Method for manufacturing a printed circuit board

Abstract

To provide a method for manufacturing a wiring circuit board capable of improving dimensional accuracy of a second conductor layer.SOLUTION: A wiring circuit board 1 manufactured by a manufacturing method comprises: a metal support layer 2; a first insulation layer 3 arranged on one surface of the metal support layer 2 in a thickness direction; a first conductor layer 4 arranged on one surface of the first insulation layer 3 in the thickness direction; a second insulation layer 5 arranged so as to cover the first conductor layer 4 on one surface of the first insulation layer 3 in the thickness direction; and a second conductor layer 6 arranged on one surface of the second insulation layer 5 in the thickness direction. The manufacturing method includes a step [4] of forming a second insulation layer 5 by sticking a film 50 made of a photosensitive resin to one surface of the first insulation layer 3 and the first conductor layer 4 in the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a printed circuit board. [Background technology]

[0002] There is known a method for manufacturing a wired circuit board that includes a metal supporting board, a first insulating layer arranged on the upper surface of the metal supporting board, a first conductor layer arranged on the upper surface of the first insulating layer, a second insulating layer arranged on the upper surface of the first insulating layer so as to cover the first conductor layer, and a second conductor layer arranged on the upper surface of the second insulating layer (see, for example, Patent Document 1 below).

[0003] In the manufacturing method described in Patent Document 1, varnish is applied to the upper surfaces of the first conductor layer and the first insulating layer to form a photosensitive coating film, which is then patterned by exposure and development to form the second insulating layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-099687 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacturing method of Patent Document 1, the second insulating layer is formed from varnish, and therefore the second insulating layer has a slope (shoulder) corresponding to the corner formed by the top surface and side surface of the first conductor layer.

[0006] Depending on the application and purpose of the printed circuit board, the second conductor layer must overlap the inclined portion, which can cause a problem of reduced dimensional accuracy of the second conductor layer.

[0007] Furthermore, there is a need to easily form the second insulating layer by patterning.

[0008] The present invention provides a method for manufacturing a wired circuit board that allows for easy formation of a second insulating layer by patterning a film and improves the dimensional accuracy of the second conductor layer. [Means for solving the problem]

[0009] The present invention (1) is a method for manufacturing a wired circuit board comprising a metal support layer, a first insulating layer arranged on one side of the metal support layer in the thickness direction, a first conductor layer arranged on one side of the first insulating layer in the thickness direction, a second insulating layer arranged on one side of the first insulating layer in the thickness direction so as to cover the first conductor layer, and a second conductor layer arranged on one side of the second insulating layer in the thickness direction, and includes a method for manufacturing a wired circuit board comprising a step of bonding a film made of a photosensitive resin to one side of the first insulating layer and the first conductor layer in the thickness direction to form the second insulating layer.

[0010] In this manufacturing method, a film made of photosensitive resin is attached to one surface of the first insulating layer and one surface of the first conductor layer in the thickness direction, which makes it easy to flatten one surface of the second insulating layer in the thickness direction, and therefore the second conductor layer can be positioned with high dimensional accuracy relative to the second insulating layer.

[0011] Furthermore, the film made of photosensitive resin after being bonded to the first insulating layer and the first conductor layer can be patterned by exposure and development to easily form the second insulating layer.

[0012] The present invention (2) includes the method for producing a wired circuit board according to (1), wherein in the step of forming the second insulating layer, the film is pressure-bonded to the first insulating layer and the first conductor layer.

[0013] In this manufacturing method, in the step of forming the second insulating layer, the film is pressure-bonded to the first insulating layer and the first conductor layer, so that one surface of the second insulating layer in the thickness direction can be reliably flattened.

[0014] The present invention (3) includes the method for producing a wired circuit board according to (1) or (2), wherein the film includes a photosensitive resin layer containing a polyamic acid resin.

[0015] In this manufacturing method, the second insulating layer including a resin layer made of polyimide resin can be easily formed by patterning the photosensitive resin layer including polyamic acid resin.

