Multilayer boards and electronic devices

Abstract

This multilayer substrate (101) is configured by stacking layers including a plurality of conductor layer-formed resin layers each of which is obtained by forming a conductor layer on a main surface of a resin layer. The conductor layer-formed resin layers each comprise a first conductor layer-formed resin layer (31) in which a first conductor layer is formed on one main surface, and a second conductor layer-formed resin layer (32) in which a second conductor layer is formed on one main surface. At least a part of the first conductor layer is a signal line (24), and at least a part of the second conductor layer is a GND electrode (23). When viewed in the stacking direction, the multilayer substrate has a cavity part (CA) in which the resin of the resin layer is absent in a region including a position where the signal line (24) overlaps the first conductor layer-formed resin layer (31), thereby exposing the signal line (24), and the thickness of the signal line (24) in the cavity part (CA) is less than the thickness of the first conductor layer at positions other than the cavity part (CA).

Description

[Technical Field]

[0001] The present invention relates to a multilayer substrate having a cavity and an electronic device including the multilayer substrate. [Background technology]

[0002] A high-speed transmission board using a flex board made of copper foil and a resin insulating substrate is disclosed, for example, in Patent Document 1. This high-speed transmission board is a laminated board having high-speed transmission signal wiring and a substrate surrounded by an air layer, and uses a flex board as a laminate unit board having a structure in which an adhesive made of a thermoplastic resin is applied between the copper foil and the resin insulating substrate and on the underside of the resin insulating substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-118361 Summary of the Invention [Problem to be solved by the invention]

[0004] The laminated substrate disclosed in Patent Document 1 requires an adhesive layer to ensure the adhesion of the copper foil. However, the surface of copper foil is generally roughened to improve adhesion, but at high frequencies, the roughness increases the skin resistance, resulting in increased transmission loss.

[0005] Therefore, an object of the present invention is to provide a multilayer substrate in which the signal line passes through a cavity, i.e., the signal line is partially in contact with the cavity, and in which the high-frequency characteristics of the signal line in the cavity where the signal line is not supported are improved, and an electronic device equipped with this multilayer substrate. [Means for solving the problem]

[0006] (1) An example of a multilayer substrate according to the present disclosure includes: a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the stacking direction, there is a hollow portion in the first conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the signal line is exposed; The thickness of the signal line in the cavity is thinner than the thickness of the first conductor layer outside the cavity.

[0007] (2) An example of a multilayer substrate according to the present disclosure includes: a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the lamination direction, there is a hollow portion in the second conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the GND electrode is exposed; The thickness of the GND electrode in the cavity is thinner than the thickness of the GND electrode outside the cavity.

[0008] (3) An example of an electronic device according to the present disclosure is a device including the multilayer substrate and a processing unit that processes a high-frequency signal propagating through the multilayer substrate. [Effects of the Invention]

