder; the mixture fills the corresponding spaces and, after curing, forms the heat dissipation layer 130. The metal paste includes silver paste or copper paste; the metal powder includes silver powder or copper powder; the metal powder, resin powder, and glass powder are all micron- to nano-sized powders. On the one hand, silver or copper has good thermal conductivity, making it suitable for heat dissipation. On the other hand, since silver or copper is commonly used in circuit board manufacturing processes, using silver or copper as the main material for the heat dissipation layer facilitates compatibility with existing technologies and is easy to implement.

[0039] Furthermore, it should be noted that when the heat dissipation filling layer 130 enters the layer containing the insulating substrate 110, it will connect the conductive lines on both sides. Therefore, the heat dissipation filling layer 130 only connects the upper and lower conductive lines (copper foil) that were originally connected by through holes in the external connection area. For the upper and lower conductive lines that were originally not connected by insulation gaps, even if they are located in the non-external connection area, the heat dissipation filling layer 130 is not provided.

[0040] In some embodiments of this application, reference is made to Figure 4 The flexible circuit board also includes: a supplementary metal layer 140, which is located between the conductive line layers and the cover film 200 on both sides, and between the heat dissipation layer 130 and the cover film 200; the supplementary metal layer 140 is a patterned metal layer structure, and the patterned shape is the same as the overall pattern of the conductive line layers and the heat dissipation layer 130; the insulating adhesive layer also fills the gaps between the patterned structures of the supplementary metal layer 140.

[0041] The flexible circuit board provided in this application has two main drawbacks. First, during the formation of the heat dissipation filling layer, a thinning and grinding process is usually required to make the heat dissipation filling layer flush with the surface of the conductive circuit layer. This may result in the overall copper thickness on that side being lower than the design value. Second, due to the limited 120mm size of the copper foil in the substrate, it often does not meet the design copper thickness. Therefore, it is usually necessary to electroplate on both sides to supplement the copper thickness and form a supplementary metal layer to meet the design value.

[0042] Figure 4The diagram also clearly shows the protective film layer 220 and the insulating adhesive layer 210 included in the cover film 200. The projections of the insulating adhesive layer 210 and the protective film layer 220 onto the insulating substrate both cover the full area of ​​the insulating substrate. The patterned shape of the supplementary metal layer 140 is the same as the overall shape of the circuit layer and the heat dissipation filling layer 130. The insulating adhesive layer 210 fills the gaps between the patterned metal layers (including the conductive circuit layer and the supplementary metal layer 140) and also covers these patterned metal layers. The protective film layer 220 covers the insulating adhesive layer.

[0043] Example 2 This embodiment provides a method for manufacturing a flexible circuit board, used to manufacture the flexible circuit board provided in Embodiment 1 above, with reference to... Figure 5 This includes the following steps: Figures 6-12 The steps illustrate the various structural states of local locations on the flexible circuit board during the manufacturing process, but only show examples such as... Figure 3 The area connecting the central and non-central regions, that is, the area near the heat dissipation layer 130a or 130b, is not shown in other locations. The conductive line layer is only simplified so that the positional relationship between the conductive line and the heat dissipation layer 130 can be shown.

[0044] refer to Figure 6 The processing substrate 100 is provided. The processing substrate 100 is a flexible substrate with copper foil 120 pasted on both sides of the insulating substrate 110. The copper foil 120 is the conductive circuit layer before processing.

[0045] refer to Figure 7 and Figure 8 A patterned copper foil 120 is used to form a conductive circuit layer; the conductive circuits in the conductive circuit layer cover areas including external connection areas and non-external connection areas.

[0046] refer to Figure 9 A window is opened in the non-external connection area, and part of the copper foil 120 located in the non-external connection area is removed to expose the insulating substrate 110 underneath.

[0047] refer to Figure 10 The window is expanded to remove part or all of the exposed insulating substrate 110. The space after removal, together with the space removed by the copper foil 120, constitutes the filling window.

[0048] refer to Figure 11 A heat dissipation layer 130 is formed in the filling window, and the main material of the heat dissipation layer 130 is metal.

