TWI899991B - Flexible circuit board and method of manufacturing thereof - Google Patents

Abstract

A flexible circuit board includes a first circuit substrate having a first metal layer, a second circuit substrate having a second metal layer and at least one electrical connection part. The electrical connection part is electrically connected between the first circuit substrate and the second circuit substrate. The electrical connection part includes a flexible part and at least one liquidmetal material. The flexible part is connected between the first circuit substrate and the second circuit substrate and has at least one passage. The passage connects the first metal layer and the second metal layer. The liquidmetal material is filled in the passage and is electrically connected between the first metal layer and the second metal layer.

Description

Flexible circuit board and manufacturing method thereof

This application relates to a circuit board and a method for manufacturing the circuit board, and in particular to a flexible and stretchable circuit board and a method for manufacturing the same.

Existing foldable or bendable electronic products typically rely on flat cables and board-to-board connectors (BTBs) to connect different modules. This not only takes up space within the electronic product but also hinders the product's slimming and miniaturization. Furthermore, the cables are prone to cracking or breaking after repeated bending or flexing, significantly reducing the product's lifespan. Furthermore, in applications where modules require frequent plugging, unplugging, or movement, vibration can easily cause poor contact between the cable or BTB connector and the module, reducing the stability and reliability of the connection.

Therefore, the present application provides a flexible circuit board comprising a first circuit substrate having a first metal layer, a second circuit substrate having a second metal layer, and at least one electrical connection portion. The at least one electrical connection portion electrically connects the first and second circuit substrates and comprises a stretchable portion and at least one liquid metal material. The stretchable portion connects the first and second circuit substrates and comprises at least one channel, wherein the at least one channel connects the first and second metal layers. The at least one liquid metal material is filled in the at least one channel, wherein the at least one liquid metal material electrically connects the first and second metal layers.

According to the flexible circuit board of this application, the stretchable part includes multiple stretchable wires, and each of the multiple stretchable wires includes the channel, and the multiple stretchable wires and the first circuit substrate and the second circuit substrate seal the liquid metal material.

According to the flexible circuit board of this application, the distance between any two adjacent stretchable wires is greater than or equal to 20 microns.

According to the flexible circuit board of the present application, each of the plurality of stretchable wires has a width, and the width decreases as the plurality of stretchable wires are stretched.

According to the flexible circuit board of this application, each of the multiple stretchable wires has a wire length, and the stretchable length of each of the multiple stretchable wires is less than or equal to 1.5 times the wire length.

According to the flexible circuit board of this application, each of the multiple stretchable wires and the liquid metal material has a first resistance value before bending, and each of the multiple stretchable wires and the liquid metal material has a second resistance value after bending, and the first resistance value is the same as the second resistance value.

The present application provides a method for manufacturing a flexible circuit board, comprising providing a first circuit substrate, wherein a first metal layer and a stretchable material layer are provided on the first circuit substrate; providing a sacrificial layer above the stretchable material layer; forming a plurality of slots on the sacrificial layer, wherein the plurality of slots expose the first metal layer below the stretchable material layer; after forming the plurality of slots on the sacrificial layer, coating the inner walls of the plurality of slots and a portion of the surface of the sacrificial layer with a stretchable material, wherein the bottoms of the plurality of slots not coated with the stretchable material expose the first metal layer; and coating the stretchable material on the inner walls of the plurality of slots and a portion of the surface of the sacrificial layer. After forming the material on the inner walls of the plurality of slots and the portion of the surface of the sacrificial layer, the plurality of slots are filled with the liquid metal so that the liquid metal material is electrically connected to the first metal layer; a second metal layer is disposed on the stretchable material and the liquid metal material so that the liquid metal in the slots is further electrically connected to the second metal layer and the liquid metal material is sealed between the first metal layer, the stretchable material and the second metal layer; at least one circuit structure is formed above the second metal layer; and after forming the at least one circuit structure, the sacrificial layer is removed.

According to an embodiment of the present disclosure, the circuit structure is formed by a build-up method, so that the circuit structure includes multiple circuit layers.

According to an embodiment of the present disclosure, a plurality of electronic components are further installed on the plurality of circuit layers.