[0016] The present invention (4) includes the method for producing a wired circuit board according to (3), wherein the film further includes a photosensitive adhesive layer made of an adhesive.

[0017] In this manufacturing method, the film further includes a photosensitive adhesive layer made of an adhesive, so that the resin layer can be adhered to the first insulating layer via the photosensitive adhesive layer, and the photosensitive film can be patterned to easily form the second insulating layer.

[0018] The present invention (5) includes the method for producing a wired circuit board according to any one of (1) to (4), further comprising the step of forming the first insulating layer by applying a varnish, exposing and developing it, or by pattern printing.

[0019] In this manufacturing method, the first insulating layer is formed by applying varnish, exposing and developing it, or by pattern printing, and the second insulating layer is formed from a film made of a photosensitive resin.This allows the first insulating layer to be formed thin, and therefore the total thickness of the first insulating layer and the second insulating layer can be made thin.

[0020] The present invention (6) includes the method for producing a wired circuit board according to any one of (1) to (5), wherein the coating film formed by coating, exposure and development, or pattern printing, contains a photosensitive polyamic acid resin.

[0021] In this manufacturing method, the first insulating layer made of polyimide resin can be formed from photosensitive polyamic acid resin.

[0022] The present invention (7) includes a method for manufacturing a wired circuit board according to any one of (1) to (6), wherein the wired circuit board further comprises a third insulating layer arranged on one side of the second insulating layer in the thickness direction so as to cover the second conductor layer, and further comprises a step of forming the third insulating layer by applying varnish, exposing and developing, or pattern printing.

[0023] The third insulating layer is formed by applying varnish, exposing and developing it, or by pattern printing, and the second insulating layer is formed from a film made of a photosensitive resin, so the third insulating layer can be formed thin, and therefore the total thickness of the third insulating layer and the second insulating layer can be made thin.

[0024] The present invention (8) includes the method for producing a wired circuit board according to (7), wherein the coating film formed by coating, exposure and development, or pattern printing, contains a photosensitive polyamic acid resin.

[0025] In this manufacturing method, the third insulating layer made of polyimide resin can be formed from photosensitive polyamic acid resin. [Effects of the Invention]

[0026] The method for producing a wired circuit board of the present invention allows the second insulating layer to be easily formed by patterning the film, and the dimensional accuracy of the second conductor layer can be improved. [Brief explanation of the drawings]

[0027] [Figure 1] 1A-1G are manufacturing process diagrams of one embodiment of the method for manufacturing a wired circuit board of the present invention. FIG. 1A is step [1]. FIG. 1B is step [2]. FIG. 1C is step [3]. FIG. 1D is step [4], which is step [4] of placing a film on a metal support layer, a first insulating layer, and a first conductor layer. FIG. 1E is step [4], which is step [4] of forming a second insulating layer. FIG. 1F is step [5]. FIG. 1G is step [6]. [Figure 2]2A-2D are manufacturing process diagrams of a modified example of the method for manufacturing a printed circuit board. FIG. 2A shows step [4], in which a film made of a resin layer is disposed on a metal support layer, a first insulating layer, and a first conductor layer. FIG. 2B shows step [4], in which a second insulating layer is formed. FIG. 2C shows steps [5] and [6]. [Figure 3] This is a conventional example in which a second conductor layer is disposed on a second insulating layer having an inclined portion. DETAILED DESCRIPTION OF THE INVENTION

[0028] 1. One embodiment of a method for manufacturing a printed circuit board An embodiment of the method for producing a wired circuit board according to the present invention will be described.

[0029] 1.1 Wired circuit board As shown in FIG. 1G, the wired circuit board 1 obtained by this manufacturing method has a thickness. The wired circuit board 1 extends in a planar direction. The planar direction is perpendicular to the thickness direction. The wired circuit board 1 has a plate shape. The thickness of the wired circuit board 1 is, for example, 10 μm or more, and, for example, 500 μm or less, preferably 300 μm or less, and more preferably 200 μm or less.

