Flexible multilayer circuit board

Abstract

This flexible multilayer circuit board is provided with: an insulating layer having a hole for a conductive section; a conductor layer disposed on one surface of the insulating layer in the thickness direction; and a conduction part disposed in the conduction part hole and electrically connected to the conductor layer, the insulation layer having a porous insulation layer and a non-porous insulation layer in contact with the porous insulation layer and the conductor layer, the conduction part hole being formed in the porous insulation layer and the non-porous insulation layer, and the conduction part being disposed in the conduction part hole and electrically connected to the conductor layer. The outermost position (P) determined below is closer to the non-porous insulating layer side than the center of the porous insulating layer in the thickness direction, and in a cross-sectional view in the thickness direction, a line segment (S) connecting a first connection point (C1) at which one surface of the insulating layer is in contact with the side surface of the hole for the conductive part, and a second connection point (C2) at which the other surface is in contact with the side surface of the hole for the conductive part, are drawn. At the second connection point, a surface on the side opposite to the conductor layer side of the hole for the conduction part is in contact with a side surface of the hole for the conduction part, and an outermost position farthest from the line segment to the outside in the side surface of the hole for the conduction part is determined in cross-sectional view.

Description

Technical Field

[0001] This invention relates to flexible multilayer circuit boards. Background Technology

[0002] A wiring circuit board is known to have a first conductor layer, an insulating layer, and a second conductor layer sequentially in the thickness direction (see, for example, Patent Document 1). In the wiring circuit board described in Patent Document 1, the insulating layer has blind vias. The wiring circuit board also has conductive portions. The conductive portions are disposed in the insulating layer on the inner side facing the blind vias. In the wiring circuit board, the first conductor layer and the second conductor layer are electrically connected by the conductive portions.

[0003] In addition, a wiring circuit board with a specific length L is proposed, comprising: an insulating layer having a through hole extending along the thickness direction; a first conductor layer disposed on one side of the insulating layer in the thickness direction; a second conductor layer disposed on the other side of the insulating layer in the thickness direction; and a conductive portion disposed on the inner side of the through hole, which electrically connects the first conductor layer and the second conductor layer (see Patent Document 2).

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2019-123851 Patent Document 2: Japanese Patent Application Publication No. 2023-77787 Summary of the Invention

[0005] The problem that the invention aims to solve If the fit between the conductive portion and the side of the via in a wiring circuit board is poor, the conductive portion is prone to peeling off from the side of the via during reliability tests such as bending, high temperature and humidity tests, and temperature cycling tests. Therefore, a high fit between the conductive portion and the side of the via is required in wiring circuit boards.

[0006] Therefore, the object of the present invention is to provide a flexible multilayer circuit board having a conductive portion having high sealing performance relative to the via of the conductive portion.

[0007] Technical solutions for solving the problem The inventors of this invention conducted in-depth research to solve the above-mentioned problems, and as a result, found that the above-mentioned problems could be solved, thus completing the present invention with the following main points.

[0008] That is, the present invention includes the following.

[0009] [1] A flexible multilayer circuit board, comprising: An insulating layer having holes for conductive portions; A conductor layer disposed on one side of the insulating layer in the thickness direction; and A conductive portion, disposed in a hole for the conductive portion, and electrically connected to the conductor layer. The insulating layer comprises a porous insulating layer and a non-porous insulating layer in contact with the porous insulating layer and the conductor layer. The conductive portion is formed by holes in the porous insulating layer and the non-porous insulating layer. The outermost position P, as determined below, is located closer to the non-porous insulating layer than the center of the porous insulating layer in the thickness direction. The outermost position P is determined as follows: In a cross-sectional view along the thickness direction, a line segment S connecting the first connection point C1 and the second connection point C2 is drawn, where one surface of the insulating layer at the first connection point C1 is in contact with the side surface of the hole for the conductive portion, and at the second connection point C2, the side of the hole for the conductive portion opposite to the side surface of the conductive portion is in contact with the side surface of the hole for the conductive portion; in the cross-sectional view, the outermost position P, furthest from the line segment S, is determined from the side surface of the hole for the conductive portion.

[0010] [2] According to the flexible multilayer circuit board described in [1], wherein the length L measured below is 5 μm or more and 20 μm or less. The length L is determined as follows: the length L is measured as the shortest distance from the line segment S to the outermost position P.

