High-frequency substrate

Abstract

This high-frequency substrate is provided with: a first laminate in which a first conductive layer and a first resin layer are laminated; a second laminate in which a second conductive layer and a second resin layer are laminated, the second laminate being disposed so as to face the first laminate; a first via hole; the first laminated body is provided with a conductive pattern, the conductive pattern is provided with a signal line and a grounding layer, the bottom surface of the first via hole is in contact with the grounding layer, the first conductive layer is conducted with the grounding layer through the first via hole, the bottom surface of the second via hole is in contact with the grounding layer, and the second conductive layer is conducted with the grounding layer through the second via hole; the first resin layer and the second resin layer are mainly composed of a resin having a linear expansion coefficient of 20 ppm / K or more at 20-120 DEG C. The first conductive layer has a first opening portion in a peripheral region of an opening of the first via hole, and the second conductive layer has a second opening portion in a peripheral region of an opening of the second via hole.

Description

Technical Field

[0001] This disclosure relates to high-frequency substrates. This application claims priority based on Japanese Application No. 2023-036979, filed on March 9, 2023, and incorporates the entire contents of that Japanese application. Background Art

[0002] High-frequency substrates are used as substrates for transmitting high-frequency signals, digital signals, etc. To prevent noise and crosstalk, shielded high-frequency substrates with stripline structures, microstrip structures, etc., are used. These stripline and microstrip structures are structures in which signal lines are arranged on one side of the dielectric layer.

[0003] In printed circuit boards (substrates) that transmit electrical signals, if the frequency of the transmitted electrical signal increases, the dielectric loss caused by the insulating material around the conductor increases. To address this, it has been proposed to use fluoropolymer resin with a small dielectric constant and dielectric loss tangent as the insulating material around the conductor in printed circuit boards (see Patent Document 1).

[0004] Existing technical documents

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-165171 Summary of the Invention

[0007] One aspect of this disclosure relates to a high-frequency substrate comprising: a first laminate having a first conductive layer and a first resin layer laminated thereon; a second laminate having a second conductive layer and a second resin layer laminated thereon and configured to face the first laminate; an adhesive layer for bonding the first resin layer and the second resin layer; a first via formed on the inner periphery and bottom of one or more connecting holes penetrating the first resin layer in the thickness direction; and a second via formed on the inner periphery and bottom of one or more connecting holes penetrating the second resin layer and the adhesive layer in the thickness direction. The first laminate has a conductive pattern laminated on the surface of the first resin layer facing the second laminate, and the conductive pattern is... An adhesive layer is embedded, and the conductive pattern has signal lines and ground lines arranged to sandwich the two sides of the signal lines. The bottom surface of the first via is in contact with the ground layer, and the first via connects the first conductive layer to the ground layer. The bottom surface of the second via is in contact with the ground layer, and the second via connects the second conductive layer to the ground layer. The first resin layer and the second resin layer are mainly composed of resin with a linear expansion coefficient of 20 ppm / K or more at 20°C to 120°C. The first conductive layer has a first opening in the peripheral region of the opening of the first via, and the second conductive layer has a second opening in the peripheral region of the opening of the second via. Attached Figure Description

[0008] Figure 1 This is a schematic partial perspective view illustrating a high-frequency substrate according to an embodiment of the present disclosure.

[0009] Figure 2 This is a schematic partial top view illustrating an embodiment of the high-frequency substrate of the present disclosure.

[0010] Figure 3 It is shown Figure 2 Cross-sectional view of the III-III direction.

[0011] Figure 4 It is shown Figure 2 A cross-sectional view of the IV-IV direction.

[0012] Figure 5 This is a schematic partial top view illustrating an embodiment of the high-frequency substrate of the present disclosure.

[0013] Figure 6 This is a schematic partial top view illustrating another embodiment of the high-frequency substrate of this disclosure.

[0014] Figure 7 This is a schematic partial top view illustrating another embodiment of the high-frequency substrate of this disclosure.

[0015] Figure 8This is a schematic partial cross-sectional view illustrating a high-frequency substrate according to another embodiment of the present disclosure.

[0016] Figure 9 This is a schematic partial cross-sectional view illustrating a high-frequency substrate according to another embodiment of the present disclosure.

[0017] Figure 10 This is a schematic partial bottom view illustrating another embodiment of the high-frequency substrate of this disclosure.

[0018] Figure 11 This is a schematic partial cross-sectional view showing the high-frequency substrate of Embodiment 1.

[0019] Figure 12 This is a schematic partial cross-sectional view showing the high-frequency substrate of Comparative Example 1. DETAILED DESCRIPTION

[0020] [The technical problem this disclosure aims to solve]

[0021] In recent years, with the miniaturization of electronic devices, there has been a desire to increase the wiring density of substrates, leading to the use of multilayer printed circuit boards (PCBs) with multiple conductive layers. In such PCBs, vias (cylindrical conductors) are formed to connect the different conductive layers. However, when using resins with excellent high-frequency characteristics but a high coefficient of linear expansion, such as fluoropolymers, the dimensional changes in the thickness direction between conductive layers become significant under environments with large temperature variations, such as thermal shock tests. This can potentially cause cracking in the conductive plating layer on the inner wall of the via due to localized stress, compromising the electrical connection reliability of the high-frequency substrate.