[0030] The wired circuit board 1 includes a metal support layer 2, a first insulating layer 3, a first conductor layer 4, a second insulating layer 5, a second conductor layer 6, and a third insulating layer 7. The wired circuit board 1 also includes a plurality of divisions 11A and 11B. Each of the divisions 11A and 11B is disposed on one side of the metal support layer 2 in the thickness direction. The divisions 11A and 11B are divided in the planar direction. The division 11B is spaced apart from the division 11A in the planar direction. As will be described later, the division 11A includes a first insulator 3A, a first wiring 4A, a second insulator 5A, a second wiring 6A, and a third insulator 7A. The division 11B includes a first insulator 3B, a first wiring 4B, a second insulator 5B, a second wiring 6B, and a third insulator 7B.

[0031] 1.1.1 Metal support layer 2 The metal support layer 2 is disposed at the other end of the wired circuit board 1 in the thickness direction. The metal support layer 2 forms the other end surface of the wired circuit board 1 in the thickness direction. The metal support layer 2 extends in the planar direction. Each of the one surface and the other surface of the metal support layer 2 in the thickness direction is a flat surface. The metal support layer 2 contacts the other surface of the divided bodies 11A, 11B in the thickness direction. The material of the metal support layer 2 is a metal. Examples of metals include stainless steel and copper alloys. The thickness of the metal support layer 2 is, for example, 10 μm or more and 1,000 μm or less.

[0032] 1.1.2 First insulating layer 3 The first insulating layer 3 is disposed on one surface of the metal support layer 2 in the thickness direction. The first insulating layer 3 extends in the planar direction. One surface of the first insulating layer 3 in the thickness direction is a flat surface. The first insulating layer 3 has a patterned shape. Specifically, the first insulating layer 3 includes a plurality of first insulators 3A, 3B. Each of the first insulators 3A, 3B is included in each of the above-mentioned divided bodies 11A, 11B. The first insulating layer 3 is used as a base insulating layer.

[0033] An example of the material for the first insulating layer 3 is a resin. Examples of the resin include polyimide resin, polyamideimide resin, acrylic resin, polyethernitrile resin, polyethersulfone resin, polyethylene terephthalate resin, polyethylene naphthalate resin, and polyvinyl chloride resin. A preferred example of the material for the first insulating layer 3 is polyimide resin. The thickness of the first insulating layer 3 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 30 μm or less, preferably 20 μm or less.

[0034] 1.1.3 First Conductor Layer 4 The first conductor layer 4 is disposed on one surface of the first insulating layer 3 in the thickness direction. The first conductor layer 4 extends in the planar direction. In this embodiment, the first conductor layer 4 has a generally rectangular cross-sectional shape. One surface of the first conductor layer 4 in the thickness direction is a flat surface.

[0035] The first conductor layer 4 includes a plurality of first wirings 4A and 4B. Each of the first wirings 4A and 4B is included in each of the divided bodies 11A and 11B. Each of the first wirings 4A and 4B extends in a first direction that is included in the planar direction. In this embodiment, the first direction is the depth direction in FIG. 1G. Each of the first wirings 4A and 4B is disposed on one side of each of the first insulators 3A and 3B in the thickness direction. The material of the first conductor layer 4 is a conductor. Examples of conductors include copper, nickel, gold, and alloys thereof. Each of the first wirings 4A and 4B has a width of, for example, 5 μm or more and, for example, 250 μm or less. The thickness of the first conductor layer 4 is, for example, 3 μm or more and, for example, 50 μm or less. The width is the length in a direction perpendicular to the first direction and the thickness direction.

[0036] 1.1.4 Second insulating layer 5 The second insulating layer 5 is disposed on one surface of the first insulating layer 3 in the thickness direction so as to cover the first conductor layer 4. Specifically, the second insulating layer 5 contacts one surface of the first insulating layer 3 in the thickness direction, both end surfaces of the first insulating layer 3 in the width direction, one surface of the first conductor layer 4 in the thickness direction, and both end surfaces of the first conductor layer 4 in the width direction. The second insulating layer 5 extends in the planar direction. One surface of the second insulating layer 5 in the thickness direction is flat.

