TWI890389B - Foldable circuit board and method of manufacturing the same - Google Patents

Abstract

A foldable circuit board and a method of manufacturing the same are provided. The foldable circuit board includes a first flexible wiring board, a second flexible wiring board and a first adhesive layer. The first flexible wiring board includes a dielectric layer, a wiring layer and an electromagnetic shielding layer. The dielectric layer has a groove in a bending area. The wiring layer and the dielectric layer are stacking. The wiring layer is exposed by the groove. The electromagnetic shielding layer is in the bending area and is disposed on the surface of the dielectric layer, and is electrically connected to the wiring layer by the groove. The first adhesive layer is in a non-bending area and connected between the first flexible wiring board and the second flexible wiring board. The foldable circuit board has a great effect on electromagnetic shielding in the bending area through the electromagnetic shielding layer and the groove.

Description

Folding circuit board and manufacturing method thereof

The present disclosure relates to a circuit board and a manufacturing method thereof, and in particular to a foldable circuit board and a manufacturing method thereof.

Foldable smartphones have already been developed. Flexible printed circuits (FPCs) are well-suited for use in these devices due to their bendable nature. These smartphones may require multiple folds at the bend area. However, since FPCs are multi-layer boards, air gaps must be maintained between the layers to ensure their durability. This makes them unsuitable for conductive vias used for electromagnetic shielding, compromising signal integrity and potentially leading to electromagnetic wave leakage.

At least one embodiment of the present disclosure provides a foldable circuit board and a manufacturing method thereof, which utilizes an electromagnetic shielding layer and a groove in a bending area to produce an electromagnetic shielding effect.

At least one embodiment of the present disclosure provides a foldable circuit board having a bend region and a non-bend region adjacent to the bend region, and includes a first flexible circuit board, a second flexible circuit board, and a first adhesive layer. The first flexible circuit board includes a first dielectric layer, a first circuit layer, and a first electromagnetic shielding layer. The first dielectric layer has a first groove located within the bend region. The first circuit layer and the first dielectric layer are stacked. The first groove exposes the first circuit layer. The first electromagnetic shielding layer is located within the bend region and disposed on a surface of the first dielectric layer, electrically conductive to the first circuit layer via the first groove. The first adhesive layer is located within the non-bend region and connected between the first flexible circuit board and the second flexible circuit board.

In at least one embodiment of the present disclosure, a second flexible circuit board includes a second dielectric layer, a second circuit layer, and a second electromagnetic shielding layer. The second dielectric layer is adjacent to the first circuit layer and has a second groove. The vertical projection of the second groove overlaps the vertical projection of the first groove. The second circuit layer and the second dielectric layer are stacked. The second groove exposes the second circuit layer. The second electromagnetic shielding layer is located within the bend region and spaced apart from the first circuit layer. The second electromagnetic shielding layer is disposed on a surface of the second dielectric layer and is electrically conductive to the second circuit layer via the second groove.

In at least one embodiment of the present disclosure, the foldable circuit board further includes a third flexible circuit board and a second adhesive layer. The third flexible circuit board is stacked on the first flexible circuit board and spaced apart from the first flexible circuit board. The first flexible circuit board is located between the second and third flexible circuit boards. The second adhesive layer is located in the non-bending region and connects the first and third flexible circuit boards.

In at least one embodiment of the present disclosure, a third flexible circuit board includes a third dielectric layer, a third wiring layer, and a third electromagnetic shielding layer. The third dielectric layer is adjacent to the first dielectric layer and has a third groove. The vertical projection of the third groove overlaps the vertical projection of the first groove. The third wiring layer and the third dielectric layer are stacked. The third groove exposes the third wiring layer. The third electromagnetic shielding layer is located within the bend region and spaced apart from the first electromagnetic shielding layer. The third electromagnetic shielding layer is disposed on a surface of the third dielectric layer and is electrically conductive to the third wiring layer via the third groove.

In at least one embodiment of the present disclosure, the foldable circuit board further includes a shielding wall. The foldable circuit board further includes a trench within the non-bending region. The trench extends from the second flexible circuit board to the surface of the first circuit layer. The shielding wall is disposed within the trench and is electrically connected to the first circuit layer.

In at least one embodiment of the present disclosure, the trench and the shielding wall surround the non-bending area.

In at least one embodiment of the present disclosure, the first flexible circuit board further includes a first cover layer and a fourth electromagnetic shielding layer. The first cover layer has a bonding agent and a fourth groove. The first cover layer is stacked on the first circuit layer and connected to the first circuit layer via the bonding agent. The fourth groove exposes the first circuit layer. The vertical projection of the fourth groove overlaps the vertical projection of the first groove. The fourth electromagnetic shielding layer is located in the bend region and disposed on the surface of the first cover layer. It is electrically connected to the first circuit layer via the fourth groove.