[0049] The flexible circuit board manufacturing method provided in this embodiment is used to manufacture the flexible circuit board provided in Embodiment 1 above. A heat dissipation layer 130 filled with metal material is added to the non-external connection area of ​​the circuit board. The heat dissipation layer 130 is located in the non-external connection area and does not directly connect to the external circuit through the pads, but it is connected to the conductive lines in the external connection area (physically in direct contact). As mentioned above, in a typical double-sided circuit board, the conductive lines on one side are concentrated in the external connection area to connect to external circuit devices (hereinafter referred to as the front side), while the conductive lines on the other side are mainly connected to the conductive lines on the front side through vias in the external connection area, and do not (or rarely) directly connect to external circuit devices through the pads (hereinafter referred to as the back side). This results in the conductive line layer on the back side mainly passively receiving the current transmitted from the external circuit devices by the conductive lines on the front side. This portion of the current, relying solely on vias in the external connection area for current transmission, has relatively small via diameters. While the current can pass smoothly to meet the requirements, the heat generated by the current is difficult to conduct quickly from the front conductive layer to the back conductive layer through these vias. This results in a significant accumulation of heat in the front conductive layer. Furthermore, since the conductive layer itself is a patterned metal layer, heat tends to accumulate locally, especially on the front side, leading to localized overheating. The flexible circuit board provided in this application directly connects the conductive lines in the external connection area to the filling heat dissipation layer 130 in the non-external connection area, establishing a new connection channel from the front conductive layer to the back conductive layer in the non-external connection area. This new connection channel provides more pathways for heat transfer, allowing more heat to be transferred from the front conductive layer to the filling heat dissipation layer and then to the back conductive layer, thus preventing localized heat accumulation and overheating. On the other hand, since the area where the heat dissipation layer is located is not used for external connections, the heat dissipation layer can occupy a large area without considering the placement of the pads for external connections. Therefore, it can form a channel area much larger than the vias in the external connection area (depending on the circuit design, it can even be larger than the total area of ​​all vias). This allows heat to be transferred more quickly from the conductive layers on the front to the conductive layers on the back, enabling the overall heat distribution of the flexible circuit board to reach a more balanced state more quickly, thus preventing heat accumulation in localized areas and avoiding localized overheating. Furthermore, since the heat dissipation layer 130 replaces part of the volume of the insulating substrate 110, it increases the metal volume of the conductive layers in the thickness direction. The metal of the heat dissipation layer 130 has a higher thermal conductivity and heat capacity than the insulating substrate. Therefore, this increased metal volume can improve the overall heat capacity of the flexible circuit board, meaning the flexible circuit board can hold a higher total amount of heat, further preventing overall or localized overheating of the flexible circuit board.Furthermore, since the heat dissipation layer 130 is a metal conductor connected to the conductive line, and serves as an extension replacement of the original conductive line's insulating substrate 110, the metal volume of the conductive line is increased in the thickness direction, thus enhancing the current carrying capacity of the conductive line.

[0050] Furthermore, in some embodiments of this application, the step of forming the heat dissipation filling layer 130 includes: filling the filling window with a corresponding material and curing and smoothing it, wherein the cured and smoothed metal top surface is flush with the surface of the conductive circuit layer on the side opposite to the insulating substrate 110, thereby forming the heat dissipation filling layer 130. The corresponding material is the material for the heat dissipation filling layer 130 as described in Embodiment 1 above.

[0051] The curing step involves using a sintering process to solidify the material filling the heat dissipation layer.

[0052] Compared to conventional annealing, sintering is more suitable for curing large-area metal slurries. Conventional annealing only uses general through-hole curing, while sintering is more suitable for large-area metal slurries and other powder mixtures.

[0053] In this embodiment, reference Figure 7 , Figure 8 The steps for patterning copper foil 120 include: A photosensitive film 300 is attached to the surface of a copper foil. After exposure and development, the circuit pattern is transferred, and the photosensitive film 300 takes on the shape of the circuit pattern. Then, using the patterned photosensitive film 300 as a mask, the copper foil 120 is etched to pattern the copper foil, completing the formation of the conductive pattern and forming a conductive circuit layer.

[0054] Furthermore, in some embodiments of this application, the steps of opening and expanding windows in non-external connection areas are performed before the step of patterning copper foil 120. Alternatively, the steps of opening and expanding windows in non-external connection areas are performed simultaneously with the step of patterning copper foil 120.

