Manufacturing method of flexible printed wiring board

Abstract

The manufacturing method of the flexible printed wiring board includes: a step of arranging a photomask 50 with a light-transmitting portion 53 facing a first region R1 and exposing a photoresist layer 40 through the light-transmitting portion 53; and a step of arranging a photomask 50 with a light-transmitting portion 53 facing a second region R2 and exposing a photoresist layer 40 through the light-transmitting portion 53. The light-transmitting portion 53 has a linear shape, which includes first and second end heads 55 and 56 with pointed shapes. The first end head 55 includes a first end 55a and curved first and second sides 55b and 55c. The second end head 56 includes a second end 56a and curved third and fourth sides 56b and 56c. The manufacturing method of the flexible printed wiring board satisfies the following formula (1).

Description

Technical Field

[0001] This invention relates to a method for manufacturing flexible printed wiring boards.

[0002] For designated countries where inclusion by reference is permitted, the contents described in Japanese Patent Application No. 2021-093839 filed on June 3, 2021, are incorporated by reference into this specification as part of its contents. Background Technology

[0003] A method for manufacturing a long, flexible wiring circuit board includes: a step of forming a metal thin film on the surface of an insulating layer; a step of forming a photoresist on the surface of the metal thin film; and a step of repeatedly exposing the photoresist while shifting a photomask relative to the photoresist along the length direction (for example, see Patent Document 1).

[0004] A photomask includes a light-transmitting portion having a shape corresponding to wiring, the light-transmitting portion being composed of a plurality of rectangular light-transmitting areas extending in a straight line. In the exposure process, the photomask is configured such that the rear end of the light-transmitting area of ​​the photomask in the first exposure overlaps with the front end of the light-transmitting area of ​​the photomask in the subsequent exposure.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-092966 Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] In the exposure process described above, it is difficult to make the front end of the light-transmitting area of ​​the photomask in the later exposure completely aligned with the rear end of the light-transmitting area of ​​the photomask in the earlier exposure; the front end will protrude from the rear end of the light-transmitting area. Therefore, due to the front end protruding from the rear end, a angular protrusion in the width direction will be formed at the connection portion of the wiring, resulting in a step on the side of the wiring accompanied by a sharp change in linewidth (for example, see Patent Document 1). Figure 2-4 The following problem exists: when the flexible wiring circuit board is bent, stress tends to concentrate at the step, resulting in the wiring breaking from the step onwards.

[0010] The purpose of this invention is to provide a method for manufacturing a flexible printed wiring board that does not produce steps on the sides of the wiring.

[0011] (II) Technical Solution

[0012] [1] The method for manufacturing a flexible printed wiring board of the present invention is a method for manufacturing a flexible printed wiring board using a photoresist, comprising: a first step of disposing a photoresist having a first region and a second region on a substrate; a second step of disposing a first photomask having a first light-transmitting portion such that the first light-transmitting portion and the first region are opposite each other, and exposing the photoresist through the first light-transmitting portion; and a third step of disposing a second photomask having a second light-transmitting portion such that the second light-transmitting portion and the second region are opposite each other, and exposing the photoresist through the second light-transmitting portion, wherein the first and second regions are adjacent to each other such that the ends of the first region and the ends of the second region overlap each other, the first light-transmitting portion has a linear shape, the linear shape includes a first end head having a pointed shape, the second light-transmitting portion has a linear shape, the linear shape includes a second end head having a pointed shape facing the side opposite to the first end head, and the third step includes aligning a second alignment target point included in the second end head with a first position. The second photomask is configured in an overlapping manner. The first position is the position where the first alignment target point included in the first end head is configured in the second process. The first end head includes: a first end head; a curved first side connected to the first end head; and a curved second side connected to the first end head and opposite to the first side. The first alignment target point is a point at a distance A from the first end head on a first center line extending along a first length direction, such that the approximate center of the first light-transmitting portion is located on a first center line extending along a first length direction. The first and second sides are located outside a first imaginary triangle. The first imaginary triangle is an imaginary triangle connecting the first intersection point of the first imaginary line and the first side, the second intersection point of the first imaginary line and the second side, and the third intersection point of the first center line and the first end head. The first imaginary line is an imaginary line extending along the first width direction of the first light-transmitting portion and passing through the first alignment target point. The first intersection point and the second intersection point are at a distance D apart. The second end head includes: a second end head; and a curved third side connected to the second end head.And a curved fourth side connected to the second end and opposite to the second side, the second alignment target point is a point at a distance A from the second end on the second center line extending along the second length direction, the third and fourth sides are located outside the second imaginary triangle, the second imaginary triangle is an imaginary triangle connecting the fourth intersection point of the second imaginary line and the third side, the fifth intersection point of the second imaginary line and the fourth side, and the sixth intersection point of the second center line and the second end, the second imaginary line is an imaginary line extending along the second width direction of the second light-transmitting part and passing through the second alignment target point, the fourth intersection point and the fifth intersection point are at a distance D, the manufacturing method of the flexible printed wiring board satisfies the following formula (1);

[0013] [Formula 1]

[0014]

[0015] In equation (1) above, Δx is the offset of the second alignment target point relative to the first position in the first length direction, Δy is the offset of the second alignment target point relative to the first position in the first width direction, θ is the offset of the second alignment target point relative to the first position in the rotation direction about the first normal, and the first normal is the normal that passes through the first position and is perpendicular to the first photomask.

[0016] [2] In the above invention, the first light-transmitting portion may further have a first main line portion connected to the first end head, the first alignment target point being located on the first end head at a position closer to the first end side than the first connecting portion connected to the first main line portion, and the second light-transmitting portion may further have a second main line portion connected to the second end head, the second alignment target point being located on the second end head at a position closer to the second end side than the second connecting portion connected to the second main line portion, and the width of the first and second main line portions is W, satisfying the following formula (2).

[0017] D≤W (2).

[0018] [3] In the above invention, the first photomask may have a plurality of first light-transmitting portions arranged side by side, and the plurality of first end heads are offset sequentially in a manner that protrudes relative to other adjacent first end heads as they move toward a first direction. The second photomask may have a plurality of second light-transmitting portions arranged side by side, and the plurality of second end heads are offset sequentially in a manner that protrudes relative to other adjacent second end heads as they move toward a second direction. The second direction is the direction of offset along the first width direction from the first position to the second alignment target point, and the first direction is the opposite direction to the second direction.