[0037] The second insulating layer 5 has a pattern shape. Specifically, the second insulating layer 5 includes a plurality of second insulators 5A and 5B. Each of the second insulators 5A and 5B is included in each of the divided bodies 11A and 11B. Each of the second insulators 5A and 5B is disposed on one side of each of the first insulators 3A and 3B so as to cover each of the first wirings 4A and 4B.

[0038] In this embodiment, the end faces of the second insulating layer 5 (each of the second insulators 5A and 5B) in the width direction are flush with the end faces of the first insulating layer 3 (each of the first insulators 3A and 3B) in the width direction. The second insulating layer 5 is an intermediate insulating layer. The thickness of the second insulating layer 5 is, for example, 3 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 30 μm or less. The total thickness of the first insulating layer 3 and the second insulating layer 5 is, for example, 80 μm or less, preferably 50 μm or less, more preferably 40 μm or less, and is 5 μm or more.

[0039] 1.1.5 Layer structure of second insulating layer 5 The second insulating layer 5 includes an adhesive layer 51 and a resin layer 52 arranged in this order toward one side in the thickness direction.

[0040] 1.1.6 Adhesive layer 51 The adhesive layer 51 is disposed at the other end of the second insulating layer 5 in the thickness direction. The adhesive layer 51 forms the other surface of the second insulating layer 5 in the thickness direction. In this embodiment, one surface of the adhesive layer 51 in the thickness direction is flat. The other surface of the adhesive layer 51 in the thickness direction follows the shape of the first conductor layer 4. Specifically, the adhesive layer 51 contacts one surface of the first insulating layer 3 in the thickness direction, both end surfaces of the first insulating layer 3 in the width direction, one surface of the first conductor layer 4 in the thickness direction, and both end surfaces of the first conductor layer 4 in the width direction. The adhesive layer 51 is an adhesive photosensitive body, which will be described later.

[0041] Examples of adhesives include epoxy resin adhesives, phenolic resin adhesives, polyester resin adhesives, and acrylic resin adhesives. These can be used alone or in combination. Examples of adhesives include those described in JP 2012-004523 A. Note that in this embodiment, the adhesive does not include polyimide resin adhesives.

[0042] The thickness of the adhesive layer 51 is, for example, 5 μm or more, preferably 10 μm or more, and for example, 45 μm or less, preferably 30 μm or less. The ratio of the thickness of the adhesive layer 51 to the thickness of the second insulating layer 5 is, for example, 0.3 or more, preferably 0.6 or more, and for example, 0.9 or less, preferably 0.8 or less. The thickness of the adhesive layer 51 is the distance in the thickness direction between one surface of the first insulating layer 3 in the thickness direction and one surface of the adhesive layer 51 in the thickness direction.

[0043] 1.1.7 Resin layer 52 The resin layer 52 is disposed at one end of the second insulating layer 5 in the thickness direction. The resin layer 52 forms one surface of the second insulating layer in the thickness direction. The resin layer 52 is disposed on one surface of the adhesive layer 51 in the thickness direction. In this embodiment, one surface of the resin layer 52 in the thickness direction is a flat surface. Examples of resins include the resins exemplified for the first insulating layer 3, and preferably, polyimide resin is used.

[0044] The thickness of the resin layer 52 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 45 μm or less, preferably 30 μm or less. The ratio of the thickness of the resin layer 52 to the thickness of the second insulating layer 5 is, for example, 0.1 or more, preferably 0.2 or more, and for example, 0.7 or less, preferably 0.4 or less. The resin layer 52 is preferably thinner than the adhesive layer 51. The ratio of the thickness of the resin layer 52 to the thickness of the adhesive layer 51 is, for example, less than 1, preferably 0.9 or less, more preferably 0.5 or less, and for example, 0.01 or more, preferably 0.1 or more. The thickness of the resin layer 52 is the distance in the thickness direction between one surface of the adhesive layer 51 in the thickness direction and one surface of the resin layer 52 in the thickness direction.