[0009] According to the multilayer substrate of the present invention, in a multilayer substrate having a structure in which a signal line partially contacts a cavity portion, a multilayer substrate in which the high-frequency characteristics of the signal line in the cavity portion where the signal line is not supported can be improved, and an electronic device equipped with this multilayer substrate can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1A, 1B, and 1C are cross-sectional views of conductor layers that form part of a multilayer substrate according to a first embodiment. [Figure 2] 2A, 2B, 2C, and 2D are cross-sectional views of the multilayer substrate according to the first embodiment at different stages in the manufacturing process. [Figure 3] 3A and 3B are cross-sectional views of a multilayer substrate 101 according to the first embodiment. [Figure 4] 4A, 4B, 4C, and 4D are cross-sectional views of the multilayer substrate according to the second embodiment at different stages in the manufacturing process. [Figure 5] 5(A) and 5(B) are cross-sectional views of a multilayer substrate 102 according to the second embodiment. [Figure 6] 6(A), 6(B), 6(C), and 6(D) are cross-sectional views of the multilayer substrate according to the third embodiment at various stages in the manufacture thereof. [Figure 7] 7A and 7B are cross-sectional views of a multilayer substrate 103 according to the third embodiment. [Figure 8] 8(A), 8(B), 8(C), and 8(D) are cross-sectional views of the multilayer substrate according to the fourth embodiment at various stages in the manufacture thereof. [Figure 9] 9(A) and 9(B) are cross-sectional views of a multilayer substrate 104 according to the fourth embodiment. [Figure 10] 10(A) and 10(B) are cross-sectional views of a multilayer substrate 105 according to the fifth embodiment. [Figure 11] 11(A) and 11(B) are cross-sectional views of a multilayer substrate 106 according to the sixth embodiment. [Figure 12]12(A) and 12(B) are cross-sectional views of a multilayer substrate 107 according to the seventh embodiment. [Figure 13] 13(A) and 13(B) are cross-sectional views of a multilayer substrate 108 according to the eighth embodiment. [Figure 14] 14(A) and 14(B) are cross-sectional views of a multilayer substrate 109 according to the ninth preferred embodiment. [Figure 15] FIG. 15 is a block diagram showing the configuration of an electronic device 201 according to the ninth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A multilayer substrate according to a first aspect of the present invention is a multilayer substrate including a plurality of conductor-layer-forming resin layers, each having a conductor layer formed on a main surface of the resin layer, and optionally including a layer of a single resin layer that does not include a conductor layer. The conductor-layer-forming resin layer includes a first conductor-layer-forming resin layer having a first conductor layer formed on one main surface, and a second conductor-layer-forming resin layer having a second conductor layer formed on one main surface. At least a portion of the first conductor layer is a signal line, and at least a portion of the second conductor layer is a GND electrode. When viewed in the stacking direction, there is no resin in the resin layer in a region of the first conductor-layer-forming resin layer that includes a position where the signal line overlaps, and the signal line The thickness of the signal line in the cavity is formed thinner by etching or the like than the thickness of the first conductor layer outside the cavity.

[0012] A second aspect of the present invention provides a multilayer substrate including a plurality of conductor-layer-forming resin layers, each having a conductor layer formed on a main surface of the resin layer, and optionally including a single resin layer without a conductor layer. The conductor-layer-forming resin layers include a first conductor-layer-forming resin layer having a first conductor layer formed on one main surface and a second conductor-layer-forming resin layer having a second conductor layer formed on one main surface. At least a portion of the first conductor layer is a signal line, and at least a portion of the second conductor layer is a GND electrode. When viewed in the stacking direction, the resin layer is absent in a region of the second conductor-layer-forming resin layer that includes a position where the signal line overlaps, forming a cavity that exposes the GND electrode. The thickness of the GND electrode in the cavity is formed thinner by etching or the like than the thickness of the GND electrode outside the cavity.

[0013] First Embodiment Figure 1(A), Figure 1(B), Figure 1(C) )teeth 1A, 1B, and 1C are cross-sectional views of a conductor layer constituting a part of a multilayer substrate according to a first embodiment. In Fig. 1A, 1B, and 1C, the conductor layer 2 is, for example, a copper foil, and has one main surface 2R and the other main surface 2S. However, hatching has been omitted in these figures.

[0014] FIG. 1(A) shows a cross-sectional view of the conductor layer 2 before processing (initial state), with one main surface 2R being a rough surface and the other main surface 2S being a smooth surface.

[0015] FIG. 1(B) is a cross-sectional view of the conductor layer 2 in a state where the surface is smoothed to some extent, with one main surface 2R having a rough surface that has been smoothed to some extent, and the other main surface 2S having a smooth surface.

[0016] 1(C) is a cross-sectional view of the conductor layer 2 in a state where the conductor layer 2 is further smoothed, and both the one principal surface 2R and the other principal surface 2S have smoothed surfaces. The conductor layer 2 is, for example, a copper foil.

[0017] As will be described later, the one main surface 2R and the other main surface 2S in the above state are effectively used.

[0018] 2(A), 2(B), 2(C), and 2(D) are cross-sectional views of the multilayer substrate according to this embodiment at various stages in its manufacture. FIG. 2(D) is a cross-sectional view of the completed manufacturing process. Note that in FIGS. 2(A), 2(B), 2(C), and 2(D), the rough surface, which is one of the principal surfaces of each resin layer, is shown with a simple array of protrusions. Furthermore, the smooth surface, which is the other principal surface of each resin layer, is shown with a simple straight line.