[0022] This disclosure is made in light of the fact that the purpose is to provide a high-frequency substrate that can reduce the stress applied to vias even when using a resin with a large coefficient of linear expansion.

[0023] [The Effects of This Disclosure]

[0024] According to this disclosure, a high-frequency substrate can be provided that reduces the stress applied to vias even when using a resin with a large coefficient of linear expansion.

[0025] [Description of embodiments of this disclosure]

[0026] First, embodiments of this disclosure will be described.

[0027] (1) A high-frequency substrate according to one aspect of this disclosure comprises: a first laminate having a first conductive layer and a first resin layer laminated thereon; a second laminate having a second conductive layer and a second resin layer laminated thereon and configured to face the first laminate; an adhesive layer for bonding the first resin layer and the second resin layer; a first via formed on the inner periphery and bottom of one or more connecting holes penetrating the first resin layer in the thickness direction; and a second via formed on the inner periphery and bottom of one or more connecting holes penetrating the second resin layer and the adhesive layer in the thickness direction, wherein the first laminate has a conductive pattern laminated on the surface of the first resin layer facing the second laminate, and the conductive pattern is coated with a conductive pattern on the surface of the first resin layer facing the second laminate. The adhesive layer is embedded, the conductive pattern has signal lines and ground lines arranged to sandwich the two sides of the signal lines, the bottom surface of the first via is in contact with the ground layer, the first via connects the first conductive layer and the ground layer, the bottom surface of the second via is in contact with the ground layer, the second via connects the second conductive layer and the ground layer, the first resin layer and the second resin layer are mainly composed of resin with a linear expansion coefficient of 20 ppm / K or more at 20°C to 120°C, the first conductive layer has a first opening in the peripheral region of the opening of the first via, and the second conductive layer has a second opening in the peripheral region of the opening of the second via.

[0028] If a resin with a high coefficient of linear expansion (e.g., 20 ppm / K or higher) is used as the main component resin of the resin layer in a high-frequency substrate, the dimensional changes in the thickness direction between conductive layers can easily become large under environments with rapid temperature changes between high and low temperatures. This can lead to cracking due to localized stress on the conductive plating layer inside the vias, impairing the electrical connection reliability of the high-frequency substrate. In the high-frequency substrate disclosed herein, a first via connecting a first conductive layer to a ground layer and a second via connecting a second conductive layer to a ground layer are provided. The first conductive layer has a first opening in the peripheral region of the opening of the first via, and the second conductive layer has a second opening in the peripheral region of the opening of the second via. Therefore, even if the high-frequency substrate is used in environments with large temperature fluctuations, such as thermal shock tests, and the resin undergoes thermal expansion, the stress generated by the thermally expanded resin is dispersed through the first and second openings. Consequently, the stress locally applied to the conductive plating layer inside the vias is reduced. Therefore, cracking in the conductive plating layer on the inner wall of the via can be suppressed. Consequently, in the high-frequency substrate of this disclosure, even when using a resin with a large coefficient of linear expansion relative to temperature changes, the stress applied to the via can be reduced, and the high-frequency substrate exhibits high resistance to thermal shock testing. This improves the electrical connection reliability of the high-frequency substrate.

[0029] Here, "coefficient of linear expansion" refers to the linear expansion rate in the thickness direction measured according to the test method for dynamic mechanical properties described in JIS-K7244-4 (1999). It is calculated based on the dimensional change of the sheet relative to temperature change under the tensile mode in thermomechanical analysis (TMA) within a temperature range of 20°C to 120°C, with a heating rate of 5°C / min, a frequency of 10Hz, and a strain of 0.05%. The principal component refers to the component with the highest content in the substance constituting the resin layer. For example, "principal component" refers to a component with a content exceeding 50% by mass. "The peripheral region of the opening of the first through-hole" means the region where, when viewed from above, the ratio of the distance from the opening end of the first through-hole to the average diameter of the opening of the first through-hole is 2 or less. Similarly, "the peripheral region of the opening of the second through-hole" means the region where, when viewed from above, the ratio of the distance from the opening end of the second through-hole to the average diameter of the opening of the second through-hole is 2 or less.

[0030] (2) In (1) above, at least one of the first conductive layer and the second conductive layer may further have a third opening, which is disposed in the first conductive layer at a position indirectly opposite to the bottom surface of the second via and in the second conductive layer at a position indirectly opposite to the bottom surface of the first via. Because at least one of the first conductive layer and the second conductive layer has a third opening, the stress generated by the thermally expanded resin is more dispersed, and the stress locally applied to the conductive plating layer on the inner wall of the via is further reduced. Therefore, cracking in the conductive plating layer on the inner wall of the via can be further suppressed. Consequently, the electrical connection reliability of the high-frequency substrate can be further improved.