[0011] [3] A flexible multilayer circuit board, comprising: An insulating layer having a first hole for a conductive portion and a second hole for a conductive portion; A first conductor layer is disposed on one side of the insulating layer in the thickness direction; A second conductor layer is disposed on the other side of the insulating layer in the thickness direction; A first conductive portion is disposed in a first hole for the conductive portion and is electrically connected to the first conductor layer; The second conductive portion is disposed in the second hole of the conductive portion and is electrically connected to the second conductor layer; and An interlayer connection portion is embedded in the insulating layer and electrically connects the first conductive portion and the second conductive portion. The lengths L1 and L2 measured below are both greater than 5 μm and less than 20 μm. The length L1 is measured as follows: In a cross-sectional view along the thickness direction, a line segment S1 connecting the first connection point C11 and the second connection point C12 is drawn. At the first connection point C11, one surface of the insulating layer is in contact with the side surface of the first hole of the conductive portion. At the second connection point C12, the side surface of the first hole of the conductive portion of the insulating layer is in contact with the surface of the first conductor layer of the interlayer connection portion. In this cross-sectional view, the outermost position P1, furthest from the side surface of the first hole of the conductive portion, is determined. The length L1 is measured as the shortest distance from the line segment S1 to the outermost position P1. The length L2 is measured as follows: In a cross-section along the thickness direction, a line segment S2 connecting the first connection point C21 and the second connection point C22 is drawn. At the first connection point C21, the other side of the insulating layer is in contact with the side of the second hole of the conductive portion. At the second connection point C22, the side of the second hole of the conductive portion of the insulating layer is in contact with the side of the second conductor layer of the interlayer connection. In the cross-section, the outermost position P2, which is furthest from the side of the second hole of the conductive portion, is determined. The length L2 is measured as the shortest distance from the line segment S2 to the outermost position P2.

[0012] [4] According to the flexible multilayer circuit board described in [3], wherein, The outermost position P1 is located in the thickness direction closer to the first conductor layer than it is near the interlayer connection. The outermost position P2 is located closer to the second conductor layer in the thickness direction than it is closer to the interlayer connection.

[0013] [5] The flexible multilayer circuit board according to [3] or [4], wherein, The insulating layer has an adhesive insulating layer, a first porous insulating layer disposed between the adhesive insulating layer and the first conductor layer, and a second porous insulating layer disposed between the adhesive insulating layer and the second conductor layer. The interlayer connection is embedded in the adhesive insulation layer.

[0014] Invention Effects According to the present invention, a flexible multilayer circuit board is provided having a conductive portion having high sealing performance relative to the via of the conductive portion. Attached Figure Description

[0015] Figure 1 This is a schematic cross-sectional view of one embodiment of a flexible multilayer circuit board.

[0016] Figure 2This is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board.

[0017] Figure 3A It is used for Figure 2 Figure (1) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0018] Figure 3B It is used for Figure 2 Figure 2 illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0019] Figure 3C It is used for Figure 2 Figure (3) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0020] Figure 3D It is used for Figure 2 Figure (4) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0021] Figure 3E It is used for Figure 2 Figure (5) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0022] Figure 3F It is used for Figure 2 Figure (6) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board.

[0023] Figure 3G It is used for Figure 2 Figure (7) illustrates one embodiment of the manufacturing method of a flexible multilayer circuit board. Detailed Implementation

[0024] (Flexible multilayer circuit board) The first embodiment of the flexible multilayer circuit board of the present invention includes an insulating layer, a conductor layer, and a conductive portion.

[0025] The insulating layer has holes for conducting parts.

[0026] The conductor layer is disposed on one face of the insulating layer in the thickness direction.

[0027] The conductive part is disposed in the conductive part hole. The conductive part is electrically connected to the conductor layer.

[0028] The insulating layer can be either porous or non-porous.

[0029] The non-porous insulating layer is in contact with the porous insulating layer and the conductor layer.

[0030] The conductive part is formed in both porous and non-porous insulating layers.

[0031] In the first embodiment, the outermost position P, as determined below, is located on the side of the non-porous insulating layer closer to the center in the thickness direction of the porous insulating layer.

[0032] The outermost position P is determined as follows: In a cross-sectional view along the thickness direction, draw the line segment S connecting the first connection point C1 and the second connection point C2. At the first connection point C1, one side of the insulating layer is in contact with the side of the hole for the conductive portion, and at the second connection point C2, the side of the hole for the conductive portion opposite to the conductor layer side is in contact with the side of the hole for the conductive portion. In the cross-sectional view, determine the outermost position P, which is furthest from the line segment S from the side of the hole for the conductive portion.

[0033] The determination of the outermost position P means that the length of the side of the hole for the conductive part is longer than the line segment S. By making the length of the side of the hole for the conductive part longer than the line segment S, the contact area between the side of the hole for the conductive part and the conductive part is increased, thereby improving the tightness of the conductive part relative to the hole for the conductive part.

[0034] Furthermore, since the outermost position P is located on the side of the non-porous insulating layer closer to the center in the thickness direction of the porous insulating layer, the non-porous insulating layer protrudes significantly in the center direction of the hole for the conductive portion in the insulating layer, and the non-porous insulating layer closes the periphery of the hole for the conductive portion. Therefore, it is expected that the sealing performance of the conductive portion filled in the hole for the conductive portion will be further improved.

