Circuit board and manufacturing method thereof

Abstract

A circuit board includes a first exterior structure, a second exterior structure, an interior structure, and a composite material layer. The first exterior structure includes a first exterior reinforcement layer disposed in the first exterior structure. The second exterior structure includes a second exterior reinforcement layer disposed in the second exterior structure. The interior structure is disposed between the first exterior structure and the second exterior structure, wherein the interior structure has a cavity extending along a first direction, the cavity is formed through the interior structure, the first exterior reinforcement layer is located on a top of the cavity , the cavity exposes a portion of the first exterior reinforcement layer, the second exterior reinforcement layer is located at a bottom of the cavity, and the cavity exposes a portion of the second exterior reinforcement layer. The composite material layer surrounds the cavity, the first exterior structure, and the second exterior structure.

Description

[Technical Field]

[0001] This invention relates to a circuit board and a method for manufacturing a circuit board, and more particularly to a circuit board having an external reinforcement layer and a method for manufacturing the same. [Previous Technology]

[0002] With the development of technologies such as 5G (5th Generation Wireless Systems) and artificial intelligence, the demand for higher density, faster transmission rates and stronger environmental adaptability is increasing, prompting flexible circuit boards to develop towards smaller line widths (or spacing) and higher layers.

[0003] Flexible printed circuits (FPCs) are flexible and suitable for applications requiring the mounting of electronic components in confined or non-planar areas, enabling complex electrical connections to be implemented in a smaller space. Compared to traditional rigid printed circuit boards (PCBs), FPCs are thinner and lighter, helping to reduce the weight of the final product.

[0004] In traditional flexible circuit boards, a steel sheet is typically placed on one side of the flexible circuit board, and electronic components are placed on the other side, with the steel sheet positioned to provide support for the electronic components. However, the steel sheet has disadvantages such as being heavy and occupying a large area. Furthermore, because the steel sheet is located on one side of the flexible circuit board, the electronic components can only be placed on the other side, which limits the number of electronic components that can be connected to the flexible circuit board, thereby reducing the ability to integrate functions. [Summary of the Invention]

[0005] The circuit board provided by the present invention has a first external reinforcement layer, a second external reinforcement layer and a composite material layer embedded inside the circuit board, so that electronic components can be additionally set at the relative positions on both sides of the outer side of the circuit board, thereby increasing the freedom of circuit design, space utilization and functional integration capability.

[0006] The circuit board provided in at least one embodiment of the present invention includes a first external structure, a second external structure, an internal structure, and a composite material layer. The first external structure includes a first external reinforcement layer disposed therein. The second external structure includes a second external reinforcement layer disposed therein. The internal structure is disposed between the first external structure and the second external structure, wherein the first external structure, the internal structure, and the second external structure are stacked sequentially along a first direction, wherein the internal structure has a cavity extending along the first direction, the cavity being formed through the internal structure, the first external reinforcement layer being located at the top of the cavity, exposing a portion of the first external reinforcement layer in the cavity, and the second external reinforcement layer being located at the bottom of the cavity, exposing a portion of the second external reinforcement layer in the cavity. The composite material layer surrounds the cavity, the first external structure, and the second external structure.

[0007] A method for manufacturing a circuit board according to at least one embodiment of the present invention includes the following steps: providing a first original external structure, an inner substrate, and a second original external structure sequentially stacked along a first direction, wherein the first original external structure includes a first original external insulating layer and a first external circuit layer facing the inner substrate, wherein the first original external insulating layer includes a first main body portion and a first extension portion connected to the first main body portion, and the first external circuit layer is disposed on the first extension portion, wherein the second original external structure includes a second original external insulating layer and a second external circuit layer facing the inner substrate, wherein the second original external insulating layer includes a second main body portion and a second extension portion connected to the second main body portion, and the second external circuit layer is disposed on the second extension portion; removing a portion of the inner substrate, a portion of the first main body portion, and a portion of the second main body portion to form a circuit layer in the inner substrate along the first direction. A through-hole is formed in one direction, exposing a portion of the sidewall of the inner substrate; a first composite material is formed on the sidewall of the inner substrate of the removed portion, the first main body portion of the removed portion, and the second main body portion of the removed portion; a first external reinforcement layer is formed on the first composite material and in the first original external insulation layer, and a second external reinforcement layer is formed on the first composite material and in the second original external insulation layer to close the through-hole and form a cavity in the inner substrate, the cavity exposing a portion of the first external reinforcement layer and a portion of the second external reinforcement layer; a second composite material is formed covering the first external reinforcement layer and the second external reinforcement layer; a first extension and a first external circuit layer are bent to cover the first main body portion; a second extension and a second external circuit layer are bent to cover the second main body portion; and a cutting step is performed to separate the first extension from the first main body portion and the second extension from the second main body portion.