At least one embodiment of the present disclosure provides a method for manufacturing a foldable circuit board, comprising: providing a first flexible substrate, wherein the first flexible substrate includes a first dielectric layer and a first metal layer, the first dielectric layer and the first metal layer being stacked; patterning the first metal layer to form a first circuit layer; forming a first groove in the first dielectric layer, wherein the first groove exposes the first circuit layer; disposing a first electromagnetic shielding layer on a portion of the surface of the first dielectric layer to form a first flexible circuit board, wherein the first electromagnetic shielding layer is electrically connected to the first circuit layer via the first groove; providing a second flexible circuit board; and bonding the first flexible circuit board to the second flexible circuit board using a first adhesive layer, wherein a vertical projection of the first electromagnetic shielding layer at least partially does not overlap with a vertical projection of the first adhesive layer.

In at least one embodiment of the present disclosure, the step of providing a second flexible circuit board includes: providing a second flexible substrate, wherein the second flexible substrate includes a second dielectric layer and a second metal layer, the second dielectric layer and the second metal layer being stacked; forming a second groove in the second dielectric layer, wherein the second dielectric layer is adjacent to the first circuit layer, the second groove exposes the second metal layer, and a vertical projection of the second groove overlaps with a vertical projection of the first groove; and disposing a second electromagnetic shielding layer on a portion of a surface of the second dielectric layer to form the second flexible circuit board, wherein the second electromagnetic shielding layer is electrically connected to the second metal layer via the second groove, and the vertical projection of the second electromagnetic shielding layer at least partially does not overlap with a vertical projection of the first adhesive layer.

In at least one embodiment of the present disclosure, the manufacturing method further includes: forming trenches on the first flexible circuit board and the second flexible circuit board, wherein the trenches extend from the second flexible circuit board to the first circuit layer; and forming shielding walls in the trenches, wherein the shielding walls are electrically connected to the first circuit layer.

Based on the above, in the foldable circuit board disclosed in the above embodiments, the electromagnetic shielding layer in the bend area can be electrically connected to the grounding plates of the upper and lower circuit layers through the grooves, so that the foldable circuit board has a good electromagnetic shielding effect in the bend area, thereby reducing signal integrity issues and electromagnetic wave leakage.

In the following text, in order to clearly present the technical features of the present invention, the dimensions (e.g., length, width, thickness, and depth) of the elements (e.g., layers, films, substrates, and regions) in the drawings will be enlarged in a non-proportional manner, and the number of some elements will be reduced. Therefore, the description and explanation of the embodiments below are not limited to the number of elements, the dimensions, and the shapes of the elements in the drawings, but should cover the dimensions, shapes, and deviations therefrom caused by actual manufacturing processes and/or tolerances. For example, a flat surface shown in the drawings may have rough and/or nonlinear features, and a sharp corner shown in the drawings may be rounded. Therefore, the elements shown in the drawings of the present invention are primarily for illustration purposes and are not intended to accurately depict the actual shape of the elements, nor are they intended to limit the scope of the patent application of the present invention.

Second, the terms "approximately," "approximately," or "substantially" used in this case encompass not only the numerical values and numerical ranges explicitly stated, but also the permissible deviations understood by one of ordinary skill in the art to which the invention pertains. This deviation may be determined by measurement errors, such as those arising from limitations of the measurement system or process conditions. Furthermore, "approximately" may mean within one or more standard deviations of the numerical value, such as ±30%, ±20%, ±10%, or ±5%. When used in this document, terms such as "approximately," "approximately," or "substantially" may be used to define acceptable deviations or standard deviations depending on the optical, etching, mechanical, or other properties. A single standard deviation is not intended to apply to all optical, etching, mechanical, or other properties.

The terms used in this application are only for describing specific embodiments and are not intended to limit the scope of the patent application. Unless otherwise limited, the singular forms "a," "an," or "the" can also be used to represent plural forms.

Figure 1 is a schematic cross-sectional view of a foldable circuit board 100 according to at least one embodiment of the present disclosure, and Figure 2 is a schematic top view of the foldable circuit board 100 in Figure 1 , wherein the cross-sectional view in Figure 1 is taken along line I-I' in Figure 2 . Referring to Figures 1 and 2 , foldable circuit board 100 includes a first flexible circuit board 110, a second flexible circuit board 120, a third flexible circuit board 130, a plurality of first adhesive layers 140, a plurality of second adhesive layers 150, a plurality of insulating layers 160, a plurality of protective layers 170, and a plurality of surface electromagnetic shielding layers 180. Foldable circuit board 100 can be used in high-frequency radio frequency antennas or high-frequency, high-speed transmission lines. The transmission line can be a microstrip line, stripline, coaxial line or other structure and can be used to provide voltage/current, ground and/or transmit signals.