[0035] These factors work together to produce a flexible multilayer circuit board with highly dense conductive parts.

[0036] It should be noted that when the center side of the hole for conducting part that is closer to the insulation layer than line segment S is set as the inner side of the hole for conducting part, and the side that is closer to the center side of the hole for conducting part that is closer to the insulation layer than line segment S is set as the outer side of the hole for conducting part, the outermost position P is located on the outer side of the hole for conducting part.

[0037] In the first embodiment, the longer the length L, as measured below, the higher the sealing performance of the conductive portion. On the other hand, if the length L is too long, poor formation of the conductive portion is likely to occur, and the connection reliability may be reduced. In this regard, the length L is preferably 1 μm or more and 20 μm or less, more preferably 5 μm or more and 20 μm or less.

[0038] Length L: The length L is measured as the shortest distance from line segment S to the outermost position P.

[0039] Figure 1 This is an example of a first embodiment of a flexible multilayer circuit board.

[0040] Figure 1 The flexible multilayer circuit board shown includes an insulating layer 1, a conductor layer 2, a conductive portion 3, and a second conductor layer 4.

[0041] The insulating layer 1 has a hole for conducting parts.

[0042] The conductor layer 2 is disposed on one surface of the insulating layer 1 in the thickness direction.

[0043] The conductive part 3 is disposed in the conductive hole. The conductive part 3 is electrically connected to the conductor layer 2. The conductive part 3 is also electrically connected to the second conductor layer 4. That is, the conductor layer 2 is electrically connected to the second conductor layer 4 via the conductive part 3.

[0044] The insulating layer 1 has a porous insulating layer 1b and a non-porous insulating layer 1a. The insulating layer 1 also has a non-porous insulating layer 1c and an adhesive insulating layer 1d.

[0045] The non-porous insulating layer 1a is in contact with the porous insulating layer 1b and the conductor layer 2.

[0046] The non-porous insulating layer 1c is in contact with the porous insulating layer 1b and the adhesive insulating layer 1d.

[0047] The adhesive insulating layer 1d is bonded to the non-porous insulating layer 1c and the second conductor layer 4.

[0048] The conductive portion has holes formed in the porous insulating layer 1b, the non-porous insulating layer 1a, the non-porous insulating layer 1c, and the adhesive insulating layer 1d.

[0049] The second conductor layer 4 is disposed on the other side of the insulating layer 1.

[0050] The outermost position P, as determined below, is located on the side of the non-porous insulating layer 1a, closer to the center of the porous insulating layer 1b in the thickness direction.

[0051] Outermost position P: In a cross-sectional view along the thickness direction, draw the line segment S connecting the first connection point C1 and the second connection point C2. At the first connection point C1, one surface of the insulating layer 1 is in contact with the side surface 1x of the hole for the conductive portion. At the second connection point C2, the surface s1 of the hole for the conductive portion, opposite to the side surface 2 of the conductor layer, is in contact with the side surface 1x of the hole for the conductive portion. In the cross-sectional view, determine the outermost position P, which is furthest from the line segment S along the side surface 1x of the hole for the conductive portion.

[0052] Figure 1 The flexible multilayer circuit board shown can be referenced Figure 2 The flexible multilayer circuit board shown is manufactured using this method.

[0053] A second embodiment of the flexible multilayer circuit board of the present invention includes an insulating layer, a first conductor layer, a second conductor layer, a first conductive portion, a second conductive portion, and an interlayer connection portion.

[0054] The insulating layer has a first hole for conducting portion and a second hole for conducting portion.

[0055] The first conductor layer is disposed on one face of the insulating layer in the thickness direction.

[0056] The second conductor layer is disposed on the other side of the insulation layer in the thickness direction.

[0057] The first conductive part is disposed in the first hole of the conductive part. The first conductive part is electrically connected to the first conductor layer.

[0058] The second conductive part is disposed in the second hole of the conductive part. The second conductive part is electrically connected to the second conductor layer.

[0059] The interlayer connection is embedded in the insulating layer. The interlayer connection electrically connects the first conductive part and the second conductive part.

[0060] In the second embodiment, the lengths L1 and L2 measured below are both 5 μm or more and 20 μm or less.

[0061] Length L1: In a cross-sectional view along the thickness direction, draw line segment S1 connecting the first connection point C11 and the second connection point C12. At the first connection point C11, one surface of the insulating layer is in contact with the side of the first hole of the conductive portion. At the second connection point C12, the side of the first hole of the insulating layer is in contact with the surface of the first conductor layer of the interlayer connection portion. In the cross-sectional view, determine the outermost position P1 furthest from the side of the first hole of the conductive portion along line segment S1. Measure the length L1 as the shortest distance from line segment S1 to the outermost position P1.

