Signal transmission board and method for manufacturing the same

Abstract

To provide a signal transmission board capable of improving transmission efficiency of signal while restraining warpage of a substrate, and to provide a manufacturing method thereof.SOLUTION: A signal transmission board includes a substrate 12 having a first face 13 and a second face 14 opposite to the first face 13, a first signal layer 331 located on the first face 13, a first insulation layer 36 located on the first signal layer 331, a first ground layer 351 located on the first insulation layer 36, a second signal layer 431 located on the second face 14, connected electrically with the first signal layer 331, and having a larger dimension than the first signal layer 331 in the width direction crossing the signal transmission direction, a second insulation layer 44 located above the second signal layer 431, and having a larger dimension than the first insulation layer 36 in the thickness direction crossing the first face 13 and a smaller degree of elasticity, and a second ground layer 451 located above the second insulation layer 44.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a signal transmission substrate and a method for manufacturing the same. [Background technology]

[0002] Conventionally, various technologies have been proposed for interposers that relay signals between motherboards and IC chips with different terminal pitches. For example, Patent Document 1 discloses an interposer equipped with through-electrodes that penetrate the glass substrate from the first surface to the second surface. According to the interposer, signals can be transmitted between an IC chip electrically connected to the signal layer on the first surface and a motherboard electrically connected to the signal layer on the second surface, via the signal layer on the first surface, the signal layer on the second surface, and the through-electrodes that electrically connect the two signal layers. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-139963 [Overview of the project] [Problems that the invention aims to solve]

[0004] To efficiently transmit signals between the motherboard and IC chips via an interposer with minimal loss, it is desirable to match the impedance between the signal layer on the first surface and the signal layer on the second surface. One method for matching impedance is to adjust the thickness of the insulating layer on the first surface and the insulating layer on the second surface.

[0005] However, even if the thickness of the insulating layer is adjusted to match the impedance, it is difficult to balance the stress on the first surface acting on the substrate from the first surface side due to the stress acting on the insulating layer on the first surface, and the stress on the substrate from the second surface side due to the stress acting on the insulating layer on the second surface. And because it is difficult to balance the stress on the first surface side and the stress on the second surface side, there is a risk that the substrate will warp.

[0006] This disclosure has been made in consideration of the above points, and aims to provide a signal transmission substrate and a method for manufacturing the same that can achieve both improved signal transmission efficiency and suppression of substrate warping. [Means for solving the problem]

[0007] To address the above issues, in one aspect of this disclosure, A substrate having a first surface and a second surface opposite to the first surface, A first signal layer located on the first surface, A first insulating layer located on the first signal layer, A first ground layer located on the first insulating layer, A second signal layer located on the second surface, electrically connected to the first signal layer, and having a larger width dimension intersecting the signal transmission direction than the first signal layer, A second insulating layer located on the second signal layer, having a larger dimension in the thickness direction intersecting the first surface than the first insulating layer, and a lower elastic modulus, A signal transmission substrate is provided, comprising a second ground layer located on the second insulating layer.

[0008] The difference between the product of the thickness direction dimension of the first insulating layer and its elastic modulus and the product of the thickness direction dimension of the second insulating layer and its elastic modulus may be a ratio of less than or equal to a threshold value with respect to the product of the thickness direction dimension of the second insulating layer and its elastic modulus.

[0009] The threshold may be 15%.

[0010] The difference between the product of the coefficient of thermal expansion, the dimension in the thickness direction, and the elastic modulus of the first insulating layer and the product of the coefficient of thermal expansion, the dimension in the thickness direction, and the elastic modulus of the second insulating layer may have a ratio equal to or less than a threshold value with respect to the product of the coefficient of thermal expansion, the dimension in the thickness direction, and the elastic modulus of the second insulating layer.

[0011] At least one layer of a third insulating layer located between the first surface and the first signal layer or on at least one of the first ground layers, At least one layer of a fourth insulating layer located between the second surface and the second signal layer or on at least one of the second ground layers; further provided with, The difference between the sum of the product of the dimension in the thickness direction and the elastic modulus of the first insulating layer and the product of the dimension in the thickness direction and the elastic modulus of the third insulating layer, and the sum of the product of the dimension in the thickness direction and the elastic modulus of the second insulating layer and the product of the dimension in the thickness direction and the elastic modulus of the fourth insulating layer may have a ratio equal to or less than a threshold value with respect to the sum of the product of the dimension in the thickness direction and the elastic modulus of the second insulating layer and the product of the dimension in the thickness direction and the elastic modulus of the fourth insulating layer.

[0012] The substrate may further include a through electrode that penetrates the substrate from the first surface to the second surface and is electrically connected to the first signal layer and the second signal layer.

[0013] A third ground layer located on the first surface and adjacent to the first signal layer in the width direction, A fourth ground layer located on the second surface and adjacent to the second signal layer in the width direction; may further be provided with,

[0014] The substrate may further include a capacitor electrically connected to the first signal layer on the first surface or to the second signal layer on the second surface.