Implementation Method

[0009] It will be understood that although terms such as "first," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of the embodiments, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0010] FIG1 is a cross-sectional schematic diagram of a circuit board 100 according to a first embodiment of the present invention. The circuit board 100 includes a first external structure 110, a second external structure 120, an internal structure 130, and a composite material layer 140. The first external structure 110 includes a first external reinforcement layer 112 disposed therein. The second external structure 120 includes a second external reinforcement layer 122 disposed therein. The internal structure 130 is disposed between the first external structure 110 and the second external structure 120, wherein the first external structure 110, the internal structure 130, and the second external structure 120 are stacked sequentially along a first direction D1, wherein the internal structure 130 has a cavity CA extending along the first direction D1, the cavity CA being formed through the internal structure 130, the first external reinforcement layer 112 being located at the top of the cavity CA, the cavity CA exposing a portion of the first external reinforcement layer 112, and the second external reinforcement layer 122 being located at the bottom of the cavity CA, the cavity CA exposing a portion of the second external reinforcement layer 122. The composite material layer 140 surrounds the cavity CA, the first external structure 110, and the second external structure 120. Specifically, the composite material layer 140 surrounds the cavity CA, the first external reinforcing layer 112, and the second external reinforcing layer 122. In other words, the cavity CA is located between the first external reinforcing layer 112 and the second external reinforcing layer 122.

[0011] As shown in Figure 1, the internal structure 130 further includes an internal insulating layer 134, a circuit layer 135, a circuit layer 136, a first internal adhesive layer 137, and a second internal adhesive layer 138. The circuit layer 135 and the circuit layer 136 are respectively disposed on both sides of the internal insulating layer 134. The first internal adhesive layer 137 is disposed between the internal insulating layer 134 and the first external structure 110. The second internal adhesive layer 138 is disposed between the internal insulating layer 134 and the second external structure 120. Specifically, the first internal adhesive layer 137 covers the circuit layer 135 and contacts one surface of the internal insulating layer 134, and the second internal adhesive layer 138 covers the circuit layer 136 and contacts the other surface of the internal insulating layer 134.

[0012] As shown in Figure 1, the first external structure 110 further includes a first external insulating layer 113, a second external insulating layer 114, a first external adhesive layer 115, a circuit layer 116, and a first external circuit layer 117. The first external insulating layer 113 is disposed on the first internal adhesive layer 137. The second external insulating layer 114 is disposed above the first external insulating layer 113 and the cavity CA, wherein a portion of the first external insulating layer 113 protrudes from the sidewall s1 of the second external insulating layer 114 in a second direction D2, and the second direction D2 is substantially perpendicular to the first direction D1. The circuit layer 116 is disposed on the first external insulating layer 113, and the first external circuit layer 117 is disposed on the second external insulating layer 114.

[0013] In detail, as shown in FIG1, a first external adhesive layer 115 is disposed between a first external insulating layer 113 and a second external insulating layer 114, wherein a first external reinforcing layer 112 is disposed between the second external insulating layer 114 and the cavity CA, and a composite material layer 140 surrounds the first external reinforcing layer 112 and contacts the first external insulating layer 113, the first external adhesive layer 115, and the second external insulating layer 114. More specifically, the composite material layer 140 surrounds most of the surface of the first external reinforcing layer 112 and exposes a portion of the surface of the first external reinforcing layer 112 facing the cavity CA. The width of the first external reinforcing layer 112 is greater than the width of the cavity CA. The width of the second external insulating layer 114 is greater than the width of the first external reinforcing layer 112.

[0014] As shown in Figure 1, the second external structure 120 further includes a third external insulating layer 123, a fourth external insulating layer 124, a second external adhesive layer 125, a wiring layer 126, and a second external wiring layer 127. The third external insulating layer 123 is disposed on the second internal adhesive layer 138. The fourth external insulating layer 124 is disposed above the third external insulating layer 123 and the cavity CA, wherein a portion of the third external insulating layer 123 protrudes from the sidewall s2 of the fourth external insulating layer 124 in the second direction D2. The wiring layer 126 is disposed on the third external insulating layer 123, and the second external wiring layer 127 is disposed on the fourth external insulating layer 124.

