Circuit board manufacturing method

Abstract

The present invention provides a "circuit board manufacturing method" that allows for the formation of multiple pixel circuits using a film with a thickness of a certain value or greater, while also enabling the appropriate connection of the wiring patterns of each pixel circuit with an appropriate amount of liquid metal. [Solution] In the first step, multiple pixel circuits 2 are formed on the PI film 1 with the pixels connected by the wiring pattern 3. In the second to second-fourth steps, the PI film 1 is processed to reduce the thickness at the positions between pixels, and the PI film 1 is divided into individual pixel pieces so that the PI film 1 is cut together with the wiring pattern 3 at the positions between pixels. This makes it possible to properly connect the wiring patterns 3 of each pixel circuit 2 with an appropriate amount of liquid metal 6 in the region where the liquid metal 6 is attached between pixels, by making the step difference between the wiring pattern 3 formed on the pixel circuit 2 and the flexible substrate 5 to which the individual pieces 4 are transferred less than a certain value, thereby enabling the wiring patterns 3 of each pixel circuit 2 to be properly connected with an appropriate amount of liquid metal 6.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a circuit board.

Background Art

[0002] In recent years, the development of flexible devices capable of bending deformation, stretching and shrinking deformation, etc. has been widely promoted. As an example of a circuit board used for a flexible device, a circuit board including a base member having stretchability or flexibility, a conductive layer including a predetermined pattern and liquid metal formed on the base member, and a coating layer laminated on the conductive layer is known (for example, see Patent Document 1).

[0003] For example, a circuit board of a stretchable film display using micro LEDs is manufactured by the procedure as shown in FIG. 6. First, a plurality of pixel circuits 102 are formed on a film 101 (first step). For the film 101, for example, a polyimide film (hereinafter referred to as PI film 101) is used. At this stage, the plurality of pixel circuits 102 formed on the PI film 101 are in a state where pixels are connected by a metal wiring pattern 103.

[0004] Next, after cutting the PI film 101 together with the wiring pattern 103 at positions between each pixel to fragment the PI film 101 into individual pieces in pixel units (second step), each individual piece 104 is transferred onto a rubber substrate 105 having stretchability and flexibility (third step). Then, stretchable wiring is formed by attaching liquid metal 106 at positions between the wiring patterns 103 of each individual piece 104 (fourth step). Finally, micro LEDs 107 are mounted on the pixel circuits 102 of each individual piece 104 (fifth step).

[0005] In the fourth step, in order to connect each individual piece 104 with the liquid metal 106, the step difference between the wiring pattern 103 formed on the pixel circuit 102 of the individual piece 104 and the rubber substrate 105 must be smaller than a certain value. If this step difference is large, as shown in Figure 7, the wiring patterns 103 of the pixel circuit 102 on the individual piece 104 will not be connected by the liquid metal 106 due to the influence of the surface tension of the liquid metal 106.

[0006] Using a thin PI film 101 makes it possible to reduce the step height. However, if the first process is carried out using a roll-to-roll method for the purpose of cost reduction or productivity improvement, it is difficult to make the thickness of the PI film 101 smaller than a certain value. If the amount of liquid metal 106 introduced in the fourth process is increased after processing the first to third processes using a PI film 101 thicker than a certain value, it is possible to connect the wiring patterns 103 of each individual piece 104 with liquid metal 106, but this results in the liquid metal 106 overflowing into unnecessary locations on the pixel circuit 102, causing a short circuit in the circuit. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7509980 [Overview of the project] [Problems that the invention aims to solve]

[0008] This disclosure was made to solve the above-mentioned problems, and aims to enable the formation of multiple pixel circuits using a film with a thickness of a certain value or more, while also enabling the proper connection of the wiring patterns of each pixel circuit with an appropriate amount of liquid metal. [Means for solving the problem]

[0009] To solve the above-mentioned problems, this disclosure includes a first step of forming multiple pixel circuits on a film with the pixels connected by wiring patterns; a second step of processing the film to reduce its thickness at least at the positions between pixels and dividing the film into pixel units so that the film is cut along with the wiring patterns at the positions between pixels; a third step of transferring the multiple pixel units on which the pixel circuits are formed on the film onto a flexible substrate; and a fourth step of forming expandable wiring by attaching liquid metal between the wiring patterns of the divided pixel circuits. [Effects of the Invention]