According to an embodiment of the present disclosure, wherein the at least one circuit structure is at least one first circuit structure, the manufacturing method further includes forming at least one second circuit structure on the first metal layer.

The following application provides many different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and configurations are described below to simplify the present application. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, a first feature is formed on or above a second feature, which may include embodiments in which the first feature and the second feature are in direct contact, and may also include embodiments in which additional features may be formed between the first feature and the second feature so that the first feature and the second feature are not in direct contact. In addition, the present application may repeatedly reference numbers and/or text in various examples. This repetition is for the purpose of simplicity and clarity and does not in itself limit the relationship between the various embodiments and/or components discussed.

Please refer to Figure 1, which is a schematic cross-sectional view of a flexible circuit board 100 according to an embodiment of the present application. Flexible circuit board 100 includes a first circuit substrate 110, a second circuit substrate 120, and at least one electrical connection portion 130. A first metal layer 111 is provided on the first circuit substrate 110, and a second metal layer 121 is provided on the second circuit substrate 120. Electrical connection portion 130 electrically connects first circuit substrate 110 and second circuit substrate 120 and includes a stretchable portion 131 (hatched area) and liquid metal material 132 (dotted area). Stretchable portion 131 is used to connect first circuit substrate 110 and second circuit substrate 120 and has at least one channel 131a. Channel 131a connects first metal layer 111 and second metal layer 121, and liquid metal material 132 fills channel 131a. Therefore, liquid metal material 132 can electrically connect first metal layer 111 and second metal layer 121, thereby achieving signal transmission between first circuit substrate 110 and second circuit substrate 120.

In the embodiment of the present application, the first circuit substrate 110 includes, but is not limited to, being electrically connected to at least one of a mainboard and a battery module, and the second circuit substrate 120 includes, but is not limited to, being electrically connected to at least one of a display screen, a camera, and an earpiece. Signal transmission between the two is achieved via a stretchable and reversibly bendable electrical connection portion 130, making the flexible circuit board 100 widely applicable to any electronic device requiring multiple bending or stretching.

Both the first circuit substrate 110 and the second circuit substrate 120 can be circuit structures having one or more circuit layers, and a variety of desired circuit components 140 can be mounted on the circuit structures. The circuit layers include at least one first metal layer 111 located on the first circuit substrate 110 and at least one second metal layer 121 located on the second circuit substrate 120. In some embodiments, the liquid metal material 132 filled in the channel 131a directly contacts the first metal layer 111 and the second metal layer 121. This allows electrical connection and signal transmission between the liquid metal material 132 and the first circuit substrate 110 and the second circuit substrate 120 without the need for additional electrical connectors or pads.

In this embodiment, the stretchable portion 131 includes a plurality of stretchable wires 131b, each of which includes the channel 131a. The stretchable wires 131b, the first circuit substrate 110, and the second circuit substrate 120 seal the liquid metal material 132. In some embodiments, each stretchable wire 131b can be arranged side by side and substantially parallel to each other. Substantially parallel means that two adjacent stretchable wires 131b may be slightly non-parallel without affecting the operation and function of the stretchable portion 131. In some embodiments, the distance d between any two adjacent stretchable wires 131b is greater than or equal to 20 micrometers (μm).

The stretchable wire 131b and the liquid metal material 132 filling it provide the stretchable portion 131 with stretchability, bendability, and shock resistance. This ensures that the stretchable portion 131 maintains electrical and signal transmission stability when stretched and bent between the first and second circuit substrates 110 and 120. In some embodiments, the liquid metal material 132 completely fills the interior of the channel 131a, leaving virtually no gaps or air within the channel 131a. This ensures a stable electrical connection between the stretchable portion 131 and the first and second circuit substrates 110 and 120.

The liquid metal material 132 is an amorphous liquid metal or metal alloy material with fluidity, plasticity, and high thermal conductivity, enabling it to deform accordingly with the stretching and bending of the stretchable wire 131b. The liquid metal material 132 includes, but is not limited to, liquid mercury, low-melting-point galvanism, cesium, lead-tin alloys, aluminum alloys, copper alloys, gallium-indium-tin alloys (galinstan), alloys of the aforementioned metals, or other liquid metal alloys. The stretchable wire 131b can be made of a gel, rubber, or other material that can recover after stretching.