It should be noted that the foldable circuit board 100 in this example is a three-layer stacked circuit board comprising a first flexible circuit board 110, a second flexible circuit board 120, and a third flexible circuit board 130. However, this is not a limitation. The foldable circuit board 100 may also comprise only the first flexible circuit board 110 and the second flexible circuit board 120, or a two-layer stacked circuit board comprising the first flexible circuit board 110 and the third flexible circuit board 130. Furthermore, the foldable circuit board 100 in this example may also be stacked with other circuit boards outside the second flexible circuit board 120 and the third flexible circuit board 130 in a build-up manner, without limitation.

Folding circuit board 100 has a bending region 101 and a non-bending region 102, wherein non-bending region 102 is adjacent to bending region 101. In this example, folding circuit board 100 has two non-bending regions 102, wherein bending region 101 is located in the middle of folding circuit board 100, and the two non-bending regions 102 are adjacent to either side of bending region 101. Folding circuit board 100 is bent by bending one non-bending region 102 toward the other non-bending region 102, causing bending region 101 to bend and the two non-bending regions 102 to overlap.

The first flexible circuit board 110 includes a dielectric layer 111, a circuit layer 112, a cover layer 113, and multiple electromagnetic shielding layers 114a and 114b. Dielectric layer 111 is a flexible substrate and can be made of a material with a low dielectric loss factor (Df), such as liquid crystal polymer (LCP), modified polyimide (MPI), or a fluorine-based material. Dielectric layer 111 has at least one groove 111a located within the bending region 101. Circuit layer 112 is stacked on dielectric layer 111 and includes a grounding pad 112a. Groove 111a exposes the grounding pad 112a of circuit layer 112.

The cover layer 113 is stacked on the circuit layer 112, and the circuit layer 112 is located between the dielectric layer 111 and the cover layer 113. The cover layer 113 has a bonding agent 113a and at least one groove 113b. The cover layer 113 is connected to the circuit layer 112 via the bonding agent 113a. The groove 113b exposes the grounding plate 112a of the circuit layer 112. Furthermore, the vertical projection of groove 113b overlaps with the vertical projection of groove 111a, wherein the vertical projection of groove 113b is the area generated by projecting groove 113b on the foldable circuit board 100 in the direction parallel to Z, for example, onto the lower surface of dielectric layer 111, and the vertical projection of groove 111a is the area generated by projecting groove 111a on the foldable circuit board 100 in the direction parallel to Z, for example, onto the upper surface of cover layer 113.

Electromagnetic shielding layers 114a and 114b are located within the bend region 101. Electromagnetic shielding layer 114a is disposed on the surface of dielectric layer 111 and electrically connected to grounding plate 112a of circuit layer 112 via groove 111a. Electromagnetic shielding layer 114b is disposed on the surface of cover layer 113 and electrically connected to grounding plate 112a of circuit layer 112 via groove 113b.

Second flexible circuit board 120 is stacked on first flexible circuit board 110 and spaced apart from first flexible circuit board 110. Second flexible circuit board 120 includes a dielectric layer 121, a circuit layer 122, and an electromagnetic shielding layer 123. Dielectric layer 121 is a flexible substrate and can be made of the same low-dielectric-loss material as dielectric layer 111. Dielectric layer 121 is adjacent to circuit layer 112 and has at least one recess 121a located within bend region 101.

Circuit layer 122 is stacked with dielectric layer 121 and includes a grounding pad 122a. Recess 121a exposes grounding pad 122a of circuit layer 122. Furthermore, the vertical projection of recess 121a overlaps with the vertical projection of recess 111a, allowing recesses 121a and 111a to align with each other. Electromagnetic shielding layer 123 is located within bend region 101. Electromagnetic shielding layer 123 is disposed on the surface of dielectric layer 121 and electrically connected to grounding pad 122a of circuit layer 122 via recess 121a.

The third flexible circuit board 130 is stacked on the first flexible circuit board 110 and spaced apart from the first flexible circuit board 110. The first flexible circuit board 110 is located between the second flexible circuit board 120 and the third flexible circuit board 130. The third flexible circuit board 130 includes a dielectric layer 131, a circuit layer 132, and an electromagnetic shielding layer 133. Dielectric layer 131 is a flexible substrate and can be made of the same low-dielectric-loss material as dielectric layer 111. Dielectric layer 131 is adjacent to dielectric layer 111 and has at least one groove 131a located within the bend region 101.