[0010] According to the present disclosure configured as described above, in the second step, the film is processed so that it becomes thinner at least at the location where the wiring pattern between pixels is formed, and the film is cut together with the wiring pattern at that location between pixels, thereby separating the film into individual pixel pieces. This makes it possible to form multiple pixel circuits in the first step using a film with a thickness of a certain value or more, while keeping the step difference in the area where the liquid metal is attached between pixels below a certain value, and to appropriately connect the wiring patterns of each pixel circuit with an appropriate amount of liquid metal. [Brief explanation of the drawing]

[0011] [Figure 1A] This is a process diagram showing a method for manufacturing a circuit board according to the first embodiment. [Figure 1B] This is a process diagram showing a method for manufacturing a circuit board according to the first embodiment. [Figure 2A] This is a process diagram showing a method for manufacturing a circuit board according to the second embodiment. [Figure 2B] This is a process diagram showing a method for manufacturing a circuit board according to the second embodiment. [Figure 3] This is a process diagram showing a method for manufacturing a circuit board according to the first modified example of the second embodiment. [Figure 4] This is a process diagram showing a method for manufacturing a circuit board according to a second modified example of the second embodiment. [Figure 5A] This is a process diagram showing a method for manufacturing a circuit board according to the third embodiment. [Figure 5B] This is a process diagram showing a method for manufacturing a circuit board according to the third embodiment. [Figure 6] This is a process diagram showing a conventional method for manufacturing circuit boards. [Figure 7] This is a diagram to explain the conventional problem. [Modes for carrying out the invention]

[0012] (First embodiment) The first embodiment will be described below with reference to the drawings. Figures 1A and 1B are process diagrams showing the manufacturing method of a circuit board according to the first embodiment. Figures 1A and 1B show the manufacturing process of a circuit board for a stretchable film display using microLEDs, and show a side cross-sectional view of a part of the circuit board.

[0013] First, as shown in Figure 1A(a), multiple pixel circuits 2 are formed on the film 1 with the pixels connected by a metal wiring pattern 3 (first step). The state in which the pixels are connected by the wiring pattern 3 means that the wiring pattern 3 is connected from the surface of one pixel circuit 2 through the side and the film 1 between the pixels to the adjacent pixel circuit 2. Although only two pixel circuits 2 are shown in Figures 1A and 1B, in reality, many more pixel circuits 2 are arranged on the film 1 (the same applies to the figures shown below).

[0014] For the film 1, for example, a polyimide film (hereinafter referred to as PI film 1) is used, but it is not limited thereto. In this first step, for the purpose of cost reduction and productivity improvement, a plurality of pixel circuits 2 are formed on the PI film 1 in a Roll-to-Roll manner. Therefore, the PI film 1 has a sufficient thickness required for Roll-to-Roll processing. For example, the thickness of the PI film 1 is 80 μm. If the PI film 1 is singulated as it is, the step becomes too large as shown in FIG. 7, and the space between the pixel circuits 2 cannot be connected by liquid metal. For convenience of explanation, the pixel circuit 2 is illustrated with a thickness that can be visually recognized, but actually the thickness is 1 μm or less.

[0015] The plurality of pixel circuits 2 formed on the PI film 1 may be arranged linearly in a row, or may be arranged in a matrix in a first direction (row direction) and a second direction (column direction) orthogonal to the first direction. When the plurality of pixel circuits 2 are arranged in a matrix, the plurality of pixel circuits 2 arranged in the first direction are connected by a wiring pattern 3 for the first wiring, and the plurality of pixel circuits 2 arranged in the second direction are connected by a wiring pattern 3 for the second wiring. Note that the pixels may be connected by the wiring pattern 3 only in one of the first direction and the second direction.

[0016] Next, as shown in FIGS. 1A(b) and (c), the PI film 1 is processed to reduce the thickness of the entire processing region of the PI film 1, and the PI film 1 is singulated into pixel units so that the PI film 1 is cut together with the wiring pattern 3 at the positions between the pixels (second step). The processing region is a region where a plurality of pixel circuits 2 exist. In the first embodiment, the second step includes an etching step (second - 1 step) in FIG. 1A(b) and a cutting step (second - 2 step) in FIG. 1A(c).