[0045] 1.1.8 Second Conductor Layer 6 The second conductor layer 6 is disposed on one surface of the second insulating layer 5 in the thickness direction. The second conductor layer 6 extends in the planar direction. In this embodiment, the second conductor layer 6 has a generally rectangular cross-sectional shape. One surface of the second conductor layer 6 in the thickness direction is a flat surface. The second conductor layer 6 includes a plurality of second wirings 6A, 6B. Each of the second wirings 6A, 6B is included in each of the divided bodies 11A, 11B described above. Each of the second wirings 6A, 6B extends in the first direction described above. Each of the second wirings 6A, 6B is disposed on one surface of each of the second insulators 5A, 5B in the thickness direction.

[0046] In this embodiment, the second wiring 6A overlaps with the first wiring 4A when projected in the thickness direction. The second wiring 6B has a portion that overlaps with the first wiring 4B when projected in the thickness direction and a portion that does not overlap with the first wiring 4B when projected in the thickness direction. Specifically, the second wiring 6B overlaps with one end face of the first wiring 4B in the width direction when projected in the thickness direction, but does not overlap with the other end face of the first wiring 4B in the width direction.

[0047] The second conductor layer 6 can be made of the same conductors as those used for the first conductor layer 4. The widths of the second wirings 6A and 6B and the thickness of the second conductor layer 6 are the same as the widths of the first wirings 4A and 4B and the thickness of the first conductor layer 4.

[0048] 1.1.9 Third insulating layer 7 The third insulating layer 7 is disposed on one surface of the second insulating layer 5 in the thickness direction so as to cover the second conductor layer 6. The third insulating layer 7 forms one surface of the wired circuit board 1 in the thickness direction. The third insulating layer 7 extends in the planar direction. The one surface of the third insulating layer 7 in the thickness direction may include an inclined portion (shoulder portion) 70. The inclined portion 70 corresponds to (faces) a corner formed by one surface in the thickness direction and an end face in the width direction of each of the second wirings 6A, 6B.

[0049] The third insulating layer 7 has a pattern shape. Specifically, the third insulating layer 7 includes a plurality of third insulators 7A, 7B. Each of the third insulators 7A, 7B is included in each of the divided bodies 11A, 11B described above. Each of the third insulators 7A, 7B is arranged on one side of each of the second insulators 5A, 5B so as to cover each of the second wirings 6A, 6B. In this embodiment, the end faces of the third insulating layer 7 (each of the third insulators 7A, 7B) in the width direction are flush with the end faces of the second insulating layer 5 (each of the second insulators 5A, 5B) in the width direction. The third insulating layer 7 is used as a cover insulating layer.

[0050] The thickness of the third insulating layer 7 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 30 μm or less, preferably 20 μm or less. The thickness of the third insulating layer 7 is the length in the thickness direction between one surface of the second insulating layer 5 in the thickness direction and one surface of the third insulating layer 7 in the thickness direction that faces the one surface without the second conductor layer 6 in between. The total thickness of the third insulating layer 7 and the second insulating layer 5 is, for example, 80 μm or less, preferably 50 μm or less, more preferably 40 μm or less, and is 5 μm or more.

[0051] 1.2 Manufacturing method 1A to 1G, the method for manufacturing the wired circuit board 1 includes steps [1] to [6]. Steps [1] to [6] are performed in this order.

[0052] 1.2.1 Process [1] In step [1], as shown in FIG. 1A, a metal support layer 2 is prepared.

[0053] 1.2.2 Process [2] 1B, the first insulating layer 3 is formed on one surface of the metal support layer 2 in the thickness direction. In this embodiment, the first insulating layer 3 is formed by applying a varnish to one surface of the metal support layer 2 in the thickness direction, exposing and developing the varnish, or by pattern printing.

[0054] When a varnish is applied, the varnish contains, for example, a photosensitizer, a resin component, and a solvent. When the first insulating layer 3 is made of a polyimide resin, the resin component preferably contains an acid dianhydride and a diamine.

