Preparation method of flexible printed circuit board and flexible printed circuit board

Abstract

The invention discloses a preparation method of a flexible printed circuit board and the flexible printed circuit board. Comprising a first copper layer, a first liquid crystal polymer layer, a second copper layer, a second liquid crystal polymer layer and a third copper layer which are sequentially stacked in the first direction. The flexible printed circuit board is provided with a hollowed-out opening, and the hollowed-out opening penetrates through the first copper layer, the first liquid crystal polymer layer and the second copper layer in the first direction. In the second direction, the first copper layer comprises a first wall part facing the hollowed-out opening, and the second copper layer comprises a second wall part facing the hollowed-out opening. The first wall part and the second wall part extend towards the center of the hollow opening in the second direction, and the second wall part exceeds the first wall part. The second copper layer includes a first surface facing the first copper layer, and the first wall portion, the first surface and the second wall portion together form a first step structure. And the step structure can bear the liquid crystal polymer of the first liquid crystal polymer layer which is casted out. The amount of excessive glue accumulated to the third copper layer is reduced, and the influence of the excessive glue on the circuit board is reduced.

Description

Technical Field

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

[0002] During the current LCP FPC lamination process, the LCP material melts due to heat, causing glue overflow. The amount of overflowed glue increases proportionally with the thickness of the board. This can lead to product quality issues such as large product expansion and contraction deviations, and glue overflowing into other areas of the product, obscuring PADs and circuits, and affecting the size of the cover opening area. This can lead to a series of problems such as reduced production yield and high scrap rate. Summary of the Invention

[0003] The present application aims to provide a flexible printed circuit board and a preparation method thereof, aiming to reduce the impact of glue overflow on the circuit board.

[0004] In a first aspect, the present application provides a method for manufacturing a flexible printed circuit board, comprising: providing a first copper layer, a second copper layer, a third copper layer, a first liquid crystal polymer layer, and a second liquid crystal polymer layer, and sequentially stacking the first copper layer, the first liquid crystal polymer layer, the second copper layer, the second liquid crystal polymer layer, and the third copper layer along a first direction. A hollow opening is formed throughout the first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer, and the second liquid crystal polymer layer, wherein the hollow opening extends through the first copper layer, the first liquid crystal polymer layer, and the second copper layer along the first direction. In a second direction, the first copper layer includes a first wall facing the hollow opening, and the second copper layer includes a second wall facing the hollow opening. Both the first wall and the second wall extend along the second direction toward the center of the hollow opening, and the second wall extends beyond the first wall. The second copper layer includes a first surface facing the first copper layer, and the first wall, the first surface, and the second wall together form a first step structure. The first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer and the second liquid crystal polymer layer are subjected to hot pressing treatment along a first direction to melt the first liquid crystal polymer layer and cast the molten first liquid crystal polymer layer onto the first step structure.

[0005] In some embodiments, the first copper layer includes a first edge, the second copper layer includes a second edge, the first edge and the second edge extend in the same direction, and the second edge extends beyond the first edge. The first edge, the first surface, and the second edge together form a fourth step structure.

[0006] When the first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer and the second liquid crystal polymer layer are subjected to a heat pressing process, the first liquid crystal polymer layer in a molten state is cast onto the fourth stepped structure.

[0007] In the above scheme, the hollow opening can remove redundant copper foil, adjust the circuit spacing of the circuit board, reduce the capacitive coupling between adjacent wires, improve the stability of signal transmission, and optimize the electrical performance of the circuit board. The first copper layer, the first liquid crystal polymer layer, the second copper layer, the second liquid crystal polymer layer and the third copper layer are stacked in sequence along the first direction, and a first step structure formed by the first wall, the first surface and the second wall is formed at the hollow opening. During the lamination process of the flexible printed circuit board, the first step structure will receive the liquid crystal polymer of the first liquid crystal polymer layer that is cast due to the pressure of the first copper layer and the second copper layer. As a result, during the lamination process, a portion of the liquid crystal polymer remains on the first surface and does not continue to cast to the third copper layer. This can reduce the amount of glue overflow accumulated on the third copper layer and reduce the impact of glue overflow on PAD (soldering board), circuits and electrical components.