[0019] [4] In the above invention, the second region may be adjacent to the first region in the first length direction.

[0020] (III) Beneficial Effects

[0021] In the manufacturing method of the flexible printed wiring board of the present invention, the first and second light-transmitting portions have pointed ends, the first and second sides are curves located outside the first imaginary triangle, the third and fourth sides are curves located outside the second imaginary triangle, and the positions of the first and second alignment target points satisfy the range of the above formula (1). Therefore, the exposure portions corresponding to the first and second ends will not be exposed from the multiple exposure portions overlapping the exposure portions exposed through the first light-transmitting portion and the exposure portions exposed through the second light-transmitting portion, and no steps are generated on the shape of the multiple exposure portions. Therefore, no steps are generated even in the resist pattern formed by developing the exposed photoresist, thus preventing steps from being generated on the side of the wiring. Attached Figure Description

[0022] Figure 1 This is a top view showing an example of a flexible printed wiring board according to an embodiment of the present invention.

[0023] Figure 2 (a)~ Figure 2 (f) is a cross-sectional view illustrating an example of a method for manufacturing a flexible printed wiring board according to an embodiment of the present invention.

[0024] Figure 3 It means in Figure 2 (b) is a top view of an example of a photoresist layer exposed during the exposure process.

[0025] Figure 4 (a) means Figure 2 (b) is a top view of an example of the first exposure process in the exposure procedure shown. Figure 4 (b) means Figure 2 (b) is a top view of an example of the second exposure process in the exposure procedure shown.

[0026] Figure 5 It means in Figure 2 (b) is a top view of an example of a photomask used in the exposure process.

[0027] Figure 6 (a) is an enlarged top view showing an example of the first end of the light-transmitting portion in an embodiment of the present invention. Figure 6 (b) is an enlarged top view showing an example of the second end head of the light-transmitting portion in an embodiment of the present invention.

[0028] Figure 7 It is a top view illustrating the positional relationship between the first end head during the first exposure process and the second end head during the second exposure process.

[0029] Figure 8 This is an explanatory diagram illustrating formula (3) in the embodiments of the present invention.

[0030] Figure 9 This is an explanatory diagram illustrating formula (6) in an embodiment of the present invention.

[0031] Figure 10 This is a top view illustrating a comparative example where the first end head and the second end head do not overlap.

[0032] Figure 11 yes Figure 4 An enlarged top view of part XI. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a top view showing an example of the flexible printed wiring board in this embodiment. Figure 2 (a)~ Figure 2 (f) is a cross-sectional view showing an example of the manufacturing method of the flexible printed wiring board 1 in this embodiment.

[0034] like Figure 1 As shown, the flexible printed wiring board 1 in this embodiment is a flexible wiring board with a planar shape in the form of a long strip. The length of the flexible printed wiring board 1 in the extending direction is not particularly limited, but is 600 mm or more. Figure 1 as well as Figure 2 As shown in (f), such a long strip of flexible printed wiring board 1 has, for example, a base film 10, a plurality of (five in this example) wirings 20, and a cover layer 30.

[0035] The base film 10 is a flexible film with a long, strip-like shape. The base film 10 is made of an electrically insulating material such as a resin material. While not particularly limited, examples of materials constituting the base film 10 include polyimide (PI), liquid crystal polymer (LCP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyetherimide (PEI), polyetheretherketone (PEEK), and aramid fibers.

[0036] A plurality of wirings 20 are formed on the base film 10. In this embodiment, the plurality of wirings 20 extend linearly along the x-direction on the base film 10. In this embodiment, the wirings 20 extend continuously from one end of the flexible printed wiring board 1 to the other end, and therefore have a long, linear shape. In addition, the plurality of wirings 20 are arranged substantially parallel to each other at approximately equal intervals.

[0037] Furthermore, the number, shape, and arrangement of the wiring 20 are not particularly limited and can be arbitrarily set. For example, in this embodiment, a generally straight wiring 20 is shown, but the wiring 20 may also have curved portions. Additionally, the wiring 20 may include through-holes, etc. The wiring 20 is made of copper. Furthermore, the material constituting the wiring 20 can be a metal other than copper, for example, silver or gold. Also, although not specifically illustrated, pads for connection to other flexible printed circuit boards or electronic components can be formed at the ends of each wiring 20.

[0038] The cover layer 30 is a layer used to protect the wiring 20. The cover layer 30 is formed on the base film 10 in such a way that it covers the portion of the wiring 20 except for the pads. The cover layer 30 is composed of a flexible film with a strip-like shape. The cover layer 30 is made of an electrically insulating material such as a resin material.

[0039] like Figure 2 As shown in (f), the cover layer 30 has a double-layer structure consisting of a protective layer 31 and an adhesive layer 32. The protective layer 31 is a layer used to protect the wiring 20. The protective layer 31 is composed of a flexible, strip-shaped film. The protective layer 31 is made of an electrically insulating material such as a resin material. Although not particularly limited, examples of materials constituting the protective layer 31 include polyimide (PI), liquid crystal polymer (LCP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyetherimide (PEI), polyetheretherketone (PEEK), and aramid fibers.

[0040] The adhesive layer 32 is used to bond the protective layer 31 to the upper surface of the base film 10. The adhesive layer 32 is made of, for example, an epoxy adhesive or an acrylic adhesive.

[0041] Next, the manufacturing method of the flexible printed wiring board 1 according to this embodiment will be described. Figure 2 As shown, the manufacturing method of the flexible printed wiring board 1 in this embodiment is a subtractive method. This method exposes and develops the photoresist formed on the metal layer to form a photoresist pattern, and then transfers the pattern shape of the photoresist pattern to the metal layer by etching.

[0042] In this subtraction method, firstly, as Figure 2 As shown in (a), a base film 10 on which a metal layer 200 is formed is prepared. For example, a copper-clad laminate (CCL) can be used as the base film 10 on which the metal layer 200 is formed. Furthermore, the length of the base film 10 in the extending direction is not particularly limited, but is 600 mm or more. In addition, the base film 10 on which the metal layer 200 is formed in this embodiment is an example of a "substrate" in this invention.