[0055] A varnish is applied to the entire surface of one side of the metal support layer 2, followed by heating to form a photosensitive coating film. The coating film contains a polyamic acid resin. The polyamic acid resin is a reaction product of an acid dianhydride and a diamine, and is a precursor material for a polyimide resin. The coating film is then exposed to light and developed, and if necessary, heated after exposure to form a first insulating layer 3 comprising first insulators 3A and 3B.

[0056] When pattern printing the varnish, the varnish contains, for example, the resin component and a solvent. For example, the varnish is screen-printed on one side of the metal support layer 2, and then heated to form a coating film including the first insulators 3A and 3B. The coating film is then heated to form the first insulating layer 3.

[0057] 1.2.3 Process [3] In step [3], as shown in the lower diagram of Fig. 1C, a first conductor layer 4 is formed. The first conductor layer 4 is formed using a known conductor pattern forming method, specifically, an additive method.

[0058] In step [4], as shown in Fig. 1E, a second insulating layer 5 is formed. In step [4], as shown in Fig. 1D, a film 50 is bonded to one side of the metal support layer 2, the first insulating layer 3, and the first conductor layer 4 in the thickness direction.

[0059] The film 50 is flexible. The film 50 has a thickness along the surface direction. The film 50 is solid at room temperature, but has another surface in the thickness direction that undergoes plastic deformation when pressed. The film 50 is made of a photosensitive resin (preferably a photosensitive resin containing a photosensitizer and a polyamic acid resin). The film 50 has a photosensitive adhesive layer 501 and a photosensitive resin layer 502, arranged in this order toward one side in the thickness direction.

[0060] The photosensitive adhesive layer 501 forms the other surface of the film 50 in the thickness direction. The photosensitive adhesive layer 501 is an uncured layer before curing. The photosensitive adhesive layer 501 is also an unphotosensitive layer before exposure to light. The photosensitive adhesive layer 501 contains an adhesive component that constitutes an adhesive and a photosensitizer.

[0061] The thickness of the photosensitive adhesive layer 501 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 30 μm or less, preferably 20 μm or less. The ratio of the thickness of the photosensitive adhesive layer 501 to the thickness of the film 50 is, for example, 0.1 or more, preferably 0.3 or more, and for example, 0.9 or less, preferably 0.7 or less.

[0062] The photosensitive resin layer 502 forms one surface of the film 50 in the thickness direction. The photosensitive resin layer 502 is disposed on one surface of the photosensitive adhesive layer 501 in the thickness direction. The photosensitive resin layer 502 is an uncured layer before curing. The photosensitive adhesive layer 501 is an unphotosensitive layer before exposure. The photosensitive resin layer 502 contains a resin component (precursor material, preferably polyamic acid resin) that constitutes the resin layer and a photosensitizer.

[0063] The thickness of the photosensitive resin layer 502 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 30 μm or less, preferably 20 μm or less. The ratio of the thickness of the photosensitive resin layer 502 to the thickness of the film 50 is, for example, 0.1 or more, preferably 0.3 or more, and for example, 0.9 or less, preferably 0.7 or less.

[0064] The film 50 has a thickness of, for example, 3 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 30 μm or less.

[0065] As shown by the imaginary lines, separators 53 may be disposed on both sides of film 50 in the thickness direction.

[0066] 1.2.4 Process [4] In step [4], the film 50 is pressure-bonded to the first insulating layer 3 and the first conductor layer 4. Specifically, the divided body 11A including the first insulator 3A and the first wiring 4A and the divided body 11B including the first insulator 3B and the first wiring 4B are embedded in the film 50. In step [4], the photosensitive adhesive layer 501 of the film 50 contacts one surface of the metal support layer 2 in the thickness direction, one surface of the first insulating layer 3 in the thickness direction, both end surfaces of the first insulating layer 3 in the width direction, one surface of the first conductor layer 4 in the thickness direction, and both end surfaces of the first conductor layer 4 in the width direction. In step [4], the film 50 and a laminate including the metal support layer 2, the first insulating layer 3, and the first conductor layer 4 are pressure-bonded using a laminator.