[0008] In a second aspect, the present application provides a flexible printed circuit board prepared according to the method described in the first aspect, comprising a first copper layer, a first liquid crystal polymer layer, a second copper layer, a second liquid crystal polymer layer, and a third copper layer stacked in sequence along a first direction. The flexible printed circuit board is provided with a hollow opening, which extends through the first copper layer, the first liquid crystal polymer layer, and the second copper layer along the first direction. In a second direction, the first copper layer includes a first wall facing the hollow opening, and the second copper layer includes a second wall facing the hollow opening. Both the first wall and the second wall extend toward the center of the hollow opening along the second direction, and the second wall extends beyond the first wall. The second copper layer includes a first surface facing the first copper layer, and the first wall, the first surface, and the second wall together form a first step structure, which is used to support a portion of the first liquid crystal polymer layer. The second direction is perpendicular to the first direction.

[0009] In the above scheme, the hollow opening can remove redundant copper foil, adjust the circuit spacing of the circuit board, reduce the capacitive coupling between adjacent wires, improve the stability of signal transmission, and optimize the electrical performance of the circuit board. The first copper layer, the first liquid crystal polymer layer, the second copper layer, the second liquid crystal polymer layer and the third copper layer are stacked in sequence along the first direction, and a first step structure formed by the first wall, the first surface and the second wall is formed at the hollow opening. During the lamination process of the flexible printed circuit board, the first step structure will receive the liquid crystal polymer of the first liquid crystal polymer layer that is cast due to the pressure of the first copper layer and the second copper layer. As a result, during the lamination process, a portion of the liquid crystal polymer remains on the first surface and does not continue to cast to the third copper layer. This can reduce the amount of glue overflow accumulated on the third copper layer and reduce the impact of glue overflow on PAD (soldering board), circuits and electrical components.

[0010] In some embodiments, the first copper layer also includes a third wall portion facing the hollow opening, and along the second direction, the third wall portion is arranged opposite to the first wall portion. The second copper layer also includes a fourth wall portion facing the hollow opening, and along the second direction, the fourth wall portion is arranged opposite to the third wall portion. The third wall portion and the fourth wall portion both extend toward the center of the hollow opening along the second direction, and the fourth wall portion extends beyond the third wall portion. The first surface, the third wall portion and the fourth wall portion together form a second step structure, and the second step structure is used to undertake part of the first liquid crystal polymer layer. Setting the third wall portion, the fourth wall portion and the first surface as the second step structure can enable the first surface to undertake more liquid crystal polymer, reduce the amount of glue overflow on the surface of the third copper layer, and reduce the impact of glue overflow on PAD (soldering board), circuits and electrical components.

[0011] In some embodiments, along the third direction, the first copper layer further includes a fifth wall portion facing the hollow opening, and the second copper layer further includes a sixth wall portion facing the hollow opening. The fifth and sixth walls both extend along the third direction toward the center of the hollow opening, and the sixth wall portion extends beyond the fifth wall portion. The first surface, the fifth wall portion, and the sixth wall portion collectively form a third step structure, which is configured to receive a portion of the first liquid crystal polymer layer. The first direction, the second direction, and the third direction are mutually perpendicular. Arranging the fifth and sixth walls and the first surface as the third step structure allows the first surface to receive more liquid crystal polymer.

[0012] In some embodiments, the first copper layer includes a first edge, the second copper layer includes a second edge, the first edge and the second edge both extend in the same direction, and the second edge extends beyond the first edge. The first edge, the first surface and the second edge together form a fourth step structure, and the fourth step structure is used to receive part of the first liquid crystal polymer layer. In the industrial preparation process, multiple flexible printed circuit boards will be pressed together at the same time, and there will be a problem of glue overflow between adjacent circuit boards affecting product performance. Setting the first edge, the second edge and the first surface as the fourth step structure can enable the portion of the first surface close to the edge to receive the liquid crystal polymer, thereby reducing the impact of excessive glue overflow between adjacent products on PAD (soldering board), circuits and electrical components.