[0015] The substrate may contain glass.

[0016] It may be possible to mount on a wiring board on the second surface side and to mount an integrated circuit on the first surface.

[0017] In another aspect of this disclosure, A step of preparing a substrate having a first surface and a second surface opposite to the first surface, The process involves forming a first signal layer on the first surface, The process involves forming a first insulating layer on the first signal layer, The process involves forming a first ground layer on the aforementioned first insulating layer, A step of forming a second signal layer on the second surface, which is electrically connected to the first signal layer and has a larger width dimension intersecting the signal transmission direction than the first signal layer, A step of forming a second insulating layer on the second signal layer, having a larger dimension in the thickness direction intersecting the first surface than the first insulating layer and a lower elastic modulus, A method for manufacturing a signal transmission substrate is provided, comprising the step of forming a second ground layer on the second insulating layer.

[0018] The step of forming the first insulating layer includes thermal curing the first insulating layer at a first temperature. The step of forming the second insulating layer includes thermal curing the second insulating layer at the first temperature when thermal curing the first insulating layer. In at least the temperature interval from the first temperature to the second temperature after heat curing, the difference between the product of the thermal expansion coefficient of the first insulating layer, the temperature change relative to the first temperature, the dimension in the thickness direction, and the modulus of elasticity, and the product of the thermal expansion coefficient of the second insulating layer, the temperature change relative to the first temperature, the dimension in the thickness direction, and the modulus of elasticity, may be less than or equal to a threshold ratio with respect to the product of the thermal expansion coefficient of the second insulating layer, the temperature change relative to the first temperature, the dimension in the thickness direction, and the modulus of elasticity. [Effects of the Invention]

[0019] According to this disclosure, it is possible to achieve both improved signal transmission efficiency and suppression of substrate warping. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view showing a signal transmission board according to this embodiment. [Figure 2] This is a cross-sectional view taken along line II-II in Figure 1, showing a signal transmission board according to this embodiment. [Figure 3] This is a cross-sectional view taken along line III-III in Figure 1, showing a signal transmission board according to this embodiment. [Figure 4] This is a cross-sectional view showing a method for manufacturing a signal transmission substrate according to this embodiment. [Figure 5] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 4. [Figure 6] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 5. [Figure 7] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 6. [Figure 8] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 7. [Figure 9] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 8. [Figure 10] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 9. [Figure 11] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 10. [Figure 12] This is a cross-sectional view showing the method for manufacturing a signal transmission substrate according to this embodiment, following Figure 11. [Figure 13] This figure shows the relationship between temperature, the stress of the first insulating layer according to the temperature, and a parameter correlated with the stress in an experimental example of a signal transmission substrate according to this embodiment. [Figure 14] This figure shows the relationship between temperature, the stress of the second insulating layer according to the temperature, and a parameter correlated with the stress in an experimental example of a signal transmission substrate according to this embodiment. [Figure 15] This is a perspective view of an indenter that can be used to measure the indentation modulus correlated with the stress of the first and second insulating layers in an experimental example of a signal transmission substrate according to this embodiment. [Figure 16]This is a cross-sectional view showing an example of measuring the indentation modulus of the first and second insulating layers in an experimental example of a signal transmission substrate according to this embodiment. [Figure 17] This graph shows an example of measuring the indentation modulus of the first and second insulating layers in an experimental example of a signal transmission substrate according to this embodiment. [Figure 18] This is a cross-sectional view of the signal layer side on the first surface showing a signal transmission substrate according to a first modification of this embodiment. [Figure 19] This is a cross-sectional view of the signal layer side on the second surface showing a signal transmission substrate according to a first modification of this embodiment. [Figure 20] This is a cross-sectional view of the signal layer side on the first surface showing a signal transmission substrate according to a second modification of this embodiment. [Figure 21] This is a cross-sectional view of the signal layer side on the second surface showing a signal transmission substrate according to a second modification of this embodiment. [Figure 22] This is a cross-sectional view showing a signal transmission board according to a third modification of this embodiment. [Figure 23] This figure shows an example of a product that incorporates a signal transmission board. [Modes for carrying out the invention]

[0021] The configuration of a signal transmission board and its manufacturing method according to the embodiments of this disclosure will be described in detail below with reference to the drawings. The embodiments shown below are examples of embodiments of this disclosure, and this disclosure is not limited to these embodiments. Furthermore, in this specification, terms such as "substrate," "base material," "sheet," and "film" are not distinguished from each other solely on the basis of name. For example, "substrate" and "base material" are concepts that include components that may be called sheets or films. Moreover, terms used in this specification to specify shape, geometric conditions, and their degree, such as "parallel" and "orthogonal," as well as values ​​of length and angle, are not strictly defined but are interpreted to include a range that allows for the expectation of similar functionality. In addition, in the drawings referenced in this embodiment, the same or similar reference numerals are used for identical parts or parts with similar functions, and repeated explanations may be omitted. Furthermore, the dimensional ratios in the drawings may differ from the actual ratios for explanatory purposes, and some components may be omitted from the drawings.