Circuit layer 132 is stacked with dielectric layer 131 and includes a grounding pad 132a. Recess 131a exposes grounding pad 132a of circuit layer 132. Furthermore, the vertical projection of recess 131a overlaps with the vertical projection of recess 111a, allowing recesses 131a and 111a to align with each other. Electromagnetic shielding layer 133 is located within bend region 101. Electromagnetic shielding layer 133 is disposed on the surface of dielectric layer 131 and electrically connected to grounding pad 132a of circuit layer 132 via recess 131a.

Multiple first adhesive layers 140 are located in the two non-bending regions 102 and connect between the first flexible circuit board 110 and the second flexible circuit board 120. These first adhesive layers 140 are not distributed in the bending region 101, so that an air gap exists between the first flexible circuit board 110 and the second flexible circuit board 120 in the bending region 101. In other words, the first adhesive layers 140 surround the grooves 121a and 113b.

Similarly, multiple second adhesive layers 150 are located in the two non-bending regions 102 and connect between the first flexible circuit board 110 and the third flexible circuit board 130. Furthermore, these second adhesive layers 150 are not distributed within the bending region 101, resulting in an air gap between the first flexible circuit board 110 and the third flexible circuit board 130 within the bending region 101. Specifically, the second adhesive layers 150 surround the grooves 111a and 131a.

Multiple insulating layers 160 are disposed on the circuit layer 122 of the second flexible circuit board 120 and the circuit layer 132 of the third flexible circuit board 130, respectively. Furthermore, multiple protective layers 170 are disposed on these insulating layers 160, respectively. This sandwiches the first flexible circuit board 110, the second flexible circuit board 120, and the third flexible circuit board 130 between the insulating layers 160 and the protective layers 170. The protective layers 170 can be made of an insulating ink or other resin material. The protective layer 170 and the insulating layer 160 have multiple connected grooves 170a, where these grooves 170a are distributed in the bending area 101 and the non-bending area 102, and extend from the protective layer 170 through the insulating layer 160 to the circuit layers 122 and 132, so that these grooves 170a reveal the grounding plate 122a of the circuit layer 122 and the grounding plate 132a of the circuit layer 132.

Furthermore, the vertical projections of the grooves 170a distributed in the bend region 101 also overlap with the vertical projections of the grooves 111a, so that the grooves 170a and 111a are aligned with each other. Multiple surface electromagnetic shielding layers 180 are respectively disposed on the surfaces of these protective layers 170 and are electrically connected to the grounding plates 122a and 132a of the circuit layers 122 and 132 through the grooves 170a. Furthermore, the grounding plates 112a, 122a, and 132a of the circuit layers 112, 122, and 132 are also electrically connected to each other.

In some other embodiments, a rust-proof metal (not shown), such as a nickel layer, may be formed between the surfaces of the grounding plates 112a, 122a, and 132a exposed by the grooves 111a, 113b, 121a, and 131a and the electromagnetic shielding layers 114a, 114b, 123, and 133, and between the surfaces of the grounding plates 122a and 132a exposed by the groove 170a and the surface electromagnetic shielding layer 180. This improves electrical conductivity between the electromagnetic shielding layers 114a, 114b, 123, and 133 and the grounding plates 112a, 122a, and 132a, and also improves electrical conductivity between the surface electromagnetic shielding layer 180 and the grounding plates 122a and 132a.

Because grooves 111a, 113b, 121a, and 131a are distributed within the bend region 101, electromagnetic shielding layers 114a, 114b, 123, and 133 within the bend region 101 can electrically connect to the grounding plates 112a, 122a, and 132a of the upper and lower circuit layers 112, 122, and 132 via the grooves 111a, 113b, 121a, and 131a, thereby forming electromagnetic shielding between the upper and lower layers and on the sides of the circuit board. Furthermore, the electromagnetic shielding layers 114a, 114b, 123, 133 adhere to the sidewalls of the grooves 111a, 113b, 121a, 131a, thereby forming a shielding side for the circuit layers 112, 122, 132. This allows the circuit layers 112, 122, 132 between the electromagnetic shielding layers 114a, 114b, 123, 133 to be similarly disposed in a closed space with a good shielding effect. In particular, the vertical projections of grooves 111a, 113b, 121a, and 131a overlap, minimizing the distances between electromagnetic shielding layers 114a and 114b, between electromagnetic shielding layer 123 and surface electromagnetic shielding layer 180, and between electromagnetic shielding layer 133 and surface electromagnetic shielding layer 180. This improves shielding effectiveness. Folding circuit board 100 exhibits excellent electromagnetic shielding effectiveness in bend region 101, reducing signal integrity issues and electromagnetic wave leakage. Furthermore, the electromagnetic shielding layers 114a, 114b, 123, 133 and the grooves 111a, 113b, 121a, 131a do not affect the bending requirements of the foldable circuit board 100. Furthermore, the grooves 111a, 113b, 121a, 131a in the foldable circuit board 100 are parallel to the fold line in the folding region 101, making the foldable circuit board 100 bend more smoothly.