[0017] As shown in FIG. 1A(b), in the etching step (the second - 1 step), a partial thickness region of the PI film 1 is immersed in the etching solution 20 from the surface (hereinafter sometimes referred to as the front surface) of the PI film 1 opposite to the surface on which the pixel circuit 2 of the PI film 1 is formed (hereinafter sometimes referred to as the back surface), thereby thinning the entire processing region of the PI film 1. As a result, the thickness of the etched PI film 1 becomes less than a certain value. The thickness less than the certain value means a thickness that can appropriately connect between the wiring patterns 3 of the pixel circuit 2 with an appropriate amount of liquid metal that does not cause a short - circuit in the circuit. For example, the thickness of the PI film 1 is set to 30 - 5 μm by etching.

[0018] As shown in FIG. 1A(c), in the cutting step (the second - 2 step) following the etching step, the etched PI film 1 is cut together with the wiring pattern 3 at the position between pixels to be fragmented into individual pieces in pixel units. Here, the PI film 1 is cut together with the wiring pattern 3 in a manner that leaves the wiring pattern 3 on the surface of the pixel circuit 2 and does not leave the wiring pattern 3 connecting between the pixel circuits 2.

[0019] Next, as shown in FIG. 1B(d), a plurality of individual pieces 4 in pixel units on which the pixel circuit 2 is formed are transferred onto the flexible substrate 5 (the third step). In the following description, when referring to the individual piece 4, it refers to the structure in which the pixel circuit 2 is formed on the cut PI film 1. The flexible substrate 5 may be a member having stretchability and / or flexibility, and for example, it can be a rubber substrate. Here, the plurality of individual pieces 4 are transferred onto the flexible substrate 5 in a manner that maintains the positional relationship between pixels when the plurality of pixel circuits 2 are formed on the PI film 1 in the first step.

[0020] Next, as shown in Figure 1B(e), expandable wiring is formed by applying liquid metal 6 between the wiring patterns 3 cut in step 2-2 (step 4). With multiple individual pieces 4 transferred onto the flexible substrate 5, the height difference between the wiring patterns 3 formed on the pixel circuit 2 and the flexible substrate 5 is less than a certain value. Therefore, it is possible to properly connect the wiring patterns 3 of each pixel circuit 2 with an appropriate amount of liquid metal 6.

[0021] Finally, as shown in Figure 1B(f), a micro LED 7 is mounted on the pixel circuit 2 of each individual piece 4 (step 5). This completes the circuit board for the stretchable film display using the micro LED 7.

[0022] As described above, according to the first embodiment, in the second step, the PI film 1 is thinned by etching, and the PI film 1 is cut together with the wiring pattern 3 at the positions between pixels, thereby forming individual pixel pieces 4. Therefore, in the region where the liquid metal 6 is attached between pixels, the step difference between the wiring pattern 3 formed on the pixel circuit 2 and the flexible substrate 5 can be kept below a certain value, which avoids a state where the wiring patterns 3 are not connected by the liquid metal 6. As a result, even when forming multiple pixel circuits 2 using a PI film 1 with a thickness of a certain value or more in the first step, the wiring patterns 3 of each pixel circuit 2 can be appropriately connected with an appropriate amount of liquid metal 6.

[0023] (Second embodiment) Next, a second embodiment will be described based on the drawings. Figures 2A and 2B are process diagrams showing the manufacturing method of a circuit board according to the second embodiment. Figures 2A and 2B also show the manufacturing process of a circuit board for a stretchable film display using micro-LEDs 7, and show a side cross-sectional view of a part of the circuit board.

[0024] First, as shown in Figure 2A(a), multiple pixel circuits 2 are formed on the film 1 with the pixels connected by a metal wiring pattern 3 (first step). This first step is the same as in the first embodiment.