[0022] Signal transmission board 10 The embodiments of this disclosure will be described below. First, the configuration of the signal transmission board according to this embodiment will be described. The signal transmission board of this embodiment can be used, for example, as an interposer board for transmitting high-frequency signals. Figure 1 is a cross-sectional view showing the signal transmission board 10 according to this embodiment. Figure 2 is a cross-sectional view taken along line II-II of Figure 1 showing the signal transmission board 10 according to this embodiment. Figure 3 is a cross-sectional view taken along line III-III of Figure 1 showing the signal transmission board 10 according to this embodiment.

[0023] As shown in Figures 1 to 3, the signal transmission board 10 comprises a substrate 12, through electrodes 22, a first wiring structure 30, and a second wiring structure 40. The individual components of the signal transmission board 10 will be described below.

[0024] (Circuit board 12) The substrate 12 includes a first surface 13 and a second surface 14 located opposite the first surface 13. The substrate 12 is also provided with multiple through-holes 20 that penetrate from the first surface 13 to the second surface 14. In Figure 1, only one through-hole 20 is shown as a representative example. The signal transmission substrate 10 can be mounted on a motherboard (not shown) on the second surface 14 side, and an IC chip (not shown), i.e., an integrated circuit, can be mounted on the first surface 13.

[0025] The substrate 12 contains an inorganic material having a certain degree of insulating properties. For example, the substrate 12 may be a glass substrate, a quartz substrate, a sapphire substrate, a resin substrate, a silicon substrate, a silicon carbide substrate, an alumina (Al2O3) substrate, an aluminum nitride (AlN) substrate, a zirconia oxide (ZrO2) substrate, or a laminate of these substrates. The substrate 12 may also partially contain a substrate made of a conductive material, such as an aluminum substrate or a stainless steel substrate.

[0026] Examples of glass used in the substrate 12 include alkali-free glass. Alkali-free glass is glass that does not contain alkaline components such as sodium or potassium. Alkali-free glass may contain, for example, boric acid instead of alkaline components. Alternatively, alkali-free glass may contain alkaline earth metal oxides such as calcium oxide or barium oxide.

[0027] In the example shown in Figure 1, the through-hole 20 formed in the substrate 12 has a shape in which the width decreases from the first surface 13 and the second surface 14 of the substrate 12 toward the center in the thickness direction D3 of the substrate 12. However, the shape of the through-hole 20 is not particularly limited. For example, the side wall 21 of the through-hole 20 may widen along the thickness direction D3. Also, a part of the side wall 21 may be curved.

[0028] (Through electrode 22) The through electrode 22 is a conductive member located inside the through hole 20. In this embodiment, the thickness of the through electrode 22 is smaller than the width of the through hole 20, and therefore there is a space inside the through hole 20 where the through electrode 22 is not present. In other words, the through electrode 22 is a so-called conformal via. In the example in Figure 1, the space inside the through hole 20 is filled with the first organic layer 34 on the first surface and the first organic layer 42 on the second surface, which will be described later, located inside the through electrode 22.

[0029] The configuration of the through electrode 22 is not particularly limited, as long as the through electrode 22 is conductive. For example, the through electrode 22 may consist of a single conductive layer, or it may include multiple conductive layers. The through electrode 22 may also include a seed layer and a plating layer arranged sequentially from the side wall 21 of the through hole 20 towards the center. In this case, an intermediate layer may be provided between the side wall 21 of the through hole 20 and the seed layer. As the material constituting the intermediate layer, for example, titanium, titanium nitride, molybdenum, molybdenum nitride, tantalum, tantalum nitride, etc., or a laminate of these can be used. The intermediate layer is formed, for example, by a physical film deposition method such as vapor deposition or sputtering. The intermediate layer plays a role in improving the adhesion of the seed layer or plating layer to the side wall 21. The intermediate layer may also play a role in suppressing the diffusion of metal elements contained in the seed layer or plating layer into the interior of the substrate 12 through the side wall 21 of the through hole 20.

[0030] (First wiring structure section 30) Next, the first wiring structure 30 will be described. The first wiring structure 30 has layers such as conductive layers and insulating layers provided on the first surface 13 side of the substrate 12 to constitute an electrical circuit. In the example in Figure 1, the first wiring structure 30 has a first conductive layer 31 on the first surface, a first organic layer 34 on the first surface which is an example of a third insulating layer, a second conductive layer 33 on the first surface, a second organic layer 36 on the first surface which is an example of a first insulating layer, and a third conductive layer 35 on the first surface.

[0031] The first wiring structure 30 has a strip line that sandwiches the front and back of the signal line between the ground plane and an insulating layer. Hereinafter, the strip line of the first wiring structure 30 will also be referred to as the strip line on the first surface 13 side. As shown in Figures 1 and 2, the strip line on the first surface 13 side has a signal layer 331, which is an example of a first signal layer, a ground layer 311, and a ground layer 351, which is an example of a first ground layer.