In some other embodiments, the foldable circuit board 100 further has at least one trench 103, 104 (see FIG. 1 and FIG. 7 ) and at least one shielding wall 190, wherein the number of shielding walls 190 is the same as the number of trenches 103, 104. In this example, multiple trenches 103, 104 and multiple shielding walls 190 are used for illustration.

These trenches 103 and 104 are respectively distributed within the non-bending regions 102 and surround the non-bending regions 102. For example, these trenches 103 and 104 may surround a portion of the boundary adjacent to the non-bending regions 102. The depth of some trenches 103 extends from the second flexible circuit board 120 to the surface of the wiring layer 112 of the first flexible circuit board 110, while the depth of other trenches 104 extends from the third flexible circuit board 130 to the surface of the wiring layer 112 of the first flexible circuit board 110.

In particular, the vertical projection of trench 103 can overlap with the vertical projection of trench 104, so that trench 103 and trench 104 can be aligned with each other. These shielding walls 190 are respectively disposed in these trenches 103 and 104 and are electrically connected to the ground plate 112a of the circuit layer 112 to form electromagnetic shielding between the upper and lower layers of the circuit board and on the sides. This allows the folded circuit board 100 to have better electromagnetic shielding when used to transmit high-frequency and high-speed signals.

Figures 3A and 3B are schematic cross-sectional views of the step of providing a first flexible circuit board 110 in the manufacturing method of the foldable circuit board 100 shown in Figure 1. Referring to Figure 3A , first, a first flexible substrate 110A is provided, comprising a dielectric layer 111 and a metal layer 115. Dielectric layer 111 and metal layer 115 are stacked. This first flexible substrate 110A can be a flexible single-sided copper-clad substrate. Next, metal layer 115 is patterned to form a circuit layer 112, wherein circuit layer 112 includes a grounding pad 112a. Next, a cover layer 113 is disposed on circuit layer 112, with cover layer 113 being connected to circuit layer 112 via adhesive 113a. The cover layer 113 has a groove 113 b , and the groove 113 b exposes the ground plate 112 a of the circuit layer 112 .

Referring to Figure 3B , a recess 111a is then formed in dielectric layer 111. Recess 111a exposes grounding pad 112a of circuit layer 112, and its vertical projection overlaps with the vertical projection of recess 113b. For example, recess 111a can be formed in dielectric layer 111 by selective etching, with the vertical projection of recess 111a overlapping with the vertical projection of recess 113b. A surface anti-rust treatment is then performed on grounding pad 112a exposed by recesses 111a and 113b. For example, a layer of anti-rust metal (not shown) is plated on the exposed grounding pad 112a. The anti-rust metal can be a nickel layer.

Next, multiple electromagnetic shielding layers 114a and 114b are disposed on portions of the surfaces of dielectric layer 111 and cover layer 113, respectively, to form first flexible circuit board 110. Electromagnetic shielding layers 114a and 114b are located in the middle region of foldable circuit board 100, which corresponds to the aforementioned bend region 101. For example, electromagnetic shielding layers 114a and 114b can be disposed on dielectric layer 111 and cover layer 113 by applying electromagnetic shielding film or printing electromagnetic shielding ink. Electromagnetic shielding layers 114a and 114b are electrically connected to circuit layer 112 via grooves 111a and 113b, respectively.

Figure 4 is a schematic cross-sectional view of the step of providing a second flexible circuit board 120 in the manufacturing method of the foldable circuit board 100 of Figure 1. Referring to Figure 4 , first, a second flexible substrate 120A is provided, comprising a dielectric layer 121 and a metal layer 124. Dielectric layer 121 and metal layer 124 are stacked. This second flexible substrate 120A can also be a flexible single-sided copper-clad substrate, and the material of dielectric layer 121 can be a low-dielectric-loss material. This second flexible substrate 120A can be similar to the first flexible substrate 110A. Next, a recess 121a is formed in dielectric layer 121, whereby the recess 121a exposes the metal layer 124. It should be noted that the positions of the grooves 121a are preset to overlap with the vertical projections of the grooves 111a and 113b, wherein the grooves 121a can also be formed on the dielectric layer 121 by selective etching.

Afterwards, the exposed metal layer 124 is also treated with a surface anti-rust treatment. Next, an electromagnetic shielding layer 123 is placed on a portion of the surface of the dielectric layer 121 to form the second flexible circuit board 120. The electromagnetic shielding layer 123 is also located in the middle area of the foldable circuit board 100, namely, the aforementioned bend area 101. The placement of the electromagnetic shielding layer 123 is similar to that of the electromagnetic shielding layers 114a and 114b and will not be further described here. The electromagnetic shielding layer 123 is electrically connected to the metal layer 124 via the groove 121a.