[0019] The multilayer substrate 101 of this embodiment shown in Figure 2(D) comprises one resin layer 1D, 1E on which no conductor layer is formed, as shown in Figure 2(A), one first conductor layer-forming resin layer 31 on which a conductor layer is formed, and two second conductor layer-forming resin layers 32.

[0020] The multilayer substrate 101 is manufactured as follows.

[0021] 2(A), the layers before lamination include a resin layer 1E, a lower second-conductor-layer-forming resin layer 32, a first-conductor-layer-forming resin layer 31, an upper second-conductor-layer-forming resin layer 32, and a resin layer 1D. The first-conductor-layer-forming resin layer 31 is a layer in which a signal line 24 and a GND electrode 25 are formed on a resin layer 1A. The upper second-conductor-layer-forming resin layer 32 is a layer in which a GND electrode 23 is formed on a resin layer 1B. Similarly, the lower second-conductor-layer-forming resin layer 32 is a layer in which a GND electrode 23 is formed on a resin layer 1C.

[0022] Next, as shown in Fig. 2(B), resin removal portions 1AR are formed in multiple locations on resin layer 1A. Resin removal portions 1BR are formed in multiple locations on resin layer 1B. Similarly, resin removal portions 1CR are formed in multiple locations on resin layer 1C. These resin removals are performed by forming a resist mask pattern in the locations where resin removal is not to be performed, and then immersing the layer in, for example, an alkaline solution or by irradiating it with laser light.

[0023] Next, the signal line 24 and the GND electrode 25 of one of the first conductor layer-forming resin layers 31 shown in FIG. 2(B) are etched. The GND electrodes 23 of the two second conductor layer-forming resin layers 32 shown in FIG. 2(B) are also etched. For example, the copper foil surface is treated with a soft etching acid solution. At this time, it is possible to remove the roughened portions of the copper foil and the anti-corrosion layer. This smooths the surface of the signal line 24 (reducing the roughness), as shown in FIG. 2(C). During this etching process, one main surface of the GND electrode 25 remains embedded in the resin layer 1A, so the bonding strength between the one main surface of the GND electrode 25 and the resin layer 1A is not reduced.

[0024] Next, the GND electrodes 23 of the two second conductor layer-forming resin layers 32 shown in Fig. 2(B) are etched. As a result, as shown in Fig. 2(C), the GND electrodes 23C in the hollow portions of the GND electrodes 23 in the portions opened by the resin-removed portions 1BR of the resin layer 1B are smoothed (their surface roughness is reduced).

[0025] The surfaces of the GND electrodes 23 and 25 may be coated to suppress oxidation of the electrodes. Similarly, the surfaces of the signal wires 24 may be coated to suppress oxidation of the signal wires 24. For example, gold plating or water-soluble preflux treatment may be performed. Furthermore, the surfaces of the signal wires 24 and the GND electrodes 23 and 25 may be oxidized to form a copper oxide film on the surfaces.

[0026] Note that a corrosion prevention treatment may be applied to the surface of the signal line 24 that is exposed in the area that will later become the cavity CA. Similarly, a corrosion prevention treatment may be applied to the surface of the GND electrode 23 that is exposed in the area that will later become the cavity CA. Examples of such corrosion prevention treatments include gold plating, water-soluble preflux treatment, and oxidation treatment.

[0027] Next, interlayer connection conductors 4 are embedded in the resin-removed portions 1AR, 1BR, and 1CR shown in Fig. 2(C), and all layers are stacked and heated as shown in Fig. 2(D) to form multilayer substrate 101. For example, before heating, interlayer connection conductors 4 are made of conductive paste or solder paste. Alternatively, through holes may be drilled with the layers stacked, and copper plating may be applied to the inside of these through holes to form interlayer connection conductors 4.

[0028] 3(A) and 3(B) are cross-sectional views of the multilayer substrate 101 according to this embodiment. Fig. 3(A) is a cross-sectional view of the multilayer substrate 101 in the same completed state as that shown in Fig. 2(D). Fig. 3(B) is a cross-sectional view of the multilayer substrate 101 in the XZ plane. Fig. 3(B) is a cross-sectional view of the multilayer substrate 101 in the YZ plane.