[0013] In some embodiments, the first copper layer further includes a third edge, and the first edge is arranged opposite to the third edge. The second copper layer includes a fourth edge, and the second edge is arranged opposite to the fourth edge. The hollow opening is located between the first edge and the third edge, and between the second edge and the fourth edge. The third edge and the fourth edge extend in the same direction, and the fourth edge exceeds the third edge. The third edge, the first surface and the fourth edge together form a fifth step structure, and the fifth step structure is used to receive part of the first liquid crystal polymer layer. Setting the third edge, the fourth edge and the first surface as the fifth step structure can enable the first surface to receive more liquid crystal polymer, thereby reducing the impact of excessive glue overflow on the PAD (soldering board), circuits and electrical components of adjacent products.

[0014] In some embodiments, the second wall extends beyond the first wall by 0.8 mm to 1.5 mm along the second direction. If the stepped surface for receiving the cast liquid crystal polymer is too small, it will not effectively reduce the amount of accumulated adhesive overflow. However, if it is too large, it will affect the circuit board's wiring layout and increase unnecessary costs. Setting the distance the second wall extends beyond the first wall to 0.8 mm to 1.5 mm can reduce the impact of the stepped structure on the circuit board's wiring and reduce the amount of accumulated adhesive overflow.

[0015] In some embodiments, the flexible printed circuit board further comprises a fourth copper layer and a third liquid crystal polymer layer. Along the first direction, the third liquid crystal polymer layer is disposed between the third and fourth copper layers, and the hollow opening extends through the third copper layer. Along the second direction, the third copper layer comprises a ninth wall portion facing the hollow opening. The ninth wall portion and the second wall portion both extend along the second direction toward the center of the hollow opening, with the ninth wall portion extending beyond the second wall portion. The third copper layer comprises a second surface facing the second copper layer, and the second surface, the second wall portion, and the ninth wall portion collectively form a sixth step structure, which is used to receive a portion of the second liquid crystal polymer layer. A fourth copper layer and a third liquid crystal polymer layer are additionally provided, and the second wall portion, the ninth wall portion, and the second surface are configured as the sixth step structure. The provision of multiple copper layers can provide the functionality of the flexible printed circuit board, while the provision of the sixth step structure can receive the liquid crystal polymer cast from the second liquid crystal polymer layer, reducing the amount of glue overflow accumulated from the fourth copper layer.

[0016] In some embodiments, the first and second liquid crystal polymer layers include adhesive resist particles. The adhesive resist particles are composed of an adhesive resist material having a lower melting point than the liquid crystal polymer. During the lamination process, the liquid crystal polymer layer melts due to heat. The adhesive resist material melts before the liquid crystal polymer, adhering to the periphery and upper portions of the liquid crystal polymer layer, thereby limiting adhesive overflow and reducing the amount of adhesive overflow that accumulates on the third copper layer.

[0017] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily described by the figures in the accompanying drawings, which are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0019] Figure 1 A schematic diagram of a flexible printed circuit board according to some embodiments of the present application;

[0020] Figure 2 A schematic diagram of lamination of a flexible printed circuit board according to some embodiments of the present application;

[0021] Figure 3 This is a schematic diagram of some prior art circuit board press-fitting techniques for this application;

[0022] Figure 4 A schematic diagram of a flexible printed circuit board according to some embodiments of the present application;

[0023] Figure 5This is a top view of a flexible printed circuit board according to some embodiments of the present application.