Figure 5 is a schematic cross-sectional view of the step of providing a third flexible circuit board 130 in the manufacturing method of the foldable circuit board 100 shown in Figure 1. Referring to Figure 5 , the step of providing the third flexible circuit board 130 is similar to the step of providing the second flexible circuit board 120. First, a third flexible substrate 130A is provided, comprising a dielectric layer 131 and a metal layer 134. This third flexible substrate 130A is similar to the second flexible substrate 120A and will not be described in detail here. Next, a recess 131a is formed in the dielectric layer 131 by selective etching, where the recess 131a exposes the metal layer 134. The recess 131a is also positioned to overlap with the perpendicular projections of the recesses 111a and 113b.

Next, the metal layer 134 exposed by the groove 131a is treated with a surface anti-rust treatment, and an electromagnetic shielding layer 133 is disposed on a portion of the surface of the dielectric layer 131, thereby forming the third flexible circuit board 130. The electromagnetic shielding layer 133 is also located in the middle area of the foldable circuit board 100, namely the aforementioned bend area 101. The electromagnetic shielding layer 133 is electrically connected to the metal layer 134 through the groove 131a.

Figure 6 is a schematic cross-sectional view of the step of joining the first flexible circuit board 110, the second flexible circuit board 120, and the third flexible circuit board 130 in the manufacturing method of the foldable circuit board 100 shown in Figure 1. First, the first flexible circuit board 110, the second flexible circuit board 120, and the third flexible circuit board 130 are arranged in sequence, with the first flexible circuit board 110 positioned between the second flexible circuit board 120 and the third flexible circuit board 130, and the cover layer 113 and dielectric layer 111 of the first flexible circuit board 110 facing the dielectric layer 121 of the second flexible circuit board 120 and the dielectric layer 131 of the third flexible circuit board 130, respectively. A plurality of first adhesive layers 140 are disposed between the first flexible circuit board 110 and the second flexible circuit board 120 , and a plurality of second adhesive layers 150 are disposed between the first flexible circuit board 110 and the third flexible circuit board 130 .

It should be noted that the first adhesive layers 140 only correspond to portions of the surfaces of the first and second flexible circuit boards 110 and 120, that is, the first adhesive layers 140 only correspond to the aforementioned non-bending regions 102. The second adhesive layers 150 only correspond to portions of the surfaces of the first and third flexible circuit boards 110 and 130, that is, the second adhesive layers 150 only correspond to the aforementioned non-bending regions 102. The vertical projections of the electromagnetic shielding layers 114a, 114b, 123, and 133 at least partially do not overlap with the vertical projections of the first and second adhesive layers 140 and 150. Next, the first flexible circuit board 110, the second flexible circuit board 120, the third flexible circuit board 130, the first adhesive layer 140, and the second adhesive layer 150 are pressed together, so that the first flexible circuit board 110 and the second flexible circuit board 120 are connected via the first adhesive layer 140, and the first flexible circuit board 110 and the third flexible circuit board 130 are connected via the second adhesive layer 150.

Figure 7 is a cross-sectional diagram illustrating the step of forming trenches 103 and 104 in the manufacturing method of the foldable circuit board 100 shown in Figure 1. First, two trenches 103 are formed on the first flexible circuit board 110 and the second flexible circuit board 120. One trench 103 encircles one side of the foldable circuit board 100 (see Figure 2), while the other trench 103 encircles the other side of the foldable circuit board 100. The trenches 103 can be formed by laser machining. Each trench 103 extends from the second flexible circuit board 120 to the surface of the circuit layer 112 of the first flexible circuit board 110. The vertical projections of the trenches 103 do not overlap with the vertical projections of the electromagnetic shielding layers 114a, 114b, 123, and 133.

Two trenches 104 are also formed on the first flexible circuit board 110 and the third flexible circuit board 130 through laser processing. One trench 104 surrounds one side of the foldable circuit board 100, while the other trench 104 surrounds the other side of the foldable circuit board 100. The depth of each trench 104 extends from the third flexible circuit board 130 to the surface of the wiring layer 112 of the first flexible circuit board 110. In particular, the vertical projections of these trenches 104 overlap with the vertical projections of trench 103.

Figure 8 is a cross-sectional diagram illustrating the steps of forming shielding wall 190, outer layer wiring, and protective layer 170 in the manufacturing method of foldable circuit board 100 shown in Figure 1. Next, shielding wall 190 is formed within trenches 103 and 104, for example, by trench plating. Shielding wall 190 is electrically connected to ground plate 112a of circuit layer 112.