[0025] After the first step, as shown in Figures 2A(b) to (e), the PI film 1 is processed to reduce the thickness at the positions between pixels and the overall thickness of the processed area, and the PI film 1 is separated into individual pixel pieces so that the PI film 1 is cut together with the wiring pattern 3 at the positions between pixels (second step). In the second embodiment, the second step includes the masking step (second-1 step) shown in Figure 2A(b), the first etching step (second-2 step) shown in Figure 2A(c), the second etching step (second-3 step) shown in Figure 2A(d), and the cutting step (second-4 step) shown in Figure 2A(e).

[0026] As shown in Figure 2A(b), in the masking step (step 2-1), a region including at least a part of the area where the wiring pattern 3 between pixels is formed is designated as a non-masked region, and the resist 8 is applied to the region excluding the non-masked region. The non-masked region, which is excluded from resist application, is the region to which the liquid metal 6 will be attached, and includes a part of the area where the wiring pattern 3 between pixels is formed, and may also include a small portion of the surrounding PI film 1. On the other hand, the region to which the resist 8 is applied includes the surface and sides of the pixel circuit 2, and the region on the PI film 1 where neither the pixel circuit 2 nor the wiring pattern 3 is formed.

[0027] In the next first etching step (step 2-2), as shown in Figure 2A(c), the portion of the PI film 1 from the surface on which the pixel circuit 2 is formed to a predetermined thickness of the PI film 1 is immersed in the etching solution 20, thereby partially thinning the unmasked areas where the resist 8 is not applied. When the unmasked areas on which the wiring patterns 3 between pixels are formed are etched as shown in Figure 2A(c), the wiring patterns 3 that are not coated with resist 8 are removed first, and then the PI film 1 is gradually removed. At this time, influenced by the portion of the wiring patterns 3 protected by resist 8, the amount removed decreases the deeper the position from the surface of the PI film 1, and an inclined surface is created in the etching region 9 of the PI film 1.

[0028] Partially thinning the non-masked areas of the PI film 1 where the wiring patterns 3 between pixels are formed means creating an etched area 9 with an inclined surface. The purpose of the first etching step is to form an inclined surface of the etched area 9 in the area to which the liquid metal 6 will be deposited. Therefore, the predetermined thickness of the portion of the PI film 1 immersed in the etching solution 20 to create this etched area 9, that is, the depth of the etched area 9 to be removed, is arbitrary and may be less than or greater than the certain value described in the first embodiment. In this embodiment, the depth of the etched area 9 is set to less than the certain value.

[0029] In the next second etching step (second-to-third step), as shown in Figure 2A(d), after removing the resist 8, a portion of the thickness of the PI film 1 is immersed in the etching solution 20 from the back surface opposite to the surface on which the pixel circuits 2 are formed, thereby thinning the entire processed area of ​​the PI film 1. This ensures that the thickness of the etched PI film 1 is less than a certain value that allows the wiring patterns 3 of the pixel circuits 2 to be connected with an appropriate amount of liquid metal 6. In this embodiment, the thickness of the PI film 1 partially removed in the first etching step (depth of the etching area 9) is smaller than the thickness of the PI film 1 etched in the second etching step (thickness after processing).

[0030] In the next cutting step (steps 2-4), as shown in Figure 2A(e), the etched PI film 1 is cut at the positions between pixels to separate it into individual pixel units. Here, the PI film 1 is cut at the etching region 9 in such a manner that all of the wiring patterns 3 that have not been removed by etching (wiring patterns 3 on the surface and sides of the pixel circuit 2 and on a portion of the PI film 1) are left intact. That is, the PI film 1 is cut at an intermediate position on the inclined surface of the etching region 9.

[0031] Next, as shown in Figure 2B(f), multiple individual pieces 4, each consisting of a pixel circuit 2 formed on the cut PI film 1, are transferred onto a flexible substrate 5 (third step). This third step is the same as in the first embodiment.

[0032] Next, as shown in Figure 2B(g), expandable wiring is formed by applying liquid metal 6 between the wiring patterns 3 cut in steps 2-4 (step 4). In the second embodiment, a portion of the wiring pattern 3 remains on the PI film 1, and liquid metal 6 is applied to connect this portion of the wiring pattern 3. This differs from the first embodiment, in which liquid metal 6 is applied to connect the wiring patterns 3 formed on the surface of the PI film 1. Here, the difference in height between the wiring patterns 3 remaining on the PI film 1 and the flexible substrate 5 is less than a certain value. Therefore, it is possible to properly connect the wiring patterns 3 of each pixel circuit 2 with an appropriate amount of liquid metal 6.