[0031] [Description of embodiments of this disclosure]

[0032] Hereinafter, with reference to the accompanying drawings, various embodiments of the high-frequency substrate involved in this disclosure will be described in detail.

[0033] <High Frequency Substrate>

[0034] The high-frequency substrate 50 is suitable for use as a wiring substrate for high-frequency transmission. (See reference...) Figure 1 and Figure 2 The high-frequency substrate 50 includes a first laminate 1, an adhesive layer 3, a second laminate 2 disposed opposite to the first laminate 1 through the adhesive layer 3, one or more first vias 4, and one or more second vias 5. It should be noted that the vias in this disclosure can also be blind vias.

[0035] The lower limit of the average thickness of the high-frequency substrate 50 can be 110 μm, 120 μm, or 130 μm. The upper limit of the average thickness of the high-frequency substrate 50 can be 450 μm, 440 μm, or 430 μm. By keeping the average thickness of the high-frequency substrate 50 within the above ranges, sufficient transmission bandwidth and desired flexibility can be obtained.

[0036] [First layer of stacked material]

[0037] The first laminate 1 includes a first resin layer 12, a first conductive layer 11, and a conductive pattern 10. In the first laminate 1, the first conductive layer 11 is laminated with the first resin layer 12. The conductive pattern 10 is laminated on the surface of the first resin layer 12 opposite to the second laminate 2.

[0038] (First resin layer)

[0039] The first resin layer 12 is a resin layer on which the conductive pattern 10 is stacked. The first resin layer 12 is mainly composed of a resin with a coefficient of linear expansion of 20 ppm / K or more at 20°C to 120°C. By using a resin with a coefficient of linear expansion of 20 ppm / K or more at 20°C to 120°C as the main component of the first resin layer 12, the high-frequency characteristics of the high-frequency substrate 50 are excellent. When the coefficient of linear expansion of the main component resin of the first resin layer 12 is 20 ppm / K or more at 20°C to 120°C, the dimensional changes in the thickness direction between conductive layers tend to increase under environments with large temperature variations, such as thermal shock tests. As a result, stress is easily applied locally to the conductive plating layer on the inner wall of the via, thus the effects of this disclosure are achieved. The upper limit of the coefficient of linear expansion of the main component resin of the first resin layer 12 at 20°C to 120°C can also be 500 ppm / K. By making the coefficient of linear expansion of the main component resin of the first resin layer 12 500 ppm / K or less, the electrical connection reliability is good.

[0040] (The main component of the first resin layer)

[0041] Specifically, fluoropolymers can be listed as the main component resin of the first resin layer 12. Examples of such fluoropolymers include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-perfluorodioxanecyclopentene copolymer (TFE / PDD).

[0042] The main resin component of the first resin layer 12 can also be FEP or PTFE. In the high-frequency substrate 50, the conductive pattern 10 (signal line 13 and ground layer 14) is disposed between the first resin layer 12 and the second resin layer 21. Fluoropolymers generally tend to have low dielectric loss tangent (tanδ) and low relative permittivity (εr). By using fluoropolymers as the main component of the first resin layer 12 and the second resin layer 21, the transmission loss of the conductive pattern 10 (especially the signal line 13) can be sufficiently reduced, and sufficient transmission speed can be obtained. Therefore, it is not necessary to thicken the first resin layer 12 and the second resin layer 21 to improve transmission characteristics. The first resin layer 12 and the second resin layer 21 can be made thinner.

[0043] The first resin layer 12 may also contain sheet-like reinforcing material. By incorporating sheet-like reinforcing material into the first resin layer 12, linear expansion is suppressed in both the thickness and planar directions. Therefore, dimensional stability can be improved, and the temperature dependence of electrical properties, such as the relative permittivity, can be reduced.

[0044] As sheet-like reinforcing materials, films, woven fabrics, and nonwoven fabrics (hereinafter, both nonwoven and woven fabrics are collectively referred to as "fabric") can be used. Among these materials, woven fabrics and nonwoven fabrics can also be used. By using woven or nonwoven fabrics as sheet-like reinforcing materials, an impregnation structure in which resin is impregnated within the sheet-like reinforcing material can be formed. As a result, linear expansion of the first resin layer 12 is easily suppressed.

[0045] From the perspective of improving dimensional stability, the main components of the raw materials constituting sheet-like reinforcing materials can also be glass and synthetic resins. Specific examples of the main components of the raw materials constituting sheet-like reinforcing materials include glass cloth obtained by processing glass fibers into a cloth-like form. In addition, fluorinated resin glass cloth obtained by impregnating such glass cloth with fluorinated resin can also be listed. Furthermore, inorganic cloth obtained by processing inorganic fibers such as metals and ceramics into a cloth-like form can also be listed. In addition, resin cloth obtained by processing synthetic resin fibers such as polytetrafluoroethylene, polyetheretherketone, aramid, and liquid crystal polymer (LCP) into a cloth-like form can also be listed. Furthermore, heat-resistant films with polytetrafluoroethylene, liquid crystal polymers, polyimide, polyamide-imide, polybenzimidazole, polyetheretherketone, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, thermosetting resin, and crosslinking resin as main components can also be listed.