Next, the metal layer 124 of the second flexible circuit board 120 is patterned to form the circuit layer 122, and the metal layer 134 of the third flexible circuit board 130 is patterned to form the circuit layer 132. It should be noted that the portions of the circuit layers 122 and 132 that are electrically connected to the electromagnetic shielding layers 123 and 133 are the grounding plates 122a and 132a. The signal plates of the circuit layers 122 and 132, which transmit signals, are not electrically connected to the electromagnetic shielding layers 123 and 133. Next, an insulating layer 160 and a protective layer 170 are sequentially formed on the circuit layers 122 and 132. The protection layer 170 and the insulation layer 160 have a plurality of communicating grooves 170a. These grooves 170a expose the grounding plates 122a and 132a of the circuit layers 122 and 132. The vertical projections of some of the grooves 170a overlap with the vertical projections of the groove 111a.

Afterwards, a surface rustproofing treatment is performed on the grounding pads 122a and 132a exposed by the grooves 170a. Next, as shown in Figure 1, multiple surface electromagnetic shielding layers 180 are placed on the surfaces of the protective layer 170, completing the fabrication of the foldable circuit board 100. The surface electromagnetic shielding layers 180 can be applied to the protective layer 170 by applying an electromagnetic shielding film or printing an electromagnetic shielding ink. The surface electromagnetic shielding layers 180 are electrically connected to the grounding pads 122a and 132a of the circuit layers 122 and 132, respectively, through the grooves 170a.

In summary, in the foldable circuit board disclosed in the above embodiments, the electromagnetic shielding layer within the bend area is electrically connected to the upper and lower circuit layers via the grooves, thereby forming electromagnetic shielding between the upper and lower layers and along the sides of the circuit board within the bend area. This provides the foldable circuit board with excellent electromagnetic shielding in the bend area, thereby reducing signal integrity issues and electromagnetic wave leakage. Furthermore, the shielding wall surrounds the non-bend area and is electrically connected to the upper and lower circuit layers, further forming electromagnetic shielding between the upper and lower layers and along the sides of the circuit board within the non-bend area, thus providing even better electromagnetic shielding when the foldable circuit board is used to transmit high-frequency and high-speed signals.

Although the present disclosure has been disclosed above with reference to the embodiments, they are not intended to limit the present disclosure. Those skilled in the art may make modifications and improvements without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the scope of the attached patent application.

100: Folding circuit board 101: Bend area 102: Non-bend area 103, 104: Grooves 110: First flexible circuit board 110A: First flexible substrate 111, 121, 131: Dielectric layer 111a, 113b, 121a, 131a, 170a: Grooves 112, 122, 132: Circuit layer 112a, 122a, 132a: Grounding plate 113: Covering layer 113a: Adhesive 114a, 114b, 123, 133: Electromagnetic shielding layer 115, 124, 134: Metal layer 120: Second flexible circuit board 120A: Second flexible substrate 130: Third flexible circuit board 130A: Third flexible substrate 140: First adhesive layer 150: Second adhesive layer 160: Insulation layer 170: Protective layer 180: Surface electromagnetic shielding layer 190: Shielding wall Z: Direction

For a more complete understanding of the embodiments and their advantages, reference is made to the following description in conjunction with the accompanying drawings, wherein: [FIG. 1] is a schematic cross-sectional view of a foldable circuit board according to at least one embodiment of the present disclosure; [FIG. 2] is a schematic top view of the foldable circuit board of FIG. 1; [FIG. 3A] and [FIG. 3B] are schematic cross-sectional views of the step of providing a first flexible circuit board in the method for manufacturing the foldable circuit board of FIG. 1; [FIG. 4] is a schematic cross-sectional view of the step of providing a second flexible circuit board in the method for manufacturing the foldable circuit board of FIG. 1; [FIG. 5] is a schematic cross-sectional view of the step of providing a third flexible circuit board in the method for manufacturing the foldable circuit board of FIG. 1; Figure 6 is a schematic cross-sectional view of the step of joining the first flexible circuit board, the second flexible circuit board, and the third flexible circuit board in the manufacturing method of the foldable circuit board of Figure 1. Figure 7 is a schematic cross-sectional view of the step of forming the trench in the manufacturing method of the foldable circuit board of Figure 1. Figure 8 is a schematic cross-sectional view of the step of forming the shielding wall, outer layer wiring, and protective layer in the manufacturing method of the foldable circuit board of Figure 1.