[0015] In detail, as shown in Figure 1, the second external adhesive layer 125 is disposed between the third external insulating layer 123 and the fourth external insulating layer 124, wherein the second external reinforcing layer 122 is disposed between the fourth external insulating layer 124 and the cavity CA, and the composite material layer 140 surrounds the second external reinforcing layer 122 and contacts the third external insulating layer 123, the second external adhesive layer 125, and the fourth external insulating layer 124. More specifically, the composite material layer 140 surrounds most of the surface of the second external reinforcing layer 122 and exposes a portion of the surface of the second external reinforcing layer 122 facing the cavity CA. The width of the second external reinforcing layer 122 is greater than the width of the cavity CA. The width of the fourth external insulating layer 124 is greater than the width of the second external reinforcing layer 122.

[0016] In some embodiments, the materials of the inner insulating layer 134, the first outer insulating layer 113, the second outer insulating layer 114, the third outer insulating layer 123, and the fourth outer insulating layer 124 may be insulating materials such as polyimide (PI), glass fiber epoxy resin (FR4), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethylene (PE), but are not limited thereto.

[0017] In some embodiments, the circuit layer 116, the first external circuit layer 117, the circuit layer 126, the second external circuit layer 127, the circuit layer 135, and the circuit layer 136 may be formed using an additive, semi-additive, or subtractive method. In some embodiments, the materials of the circuit layer 116, the first external circuit layer 117, the circuit layer 126, the second external circuit layer 127, the circuit layer 135, and the circuit layer 136 may be conductive materials such as copper, gold, or silver, but are not limited thereto.

[0018] In some embodiments, the materials of the first outer adhesive layer 115, the second outer adhesive layer 125, the first inner adhesive layer 137 and the second inner adhesive layer 138 may be low-flow prepreg or non-flow prepreg.

[0019] It is understood that the number of insulating layers (e.g., inner insulating layer 134, first outer insulating layer 113, second outer insulating layer 114, third outer insulating layer 123, and fourth outer insulating layer 124) and the number of circuit layers (e.g., circuit layer 116, circuit layer 126, circuit layer 135, and circuit layer 136) in the circuit board 100 are not limited to those shown in FIG1. ​​In other words, in other embodiments, the circuit board 100 may include more layers of insulating layers and circuit layers.

[0020] In the first embodiment of FIG1, the first external reinforcement layer 112, the second external reinforcement layer 122, and the cavity CA are aligned with each other in the first direction D1. In some embodiments, the projection of the first external circuit layer 117 onto the internal insulating layer 134 overlaps with the projection of the second external circuit layer 127 onto the internal insulating layer 134.

[0021] The first outer reinforcing layer 112 and the second outer reinforcing layer 122 of FIG. 1 can also be referred to as glass fiber reinforced plastic (GFRP). In some embodiments, the materials of the first outer reinforcing layer 112 and the second outer reinforcing layer 122 comprise glass fiber and thermosetting resin. The thermosetting resin may be, for example, epoxy resin or polyester resin, but is not limited thereto. In one specific example, the materials of the first outer reinforcing layer 112 and the second outer reinforcing layer 122 each comprise 62% glass fiber and 38% thermosetting resin. Compared with conventional metal materials such as steel sheets, the first outer reinforcing layer 112 and the second outer reinforcing layer 122 have the characteristics of high strength and light weight. Therefore, the first outer reinforcing layer 112 and the second outer reinforcing layer 122 can provide good mechanical properties for the circuit board 100 and help reduce the weight of the circuit board 100.

[0022] As shown in Figure 1, the composite material layer 140 is also disposed on the sidewall s3 of the inner insulating layer 134, the sidewall s4 of the first inner adhesive layer 137, and the sidewall s5 of the second inner adhesive layer 138. In other words, the composite material layer 140 is disposed between the sidewall s3 and the cavity CA, between the sidewall s4 and the cavity CA, and between the sidewall s5 and the cavity CA. The composite material layer 140 in the inner structure 130, the first outer reinforcing layer 112 in the first outer structure 110, and the second outer reinforcing layer 122 in the second outer structure 120 form the cavity CA.

[0023] The composite material layer 140 is composed of multiple columnar materials, each columnar material extending along a third direction D3 substantially perpendicular to the first direction D1. It can be understood that the first direction D1, the second direction D2, and the third direction D3 are substantially perpendicular to each other. The multiple columnar materials are arranged in a closed structure. Specifically, the columnar materials have a circular cross-section, as shown in Figure 1. The composite material layer 140 can also be understood as being composed of multiple cylindrical materials.