[0046] The first resin layer 12 may also contain any other components as needed, in addition to the main resin component mentioned above. Examples of any components of the first resin layer 12 include flame retardants, flame retardant additives, pigments, antioxidants, reflective agents, masking agents, lubricants, processing stabilizers, plasticizers, and foaming agents.

[0047] The lower limit of the average thickness of the first resin layer 12 can be 40 μm or 45 μm. If the average thickness of the first resin layer 12 is less than 40 μm, there is a possibility that the dielectric loss tangent will increase, making it impossible to sufficiently reduce transmission loss, and the manufacturing process of the high-frequency substrate 50 may become difficult. The upper limit of the average thickness of the first resin layer 12 can be 130 μm or 125 μm. If the average thickness of the first resin layer 12 exceeds 130 μm, the thickness of the first resin layer 12 and the high-frequency substrate 50 will need to be unnecessarily increased, and sufficient flexibility may not be achieved. Here, "average thickness" refers to the average value of the thickness measured at any 100 points. It should be noted that the same definition applies when referring to "average thickness" for other components, etc., below.

[0048] [Conductive pattern]

[0049] like Figure 3 As shown, the first laminate 1 has a conductive pattern 10 stacked in the first resin layer 12 on the side opposite to the second laminate 2. Furthermore, the conductive pattern 10 is embedded by an adhesive layer 3. The conductive pattern 10 includes a signal line 13 for high-frequency signals and a ground layer 14. In this embodiment, the conductive pattern 10 has a signal line 13 and two ground layers 14 arranged to sandwich the two sides of the signal line 13.

[0050] (Signal line)

[0051] like Figure 4 As shown, the signal line 13 is formed in a straight line on the surface of the first resin layer 12. The signal line 13 is disposed near the center on the surface of the first resin layer 12 in a direction perpendicular to the length direction of the conductive pattern 10.

[0052] The lower limit of the average thickness of signal line 13 can be 1 μm, 3 μm, or 5 μm. The upper limit of the average thickness of signal line 13 can be 40 μm, 30 μm, or 20 μm. If the average thickness of signal line 13 is less than 1 μm, the transmission loss in signal line 13 may become too large. If the average thickness of signal line 13 exceeds 40 μm, the manufacturing cost may increase and the flexibility may decrease due to the unnecessary thickening of the high-frequency substrate 50.

[0053] The average width of signal line 13 is determined based on the required impedance and is not particularly limited. The lower limit of the average width of signal line 13 can be 20 μm, 30 μm, or 40 μm. The upper limit of the average width of signal line 13 can be 300 μm or 200 μm. If the average width of signal line 13 is less than 20 μm, the transmission loss in signal line 13 may become excessive. If the average width of signal line 13 exceeds 500 μm, the increased capacitance between signal line 13 and ground plane 14 may prevent sufficient reduction of the characteristic impedance deviation of signal line 13.

[0054] (Grounding layer)

[0055] A pair of grounding layers 14 are arranged such that they sandwich the signal line 13 and are spaced apart from the signal line 13. The pair of grounding layers 14 are arranged such that they extend along the long side 150 of the first resin layer 12 in the length direction.

[0056] The average thickness of the ground layer 14 is not particularly limited. The lower limit of the average thickness of the ground layer 14 can be 1 μm, 3 μm, or 5 μm. The upper limit of the average thickness of the ground layer 14 can be 40 μm, 30 μm, or 20 μm. If the average thickness of the ground layer 14 is less than 1 μm, the conductivity of the ground layer 14 itself may not be fully utilized, and the shielding effect provided by the ground layer 14 may not be fully achieved. If the average thickness of the ground layer 14 exceeds 40 μm, the flexibility of the high-frequency substrate 50 may be excessively reduced, and the ground layer 14 may affect parasitic capacitance, making it difficult to achieve impedance matching.

[0057] The average width of the ground layer 14 is not particularly limited. The lower limit of the average width of the ground layer 14 can be 100 μm or 200 μm. The upper limit of the average width of the ground layer 14 can be 600 μm or 500 μm. If the average width of the ground layer 14 is less than 100 μm, the conductivity of the ground layer 14 itself may not be fully utilized, and the shielding effect provided by the ground layer 14 may not be fully achieved. If the average width of the ground layer 14 exceeds 600 μm, the high-frequency substrate 50 may become too large in the width direction.

[0058] The average spacing in the width direction between signal line 13 and ground plane 14 is not particularly limited. The lower limit of the average spacing can be 50 μm or 100 μm. The upper limit of the average spacing can be 600 μm, 500 μm, or 400 μm. By keeping the average spacing within the above range, the influence of ground plane 14 on parasitic capacitance can be suppressed, resulting in good impedance matching.