[0043] Next, as Figure 2 As shown in (a), a photoresist layer 40 is formed on the metal layer 200 (first step). The photoresist layer 40 only needs to be formed on the surface of the metal layer 200 near the area where the above-mentioned wiring 20 is formed.

[0044] In this embodiment, the photoresist layer 40 is composed of a negative photoresist. In this negative photoresist, the portion exposed to light does not dissolve in the developer, while the portion not exposed to light dissolves in the developer. Although not particularly limited, the photoresist layer 40 can be formed by attaching a negative dry film resist to the metal layer 200. Furthermore, the formation process of the photoresist layer 40 in this embodiment is an example of the "first process" in this invention.

[0045] Next, as Figure 2 As shown in (b), the photoresist layer 40 is exposed via photomask 50. Furthermore, the photomask 50 in this embodiment is an example of the "first photomask" and "second photomask" in this invention.

[0046] Figure 3 It means in Figure 2 (b) is a top view of an example of the photoresist layer 40 exposed during the exposure process shown. Figure 4 It means Figure 2 (b) is a top view of an example of the first and second exposure processes in the exposure process shown. In this exposure process, as Figure 3 As shown, an exposure pattern 41 with a shape corresponding to the wiring 20 is formed on the photoresist layer 40. However, since the width of the photomask 50 is smaller than the length of the wiring 20, the exposure process needs to be performed multiple times.

[0047] Therefore, as Figure 4 As shown in (a), firstly, a photomask 50 is positioned opposite to the first region R1 of the photoresist layer 40 and a first exposure process is performed. Then, as... Figure 4 As shown in (b), a photomask 50 is disposed opposite to a second region R2 adjacent to the first region R1 and a second exposure process is performed.

[0048] Furthermore, in order to interconnect multiple exposure sections, in a top view, the ends of the first region R1 overlap with the ends of the second region R2. That is, the photoresist layer 40 has an overlapping region R where the ends of the first region R1 in the +x direction and the ends of the second region R2 in the -x direction overlap. m1 .like Figure 4 As shown in (b), in the second exposure process, in the overlapping region R m1 In the first exposure process, the photomask 50 is disposed opposite to the photoresist layer 40 such that the second end head 56 overlaps with the first end head 55 of the light-transmitting portion 53.

[0049] The result is, as Figure 3 As shown, the exposure pattern 41 includes a first exposure section 42 exposed by a first exposure process, a second exposure section 43 exposed by a second exposure process, and a multiple exposure section 44 that is doubly exposed by both the first and second exposure processes. The first exposure section 42 and the second exposure section 43 are connected through the multiple exposure section 44. Thus, in the exposure process of this embodiment, the exposure pattern 41 is formed by performing the exposure of the photoresist layer 40 multiple times and connecting the multiple exposure sections to each other.

[0050] Furthermore, the first exposure process in this embodiment is equivalent to an example of the "second process" in this invention, and the second exposure process in this embodiment is equivalent to an example of the "third process" in this invention.

[0051] In this embodiment, the case where the wiring 20 is formed by two exposure processes is illustrated, but it is not limited to this. For example, the wiring 20 may also be formed by performing three or more exposure processes. In this case, it is not necessary to expose adjacent regions along the length direction sequentially along the length direction; instead, the intermittent regions sandwiched between the exposed regions may be exposed after intermittent exposure along the length direction.

[0052] Figure 5 It means in Figure 2 (b) is a top view of an example of the photomask 50 used in the exposure process shown. Figure 6 This is an enlarged top view showing an example of the first and second end heads 55, 56 of the light-transmitting portion 53 in this embodiment.

[0053] like Figure 5 and Figure 2 As shown in (b), the photomask 50 has a transparent substrate 51 and a light-shielding film 52. The transparent substrate 51 is a transparent, light-transmitting plate-shaped component. The transparent substrate 51 is made of a transparent material such as glass.

[0054] The light-shielding film 52 is an opaque film that is not transparent to light, and is formed on one of the main surfaces of the transparent substrate 51. As a material constituting the light-shielding film 52, a metal oxide such as chromium oxide can be used, for example. The light-shielding film 52 can be formed, for example, by vapor-depositing a metal oxide film onto the surface of the transparent substrate 51.

[0055] like Figure 5 As shown, the light-shielding film 52 has five linear openings 52a, the same number as the wiring 20, through which the transparent substrate 51 is exposed. The light-transmitting portion 53 is the portion of the transparent substrate 51 exposed through the openings 52a. Furthermore, the light-transmitting portion 53 in this embodiment corresponds to an example of the "first light-transmitting portion" and the "second light-transmitting portion" in this invention.

[0056] The light-transmitting portion 53 has a linear planar shape that is identical to the planar shape of the opening 52a. Furthermore, a plurality of light-transmitting portions 53 are arranged side-by-side at approximately equal intervals along the width direction (y-direction in the figure) of the light-transmitting portion 53. Additionally, the light-transmitting portion 53 includes: a main line portion 54; a first end head 55 disposed at one end of the main line portion 54; and a second end head 56 disposed at the other end of the main line portion 54.

[0057] The main line portion 54 is a straight section with a substantially constant width W, extending along the length direction (x direction in the figure) of the light-transmitting portion 53. For example... Figure 6 As shown in (a), the main line portion 54 has a straight first side 54a extending along the length direction of the light-transmitting portion 53, and a second side 54b extending substantially parallel to and opposite the first side 54a. In this embodiment, the first and second sides 54a and 54b are symmetrical with respect to the center line CL of the light-transmitting portion 53. Furthermore, the center line CL is a straight line passing through the center of the light-transmitting portion 53 in the width direction and extending along the length direction of the light-transmitting portion 53.

[0058] Furthermore, the width direction of the light-transmitting portion 53 in this embodiment corresponds to an example of the "first width direction" and "second width direction" in the present invention. Additionally, the length direction of the light-transmitting portion 53 in this embodiment corresponds to an example of the "first length direction" and "second length direction" in the present invention.

[0059] like Figure 6As shown in (a), the first end head 55 is a pointed end head with a width that gradually tapers in the +x direction, and is connected to the main line portion 54 at the first connecting portion 57. The first end head 55 includes: a first end portion 55a, a first side 55b, a second side 55c, a first connecting side 55d, and a second connecting side 55e.

[0060] The first end 55a is the end located on the center line CL of the light-transmitting portion 53. In this embodiment, the first end 55a is the point where the first and second sides 55b and 55c intersect.

