Method for manufacturing flexible printed circuit board, flexible printed circuit board, semiconductor package, and electronic device

Abstract

To provide a method of manufacturing a flexible printed circuit board, which can manufacture the flexible printed circuit board having fine wiring without lowering a yield.SOLUTION: The method for manufacturing a flexible printed circuit board includes a step of forming a plating resist layer 4 on an insulating layer 2 by using a photosensitive dry film resist, and a step of exposing and developing the plating resist layer 4 in a predetermined pattern. The plating resist layer 4 is a layer satisfying a first condition and a second condition. The first condition is that the resolution of the plating resist layer 4 is 7 μm or less. The second condition is that the minimum diameter of the cylindrical mandrel capable of maintaining the plating resist layer 4 in a sound state is 4 mm or less after bending the plating resist layer 4 by 180 degrees using the cylindrical mandrel and returning the plating resist layer 4 to the state before bending are repeated twice.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a flexible printed circuit board using a dry film resist, a flexible printed circuit board, a semiconductor package, and an electronic device. [Background technology]

[0002] Conventionally, various wires provided on a wired circuit board have been formed using, for example, photolithography technology. Patent Document 1 describes a method for manufacturing a multilayer printed wiring board as an example of a method for manufacturing a wired circuit board using photolithography technology.

[0003] In the method for manufacturing a multilayer printed wiring board, a seed layer (conductor layer) is formed on an insulating layer (insulating resin layer) of a base substrate, and then a plating resist layer (dry film resist layer) made of a dry film resist is formed on the seed layer. Using photolithography, an opening patterned according to the shape of the wiring is formed in the plating resist layer. Next, a groove is formed in a portion of the seed layer so that the portion of the seed layer exposed through the opening in the plating resist layer is recessed relative to the other portion of the seed layer covered by the plating resist layer. Electrolytic plating is applied to the exposed portion of the seed layer (the portion where the groove is formed) through the opening in the plating resist layer. This forms a conductor layer (conductor pattern) as wiring within the opening in the plating resist layer. Finally, the plating resist layer is removed. Furthermore, the other portion of the seed layer exposed by the removal of the plating resist layer is also removed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-204099 Summary of the Invention [Problem to be solved by the invention]

[0005] Wired circuit boards include flexible printed circuit boards and rigid printed circuit boards. Flexible printed circuit boards have higher flexibility than rigid printed circuit boards and can be easily made smaller and thinner.

[0006] In flexible printed circuit boards, miniaturization of wiring is desired to form wiring at high density on a board with a limited size. When manufacturing flexible printed circuit boards using photolithography technology, achieving miniaturization of wiring requires forming finer and more accurate openings in the plating resist layer.

[0007] During development, the plating resist layer swells due to the developer seeping into the plating resist layer. This swelling hinders the miniaturization of wiring. Therefore, in order to achieve miniaturization of wiring, it is conceivable to use a dry film resist, which is resistant to developer penetration, as the material for the plating resist layer. However, dry film resists, which are resistant to developer penetration, are less flexible and harder than dry film resists, which are easily penetrated by developer.

[0008] Flexible printed circuit boards are manufactured, for example, by the roll-to-roll process. During roll-to-roll manufacturing of flexible printed circuit boards, an intermediate body consisting of multiple layers, including a dry film resist, is wound onto a roll and then unwound from the roll. In other words, during roll-to-roll manufacturing of flexible printed circuit boards, the intermediate body is significantly deformed. Therefore, if a hard dry film resist is used for flexible printed circuit boards, there is a possibility that chips or other defects will occur in the plating resist layer after exposure and development. The occurrence of chips or other defects in the plating resist layer reduces the yield of flexible printed circuit boards.

[0009] In addition to the roll-to-roll method, flexible printed circuit boards are also manufactured using the sheet-fed method. When manufacturing flexible printed circuit boards using the sheet-fed method, an intermediate body consisting of multiple layers including a dry film resist is cut into a sheet of a predetermined size. The sheet-like intermediate body (hereinafter referred to as the intermediate sheet) is then fixed to a support plate such as a transport board and transported.

[0010] Here, in consideration of processability and handling, only a portion of the intermediate sheet is fixed to the support plate. If stress is applied to the intermediate sheet during transportation involving various processes, the portion of the intermediate sheet that is not fixed to the support plate may be significantly deformed. Therefore, if a hard dry film resist is used for a flexible printed circuit board, the hard dry film may not be able to follow the deformation of the intermediate sheet, and chips or other defects may occur in the plating resist layer after exposure and development. The occurrence of chips or other defects in the plating resist layer reduces the yield of flexible printed circuit boards.

[0011] An object of the present invention is to provide a method for manufacturing a flexible printed circuit board that enables the manufacture of a flexible printed circuit board having fine wiring without reducing yield, a flexible printed circuit board, a semiconductor package, and an electronic device. [Means for solving the problem]

[0012] As described above, in the past, when a hard dry film resist was used to realize fine wiring in the manufacture of flexible printed circuit boards, defects occurred in the plating resist layer after development, resulting in a significant decrease in yield. For this reason, no research had been conducted into what physical properties a dry film resist should have to realize finer wiring.

[0013] In response to this, the present inventors pursued the possibility of achieving finer wiring using dry film resist, and succeeded in finding the conditions for a dry film resist suitable for finer wiring, resulting in the invention described below.

[0014] A method for manufacturing a flexible printed circuit board according to one aspect of the present invention includes the steps of: forming an insulating layer on a support substrate; forming a resist layer on the insulating layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer, the openings having the predetermined pattern or a pattern opposite to the predetermined pattern; forming a conductor layer in the openings; and removing the resist layer, wherein the resist layer satisfies a first condition and a second condition, the first condition being that the resolution of the resist layer is 7 μm or less, and the second condition being that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after twice repeating bending the resist layer 180 degrees using a cylindrical mandrel and returning the resist layer to its unbent state is 4 mm or less.

[0015] A flexible printed circuit board according to another aspect of the present invention is a manufacturing method for a flexible printed circuit board, the manufacturing method including the steps of: preparing a laminate in which a conductor layer is laminated on an insulating layer; forming a resist layer on the conductor layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer, the openings having the predetermined pattern or a pattern opposite to the predetermined pattern; removing portions of the conductor layer exposed in the openings; and removing the resist layer, wherein the resist layer satisfies a first condition and a second condition, the first condition being that the resolution of the resist layer is 7 μm or less, and the second condition being that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after two cycles of bending the resist layer 180 degrees using a cylindrical mandrel and then returning the resist layer to its unbent state are 4 mm or less.

[0016] A semiconductor package according to yet another aspect of the present invention is manufactured by the above-described method for manufacturing a flexible printed circuit board.

[0017] An electronic device according to yet another aspect of the present invention includes the above-described semiconductor package. [Effects of the Invention]

[0018] According to the present invention, it is possible to manufacture a flexible printed circuit board having fine wiring while suppressing a decrease in the yield of manufacturing the flexible printed circuit board. [Brief explanation of the drawings]

[0019] [Figure 1] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 2] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 3]5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 4] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 5] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 6] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 7] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 8] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 9] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 10] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 11] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 12] 5A to 5C are manufacturing process diagrams illustrating an example of a method for manufacturing the flexible printed circuit board according to the first embodiment. [Figure 13] FIG. 10 is a diagram for explaining a third condition. [Figure 14] FIG. 1 is a schematic diagram showing an example of the configuration of a roll-to-roll apparatus used in a method for producing a flexible printed circuit board. [Figure 15] 10A to 10C are manufacturing process diagrams illustrating an example of a method for manufacturing a flexible printed circuit board according to a second embodiment. [Figure 16]10A to 10C are manufacturing process diagrams illustrating an example of a method for manufacturing a flexible printed circuit board according to a second embodiment. [Figure 17] 10A to 10C are manufacturing process diagrams illustrating an example of a method for manufacturing a flexible printed circuit board according to a third embodiment. [Figure 18] 10A and 10B are diagrams for explaining an application example of a rewiring substrate fabricated using a plating resist layer that satisfies the first and second conditions. [Figure 19] 1 is a table showing test results regarding the relationship between the material of the plating resist layer and the degree to which fine wiring can be formed in a flexible printed circuit board. [Figure 20] 1 is a table showing test results regarding the flexibility of a plating resist layer. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a flexible printed circuit board, ... semiconductor package, and an electronic device according to an embodiment of the present invention will be described below with reference to the drawings.