[0059] For example, the conductive pattern 10 is formed by etching a metal layer stacked on one side of the first resin layer 12. The metal layer can be formed from a conductive material. By forming the metal layer with copper foil, patterns of the desired shape can be easily and reliably formed. The surface of the conductive pattern 10 can also be plated. The plating process can also use tin plating, gold plating, or solder plating.

[0060] (First conductive layer)

[0061] The first conductive layer 11 functions as a grounding layer and shielding element for the signal line 13. The first conductive layer 11 is laminated in the first resin layer 12 on the side opposite to the surface of the second laminate 2. The first conductive layer 11 can be composed of a metal layer. The metal layer constituting the first conductive layer 11 can also be the same as the metal layer constituting the conductive pattern 10.

[0062] like Figure 1 As shown, the first conductive layer 11 and the second conductive layer 20 are similarly configured as a single surface. This improves the shielding effect of the first stack 1 of the high-frequency substrate 50. It should be noted that "single surface" means that, when viewed from above, it is substantially free of openings, at least in the area overlapping with the signal line 13. It should also be noted that "substantially free of openings" includes not only the complete absence of openings but also the presence of tiny holes for removing air bubbles, etc.

[0063] The lower limit of the average thickness of the first conductive layer 11 can be 10 μm or 20 μm. The upper limit of the average thickness of the first conductive layer 11 can be 60 μm or 50 μm.

[0064] [Second layer stack]

[0065] like Figures 1 to 3 As shown, the second laminate 2 is disposed opposite to the first laminate 1 through an adhesive layer 3. The second laminate 2 has a second conductive layer 20 and a second resin layer 21 laminated on it.

[0066] (Second conductive layer)

[0067] The second conductive layer 20 serves as both a grounding layer and a shield for the signal line 13. The second conductive layer 20 is laminated in the second resin layer 21 on the side opposite to the surface of the first laminate 1. The second conductive layer 20 can be composed of a metal layer, similar to the first conductive layer 11, and the metal layer constituting the second conductive layer 20 can be the same as the metal layer constituting the conductive pattern 10. Figure 1As shown, the second conductive layer 20 is formed in the same manner as the first conductive layer 11. This improves the shielding effect of the second stack 2 of the high-frequency substrate 50. Furthermore, the first conductive layer 11 and the second conductive layer 20 are stacked on the outer surfaces of the first resin layer 12 and the second resin layer 21 of the high-frequency substrate 50. That is, a conductive pattern 10 (signal line 13) is disposed between the first conductive layer 11 and the second conductive layer 20. Therefore, the first conductive layer 11 and the second conductive layer 20 can function as shielding elements against the conductive pattern 10 (signal line 13).

[0068] The lower limit of the average thickness of the second conductive layer 20 can be 10 μm or 20 μm. The upper limit of the average thickness of the second conductive layer 20 can be 60 μm or 50 μm. The lower limit of the average thickness of the second conductive layer 20 can also be the same as the lower limit of the average thickness of the first conductive layer 11. The upper limit of the average thickness of the second conductive layer 20 can also be the same as the upper limit of the average thickness of the first conductive layer 11.

[0069] (Second resin layer)

[0070] The second resin layer 21 may also be mainly composed of a resin with a linear expansion coefficient of 20 ppm / K or higher at temperatures ranging from 20°C to 120°C, and may include sheet-like reinforcing materials and any other components besides the main resin component. The main resin component, sheet-like reinforcing materials, and any other components of the second resin layer 21 may also be the same as those of the first resin layer 12.

[0071] [Adhesive layer]

[0072] Adhesive layer 3 is disposed between the first laminate 1 and the second laminate 2. Adhesive layer 3 bonds the first resin layer 12 and the second resin layer 21.

[0073] The material constituting adhesive layer 3 is not particularly limited if it is an insulating and adhesive material. The material constituting adhesive layer 3 can be selected from known materials, such as fluoropolymers.

[0074] As the fluororesin used for the adhesive layer 3, fluororesin, for example, can be exemplified as the main component resin of the first resin layer 12. By forming the adhesive layer 3 from a material primarily composed of fluororesin, the signal line 13 is embedded in an insulating material primarily composed of fluororesin. By surrounding the signal line 13 with the insulating material primarily composed of fluororesin, namely the adhesive layer 3 and the first resin layer 12, transmission loss in the signal line 13 can be sufficiently reduced, and sufficient transmission speed can be obtained.

[0075] There is no particular limitation if the average thickness of the adhesive layer 3 is greater than the average thickness of the conductive pattern 10. The lower limit of the average thickness of the adhesive layer 3 can be 10 μm or 20 μm. The upper limit of the average thickness of the adhesive layer 3 can be 60 μm or 50 μm. By making the average thickness of the adhesive layer 3 10 μm or more, the formation of the adhesive layer 3 becomes easier, and a good bonding state between the first laminate 1 and the second laminate 2 can be obtained. By making the average thickness of the adhesive layer 3 60 μm or less, the flexibility of the high-frequency substrate 50 can be well maintained, and the increase of dielectric loss in the adhesive layer 3 can be suppressed.