[0062] Length L2: In a cross-sectional view along the thickness direction, draw line segment S2 connecting the first connection point C21 and the second connection point C22. At the first connection point C21, the other side of the insulating layer is in contact with the side of the second hole of the conductive portion. At the second connection point C22, the side of the second hole of the insulating layer is in contact with the side of the second conductor layer of the interlayer connection portion. In the cross-section, determine the outermost position P2 furthest from the side of the second hole of the conductive portion. Measure the length L2 as the shortest distance from line segment S2 to the outermost position P2.

[0063] By making the side of the first hole of the conductive portion longer than the line segment S1, the contact area between the insulating layer and the first conductive portion is increased, thereby improving the sealing performance of the first conductive portion. Furthermore, by making L1 5 μm or more, the contact area between the insulating layer and the first conductive portion is further increased, and the sealing performance of the first conductive portion is further improved.

[0064] By making L1 less than 20μm, it is difficult to cause poor formation of the first conductive part, thus improving the connection reliability.

[0065] By making the side of the second hole of the conductive part longer than the line segment S2, the contact area between the insulating layer and the second conductive part is increased, thereby improving the sealing performance of the second conductive part. Furthermore, by making L2 5 μm or more, the contact area between the insulating layer and the second conductive part is further increased, and the sealing performance of the second conductive part is further improved.

[0066] By making L2 less than 20μm, it is difficult to cause poor formation of the first conductive part, thus improving the connection reliability.

[0067] When the flexible multilayer circuit board of the second embodiment, which has conductor layers on both sides, is bent, tensile stress is generated in one conductor layer (e.g., the first conductor layer) and compressive stress is generated in the other conductor layer (e.g., the second conductor layer). Even under such conditions, the flexible multilayer circuit board of the second embodiment of the present invention, which exhibits excellent adhesion of the conductive portions, is able to suppress interface delamination between the conductive portions and the conductor layers.

[0068] In the second embodiment, the outermost position P1 is preferably located in the thickness direction closer to the first conductor layer than to the interlayer connection portion. This results in a situation where the surface of the insulating layer adhering to the first conductor layer protrudes significantly in the center direction of the first hole for the conductive portion, and the surface of the insulating layer adhering to the first conductor layer closes the periphery of the first hole for the conductive portion. Therefore, it is expected that the sealing performance of the first conductive portion filling the first hole for the conductive portion will be further improved.

[0069] In the second embodiment, the outermost position P2 is preferably located closer to the second conductor layer in the thickness direction than the position near the interlayer connection. This results in a situation where the surface of the insulating layer adhering to the second conductor layer protrudes significantly in the center direction of the second hole for the conductive portion, and the surface of the insulating layer adhering to the second conductor layer closes the periphery of the second hole for the conductive portion. Therefore, it is expected that the sealing performance of the second conductive portion filling the second hole for the conductive portion will be further improved.

[0070] It should be noted that when the center side of the first hole for the conductive part closer to the insulating layer than line segment S1 is set as the inner side of the first hole for the conductive part, and the side of the first hole for the conductive part that is opposite to the center side of the first hole for the conductive part than line segment S1 is set as the outer side of the first hole for the conductive part, the outermost position P1 is located outside the first hole for the conductive part.

[0071] When the center side of the second hole for the conductive part closer to the insulating layer than line segment S2 is set as the inner side of the second hole for the conductive part, and the side of the second hole for the conductive part that is opposite to the center side of the second hole for the conductive part than line segment S2 is set as the outer side of the second hole for the conductive part, the outermost position P2 is located on the outer side of the second hole for the conductive part.

[0072] In the second embodiment, for example, the insulating layer includes an adhesive insulating layer, a first porous insulating layer disposed between the adhesive insulating layer and the first conductor layer, and a second porous insulating layer disposed between the adhesive insulating layer and the second conductor layer. Furthermore, the interlayer connection portion is embedded in the adhesive insulating layer.

[0073] The following is an explanation of each structure.

[0074] <Insulation layer> Materials used as the insulating layer include, for example, resins. The type of resin is not limited. Examples of resins include polycarbonate resins, polyimide resins, fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting polyurethane resins, fluororesins, and liquid crystal polymers. Polyimide resins and liquid crystal polymers are preferred.

[0075] The insulating layer can be a single-layer structure or a multi-layer structure.

[0076] The insulating layer may be, for example, a porous insulating layer (a porous insulating layer, a first porous insulating layer, and a second porous insulating layer).

[0077] The insulating layer may be, for example, a porous insulating layer and a non-porous insulating layer (a non-porous insulating layer, a first non-porous insulating layer, a second non-porous insulating layer, a third non-porous insulating layer, and a fourth non-porous insulating layer).

[0078] The insulating layer may, for example, be an adhesive insulating layer.

[0079] Materials used as porous or non-porous insulating layers include, for example, resins, which are used as insulating layer materials.