[0061] The first side 55b is a curve convex in the +y direction as shown in the figure, sandwiched between the first end 55a and the first connecting side 55d, connecting intersection points P1 and P2. On the other hand, the second side 55c is a curve convex in the -y direction as shown in the figure, sandwiched between the first end 55a and the second connecting side 55e, connecting intersection points P1 and P3. The first and second sides 55b and 55c curve towards each other as they approach the first end 55a, intersecting at the first end 55a. In this embodiment, the first and second sides 55b and 55c are linearly symmetrical about each other with respect to the center line CL. Both the first and second sides 55b and 55c are located outside the first imaginary triangle TR1. That is, at the first end 55, the first side 55b is located outside the side P1P2 of the first imaginary triangle TR1, and the second side 55c is located outside the side P1P3 of the first imaginary triangle TR1.

[0062] Furthermore, the aforementioned intersection point P1 is the intersection of the center line CL and the first end point 55a. Intersection point P2 is the intersection of the first imaginary line VL1 and the first side 55b, and intersection point P3 is the intersection of the first imaginary line VL1 and the second side 55c. Additionally, intersection point P2 is also the intersection of the first side 55b and the first connecting side 55d, and intersection point P3 is also the intersection of the second side 55c and the second connecting side 55e. In this embodiment, intersection point P1 is an example of the "first intersection point" in this invention, intersection point P2 is an example of the "second intersection point" in this invention, and intersection point P3 is an example of the "third intersection point" in this invention.

[0063] The first imaginary straight line VL1 is an imaginary straight line extending along the width direction (y direction in the figure) of the light-transmitting portion 53 and passing through the first alignment target point S1. The intersection point P2 and the intersection point P3 are separated by a distance D. This distance D is less than or equal to the aforementioned width W (D≤W).

[0064] The first alignment target point S1 is processed in the second exposure (refer to...). Figure 4In (b)), there is a hypothetical point for alignment of the second end head 56. The first alignment target point S1 is located at a distance A from the first end head 55a on the center line CL. The first alignment target point S1 is located inside the first end head 55, on the side closer to the first end head 55a than the first connecting portion 57. In the second exposure process, the photomask 50 is aligned such that the second alignment target point S2 (described later) of the second end head 56 is positioned at the first position where the first alignment target point S1 was located during the first exposure process.

[0065] While not particularly limited, alignment can be performed using image processing methods such as those employed by a camera. For example, multiple alignment marks (not shown) can be formed on the base film 10 beforehand, and the base film 10 can be photographed through multiple through-holes (not shown) provided in the photomask 50. Furthermore, alignment can be achieved by fixing the photomask 50 at the position where the alignment marks are reflected in the photographing range across the through-holes.

[0066] like Figure 6 As shown in (a), the first connecting edge 55d protrudes in the +y direction in the figure and is a curve with a curvature smaller than that of the first edge 55b. This first connecting edge 55d is sandwiched between the first edge 55b and the first side edge 54a, connecting intersection point P2 and intersection point P7. Furthermore, intersection point P7 is the intersection point of the first connecting edge 55d and the first side edge 54a.

[0067] The second connecting edge 55e bulges towards the -y direction in the figure and is a curve with a smaller curvature than the second edge 55c. This second connecting edge 55e is sandwiched between the second edge 55c and the second side edge 54b, connecting intersection points P3 and P8. The third and fourth connecting edges 56d and 56e are linearly symmetrical about the center line CL. Furthermore, intersection point P8 is the intersection of the second connecting edge 55e and the second side edge 54b.

[0068] The first and second connecting edges 55d and 55e are both located outside the imaginary rectangle RE. For example... Figure 5 As shown, the imaginary rectangle RE refers to the imaginary rectangle connecting intersection points P2, P3, P5 (described later), and P6 (described later). Figure 5 As shown, the imaginary rectangle RE is sandwiched between the first imaginary triangle TR1 and the second imaginary triangle TR2. That is, in the main line section 54, the first connecting edge 55d is located outside the long side P2P5 of the imaginary rectangle, and the second connecting edge 55e is located outside the long side P3P6 of the imaginary rectangle.

[0069] like Figure 6As shown in (b), the second end head 56 has a pointed shape facing in the opposite direction to the first end head 55, and is connected to the main line portion 54 at the second connecting portion 58. The second end head 56 includes: a second end portion 56a, a third side 56b, a fourth side 56c, a third connecting side 56d, and a fourth connecting side 56e.

[0070] The second end 56a is the end located on the center line CL of the light-transmitting portion 53. In this embodiment, the first end 55a is the point where the first and second sides 55b and 55c intersect.

[0071] The third side 56b is a curve obtained by reversing the first side 55b of the first end 55 horizontally. This third side 56b is sandwiched between the second end 56a and the third connecting side 56d, connecting intersection points P4 and P5. On the other hand, the fourth side 56c is a curve obtained by reversing the second side 55c of the first end 55 horizontally, sandwiched between the second end 56a and the fourth connecting side 56e, connecting intersection points P4 and P6. The third and fourth sides 56b and 56c curve towards each other as they approach the second end 56a, intersecting at the second end 56a. In this embodiment, the third and fourth sides 56b and 56c are linearly symmetrical about the center line CL. Both the third and fourth sides 56b and 56c are located outside the second imaginary triangle TR2. That is, at the second end 56, the third side 56b is located outside the sides P4P5 of the second imaginary triangle TR2, and the fourth side 56c is located outside the sides P4P6 of the second imaginary triangle TR2.

[0072] Furthermore, the second imaginary triangle TR2 has a shape obtained by reversing the first imaginary triangle TR1 horizontally. This second imaginary triangle TR2 is an imaginary triangle formed by connecting intersection points P4 to P6 in the second end 56. Intersection point P4 is the intersection of the center line CL and the second end 56a. Intersection point P5 is the intersection of the second imaginary line VL2 and the third side 56b, and intersection point P6 is the intersection of the second imaginary line VL2 and the fourth side 56c. Additionally, intersection point P5 is also the intersection of the third side 56b and the third connecting side 56d, and intersection point P6 is also the intersection of the fourth side 56c and the fourth connecting side 56e. In this embodiment, intersection point P4 is an example of the "fourth intersection point" in this invention, intersection point P5 is an example of the "fifth intersection point" in this invention, and intersection point P6 is an example of the "sixth intersection point" in this invention.