[0024] The composite material layer 140 in Figure 1 is configured to provide local support for the circuit board 100. Specifically, when the circuit board 100 is subjected to external forces, the columnar material in the composite material layer 140 provides good mechanical properties. More specifically, the composite material layer 140 has a small surface area to volume ratio. Specifically, compared to other shapes (e.g., cuboids), a cylinder of the same volume has a smaller surface area. This means that under a given external force, the pressure per unit area is relatively low, which helps to improve the compressive strength of the material.

[0025] In some embodiments, each columnar material in the composite material layer 140 comprises a plurality of ceramic particles, fiber reinforcement, and graphene material. The ceramic particles may be, for example, alumina or silicon carbide. The fiber reinforcement may be, for example, glass fiber or carbon fiber. The content of each of the ceramic particles, fiber reinforcement, and graphene material may be adjusted according to specific performance requirements.

[0026] Referring to Figure 1, the circuit board 100 further includes a dielectric layer 152, a cover layer 162, a solder resist layer 172, a gold plating layer 182, solder paste 192, and an electronic component EC1. The dielectric layer 152 is disposed on the first external insulating layer 113, the cover layer 162 is disposed on the dielectric layer 152, the solder resist layer 172 is disposed on the second external insulating layer 114, the gold plating layer 182 and the solder paste 192 are disposed in the solder resist layer 172, and the electronic component EC1 is disposed on the solder paste 192.

[0027] Referring to Figure 1, the circuit board 100 further includes a dielectric layer 154, a cover layer 164, a solder resist layer 174, a gold plating layer 184, solder paste 194, and an electronic component EC2. The dielectric layer 154 is disposed on the third external insulating layer 123, the cover layer 164 is disposed on the dielectric layer 154, the solder resist layer 174 is disposed on the fourth external insulating layer 124, the gold plating layer 184 and the solder paste 194 are disposed in the solder resist layer 174, and the electronic component EC2 is disposed on the solder paste 194. The electronic component EC1 and the electronic component EC2 can be, for example, an active component and a passive component.

[0028] The first external circuit layer 117 and the second external circuit layer 127 of FIG1 are located on opposite sides of the circuit board 100, so electronic components (i.e., electronic component EC1 and electronic component EC2) can be provided on both sides of the circuit board 100, thereby increasing the functional integration capability of the circuit board 100. The circuit board 100 may be, for example, a flexible circuit board.

[0029] Compared to a solid circuit board, the cavity CA inside the circuit board 100 of the present invention is more resistant to bending stress. In other words, the circuit board 100 can increase the moment of inertia (also known as the second-order moment of inertia). Specifically, for a given mass or amount of material, by arranging the material away from the central axis, the moment of inertia of the cross section about that axis can be significantly increased. This means that under the same bending force, a component with a larger moment of inertia is better able to resist deformation. The cavity CA structure effectively increases its moment of inertia by using material at the edges while leaving the interior empty.

[0030] The circuit board 100 of the present invention has a support formed by an embedded external reinforcement layer (i.e., a first external reinforcement layer 112 and a second external reinforcement layer 122) and a composite material layer 140 to provide support for electronic components (i.e., electronic components EC1 and EC2). This design provides support for double-sided electronic components without compromising the structure of the circuit board 100, thus improving the structural stability of the circuit board 100. Furthermore, the cavity CA provided within the support can reduce stress generated during bending, improving the flexibility of the flexible circuit board. For example, better isolation can be achieved by placing certain sensitive circuits on one side and the power supply section on the other. By arranging components on both sides of the circuit board, the space utilization of the circuit board can be improved. Properly utilizing a double-sided layout can shorten signal paths, reduce interference, and thus increase the electrical performance of the entire system. For example, in high-frequency applications, shorter traces can help reduce electromagnetic interference (EMI).

[0031] In the first embodiment of FIG1, two supports (i.e., a first outer reinforcing layer 112, a second outer reinforcing layer 122, and a composite material layer 140) are shown, wherein the composite material layer 140 on one side of each support extends substantially along a first direction D1 from a second outer insulating layer 114, a first outer adhesive layer 115, a first outer insulating layer 113, a first inner adhesive layer 137, an inner insulating layer 134, a second inner adhesive layer 138, a third outer insulating layer 123, a second outer adhesive layer 125, and a fourth outer insulating layer 124. The cross-sections of both supports in FIG1 have a similar C-shaped profile.