In the embodiment of the present application, when the stretchable wire 131b is stretched, the width of the stretchable wire 131b gradually narrows inward as the length of the wire increases, correspondingly affecting the shape of the liquid metal material 132 filled within the stretchable wire 131b. As shown in Figure 1, when the stretchable wire 131b is not stretched, each stretchable wire 131b has a length of L and a width of W.

As the first circuit substrate 110 and the second circuit substrate 120 gradually move away from each other due to the stretching of the stretchable wire 131b, the wire length L gradually increases and the width W gradually narrows. At the same time, changes in the wire length L and width W of the stretchable wire 131b also affect the overall on-resistance. Specifically, the on-resistance gradually increases as the wire length L gradually increases and the width W gradually narrows. In some embodiments, the maximum stretchable length of each stretchable wire is less than or equal to 1.5 times the wire length L.

Please refer to Figure 2, which illustrates an electrical connection portion 130 bent between a first circuit substrate 110 and a second circuit substrate 120, according to some embodiments of the present application. While the first circuit substrate 110 and the second circuit substrate 120 can each be electrically connected to two electronic devices or circuits (e.g., a motherboard and a display), the present invention is not limited thereto.

When the stretchable wire 131b is simply bent without stretching, the on-resistance and wire length L of the stretchable wire 131b and the liquid metal material 132 are substantially the same as when not bent. For example, if the stretchable wire 131b and the liquid metal material 132 filled therein have a first resistance value before bending and a second resistance value after bending, the first resistance value and the second resistance value are substantially the same, or the difference does not exceed a preset value.

This is because the material of the stretchable wire 131b is pliable and elastic, and the liquid metal material 132 filled in the channel 131a is fluid and plastic. This allows the electrical connection portion 130 to maintain the inner diameter of the channel 131a when bent, thereby not significantly changing the overall on-resistance of the stretchable wire 131b and the liquid metal material 132. It should be understood that although Figure 2 only depicts the electrical connection portion 130 having a single stretchable wire 131b, the electrical connection portion 130 can actually have multiple stretchable wires 131b as shown in Figure 1.

Please refer to Figure 3A, which is a schematic diagram illustrating a rotational layout of a stretchable wire 131b of an electrical connection portion 130 according to some embodiments of the present application. In the example of Figure 3A, the electrical connection portion 130 between the first circuit substrate 110 and the second circuit substrate 120 includes multiple stretchable wires 131b, each filled with a liquid metal material 132 (not shown). Each stretchable wire 131b can be arranged in any desired three-dimensional configuration, such as staggered or overlapping, allowing the flexible circuit board 100 of the present application to be more flexibly and snugly accommodated in various electronic devices.

Please refer to Figure 3B, which is a schematic diagram of an electronic device having multiple electrical connections 130 and circuits 1-4 according to some embodiments of the present application. Each pair of circuit modules and one electrical connection 130 in circuits 1-4 can be considered a flexible circuit board 100 as shown in Figure 1. Circuits 1-4 include multiple electrical connections 130 to achieve electrical connections between them. Due to the properties of the stretchable portions 131 and liquid metal material 132 (not shown) within the electrical connections 130, the multiple flexible circuit boards 100 in the electronic device can conform to various curves and shapes, maintaining excellent electrical properties even when bent, stretched, or twisted.

Please refer to Figures 4A to 4G, which are schematic diagrams of a manufacturing process for a flexible circuit board according to some embodiments of the present application. Hereinafter, flexible circuit board 400 is similar to flexible circuit board 100 shown in Figure 1, and the manufacturing process of Figures 4A to 4G can be used to manufacture flexible circuit board 100 as shown in Figure 1. It should be understood that although only some operations are briefly described below, the manufacturing process may actually include other additional operations, and the manufacturing sequence provided is not intended to be limiting. For example, certain operations may be performed in a different order, and some additional operations may be appropriately modified.

In FIG4A , a first circuit substrate 410 ′ is first provided. A first metal layer 411 , such as a copper layer, may be formed on the first circuit substrate 410 ′. The first metal layer 411 , such as a circuit layer, may be formed by a semi-additive process or a subtractive process, i.e., the first metal layer 411 may be formed by lithography and etching. Next, a sacrificial layer 460 is disposed above the first metal layer 411 . In an embodiment of the present application, a stretchable material layer 450 may be formed above the first circuit substrate 410 ′ and the first metal layer 411 before forming the sacrificial layer 460 .