[0033] Furthermore, an etched area 9 is formed in the portion of the wiring pattern 3 that remains on the PI film 1. The second embodiment differs from the first embodiment in that the liquid metal 6 is applied to the 90-degree corner portion where there is no sloping surface, in that the liquid metal 6 is applied to this sloping surface. By applying the liquid metal 6 to the sloping surface, the liquid metal 6 can be given sufficient thickness even in the sloping portion, and the risk of the liquid metal 6 becoming thin at the corner portion and causing disconnection can be reduced.

[0034] Finally, as shown in Figure 2B(h), the micro LEDs 7 are mounted on the pixel circuits 2 of each individual piece 4 (step 5). This completes the circuit board for the stretchable film display using the micro LEDs 7.

[0035] As described above, according to the second embodiment, in the second step, after forming an etching region 9 having an inclined surface on the surface of the PI film 1, the entire processed region of the PI film 1 is thinned by etching, and the PI film 1 is cut at the position between pixels to form individual pixel pieces 4. Therefore, in the region where the liquid metal 6 is attached between pixels, it is possible to keep the step difference between the wiring pattern 3 formed on the pixel circuit 2 and the flexible substrate 5 below a certain value. As a result, even when forming multiple pixel circuits 2 using a PI film 1 with a thickness of a certain value or more in the first step, the wiring patterns 3 of each pixel circuit 2 can be appropriately connected with an appropriate amount of liquid metal 6. Furthermore, by attaching the liquid metal 6 to the inclined surface, the risk of the liquid metal 6 becoming thin and causing disconnection can be reduced.

[0036] (First variation) In the second embodiment described above, the second etching step (second-third step) may be omitted. In this case, the process performed after the first etching step (second-second step) is as shown in Figure 3. Figure 3 is a process diagram showing a method for manufacturing a circuit board according to the first modified example of the second embodiment.

[0037] As shown in Figure 3(a), in the cutting process (2-4th step) following the etching process (2-2nd step) shown in Figure 2A(c), the PI film 1 is cut at an intermediate position on the inclined surface of the etching region 9 to create individual pixel pieces. Here, the PI film 1 is cut at a position where the side edges of adjacent pieces 4 are closer to each other than the cutting position shown in Figure 2A(e).

[0038] Next, as shown in Figure 3(b), a plurality of individual pieces 4, each consisting of a pixel circuit 2 formed on the cut PI film 1, are transferred onto a flexible substrate 5 (third step). The third step of the first modified example is the same as that of the second embodiment described above.

[0039] Next, as shown in Figure 3(c), expandable wiring is formed by depositing liquid metal 6 between the wiring patterns 3 cut in steps 2-4 shown in Figure 3(a) (step 4). The first modified example is the same as the second embodiment described above in that the liquid metal 6 is deposited to connect the wiring patterns 3 that remain on part of the PI film 1, and the liquid metal 6 is introduced into the etching area 9.

[0040] In the first modified example shown in Figure 3, the step difference between the wiring pattern 3 remaining on a portion of the PI film 1 and the flexible substrate 5 is greater than a certain value. However, because the side edges of adjacent individual pieces 4 are close to each other, the liquid metal 6 adheres to the narrow gaps between the individual pieces 4 due to the effects of the viscosity and surface tension of the liquid metal 6. Since the step difference between the wiring pattern 3 and the upper edge of the narrow gap is less than a certain value, it is possible to properly connect the wiring patterns 3 of each pixel circuit 2 with an appropriate amount of liquid metal 6.

[0041] Finally, as shown in Figure 3(d), a micro LED 7 is mounted on the pixel circuit 2 of each individual piece 4 (fifth step). The fifth step of the first modified example is the same as that of the second embodiment described above. This completes the circuit board for the stretchable film display using micro LEDs 7.