[0021] 1. First embodiment <1> Manufacturing method for flexible printed circuit board 1 to 12 are manufacturing process diagrams illustrating an example of a manufacturing method for a flexible printed circuit board according to the first embodiment. First, a roll (hereinafter referred to as a payout roll) around which a long metal supporting board 1 is wound is prepared, and the metal supporting board 1 is paid out from the prepared payout roll. The metal supporting board 1 paid out from the payout roll is taken up onto another roll (hereinafter referred to as a take-up roll). Various processes (described later) are performed on multiple parts of the metal supporting board 1 being transported from the payout roll to the take-up roll (roll-to-roll process). FIG. 1 shows a part of the metal supporting board 1 paid out from the payout roll. The metal supporting board 1 according to this embodiment is a supporting board made of stainless steel. Note that the metal supporting board 1 may be made of a metal material other than stainless steel (gold, silver, copper, iron, aluminum, or an alloy thereof, etc.).

[0022] The thickness of the metal supporting board 1 is preferably 10 μm or more and 100 μm or less, and is 20 μm in this embodiment. When the thickness of the metal supporting board 1 is 10 μm or more, the metal supporting board 1 ensures the rigidity required for manufacturing flexible printed circuit boards by roll-to-roll. When the thickness of the metal supporting board 1 is 100 μm or less, the metal supporting board 1 ensures the flexibility required for manufacturing flexible printed circuit boards by roll-to-roll.

[0023] 2, an insulating layer 2 made of photosensitive polyimide is formed on a partial region of the upper surface of the unwound metal supporting board 1. The thickness of the insulating layer 2 is 1 μm or more and 30 μm or less.

[0024] Next, as shown in FIG. 3 , a seed layer 3 is formed so as to cover the upper surface of the insulating layer 2, the side surfaces of the insulating layer 2, and portions of the upper surface of the metal supporting board 1 where the insulating layer 2 is not formed. The seed layer 3 has a configuration in which a copper thin film is further laminated on an underlayer formed of two or more thin films selected from the group consisting of a chromium thin film, a nickel thin film, a titanium thin film, and a chromium-nickel alloy thin film. The seed layer 3 may also have a configuration in which a copper thin film is laminated on an underlayer formed of one thin film selected from the group consisting of a chromium thin film, a nickel thin film, a titanium thin film, and a chromium-nickel alloy thin film. Each thin film constituting the seed layer 3 is formed by, for example, sputtering or electroless plating. The thickness of the seed layer 3 is 0.01 μm or more and 1 μm or less.

[0025] Next, a dry film resist is applied onto the seed layer 3 so as to cover the entire seed layer 3. Thereby, a plating resist layer 4 made of the dry film resist is formed on the seed layer 3, as shown in FIG.

[0026] The dry film resist is made of a negative photosensitive resin. A dry film resist made of a negative photosensitive resin has relatively high flexibility. Therefore, when the dry film resist is bonded onto the seed layer 3, the dry film resist deforms to follow the shapes of the metal supporting board 1, the insulating layer 2, and the seed layer 3. This reduces the occurrence of voids between the plating resist layer 4 and the seed layer 3 and insulating layer 2.

[0027] The dry film resist used in this embodiment is made of a negative photosensitive acrylic resin, and the thickness of the dry film resist (thickness of the plating resist layer 4) is 7 μm or more and 25 μm or less.

[0028] Next, the plating resist layer 4 is exposed to light in a predetermined pattern. The plating resist layer 4 is exposed to light by, for example, an exposure device 50 shown in FIG. 5. The exposure device 50 includes a mask 51, a light source 52, and a contact drive unit 59. The mask 51 has light-transmitting portions 51a and light-shielding portions 51b, and is positioned above the metal supporting board 1 being transported. The light-transmitting portions 51a are formed in a predetermined pattern in the mask 51. The light source 52 is mainly composed of a lamp 52a and a mirror 52b, and is positioned to face the plating resist layer 4 with the mask 51 in between. The lamp 52a generates exposure light corresponding to the plating resist layer 4. The mirror 52b reflects the exposure light generated by the lamp 52a toward the mask 51.

[0029] Here, in the manufacturing method for a flexible printed circuit board according to the present embodiment, before exposing plating resist layer 4 to light, contact drive unit 59 presses metal supporting board 1 toward mask 51 as shown by the outline arrow in Fig. 5. Alternatively, contact drive unit 59 presses mask 51 toward metal supporting board 1. This brings the upper surface of plating resist layer 4 into contact with the lower surface of mask 51. At this time, a pressure equal to or greater than a predetermined pressure (compression force) acts between plating resist layer 4 and mask 51.

[0030] The contact driving unit 59 may have, for example, a lower surface contact member that comes into contact with the lower surface of the metal supporting board 1, and an actuator that moves the lower surface contact member so that the metal supporting board 1 is pressed toward the mask 51. Alternatively, the contact driving unit 59 may have an upper surface contact member that comes into contact with the upper surface of the mask 51, and an actuator that moves the upper surface contact member so that the mask 51 is pressed toward the metal supporting board 1.

[0031] With the plating resist layer 4 pressed against the underside of the mask 51, exposure light is generated from the light source 52, as shown in Fig. 6. In this case, light that passes through the light-transmitting portions 51a of the mask 51 is incident on the plating resist layer 4. This exposes the plating resist layer 4 in a predetermined pattern. This process of bringing the plating resist layer 4 and the mask 51 into contact with each other and performing exposure while applying a pressure between the plating resist layer 4 and the mask 51 that is equal to or greater than a predetermined pressure value is called hard contact exposure.

[0032] The plating resist layer 4 may be exposed by a method other than the above-mentioned hard contact exposure. That is, in the present invention, the exposure method of the plating resist layer 4 is not limited to hard contact exposure. The plating resist layer 4 may be exposed by other exposure methods such as projection exposure or direct imaging exposure.

[0033] Projection exposure is an exposure method in which the plating resist layer is exposed by projecting an image of a mask onto the plating resist layer using an optical system such as a lens, while the mask and plating resist layer are not in contact (non-contact state).

[0034] Fig. 7 shows an example of the configuration of an exposure apparatus 50X that supports projection exposure. As shown in Fig. 7, the exposure apparatus 50X that supports projection exposure includes an optical system 53 in addition to the mask 51 and light source 52 of Fig. 5. The optical system 53 of Fig. 7 includes two lenses. When exposing the plating resist layer 4 by projection exposure, part of the exposure light generated from the light source 52 passes through the light-transmitting portion 51a of the mask 51 and the optical system 53 and is incident on the plating resist layer 4 in a predetermined pattern.

[0035] Direct imaging exposure is an exposure method that does not use a mask and involves scanning a laser beam based on predetermined circuit pattern design data to directly transfer a pattern corresponding to the design data onto a plating resist layer.

[0036] FIG. 8 shows an example of the configuration of an exposure apparatus 50Y compatible with direct imaging exposure. As shown in FIG. 8, the exposure apparatus 50Y compatible with direct imaging exposure includes a laser device 54, an optical scanning unit 55, and a scanning control unit 56, instead of the mask 51 and light source 52 of FIG. 5. The laser device 54 has a semiconductor laser element and generates laser light as exposure light. The laser device 54 also emits the generated laser light in one direction. The optical scanning unit 55 has, for example, a DMD (digital micromirror device) or an optical deflector, and can change the traveling direction of the laser light emitted from the laser device 54 to a direction other than the one direction. The scanning control unit 56 is configured, for example, with a CPU (central processing unit) and a memory or a microcomputer, and stores design data for the circuit pattern.

[0037] When exposing the plating resist layer 4 by direct imaging exposure, a laser beam emitted from a laser device 54 is incident on an optical scanning unit 55. In this state, a scanning control unit 56 controls the optical scanning unit 55 based on design data of the circuit pattern. As a result, the laser beam is scanned as exposure light on the plating resist layer 4.

[0038] Next, as shown in FIG. 9 , the exposed plating resist layer 4 is developed. At this time, the plating resist layer 4 is developed by a developing device 60. The developing device 60 includes a plurality of developing nozzles 61. Each developing nozzle 61 is a spray nozzle positioned above the transported metal supporting board 1, and sprays a developing solution toward the metal supporting board 1. As described above, the dry film resist constituting the plating resist layer 4 is made of a negative photosensitive resin. In this case, the unexposed portions are dissolved in the developing solution and removed. As a result, openings 4a of a predetermined pattern are formed in the plating resist layer 4. In the openings 4a, the seed layer 3 is exposed upward. Of the openings 4a formed to extend in one direction, the pattern width of the openings 4a in a cross section perpendicular to the one direction is 1 μm or more and 7 μm or less.

[0039] Next, as shown in Fig. 10, a conductor layer 5 having a predetermined pattern is formed by electrolytic plating on the portion of the seed layer 3 exposed in the opening 4a (Fig. 9) of the plating resist layer 4. The thickness of the conductor layer 5 is 1 µm or more and 15 µm or less. Furthermore, the pattern width of the conductor layer 5 formed to extend in one direction in a cross section perpendicular to the one direction is 1 µm or more and 7 µm or less.