[0029] 3(A) and 3(B), the signal line 24 extends in the Y direction. Similarly, the GND electrodes 23 and 25 also extend in the Y direction. In this example, the GND electrode 25 extends in the Y direction like the GND electrode 23, but the GND electrode 25 can also be formed only on the interlayer connection conductor portion.

[0030] 3(A) provides electrical continuity between the upper and lower GND electrodes 23 via the GND electrode 25. In this way, a coaxial line is formed by surrounding the periphery of the signal line 24 with the GND electrodes 23 and 25. The interlayer connection conductors 4 are arranged at predetermined intervals in the extension direction of the signal line 24. These intervals are narrow enough that electromagnetic waves in the frequency band of the high-frequency signal propagating through the coaxial line hardly leak sideways (in the X direction).

[0031] According to this embodiment, the following effects are achieved.

[0032] (1) The GND electrodes 23, 25 (copper foil) pressed and adhered to the resin layers 1A, 1B, 1C, respectively, are highly roughened, so that the adhesive strength between the resin portion and the copper foil is high.

[0033] (2) The area of ​​the GND electrode 23 exposed in the cavity CA and the area of ​​the signal line (copper foil) 24 exposed in the cavity CA are only slightly roughened, resulting in low skin resistance and low high-frequency transmission loss of the signal line 24. In particular, the roughening of the signal line 24 has a greater effect on transmission loss than the GND electrode 23.

[0034] (3) The roughened portion of the copper foil can be easily removed by etching.

[0035] (4) When a nickel layer is formed on the surface of copper foil as an anti-rust layer (anti-corrosion layer), the high electrical resistance of the nickel layer can cause transmission loss problems. However, the nickel layer can be removed by the etching process described above, which also reduces transmission loss.

[0036] (5) Although the portion of the GND electrode 23 that is in the cavity CA is exposed to the air in the cavity CA, the roughening of the GND electrode 23 (copper foil) is small. Therefore, the contact area with the air in the cavity CA is small, and the oxidation speed of the GND electrode 23 is slow.

[0037] (6) By etching the signal line 24 and reducing its thickness, the distance between the signal line 24 and the GND electrode 23 is increased. Paradoxically, even if the distance between the signal line 24 and the GND electrode 23 is narrowed, high high-frequency characteristics can be maintained due to the smooth surfaces of the signal line 24 and the GND electrode 23. Therefore, narrowing the distance between the signal line 24 and the GND electrode 23 allows for the construction of a thin multilayer substrate. Even if the signal line 24 is thinned by etching, the resistance value of the signal line 24 can be reduced by widening the line width of the signal line 24. This reduces transmission loss. Furthermore, by setting the line width of the signal line 24, a transmission line with a predetermined characteristic impedance can be easily obtained.

[0038] (7) By coating the surfaces of the GND electrodes 23 and 25 and / or the surfaces of the signal lines 24, or by forming an oxide film thereon, it is possible to suppress deterioration of electrical characteristics over time.

[0039] Second Embodiment In the second embodiment, a multilayer substrate in which the area of ​​the GND electrode 23 exposed in the cavity CA is roughened to a smaller extent is shown.

[0040] Figure 4(A), Figure 4(B), Figure 4(C), Figure 4(D) is the multilayer substrate according to this embodiment. At each stage of manufacturing 4(D) is a cross-sectional view of the multilayer substrate 102 according to this embodiment.

[0041] The manufacturing method of the multilayer substrate 102 is almost the same as that of the multilayer substrate 101 shown in the first embodiment. The state in Figures 4(A) and 4(B) is the same as that shown in Figures 2(A) and 2(B). In the step shown in Figure 4(C), the GND electrodes 23 of the two second conductor layer-forming resin layers 32 shown in Figure 4(B) are First embodiment 4C, the GND electrode 23C in the cavity of the GND electrode 23 in the portion opened by the resin removed portion 1BR of the resin layer 1B is made thinner (the surface roughness is reduced). This strong etching also makes the signal line 24 thinner.

[0042] The other configurations are the same as those of the multilayer substrate 101 shown in the first embodiment.