[0067] In step [4], as shown in FIG. 1E, the film 50 is then exposed through a photomask (not shown), followed by development and then post-exposure baking to form a second insulating layer 5 having second insulators 5A and 5B.

[0068] 1.2.5 Process [5] In step [5], as shown in Fig. 1F, a second conductor layer 6 is formed. The second conductor layer 6 is formed using a known conductor pattern forming method, specifically an additive method.

[0069] 1.2.6 Process [6] In step [6], as shown in Fig. 1G, the third insulating layer 7 is formed. In this embodiment, a varnish is applied to one surface of the second insulating layer 5 and the second conductor layer 6 in the thickness direction, and then exposed and developed, or pattern printed to form a coating film.

[0070] When a varnish is applied, the varnish contains, for example, a photosensitizer, a resin component, and a solvent. When the third insulating layer 7 is made of a polyimide resin, the resin component preferably contains an acid dianhydride and a diamine.

[0071] A varnish is applied to one side of the second insulating layer 5 and the second conductor layer 6, and then heated to form a photosensitive coating film. The coating film contains a polyamic acid resin. The polyamic acid resin is a reaction product of an acid dianhydride and a diamine, and is a precursor material for a polyimide resin. The coating film is then exposed to light and developed, and if necessary, heated after exposure to form a third insulating layer 7 comprising third insulators 7A and 7B.

[0072] When the varnish is pattern-printed, the varnish contains, for example, the resin component and a solvent described above. For example, the varnish is screen-printed on one side of the second insulating layer 5 and the second conductor layer 6, and then heated to form the third insulating layer 7 including the third insulators 7A and 7B.

[0073] In this way, the wired circuit board 1 is manufactured.

[0074] 2. Effects of one embodiment When the second insulating layer 5 is formed using varnish in step [4], an inclined portion 55 is likely to be formed on one surface of the second insulating layer 5 in the thickness direction, as shown in Fig. 3. Then, when the second wiring 6B is formed on the inclined portion 55 in the subsequent step [5], the dimensional accuracy of the second wiring 6B decreases.

[0075] However, in this embodiment, in step [4], as shown in Fig. 1D, in this manufacturing method, a film 50 made of a photosensitive resin is attached to one surface of the first insulating layer 3 and the first conductor layer 4 in the thickness direction. Therefore, as shown in Fig. 1E, one surface of the second insulating layer 5 in the thickness direction can be easily flattened. Therefore, the second conductor layer 6 can be positioned with high dimensional accuracy relative to the second insulating layer 5.

[0076] As shown in Figure 1D, the film 50 made of photosensitive resin after being bonded to the first insulating layer 3 and the first conductor layer 4 can then be patterned by exposure and development, as shown in Figure 1E, to easily form the second insulating layer 5.

[0077] Furthermore, as shown in FIG. 1D, in this manufacturing method, in step [4], the film 50 is pressed against the first insulating layer 3 and the first conductor layer 4, so that one side of the second insulating layer 5 in the thickness direction can be reliably flattened.

[0078] In this manufacturing method, the second insulating layer including the resin layer 52 made of polyimide resin can be easily formed by patterning the photosensitive polyamic acid resin.

[0079] In addition, in this manufacturing method, the film 50 further includes an adhesive layer 51 made of a photosensitive adhesive, so that the resin layer 52 can be adhered to the first insulating layer 3 via the adhesive layer 51, and further, the photosensitive film 50 can be patterned to easily form the second insulating layer 5.

[0080] Furthermore, in this manufacturing method, in step [2], the first insulating layer 3 is formed by applying varnish, exposing and developing it, or by pattern printing, and in step [4], the second insulating layer 5 is formed from a film 50 made of a photosensitive resin. This allows the first insulating layer 3 to be formed thin, and therefore the total thickness of the first insulating layer 3 and the second insulating layer 5 can be made thin.

[0081] In this manufacturing method, the first insulating layer 3 made of polyimide resin can be formed from photosensitive polyamic acid resin.