[0040] 11, the plating resist layer 4 attached on the seed layer 3 is peeled off and removed from the seed layer 3. This exposes the portion of the seed layer 3 on which the conductor layer 5 is not formed. Finally, as shown in FIG. 12, the exposed unnecessary portion of the seed layer 3 is removed by, for example, wet etching.

[0041] In this way, a laminate of the metal supporting board 1, the insulating layer 2, the seed layer 3, and the conductor layer 5 is completed as a flexible printed circuit board 6. The seed layer 3 and the conductor layer 5 formed in a predetermined pattern on the insulating layer 2 constitute the wiring of the flexible printed circuit board 6. The metal supporting board 1 including the completed flexible printed circuit board 6 is taken up on a take-up roll.

[0042] <2> Essential conditions required for plating resist layer 4 In the flexible printed circuit board 6 manufactured by the method of FIGS. 1 to 12, the plating resist layer 4 after exposure and development satisfies the first and second conditions described below.

[0043] (1) First condition The first condition is that the resolution of the plating resist layer 4 is 7 μm or less. In this embodiment, the resolution of the plating resist layer 4 refers to the minimum limit of the reproducible line width of the plating resist layer 4 when a line-shaped plating resist layer 4 is formed by exposing and developing the plating resist layer 4.

[0044] More specifically, the resolution according to this embodiment is the line width of the line-shaped plating resist layer 4 when the line-shaped plating resist layer 4 extending in one direction is formed on the insulating layer 2, and is the minimum reproducible line width. The line width of the line-shaped plating resist layer 4 is the length (dimension) of the plating resist layer 4 in a direction parallel to the surface on which the plating resist layer 4 is formed and perpendicular to the direction in which the plating resist layer 4 extends.

[0045] Conventionally, a plating resist layer 4 with a resolution of 7 μm or less has not been used in the manufacture of flexible printed circuit boards. Therefore, when the first condition is satisfied, it becomes possible to form finer wiring than when the resolution of the plating resist layer 4 is greater than 7 μm. For example, when the line width of each of the multiple wirings in the flexible printed circuit board 6 and the spacing between two adjacent wirings are expressed as L / S, it becomes possible to manufacture a flexible printed circuit board 6 with an L / S of at least about 7 μm / 7 μm or less.

[0046] The first condition may be that the resolution of the plating resist layer 4 is 6 μm or less, or that the resolution of the plating resist layer 4 is 5 μm or less, when the second condition described below is satisfied. Alternatively, the first condition may be that the resolution of the plating resist layer 4 is 4 μm or less, or that the resolution of the plating resist layer 4 is 3 μm or less, or that the resolution of the plating resist layer 4 is 2 μm or less, when the second condition described below is satisfied.

[0047] (2) Second condition Here, the series of operations of bending the plating resist layer 4 180 degrees using a cylindrical mandrel and then returning the plating resist layer 4 to its pre-bending state, repeated twice, is referred to as the mandrel evaluation operation. The minimum diameter of the cylindrical mandrel that can maintain the plating resist layer 4 in good condition after the mandrel evaluation operation is referred to as the minimum mandrel diameter. In this case, it can be said that the smaller the minimum mandrel diameter, the higher the flexibility of the plating resist layer 4, and the larger the minimum mandrel diameter, the lower the flexibility.

[0048] In addition, being able to maintain the plating resist layer 4 in a healthy state means that after the mandrel evaluation work, the bent portion of the plating resist layer 4 has not peeled off from the seed layer 3 and no damage such as cracks can be found in that portion.

[0049] The second condition relates to the flexibility of the plating resist layer 4 after exposure and development, and is that the minimum mandrel diameter be 4 mm or less. In this case, the plating resist layer 4 has higher flexibility than when the minimum mandrel diameter is greater than 4 mm. Therefore, even if the metal supporting board 1 and the insulating layer 2 deform in a process after the formation of the plating resist layer 4, the plating resist layer 4 follows the deformation of the metal supporting board 1 and the insulating layer 2. This reduces the occurrence of missing portions such as chips in the plating resist layer 4 after exposure and development, and the peeling of the plating resist layer 4 from the insulating layer 2. This reduces a decrease in the yield of the flexible printed circuit board 6.

[0050] <3> Preferred conditions required for plating resist layer 4 After exposure and development, the plating resist layer 4 preferably satisfies the third, fourth and fifth conditions described below in addition to the first and second conditions described above.

[0051] (1) Third condition In the following description, the portion of the plating resist layer 4 after exposure and development that is formed in lines extending in one direction is referred to as the line resist layer. Fig. 13 is a diagram for explaining the third condition. Fig. 13 shows a partially enlarged cross-sectional view of an intermediate flexible printed circuit board 6 cut by a plane perpendicular to the line resist layer 4L.

[0052] 13, the line resist layer 4L has a substantially rectangular cross section extending upward from the upper surface of the seed layer 3. The lower end portion of the line resist layer 4L and its neighboring portion extend to both sides (both left and right sides in FIG. 13). As a result, in the cross-sectional view of FIG. 13, the width of the lower end portion of the line resist layer 4L and its neighboring portion is larger than the width of other portions of the line resist layer 4L.

[0053] The third condition is that the maximum width W2 of the line resist layer 4L is 1.2 times or less the minimum width W1 of the line resist layer 4L in any cross section of the line resist layer 4L (a cross section perpendicular to the line resist layer 4L). In this case, it becomes possible to form finer wiring than when the maximum width W2 of the line resist layer 4L is greater than 1.2 times the minimum width W1 of the line resist layer 4L.

[0054] The portions extending outward from the two sides of the line resist layer 4L at the bottom end and its vicinity are called footing portions HP. In Figure 13, the two footing portions HP are indicated by dotted-line frames. The width of each footing portion HP is called the footing width W3.

[0055] In any cross section of the line resist layer 4L, the foot widths W3 of the two foot portions HP are considered to be approximately equal. In this case, the difference between the minimum width W1 and the maximum width W2 is approximately equal to the sum of the foot widths W3 of the two foot portions HP. Therefore, the third condition may be that the foot width W3 of one foot portion HP is 0.1 times or less the minimum width W1 of the line resist layer 4L. Even in this case, it is possible to form finer wiring than when the maximum width W2 of the line resist layer 4L is greater than 1.2 times the minimum width W1 of the line resist layer 4L. Therefore, when the minimum width W1 of the line resist layer 4L is 5 μm, the foot width W3 of the foot portion HP generated on one side of the line resist layer 4L is preferably 0.5 μm or less.

[0056] The line width of the plating resist layer 4 described in the first condition means the line width of the line resist layer 4L excluding the footing portion HP, and corresponds to the minimum width W1 of the line resist layer 4L in FIG.

[0057] (2) Fourth condition The fourth condition is that the elastic modulus of the plating resist layer 4 after exposure and development is 3.5 GPa or more. In this case, the handleability of the intermediate body from the time the plating resist layer 4 is exposed and developed until the time the plating resist layer 4 is peeled off from the seed layer 3 is improved compared to when a plating resist layer 4 having an elastic modulus lower than 3.5 GPa is used.

[0058] (3) Fifth condition The fifth condition is that the aspect ratio, which is the ratio of the thickness of the line resist layer 4L formed by exposure and development to the line width of the line resist layer 4L, is between 1 and 3. The aspect ratio of the line resist layer 4L according to this embodiment is obtained by dividing the thickness T1 of the line resist layer 4L in FIG. 13 by the minimum width W1 of the line resist layer 4L in FIG. 13.

[0059] In the manufacturing method of the flexible printed circuit board 6 according to this embodiment, as described above, the plating resist layer 4 has flexibility corresponding to the second physical property. This makes it easier for the plating resist layer 4 to be maintained in a sound state after exposure and development. Therefore, the line resist layer 4L can be formed with an aspect ratio in a relatively wide range of 1 or more and 3 or less.

[0060] By ensuring a wide range of aspect ratios in which the line resist layer 4L can be formed, it becomes possible to increase the density of the wiring formed on the flexible printed circuit board 6 and improve the degree of freedom in designing the wiring. In order to form wiring with a higher aspect ratio, it is more preferable that the aspect ratio of the line resist layer 4L is 3.

[0061] <4> Roll-to-roll equipment A series of processes for manufacturing the flexible printed circuit board 6 is performed using, for example, one roll-to-roll apparatus. Fig. 14 is a schematic diagram showing an example of the configuration of a roll-to-roll apparatus used in the method for manufacturing the flexible printed circuit board 6.

[0062] 14 includes an unwinding unit 501, a winding unit 502, and a plurality of processing units 510, 520, etc. First, a roll (unwinding roll) R1 around which a long metal supporting board 1 is wound is prepared and set in the unwinding unit 501 of the roll-to-roll apparatus 500.

[0063] Thereafter, as described above, the metal supporting board 1 is unwound from the prepared unwound roll R1. The unwound metal supporting board 1 is taken up by another roll (take-up roll) R2 set in the take-up unit 502, as shown by the dotted arrow in FIG.