[0076] [First Through Hole]

[0077] The high-frequency substrate 50 includes first vias 4 formed on the inner periphery and bottom of a plurality of connection holes penetrating the first resin layer 12 in the thickness direction. That is, a plurality of first vias 4 are provided in the first resin layer 12. In multilayer high-frequency substrates where the wiring density of the substrate has increased due to the miniaturization of electronic devices, vias (cylindrical conductors) are formed to connect different conductive layers. Figure 3 and Figure 4 As shown, the bottom surface of the first via 4 contacts the ground layer 14, and the first via 4 connects the first conductive layer 11 to the ground layer 14. The first via 4 penetrates the first resin layer 12 in the thickness direction on both sides sandwiching the signal line 13, and is connected to the ground layer 14.

[0078] The inner diameter of the first via 4 is not particularly limited. The inner diameter of the first via 4 can also be 0.5mm or more. The placement, number, and size of the first via 4 are not particularly limited and can be designed appropriately.

[0079] [Second via]

[0080] The high-frequency substrate 50 includes second vias 5 formed on the inner periphery and bottom of a plurality of connection holes that penetrate the second resin layer 21 and the adhesive layer 3 in the thickness direction. A plurality of second vias 5 are provided in the second resin layer 21 and the adhesive layer 3. Figure 3 and Figure 4 As shown, the bottom surface of the second via 5 contacts the ground layer 14, and the second via 5 connects the second conductive layer 20 to the ground layer 14. These second vias 5 penetrate the second resin layer 21 and the adhesive layer 3 in the thickness direction at both ends of the signal line 13, and are connected to the ground layer 14.

[0081] The inner diameter of the second via 5 is not particularly limited. The inner diameter of the second via 5 can also be 0.5 mm or more. The location, number, and size of the second via 5 are not particularly limited and can be designed appropriately.

[0082] [First opening and second opening]

[0083] like Figure 5 As shown, in the high-frequency substrate 50, the second conductive layer 20 has two second openings 30 in the peripheral region of the opening of the second via 5. The semi-circular second openings 30 are arranged opposite to each other around the opening of the second via 5. In other words, the second conductive layer 20 is not present on the upper surface of the second resin layer 21 in the region of the second openings 30. Furthermore, as... Figure 1 As shown, the peripheral region of the opening of the first via 4 in the first conductive layer 11 has two semi-circular arc-shaped first openings 31. By having the high-frequency substrate 50 have the second opening 30 and the first opening 31, even when the resin with a high coefficient of linear expansion undergoes thermal expansion due to large temperature variations, such as in a thermal shock test, the stress generated by the thermally expanded resin is dispersed. The stress locally applied to the conductive plating layer on the inner walls of the first via 4 and the second via 5 is reduced. Therefore, cracking in the conductive plating layer on the inner walls of the first via 4 and the second via 5 can be suppressed.

[0084] The shapes of the first opening 31 and the second opening 30 are not particularly limited.

[0085] like Figure 6 As shown, in the high-frequency substrate 60, the second conductive layer 20 has a second opening 34 surrounding the periphery 24 of the openings of the two second vias 5. Specifically, the second opening 34, when viewed from above, has a flat shape having a pair of curved surfaces 341 and a pair of straight surfaces 342 connecting the pair of curved surfaces 341. Each curved surface 341 surrounds the area on both sides of the two peripheral portions 24 facing each other when viewed from above.

[0086] like Figure 7 As shown, in the high-frequency substrate 70, the second conductive layer 20 has a second opening 35 in the peripheral region of the opening of the second via 5. The second opening 35 is provided in the region other than the peripheral region 25 of the opening of the second via 5. Figure 8 As shown, the first conductive layer 11 has a first opening 45 in the peripheral region of the opening of the first via 4. The first opening 45 is provided in the region other than the peripheral region 40 of the opening of the first via 4. In the high-frequency substrate 70, by having both the second opening 35 and the first opening 45, the stress generated by the thermally expanded resin, which has a high coefficient of linear expansion, is dispersed when used in environments with large temperature variations such as thermal shock tests. The stress of the conductive plating layer locally applied to the inner walls of the first via 4 and the second via 5 is reduced.

[0087] [Manufacturing method of high-frequency substrate]

[0088] For example, a high-frequency substrate can be obtained through a manufacturing method that includes the following five steps.

[0089] (1) The process of forming a conductive pattern on one side of the first resin layer (conductive pattern forming process) (2) The process of bonding the first laminate and the second laminate (laminate bonding process)

[0090] (3) The process of forming the first via (the process of forming the first via)

[0091] (4) The process of forming the second via (the process of forming the second via)

[0092] (5) Process for forming the opening (opening forming process)

[0093] (Conductive pattern formation process)

[0094] In the conductive pattern formation process, a first resin layer is first prepared, on one side having a first conductive layer and on the other side having a conductive pattern layer. Then, a conductive pattern (signal line and ground layer) is formed on the side of the first resin layer where the conductive layer is deposited. Specifically, a conductive pattern (signal line and ground layer) is formed on one side of the first resin layer by patterning the conductive layer for the conductive pattern. Patterning can also be performed using known etching methods, such as dry etching or wet etching. From a productivity perspective based on etching speed, wet etching is more advantageous. For example, wet etching is performed by masking the conductive layer that forms the conductive pattern and using an etching solution to remove the desired portion of the conductive layer (the unmasked portion). The etching solution can also be, for example, a sulfuric acid-hydrogen peroxide mixture (a mixture of sulfuric acid and an aqueous solution of hydrogen peroxide) or sodium persulfate.