[0043] 5(A) and 5(B) are cross-sectional views of the multilayer substrate 102 according to this embodiment. FIG. 5(A) is a cross-sectional view of the multilayer substrate 102 in the same completed state as that shown in FIG. 4(D). It is a cross-sectional view on the XZ plane. FIG. 5(B) is a cross-sectional view on the YZ plane. The structure of the multilayer substrate 101 according to this embodiment is similar to that of the multilayer substrate 101 shown in FIGS. 3(A) and 3(B) in the first embodiment, but the GND electrode 23C exposed in the cavity CA is more strongly etched, GND electrode 23C The surface of the signal line 24 is smoother (less rough) than that of the first embodiment. Also, this strong etching makes the signal line 24 thinner.

[0044] According to the second embodiment, the area of ​​the GND electrode 23 exposed in the cavity CA and the signal line (copper foil) 24 are only slightly roughened, resulting in a small skin resistance and low high-frequency transmission loss of the signal line 24. Furthermore, since the thickness inside the cavity can be increased, a thinner multilayer board can be constructed.

[0045] Third Embodiment In the third embodiment, a multilayer substrate in which the roughened surface of the GND electrode is different from the examples shown in the first and second embodiments will be illustrated.

[0046] Figure 6(A), Figure 6(B), Figure 6(C), Figure 6(D) is the multilayer substrate according to this embodiment. At each stage of manufacturing 6(B) and 6(C), resin layers 1A, 1B, and 1C forming GND electrodes 23 and 25 have openings at locations where interlayer connection conductors 4 are to be formed. FIG. 6(D) is a cross-sectional view of multilayer substrate 103 according to this embodiment.

[0047] The method for manufacturing the multilayer substrate 103 is almost the same as that for the multilayer substrate 101 shown in the first embodiment. The method for manufacturing the multilayer substrate 103 is as follows.

[0048] First, as shown in FIG. 6(A), as the layers before lamination, a resin layer 1 C , the resin layer 1 on which the lower GND electrode 23 is formed E , a resin layer 1A on which a signal line 24 and a GND electrode 25 are formed, a resin layer 1F, and a resin layer 1B on which an upper GND electrode 23 is formed. D and resin layer 1 B Equipped with.

[0049] In this embodiment, the roughened surface of the GND electrode 23 is on the surface that is not exposed in the cavity CA shown in Fig. 6(D) The other configurations are the same as those of the multilayer substrates 101 and 102 according to the first and second embodiments.

[0050] 7(A) and 7(B) are cross-sectional views of the multilayer substrate 103 according to this embodiment. Fig. 7(A) is a cross-sectional view of the multilayer substrate 103 in the same completed state as that shown in Fig. 6(D). Fig. 7(B) is a cross-sectional view of the multilayer substrate 103 in the XZ plane. Fig. 7(B) is a cross-sectional view of the multilayer substrate 103 in the YZ plane.

[0051] According to this embodiment, the GND electrode 23 has high adhesion to the resin layers 1D and 1E, resulting in a stronger adhesion of the surface resin layer compared to the first and second embodiments. Furthermore, since the smooth side of the copper foil of the GND electrode 23 is originally located on the signal line 24 side, the surface resistance is small even without etching, resulting in good high-frequency characteristics. In other words, since there is no need to etch the GND electrode 23, characteristic degradation due to poor etching is unlikely to occur.

[0052] As in the second embodiment, if the GND electrodes 23 and 25 and the signal line 24 are heavily etched, the thickness inside the cavity can be increased, which may lead to a thinner device and improved high frequency characteristics.

[0053] Fourth Embodiment In the fourth embodiment, a multilayer substrate without a cavity below the signal lines will be exemplified.

[0054] Figure 8(A), Figure 8(B), Figure 8(C), Figure 8(D) is the multilayer substrate according to this embodiment. At each stage of manufacturing 8(D) is a cross-sectional view of the multilayer substrate 104 according to this embodiment.

[0055] The method for manufacturing the multilayer substrate 104 is almost the same as that for the multilayer substrate 101 shown in the first embodiment. The method for manufacturing the multilayer substrate 104 is as follows.