[0064] In the roll-to-roll apparatus 500, a plurality of processing sections 510, 520, ... are arranged between two rolls (R1, R2) so as to be aligned along the moving direction of the metal supporting board 1. Each of the plurality of processing sections 510, 520, ... performs a process assigned to that processing section on the long metal supporting board 1 moving between the two rolls (R1, R2). The process assigned to the processing section is one of the above-mentioned plurality of processes (a process for forming the insulating layer 2, a process for forming the seed layer 3, a process for forming the plating resist layer 4, an exposure process for the plating resist layer 4, a development process for the plating resist layer 4, etc.). As a result, a plurality of flexible printed circuit boards 6 are formed on the metal supporting board 1 taken up by the take-up roll R2.

[0065] In addition to the above examples, the flexible printed circuit board 6 may be manufactured using a plurality of roll-to-roll apparatuses. Specifically, the flexible printed circuit board 6 may be manufactured using a plurality of roll-to-roll apparatuses that independently perform the processes of forming the insulating layer 2, forming the seed layer 3, forming the plating resist layer 4, exposing the plating resist layer 4, developing the plating resist layer 4, forming the conductor layer 5, stripping the plating resist layer 4, and removing the seed layer 3.

[0066] <5> Effects of the First Embodiment (a) In the above-described method for manufacturing a flexible printed circuit board 6, the plating resist layer 4 after exposure and development satisfies the first condition that the resolution is 7 μm or less and the second condition that the minimum mandrel diameter is 4 mm or less. This makes it possible to manufacture a flexible printed circuit board 6 having fine wiring without reducing the yield.

[0067] (b) Furthermore, in the above-described method for manufacturing a flexible printed circuit board 6, it is preferable that the plating resist layer 4 after exposure and development satisfy a third condition that the maximum width W2 of the line resist layer 4L is 1.2 times or less the minimum width W1 of the line resist layer 4L. This enables the formation of finer wiring.

[0068] (c) Furthermore, in the above-described method for producing a flexible printed circuit board 6, it is preferable that the plating resist layer 4 after exposure and development satisfy a fourth condition that the elastic modulus is 3.5 GPa or more. This improves the handleability of the intermediate flexible printed circuit board 6.

[0069] Now, assume that multiple roll-to-roll apparatuses are used, and an intermediate body including the plating resist layer 4 after exposure and development is wound onto one roll. In this case, the intermediate body including the plating resist layer 4, the seed layer 3, the insulating layer 2, and the metal supporting board 1 is wound onto one roll multiple times. That is, multiple portions of the intermediate body are stacked in the radial direction on the one roll.

[0070] Even in such a case, if the plating resist layer 4 satisfies the fourth condition, a certain level of strength is ensured for the plating resist layer 4. As a result, even if pressure acts on each part of the plating resist layer 4 due to multiple parts of the intermediate body overlapping each other within one roll, the plating resist layer 4 is prevented from undergoing plastic deformation.

[0071] (d) Furthermore, in the manufacturing method of the flexible printed circuit board 6 described above, it is preferable to satisfy a fifth condition that the aspect ratio, which is the ratio of the thickness of the line resist layer 4L formed by exposure and development to the line width of the line resist layer 4L, be between 1 and 3. This allows for a higher density of wiring formed on the flexible printed circuit board 6 and improves the degree of freedom in wiring design.

[0072] (e) In the manufacturing method of the flexible printed circuit board 6 described above, the plating resist layer 4 is exposed by, for example, hard contact exposure. In hard contact exposure, the mask 51 and the plating resist layer 4 come into contact with each other, thereby fixing the positional relationship between the mask 51 and the plating resist layer 4. Furthermore, since no gap (space) is formed between the mask 51 and the plating resist layer 4, the spread of exposure light is suppressed. As a result, it is possible to expose a fine pattern with relatively high precision.

[0073] Furthermore, as described above, in the manufacturing method of the flexible printed circuit board 6, the plating resist layer 4 may be exposed by projection exposure or direct imaging exposure instead of hard contact exposure. Projection exposure and direct imaging exposure, like hard contact exposure, enable exposure of fine patterns with relatively high accuracy. Therefore, when the plating resist layer 4 is exposed by either hard contact exposure, projection exposure, or direct imaging exposure, it is possible to expose the desired pattern with higher resolution than when the plating resist layer 4 is exposed by proximity exposure. Thus, exposing the plating resist layer 4 by hard contact exposure, projection exposure, or direct imaging exposure is advantageous for forming fine wiring. On the other hand, exposing the plating resist layer 4 by proximity exposure does not allow for the formation of fine wiring.

[0074] Proximity exposure is an exposure method in which a plating resist layer is exposed by projecting an image of the mask onto the plating resist layer while forming a minute gap (a few μm or tens of μm) between the mask and the plating resist layer. Thus, proximity exposure differs from projection exposure in that the distance between the mask and the plating resist layer is set short and no optical system is placed between the mask and the plating resist.

[0075] (f) In the above-described method for manufacturing the flexible printed circuit board 6, the dry film resist that forms the plating resist layer 4 is made of a highly flexible negative photosensitive resin. In this case, as described above, when the dry film resist is bonded onto the seed layer 3, the occurrence of voids between the plating resist layer 4 and the seed layer 3 and between the plating resist layer 4 and the insulating layer 2 is reduced.

[0076] Furthermore, the flexibility of the dry film resist continues to be maintained even after the exposure and development of the plating resist layer 4. Therefore, even if the metal supporting board 1, the insulating layer 2, etc. are deformed after the exposure and development of the plating resist layer 4, the occurrence of missing portions such as chips in the plating resist layer 4 due to the deformation and the peeling of the plating resist layer 4 from the insulating layer 2 are reduced.

[0077] (g) In the above-described method for manufacturing a flexible printed circuit board 6, after the insulating layer 2 is formed on the metal supporting board 1, the seed layer 3 is formed so as to cover the upper surface of the insulating layer 2, the side surfaces of the insulating layer 2, and part of the upper surface of the metal supporting board 1. Thereafter, a plating resist layer 4 is formed, and an opening 4a is formed in the plating resist layer 4. This allows the conductor layer 5 to be easily formed by electrolytic plating on the seed layer 3 exposed through the opening 4a.

[0078] 2. Second embodiment 12 according to the first embodiment has a configuration in which a plurality of wirings are formed on the upper surface of the metal supporting board 1, and no wirings are formed on the lower surface of the metal supporting board 1. The flexible printed circuit board may have a configuration in which wirings are formed on the upper surface of the metal supporting board 1 and wirings are formed on the lower surface of the metal supporting board 1.

[0079] Hereinafter, a method for manufacturing a flexible printed circuit board in which wiring is formed on the upper and lower surfaces of the metal supporting board 1 will be described as a method for manufacturing a flexible printed circuit board according to the second embodiment.

[0080] 15 and 16 are manufacturing process diagrams illustrating an example of a manufacturing method for a flexible printed circuit board according to the second embodiment. The flexible printed circuit board according to this embodiment is also manufactured by roll-to-roll, like the flexible printed circuit board 6 according to the first embodiment.

[0081] First, a feed roll around which the metal supporting board 1 is wound is prepared. The metal supporting board 1 is then fed from the feed roll. Next, as shown in the cross-sectional view in the first row from the top of FIG. 15 , an insulating layer 2 made of photosensitive polyimide is formed on a partial region of the upper surface of the metal supporting board 1 and on a partial region of the lower surface of the metal supporting board 1.

[0082] Next, as shown in the second cross-sectional view from the top in FIG. 15, a seed layer 3 is formed to cover the exposed portions of the upper and lower insulating layers 2 and to cover the exposed portions of the upper and lower surfaces of the metal supporting board 1.

[0083] Next, as shown in the third cross-sectional view from the top in Fig. 15 , a plating resist layer 4 is formed on the upper surface of the metal supporting board 1 via the insulating layer 2 and the seed layer 3. In addition, a plating resist layer 4 is formed on the upper surface of the metal supporting board 1 via the insulating layer 2 and the seed layer 3. The method for forming the plating resist layer 4 is the same as the method for forming the plating resist layer 4 according to the first embodiment.

[0084] Next, as shown in the fourth cross-sectional view from the top in FIG. 15 , the upper and lower plating resist layers 4 are exposed to light in a predetermined pattern and developed. As a result, openings 4a in a predetermined pattern are formed in the upper and lower plating resist layers 4 of the metal supporting board 1. The method for exposing and developing the plating resist layer 4 is the same as the method for exposing and developing the plating resist layer 4 according to the first embodiment. Therefore, in this embodiment, the exposure of the plating resist layer 4 may be performed by hard contact exposure, projection exposure, or direct imaging exposure. Note that in this embodiment, plating resist layers 4 are present on the top and bottom of the metal supporting board 1. Therefore, the exposure process of the plating resist layer 4 on the top surface of the metal supporting board 1 and the exposure process of the plating resist layer 4 on the bottom surface of the metal supporting board 1 may be performed at different times. Furthermore, the development process of the plating resist layer 4 on the top surface of the metal supporting board 1 and the development process of the plating resist layer 4 on the bottom surface of the metal supporting board 1 may be performed at different times.