[0024] Explanation of reference numerals: 11, first copper layer; 111, first wall portion; 112, third wall portion; 113, fifth wall portion; 114, first edge; 115, third edge; 12, second copper layer; 121, second wall portion; 122, fourth wall portion; 123, first surface; 124, sixth wall portion; 125, second edge; 126, fourth edge; 13, third copper layer; 131, ninth wall portion; 132, second surface; 14, fourth copper layer;

[0025] 21. First liquid crystal polymer layer; 22. Second liquid crystal polymer layer; 23. Third liquid crystal polymer layer;

[0026] 3. Hollow mouth;

[0027] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0029] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0030] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0031] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0032] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0033] In the production process of flexible printed circuit boards, the copper layer needs to be pressed together with the LCP material (liquid crystal polymer). Figure 1 During the lamination process, liquid crystal polymer (LCP) can flow out and accumulate on the copper layer, a phenomenon known as overflow. For flexible circuit boards with cutouts, excessive overflow can obscure the pads (pads) and traces, affecting the operation of components like resistors and capacitors and affecting the size of the cutout areas.

[0034] In order to solve the above problems, the present application proposes a flexible printed circuit board. Figure 2 . It includes a first copper layer 11, a first liquid crystal polymer layer 21, a second copper layer 12, a second liquid crystal polymer layer 22 and a third copper layer 13 stacked in sequence along a first direction x. The flexible printed circuit board is provided with a hollow opening 3, which passes through the first copper layer 11, the first liquid crystal polymer layer 21 and the second copper layer 12 along the first direction x. Along the second direction y, the first copper layer 11 includes a first wall portion 111 facing the hollow opening 3, and the second copper layer 12 includes a second wall portion 121 facing the hollow opening 3. The first wall portion 111 and the second wall portion 121 both extend toward the center of the hollow opening 3 along the second direction y, and the second wall portion 121 exceeds the first wall portion 111. The second copper layer 12 includes a first surface 123 facing the first copper layer 11. The first wall portion 111, the first surface 123 and the second wall portion 121 together form a first step structure, which is used to support part of the first liquid crystal polymer layer 21. The second direction y is perpendicular to the first direction x. It can be understood that the wall surfaces of the first wall portion 111 and the second wall portion 121 can be curved surfaces or flat surfaces. For example, when the shape of the hollow opening 3 is circular, the wall surfaces of the first wall portion 111 and the second wall portion 121 are curved surfaces. When the shape of the hollow opening 3 is rectangular, the wall surfaces of the first wall portion 111 and the second wall portion 121 are flat surfaces.

[0035] In the above solution, the hollow opening 3 can remove redundant copper foil, adjust the circuit spacing of the circuit board, reduce the capacitive coupling between adjacent wires, improve the stability of signal transmission, and optimize the electrical performance of the circuit board. The first copper layer 11, the first liquid crystal polymer layer 21, the second copper layer 12, the second liquid crystal polymer layer 22 and the third copper layer 13 are stacked in sequence along the first direction x, and a first step structure formed by the first wall portion 111, the first surface 123 and the second wall portion 121 is formed at the hollow opening 3. Please refer to Figure 3During the lamination process of the flexible printed circuit board, the first step structure receives the liquid crystal polymer of the first liquid crystal polymer layer 21 that is cast due to the pressure of the first copper layer 11 and the second copper layer 12. As a result, during the lamination process, a portion of the liquid crystal polymer remains on the first surface 123 and does not continue to cast onto the third copper layer 13. This reduces the amount of glue overflowing onto the third copper layer 13, thereby reducing the impact of glue overflow on the PAD (solder pad), circuits, and electrical components.

[0036] In some embodiments, please refer to Figure 2 . The first copper layer 11 also includes a third wall portion 112 facing the hollow opening 3, and the third wall portion 112 is arranged opposite to the first wall portion 111 along the second direction y. The second copper layer 12 also includes a fourth wall portion 122 facing the hollow opening 3, and the fourth wall portion 122 is arranged opposite to the third wall portion 112 along the second direction y. The third wall portion 112 and the fourth wall portion 122 both extend toward the center of the hollow opening 3 along the second direction y, and the fourth wall portion 122 exceeds the third wall portion 112. The first surface 123, the third wall portion 112 and the fourth wall portion 122 together form a second step structure, and the second step structure is used to support part of the first liquid crystal polymer layer 21. Setting the third wall portion 112, the fourth wall portion 122 and the first surface 123 as the second step structure can enable the first surface 123 to support more liquid crystal polymer, reduce the amount of glue overflow on the surface of the third copper layer 13, and reduce the impact of glue overflow on PAD (soldering board), circuits and electrical components.