[0032] [First surface, first conductive layer 31] The first conductive layer 31 on the first surface is a conductive layer located on the first surface 13 of the substrate 12. The ground layer 311 in the strip line on the first surface 13 side is composed of a portion of the first conductive layer 31 on the first surface.

[0033] As shown in Figure 1, the first conductive layer 31 on the first surface has a seed layer 221 and a plating layer 222. The seed layer 221 is located on the first surface 13 of the substrate 12. The plating layer 222 is located on the seed layer 221.

[0034] The seed layer 221 is a conductive layer that serves as a base for depositing metal ions in the plating solution and growing the plating layer 222 during the electroplating process in which the plating layer 222 is formed by electroplating. The material of the seed layer 221 can be a conductive material such as copper. The material of the seed layer 221 may be the same as or different from the material of the plating layer 222. For example, the seed layer 221 may be a multilayer film of titanium and copper stacked in sequence, or chromium. The seed layer 221 may be formed by, for example, sputtering, vapor deposition, or electroless plating.

[0035] The plating layer 222 is a conductive layer formed by a plating process. The plating layer 222 contains copper. The plating layer 222 may also contain an alloy of copper with a metal other than copper, such as gold, silver, platinum, rhodium, tin, aluminum, nickel, or chromium, or it may be a laminate of copper and a metal other than copper.

[0036] [Ground Layer 311] The ground layer 311 is located on the first surface 13, electrically connected to a reference potential such as ground potential, and electrically insulated from the through electrode 22. It is a layer that controls the characteristic impedance of the signal layer 331. The ground layer 311 is located on the first surface 13, adjacent to the signal layer 331, with a gap in the lower D32 direction in Figure 1, within the thickness direction D3 that is perpendicular to, i.e., intersects with, the first surface 13. In the examples in Figures 1 and 2, the ground layer 311 faces the signal layer 331 with the first organic layer 34 of the first surface sandwiched between them. The ground layer 311 has a larger total area than the signal layer 331. In order to control the characteristic impedance of the signal layer 331 to a desired value, the ground layer 311 has a predetermined gap d3 in the thickness direction D3 between it and the signal layer 331.

[0037] [First surface first organic layer 34] The first organic layer 34 on the first surface is located on the first surface 13 or the first conductive layer 31 on the first surface, contains an organic material, and is an insulating layer.

[0038] The first organic layer 34 on the first surface may have a thickness h3, which is a dimension in the thickness direction D3, that is, a thickness h3, that takes into account both impedance matching of the transmission line between the first surface 13 and the second surface 14 and the balance of stress due to the insulating layer. Furthermore, the first organic layer 34 on the first surface may have an elastic modulus that takes into account both the impedance matching and the balance of stress. For example, the first organic layer 34 on the first surface may have a thickness h3 of 10 μm and an indentation modulus of 3.70 GPa at 25°C, i.e., room temperature.

[0039] The first organic layer 34 on the first surface may contain an organic material having a dielectric loss tangent of 0.003 or less, preferably 0.002 or less, and more preferably 0.001 or less. Polyimide, epoxy resin, and the like can be used as the organic material for the first organic layer 34 on the first surface. By constructing the first organic layer 34 on the first surface using an organic material with a small dielectric loss tangent, it is possible to suppress the passing of a portion of the electrical signal that should pass through the signal layer 331 through the first organic layer 34 on the first surface. This allows the bandwidth of the signal transmission substrate 10 to be extended to the high-frequency side.

[0040] The first organic layer 34 on the first surface may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying.

[0041] [Second conductive layer 33 on the first surface] The first surface second conductive layer 33 is a conductive layer located on the first surface 13, adjacent to the first surface first conductive layer 31, with a gap in the thickness direction D3, in the upward direction D31 in Figure 1. In the example in Figure 1, the first surface second conductive layer 33 is located on the first surface first organic layer 34. The signal layer 331 in the strip line on the first surface 13 side is composed of a portion of the first surface second conductive layer 33.

[0042] The thickness of the second conductive layer 33 on the first surface may be the same as or different from the thickness of the first conductive layer 31 on the first surface.

[0043] The first surface second conductive layer 33 may include a seed layer and a plating layer sequentially laminated on the first surface first organic layer 34, similar to the through electrode 22 and the first surface first conductive layer 31. The material constituting the first surface second conductive layer 33 is the same as the material constituting the through electrode 22 and the first surface first conductive layer 31.

[0044] [Signal layer 331] The signal layer 331 is located on the first organic layer 34 of the first surface 13, which is an example of the first surface 13, and is electrically connected to the through electrode 22. It is a layer that transmits electrical signals such as high-frequency signals. Examples of high-frequency signals include electrical signals of 0.1 GHz or higher. The signal layer 331 extends along the first surface 13 in the extension direction D1 in Figure 1, which is an example of the signal transmission direction, and is the direction perpendicular to the plane of the paper in Figure 2. In the example in Figure 1, the signal layer 331 is electrically connected to the through electrode 22 at one end in the extension direction D1 via a portion of the first conductive layer 31 of the first surface.