[0085] Next, as shown in the first cross-sectional view from the top of Figure 16, a conductor layer 5 of a predetermined pattern is formed by electrolytic plating on the portion of the seed layer 3 exposed within the opening 4a of the plating resist layer 4 (see the fourth cross-sectional view from the top of Figure 15).

[0086] Next, as shown in the second cross-sectional view from the top in Fig. 16, the plating resist layers 4 on the top and bottom of the metal supporting board 1 are peeled off and removed from the seed layer 3. Finally, as shown in the third cross-sectional view from the top in Fig. 16, the exposed unnecessary portion of the seed layer 3 is removed by, for example, wet etching. This completes a flexible printed circuit board 7 having wiring on the top and bottom.

[0087] In the method for manufacturing a flexible printed circuit board 7 according to this embodiment, the plating resist layer 4 after exposure and development also satisfies the first and second conditions described above, making it possible to manufacture a flexible printed circuit board 7 having fine wiring without reducing yield.

[0088] 3. Third Embodiment The wiring of the flexible printed circuit board 6 according to the first embodiment is formed by a so-called semi-additive method, but the wiring of the flexible printed circuit board may also be formed by a so-called subtractive method.

[0089] The method for manufacturing a flexible printed circuit board according to the third embodiment will be described below in terms of differences from the method for manufacturing the flexible printed circuit board 6 according to the first embodiment. In the method for manufacturing a flexible printed circuit board according to the third embodiment, wiring is formed by a subtractive method.

[0090] Fig. 17 is a manufacturing process diagram for explaining an example of a manufacturing method for a flexible printed circuit board according to the third embodiment. In this embodiment, as shown in the cross-sectional view in the first row from the top of Fig. 17, first, a long laminated base material is prepared in which a conductor layer 11 is laminated on an insulating layer 12.

[0091] Next, as shown in the second cross-sectional view from the top in Fig. 17, a dry film resist is applied to the upper surface of the conductor layer 11 so as to cover the entire exposed surface (the upper surface in this example) of the conductor layer 11. This forms an etching resist layer 13 made of the dry film resist on the conductor layer 11. The etching resist layer 13 formed here has the same configuration and shape as the plating resist layer 4 according to the first embodiment.

[0092] Next, as shown in the third cross-sectional view from the top in FIG. 17, the etching resist layer 13 is exposed to light in a predetermined pattern and developed. As a result, openings 13a in the predetermined pattern are formed in the etching resist layer 13. The method for exposing and developing the etching resist layer 13 is the same as the method for exposing and developing the plating resist layer 4 in the first embodiment. Therefore, in this embodiment, the exposure of the etching resist layer 13 may be performed by hard contact exposure, projection exposure, or direct imaging exposure.

[0093] Next, as shown in the fourth cross-sectional view from the top of Fig. 17, the unnecessary exposed portion of the conductor layer 11 is removed, for example, by wet etching. In the fourth cross-sectional view from the top of Fig. 17, the removed portion of the conductor layer 11 is shown as a conductor-removed portion 11a.

[0094] 17, the etching resist layer 13 is peeled off and removed from the conductor layer 11. In this way, the flexible printed circuit board 14 is completed.

[0095] In the method for manufacturing a flexible printed circuit board 14 according to this embodiment, the etching resist layer 13 after exposure and development also satisfies the first and second conditions described above, which makes it possible to manufacture a flexible printed circuit board 14 having fine wiring without reducing yield.

[0096] 4. Application examples of flexible printed circuit boards 6, 7, and 14 According to the manufacturing method of the above embodiment, it is also possible to manufacture a flexible printed circuit board in which multiple insulating layers (e.g., two or more insulating layers) are stacked with multiple wirings sandwiched between them. For example, each time an insulating layer is formed, a resist layer (4, 13) that satisfies the first and second conditions in a predetermined pattern is formed on the insulating layer, and wiring corresponding to the insulating layer is formed. In addition, vias are formed in parts of the insulating layer to electrically connect the upper and lower wirings. This makes it possible to manufacture a flexible printed circuit board with a multilayer wiring structure.

[0097] One example of such a flexible printed circuit board is a flexible rewiring board. The rewiring board is placed between an electronic component such as a semiconductor device and another wired circuit board such as a rigid printed circuit board, and serves to convert the pitch between the fine pattern of the electronic component and the coarse pattern of the other wired circuit board. The rewiring board is also called an interposer board.

[0098] Fig. 18 is a diagram illustrating an application example of a rewiring substrate fabricated using a plating resist layer that satisfies the first and second conditions. Fig. 18 shows a configuration in which a rewiring substrate 100 is disposed between a semiconductor chip 200 and a rigid substrate 300. A plurality of terminal portions 101 are formed on the upper surface of the rewiring substrate 100 in this example.

[0099] The semiconductor chip 200 has a plurality of connection terminals 201. The tip of each connection terminal 201 is joined via solder S to a terminal portion 101 of a pre-assigned rewiring substrate 100. An underfill 410 is filled between the semiconductor chip 200 and the upper surface of the rewiring substrate 100. The underfill 410 is made of, for example, epoxy resin. A lid member (not shown) that covers the semiconductor chip 200 may be provided on the upper surface of the rewiring substrate 100. The semiconductor chip 200 is mounted on the upper surface of the rewiring substrate 100 and further sealed with resin to form a semiconductor package 400.

[0100] In this embodiment, the semiconductor package 400 is, for example, an FC-CSP (Flip Chip-Chip Scale Package), an MIS-BGA (Molded Interconnect Substrate-Ball Grid Array) package, an ETS-BGA (Embedded Trace Substrate-Ball Grid Array) package, a Fan-out WLP (Wafer Level Package), a Fan-in WLP, a Fan-out PLP (Panel Level Package), a Fan-in PLP, an FC-BGA (Flip Chip-Chip, -Ball Grid Array), a high-end 2.5D or 3D package, or the like.

[0101] In this example, a plurality of terminal portions 102 are formed on the lower surface of the rewiring substrate 100. The rigid substrate 300 has a plurality of electrode pads 301 as a plurality of connection terminals of the rigid substrate 300. The electrode pads 301 are bonded via solder S to the terminal portions 102 of the rewiring substrate 100 that are previously associated with each other.

[0102] 18, semiconductor package 400 is incorporated into electronic device 800 by being mounted on, for example, rigid substrate 300. In this embodiment, electronic device 800 is, for example, a mobile terminal such as a smartphone, a tablet terminal, or a wearable terminal. Alternatively, electronic device 800 is, for example, a desktop or notebook personal computer.

[0103] The rewiring substrate 100 is manufactured by forming a resist layer (4, 13) that satisfies the first and second conditions according to the manufacturing methods of the first to third embodiments. This prevents a decrease in the yield of the rewiring substrate 100. Furthermore, high-density wiring in the rewiring substrate 100 is achieved.

[0104] The rewiring substrate 100 can be made smaller and thinner than a rigid printed circuit board. Furthermore, since the rewiring substrate 100 is manufactured according to the manufacturing methods of the first to third embodiments, it has fine wiring. This allows for the realization of a semiconductor package 400 that is highly versatile in terms of mounting position and mounting target.

[0105] As described above, the semiconductor package 400 can be easily made smaller and thinner. Therefore, by using the semiconductor package 400 as part of the electronic device 800, the electronic device 800 can be easily made smaller and thinner.

[0106] 5. The degree to which fine wiring can be formed on the flexible printed circuit boards 6, 7, and 14 It is believed that the degree to which fine wiring can be formed on the flexible printed circuit boards 6, 7, and 14 depends on the material of the resist layers (4, 13). In other words, it is believed that different materials for the resist layers (4, 13) will result in different degrees to which fine wiring can be formed on the flexible printed circuit boards 6, 7, and 14. The present inventors conducted the following tests to confirm this point.

[0107] In the following description, the sheet-like member having the above-described multiple flexible printed circuit boards 6, 7, and 14 will be referred to as an assembly sheet. The assembly sheet corresponds to the metal supporting board 1 that is wound around a take-up roll in the manufacturing process of the flexible printed circuit boards 6, 7, and 14. The assembly sheet described below includes 114 flexible printed circuit boards arranged in a 12 × 12 matrix.