[0037] In some embodiments, please refer to Figure 4 Along the third direction z, the first copper layer 11 further includes a fifth wall portion 113 facing the hollow opening 3, and the second copper layer 12 further includes a sixth wall portion 124 facing the hollow opening 3. The fifth wall portion 113 and the sixth wall portion 124 both extend along the third direction z toward the center of the hollow opening 3, and the sixth wall portion 124 extends beyond the fifth wall portion 113. The first surface 123, the fifth wall portion 113, and the sixth wall portion 124 together form a third step structure, which is used to support a portion of the first liquid crystal polymer layer 21. The first direction x, the second direction y, and the third direction z are mutually perpendicular. Arranging the fifth wall portion 113, the sixth wall portion 124, and the first surface 123 into a third step structure allows the first surface 123 to support more liquid crystal polymer. In the above solution, the third direction z can be a direction perpendicular to the first direction x and the second direction y, or it can be other directions on the surface of the first copper layer 11. Similarly, there may be more similar step structures. For example, the first copper layer 11 further includes a seventh wall portion, and the second copper layer 12 further includes an eighth wall portion. The seventh wall portion, the eighth wall portion, and the first surface 123 constitute a step structure.

[0038] In some embodiments, please refer to Figure 3, the first copper layer 11 includes a first edge 114, and the second copper layer 12 includes a second edge 125. The first edge 114 and the second edge 125 extend in the same direction, and the second edge 125 exceeds the first edge 114. The first edge 114, the first surface 123 and the second edge 125 together form a fourth step structure, and the fourth step structure is used to receive part of the first liquid crystal polymer layer 21. In the industrial preparation process, multiple flexible printed circuit boards will be pressed together at the same time, and there will be a problem of glue overflow between adjacent circuit boards affecting product performance. Setting the first edge 114, the second edge 125 and the first surface 123 as the fourth step structure can make the part of the first surface 123 close to the edge receive the liquid crystal polymer, reducing the impact of excessive glue overflow between adjacent products on PAD (soldering board), circuits and electrical components.

[0039] In some embodiments, please refer to Figure 3 The first copper layer 11 further includes a third edge 115, with the first edge 114 being disposed opposite the third edge 115. The second copper layer 12 includes a fourth edge 126, with the second edge 125 being disposed opposite the fourth edge 126. The hollow opening 3 is located between the first edge 114 and the third edge 115, and between the second edge 125 and the fourth edge 126.

[0040] The third edge 115 and the fourth edge 126 extend in the same direction, with the fourth edge 126 extending beyond the third edge 115. The third edge 115, the first surface 123, and the fourth edge 126 collectively form a fifth step structure, which is used to receive a portion of the first liquid crystal polymer layer 21. Arranging the third edge 115, the fourth edge 126, and the first surface 123 into the fifth step structure allows the first surface 123 to receive more liquid crystal polymer, reducing the impact of excessive adhesive overflow on the PAD (solder pad), circuits, and electrical components of adjacent products.

[0041] In some embodiments, along the second direction y, the second wall portion 121 extends beyond the first wall portion 111 by 0.8 mm to 1.5 mm. If the stepped surface for receiving the cast liquid crystal polymer is too small, it will not effectively reduce the amount of accumulated glue overflow. If it is too large, it will affect the circuit board's wiring layout and increase unnecessary costs. Setting the distance between the second wall portion 121 and the first wall portion 111 to 0.8 mm to 1.5 mm can reduce the impact of the stepped structure on the circuit board's wiring and reduce the amount of accumulated glue overflow.