[0095] The conductive pattern can also be patterned before the conductive layer is laminated onto the surface of the first resin layer. For example, patterning before lamination can be performed by bonding the conductive layer formed on the surface of the release film to the surface of the first resin layer after patterning the conductive layer, or by laminating the stamped conductive layer onto the surface of the first resin layer.

[0096] (Laminated body bonding process)

[0097] In the laminate bonding process, a second laminate having a second conductive layer on one side is bonded to a first laminate having a conductive pattern formed on one side. In this process, pressure and heat are applied while the adhesive constituting the adhesive layer is positioned between the first and second laminates. This bonds the first and second laminates together. The adhesive is not particularly limited to materials possessing both insulating and adhesive properties. The adhesive can be selected from known materials, and fluoropolymers can be used as described above.

[0098] (First via formation process)

[0099] The first via formation process forms the first via in the first laminate 1. For example, the first via can be formed by plating the inner wall of the through-hole after it has been formed. Alternatively, the first via can be formed by filling the through-hole with a conductor. For example, the through-hole can be formed by etching a photomask or by laser processing. When plating the inner wall of the through-hole, electroless plating can be used, for example. When filling the through-hole with a conductor, conductor paste can be used, for example.

[0100] (Second via formation process)

[0101] The second via formation process is the process of forming a second via in the first laminate and the adhesive layer. The second via formation process can also be, for example, the same process as the first via formation process.

[0102] (Opening formation process)

[0103] In the opening formation process, a first opening is formed in a first conductive layer, and a second opening is formed in a second conductive layer. For example, the first and second openings can be formed by etching with a photomask or by laser processing.

[0104] The components of the high-frequency substrate obtained by the above manufacturing method are as described above.

[0105] According to the high-frequency substrate disclosed herein, even when using a resin with a large coefficient of linear expansion relative to temperature changes, it is possible to reduce the stress applied to the vias.

[0106] Alternatively, at least one of the first conductive layer and the second conductive layer may further have a third opening, which is disposed in the first conductive layer at a position indirectly opposite to the bottom surface of the second via, and in the second conductive layer at a position indirectly opposite to the bottom surface of the first via. Because at least one of the first and second conductive layers has a third opening, the stress generated by the thermally expanded resin is more dispersed, and the stress locally applied to the conductive plating layer on the inner wall of the via is further reduced. Therefore, cracking in the conductive plating layer on the inner wall of the via can be further suppressed. Consequently, the electrical connection reliability of the high-frequency substrate can be further improved. (Refer to...) Figure 9 and Figure 10The first conductive layer 11 has a third opening 36, which is circular when viewed from above, located indirectly opposite the bottom surface of the second via 5. Because the first conductive layer 11 has this third opening 36, the stress applied to the second via 5 can be further reduced, even when using a resin with a large coefficient of linear expansion relative to temperature changes. In the high-frequency substrate 80, when viewed in cross-section, the aperture L of the third opening 36 is equal to the maximum value of the inner diameter of the second via 5, the width of the periphery at both ends of the second via 5, and the sum W of the widths of the second openings 30 adjacent to the periphery at both ends.

[0107] The shape of the third opening when viewed from above can also be appropriately set according to the shapes of the first and second vias. In addition, the length of the third opening in the longitudinal direction of the grounding layer when viewed in cross section can also be appropriately set.

[0108] This disclosure also applies to electronic components on high-frequency substrates. Specifically, in this disclosure, electronic components, such as those with circuit elements like semiconductor devices and chip resistors electrically connected to a high-frequency substrate like the one described in this embodiment, are also within the scope of this disclosure.

[0109] The first and second vias are not limited to a generally cylindrical shape that expands from the lower surface to the upper surface as in this embodiment. They can also be shapes with uneven average diameters (shapes that narrow from the lower surface to the upper surface, or shapes with necking). The cross-sectional shape is also not limited to a circle, and can also be polygonal, etc.

[0110] Example

[0111] [Example 1]

[0112] As a high-frequency substrate of Example 1, a high-frequency substrate was fabricated. Figure 11 The high-frequency substrate 90 shown is an example. The high-frequency substrate 90 includes a first laminate 1, an adhesive layer 3, a second laminate 2 disposed opposite to the first laminate 1 via the adhesive layer 3, and a second via 5 with a maximum inner diameter of 250 μm. The first laminate 1 has a first conductive layer 11 and a first resin layer 12 laminated thereon, and has a ground layer 14 laminated in the first resin layer 12 on the surface opposite to the second laminate 2. The second laminate 2 has a second conductive layer 20 and a second resin layer 21 laminated thereon. Furthermore, the second conductive layer 20 has two second openings 30 with a width of 200 μm in the peripheral region of the opening of the second via 5. Moreover, the first conductive layer 11 has a position in the first conductive layer 11 indirectly opposite to the bottom surface of the second via 5, as shown in the figure. Figure 10 The third opening 36 has a diameter of 850 μm, as shown.