[0108] The inventors prepared four types of dry film resists made of different photosensitive resin materials. In the following description, when distinguishing between the four types of dry film resists, they will be referred to as the first dry film resist, the second dry film resist, the third dry film resist, and the fourth dry film resist. The resin material constituting the first dry film resist will be referred to as resin A, and the resin material constituting the second dry film resist will be referred to as resin B. The resin material constituting the third dry film resist will be referred to as resin C, and the resin material constituting the fourth dry film resist will be referred to as resin D. Resins A to D are negative-type photosensitive acrylic resins and have different physical properties.

[0109] The inventors also produced three assembly sheets each of Samples 1 to 7 using the four types of dry film resist described above, according to the manufacturing methods shown in FIGS. 1 to 12. These were produced by a sheet-by-sheet method, not a roll-to-roll method. When producing each assembly sheet, the design L / S of the wiring included in the assembly sheet was set to 5 μm / 5 μm. In this test, wiring formed with an L / S of 5 μm / 5 μm is considered an example of fine wiring.

[0110] The plating resist layer 4 of the assembly sheet of Sample 1 was formed using the first dry film resist. Therefore, the plating resist layer 4 of Sample 1 was made of Resin A. The elastic modulus of the plating resist layer 4 of Sample 1 was 4.04 GPa, and the thickness of the plating resist layer 4 of Sample 1 was 15 μm. Furthermore, in the assembly sheet of Sample 1, the insulating layer 2 was formed of polyimide, and a stainless steel supporting substrate was used as the metal supporting board 1. The assembly sheet of Sample 2 was produced to have the same configuration as the assembly sheet of Sample 1, except that the insulating layer 2 was formed of epoxy resin.

[0111] The plating resist layer 4 of the assembly sheet of Sample 3 was formed using the second dry film resist. Therefore, the plating resist layer 4 of Sample 3 was made of Resin B. The elastic modulus of the plating resist layer 4 of Sample 3 was 3.75 GPa, and the thickness of the plating resist layer 4 of Sample 3 was 15 μm. Furthermore, in the assembly sheet of Sample 3, the insulating layer 2 was made of polyimide, and a stainless steel supporting substrate was used as the metal supporting board 1. The assembly sheet of Sample 4 was produced to have the same configuration as the assembly sheet of Sample 3, except that the insulating layer 2 was made of epoxy resin.

[0112] The plating resist layer 4 of the assembly sheet of Sample 5 was formed using the third dry film resist. Therefore, the plating resist layer 4 of Sample 5 was made of Resin C. The elastic modulus of the plating resist layer 4 of Sample 5 was 4.57 GPa, and the thickness of the plating resist layer 4 of Sample 5 was 15 μm. Furthermore, in the assembly sheet of Sample 5, the insulating layer 2 was formed of polyimide, and a stainless steel supporting substrate was used as the metal supporting board 1. The assembly sheet of Sample 6 was produced to have the same configuration as the assembly sheet of Sample 5, except that the insulating layer 2 was formed of epoxy resin.

[0113] The plating resist layer 4 of the assembly sheet of Sample 7 was formed using the fourth dry film resist. Therefore, the plating resist layer 4 of Sample 7 was made of Resin D. The elastic modulus of the plating resist layer 4 of Sample 7 was 4.52 GPa, and the thickness of the plating resist layer 4 of Sample 7 was 20 μm. Furthermore, the insulating layer 2 was made of polyimide, and a stainless steel supporting substrate was used as the metal supporting board 1.

[0114] The thickness of the plating resist layer 4 of Samples 1 to 7 is the thickness of the dry film resist used to form the plating resist layer 4. The elastic modulus of the plating resist layer 4 of Samples 1 to 7 is a value measured by nanoindentation using a nanoindenter (Triboindenter, manufactured by Hysitron). Specifically, during the production of each of Samples 1 to 7, the inventors cut out a portion including the plating resist layer 4 from an intermediate product after exposure of the plating resist layer 4 but before the formation of the conductor layer 5, to prepare a 1 cm square test piece. The inventors also fixed each test piece on a glass slide, set it in the nanoindenter, and pressed an indenter against the plating resist layer 4 of the test piece. The measurement mode was single indentation measurement, and the measurement temperature was 25°C. The indenter was pressed to a depth of 500 nm into the plating resist layer 4.

[0115] For each of the assembly sheets of Samples 1 to 7 prepared as described above, the inventors confirmed whether the wiring corresponding to each of the 114 flexible printed circuit boards was properly formed according to the pre-designed L / S. This confirmation was performed by the inventors observing each flexible printed circuit board at 200x and 300x magnifications using a laser microscope (Keyence Corporation; VK-X3000) to determine whether there was any breakage, short circuit, wiring collapse, or wiring deformation.

[0116] Here, flexible printed circuit boards in which no breaks, short circuits, wiring collapse, or wiring deformation were found through the above-mentioned confirmation work were considered to be good products. On the other hand, flexible printed circuit boards in which breaks, short circuits, wiring collapse, or wiring deformation were found to be bad products. Then, for each of Samples 1 to 7, the inventors counted the number of good flexible printed circuit boards among all flexible printed circuit boards in the three assembly sheets, i.e., among the 432 flexible printed circuit boards.

[0117] As a result, for Sample 1, 303 or more of the 432 flexible printed circuit boards were found to be non-defective. For Sample 2, as with Sample 1, 303 or more of the 432 flexible printed circuit boards were found to be non-defective. Here, the ratio of the number of non-defective flexible printed circuit boards to the total number of flexible printed circuit boards produced is called the non-defective rate, which indicates the degree to which fine wiring can be formed on a flexible printed circuit board. In this case, the non-defective rate for Samples 1 and 2 was approximately 70% or higher.

[0118] For Sample 3, 260 to 302 flexible printed circuit boards out of 432 flexible printed circuit boards were found to be non-defective. For Sample 4, similar to the example of Sample 3, 260 to 302 flexible printed circuit boards out of 432 flexible printed circuit boards were found to be non-defective. Thus, for Samples 3 and 4, the non-defective rate was generally 60% to less than 70%.

[0119] For Sample 5, 259 or less flexible printed circuit boards out of 432 flexible printed circuit boards were found to be non-defective. For Samples 6 and 7, similar to the example of Sample 5, 259 or less flexible printed circuit boards out of 432 flexible printed circuit boards were found to be non-defective. Thus, for Samples 5, 6, and 7, the non-defective rate was generally less than 60%.

[0120] Fig. 19 is a table showing test results regarding the relationship between the material of the plating resist layer and the degree to which fine wiring can be formed on a flexible printed circuit board. The table in Fig. 19 shows some information about multiple samples 1 to 7 (such as the material, elastic modulus, and thickness of the plating resist layer) as well as the yield rate as a test result.

[0121] Samples 1 to 7 have roughly the same thickness of the plating resist layer (15 μm to 20 μm). The elastic modulus of the plating resist layer is also roughly the same (3.75 GPa to 4.57 GPa). Furthermore, between two samples with the same plating resist layer material, the yield rate is also the same even when the insulating layer 2 material is different.

[0122] From these points, it has been confirmed that the degree to which fine wiring can be formed on the flexible printed circuit boards 6, 7, and 14 is largely determined by the material of the resist layers (4, 13). Therefore, when manufacturing the flexible printed circuit boards 6, 7, and 14 according to this embodiment, it is preferable to use a material that can achieve a higher yield rate as the material for the resist layers (4, 13). This improves the manufacturing yield of the flexible printed circuit boards 6, 7, and 14.

[0123] 6. Flexibility of the resist layer (4, 13) The inventors of the present invention have considered that the more flexible the resist layer (4, 13) is made of after exposure and development, the higher the yield of the flexible printed circuit boards. To confirm this, the inventors of the present invention conducted the following test.

[0124] First, the inventors prepared an intermediate assembly sheet corresponding to Sample 1 above after the exposure of the plating resist layer 4 and before the formation of the conductor layer 5, and cut three 100 mm × 20 mm test pieces from the intermediate. The inventors designated the three cut test pieces as Sample 11. Next, the inventors prepared an intermediate assembly sheet corresponding to Sample 2 above after the exposure of the plating resist layer 4 and before the formation of the conductor layer 5, and cut three 100 mm × 20 mm test pieces from the intermediate. These three test pieces were designated Sample 12. Furthermore, the inventors prepared Samples 13 to 17, respectively, from intermediate assembly sheets corresponding to Samples 3 to 7 above, similar to the examples of Samples 11 and 12. These samples were prepared by a sheet-to-sheet method rather than a roll-to-roll method.

[0125] Next, the inventors performed a bending test on the test pieces of each of Samples 11 to 17 using a mandrel testing machine (BEVS Industrial; BEVS1603) at a measurement temperature of 25°C with N = 3. The bending test procedure was as follows.

[0126] First, the inventors prepared six cylindrical mandrels each having a different diameter: 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, and 10 mm.