100: Folding circuit board

101: Bend Area

102: Non-bending area

103,104: Grooves

110: First flexible circuit board

111,121,131: Dielectric layer

111a, 113b, 121a, 131a, 170a: Grooves

112,122,132: Line layer

112a, 122a, 132a: Grounding plates

113: Covering layer

113a: Follow-up agent

114a, 114b, 123, 133: Electromagnetic shielding layer

120: Second flexible circuit board

130: Third flexible circuit board

140: First adhesive layer

150: Second adhesive layer

160: Insulating layer

170: Protective layer

180: Surface electromagnetic shielding layer

190: Shielding Wall

Z: Direction

Claims (9)

A foldable circuit board has a bend region and a non-bend region adjacent to the bend region, and comprises: A first flexible circuit board comprising: A first dielectric layer having a first groove located within the bend region; A first circuit layer stacked with the first dielectric layer, wherein the first groove exposes the first circuit layer; A first electromagnetic shielding layer located within the bend region, disposed on a surface of the first dielectric layer, and electrically connected to the first circuit layer via the first groove; A second flexible circuit board; and A first adhesive layer located within the non-bend region and connected between the first and second flexible circuit boards; The second flexible circuit board comprises: A second dielectric layer, adjacent to the first wiring layer and having a second recess, wherein a vertical projection of the second recess overlaps a vertical projection of the first recess; A second wiring layer, stacked with the second dielectric layer, wherein the second recess exposes the second wiring layer; and A second electromagnetic shielding layer, located within the bend region and spaced apart from the first wiring layer, wherein the second electromagnetic shielding layer is disposed on a surface of the second dielectric layer and electrically connected to the second wiring layer via the second recess. The foldable circuit board of claim 1 further comprises: A third flexible circuit board stacked on and spaced apart from the first flexible circuit board, wherein the first flexible circuit board is located between the second and third flexible circuit boards; and A second adhesive layer located in the non-bending region and connected between the first and third flexible circuit boards. The foldable circuit board of claim 2, wherein the third flexible circuit board comprises: a third dielectric layer, adjacent to the first dielectric layer and having a third recess, wherein a vertical projection of the third recess overlaps a vertical projection of the first recess; a third wiring layer, stacked with the third dielectric layer, wherein the third recess exposes the third wiring layer; and a third electromagnetic shielding layer, located within the bend region and spaced apart from the first electromagnetic shielding layer, wherein the third electromagnetic shielding layer is disposed on a surface of the third dielectric layer and electrically conductively connected to the third wiring layer via the third recess. The foldable circuit board as described in claim 1 further includes a shielding wall. The foldable circuit board also has a trench in the non-bending area. The trench extends from the second flexible circuit board to the surface of the first circuit layer. The shielding wall is arranged in the trench and is electrically connected to the first circuit layer. The foldable circuit board as described in claim 4, wherein the groove and the shielding wall surround the non-bending area. The foldable circuit board as described in claim 1, wherein the first flexible circuit board further comprises: a first cover layer having a bonding agent and a fourth recess, the first cover layer being stacked on the first circuit layer and connected to the first circuit layer via the bonding agent, the fourth recess exposing the first circuit layer, the vertical projection of the fourth recess overlapping the vertical projection of the first recess; and a fourth electromagnetic shielding layer located in the bend region and disposed on a surface of the first cover layer, electrically conductively connected to the first circuit layer via the fourth recess. A method for manufacturing a foldable circuit board comprises: Providing a first flexible substrate, wherein the first flexible substrate comprises a first dielectric layer and a first metal layer, the first dielectric layer and the first metal layer being stacked; Patterning the first metal layer to form a first circuit layer; Forming a first recess in the first dielectric layer, wherein the first recess exposes the first circuit layer; Providing a first electromagnetic shielding layer on a portion of the surface of the first dielectric layer to form a first flexible circuit board, wherein the first electromagnetic shielding layer is electrically conductive with the first circuit layer via the first recess; Providing a second flexible circuit board; and Combining the first flexible circuit board and the second flexible circuit board using a first adhesive layer, wherein a vertical projection of the first electromagnetic shielding layer at least partially does not overlap with a vertical projection of the first adhesive layer. The manufacturing method of claim 7, wherein the step of providing the second flexible circuit board comprises: Providing a second flexible substrate, wherein the second flexible substrate comprises a second dielectric layer and a second metal layer, wherein the second dielectric layer and the second metal layer are stacked; Forming a second recess in the second dielectric layer, wherein the second dielectric layer is adjacent to the first circuit layer, the second recess exposing the second metal layer, and a vertical projection of the second recess overlapping with a vertical projection of the first recess; and Providing a second electromagnetic shielding layer on a portion of a surface of the second dielectric layer to form the second flexible circuit board, wherein the second electromagnetic shielding layer is electrically conductive with the second metal layer via the second recess, and the vertical projection of the second electromagnetic shielding layer at least partially does not overlap with a vertical projection of the first adhesive layer. The manufacturing method of claim 7 further comprises: forming a trench on the first flexible circuit board and the second flexible circuit board, wherein the trench extends from the second flexible circuit board to the first wiring layer; and forming a shielding wall within the trench, wherein the shielding wall is electrically connected to the first wiring layer.