[0056] First, as shown in FIG. 8(A), the layers before lamination include a resin layer 1E, a resin layer 1C on which a lower GND electrode 23 is formed, a resin layer 1A on which a signal line 24 and a GND electrode 25 are formed, a resin layer 1B on which an upper GND electrode 23 is formed, and a resin layer 1D.

[0057] In this embodiment, the signal line 24 remains attached to the resin layer 1A at the stage shown in Fig. 8(B) The other configurations are the same as those of the multilayer substrates 101 and 102 according to the first and second embodiments.

[0058] 9(A) and 9(B) are cross-sectional views of the multilayer substrate 104 according to this embodiment. Fig. 9(A) is a cross-sectional view of the multilayer substrate 104 in the same completed state as that shown in Fig. 8(D). Fig. 9(B) is a cross-sectional view of the multilayer substrate 104 in the XZ plane. Fig. 9(B) is a cross-sectional view of the multilayer substrate 104 in the YZ plane.

[0059] According to this embodiment, the roughened surface of the signal line 24 remains, but the resin layer 1A on which the signal line is formed remains, so that a multilayer substrate having high strength overall can be obtained.

[0060] Fifth Embodiment The fifth embodiment differs from the fourth embodiment in that a multilayer substrate in which the roughened surface of the signal line faces the cavity portion is exemplified.

[0061] 10(A) and 10(B) are cross-sectional views of a multilayer substrate 105 according to this embodiment. Fig. 10(A) is a cross-sectional view taken along the XZ plane, and Fig. 10(B) is a cross-sectional view taken along the YZ plane.

[0062] This multilayer substrate 105 includes a resin layer 1E, a lower GND electrode 23, a resin layer 1C, a signal line 24 and a GND electrode 25, a resin layer 1A, a resin layer 1F, an upper GND electrode 23, a resin layer 1B, and a resin layer 1D.

[0063] According to this embodiment, the surface (both surfaces) of the signal line 24 do not need to be roughened.

[0064] Sixth Embodiment In the sixth embodiment, a multilayer substrate having a cavity formation structure different from that of the embodiments shown so far will be illustrated.

[0065] 11(A) and 11(B) are cross-sectional views of the multilayer substrate 106 according to this embodiment. Fig. 11(A) is a cross-sectional view of the multilayer substrate 106 taken along the XZ plane, and Fig. 11(B) is a cross-sectional view of the multilayer substrate 106 taken along the YZ plane.

[0066] This multilayer substrate 106 includes a resin layer 1E, a lower GND electrode 23, resin layers 1C and 1A, a signal line 24 and a GND electrode 25, a resin layer 1F, a resin layer 1B, an upper GND electrode 23, and a resin layer 1D.

[0067] In this way, a cavity CA may be formed in which resin layers are present on the top, bottom, left, and right sides of the inner surface. With this structure, the GND electrode 23 is not exposed in the cavity but is covered with resin, and only the signal line 24 can be made less rough on the electrode in the cavity, allowing for a thinner thickness.

[0068] Seventh Embodiment In the specific examples described above, the configuration of the transmission line portion of a stripline is shown, but in the seventh embodiment, a multilayer substrate in which a transmission line of a microstripline is configured will be illustrated.

[0069] 12(A) and 12(B) are cross-sectional views of the multilayer substrate 107 according to this embodiment. Fig. 12(A) is a cross-sectional view taken along the XZ plane, and Fig. 11(B) is a cross-sectional view taken along the YZ plane.

[0070] Multilayer substrate 107 of this embodiment is configured using resin layers 1A, 1C, and 1E shown in Fig. 8(A) in the fourth embodiment, for example. In other words, multilayer substrate 106 of this embodiment is a multilayer substrate configured by laminating resin layers 1A, 1C, and 1E shown in Fig. 8(C).

[0071] According to this embodiment, an overall thinner multilayer substrate including microstrip lines can be obtained.

[0072] Eighth Embodiment In the eighth embodiment, a multilayer substrate will be exemplified in which necessary layers are bonded together via an adhesive layer and a material different from the base material is used for the surface layer of the laminate.

[0073] 13(A) and 13(B) are cross-sectional views of the multilayer substrate 108 according to this embodiment. Fig. 13(A) is a cross-sectional view taken along the XZ plane, and Fig. 13(B) is a cross-sectional view taken along the YZ plane.