[0082] In this manufacturing method, in step [6], the third insulating layer 7 is formed by applying varnish, exposing and developing it, or by pattern printing, and in step [4], the second insulating layer 5 is formed from a film made of a photosensitive resin.This makes it possible to form the third insulating layer 7 thin, and therefore the total thickness of the third insulating layer 7 and the second insulating layer 5 can be made thin.

[0083] In this manufacturing method, as shown in FIG. 1G, a third insulating layer 7 made of a polyimide resin can be formed from a photosensitive polyamic acid resin.

[0084] 4. Variations In the modified example, the same components and steps as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modified example can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and its modified example can be combined as appropriate.

[0085] 2A, the film 50 does not include the photosensitive adhesive layer 501, but includes only the photosensitive resin layer 502. In step [4], the film 50 including the photosensitive resin layer 502 is bonded to one side of the metal support layer 2, the first insulating layer 3, and the first conductor layer 4 in the thickness direction.

[0086] Thereafter, as shown in FIG. 2B, the film 50 made of the photosensitive resin layer 502 is exposed to light, developed, and heated after exposure to form the second insulating layer 5.

[0087] Thereafter, as shown in FIG. 2C, steps [5] and [6] are carried out in this order to form the second conductor layer 6 and the third insulating layer 7 in this order.

[0088] Although not shown, the photosensitive resin layer 502 may be made up of multiple layers of different types in the thickness direction.

[0089] Although not shown, the first insulating layer 3 may be formed from a photosensitive film. In this case, a two-layer base material in which the metal support layer 2 and the film are laminated is used.

[0090] The first insulating layer 3 and / or the third insulating layer 7 may be formed from a photosensitive film.

[0091] Although not shown, the adhesive may include a polyimide resin adhesive. In this modification, if the resin of the resin layer 52 is a polyimide resin, the material of the second insulating layer 5 is also a polyimide resin. [Explanation of symbols]

[0092] 1 Wiring circuit board 2 Metal support layer 3 First insulating layer 4 First conductor layer 5 Second insulating layer 6 Second conductor layer 7 Third insulating layer 50 films 51 Adhesive layer 52 Resin layer 501 Photosensitive adhesive layer 502 Photosensitive resin layer

Claims

1. A method for manufacturing a wired circuit board comprising: a metal support layer; a first insulating layer disposed on one surface of the metal support layer in a thickness direction; a first conductor layer disposed on one surface of the first insulating layer in the thickness direction; a second insulating layer disposed on one surface of the first insulating layer in the thickness direction so as to cover the first conductor layer; and a second conductor layer disposed on one surface of the second insulating layer in the thickness direction, A method for manufacturing a wired circuit board, comprising a step of bonding a film made of uncured photosensitive resin to one side of the first insulating layer and the first conductor layer in the thickness direction to form the second insulating layer.

2. 2. The method for manufacturing a wired circuit board according to claim 1, wherein in the step of forming the second insulating layer, the film is pressure-bonded to the first insulating layer and the first conductor layer.

3. 3. The method for producing a wired circuit board according to claim 1, wherein the film includes an uncured photosensitive resin layer containing a polyamic acid resin.

4. The method for producing a wired circuit board according to claim 3 , wherein the film further includes an uncured photosensitive adhesive layer made of an adhesive.

5. The method for producing a wired circuit board according to claim 1 , further comprising the step of forming the first insulating layer from a coating film formed by applying a varnish or by screen printing a varnish.

6. A method for manufacturing a wired circuit board as described in Claim 5, wherein the coating film in the step of forming the first insulating layer contains a polyamic acid resin.

7. the wired circuit board further includes a third insulating layer disposed on one surface of the second insulating layer in a thickness direction so as to cover the second conductor layer, The method for producing a wired circuit board according to claim 1 , further comprising the step of forming the third insulating layer from a coating film formed by applying varnish.

8. A method for manufacturing a wired circuit board as described in Claim 7, wherein the coating film in the step of forming the third insulating layer contains a polyamic acid resin.

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