[0055] The steps of window etching in non-external connection areas and further expanding the window to ablate the substrate can be performed separately before the patterned copper foil step, or simultaneously during the patterned copper foil step. That is, when etching the copper foil, the copper foil corresponding to the preset position of the non-conductive heat dissipation layer is removed at the same time. Both methods are feasible and compatible with different process requirements.

[0056] Furthermore, it should be noted that the figure only shows the steps of patterning the copper foil 120 on one side and forming the heat dissipation layer 130. The copper foil 120 on the other side also underwent the steps of film application and patterning, but did not undergo windowing and filling to form the heat dissipation layer 130. Therefore, the display of film application and patterning of the copper foil 120 on the other side is omitted, and only the position of the copper foil 120 is shown.

[0057] In some embodiments of this application, the step of providing the processed substrate includes: Cutting: The roll of flexible substrate with copper foil 120 pasted on both sides of the insulating substrate 110 is cut according to the process design dimensions to form a processing substrate of the preset size.

[0058] Before the patterned copper foil 120 forms a conductive circuit, it also includes: Drilling holes in the substrate to form through holes that penetrate the substrate; Electroplating involves plating copper onto the inner wall of a through-hole to make the upper and lower surfaces of the through-hole electrically connected. The substrate drilling and copper plating processes are carried out in the external connection area.

[0059] In some embodiments, the process further includes forming an initial supplementary metal layer covering the copper foil 120 and filling the heat dissipation layer 130, and then patterning the copper foil 120 together with the copper foil 120 to form a patterned supplementary metal layer 140.

[0060] After forming the heat dissipation filling layer, it also includes: refer to Figure 12 A cover film 200 is laid, covering the surface of the conductive circuit layer facing away from the insulating substrate 110, the surface of the insulating adhesive layer facing away from the insulating substrate, and the top surface of the heat dissipation layer 130. The cover film 200 includes a protective film layer and an insulating adhesive layer. The insulating adhesive layer fills the space on the surface of the insulating substrate not covered by the conductive circuit layer and covers the conductive circuit layer. The protective film layer covers the insulating adhesive layer (for simplicity, ...). Figure 12 Only the cover film 200 is shown, and the protective film layer and the insulating adhesive layer are not clearly distinguished. If there is a supplementary metal layer 140, it covers the surface of the supplementary metal layer 140 facing away from the insulating substrate 110 and the surface of the insulating adhesive layer facing away from the insulating substrate.

[0061] The solutions of this application have been disclosed above through embodiments. Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A flexible circuit board, characterized in that, include: Insulating substrate; Conductive circuit layers are located on opposite sides of the insulating substrate; A cover film is applied to the side of the conductive circuit layer facing away from the insulating substrate, and the projection of the cover film onto the insulating substrate completely covers the insulating substrate; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer filling the space on the surface of the insulating substrate not covered by the conductive circuit layer, and covering the conductive circuit layer; The protective film layer covers the insulating adhesive layer; Also includes: A heat dissipation layer is provided, the main material of which is metal. Part of the heat dissipation layer is in the same layer as the conductive circuit layer and part of which is in the same layer as the insulating substrate. The cover film also completely covers the heat dissipation layer. The conductive circuit layer of the flexible circuit board covers an area including an external connection area and a non-external connection area; the external connection area is provided with pads for connecting to external circuits and is connected to the conductive circuit layer; the heat dissipation filling layer is located in the non-external connection area and is connected to the conductive circuits in the conductive circuit layer.

2. The flexible circuit board according to claim 1, characterized in that, The external connection area includes a first external connection area and a second external connection area, which are insulated from each other. The non-external connection area includes a first non-external connection area and a second non-external connection area. The first non-external connection area is provided with a first heat dissipation filling layer, and the second non-external connection area is provided with a second heat dissipation filling layer. The first heat dissipation filling layer and the second heat dissipation filling layer are insulated from each other. The first heat dissipation filling layer is connected to the conductive line layer of the first external connection area, and the second heat dissipation filling layer is connected to the conductive line layer of the second external connection area.

3. The flexible circuit board according to claim 2, characterized in that, The first external connection area includes multiple first sub-line areas, and a first non-external connection area is provided between adjacent first sub-line areas. The first heat dissipation filling layer is provided in the first non-external connection area. The second external connection area includes multiple second sub-line areas, and a second non-external connection area is provided between adjacent second sub-line areas. The second heat dissipation filling layer is provided in the second non-external connection area.