[0127] Next, the inventors performed the mandrel evaluation procedure described above for the test specimens of Samples 11 to 17 using the six prepared cylindrical mandrels and the mandrel testing machine described above. Specifically, the test specimen of one sample was placed in the mandrel testing machine, and the test specimen was bent 180° using the largest cylindrical mandrel with a diameter of 10 mm and then returned to its original state, repeating this process twice. The inventors then visually confirmed whether the test specimen was sound. The inventors also repeated the above series of procedures, decreasing the diameter of the cylindrical mandrel used, until the test specimen was determined to be unsound. The inventors then determined the minimum diameter of the cylindrical mandrel required for the test specimen of one sample to be sound as the minimum mandrel diameter.

[0128] Fig. 20 is a table showing the test results regarding the flexibility of the plating resist layer 4. As in the example of Fig. 19, the table in Fig. 20 shows the results of the bending test described above together with some information about a plurality of samples 11 to 17 (such as the material, elastic modulus, and thickness of the plating resist layer).

[0129] As shown in FIG. 20, the minimum mandrel diameter of Samples 11 and 12, which was the result of the bending test, was 4 mm. On the other hand, the minimum mandrel diameter of Samples 13 to 16, which was the result of the bending test, was 5 mm. The minimum mandrel diameter of Sample 17, which was the result of the bending test, was 6 mm. These test results show that the flexibility of the plating resist layer 4 of Samples 11 and 12 is higher than the flexibility of the plating resist layer 4 of Samples 13 to 16. Considering this, it is thought that the reason the yield rate of Samples 1 and 2 is higher than the yield rate of Samples 3 to 7 in the test of FIG. 19 is due to the flexibility of the plating resist layer 4.

[0130] The present inventors observed the plating resist layer 4 of each of the above Samples 11 to 17 at 1000x and 5000x magnifications using a scanning electron microscope (SEM). Then, the present inventors determined whether or not microscopic cracks had occurred on the surface of the plating resist layer 4 of each of the prepared Samples 11 to 17.

[0131] 20 also shows the results of observation of the plating resist layer 4 with a scanning electron microscope. As shown in FIG. 20, the results of observation of the plating resist layer 4 with a scanning electron microscope showed that no cracks were observed in the plating resist layer 4 of Samples 11 and 12. On the other hand, cracks were observed in the plating resist layer 4 of Samples 13 to 17. These results show that the high flexibility of the plating resist layer 4 also contributes to improving the reliability of the plating resist layer 4.

[0132] 7. Other Embodiments (a) The manufacturing methods for the flexible printed circuit boards 6 and 7 according to the first and second embodiments utilize a semi-additive process. On the other hand, the manufacturing method for the flexible printed circuit board 14 according to the third embodiment utilizes a subtractive process. However, the present invention is not limited to these. The flexible printed circuit board may also be manufactured using a modified semi-additive process.

[0133] (b) In the manufacturing methods of the flexible printed circuit boards 6 and 7 according to the first and second embodiments, the insulating layer 2 is formed on a partial region of the upper surface of the metal supporting board 1, but the present invention is not limited to this. The insulating layer 2 may be formed so as to cover the entire upper surface of the metal supporting board 1.

[0134] (c) Although the flexible printed circuit boards 6, 7, and 14 according to the above-described embodiments are manufactured by roll-to-roll, the present invention is not limited to this. The flexible printed circuit boards 6, 7, and 14 may be manufactured by methods other than roll-to-roll. For example, they may be manufactured by a sheet-by-sheet method in which processing is performed sequentially on a single sheet.

[0135] 8. Correspondence between each part of the embodiment and each element of the claims The following describes examples of correspondence between the elements of the claims and the elements of the embodiments. Various other elements having the configurations or functions described in the claims may also be used as the elements of the claims.

[0136] In the above-described embodiments, flexible printed circuit boards 6, 7, and 14 are examples of flexible printed circuit boards, plating resist layer 4 and etching resist layer 13 are examples of resist layers, metal supporting board 1 is an example of a supporting board and a metal supporting board, openings 4a and 13a are examples of openings, conductor layers 5 and 11 are examples of conductor layers, insulating layers 2 and 12 are examples of insulating layers, mask 51 is an example of a mask, a long laminated base material in which conductor layer 11 is laminated on insulating layer 12 is an example of a laminate, semiconductor package 400 is an example of a semiconductor package, and electronic device 800 is an example of an electronic device.

[0137] 9. Summary of the embodiment (Item 1) The manufacturing method of the flexible printed circuit board according to item 1 is as follows: forming an insulating layer on a support substrate; forming a resist layer on the insulating layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer in the predetermined pattern or a pattern opposite to the predetermined pattern; forming a conductor layer in the opening; removing the resist layer; the resist layer is a layer that satisfies a first condition and a second condition, the first condition is that the resolution of the resist layer is 7 μm or less; The second condition is that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after the resist layer is bent 180 degrees using the cylindrical mandrel and then returned to its unbent state twice is 4 mm or less.

[0138] In the manufacturing method for the flexible printed circuit board, a resist layer that satisfies the first and second conditions is formed using a dry film resist. The first condition is that the resolution of the resist layer is 7 μm or less. This makes it possible to form finer wiring than when the resolution of the resist layer is greater than 7 μm.

[0139] The series of operations, which involves bending the resist layer 180 degrees using a cylindrical mandrel and then returning the resist layer to its unbent state twice, is called the mandrel evaluation operation. The minimum diameter of the cylindrical mandrel that can maintain the integrity of the resist layer after the mandrel evaluation operation is called the minimum mandrel diameter. In this case, the smaller the minimum mandrel diameter, the higher the flexibility of the resist layer, and the larger the minimum mandrel diameter, the lower the flexibility.

[0140] The second condition is that the minimum mandrel diameter of the resist layer is 4 mm or less. In this case, the resist layer has higher flexibility than when the minimum mandrel diameter is greater than 4 mm. Therefore, even if the support substrate and insulating layer deform in processes after the resist layer is formed, the resist layer follows the deformation of the support substrate and insulating layer. This reduces the occurrence of chips or other defects in the resist layer after the opening is formed, and reduces peeling of the resist layer from the insulating layer.

[0141] As a result, by making the resist layer satisfy the above first and second conditions, it becomes possible to manufacture flexible printed circuit boards having fine wiring without reducing yield.

[0142] (Item 2) In the manufacturing method of a flexible printed circuit board according to item 1, The resist layer is a layer that further satisfies a third condition, The third condition may be that, when a linear resist layer is formed on the insulating layer, extending in a first direction and having a width in a second direction on the insulating layer perpendicular to the first direction, the maximum width of the resist layer in a cross section of any portion of the linear resist layer cut by a virtual plane perpendicular to the first direction is 1.2 times or less than the minimum width of the resist layer.

[0143] In this case, it becomes possible to form finer wiring than when the maximum width of the resist layer is greater than 1.2 times the minimum width of the resist layer.

[0144] (Item 3) In the method for manufacturing a flexible printed circuit board according to item 1 or 2, The resist layer is a layer that further satisfies a fourth condition, The fourth condition may be that the resist layer has an elastic modulus of 3.5 GPa or more.

[0145] In this case, the handleability of the intermediate body is improved from the time the resist layer is formed on the insulating layer until the time the resist layer is removed, compared to when a resist layer with an elastic modulus lower than 3.5 GPa is used.

[0146] (Item 4) In the method for manufacturing a flexible printed circuit board according to any one of items 1 to 3, The resist layer is a layer that further satisfies a fifth condition, the step of exposing the resist layer to the predetermined pattern and developing the exposed resist layer includes forming a line-shaped resist layer; The fifth condition may be that the aspect ratio, which is the ratio of the thickness of the resist layer to the line width of the linear resist layer, is 1 or more and 3 or less.

[0147] Because the resist layer has flexibility corresponding to the second physical property, it is possible to form a line-shaped resist layer with an aspect ratio in a relatively wide range of 1 to 3. This enables higher density wiring and improves the degree of freedom in wiring design.

[0148] (Item 5) In the method for manufacturing a flexible printed circuit board according to any one of items 1 to 4, The step of exposing the resist layer to a predetermined pattern and developing the exposed resist layer may include performing contact exposure in which a mask corresponding to the predetermined pattern and the resist layer are brought into contact with each other, and exposure light is irradiated onto the resist layer through the mask.

[0149] In this case, the mask and the resist layer come into contact with each other, thereby fixing the positional relationship between the mask and the resist layer. Also, since no gap (space) is formed between the mask and the resist layer, the spread of the exposure light is suppressed. As a result, it is possible to expose a fine pattern with high precision.

[0150] (Item 6) In the method for manufacturing a flexible printed circuit board according to any one of Items 1 to 5, The dry film resist may be made of a negative photosensitive resin.