In Figure 4B , multiple slots 461 are then formed in the sacrificial layer 460 to expose the first metal layer 411 beneath the sacrificial layer 460. Specifically, in the embodiment including the stretchable material layer 450, the slots 461 also extend through the stretchable material layer 450 disposed above the first circuit substrate 410' and the first metal layer 411 to expose a portion of the surface of the first metal layer 411. The slots 461 can be formed using methods such as die stamping, laser grooving, laser ablation, wet etching, or dry etching, but the present application is not limited thereto.

In FIG4C , after a plurality of slots 461 are formed in the sacrificial layer 460, a stretchable material 451 is coated on the inner wall of each slot 461 and a portion of the surface of the sacrificial layer 460, and the stretchable material 451 extends to connect to the stretchable material layer 450 below the sacrificial layer 460. The first metal layer 411 is exposed at the bottom of the slot 461 not coated with the stretchable material 451. At this point, the stretchable material layer 450 and the stretchable material 451 can form the stretchable portion 131 shown in FIG1 , and the space in the slot 461 not filled with the stretchable material 451 forms the channel 131a shown in FIG1 . In the embodiment of the present application, the materials used for the stretchable material 451 and the stretchable material layer 450 can be the same or different. When the two materials are the same, they can be better connected or fused.

In Figure 4D , after stretchable material 451 is coated on the inner walls of slots 461 and a portion of the surface of sacrificial layer 460, liquid metal material 432 is filled into each slot 461, electrically connecting the liquid metal material 432 to the first metal layer 411. Next, a second metal layer 421 is disposed on the stretchable material 451 and the liquid metal material 432, electrically connecting the liquid metal material 432 to the second metal layer 421 within the slots 461. Subsequently, the liquid metal material 432 is sealed between the first metal layer 411, the stretchable material 451, and the second metal layer 421 using methods such as heat or pressure. The liquid metal material 432 can be filled into each slot 461 using methods such as printing, spraying, or pouring.

In Figure 4E , after sealing liquid metal material 432 between first metal layer 411, stretchable material 451, and second metal layer 421, at least one circuit structure 470 is formed above second metal layer 421. Circuit structure 470 can be formed using a build-up method, such that circuit structure 470 includes multiple circuit layers. Each circuit layer can include second metal layer 421. In some embodiments, at least one circuit structure (not shown) is also formed on first metal layer 411, and can also be formed using a build-up method.

In FIG4F , a plurality of circuit elements 440 are mounted on the circuit layer of the circuit structure 470. The circuit elements 440 may be, for example, connectors, capacitors, inductors, transistors, resistors, diodes, or any other desired electronic components to implement functional circuits on the flexible circuit board 400.

Finally, referring to FIG. 4G , after forming the circuit structure 470, the sacrificial layer 460 is removed. The sacrificial layer 460 can be removed using a peeling technique, chemical treatment, or physical methods such as grinding or scraping. At this point, the flexible circuit board 400 is essentially complete.

The flexible circuit board and its manufacturing method of this application utilize the properties of the stretchable portion and the liquid metal material filled therein to make the flexible circuit board less susceptible to cracking or breaking after bending or flexing, effectively improving the flexible circuit board's bending resistance, heat dissipation, and vibration resistance. Furthermore, this application utilizes the stretchable portion and liquid metal material to replace flat cables and board-to-board connectors, sealing the liquid metal material between two circuit substrates to achieve an electrical connection, reducing the risk of poor contact and improving the reliability of the electrical connection.

Although this application has been disclosed above through various embodiments, they are not intended to limit this application. Anyone with ordinary skill in the art may make slight modifications and improvements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the scope of the attached patent application.