[0045] The thickness of the signal layer 331 is preferably 5 μm or more. By making the thickness of the signal layer 331 5 μm or more, the conductor resistance loss of the signal layer 331 can be reduced, thereby suppressing signal transmission loss. The thickness of the signal layer 331 is more preferably 20 μm or less. By making the thickness of the signal layer 331 20 μm or less, interfacial stress between the signal layer 331 and the first organic layer 34 on the first surface can be suppressed, thereby suppressing delamination of the signal layer 331.

[0046] On the first surface 13 side, IC chips with a smaller terminal pitch compared to the motherboard are electrically connected. For this reason, it is desirable that the signal layer 331 on the first surface 13 side has a small width direction D2, which is perpendicular to the extension direction D1 indicated by the symbol W1 in Figure 2, i.e., a wiring width W1, that matches the terminal pitch of the IC chip. As an example, the wiring width W1 of the signal layer 331 may be 300 μm or less.

[0047] [First surface second organic layer 36] The first surface second organic layer 36 is located on the first surface first organic layer 34 or the first surface second conductive layer 33, and is a layer that contains an organic material and has insulating properties.

[0048] The second organic layer 36 on the first surface has a thickness h1 and elastic modulus that take into account both impedance matching of the transmission path between the first surface 13 and the second surface 14, and stress balance due to the insulating layer. For example, the second organic layer 36 on the first surface may have a thickness h1 of 10 μm and an indentation modulus of 3.70 GPa at 25°C. In this way, by having the second organic layer 36 on the first surface have a thickness h1 and elastic modulus that take into account both impedance matching and stress balance, both impedance matching and stress balance can be ensured. By ensuring both impedance matching and stress balance, it is possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0049] Similar to the first organic layer 34 on the first surface, the second organic layer 36 on the first surface may contain an organic material having a dielectric loss tangent of 0.003 or less, preferably 0.002 or less, and more preferably 0.001 or less. As the organic material for the second organic layer 36 on the first surface, polyimide, epoxy resin, etc., can be used. By constructing the second organic layer 36 on the first surface using an organic material with a small dielectric loss tangent, it is possible to suppress the fact that a portion of the electrical signal that should pass through the signal layer 331 passes through the second organic layer 36 on the first surface. This makes it possible to further suitably extend the bandwidth of the signal transmission substrate 10 to the high-frequency side.

[0050] In addition, similar to the first organic layer 34 on the first surface, the second organic layer 36 on the first surface may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying.

[0051] [First surface, third conductive layer 35] The third conductive layer 35 of the first surface is a conductive layer located on the first surface 13, adjacent to the second conductive layer 33 of the first surface, i.e., the signal layer 331, with a gap in the upward direction D31 in Figure 1. In the example of Figure 1, the third conductive layer 35 of the first surface is located on the second organic layer 36 of the first surface.

[0052] The ground layer 351 in the strip line on the first surface 13 side is composed of a portion of the first surface third conductive layer 35. The portion of the first surface third conductive layer 35 other than the ground layer 351 constitutes a terminal portion 352 to which the IC chip is electrically connected, and the terminal portion 352 is electrically connected to the through electrode 22 via the signal layer 331.

[0053] The thickness of the third conductive layer 35 on the first surface may be the same as or different from the thickness of the first conductive layer 31 on the first surface.

[0054] The third conductive layer 35 on the first surface may include sequentially stacked seed layers and plating layers, similar to the through-electrode 22 and the first conductive layer 31 on the first surface. The material constituting the third conductive layer 35 on the first surface is the same as the material constituting the through-electrode 22 and the first conductive layer 31 on the first surface.

[0055] [Ground Layer 351] The ground layer 351 is located on the first surface second organic layer 36, is electrically connected to a reference potential such as ground potential, and is electrically insulated from the through electrode 22. It is a layer that controls the characteristic impedance of the signal layer 331. The ground layer 351 has a larger total area than the signal layer 331. The ground layer 351 faces the signal layer 331 in the thickness direction D3, with the first surface second organic layer 36 sandwiched between them. In order to control the characteristic impedance of the signal layer 331 to a desired value, the ground layer 351 has a predetermined gap d1 in the thickness direction D3 between it and the signal layer 331.

[0056] (Second wiring structure section 40) Next, the second wiring structure 40 will be described. The second wiring structure 40 has layers such as conductive layers and insulating layers provided on the second surface 14 side of the substrate 12 to constitute an electrical circuit. In the example in Figure 1, the second wiring structure 40 has a second surface first conductive layer 41, a second surface first organic layer 42 which is an example of a fourth insulating layer, a second surface second conductive layer 43, a second surface second organic layer 44 which is an example of a second insulating layer, and a second surface third conductive layer 45.