[0151] Dry film resists made of negative photosensitive resins have relatively high flexibility. Therefore, when the dry film resist is applied to an insulating layer to form a resist layer, the dry film resist deforms to conform to the shape of the insulating layer. This reduces the occurrence of voids between the resist layer and the insulating layer. This results in a highly reliable resist layer. Furthermore, the occurrence of chips or other missing portions in the resist layer after openings are formed is reduced.

[0152] (Item 7) In the method for manufacturing a flexible printed circuit board according to item 6, The photosensitive resin may be a photosensitive acrylic resin.

[0153] In this case, a resist layer made of a photosensitive acrylic resin is formed.

[0154] (Item 8) In the method for manufacturing a flexible printed circuit board according to any one of items 1 to 7, the supporting substrate is a metal supporting substrate having a first surface, the step of forming the insulating layer includes forming the insulating layer on a partial region of the first surface of the metal supporting board, and not forming the insulating layer on another partial region of the first surface, The insulating layer is a second surface of the metal supporting board facing in the same direction as the first surface; a side surface connecting an outer edge of the second surface and the first surface; The method for manufacturing the flexible printed circuit board includes: the method further includes, after the step of forming the insulating layer and before the step of forming the resist layer, a step of forming a seed layer that covers the first surface of the metal supporting board, the second surface of the insulating layer, and the side surface of the insulating layer; The step of forming the conductor layer may include forming the conductor layer on the seed layer by electrolytic plating, in which case the conductor layer can be easily formed on the seed layer by electrolytic plating.

[0155] (Item 9) The manufacturing method of the flexible printed circuit board according to item 9 includes: preparing a laminate in which a conductor layer is laminated on an insulating layer; forming a resist layer on the conductor layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer in the predetermined pattern or a pattern opposite to the predetermined pattern; removing the portion of the conductor layer exposed in the opening; removing the resist layer; the resist layer is a layer that satisfies a first condition and a second condition, the first condition is that the resolution of the resist layer is 7 μm or less; The second condition is that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after the resist layer is bent 180 degrees using the cylindrical mandrel and then returned to its unbent state twice is 4 mm or less.

[0156] In the manufacturing method for the flexible printed circuit board, a resist layer that satisfies the first and second conditions is formed using a dry film resist. The first condition is that the resolution of the resist layer is 7 μm or less. This makes it possible to form finer wiring than when the resolution of the resist layer is greater than 7 μm.

[0157] The series of operations, which involves bending the resist layer 180 degrees using a cylindrical mandrel and then returning the resist layer to its unbent state twice, is called the mandrel evaluation operation. The minimum diameter of the cylindrical mandrel that can maintain the integrity of the resist layer after the mandrel evaluation operation is called the minimum mandrel diameter. In this case, the smaller the minimum mandrel diameter, the higher the flexibility of the resist layer, and the larger the minimum mandrel diameter, the lower the flexibility.

[0158] The second condition is that the minimum mandrel diameter of the resist layer is 4 mm or less. In this case, the resist layer has higher flexibility than when the minimum mandrel diameter is greater than 4 mm. Therefore, even if the support substrate and insulating layer deform in processes after the resist layer is formed, the resist layer follows the deformation of the support substrate and insulating layer. This reduces the occurrence of chips or other defects in the resist layer after the opening is formed, and reduces peeling of the resist layer from the insulating layer.

[0159] As a result, when the resist layer satisfies the first and second conditions described above, it becomes possible to manufacture a flexible printed circuit board having fine wiring without reducing the yield.

[0160] (Item 10) The flexible printed circuit board according to item 10 is The flexible printed circuit board is manufactured by the manufacturing method of any one of items 1 to 9.

[0161] The flexible printed circuit board is manufactured by the above-described method for manufacturing a flexible printed circuit board, which prevents a decrease in yield of the flexible printed circuit board and realizes high-density wiring in the flexible printed circuit board.

[0162] (Item 11) The semiconductor package according to item 11 is The flexible printed circuit board according to claim 10 is included.

[0163] The flexible printed circuit board can be made smaller and thinner than a rigid printed circuit board. The flexible printed circuit board also has fine wiring. This allows for versatile semiconductor packages to be mounted on various locations and targets.

[0164] (Article 12) The electronic equipment referred to in paragraph 12 is The semiconductor package according to claim 11 is included.

[0165] The electronic device includes the semiconductor package, and therefore can be made smaller and thinner. [Explanation of symbols]

[0166] 1...metal supporting substrate, 2, 12...insulating layer, 3...seed layer, 4...plating resist layer, 4L...line resist layer, 4a, 13a...opening, 5, 11...conductor layer, 6, 7, 14...flexible printed circuit board, 11a...conductor removal portion, 13...etching resist layer, 50, 50X, 50Y...exposure device, 51...mask, 51a...light-transmitting portion, 51b...light-shielding portion, 52...light source, 52a...lamp, 52b...mirror, 53...optical system, 54...laser device, 55...light scanning portion, 56...scanning Control unit, 59...contact drive unit, 60...developing device, 61...developing nozzle, 100...rewiring board, 101, 102...terminal unit, 200...semiconductor chip, 201...connecting terminal, 300...rigid board, 301...electrode pad, 400...semiconductor package, 410...underfill, 500...roll device, 501...unwinding unit, 502...winding unit, 510, 520...processing unit, 800...electronic device, HP...footing unit, R1...unwinding roll, R2...winding roll, S...solder

Claims

1. A method for manufacturing a flexible printed circuit board, comprising: forming an insulating layer on a support substrate; forming a resist layer on the insulating layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer in the predetermined pattern or a pattern opposite to the predetermined pattern; forming a conductor layer in the opening; removing the resist layer; the resist layer is a layer that satisfies a first condition and a second condition, the first condition is that the resolution of the resist layer is 7 μm or less; the second condition is that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after repeating twice the process of bending the resist layer 180 degrees using a cylindrical mandrel and returning the resist layer to its unbent state is 4 mm or less.

2. The resist layer is a layer that further satisfies a third condition, 2. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the third condition is that when a line-shaped resist layer is formed on the insulating layer, extending in a first direction and having a width in a second direction on the insulating layer perpendicular to the first direction, in a cross section when any portion of the line-shaped resist layer is cut with an imaginary plane perpendicular to the first direction, the maximum value of the width of the resist layer is 1.2 times or less than the minimum value of the width of the resist layer.

3. The resist layer is a layer that further satisfies a fourth condition, 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the fourth condition is that the resist layer has a modulus of elasticity of 3.5 GPa or more.

4. The resist layer is a layer that further satisfies a fifth condition, the step of exposing the resist layer to the predetermined pattern and developing the exposed resist layer includes forming a line-shaped resist layer; 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the fifth condition is that an aspect ratio, which is a ratio of a thickness of the resist layer to a line width of the linear resist layer, is 1 or more and 3 or less.

5. 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the step of exposing the resist layer to a predetermined pattern and developing the exposed resist layer includes performing contact exposure in which a mask corresponding to the predetermined pattern and the resist layer are brought into contact with each other, and exposure light is irradiated onto the resist layer through the mask.

6. 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the dry film resist is made of a negative photosensitive resin.

7. 7. The method for manufacturing a flexible printed circuit board according to claim 6, wherein the photosensitive resin is a photosensitive acrylic resin.

8. the supporting substrate is a metal supporting substrate having a first surface, the step of forming the insulating layer includes forming the insulating layer on a partial region of the first surface of the metal supporting board, and not forming the insulating layer on another partial region of the first surface, The insulating layer is a second surface of the metal supporting board facing in the same direction as the first surface; a side surface connecting an outer edge of the second surface and the first surface; The method for manufacturing the flexible printed circuit board includes: the method further includes, after the step of forming the insulating layer and before the step of forming the resist layer, a step of forming a seed layer that covers the first surface of the metal supporting board, the second surface of the insulating layer, and the side surface of the insulating layer; 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the step of forming the conductor layer includes forming the conductor layer on the seed layer by electrolytic plating.

9. A method for manufacturing a flexible printed circuit board, comprising: preparing a laminate in which a conductor layer is laminated on an insulating layer; forming a resist layer on the conductor layer using a photosensitive dry film resist; exposing the resist layer to light in a predetermined pattern and developing the exposed resist layer to form openings in the resist layer in the predetermined pattern or a pattern opposite to the predetermined pattern; removing the portion of the conductor layer exposed in the opening; removing the resist layer; the resist layer is a layer that satisfies a first condition and a second condition, the first condition is that the resolution of the resist layer is 7 μm or less; the second condition is that the minimum diameter of the cylindrical mandrel that can maintain the resist layer in good condition after repeating twice the process of bending the resist layer 180 degrees using a cylindrical mandrel and returning the resist layer to its unbent state is 4 mm or less.

10. A flexible printed circuit board manufactured by the method for manufacturing a flexible printed circuit board according to claim 1 or 2.

11. A semiconductor package comprising the flexible printed circuit board of claim 10.

12. An electronic device comprising the semiconductor package according to claim 11.

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