[0073] The second imaginary straight line VL2 is an imaginary straight line extending along the width direction (y direction in the figure) of the light-transmitting portion 53 and passing through the first alignment target point S2. The intersection point P5 and the intersection point P6 are separated by a distance D. This distance D is less than or equal to the aforementioned width W (D≤W).

[0074] The second alignment target point S2 is located at a distance A from the second end portion 56a on the center line CL. The second alignment target point S2 is located on the inner side of the second end head 56, closer to the second end portion 56a than the second connecting portion 58.

[0075] like Figure 6 As shown in (b), the third connecting edge 56d is a curve obtained by reversing the first connecting edge 55d horizontally. This third connecting edge 56d is sandwiched between the third edge 55b and the first side edge 54a, connecting the intersection point P5 and the intersection point P9. Furthermore, the intersection point P9 is the intersection point of the third connecting edge 56d and the first side edge 54a.

[0076] The fourth connecting edge 56e is a curve obtained by reversing the second connecting edge 55e horizontally. This fourth connecting edge 56e is sandwiched between the fourth edge 56c and the second side edge 54b, connecting intersection point P3 and intersection point P. 10 The third and fourth connecting edges 56d and 56e are symmetrical about each other with respect to the center line CL. Furthermore, the intersection point P... 10 It is the intersection of the fourth connecting edge 56e and the second side edge 54b. The third and fourth connecting edges 56d and 56e are both located outside the imaginary rectangle RE. That is, in the main line part 54, the third connecting edge 56d is located outside the long side P2P5 of the imaginary rectangle, and the fourth connecting edge 56e is located outside the long side P3P6 of the imaginary rectangle.

[0077] Figure 7 This is an enlarged top view illustrating the positional relationship between the first end head 55 during the first exposure process and the second end head 56 during the second exposure process, equivalent to... Figure 4 (b) An enlarged top view of part VII. As described above, in the second exposure process, the second end head 56 is overlapped with the first end head 55 during the first exposure process. At this time, the photomask 50 is aligned such that the second alignment target point S2 is located at the first position FP where the first alignment target point S1 during the first exposure process is located.

[0078] However, it is difficult to make the second alignment target point S2 perfectly aligned with the first position FP, resulting in an offset (Δx, Δy, θ). Here, Δx is the offset of the second alignment target point S2 relative to the first position FP in the length direction (x-direction) of the light-transmitting portion 53. Δy is the offset of the second alignment target point S2 relative to the first position FP in the width direction (y-direction) of the light-transmitting portion 53. θ is the offset of the second alignment target point S2 relative to the first position FP in the rotation direction about the first normal NL. The first normal NL is a straight line passing through the first position FP and extending in a direction perpendicular to the main surface of the photomask 50 (the z-direction in the figure). The value of θ is the angle between the light-transmitting portion 53 during the first exposure process and the light-transmitting portion 53 during the second exposure process, for example, equal to the angle between the center line CL during the first exposure process and the center line CL during the second exposure process.

[0079] In the event of an offset (Δx, Δy, θ), sometimes the first end of the first exposure process is exposed from the second end head and the main line portion of the second exposure process, or the second end of the second exposure process is exposed from the first end head and the main line portion of the first exposure process. As a result, steps or protrusions will be generated on the wiring.

[0080] In this embodiment, it is assumed that an offset (Δx, Δy, θ) is generated, and the positions of the first and second alignment target points S1 and S2 are set to satisfy the following equation (3) so that the first and second ends do not become exposed.

[0081] [Formula 2]

[0082]

[0083] Figure 8 This is an explanatory diagram illustrating the above-described equation (3) in this embodiment. Furthermore, in this… Figure 8 In the diagram, the right end of the first imaginary triangle TR1 and the imaginary rectangle during the first exposure process is represented by dashed lines, and the left end of the second imaginary triangle TR2 and the imaginary rectangle during the second exposure process is represented by solid lines.

[0084] In addition, in Figure 8The example illustrates the case where all offset values ​​(Δx, Δy, θ) are positive. Here, with the center line CL from the first exposure process as the x-axis, the first imaginary line VL1 as the y-axis, and the first alignment target point S1 as the origin, the sign of Δx is positive when the second alignment target point S2 is located to the right (+x direction) of the y-axis, and negative when it is located to the left (-x direction). Similarly, the signs of Δy and θ are positive when the second alignment target point S2 is located above the x-axis (+y direction), and negative when it is located below the x-axis (-y direction).

[0085] In Figure 8 In order to prevent the first end 55a from being exposed, it is sufficient that the first end 55a (intersection point P1) is located inside the imaginary rectangle RE. That is, as described in equation (4) below, Figure 8 The length L in the diagram must be less than D / 2. This length L is the distance from intersection point P7 to intersection point P8. Intersection point P7 is the intersection of the perpendicular line extending from intersection point P1 in the -y direction with the imaginary rectangle RE from the second exposure process. Intersection point P8 is the intersection of this perpendicular line with the extension of the lower edge of the imaginary rectangle RE from the first exposure process. For example... Figure 8 As shown, the value of L can be expressed as in equation (5) below.

[0086] [Formula 3]

[0087]

[0088] [Formula 4]

[0089] L=Ay+r+R×tan0···(5)

[0090] The r in equation (5) above can be expressed as equation (6) below. Figure 9 This is an explanatory diagram illustrating equation (6) in this embodiment. Figure 9 Intersection point P 11 It is the intersection of the straight line extending from the second target point S2 in the -y direction and the arc of the imaginary circle C. Furthermore, as... Figure 8 As shown, the center of the imaginary circle C is the second aligned target point S2, and its radius is D / 2. Furthermore, the central angle of the arc of the imaginary circle C is θ. Additionally, as... Figure 9 As shown, intersection point P 12 It is the intersection of the straight line extending from the intersection point P6 in the -x direction and the perpendicular line, which connects the second alignment target point S2 and the intersection point. 11 .