[0080] The porous insulation layer is porous. The porous insulation layer contains individual bubbles and / or continuous bubbles.

[0081] The porosity of the porous insulating layer is, for example, 50% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. It should be noted that the porosity of the porous insulating layer is, for example, less than 100%, and even more preferably 99% or less. When the material of the porous insulating layer is polyimide resin, the porosity of the porous insulating layer is calculated based on the following formula.

[0082] The relative permittivity of a porous insulating layer = the relative permittivity of air × porosity + the relative permittivity of polyimide × (1 - porosity) Here, the relative permittivity of air is 1, and the relative permittivity of polyimide resin is 3.5. Therefore, The relative permittivity of a porous insulating layer = porosity + 3.5(1 - porosity) Porosity (%) = [(3.5 - relative permittivity of porous insulating layer) / 2.5] × 100 The relative permittivity of the porous insulating layer at a frequency of 60 GHz is, for example, 2.5 or less, preferably 1.9 or less, more preferably 1.6 or less, and also, for example, greater than 1.0. The relative permittivity of the porous insulating layer is measured by using a resonator method at a frequency of 60 GHz.

[0083] The dielectric loss tangent of the porous insulating layer at a frequency of 60 GHz is, for example, less than 0.006, and even, for example, greater than 0. The dielectric loss tangent of the porous insulating layer is measured using a resonator method at a frequency of 60 GHz.

[0084] There are no particular limitations on the materials used for bonding and insulating layers. Various types of adhesives can be cited, such as hot melt adhesives and thermosetting adhesives. Specifically, examples include acrylic adhesives, epoxy adhesives, and silicone adhesives.

[0085] There are no particular limitations on the thickness of the insulating layer, for example, it is 5 μm or more, preferably 10 μm or more, and for example, it is 100 μm or less, preferably 80 μm or less.

[0086] <Conductor Layer> There are no particular limitations on the material used for the conductor layers (conductor layer, first conductor layer, second conductor layer), and examples include copper, iron, silver, gold, aluminum, nickel, and their alloys (e.g., stainless steel, bronze). Copper is a preferred material.

[0087] There are no particular limitations on the thickness of the conductor layer, for example, it is 5 μm or more, preferably 10 μm or more, and for example, it is 100 μm or less, preferably 80 μm or less.

[0088] <Conduction Section> There are no particular restrictions on the material used for the conductive parts (conductive part, first conductive part, second conductive part), and conductors can be used as examples. Examples of conductors include copper, iron, silver, gold, aluminum, nickel, and their alloys (e.g., stainless steel, bronze). Copper is preferred.

[0089] There are no particular limitations on the size of the conductive part, but the diameter is preferably 50 μm or more, more preferably 75 μm or more, and preferably 300 μm or less, more preferably 200 μm or less.

[0090] Interlayer connection section There are no particular restrictions on the material used for interlayer connections; examples include copper, iron, silver, gold, aluminum, nickel, and their alloys (such as stainless steel and bronze). Copper is a preferred material.

[0091] The thickness of the interlayer connection is not particularly limited, but it is, for example, 5 μm or more, preferably 10 μm or more, and preferably 100 μm or less, preferably 80 μm or less.

[0092] Figure 2 This is an example of a second embodiment of a flexible multilayer circuit board.

[0093] Figure 2 The flexible multilayer circuit board shown includes an insulating layer 11, a first conductor layer 12, a second conductor layer 13, a first conductive portion 14, a second conductive portion 15, and an interlayer connection portion 16.

[0094] The insulating layer 11 has a first hole for conducting portion and a second hole for conducting portion.

[0095] The first conductor layer 12 is disposed on one surface of the insulating layer 11 in the thickness direction.

[0096] The second conductor layer 13 is disposed on the other side of the insulating layer 11 in the thickness direction.

[0097] The first conductive part 14 is disposed in the first hole of the conductive part and is electrically connected to the first conductor layer 12.

[0098] The second conductive part 15 is disposed in the second hole of the conductive part and is electrically connected to the second conductor layer 13.

[0099] Interlayer connection 16 is embedded in insulating layer 11 and electrically connects first conductive part 14 and second conductive part 15.

[0100] The insulating layer 11 sequentially comprises a first non-porous insulating layer 11a, a first porous insulating layer 11b, a second non-porous insulating layer 11c, an adhesive insulating layer 11g, a fourth non-porous insulating layer 11f, a second porous insulating layer 11e, and a third non-porous insulating layer 11d.

[0101] Interlayer connection 16 is embedded in adhesive insulation layer 11g. Figure 2 In this process, the end of the interlayer connection 16 penetrates into the adhesive insulating layer 11g. As a result, the connection reliability of the interlayer connection is excellent.

[0102] The lengths L1 and L2 measured below are each greater than 5 μm and less than 20 μm.