[0057] Similar to the first wiring structure 30, the second wiring structure 40 has a strip line that sandwiches the front and back of the signal line between the ground plane and an insulating layer. Hereinafter, the strip line of the second wiring structure 40 will also be referred to as the strip line on the second surface 14 side. The strip line on the second surface 14 side is electrically connected to the strip line on the first surface 13 side via a through electrode 22. As shown in Figures 1 and 3, the strip line on the second surface 14 side has a signal layer 431, which is an example of a second signal layer, a ground layer 411, and a ground layer 451, which is an example of a second ground layer.

[0058] [Second surface, first conductive layer 41] The second surface first conductive layer 41 is a conductive layer located on the second surface 14 of the substrate 12. The ground layer 411 in the strip line on the second surface 14 side is composed of a portion of the second surface first conductive layer 41.

[0059] As shown in Figure 1, the second surface first conductive layer 41, like the first surface first conductive layer 31, has a seed layer 221 and a plating layer 222. The seed layer 221 is located on the second surface 14 of the substrate 12. The plating layer 222 is located on the seed layer 221.

[0060] [Ground Layer 411] The ground layer 411 is located on the second surface 14, electrically connected to a reference potential such as ground potential, and electrically insulated from the through electrode 22. It is a layer that controls the characteristic impedance of the signal layer 431. The ground layer 411 has a larger total area than the signal layer 431. The ground layer 411 is located on the second surface 14, adjacent to the signal layer 431 with a gap in the upper D31 of the thickness direction D3 as shown in Figure 1. In the examples of Figures 1 and 3, the ground layer 411 faces the signal layer 431 with the second surface first organic layer 42 sandwiched between them. To control the characteristic impedance of the signal layer 431 to a desired value, the ground layer 411 has a predetermined gap d4 in the thickness direction D3 between it and the signal layer 431.

[0061] [Second side first organic layer 42] The second surface first organic layer 42 is located on the second surface 14 or the second surface first conductive layer 41, contains an organic material, and is an insulating layer.

[0062] The second surface first organic layer 42 may have a thickness h4 and elastic modulus that take into account both impedance matching and stress balance of the transmission line between the first surface 13 and the second surface 14. For example, the second surface first organic layer 42 may have a greater thickness and a lower elastic modulus than the first surface first organic layer 34. In other words, the difference in the product of thickness and elastic modulus between the first surface first organic layer 34 and the second surface first organic layer 42 is kept below a threshold. As an example, the second surface first organic layer 42 may have a thickness h4 of 19 μm and an indentation modulus of 2.10 GPa at 25°C.

[0063] Similar to the first organic layer 34 on the first surface, the first organic layer 42 on the second surface may contain an organic material having a dielectric loss tangent of 0.003 or less, preferably 0.002 or less, and more preferably 0.001 or less. As the organic material for the first organic layer 42 on the second surface, polyimide, epoxy resin, etc., can be used. By constructing the first organic layer 42 on the second surface using an organic material with a small dielectric loss tangent, it is possible to suppress the fact that a portion of the electrical signal that should pass through the signal layer 431 passes through the first organic layer 42 on the second surface. This makes it possible to broaden the bandwidth of the signal transmission substrate 10 to the high-frequency side.

[0064] The first organic layer 42 on the second surface may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying.

[0065] [Second surface, second conductive layer 43] The second conductive layer 43 of the second surface is a conductive layer located on the second surface 14, adjacent to the first conductive layer 41 of the second surface, with a gap in the downward direction D32 of Figure 1 within the thickness direction D3. In the example of Figure 1, the second conductive layer 43 of the second surface is located on the first organic layer 42 of the second surface. The signal layer 431 in the strip line on the second surface 14 side is composed of a portion of the second conductive layer 43 of the second surface.

[0066] The thickness of the second conductive layer 43 on the second surface may be the same as or different from the thickness of the first conductive layer 41 on the second surface.

[0067] The second conductive layer 43 on the second surface may include a seed layer and a plating layer sequentially laminated on the first organic layer 42 on the second surface, similar to the through electrode 22 and the first conductive layer 31 on the first surface. The material constituting the second conductive layer 43 on the second surface is the same as the material constituting the through electrode 22 and the first conductive layer 31 on the first surface.

[0068] [Signal layer 431] The signal layer 431 is located on the second surface first organic layer 42, which is an example on the second surface 14, and is electrically connected to the signal layer 331 on the first surface 13 via a through electrode 22. Together with the signal layer 331, it transmits electrical signals such as high-frequency signals. The signal layer 431 extends along the first surface 13 in the extension direction D1 shown in Figure 1. In the example in Figure 1, the signal layer 431 is electrically connected to the through electrode 22 at one end in the extension direction D1.

[0069] The thickness of the signal layer 431 is preferably 5 μm or more. By making the thickness of the signal layer 431 5 μm or more, the conductor resistance loss of the signal layer 431 can be reduced, thereby suppressing signal transmission loss. The thickness of the signal layer 431 is more preferably 20 μm or less. By making the thickness of the signal layer 431 20 μm or less, interfacial stress between the signal layer 431 and the second surface first organic layer 42 can be suppressed, thereby suppressing delamination of the signal layer 431.

