US-20260129754-A1 - CIRCUIT BOARD AND METHOD OF MANUFACTURING CIRCUIT BOARD

Abstract

A circuit board includes a fluororesin layer, an adherend layer and an adhesion layer bonding the fluororesin layer and the adherend layer together, the fluororesin layer contains polytetrafluoroethylene and a first inorganic filler, a content of the first inorganic filler in the fluororesin layer is 50% by volume to 66% by volume, the adhesion layer contains a resin and a second inorganic filler, a content of a fluororesin in the resin is 5% by mass or less, a content of the second inorganic filler in the adhesion layer is 29% by volume to 47% by volume, and a through-hole extending through the fluororesin layer and the adhesion layer is formed.

Inventors

• Shingo Kaimori
• Satoshi KIYA
• Hiroshi Ueda
• Motohiko SUGIURA
• Eiko Imazaki

Assignees

• SUMITOMO ELECTRIC INDUSTRIES, LTD.
• SUMITOMO ELECTRIC PRINTED CIRCUITS, INC.

Dates

Publication Date

20260507

Application Date

20230904

Priority Date

20221007

Claims (20)

1. 1 . A circuit board comprising: a fluororesin layer; an adherend layer; and an adhesion layer bonding the fluororesin layer and the adherend layer together, wherein the fluororesin layer contains polytetrafluoroethylene and a first inorganic filler, a content of the first inorganic filler in the fluororesin layer is 50% by volume to 66% by volume, the adhesion layer contains a resin and a second inorganic filler, a content of a fluororesin in the resin is 5% by mass or less, a content of the second inorganic filler in the adhesion layer is 29% by volume to 47% by volume, and a through-hole extending through the fluororesin layer and the adhesion layer is formed.
2. 2 . The circuit board according to claim 1 , wherein the first inorganic filler contains silica.
3. 3 . The circuit board according to claim 1 , wherein the second inorganic filler contains silica.
4. 4 . The circuit board according to claim 1 , wherein the second inorganic filler contains boron nitride.
5. 5 . The circuit board according to claim 1 , wherein at least one of an inner wall surface of the fluororesin layer defining a part of the through-hole and an inner wall surface of the adhesion layer defining a part of the through-hole has a scooped part, and the scooped part has a length of less than 25 μm.
6. 6 . The circuit board according to claim 1 , wherein the adhesion layer has a ratio A/B of an elastic modulus A at 160° C. to an elastic modulus B at 20° C. of 0.08 or less.
7. 7 . The circuit board according to claim 1 , wherein the resin contains a polyolefin or a polystyrene-based elastomer.
8. 8 . The circuit board according to claim 1 , wherein the adherend layer includes a first metal layer and a first resin layer, and the first metal layer is disposed on a surface of the first resin layer facing the fluororesin layer.
9. 9 . The circuit board according to claim 1 ; wherein the adherend layer includes a first metal layer and a first resin layer, and the first resin layer is disposed on a surface of the first metal layer facing the fluororesin layer.
10. 10 . The circuit board according to claim 8 , wherein the fluororesin layer has a first main surface facing the adhesion layer and a second main surface opposite to the first main surface, and the circuit board further comprises a second metal layer disposed on the second main surface.
11. 11 . The circuit board according to claim 10 , further comprising a connecting portion electrically connecting the first metal layer and the second metal layer to each other, wherein the connecting portion is formed in the through-hole.
12. 12 . The circuit board according to claim 10 , wherein, when viewed from a direction perpendicular to the second main surface, the first metal layer is formed in a region overlapping the through-hole.
13. 13 . The circuit board according to claim 10 , wherein, when viewed from a direction perpendicular to the first main surface, the second metal layer is formed in a region overlapping the through-hole.
14. 14 . A method of manufacturing the circuit board according to claim 1 , the method comprising: holding a laminate in which the fluororesin layer, the adhesion layer, and the adherend layer are stacked in this order at a temperature of 180° C. or lower to soften the adhesion layer, thereby bonding the fluororesin layer and the adherend layer together.
15. 15 . A method of manufacturing a circuit board, the method comprising: preparing a fluororesin laminate including a fluororesin layer having a first main surface and a second main surface opposite to the first main surface, and a second metal layer disposed on the second main surface; preparing a first resin laminate including a first resin layer having a third main surface and a fourth main surface opposite to the third main surface, and a first metal layer disposed on the third main surface; preparing an adhesion layer; forming a first laminate by stacking the fluororesin laminate, the adhesion layer, and the first resin laminate in this order such that the first main surface is in contact with the adhesion layer and holding the adhesion layer at a temperature of 180° C. or lower to soften the adhesion layer, thereby bonding the fluororesin laminate and the first resin laminate together; removing at least a part of the fluororesin layer and at least a part of the adhesion layer to form a through-hole extending through the fluororesin layer and the adhesion layer; and forming a connecting portion on an inner wall surface of the fluororesin layer defining a part of the through-hole and an inner wall surface of the adhesion layer defining a part of the through-hole, wherein the fluororesin layer contains polytetrafluoroethylene and a first inorganic filler, a content of the first inorganic filler in the fluororesin layer is 50% by volume to 66% by volume, the adhesion layer contains a resin and a second inorganic filler, a content of a fluororesin in the resin is 5% by mass or less, and a content of the second inorganic filler in the adhesion layer is 29% by volume to 47% by volume.
16. 16 . The method of manufacturing a circuit board according to claim 15 , wherein the preparing the first resin laminate further includes forming a first circuit on the first resin laminate by etching at least a part of the first metal layer.
17. 17 . The method of manufacturing a circuit board according to claim 15 , wherein the preparing the fluororesin laminate further includes forming a second circuit on the fluororesin laminate by etching at least a part of the second metal layer.
18. 18 . The method of manufacturing a circuit board according to claim 15 , wherein the forming the first laminate further includes forming a second circuit on the fluororesin laminate by etching at least a part of the second metal layer.
19. 19 . The method of manufacturing a circuit board according to claim 15 , wherein the through-hole is formed by laser processing.
20. 20 . The method of manufacturing a circuit board according to claim 15 , wherein at least one of the inner wall surface of the fluororesin layer and the inner wall surface of the adhesion layer has a scooped part, and the scooped part has a length of less than 25 μm.