[0103] Length L1: In a cross-sectional view along the thickness direction, draw line segment S1 connecting the first connection point C11 and the second connection point C12. At the first connection point C11, one surface of the insulating layer 11 is in contact with the side surface 11x of the first hole of the conductive portion. At the second connection point C12, the side surface 11x of the first hole of the conductive portion of the insulating layer 11 is in contact with the surface of the first conductor layer 12 of the interlayer connection portion 16. In the cross-sectional view, determine the outermost position P1 furthest from the line segment S1 along the side surface 11x of the first hole of the conductive portion. Measure the length L1 as the shortest distance from line segment S1 to the outermost position P1.

[0104] Length L2: In a cross-sectional view along the thickness direction, draw line segment S2 connecting the first connection point C21 and the second connection point C22. At the first connection point C21, the other side of the insulating layer 11 is in contact with the side surface 21x of the second hole of the conductive portion. At the second connection point C22, the side surface 21x of the second hole of the conductive portion of the insulating layer 11 is in contact with the side surface 21x of the second hole of the interlayer connection portion 16 on the side of the second conductor layer 13. In the cross-section, determine the outermost position P2 furthest from the line segment S2 along the side surface 21x of the second hole of the conductive portion. Measure the length L2 as the shortest distance from the line segment S2 to the outermost position P2.

[0105] Hereinafter, a manufacturing example of the second embodiment of the flexible multilayer circuit board will be described using the accompanying drawings.

[0106] Figures 3A to 3G It is used for Figure 2 A schematic diagram illustrating an example of manufacturing a flexible multilayer circuit board.

[0107] First, prepare a laminate consisting of a first conductive film 12A, a first non-porous insulating layer 11a, a first porous insulating layer 11b, a second non-porous insulating layer 11c, an adhesive insulating layer 11g-1, and a third conductive layer 16A, which are sequentially stacked. Figure 3A The material of the first conductor film 12A can be, for example, the same material used in the formation of the first conductive portion 14. Copper is preferred as such a material.

[0108] Next, the third conductor layer 16A is patterned using photolithography (e.g., subtractive method) with photoresist, thereby forming the interlayer connection portion 16. Figure 3B It should be noted that the interlayer connection portion 16 is formed as a quadrilateral shape when viewed from a direction orthogonal to the thickness direction.

[0109] Next, a laminated body is prepared by sequentially stacking the second conductive film 13A, the third non-porous insulating layer 11d, the second porous insulating layer 11e, the fourth non-porous insulating layer 11f, and the adhesive insulating layer 11g-2. Figure 3C The material of the second conductor film 13A can be, for example, the same material used in the formation of the conductor in the second conductive section 15. Copper is preferred as such a material.

[0110] Next, Figure 3B Layered bodies and Figure 3C The laminate prepared herein is configured with adhesive insulating layer 11g-1 and adhesive insulating layer 11g-2 facing each other, and the two adhesive resin layers are bonded together. Figure 3D ).

[0111] Thus, the two adhesive insulating layers are integrated to form adhesive insulating layer 11g, and a laminate having a first conductor film 12A, an insulating layer 11, and a second conductor film 13A sequentially from one side of the thickness direction to the other is obtained. Figure 3E The insulating layer 11 comprises, sequentially from one side of the thickness direction to the other, a first non-porous insulating layer 11a, a first porous insulating layer 11b, a second non-porous insulating layer 11c, an adhesive insulating layer 11g, a fourth non-porous insulating layer 11f, a second porous insulating layer 11e, and a third non-porous insulating layer 11d. At this time, the interlayer connection portion 16 is embedded in the adhesive insulating layer 11g.

[0112] Next, from one side in the thickness direction, a first hole 14A (via) for a conductive portion reaching the interlayer connection 16 is formed in the first conductive film 12A, the first non-porous insulating layer 11a, the first porous insulating layer 11b, the second non-porous insulating layer 11c, and the adhesive insulating layer 11g. From the other side in the thickness direction, a second hole 15A (via) for a conductive portion reaching the interlayer connection 16 is formed in the second conductive film 13A, the third non-porous insulating layer 11d, the second porous insulating layer 11e, the fourth non-porous insulating layer 11f, and the adhesive insulating layer 11g. Figure 3F ).

[0113] The conductive portion is formed by irradiating a first hole 14A and a second hole 15A with a laser. For example, the method described in Japanese Patent Application Publication No. 2023-77787 can be cited as a laser irradiation method.

[0114] When multiple holes for conductive parts exist, the process of forming each hole can be divided into steps, and the holes can be formed alternately. For example, after the first hole 14A for conductive parts is formed halfway through, the second hole 15A for conductive parts is formed halfway through. Then, after the first hole 14A for conductive parts is formed to the end, the second hole 15A for conductive parts is formed to the end. As a result, compared with the case of forming a single hole continuously, the heat damage during hole-making can be reduced.