[0074] In this embodiment, the resin layer 1A on which the signal line 24 and the GND electrode 25 are formed and the resin layer 1B on which the GND electrode 23 is formed are bonded together via an adhesive layer 5. Similarly, the resin layer 1C on which the GND electrode 23 is formed and the resin layer 1A are bonded together via an adhesive layer 5.

[0075] In this embodiment, a resist layer 6 made of a material different from the base material is formed on the surface of the laminate.

[0076] According to this embodiment, there is no need to self-adhere the resin layers, which makes processing easier. Furthermore, there is no need for high-temperature, high-pressure press processing, which can prevent deformation of the cavity. Furthermore, a material different from the base material of the laminate can be used for the surface layer of the laminate, which makes it easy to form the solder resist layer.

[0077] Ninth Embodiment In the ninth embodiment, a multilayer substrate having a different laminate structure of conductor layer-forming resin layers from the embodiments shown so far will be exemplified.

[0078] 14(A) and 14(B) are cross-sectional views of multilayer substrate 109 according to this embodiment. Fig. 14(A) is a cross-sectional view of multilayer substrate 109 taken along the XZ plane, and Fig. 14(B) is a cross-sectional view of multilayer substrate 109 taken along the YZ plane.

[0079] The multilayer substrate 109 includes resin layers 1A, 1B, 1C, 1G, and 1H, a lower GND electrode 23, an upper GND electrode 23, a signal line 24, a GND electrode 25, an interlayer connection conductor 4, and a resist layer 6.

[0080] A signal line 24 and a GND electrode 25 are formed on the upper surface of resin layer 1A. An upper GND electrode 23 is formed on the upper surface of resin layer 1B, and a lower GND electrode 23 is formed on the lower surface of resin layer 1H. A GND electrode 25 is formed on the upper surface of resin layer 1C, and a GND electrode 25 is formed on the lower surface of resin layer 1G.

[0081] In this manner, a conductor layer is formed on one surface of each of the resin layers 1A, 1B, 1C, 1G, and 1H. The surfaces of the resin layer 1A and the resin layer 1G that do not have a conductor layer are joined together.

[0082] 14(B), in this example, both surfaces of the signal line 24 exposed in the cavity CA are thinned by etching, polishing, grinding, etc. By using such a shape, the signal line 24 exposed in the cavity CA may be thinned.

[0083] 13, a resist layer 6 made of a material different from the substrate is formed on the surface of the laminate. This structure protects the upper GND electrode 23 and the lower GND electrode 23 and electrically insulates them.

[0084] Tenth Embodiment In the tenth embodiment, an electronic device according to the present invention will be illustrated.

[0085] Figure 15 teeth 1 is a block diagram showing the main configuration of an electronic device according to this embodiment. This electronic device 201 includes a transmitting / receiving circuit and an antenna, and a transmission line is provided between this transmitting / receiving circuit and the antenna. The transmitting / receiving circuit is an example of a "processing unit that processes high-frequency signals." The transmission line in this electronic device 201 is formed from a multilayer substrate according to the present invention, and is formed from the multilayer substrate shown in each of the first to seventh embodiments. A high-frequency signal in the 1 GHz to 1 THz band, for example, is propagated through this transmission line.

[0086] Finally, the present invention is not limited to the above-described embodiments. Those skilled in the art can make appropriate modifications and variations. The scope of the present invention is defined not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention includes modifications and variations from the embodiments within the scope of the claims and their equivalents.

[0087] For example, although the interlayer connection conductors 4 are located at the same positions above and below the GND electrode 25 in each embodiment, they may be located at different positions (shifted positions).

[0088] For example, although each embodiment has been described with respect to a single transmission line portion, the present invention can be similarly applied to a multi-layer substrate having a plurality of transmission lines.

[0089] The multilayer substrate and electronic device of the present invention may be provided in the following aspects.

[0090] <1> a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the stacking direction, there is a hollow portion in the first conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the signal line is exposed; a thickness of the signal line in the cavity portion is smaller than a thickness of the first conductor layer outside the cavity portion; Multilayer board.