4. The flexible circuit board according to claim 3, characterized in that, A portion of the first sub-line area extends along a first direction, and a portion of the first sub-line area extends along a second direction; the first filling heat dissipation layer is located between the first sub-line area extending along the first direction and the first sub-line area extending along the second direction, and the first filling heat dissipation layer itself extends partly along the first direction and partly along the second direction. A portion of the second sub-circuit area extends along the first direction, and a portion of the second sub-circuit area extends along the second direction; the second filling heat dissipation layer is located between the second sub-circuit area extending along the first direction and the second sub-circuit area extending along the second direction, and the second filling heat dissipation layer itself extends partly along the first direction and partly along the second direction; The first direction and the second direction have an angle greater than 0.

5. The flexible circuit board according to any one of claims 1-4, characterized in that, The material filling the heat dissipation layer includes a mixture of metal paste, metal powder, resin powder and glass powder; the metal powder includes silver powder or copper powder; the metal paste includes silver paste or copper paste; the metal powder, the resin powder and the glass powder are all micron- to nano-sized powders.

6. The flexible circuit board according to any one of claims 1-4, characterized in that, Also includes: A supplementary metal layer is provided, located between the conductive circuit layer and the cover film, and between the heat dissipation filling layer and the cover film; the supplementary metal layer is a patterned metal layer structure, and the patterned shape is the same as the overall pattern of the conductive circuit layer and the heat dissipation filling layer. The insulating adhesive layer also fills the gaps between the patterned structures of the supplementary metal layer.

7. A method for manufacturing a flexible circuit board, used to manufacture the flexible circuit board according to any one of claims 1-6, characterized in that, Includes the following steps: A processing substrate is provided, wherein the processing substrate is a flexible substrate with copper foil pasted on both sides of an insulating substrate; The copper foil is patterned to form a conductive circuit layer; The conductive lines in the conductive line layer cover an area that includes an external connection area and a non-external connection area. Open a window in the non-external connection area, remove part of the copper foil in the non-external connection area, and expose the insulating substrate underneath; The expanded window removes part or all of the exposed insulating substrate, and the space after removal, together with the space where the copper foil is removed, forms a filling window. A heat dissipation filling layer is formed in the filling window, and the main material of the heat dissipation filling layer is metal.

8. The method for manufacturing a flexible circuit board according to claim 7, characterized in that, The step of forming the heat dissipation filling layer includes: The appropriate material is filled into the filling window and cured and smoothed. The cured and smoothed metal top surface is flush with the surface of the conductive circuit layer on the side away from the insulating substrate, forming the filling heat dissipation layer. The curing step involves using a sintering process to solidify the material filling the heat dissipation layer.

9. The method for manufacturing a flexible circuit board according to claim 7, characterized in that, The steps of opening a window in the non-external connection area and expanding the window are performed before the step of graphically representing the copper foil. or, The steps of opening a window in the non-external connection area and expanding the window are performed simultaneously with the step of graphically representing the copper foil.

10. The method for manufacturing a flexible circuit board according to claim 7, characterized in that, The steps for providing the processing substrate include: Cutting involves cutting a roll of flexible substrate with copper foil adhered to both sides of the insulating substrate according to the dimensions designed in the process, forming a pre-designed processing substrate. Before patterning the copper foil to form the conductive circuit, the method further includes: Drilling holes in the substrate to form through holes penetrating the processed substrate; Electroplating involves plating copper onto the inner wall of a through-hole to make the upper and lower surfaces of the through-hole electrically connected. The substrate drilling and copper plating steps are performed in the external connection area; After forming the heat dissipation filling layer, the method further includes: A cover film is laid, which covers the surface of the conductive circuit layer facing away from the insulating substrate, the surface of the insulating adhesive layer facing away from the insulating substrate, and the top surface of the heat dissipation filling layer; the cover film includes a protective film layer and an insulating adhesive layer, the insulating adhesive layer fills the space on the surface of the insulating substrate not covered by the conductive circuit layer and covers the conductive circuit layer, and the protective film layer covers the insulating adhesive layer.

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