[0115] Examples of lasers include YAG lasers and carbon dioxide gas lasers. The laser irradiation process can be single or multiple; from the viewpoint of high manufacturing efficiency and achieving a good via shape, two irradiation processes are preferred. That is, the processes of forming the first via 14A for the conductive portion and the second via 15A for the conductive portion respectively include a first irradiation process and a second irradiation process sequentially.

[0116] Here, the energy density in the second irradiation step is lower than the energy density in the first irradiation step. In the first irradiation step, holes need to be formed in the conductor films (first conductor film 12A and second conductor film 13A), so laser irradiation is performed with a relatively high energy density. On the other hand, the energy density when forming holes in the insulating layer can be lower than the energy density when forming holes in the conductor film, so the energy density is reduced in the second irradiation step. In the first irradiation step, when holes are formed in the conductor film, the insulating layer near the conductor film is also irradiated with a relatively high energy density laser, so the holes in the insulating layer near the conductor film become larger. On the other hand, when a non-porous insulating layer and a porous insulating layer are sequentially stacked from the side in contact with the conductor film, since the non-porous insulating layer is less ablated by the laser than the porous insulating layer, the holes in the non-porous insulating layer near the conductor film become smaller than the holes in the porous insulating layer. As a result, a Figure 3F The conductive portion, as shown, uses a first hole 14A and a second hole 15A. In other words, in Figure 2 In the middle, the outermost position P1 is located closer to the first conductor layer 12 in the thickness direction than the interlayer connection portion 16, and the outermost position P2 is located closer to the second conductor layer 13 in the thickness direction than the interlayer connection portion 16.

[0117] The energy density in the first irradiation process is, for example, 1 J / cm³. 2 The above is preferably 10 J / cm. 2 The above, in addition, for example, is 20J / cm 2 The preferred value is 18 J / cm. 2The following applies. If the energy density in the first irradiation process is above or below the aforementioned lower limit, manufacturing efficiency can be improved. If the energy density in the first irradiation process is below or below the aforementioned upper limit, the lengths L1 and L2 can be controlled to be below or below the aforementioned upper limit, and the first hole 14A and the second hole 15A for the conductive portion can be tapered.

[0118] The energy density in the second irradiation process is, for example, lower than the energy density in the first irradiation process. By making the energy density of the second irradiation process lower than the energy density of the first irradiation process, each layer up to the adhesive insulating layer 11g can be removed while retaining the interlayer connection portion 16.

[0119] Specifically, the ratio of the energy density in the second irradiation step to the energy density in the first irradiation step is, for example, 0.01 or more, preferably 0.02 or more, and also, for example, 0.4 or less, preferably 0.1 or less. Specifically, the energy density in the second irradiation step is, for example, 0.01 J / cm³. 2 The above, in addition, for example, is 0.1 J / cm 2 the following.

[0120] In the processes of forming the first hole 14A and the second hole 15A for the conductive portion, the following methods are used: an irradiation method in which the laser rotates from the inside to the outside while being observed along the thickness direction; and an irradiation method in which the laser rotates from the outside to the inside while being observed. The number of rotations is multiple. Preferably, the laser rotates from the inside to the outside while being observed along the thickness direction. With this irradiation method, the point of maximum energy during laser irradiation exists on the wall of the hole for the first half of the irradiation time, thus enabling the side of the insulating layer to appear tapered when its cross-section is observed macroscopically.

[0121] Next, the conductive portions of the first conductive film 12A, the first non-porous insulating layer 11a, the first porous insulating layer 11b, the second non-porous insulating layer 11c, and the adhesive insulating layer 11g are plated with the first hole 14A and the surface of the first conductive film 12A. Thus, a conductor is filled into the conductive portion through the first hole 14A, forming the first conductive portion 14. Furthermore, the first conductive film 12A and the plating layer 12B on the first conductive film 12A become integral, forming the first conductive layer 12.

[0122] Furthermore, the conductive portions of the second conductive film 13A, the third non-porous insulating layer 11d, the second porous insulating layer 11e, the fourth non-porous insulating layer 11f, and the adhesive insulating layer 11g are plated with the second hole 15A and the surface of the second conductive film 13A. Thus, a conductor is filled into the conductive portion through the second hole 15A, forming the second conductive portion 15. Additionally, the second conductive film 13A and the plating layer 13B on the second conductive film 13A become integrated to form the second conductive layer 13. Figure 3G ).

[0123] Through the above steps, we obtain Figure 2 The flexible multilayer circuit board shown.