[0042] (Second variation) In the second embodiment described above, an example was shown in which the depth of the etching region 9 is less than a certain value, but as mentioned above, it may be greater than or equal to a certain value. Also, in the second embodiment described above, an example was shown in which the depth of the etching region 9 is smaller than the thickness of the PI film 1 etched in the second etching step, but it may be made larger. As a result, the cutting step (steps 2-4) shown in Figure 2A(e) may be omitted. Figure 4 is a process diagram showing the manufacturing method of the circuit board in this case.

[0043] In the second modified example shown in Figure 4, the first etching step (step 2-2) is the same as in the second embodiment shown in Figure 2A(c), but the etching region 9 may be formed deeper. As shown in Figure 4(a), in the second etching step (step 2-3), the entire processed area of ​​the PI film 1 is thinned by immersing the back surface of the PI film 1 opposite to the surface on which the pixel circuit 2 is formed in the etching solution 20, up to the thickness of the bottom surface of the etching region 9 that was partially thinned in the first etching step. This separates the PI film 1 at the positions between pixels, creating individual pieces for each pixel. Since individual pieces 4 can be formed by this etching, the cutting step (step 2-4) shown in Figure 2A(e) is unnecessary.

[0044] Next, as shown in Figure 4(b), the multiple pieces 4 formed in the second etching step are transferred onto the flexible substrate 5 (third step). The third step of the second modified example is the same as that of the second embodiment described above. Next, as shown in Figure 4(c), stretchable wiring is formed by depositing liquid metal 6 between the cut wiring patterns 3 (fourth step). The second modified example is the same as that of the second embodiment described above in that the liquid metal 6 is deposited to connect the wiring patterns 3 that remain on part of the PI film 1, and the liquid metal 6 is introduced into the etching area 9.

[0045] In the second modified example shown in Figure 4, the height difference between the wiring pattern 3 remaining on a portion of the PI film 1 and the flexible substrate 5 is less than a certain value, so it is possible to properly connect the wiring patterns 3 of each pixel circuit 2 with an appropriate amount of liquid metal 6. Finally, as shown in Figure 4(d), micro LEDs 7 are mounted on the pixel circuits 2 of each individual piece 4 (fifth step). The fifth step of the second modified example is the same as that of the second embodiment described above. This completes the circuit board for the stretchable film display using micro LEDs 7.

[0046] (Third embodiment) Next, a third embodiment will be described based on the drawings. Figures 5A and 5B are process diagrams showing the manufacturing method of a circuit board according to the third embodiment. Figures 5A and 5B also show the manufacturing process of a circuit board for a stretchable film display using micro-LEDs 7, and show a side cross-sectional view of a part of the circuit board.

[0047] First, as shown in Figure 5A(a), multiple pixel circuits 2 are formed on the film 1 with the pixels connected by a metal wiring pattern 3 (first step). This first step is the same as in the second embodiment.

[0048] After the first step, as shown in Figures 2A(b) to (c), the PI film 1 is processed to reduce the thickness at the positions between pixels and the overall thickness of the processed area, and the PI film 1 is separated into individual pixel pieces so that the PI film 1 is cut together with the wiring pattern 3 at the positions between pixels (second step). In the third embodiment, the second step includes the masking step (second-first step) shown in Figure 5A(b) and the etching step (second-second step) shown in Figure 5A(c).

[0049] As shown in Figure 5A(b), in the masking step (step 2-1), a region including at least a part of the area where the wiring pattern 3 between pixels is formed is designated as a non-masked region, and the resist 8 is applied to the region excluding the non-masked region. This masking step is the same as in the second embodiment.

[0050] In the next etching step (step 2-2), as shown in Figure 5A(c), the entire PI film 1, pixel circuit 2, inter-pixel wiring pattern 3, and resist 8 are immersed in etching solution 20. This partially thins the non-masked area from the surface of the PI film 1 where the pixel circuit 2 is formed, thins the entire processed area of ​​the PI film 1 from the back surface opposite to the surface where the pixel circuit 2 is formed, and separates the PI film 1 at the positions between pixels, creating individual pixel units.

[0051] The etching process shown in Figure 5A(c) corresponds to a process in which the first etching process from the surface of the PI film 1 shown in Figure 2A(c) and the second etching process from the back surface of the PI film 1 shown in Figure 4(a) are performed simultaneously. The temperature of the etching solution 20 and the etching time are appropriately controlled so that the etched region 9 formed by this etching is in the state shown in Figure 5A(c).