[0113] The materials and average thicknesses of the components constituting the high-frequency substrate 90 are shown below.

[0114] First conductive layer: copper foil, average thickness 12μm

[0115] First resin layer: fluororesin, average thickness 100μm

[0116] Adhesive layer: epoxy resin, average thickness 25μm

[0117] Grounding layer: copper foil, average thickness 12μm

[0118] Second conductive layer: copper foil, average thickness 12μm

[0119] Second resin layer: Fluoropolymer resin, average thickness 100μm

[0120] [Comparative Example 1]

[0121] Made Figure 12 The high-frequency substrate 100 shown in Comparative Example 1 is the same as that in Example 1 except that it does not have a second opening and a third opening.

[0122] [evaluate]

[0123] For the high-frequency substrates of Example 1 and Comparative Example 1 (each having 250,000 vias), the connection reliability was evaluated by thermal shock testing.

[0124] Thermal shock tests were conducted by repeatedly exposing the high-frequency substrate to low and high temperature environments at certain cycles. Specifically, the substrate was repeatedly exposed to -60°C and 125°C in 15-minute cycles, and the connection resistance was measured and the resistance value change rate was calculated. An abnormality was judged when the resistance value change rate was +5% or more or -5% or less. In the thermal shock test, in Example 1, a portion of the sample experienced wire breakage after 2000 cycles, with a resistance value change rate of +5% or more. In Comparative Example 1, all samples experienced wire breakage after 1000 cycles, with a resistance value change rate of +5% or more. Thus, the result is that the connection reliability of the high-frequency substrate of Comparative Example 1 is lower than that of the high-frequency substrate of Example 1.

[0125] The above results demonstrate that the high-frequency substrate disclosed herein can reduce the stress applied to vias even when using a resin with a large coefficient of linear expansion relative to temperature changes.

[0126] It should be understood that the embodiments disclosed herein are exemplary in all respects and not restrictive. The scope of the invention is not limited to the configuration of the above embodiments, but is shown by the claims and is intended to include all modifications with the same meaning and scope as the claims.

[0127] Explanation of reference numerals in the attached figures

[0128] 1. First layer of stacked body

[0129] 2 Second layer stack

[0130] 3 Adhesive layer

[0131] 4 First Through Hole

[0132] 5 Second via

[0133] 10 Conductive Patterns

[0134] 11 First conductive layer

[0135] 12 First resin layer

[0136] 13 signal lines

[0137] 14 Grounding layer

[0138] 20 Second conductive layer

[0139] 21 Second resin layer

[0140] 24, 25 Peripheral part of the opening of the second through hole

[0141] 30, 34, 35 Second opening

[0142] 31, 45 First opening

[0143] 36 Third opening

[0144] 40 Peripheral part of the opening of the first through hole

[0145] 50, 60, 70, 80, 90, 100 high-frequency substrates

[0146] 150 long side

[0147] 341 Curved face

[0148] 342. Straight section.

Claims

1. A high-frequency substrate, comprising: The first laminate has a first conductive layer and a first resin layer stacked on it; The second laminate has a second conductive layer and a second resin layer stacked on it, and is configured to be opposite to the first laminate. An adhesive layer is used to bond the first resin layer to the second resin layer. The first through hole is formed on the inner periphery and bottom of one or more connecting holes that penetrate the first resin layer in the thickness direction; as well as The second via is formed on the inner periphery and bottom of one or more connecting holes that penetrate the second resin layer and the adhesive layer in the thickness direction. The first laminate has a conductive pattern on the surface of the first resin layer opposite to the second laminate. The conductive pattern is embedded in the adhesive layer. The conductive pattern has signal lines and ground lines arranged to sandwich the two sides of the signal lines. The bottom surface of the first via is in contact with the ground layer, and the first via connects the first conductive layer to the ground layer. The bottom surface of the second via is in contact with the ground layer, and the second via connects the second conductive layer to the ground layer. The first resin layer and the second resin layer are mainly composed of resins with a linear expansion coefficient of 20 ppm / K or higher at temperatures ranging from 20°C to 120°C. The first conductive layer has a first opening in the peripheral region of the opening of the first via. The second conductive layer has a second opening in the peripheral region of the opening of the second via.

2. The high-frequency substrate according to claim 1, wherein, At least one of the first conductive layer and the second conductive layer further has a third opening. The third opening is located in the first conductive layer at a position indirectly opposite to the bottom surface of the second via, and in the second conductive layer at a position indirectly opposite to the bottom surface of the first via.

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