[0032] FIG2 is a schematic cross-sectional view of a circuit board 200 according to a second embodiment of the present invention. The circuit board 200 of FIG2 is similar to the circuit board 100 of FIG1, except that in the second embodiment of FIG2, the cross-sections of the two supports (i.e., the first external reinforcing layer 112, the second external reinforcing layer 122, and the composite material layer 140) have a similar I-shaped shape. In other words, the first external reinforcing layer 112 and the second external reinforcing layer 122 in both supports expose the middle portion.

[0033] FIG3 is a cross-sectional schematic diagram of a circuit board 300 according to a third embodiment of the present invention. The circuit board 300 in FIG3 is similar to the circuit board 100 in FIG1, except that in the third embodiment of FIG3, one support (i.e., the first external reinforcing layer 112, the second external reinforcing layer 122 and the composite material layer 140) has a cross-section with a similar I-shaped shape, and the other support has a cross-section with a similar C-shaped shape.

[0034] Figures 4A to 4C are schematic cross-sectional views of an internal substrate 400 (see Figure 4C) at various stages of the manufacturing process according to some embodiments of the present invention. Referring to Figure 4A, an initial circuit layer 420 and a metal layer 430 are respectively provided on both sides of the initial insulating layer 410. A plurality of holes H1 can be formed in the initial circuit layer 420 and the initial insulating layer 410 by laser drilling.

[0035] Referring to Figures 4A and 4B, electroplating and / or electroless plating are performed to form a plurality of vias H1' in the initial circuit layer 420 and the initial insulating layer 410. Then, a photoresist layer 440 is formed on the initial circuit layer 420, and a photoresist layer 450 is formed on the metal layer 430. A photolithography process is performed using a photomask (not shown) to form an internal substrate 400 including circuit layers 460 and 470, as shown in Figure 4C.

[0036] Figures 5A and 5B are schematic cross-sectional views of a first original external structure 510 (or second original external structure 520) (see Figure 5B) at various stages of the manufacturing process according to some embodiments of the present invention. Referring to Figure 5A, a metal layer 530 and a metal layer 540 are respectively disposed on both sides of the first original external insulating layer 512 (or second original external insulating layer 522). Then, a photoresist layer 550 is formed on the metal layer 530, and a photoresist layer 560 is formed on the metal layer 540. After performing exposure and development processes using a photomask (not shown), etching and removal processes are then performed to form a first original external structure 510 (or second original external structure 520) having a circuit layer 514 (or circuit layer 524) and a first external circuit layer 516 (or second external circuit layer 526), ​​as shown in Figure 5B.

[0037] Figures 6A to 6F are schematic cross-sectional views of the circuit board 100a (please refer to Figure 6F) at various stages of the manufacturing process according to the first embodiment of the present invention. As shown in Figure 6A, a first original external structure 510, an inner substrate 400, and a second original external structure 520 are provided, which are sequentially stacked along the first direction D1.

[0038] As shown in FIG6A, a first internal adhesive layer 137 is formed between the first original external structure 510 and the internal substrate 400, and a second internal adhesive layer 138 is formed between the second original external structure 520 and the internal substrate 400. The first original external structure 510, the first internal adhesive layer 137, the internal substrate 400, the second internal adhesive layer 138, and the second original external structure 520 can be integrally formed by pressing.

[0039] As shown in FIG6A, the first original external structure 510 includes a first original external insulating layer 512 and a first external circuit layer 516 facing the internal substrate 400. The first original external insulating layer 512 includes a first main body portion 512a and a first extension portion 512b connected to the first main body portion 512a. The circuit layer 514 and the first external circuit layer 516 are respectively disposed on both sides of the first original external insulating layer 512. In detail, the circuit layer 514 is disposed on the first main body portion 512a and the first extension portion 512b, and the first external circuit layer 516 is disposed on the first extension portion 512b. In other words, the first external circuit layer 516 is not disposed on the first main body portion 512a.

[0040] As shown in FIG6A, the second original external structure 520 includes a second original external insulating layer 522 and a second external circuit layer 526 facing the inner substrate 400. The second original external insulating layer 522 includes a second main body portion 522a and a second extension portion 522b connected to the second main body portion 522a. The circuit layer 524 and the second external circuit layer 526 are respectively disposed on both sides of the second original external insulating layer 522. In detail, the circuit layer 524 is disposed on the second main body portion 522a and the second extension portion 522b, and the second external circuit layer 526 is disposed on the second extension portion 522b. In other words, the second external circuit layer 526 is not disposed on the second main body portion 522a.