[0042] In some embodiments, the flexible printed circuit board further includes a fourth copper layer 14 and a third liquid crystal polymer layer 23. Along the first direction x, the third liquid crystal polymer layer 23 is disposed between the third copper layer 13 and the fourth copper layer 14, with the hollow opening 3 penetrating the third copper layer 13. Along the second direction y, the third copper layer 13 includes a ninth wall portion 131 facing the hollow opening 3. Both the ninth wall portion 131 and the second wall portion 121 extend toward the center of the hollow opening 3 along the second direction y, with the ninth wall portion 131 extending beyond the second wall portion 121. The third copper layer 13 includes a second surface 132 facing the second copper layer 12. The second surface 132, the second wall portion 121, and the ninth wall portion 131 collectively form a sixth step structure for supporting a portion of the second liquid crystal polymer layer 22. The fourth copper layer 14 and the third liquid crystal polymer layer 23 are additionally provided, and the second wall portion 121, the ninth wall portion 131, and the second surface 132 are configured as the sixth step structure. The additional copper layers can provide the functionality of the flexible printed circuit board. Meanwhile, the sixth step structure can receive the liquid crystal polymer cast from the second liquid crystal polymer layer 22 , thereby reducing the accumulated glue overflow of the fourth copper layer 14 .

[0043] In some embodiments, the first liquid crystal polymer layer 21 and the second liquid crystal polymer layer 22 include adhesive resist particles. The adhesive resist particles are made of an adhesive resist material with a lower melting point than the liquid crystal polymer. During the lamination process, the liquid crystal polymer layer melts due to heat, and the adhesive resist material melts before the liquid crystal polymer, adhering to the periphery and upper portion of the liquid crystal polymer layer, thereby limiting adhesive overflow and reducing the amount of adhesive overflow that accumulates on the third copper layer 13.

[0044] The adhesive resistance material may be a high-density polyethylene material, or a resin material such as epoxy resin or acrylic resin.

[0045] In a second aspect, the present application further proposes a method for preparing a flexible printed circuit board, comprising:

[0046] A first copper layer 11, a second copper layer 12, a third copper layer 13, a first liquid crystal polymer layer 21 and a second liquid crystal polymer layer 22 are provided, and the first copper layer 11, the first liquid crystal polymer layer 21, the second copper layer 12, the second liquid crystal polymer layer 22 and the third copper layer 13 are stacked in sequence along a first direction x.

[0047] A hollow opening 3 is formed throughout the first copper layer 11, the second copper layer 12, the third copper layer 13, the first liquid crystal polymer layer 21, and the second liquid crystal polymer layer 22. Along a first direction x, the hollow opening 3 penetrates the first copper layer 11, the first liquid crystal polymer layer 21, and the second copper layer 12. Along a second direction y, the first copper layer 11 includes a first wall 111 facing the hollow opening 3, and the second copper layer 12 includes a second wall 121 facing the hollow opening 3. Both the first wall 111 and the second wall 121 extend toward the center of the hollow opening 3 along the second direction y, with the second wall 121 extending beyond the first wall 111. The second copper layer 12 includes a first surface 123 facing the first copper layer 11. The first wall 111, the first surface 123, and the second wall 121 collectively form a first step structure.

[0048] The first copper layer 11, the second copper layer 12, the third copper layer 13, the first liquid crystal polymer layer 21 and the second liquid crystal polymer layer 22 are subjected to a hot pressing process along the first direction x, so that the first liquid crystal polymer layer 21 is melted, and the molten first liquid crystal polymer layer 21 is cast to the first step structure.

[0049] In the above-described preparation method, the first copper layer 11, the first liquid crystal polymer layer 21, the second copper layer 12, the second liquid crystal polymer layer 22, and the third copper layer 13 are stacked in sequence along the first direction x, and a first step structure formed by the first wall portion 111, the first surface 123, and the second wall portion 121 is formed at the hollow opening 3. During the lamination process of the flexible printed circuit board, the first step structure receives the liquid crystal polymer of the first liquid crystal polymer layer 21 that is cast due to the pressure of the first copper layer 11 and the second copper layer 12. As a result, during the lamination process, a portion of the liquid crystal polymer is retained on the first surface 123 and does not continue to cast onto the third copper layer 13. This can reduce the amount of glue overflowing the third copper layer 13, thereby reducing the impact of the glue overflow on the PAD (solder board), circuits, and electrical components.