[0052] After the etching process, the resist 8 is removed and the process shown in Figure 5B is performed. Steps 3 through 5 shown in Figure 5B are the same as in the second embodiment.

[0053] According to the third embodiment described above, the formation of the etching region 9, the thinning of the PI film 1, and the formation of individual pieces 4 can all be performed in a single etching process, significantly reducing the number of steps required.

[0054] The embodiments and modifications described above are merely examples of how this disclosure may be implemented, and the technical scope of this disclosure should not be limited by them. In other words, this disclosure can be implemented in various ways without departing from its essence or its main features.

[0055] For example, in the above embodiment and modified examples, the fourth and fifth steps may be performed in reverse order.

[0056] Furthermore, although the above embodiments and modifications describe an example of manufacturing a circuit board for a stretchable film display using micro-LEDs 7, the examples are not limited to those in which micro-LEDs 7 are mounted. For example, mini-LEDs may also be mounted. [Explanation of Symbols]

[0057] 1...Film, 2...Pixel circuit, 3...Wiring pattern, 4...Individual piece, 5...Flexible substrate, 5...Liquid metal, 7...Micro LED, 8...Resist, 9...Etching area, 20...Etching solution

Claims

1. The first step involves forming multiple pixel circuits on a film with the pixels connected by a wiring pattern, A second step involves processing the above film to reduce its thickness at least at the positions between the pixels, and separating the film into individual pixel units such that the film is cut along with the wiring pattern at the positions between the pixels. A third step involves transferring a plurality of individual pixel units, each having the pixel circuit formed on the film, onto a flexible substrate. The process includes a fourth step of forming expandable wiring by applying liquid metal between the wiring patterns cut in the second step. A method for manufacturing a circuit board, characterized by the following:

2. The second step described above is: An etching process to thin the film by immersing a portion of the film's thickness in an etching solution from the side of the film opposite to the side on which the pixel circuit is formed, The process includes a cutting step which involves cutting the etched film together with the wiring pattern at the positions between the pixels to separate it into individual pixel units. A method for manufacturing a circuit board according to claim 1.

3. The second step described above is: A masking step in which a region including at least a part of the region in which the above wiring pattern between the above pixels is formed is designated as a non-masked region, and a resist is applied to the region excluding the non-masked region. An etching step is performed to partially thin the non-masked area by immersing the portion of the film from the surface on which the pixel circuit is formed to a predetermined thickness of the film in an etching solution, The process includes a cutting step which involves cutting the etched film at the positions between the pixels to separate it into individual pixel units. A method for manufacturing a circuit board according to claim 1.

4. The above etching process is referred to as the first etching process. Between the first etching step and the cutting step, there is a second etching step in which the film is thinned by immersing a portion of the film's thickness in an etching solution from the side of the film opposite to the side on which the pixel circuit is formed. The method for manufacturing a circuit board according to claim 3, characterized in that it is a circuit board manufacturing method.

5. The second step described above is: A masking step in which a region including at least a part of the region in which the above wiring pattern between the above pixels is formed is designated as a non-masked region, and a resist is applied to the region excluding the non-masked region. A first etching step involves immersing the portion of the film from the surface on which the pixel circuit is formed to a predetermined thickness of the film in an etching solution to partially thin the non-masked area. The etching process includes a second etching step in which, from the side of the film opposite to the side on which the pixel circuit is formed, the film is thinned by immersing a thickness region that reaches the bottom surface of the region partially thinned in the first etching step in an etching solution, and the film is separated at the positions between the pixels to form individual pixel units. A method for manufacturing a circuit board according to claim 1.

6. The second step described above is: A masking step in which a region including at least a part of the region in which the above wiring pattern between the above pixels is formed is designated as a non-masked region, and a resist is applied to the region excluding the non-masked region. The etching process involves immersing the entire film, the pixel circuit, the wiring pattern between pixels, and the resist in an etching solution to partially thin the non-masked area of ​​the film from the side where the pixel circuit is formed, thin the film from the side opposite to the side where the pixel circuit is formed, and separate the film at the positions between pixels to create individual pixel units. A method for manufacturing a circuit board according to claim 1.

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