[0070] In Figure 3, the dimension of the signal layer 431 in the width direction D2, indicated by the symbol W2, i.e., the wiring width W2, is a wiring width W2 that takes into account the impedance matching of the transmission path between the first surface 13 and the second surface 14. Specifically, the wiring width W2 of the signal layer 431 is larger than the wiring width W1 of the signal layer 331 on the first surface 13. For example, in order to match the capacitive component of the characteristic impedance with the signal layer 331, the ratio S2 / d2 of the area S2 of the signal layer 431 to the distance d2 between the signal layer 431 and the ground layer 451 may have a predetermined proportional relationship with the ratio S1 / d1 of the area S1 of the signal layer 331 to the distance d1 between the signal layer 331 and the ground layer 351, or for example, they may be the same. Furthermore, the ratio S2 / d4 of the area S2 of the signal layer 431 to the distance d4 between the signal layer 431 and the ground layer 411 may have a predetermined proportional relationship with S1 / d3 of the ratio S1 / d3 of the area S1 of the signal layer 331 to the distance d3 between the signal layer 331 and the ground layer 311, for example, they may be identical. In this way, by having the signal layer 431 have a relationship of wiring widths W2 and W1 that takes impedance matching with the signal layer 331 as one of the conditions, both impedance matching and stress balance can be ensured. This makes it possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0071] [Second surface second organic layer 44] The second organic layer 44 on the second surface is located on the first organic layer 42 on the second surface or the second conductive layer 43 on the second surface, and is a layer that contains an organic material and has insulating properties.

[0072] Similar to the first organic layer 34 on the first surface, the second organic layer 36 on the first surface, and the first organic layer 42 on the second surface, the second organic layer 44 on the second surface has a thickness h2 and elastic modulus that take into account both impedance matching and stress balance of the transmission line between the first surface 13 side and the second surface 14 side.

[0073] Specifically, the second organic layer 44 on the second surface is thicker and has a lower elastic modulus than the second organic layer 36 on the first surface. A lower elastic modulus means lower rigidity, or in other words, it is softer.