[0041] Referring again to FIG. 6A, in detail, the first internal adhesive layer 137 is disposed between the initial insulating layer 410 and the first original external insulating layer 512, and the first internal adhesive layer 137 does not contact the first external circuit layer 516. The second internal adhesive layer 138 is disposed between the initial insulating layer 410 and the second original external insulating layer 522, and the second internal adhesive layer 138 does not contact the second external circuit layer 526.

[0042] Referring again to FIG6A, after the lamination step, at least one hole H2 can be formed in the first inner adhesive layer 137, the first original outer insulating layer 512, and the wiring layer 514 by laser drilling. Similarly, at least one hole H3 can be formed in the second inner adhesive layer 138, the second original outer insulating layer 522, and the wiring layer 524 by laser drilling.

[0043] Referring to Figures 6A and 6B, electroplating and / or electroless plating are performed to form at least one via H2' in the first inner adhesive layer 137, the first original outer insulating layer 512, and the wiring layer 514 (refer to Figure 6A). Similarly, electroplating and / or electroless plating are performed to form at least one via H3' in the second inner adhesive layer 138, the second original outer insulating layer 522, and the wiring layer 524 (refer to Figure 6A).

[0044] Referring again to FIG6B, after forming vias H2' and H3', a photomask (not shown) is used to perform a photolithography process to form patterned circuit layers 116 and 126 on circuit layers 514 and 524, respectively, as shown in FIG6B.

[0045] Referring to Figures 6B and 6C, a portion of the inner substrate 400, a portion of the first main body portion 512a, and a portion of the second main body portion 522a are removed to form a through-hole TH extending along the first direction D1 in the inner substrate 400, exposing a portion of the sidewall s3 of the inner substrate 400. Specifically, a portion of the initial insulating layer 410 in Figure 6B is removed to form the inner insulating layer 134 in Figure 6C.

[0046] Referring still to FIG. 6C, after removing part of the first main body portion 512a, a portion of the upper surface ts1 and sidewall s4 of the first internal adhesive layer 137 are exposed. After removing part of the second main body portion 522a, a portion of the upper surface ts2 and sidewall s5 of the second internal adhesive layer 138 are exposed.

[0047] Referring again to FIG. 6C, a first extension 512b of the recessed portion forms a groove R1 within it, wherein the groove R1 is disposed relative to the first outer circuit layer 516. A second extension 522b of the recessed portion forms a groove R2 within it, wherein the groove R2 is disposed relative to the second outer circuit layer 526. In the embodiment of FIG. 6C, the projection of the groove R1 onto the inner insulating layer 134 overlaps with the projection of the groove R2 onto the inner insulating layer 134.

[0048] Referring again to FIG. 6C, a first composite material 140a is formed on the upper surface ts1 and sidewall s4 of the first internal adhesive layer 137, and a first composite material 140a is formed on the upper surface ts2 and sidewall s5 of the second internal adhesive layer 138. It can be understood that the first composite material 140a is formed on the first main body portion 512a and the second main body portion 522a of the removed portion. In detail, the first composite material 140a is also formed on the sidewall s3 of the inner substrate 400 (e.g., the inner insulating layer 134) of the removed portion.

[0049] Referring to Figures 6C and 6D, a first external reinforcing layer 112 is formed on the first composite material 140a and in the first original external insulating layer 512, and a second external reinforcing layer 122 is formed on the first composite material 140a and in the second original external insulating layer 522 to close the through-hole TH and form a cavity CA in the inner substrate 400. The cavity CA exposes a portion of the first external reinforcing layer 112 and a portion of the second external reinforcing layer 122.

[0050] Referring again to FIG6D, a second composite material 140b is formed covering the first external reinforcing layer 112 and the second external reinforcing layer 122. It is understood that the composite material layer 140 is composed of the first composite material 140a and the second composite material 140b, wherein the materials of the first composite material 140a and the second composite material 140b are the same as the material of the composite material layer 140.

[0051] Referring again to FIG. 6D, a first external adhesive layer 115 is formed on the first original external insulating layer 512, and a second external adhesive layer 125 is formed on the second original external insulating layer 522. In detail, the first external adhesive layer 115 and the second external adhesive layer 125 are respectively formed around the composite material layer 140.