[0050] In the above scheme, the hollow opening 3 can remove redundant copper foil, adjust the circuit spacing of the circuit board, reduce the capacitive coupling between adjacent wires, improve the stability of signal transmission, and optimize the electrical performance of the circuit board. The first copper layer 11, the first liquid crystal polymer layer 21, the second copper layer 12, the second liquid crystal polymer layer 22, and the third copper layer 13 are stacked in sequence along the first direction X, and a first step structure formed by the first wall portion 111, the first surface 123, and the second wall portion 121 is formed at the hollow opening 3. During the lamination process of the flexible printed circuit board, the first step structure will receive the liquid crystal polymer of the first liquid crystal polymer layer 21 that is cast due to the pressure of the first copper layer 11 and the second copper layer 12. As a result, during the lamination process, a portion of the liquid crystal polymer is retained on the first surface and will not continue to cast onto the third copper layer 13. This can reduce the amount of glue overflow accumulated on the third copper layer 13, reducing the impact of glue overflow on the PAD (solder board), circuits, and electrical components.

[0051] In some embodiments, the preparation method further includes: the first copper layer 11 includes a first edge 114, the second copper layer 12 includes a second edge 125, the first edge 114 and the second edge 125 extend in the same direction, and the second edge 125 extends beyond the first edge 114. The first edge 114, the first surface 123, and the second edge 125 together form a fourth step structure. When the first copper layer 11, the second copper layer 12, the third copper layer 13, the first liquid crystal polymer layer 21, and the second liquid crystal polymer layer 22 are subjected to a hot pressing process, the molten first liquid crystal polymer layer 21 is cast onto the fourth step structure. Setting the third wall portion 112, the fourth wall portion 122, and the first surface 123 as the second step structure can allow the first surface 123 to receive more liquid crystal polymer, thereby reducing the amount of glue overflow on the surface of the third copper layer 13.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a flexible printed circuit board, characterized in that: include: Providing a first copper layer, a second copper layer, a third copper layer, a first liquid crystal polymer layer, and a second liquid crystal polymer layer, and sequentially stacking the first copper layer, the first liquid crystal polymer layer, the second copper layer, the second liquid crystal polymer layer, and the third copper layer along a first direction; A hollow opening is formed in the first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer, and the second liquid crystal polymer layer, wherein the hollow opening passes through the first copper layer, the first liquid crystal polymer layer, and the second copper layer along the first direction; wherein, along the second direction, the first copper layer includes a first wall portion facing the hollow opening, and the second copper layer includes a second wall portion facing the hollow opening; the first wall portion and the second wall portion both extend toward the center of the hollow opening along the second direction, and the second wall portion extends beyond the first wall portion; the second copper layer includes a first surface facing the first copper layer, and the first wall portion, the first surface, and the second wall portion together form a first step structure; The first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer and the second liquid crystal polymer layer are subjected to hot pressing treatment along a first direction to melt the first liquid crystal polymer layer and cast the molten first liquid crystal polymer layer onto the first step structure.

2. The method according to claim 1, characterized in that include: The first copper layer includes a first edge, the second copper layer includes a second edge, the first edge and the second edge extend in the same direction, and the second edge exceeds the first edge; the first edge, the first surface, and the second edge together form a fourth step structure; When the first copper layer, the second copper layer, the third copper layer, the first liquid crystal polymer layer and the second liquid crystal polymer layer are subjected to a heat pressing process, the first liquid crystal polymer layer in a molten state is cast onto the fourth stepped structure.