Description

TECHNICAL FIELD The present disclosure relates to a circuit board and a method of manufacturing a circuit board. The present application claims priority based on Japanese Patent Application No. 2022-162209 filed on Oct. 7, 2022, and the entire contents of the Japanese patent application are incorporated herein by reference. BACKGROUND ART In order to improve high-frequency characteristics of printed circuit boards, studies have been conducted on the use of a fluororesin layer containing a fluororesin, such as polytetrafluoroethylene, and an inorganic filler, such as silica, as a dielectric layer (PTL 1). To stack a board (circuit board) on which circuits have been formed by processing a metal layer of a substrate, and another substrate or another circuit board, a bonding sheet is used. For example, a circuit board, a bonding sheet, and another substrate are stacked in this order and then heated until the bonding sheet is softened. In the state where the bonding sheet is softened, the bonding sheet is deformed by applying a pressure. The circuit board and the other substrate are bonded together while gaps between circuits are filled with the bonding sheet (PTL 2). CITATION LIST Patent Literature PTL 1: International Publication No. 2021/235276PTL 2: Japanese Unexamined Patent Application Publication No. 2016-27131 SUMMARY OF INVENTION A circuit board according to the present disclosure includes: a fluororesin layer;an adherend layer; andan adhesion layer bonding the fluororesin layer and the adherend layer together,wherein the fluororesin layer contains polytetrafluoroethylene and a first inorganic filler,a content of the first inorganic filler in the fluororesin layer is 50% by volume to 66% by volume.the adhesion layer contains a resin and a second inorganic filler,a content of a fluororesin in the resin is 5% by mass or less,a content of the second inorganic filler in the adhesion layer is 29% by volume to 47% by volume, anda through-hole extending through the fluororesin layer and the adhesion layer is formed. A method of manufacturing a circuit board according to the present disclosure is a method of manufacturing the above circuit board, the method including: holding a laminate in which the fluororesin layer, the adhesion layer, and the adherend layer are stacked in this order at a temperature of 180° C. or lower to soften the adhesion layer, thereby bonding the fluororesin layer and the adherend layer together. A method of manufacturing a circuit board according to the present disclosure includes: preparing a fluororesin laminate including a fluororesin layer having a first main surface and a second main surface opposite to the first main surface, and a second metal layer composed of a metal and disposed on the second main surface;preparing a first resin laminate including a first resin layer having a third main surface and a fourth main surface opposite to the third main surface, and a first metal layer disposed on the third main surface;preparing an adhesion layer;forming a first laminate by stacking the fluororesin laminate, the adhesion layer, and the first resin laminate in this order such that the first main surface is in contact with the adhesion layer and holding the adhesion layer at a temperature of 180° C. or lower to soften the adhesion layer, thereby bonding the fluororesin laminate and the first resin laminate together;removing at least a part of the fluororesin layer and at least a part of the adhesion layer to form a through-hole extending through the fluororesin layer and the adhesion layer; andforming a connecting portion on an inner wall surface of the fluororesin layer defining a part of the through-hole and an inner wall surface of the adhesion layer defining a part of the through-hole,wherein the fluororesin layer contains polytetrafluoroethylene and a first inorganic filler,a content of the first inorganic filler in the fluororesin layer is 50% by volume to 66% by volume,the adhesion layer contains a resin and a second inorganic filler,a content of a fluororesin in the resin is 5% by mass or less, anda content of the second inorganic filler in the adhesion layer is 29% by volume to 47% by volume. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic cross-sectional view of a circuit board according to Embodiment 1. FIG. 2A is a view illustrating a method of manufacturing a circuit board according to Embodiment 2. FIG. 2B is a view illustrating the method of manufacturing a circuit board according to Embodiment 2. FIG. 2C is a view illustrating the method of manufacturing a circuit board according to Embodiment 2. FIG. 3 is a schematic cross-sectional view of a circuit board according to Embodiment 3. FIG. 4A is a view illustrating a method of manufacturing a circuit board according to Embodiment 3. FIG. 4B is a view illustrating the method of manufacturing a circuit board according to Embodiment 3. FIG. 4C is a view illustrating the method of manufacturing a circuit board accordin