[0091] [Formula 5]

[0092]

[0093] like Figure 9 As shown, r can be obtained by subtracting the side S2P of the imaginary right triangle TR3 from the radius D / 2. 12 The length B is calculated (r = D / 2 - B). Furthermore, right triangle TR3 connects points P6 and P... 12 An imaginary right triangle S2. The ∠P6P of this right triangle TR3. 12 S2 is 90° (∠P6P) 12 S2=90°), ∠P6S2P 12 For θ°(∠P6S2P) 12 =θ°). Therefore, edge S2P 12 The length B is D / 2×cosθ (B=D / 2×cosθ), and r can be expressed as the above equation (6).

[0094] Furthermore, R in equation (5) above can be expressed as equation (7) below. That is, as follows: Figure 8 As shown, R can be calculated by subtracting Δx and H from A. Here, as... Figure 9 As shown, H is the side P6P of right triangle TR3. 12 The length of R is therefore D / 2×sinθ (H=D / 2×sinθ). Thus, R can be expressed as the following equation (7).

[0095] [Formula 6]

[0096]

[0097] Substituting equations (5) to (7) obtained in this way into equation (4) above, we can obtain equation (8) below. Equation (8) is the right-hand side of equation (3) above. That is, by making the distance A between the first alignment target point S1 and the first end 55a satisfy equation (8) below, we can prevent the first end 55a from being exposed from the second imaginary triangle TR2. In addition, since the second imaginary triangle TR2 has a shape obtained by reversing the first imaginary triangle TR1 left and right, by making the distance A between the second alignment target point S2 and the second end 56a satisfy equation (8) below, we can also prevent the second end 56a from being exposed from the first imaginary triangle TR1.

[0098] [Formula 7]

[0099]

[0100] Furthermore, the first and second sides 55b and 55c are located outside the first imaginary triangle TR1, and the third and fourth sides 56b and 56c are located outside the second imaginary triangle TR2. Therefore, the first end 55a is located between the third and fourth sides 56b and 56c, and the second end 56a is located between the first and second sides 55b and 55c, so the first and second ends 55a and 56a do not protrude from the second and first end heads 56 and 55. Therefore, by satisfying the above equation (8) through the positions of the first and second alignment target points S1 and S2, no steps or protrusions are generated on the side of the wiring 20.

[0101] Figure 10 This is a top view illustrating a comparative example where the first and second ends do not overlap. For example... Figure 10 As shown, when the value of Δx is greater than the total distance 2A (Δx > 2A) between the distance A from the first alignment target point S1 to the first end 55a and the distance A from the second alignment target point S2 to the second end 56a, multiple exposure sections are not formed, and the wiring becomes discontinuous. Therefore, the distance A needs to be at least greater than Δx / 2 (Δx / 2 < A). Furthermore, considering the deviation in the completion of the loop width in the subsequent process, namely the etching process of the metal layer 200, the wiring may become discontinuous when the distance A is a value close to Δx / 2. Therefore, as shown in equation (9) below, the distance A needs to be set to a value greater than Δx. Equation (9) is the left side of equation (3) above. Therefore, the wiring 20 will not be broken when the positions of the first and second alignment target points S1 and S2 satisfy equation (9) below.

[0102] [Formula 8]

[0103] Δx<A···(9)

[0104] Furthermore, the values ​​of Δx, Δy, and θ are not particularly limited; they are values ​​corresponding to the type of exposure device, the precision of the alignment device, etc., and are values ​​obtained in advance during experimental exposures. For example, Δx can be -50μm to below +50μm (-50μm≤Δx≤+50μm), Δy can be -50μm to +50μm (-50μm≤Δy≤+50μm), and θ can be -1° to +1° (-1°≤θ≤+1°).

[0105] In addition, such as Figure 4 As shown, the plurality of light-transmitting portions 53 are sequentially offset in the width direction (y direction in the figure) and in the length direction (x direction in the figure) in a manner that protrudes relative to adjacent light-transmitting portions 53. Therefore, the plurality of first end heads 55 are sequentially offset in the -y direction in the figure and in a manner that protrudes relative to adjacent first end heads 55, and the plurality of second end heads 56 are sequentially offset in the +y direction in the figure and in a manner that protrudes relative to adjacent second end heads 56.

[0106] In the second exposure process, when the light-transmitting portion 53 shifts in the y-direction due to the influence of Δy and θ, a portion is formed in the multiple exposure section where the distance (spacing) between the exposure patterns narrows and the distance (spacing) between the wirings narrows. To address this, as shown in this embodiment, the plurality of light-transmitting portions 53 are sequentially shifted in the length direction, thereby suppressing the narrowing of the distance (spacing) between the exposure patterns 41 and the narrowing of the distance (spacing) between the wirings 20.

[0107] Figure 11 yes Figure 5 An enlarged top view of section XI. Figure 11 In this example, the case where the direction of the offset Δy of the light-transmitting portion 53 along the width direction in the second exposure process is the +y direction is shown. In this case, the -y direction in this embodiment corresponds to an example of the "first direction" in the present invention, and the +y direction in this embodiment corresponds to an example of the "second direction" in the present invention.

[0108] In this example, the first end head 55 shifts sequentially towards the -y direction (opposite to the +y direction) in a manner that protrudes relative to adjacent first end heads 55. Simultaneously, the second end head 56 shifts sequentially towards the +y direction in a manner that protrudes relative to adjacent second end heads 56. Therefore, in the overlapping portion of the first end head 55 and the second end head 56, the spacing between the light-transmitting portions 53 does not narrow. Thus, the narrowing of the spacing between the wirings 20 can be suppressed.

[0109] Furthermore, although not specifically illustrated, if the direction of offset of the light-transmitting portion 53 in the second exposure process along the y direction is the -y direction, if the first end head 55 is offset sequentially in the +y direction in a manner that protrudes relative to the other adjacent first end head 55, and at the same time, the second end head 56 is offset sequentially in the -y direction in a manner that protrudes relative to the other adjacent second end head 56, then the narrowing of the spacing between the wirings 20 can be suppressed in the same way as described above.

[0110] After the exposure process is completed, such as Figure 2 As shown in (c), a development process is performed. In this development process, the unexposed portions of the photoresist layer 40 are dissolved by the developing solution. As a result, the exposure pattern 41 (see reference) is formed on the upper surface of the metal layer 200. Figure 3 A resist pattern 45 of approximately the same shape. This resist pattern 45 functions as an etching mask in the next process.

[0111] As a developer, alkaline solutions such as tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH) can be used.