[0091] <2> a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the lamination direction, there is a hollow portion in the second conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the GND electrode is exposed; the thickness of the GND electrode in the cavity is thinner than the thickness of the GND electrode outside the cavity; Multilayer board.

[0092] <3> the surface roughness of the signal line in the cavity is smaller than the surface roughness of the first conductor layer and the second conductor layer outside the cavity; <1> The multilayer substrate according to claim 1.

[0093] <4> the surface roughness of the GND electrode in the cavity is smaller than the surface roughness of the second conductor layer outside the cavity; <2> The multilayer substrate according to claim 1.

[0094] <5> a corrosion prevention layer is formed on the surface of the signal line that is exposed to the cavity portion of the signal line; <1> or <3> The multilayer substrate according to claim 1.

[0095] <6> a corrosion prevention layer is formed on the surface of the GND electrode that is exposed to the cavity portion; <2> or <4> The multilayer substrate according to claim 1.

[0096] <7> an interlayer connection conductor that electrically connects the first conductor layer and the second conductor layer; the first conductor layer-forming resin layer, the second conductor layer-forming resin layer, the GND electrode, and the signal line By The frequency band of the signal propagating through the configured stripline or microstripline is a high-frequency signal in the 1 GHz to 1 THz band. <1> from <6> 10. The multilayer substrate according to claim 9, wherein

[0097] <8> <7> and a processing unit that processes the high-frequency signal propagating through the multilayer substrate. [Explanation of symbols]

[0098] CA…Cavity part 1A,1B,1C,1D,1E,1F,1G,1H…Resin layer 1AR, 1BR, 1CR...Resin removal section 2...Conductor layer 2R…One main surface 2S...other main surface 4...Interlayer connecting conductor 5...Adhesive layer 6...Resist layer 23,23C,25…GND electrode 24...Signal line 31...First conductor layer forming resin layer 32...Second conductor layer forming resin layer 101,102,103,104,105,106,107,108...Multilayer board 201…Electronic equipment

Claims

1. a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the stacking direction, there is a hollow portion in the first conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the signal line is exposed; a thickness of the signal line in the cavity portion is smaller than a thickness of the first conductor layer outside the cavity portion; Multilayer board.

2. a multilayer substrate formed by laminating layers including a plurality of conductor-layer-forming resin layers, each of which has a conductor layer formed on a main surface of a resin layer; the conductor layer-forming resin layer includes a first conductor layer-forming resin layer having a first conductor layer formed on one main surface thereof, and a second conductor layer-forming resin layer having a second conductor layer formed on one main surface thereof, At least a portion of the first conductor layer is a signal line, At least a part of the second conductor layer is a GND electrode, When viewed in the stacking direction, there is a hollow portion in the second conductor layer-forming resin layer where the resin layer is absent in a region including a position where the signal line overlaps, and the GND electrode is exposed, the thickness of the GND electrode in the cavity is thinner than the thickness of the GND electrode outside the cavity; Multilayer board.

3. a surface roughness of the signal line in the cavity portion is smaller than a surface roughness of the first conductor layer and the second conductor layer other than the cavity portion; The multilayer substrate according to claim 1 .

4. a surface roughness of the GND electrode in the cavity portion is smaller than a surface roughness of the second conductor layer other than the cavity portion; The multilayer substrate according to claim 2 .

5. a corrosion prevention layer is formed on the surface of the signal line that is exposed to the cavity portion of the signal line; The multilayer substrate according to claim 1 or 3.

6. a corrosion prevention layer is formed on a surface of the GND electrode that is exposed to the cavity; The multilayer substrate according to claim 2 or 4.

7. an interlayer connection conductor that electrically connects the first conductor layer and the second conductor layer; a frequency band of a signal propagating through a stripline or a microstripline constituted by the first conductor layer-forming resin layer, the second conductor layer-forming resin layer, the GND electrode, and the signal line is a high-frequency signal in the 1 GHz to 1 THz band; The multilayer substrate according to any one of claims 1 to 4.

8. An electronic device comprising: the multilayer substrate according to claim 7; and a processing unit that processes the high-frequency signal propagating through the multilayer substrate.

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