[0052] Referring to Figures 6D and 6E, the first extension 512b and the first external circuit layer 516 are bent to cover the first main body 512a. The second extension 522b and the second external circuit layer 526 are bent to cover the second main body 522a. In detail, the groove R1 of the first extension 512b (refer to Figure 6D) is formed relative to the structure of the first external reinforcing layer 112 and the second composite material 140b, and the groove R2 of the second extension 522b (refer to Figure 6D) is formed relative to the structure of the second external reinforcing layer 122 and the second composite material 140b.

[0053] Referring to Figures 6E and 6F, perform the cutting step to separate the first extension 512b from the first main body 512a and the second extension 522b from the second main body 522a. It is understood that the first main body 512a, first extension 512b, first external circuit layer 516, second main body 522a, second extension 522b, and second external circuit layer 526 in the circuit board 100a of Figure 6F correspond to the first external insulating layer 113, second external insulating layer 114, first external circuit layer 117, third external insulating layer 123, fourth external insulating layer 124, and second external circuit layer 127 in the circuit board 100 of Figure 1. Circuit layer 460 and circuit layer 470 in the circuit board 100a of Figure 6F correspond to circuit layer 135 and circuit layer 136 in the circuit board 100 of Figure 1.

[0054] The manufacturing methods of the circuit board 200 in FIG2 and the circuit board 300 in FIG3 are similar to the manufacturing methods of the circuit board 100a in FIG6A to FIG6F described above, and will not be repeated here.

[0055] The circuit board of the present invention can be widely used in consumer electronics products (e.g., portable devices such as smartphones or tablets), automotive fields (e.g., signal transmission between in-vehicle sensors and control units), medical fields (e.g., wearable health monitoring devices or implantable medical devices), aerospace fields (e.g., feather-light and highly reliable communication systems), and Internet of Things (IoT) (e.g., the construction of miniaturized sensor networks in fields such as smart homes and smart cities), but is not limited thereto.

[0056] In summary, the circuit board provided by the present invention has a first external reinforcement layer, a second external reinforcement layer and a composite material layer embedded inside the circuit board, so that electronic components can be additionally set on both sides of the circuit board, thereby increasing the freedom of circuit design, space utilization and functional integration capability.

[0057] The foregoing summary of the features of various embodiments enables those skilled in the art to better understand the nature of this application. Those skilled in the art should understand that this application can be readily used as the basis for designing or modifying other processes and structures to achieve the same purpose and / or realize the same advantages of the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of this application, and various changes, substitutions, and modifications can be made without departing from the spirit and scope of this application. [Simplified Explanation of the Diagram]

[0008] The various aspects of this application can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be understood that, according to industry standard practice, the various features are not drawn to scale. In fact, for clarity, the dimensions of various features can be arbitrarily increased or decreased. FIG1 is a schematic cross-sectional view of a circuit board according to a first embodiment of the present invention. FIG2 is a schematic cross-sectional view of a circuit board according to a second embodiment of the present invention. FIG3 is a schematic cross-sectional view of a circuit board according to a third embodiment of the present invention. FIG4A to FIG4C are schematic cross-sectional views of an internal substrate at various stages of the manufacturing process according to some embodiments of the present invention. FIG5A and FIG5B are schematic cross-sectional views of a first original external structure (or a second original external structure) at various stages of the manufacturing process according to some embodiments of the present invention. FIG6A to FIG6F are schematic cross-sectional views of a circuit board at various stages of the manufacturing process according to a first embodiment of the present invention.

Claims

1. A circuit board comprising: a first external structure including a first external reinforcement layer disposed therein; a second external structure including a second external reinforcement layer disposed therein; an internal structure disposed between the first external structure and the second external structure, wherein the first external structure, the internal structure, and the second external structure are stacked sequentially along a first direction, wherein the internal structure has a cavity extending along the first direction, the cavity being formed through the internal structure, the first external reinforcement layer being located at a top of the cavity, the cavity exposing a portion of the first external reinforcement layer, and the second external reinforcement layer being located at a bottom of the cavity, the cavity exposing a portion of the second external reinforcement layer; and a composite material layer surrounding the cavity, the first external structure, and the second external structure.

2. The circuit board as claimed in claim 1, wherein the internal structure further comprises: an internal insulating layer, wherein the composite material layer is further disposed on a sidewall of the internal insulating layer; a first internal adhesive layer disposed between the internal insulating layer and the first external structure, wherein the composite material layer is further disposed on a sidewall of the first internal adhesive layer; and a second internal adhesive layer disposed between the internal insulating layer and the second external structure, wherein the composite material layer is further disposed on a sidewall of the second internal adhesive layer.