3. A flexible printed circuit board prepared by the method of claim 1 or 2, characterized in that: The flexible printed circuit board comprises a first copper layer, a first liquid crystal polymer layer, a second copper layer, a second liquid crystal polymer layer, and a third copper layer stacked in sequence along a first direction; the flexible printed circuit board is provided with a hollow opening, and along the first direction, the hollow opening passes through the first copper layer, the first liquid crystal polymer layer, and the second copper layer; Along the second direction, the first copper layer includes a first wall portion facing the hollow opening, and the second copper layer includes a second wall portion facing the hollow opening; the first wall portion and the second wall portion both extend toward the center of the hollow opening along the second direction, and the second wall portion exceeds the first wall portion; The second copper layer includes a first surface facing the first copper layer, the first wall portion, the first surface and the second wall portion together form a first step structure, and the first step structure is used to receive a portion of the first liquid crystal polymer layer; The second direction is perpendicular to the first direction.

4. The flexible printed circuit board according to claim 3, wherein: The first copper layer further includes a third wall portion facing the hollow opening, and along the second direction, the third wall portion is arranged opposite to the first wall portion; The second copper layer further includes a fourth wall portion facing the hollow opening, wherein the fourth wall portion is arranged opposite to the third wall portion along the second direction; the third wall portion and the fourth wall portion both extend toward the center of the hollow opening along the second direction, and the fourth wall portion extends beyond the third wall portion; The first surface, the third wall portion, and the fourth wall portion together form a second step structure, and the second step structure is used to receive a portion of the first liquid crystal polymer layer.

5. The flexible printed circuit board according to claim 3, wherein: Along the third direction, the first copper layer further includes a fifth wall portion facing the hollow opening, and the second copper layer further includes a sixth wall portion facing the hollow opening, the fifth wall portion and the sixth wall portion both extending along the third direction toward the center of the hollow opening, and the sixth wall portion exceeds the fifth wall portion; The first surface, the fifth wall portion, and the sixth wall portion together form a third step structure, and the third step structure is used to receive a portion of the first liquid crystal polymer layer. The first direction, the second direction, and the third direction are perpendicular to each other.

6. The flexible printed circuit board according to claim 3, wherein: The first copper layer includes a first edge, the second copper layer includes a second edge, the first edge and the second edge extend in the same direction, and the second edge exceeds the first edge; the first edge, the first surface and the second edge together form a fourth step structure, and the fourth step structure is used to support part of the first liquid crystal polymer layer.

7. The flexible printed circuit board according to claim 3, wherein: The first copper layer further includes a third edge, the first edge being disposed opposite to the third edge; the second copper layer includes a fourth edge, the second edge being disposed opposite to the fourth edge; the hollow opening is located between the first edge and the third edge, and between the second edge and the fourth edge; The third edge and the fourth edge extend in the same direction, and the fourth edge extends beyond the third edge; the third edge, the first surface and the fourth edge together form a fifth step structure, and the fifth step structure is used to support part of the first liquid crystal polymer layer.

8. The flexible printed circuit board according to claim 3, wherein: Along the second direction, the second wall portion extends beyond the first wall portion by 0.8 mm to 1.5 mm.

9. The flexible printed circuit board according to claim 3, wherein: The flexible printed circuit board further includes a fourth copper layer and a third liquid crystal polymer layer; Along the first direction, the third liquid crystal polymer layer is disposed between the third copper layer and the fourth copper layer, and the hollow opening penetrates the third copper layer. Along the second direction, the third copper layer includes a ninth wall portion disposed facing the hollow opening, and both the ninth wall portion and the second wall portion extend along the second direction toward the center of the hollow opening, and the ninth wall portion extends beyond the second wall portion. The third copper layer includes a second surface facing the second copper layer. The second surface, the second wall portion, and the ninth wall portion together form a sixth step structure. The sixth step structure is used to receive a portion of the second liquid crystal polymer layer.

10. The flexible printed circuit board according to claim 3, wherein: The first liquid crystal polymer layer and the second liquid crystal polymer layer include glue-stop particles.

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