[0112] Next, as Figure 2 As shown in (d), an etching process is performed. In this etching process, the portion exposed from the resist pattern 45 is removed by etching. As a result, the shape of the resist pattern 45 is transferred to the metal layer 200 to form wiring 20.

[0113] There are no particular limitations on the etching method; a spray etching method, in which etching solution is sprayed onto a metal foil from a spray nozzle (not shown), can be used. Alternatively, ferric chloride solution or copper chloride solution can be used as the etching solution. Furthermore, the etching method is not limited to spray etching; for example, an immersion etching method, in which the metal foil is immersed in the etching solution, can also be used. Additionally, a dry etching method using etching gas can be used instead of a wet etching method.

[0114] Next, as Figure 2 As shown in (e), a stripping process is performed on the resist pattern 45. The resist pattern 45 can be stripped using a stripping solution. This exposes the wiring 20. An alkaline solution such as sodium hydroxide can be used as the stripping solution.

[0115] Next, as Figure 2 As shown in (f), a cover layer forming process is performed to form a cover layer 30. The cover layer 30 can be formed by attaching the adhesive layer 32 of the cover layer 30 as described above from the wiring 20 side to the base film 10.

[0116] Furthermore, the method for forming the cover layer 30 is not particularly limited to the above-described methods. For example, a dry film made of a photosensitive cover layer material may be used instead of the resin film described above to form the cover layer 30. Alternatively, the cover layer 30 may be formed by coating a liquid photosensitive cover layer material onto the base film 10 and then exposing and developing it. Alternatively, the cover layer 30 may be formed by printing a liquid cover layer ink onto the base film 10.

[0117] Alternatively, the cover layer 30 can be formed using a so-called solder resist. Specifically, the cover layer 30 can be formed using a dry film made of a photosensitive resist material. Alternatively, the cover layer 30 can be formed by coating a liquid photosensitive resist material onto the base film 10 and then exposing and developing it. Alternatively, the cover layer 30 can be formed by printing a liquid solder resist ink onto the base film 10.

[0118] Specific examples of the aforementioned photosensitive coating material or photosensitive resist material include materials using polyester, epoxy resin, acrylic, polyimide, polyurethane, etc. Additionally, specific examples of the aforementioned coating ink or solder resist ink include materials based on polyimide or epoxy resin.

[0119] As described above, a flexible printed wiring board 1 can be manufactured. In the manufacturing method of the flexible printed wiring board 1 in this embodiment, the first and second end heads 55 and 56 in the light-transmitting portion 53 have pointed shapes, the first and second sides 55b and 55c are curves located outside the first imaginary triangle TR1, the third and fourth sides 56b and 56c are curves located outside the second imaginary triangle TR1, and the positions of the first and second alignment target points S1 and S2 satisfy the range of the above formula (3). Therefore, the exposure portions corresponding to the first and second end heads 55a and 56a will not be exposed from the multiple exposure portion 44, and thus the shape of the multiple exposure portion 44 will not have steps.

[0120] Furthermore, since the first to fourth sides 55b, 55c, 56b, and 56c are curves, no steps are generated at the intersections of these sides of the multiple exposure section 44.

[0121] Therefore, no steps are generated in the resist pattern 45 obtained by developing the exposed photoresist 40, thus preventing steps from being generated on the side of the wiring.

[0122] Furthermore, both the first and second end heads 55 and 56 have pointed shapes, so the width of the multiple exposure section 44 will not become too wide. Therefore, even in the resist pattern 45, it is not easy to form a portion that is too wide, thereby preventing the wiring 20 from having an excessively wide portion.

[0123] Furthermore, in existing manufacturing methods, the multiple exposure section is exposed twice via the first and second end heads of the same width, resulting in overexposure at the multiple exposure section. As a result, the width of the portion corresponding to the multiple exposure section in the wiring sometimes becomes wider.

[0124] In this embodiment, in the tapered first end head 55, the first alignment target point S1 is located on the side closer to the first end portion 55a relative to the first connecting portion 57, and in the tapered first end head 55 facing the opposite direction to the first end head 55, the second alignment target point S2 is located on the side closer to the second end portion 56a relative to the second connecting portion 58. That is, in the first end head 55, the tip tapers from the side closer to the first connecting portion 57 than the first alignment target point S1, and at the same time, in the second end head 56, the tip tapers from the side closer to the second connecting portion 58 than the second alignment target point S2.

[0125] Therefore, in the multiple exposure section 44, the wider portion of the first end head 55 overlaps with the narrower portion of the second end head 56, and vice versa. This allows for uniform exposure in the multiple exposure section 44. Consequently, the width of the wiring 20 corresponding to the multiple exposure section 44 does not become excessively wide.

[0126] Furthermore, the embodiments described above are provided for ease of understanding of the present invention and are not intended to limit the present invention. Therefore, the elements disclosed in the above embodiments are also intended to include all design changes or equivalents that fall within the scope of the present invention.

[0127] For example, in the exposure process described above, an example of using the same photomask 50 for both the first and second exposure processes was given, but this is not a limitation. The first photomask used in the first exposure process and the second photomask used in the second exposure process can be different types of photomasks. In this case, a photomask having a light-transmitting portion having first and second end heads that satisfy the above formula (3) is also used.

[0128] Furthermore, in the above-described embodiment, the first to fourth sides 55b, 55c, 56b, and 56c are all curves with only one convex portion protruding in one direction, but this is not a limitation. The first to fourth sides 55b, 55c, 56b, and 56c can be curves of any shape, as long as they are located outside the first and second imaginary triangles TR1 and TR2. For example, they can be meandering curves with multiple convex portions as described above. Similarly, the first to fourth connecting sides 55d, 55e, 56d, and 56e can also be meandering curves with multiple convex portions.

[0129] Furthermore, while the above-described embodiment illustrates a manufacturing method using a subtractive process, it is not limited to this; flexible printed wiring boards can also be manufactured using a so-called semi-additive process. In this semi-additive process, a photoresist layer 40, composed of a positive resist whose photosensitive portion is dissolved in a developer, is formed on a base film 10. After multiple exposures through a photomask 50 as described above, the resist pattern is developed. In this case, the photoresist layer is removed along the shape of the exposed pattern. Then, wiring 20 is formed on the main surface of the base film 10 exposed by removing the photoresist layer through plating or the like.