3. The circuit board as claimed in claim 2, wherein the first external structure further comprises: a first external insulating layer disposed on the first internal adhesive layer; a second external insulating layer disposed on the first external insulating layer and the cavity, wherein a portion of the first external insulating layer protrudes from a sidewall of the second external insulating layer in a second direction, the second direction being perpendicular to the first direction; and a first external adhesive layer disposed between the first external insulating layer and the second external insulating layer, wherein the first external reinforcing layer is disposed between the second external insulating layer and the cavity, and the composite material layer surrounds the first external reinforcing layer and contacts the first external insulating layer, the first external adhesive layer, and the second external insulating layer.

4. The circuit board as claimed in claim 3, wherein the second external structure further comprises: a third external insulating layer disposed on the second internal adhesive layer; a fourth external insulating layer disposed on the third external insulating layer and the cavity, wherein a portion of the third external insulating layer protrudes from a sidewall of the fourth external insulating layer in the second direction; and a second external adhesive layer disposed between the third external insulating layer and the fourth external insulating layer, wherein the second external reinforcing layer is disposed between the fourth external insulating layer and the cavity, and the composite material layer surrounds the second external reinforcing layer and contacts the third external insulating layer, the second external adhesive layer, and the fourth external insulating layer.

5. The circuit board as claimed in claim 1, wherein the composite material layer is composed of a plurality of columnar materials arranged in a closed structure, each of the plurality of columnar materials extending along a third direction perpendicular to the first direction, and each of the plurality of columnar materials comprising a plurality of ceramic particles, a fiber reinforcement material, and a graphene material.

6. The circuit board as claimed in claim 1, wherein the materials of the first external reinforcement layer and the second external reinforcement layer comprise glass fiber and thermosetting resin.

7. A method of manufacturing a circuit board, comprising: providing a first original external structure, an inner substrate, and a second original external structure sequentially stacked along a first direction, wherein the first original external structure includes a first original external insulating layer and a first external circuit layer facing the inner substrate, wherein the first original external insulating layer includes a first body portion and a first extension portion connected to the first body portion, and the first external circuit layer is disposed on the first extension portion; wherein the second original external structure includes a second original external insulating layer and a second external circuit layer facing the inner substrate, wherein the second original external insulating layer includes a second body portion and a second extension portion connected to the second body portion, and the second external circuit layer is disposed on the second extension portion; removing a portion of the inner substrate, a portion of the first body portion, and a portion of the second body portion to form a through-hole in the inner substrate along the first direction and expose a portion of a sidewall of the inner substrate. A first composite material is formed on the sidewall of the inner substrate of the portion, the first main body portion of the portion, and the second main body portion of the portion; a first external reinforcement layer is formed on the first composite material and in the first original external insulation layer, and a second external reinforcement layer is formed on the first composite material and in the second original external insulation layer to close the through hole and form a cavity in the inner substrate, the cavity exposing a portion of the first external reinforcement layer and a portion of the second external reinforcement layer; a second composite material is formed covering the first external reinforcement layer and the second external reinforcement layer; the first extension and the first external circuit layer are bent to cover the first main body portion; the second extension and the second external circuit layer are bent to cover the second main body portion; And perform a cutting step to separate the first extension from the first main body and the second extension from the second main body.

8. The method of manufacturing a circuit board as claimed in claim 7 further comprises: forming a first internal adhesive layer between the first original external structure and the internal substrate; and forming a second internal adhesive layer between the second original external structure and the internal substrate; After removing the first main body portion, a portion of the upper surface of the first internal adhesive layer is exposed; After removing the second main body portion, a portion of the upper surface of the second internal adhesive layer is exposed; The first composite material is formed on the upper surface and one sidewall of the first internal adhesive layer; and the first composite material is formed on the upper surface and one sidewall of the second internal adhesive layer.

9. The method of manufacturing a circuit board as claimed in claim 7 further comprises: forming a first external adhesive layer on the first original external insulating layer before bending the first extension and the first external circuit layer; and forming a second external adhesive layer on the second original external insulating layer before bending the second extension and the second external circuit layer.

10. The method of manufacturing a circuit board as claimed in claim 7 further comprises: before bending the first extension and the first external circuit layer and bending the second extension and the second external circuit layer, recessing a portion of the first extension and a portion of the second extension.

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