[0124] Symbol Explanation 1: Insulation layer 1a: Non-porous insulating layer 1b: Porous insulating layer 1c: Non-porous insulating layer 1d: Adhesive insulation layer 1x: Side view 2: Conductor layer 3: Conductor section 4: Second conductor layer 11: Insulation layer 11a: First non-porous insulating layer 11b: First porous insulating layer 11c: Second non-porous insulating layer 11d: Third non-porous insulating layer 11e: Second porous insulating layer 11f: Fourth non-porous insulating layer 11g: Adhesive insulation layer 11g-1: Adhesive insulation layer 11g-2: Adhesive insulation layer 11x: Side view 12: First conductor layer 12A: First Conductor Film 12B: Coating 13: Second conductor layer 13A: Second conductor film 13B: Coating 14: First Conductor Section 14A: First hole for conductive part 15: Second Conductor 15A: Second hole for conductive part 16: Interlayer connection section 16A: Third conductor layer 21x: Side view C1: First connection point C2: Second connection point C11: First connection point C12: Second connection point C21: First connection point C22: Second connection point P: Outermost position P1: Outermost position P2: Outermost position S: line segment S1: Line segment S2: Line segment s1: surface.

Claims

1. A flexible multilayer circuit substrate comprising: an insulating layer having a via hole; a conductor layer disposed on one face in a thickness direction of the insulating layer; and a via disposed in the via hole and electrically connected to the conductor layer, wherein the insulating layer has a porous insulating layer and a non-porous insulating layer that is in contact with the porous insulating layer and the conductor layer, the via hole is formed in the porous insulating layer and the non-porous insulating layer, an outermost position P determined as follows is located on a side of the non-porous insulating layer than a center of the thickness direction of the porous insulating layer, the outermost position P is determined as follows: in a cross section in the thickness direction, a line segment S connecting a first connection point Cl at which a side face of the via hole is in contact with the one face of the insulating layer and a second connection point C2 at which a side face of the via hole is in contact with a face on a side opposite to the conductor layer of the via hole is drawn, and an outermost position P farthest outward from the line segment S on the side face of the via hole is determined in the cross section, and a length L determined as follows is 5 μm or more and 20 μm or less, the length L is determined as a shortest distance from the line segment S to the outermost position P.

3. A flexible multilayer circuit substrate comprising: an insulating layer having a first via hole and a second via hole; a first conductor layer disposed on one face in a thickness direction of the insulating layer; a second conductor layer disposed on another face in the thickness direction of the insulating layer; a first via disposed in the first via hole and electrically connected to the first conductor layer; a second via disposed in the second via hole and electrically connected to the second conductor layer; and an interlayer connection portion embedded in the insulating layer and electrically connecting the first via and the second via, wherein a length LI and a length L2 determined as follows are each 5 μm or more and 20 μm or less, the length LI is determined as follows: in a cross section in the thickness direction, a line segment SI connecting a first connection point Cl l at which a side face of the first via hole is in contact with the one face of the insulating layer and a second connection point C12 at which a side face of the first via hole of the insulating layer is in contact with a face on a side of the first conductor layer of the interlayer connection portion is drawn, an outermost position Pl farthest outward from the line segment SI on the side face of the first via hole is determined in the cross section, and the length LI is determined as a shortest distance from the line segment SI to the outermost position Pl, and the length L2 is determined as follows: in the cross section in the thickness direction, a line segment S2 connecting a first connection point C21 at which a side face of the second via hole is in contact with the one face of the insulating layer and a second connection point C22 at which a side face of the second via hole is in contact with a face on a side of the second conductor layer of the interlayer connection portion is drawn, an outermost position P2 farthest outward from the line segment S2 on the side face of the second via hole is determined in the cross section, and the length L2 is determined as a shortest distance from the line segment S2 to the outermost position P2. ​ ​ ​ ​ ​ ​ 2. The flexible multilayer circuit substrate according to claim 1, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The length L2 is measured as follows: in a cross section in the thickness direction, a line segment S2 is drawn connecting the first connection point C21 at which the other face of the insulating layer and the side face of the second hole for the conduction part are continuous, and the second connection point C22 at which the side face of the second hole for the conduction part of the insulating layer and the face of the second conductor layer side of the interlayer connection part are continuous; in the cross section, the outermost position P2 is determined which is farthest from the line segment S2 outward of the side face of the second hole for the conduction part; and the length L2 is measured as the shortest distance from the line segment S2 to the outermost position P2.

4. The flexible multilayer circuit substrate according to claim 3, wherein the outermost position P1 is located closer to the first conductor layer than to the interlayer connection part in the thickness direction, the outermost position P2 is located closer to the second conductor layer than to the interlayer connection part in the thickness direction.

5. The flexible multilayer circuit substrate according to claim 3, wherein the insulating layer has a bonding insulating layer, a first porous insulating layer disposed between the bonding insulating layer and the first conductor layer, and a second porous insulating layer disposed between the bonding insulating layer and the second conductor layer, the interlayer connection part is embedded in the bonding insulating layer.

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