[0130] Furthermore, while the first and second alignment target points S1 and S2 in the above embodiment are located on the center line CL, this is not a limitation. When the value of the distance D is sufficiently greater than the offset Δy of the light-transmitting portion 53 during the second exposure process, the first and second alignment target points S1 and S2 can be slightly offset from the center line CL in the y-direction. However, the first and second alignment target points S1 and S2 are set such that the sum of the distance from the center line CL to the first and second alignment target points S1 and S2 in the y-direction and the offset Δy is D / 2 or less, so that the first and second ends 55a and 56a are not exposed.

[0131] Furthermore, the first and second alignment target points S1 and S2 in the above embodiment are disposed approximately at the center along the length of the first and second end heads 55 and 56, but are not limited thereto. The first and second alignment target points S1 and S2 may be disposed on the side closer to the first and second end heads 55a and 56a than the center in the length direction, or they may be disposed on the side closer to the first and second connecting portions 57 and 58 than the center.

[0132] In addition, in the above embodiment, the first and second ends 55a and 56a are points, but are not limited to this, and can also be straight lines or curves with a length of D or less in the width direction (y direction in the figure).

[0133] Explanation of reference numerals in the attached figures

[0134] 1 Flexible printed wiring board

[0135] 10 Base film

[0136] 20. Wiring

[0137] 30 Covering layer

[0138] 31 Protective Layer

[0139] 32 Adhesive layer

[0140] 40 Photoresist layer

[0141] 41 Exposure Pattern

[0142] 42 First Exposure Department

[0143] 43 Second Exposure Department

[0144] 44 Multiple Exposure Department

[0145] 45. Resist Pattern

[0146] 50 photomask

[0147] 51 Transparent substrate

[0148] 52 shading film

[0149] 53 Light-transmitting section

[0150] 54 Main Story Section

[0151] 54a, 54b First and second sides

[0152] 55 First end head

[0153] 55a First end

[0154] 55b, 55c First and second sides

[0155] 55d, 55e First and second connecting edges

[0156] 56 Second end head

[0157] 56a Second end

[0158] 56b, 56c Third and Fourth Sides

[0159] 56d, 56e Third and fourth connecting edges

[0160] 57, 58 First and second connecting parts

[0161] S1, S2, and the first and second aligned target points

[0162] R1, R2 and the first and second regions

[0163] R m1 Overlapping areas

[0164] TR1, TR2, and the first and second imaginary triangles

[0165] RE is an imaginary rectangle.

Claims

1. A method for manufacturing a flexible printed wiring board, comprising using a photoresist to manufacture the flexible printed wiring board, and comprising: The first step involves depositing a photoresist having a first region and a second region onto a substrate. In the second step, a first photomask having a first light-transmitting portion is arranged such that the first light-transmitting portion is opposite to the first region, and the photoresist is exposed through the first light-transmitting portion. as well as In the third step, a second photomask having a second light-transmitting portion is arranged such that the second light-transmitting portion and the second region are opposite each other, and the photoresist is exposed through the second light-transmitting portion. The first region and the second region are adjacent to each other in such a way that the ends of the first region and the ends of the second region overlap. The first light-transmitting portion has a linear shape, and the linear shape includes a first end head with a pointed shape. The second light-transmitting portion has a linear shape, the linear shape including a second end head having a pointed shape facing the side opposite to the first end head. The third step includes configuring the second photomask in such a way that the second alignment target point contained in the second end head overlaps with the first position. The first position is the position where the first alignment target point contained in the first end head is configured in the second process. The first end head includes: First end; The curved first side connected to the first end; and A curved second side that connects to the first end and is opposite to the first side. The first alignment target point is a point located at a distance A from the first end on a first center line extending along the first length direction, such that the approximate center of the first light-transmitting portion is at the same distance. The first side and the second side are located outside the first imaginary triangle. The first imaginary triangle is an imaginary triangle connecting the first intersection point of the first center line and the first end point, the second intersection point of the first imaginary line and the first side, and the third intersection point of the first imaginary line and the second side. The first imaginary straight line is an imaginary straight line that extends along the first width direction of the first light-transmitting portion and passes through the first alignment target point. The distance D between the second intersection point and the third intersection point The second end head includes: Second end; The curved third side connected to the second end; and A curved fourth side that connects to the second end and opposes the second side. The second alignment target point is a point located at a distance A from the second end on the second center line extending along the second length direction, such that the approximate center of the second light-transmitting portion is at the same distance. The third and fourth sides are located outside the second imaginary triangle. The second imaginary triangle is an imaginary triangle connecting the fourth intersection point of the second center line and the second end point, the fifth intersection point of the second imaginary line and the third side, and the sixth intersection point of the second imaginary line and the fourth side. The second imaginary straight line is an imaginary straight line that extends along the second width direction of the second light-transmitting portion and passes through the second alignment target point. The distance D between the fifth intersection point and the sixth intersection point The manufacturing method of the flexible printed wiring board satisfies the following equation (1). [Formula 1] In equation (1) above, Δx is the offset of the second alignment target point relative to the first position in the first length direction, Δy is the offset of the second alignment target point relative to the first position in the first width direction, θ is the offset of the second alignment target point relative to the first position in the rotation direction about the first normal, and the first normal is the normal that passes through the first position and is perpendicular to the first photomask.

2. The method for manufacturing a flexible printed wiring board according to claim 1, characterized in that, The first light-transmitting portion also has a first main line portion connected to the first end head. The first alignment target point is located on the first end head at a position closer to the first end side than the first connecting part connected to the first main line part. The second light-transmitting portion also has a second main line portion connected to the second end head. The second alignment target point is located on the second end head at a position closer to the second end side than the second connecting part that connects to the second main line part. The width of the first main line section and the second main line section is W. The manufacturing method of the flexible printed wiring board satisfies the following equation (2). D≤W (2).

3. The method for manufacturing a flexible printed wiring board according to claim 1 or 2, characterized in that, The first photomask has a plurality of first light-transmitting portions arranged side by side. The plurality of first end heads are sequentially offset relative to adjacent first end heads as they face a first direction. The second photomask has a plurality of second light-transmitting portions arranged side by side. The plurality of second end heads are sequentially offset in a manner that protrudes relative to adjacent second end heads as they face the second direction. The second direction is the direction offset from the first position towards the second alignment target point along the first width direction. The first direction is the opposite of the second direction.

Images