100: Flexible circuit board 110: First circuit substrate 111: First metal layer 120: Second circuit substrate 121: Second metal layer 130: Electrical connection 131: Stretchable portion 131a: Channel 131b: Stretchable wire 132: Liquid metal material 140: Circuit component 400: Flexible circuit board 410': First circuit substrate 411: First metal layer 421: Second metal layer 432: Liquid metal material 440: Circuit component 450: Stretchable material layer 451: Stretchable material 460: Sacrificial layer 461: Slot 470: Circuit structure d: Distance L: Cable length W: Width

To facilitate understanding of the above and other features, advantages, and embodiments of the present invention, the accompanying drawings are described as follows: Figure 1 is a schematic cross-sectional view of a flexible circuit board according to some embodiments of the present application; Figure 2 is a schematic view of an electrical connection portion bent between a first circuit substrate and a second circuit substrate according to some embodiments of the present application; Figure 3A is a schematic view of a stretchable wire of an electrical connection portion exhibiting a rotational wiring configuration according to some embodiments of the present application; Figure 3B is a schematic view of an electronic device having multiple electrical connections and circuits according to some embodiments of the present application; and Figures 4A to 4G are schematic views of a manufacturing process for a flexible circuit board according to some embodiments of the present application.

100: Flexible circuit board

110: First circuit board

111: First metal layer

120: Second circuit board

121: Second metal layer

130: Electrical connection part

131: Stretchable part

131a: Passageway

131b: Stretchable wire

132: Liquid Metal Materials

140: Circuit components

d: distance

L: Cable length

W: Width

Claims (10)

A flexible circuit board comprises: a first circuit substrate having at least one first metal layer; a second circuit substrate having at least one second metal layer; and at least one electrical connection portion electrically connected between the first circuit substrate and the second circuit substrate, comprising: a stretchable portion connected between the first circuit substrate and the second circuit substrate, having at least one channel, wherein the at least one channel connects the first metal layer and the second metal layer; and at least one liquid metal material filled in the at least one channel, wherein the at least one liquid metal material electrically connects between the first metal layer and the second metal layer. The flexible circuit board of claim 1, wherein the stretchable portion comprises: A plurality of stretchable wires, wherein each of the plurality of stretchable wires comprises the channel, and the plurality of stretchable wires, the first circuit substrate, and the second circuit substrate seal the liquid metal material. A flexible circuit board as described in claim 2, wherein the distance between any two adjacent stretchable wires is greater than or equal to 20 microns. A flexible circuit board as described in claim 2, wherein each of the plurality of stretchable wires has a width, and the width decreases as the plurality of stretchable wires are stretched. A flexible circuit board as described in claim 2, wherein each of the multiple stretchable wires has a wire length, and a stretchable length of each of the multiple stretchable wires is less than or equal to 1.5 times the wire length. A flexible circuit board as described in claim 2, wherein each of the multiple stretchable wires and the liquid metal material has a first resistance value before bending, and each of the multiple stretchable wires and the liquid metal material has a second resistance value after bending, and the first resistance value is the same as the second resistance value. A method for manufacturing a flexible circuit board comprises: Providing a first circuit substrate, wherein the first circuit substrate is provided with a first metal layer; Disposing a stretchable material layer above the first metal layer; Disposing a sacrificial layer above the stretchable material layer; Forming a plurality of slots in the sacrificial layer, wherein the slots partially expose the first metal layer; After forming the slots in the sacrificial layer, coating an inner wall of the slots and a portion of the surface of the sacrificial layer with a stretchable material, wherein a bottom portion of the slots not coated with the stretchable material exposes a portion of the first metal layer; After coating the inner walls of the plurality of slots and the portion of the surface of the sacrificial layer with the stretchable material, a liquid metal material is filled into the plurality of slots so that the liquid metal material is electrically connected to the first metal layer. A second metal layer is disposed over the stretchable material and the liquid metal material so that the liquid metal material in the slots is further electrically connected to the second metal layer and the liquid metal material is sealed between the first metal layer, the stretchable material, and the second metal layer. At least one circuit structure is formed above the second metal layer. After forming the at least one circuit structure, the sacrificial layer is removed. The manufacturing method of claim 7 further comprises: Forming the circuit structure using a build-up method, such that the circuit structure includes multiple circuit layers. The manufacturing method of claim 8 further comprises: Installing a plurality of circuit components on the plurality of circuit layers. The manufacturing method of claim 7, wherein the at least one circuit structure is at least one first circuit structure, further comprising: forming at least one second circuit structure on the first metal layer.