[0074] In this embodiment, considering the electrical connection with an IC chip with a narrow terminal pitch, the wiring width W1 of the signal layer 331 on the first surface 13 where the IC chip is mounted is made smaller than the wiring width W2 of the signal layer 431 on the second surface 14 where it is mounted on the motherboard. Furthermore, in order to match the impedance between the signal layers 331 and 431 with different wiring widths W1 and W2, the thickness h2 of the second organic layer 44 on the second surface, which is proportional to the distance d2 between the signal layer 431 with a larger wiring width W2 and the ground layer 451, is made larger than the thickness h1 of the second organic layer 36 on the first surface, which is proportional to the distance d1 between the signal layer 331 with a smaller wiring width W1 and the ground layer 351. Furthermore, in order to balance the stress on the second surface 14 side due to the thicker second organic layer 44 and the stress on the first surface 13 side due to the thinner second organic layer 36 on the first surface, the elastic modulus of the thicker second organic layer 44 is made smaller than that of the thinner second organic layer 36 on the first surface. In this way, the second organic layer 36 on the first surface and the second organic layer 44 on the second surface have a relationship in terms of thickness and elastic modulus that takes into account both impedance matching and stress balance, thereby ensuring both impedance matching and stress balance. This makes it possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0075] The second organic layer 44 on the second surface may have a difference in the product of thickness and elastic modulus between it and the second organic layer 36 on the first surface that is below a threshold. Specifically, the difference between the product of thickness and elastic modulus of the second organic layer 36 on the first surface and the product of thickness and elastic modulus of the second organic layer 44 on the second surface may have a ratio of less than or equal to a threshold with respect to the product of thickness and elastic modulus of the second organic layer 44 on the second surface. The threshold may be 15%. As an example, the second organic layer 44 on the second surface may have a thickness h4 of 19 μm and an indentation modulus of 2.10 GPa at 25°C. The product of thickness and elastic modulus of organic layers 36 and 44 is proportional to the stress acting on organic layers 36 and 44. Therefore, by making the difference in the product of thickness and elastic modulus, which is proportional to the stress, between the second organic layer 36 on the first surface and the second organic layer 44 on the second surface below a threshold, both impedance matching and stress balance can be more effectively ensured. This makes it possible to more effectively achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0076] The difference between the product of the thermal expansion coefficient, thickness, and elastic modulus of the second organic layer 44 on the second surface and the product of the thermal expansion coefficient, thickness, and elastic modulus of the second organic layer 36 on the first surface may be less than or equal to a threshold. Specifically, the difference between the product of the thermal expansion coefficient, thickness, and elastic modulus of the second organic layer 36 on the first surface and the product of the thermal expansion coefficient, thickness, and elastic modulus of the second organic layer 44 on the second surface may have a ratio of less than or equal to a threshold with respect to the product of the thermal expansion coefficient, thickness, and elastic modulus of the second organic layer 44 on the second surface. The threshold may be 15%. The product of the thermal expansion coefficient, thickness, and elastic modulus of the organic layers 36 and 44 is proportional to the stress of the organic layers 36 and 44 more precisely than the product of thickness and elastic modulus. Therefore, by making the difference between the product of the thermal expansion coefficient, thickness, and elastic modulus that is precisely proportional to the stress between the second organic layer 36 on the first surface and the second organic layer 44 on the second surface less than or equal to a threshold, both impedance matching and stress balance can be more effectively ensured. This makes it possible to more effectively achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0077] The sum of the product of the thickness h1 and elastic modulus of the first surface second organic layer 36 and the product of the thickness h3 and elastic modulus of the first surface first organic layer 34 may have a difference of less than or equal to a threshold of the sum of the product of the thickness h2 and elastic modulus of the second surface second organic layer 44 and the product of the thickness h4 and elastic modulus of the second surface first organic layer 42. Specifically, the difference between the sum of the product of the thickness h1 and elastic modulus of the first surface second organic layer 36 and the product of the thickness h3 and elastic modulus of the first surface first organic layer 34, and the sum of the product of the thickness h2 and elastic modulus of the second surface second organic layer 44 and the product of the thickness h4 and elastic modulus of the second surface first organic layer 42, may have a ratio of less than or equal to a threshold of the sum of the product of the thickness h2 and elastic modulus of the second surface second organic layer 44 and the product of the thickness h4 and elastic modulus of the second surface first organic layer 42. The threshold may be 15%. The stress on the first surface 13 side involves the stress acting on each of the organic layers 34 and 36 on the first surface 13. Similarly, the stress on the second surface 14 side involves the stress acting on each of the organic layers 42 and 44 on the second surface 14. Therefore, by ensuring that the sum of the product of the thickness h1 of the second organic layer 36 on the first surface and its elastic modulus, and the product of the thickness h3 of the first organic layer 34 on the first surface and its elastic modulus, is less than or equal to a threshold difference from the sum of the product of the thickness h2 of the second organic layer 44 on the second surface and its elastic modulus, and the product of the thickness h4 of the first organic layer 42 on the second surface and its elastic modulus, the stress balance can be more effectively ensured. This makes it possible to more effectively achieve both improved signal transmission efficiency and suppression of warping of the substrate 12. Thus, the configuration in which the sum of the products of the thickness and elastic modulus of the organic layer differs by less than or equal to a threshold between the first surface 13 side and the second surface 14 side may also be the case when an additional organic layer, i.e., a third insulating layer, is provided on the ground layer 351, and an additional organic layer, i.e., a fourth insulating layer, is provided on the ground layer 451.

[0078] Similar to the first organic layer 34 on the first surface, the second organic layer 44 on the second surface contains an organic material having a dielectric loss tangent of 0.003 or less, preferably 0.002 or less, and more preferably 0.001 or less. As the organic material for the second organic layer 44 on the second surface, polyimide, epoxy resin, etc., can be used. By constructing the second organic layer 44 on the second surface using an organic material with a small dielectric loss tangent, it is possible to suppress the fact that a portion of the electrical signal that should pass through the signal layer 431 passes through the second organic layer 44 on the second surface. This makes it possible to further suitably extend the bandwidth of the signal transmission substrate 10 to the high-frequency side.

[0079] In addition, similar to the first organic layer 34 on the first surface, the second organic layer 44 on the second surface may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying.

[0080] [Second surface, third conductive layer 45] The second surface third conductive layer 45 is a conductive layer located on the first surface 13, adjacent to the second surface second conductive layer 43, i.e., the signal layer 431, with a gap in the downward direction D32 in Figure 1. In the example in Figure 1, the second surface third conductive layer 45 is located on the second surface second organic layer 44. The ground layer 4511 in the strip line on the second surface 14 side is composed of a portion of the second surface third conductive layer 45. The portion of the second surface third conductive layer 45 other than the ground layer 451 constitutes a terminal portion 452 that is electrically connected to the motherboard, and the terminal portion 452 is electrically connected to the through electrode 22 via the signal layer 431.

[0081] The thickness of the third conductive layer 45 on the second surface may be the same as or different from the thickness of the first conductive layer 41 on the second surface.

[0082] The second surface third conductive layer 45 may include sequentially stacked seed layers and plating layers, similar to the through-electrode 22 and the first surface first conductive layer 31. The material constituting the second surface third conductive layer 45 is the same as the material constituting the through-electrode 22 and the first surface first conductive layer 31.

[0083] [Ground Layer 451] The ground layer 451 is located on the second organic layer 44 of the second surface, electrically connected to a reference potential such as the ground potential, and electrically insulated from the through electrode 22. It is a layer that controls the characteristic impedance of the signal layer 431. The ground layer 451 has a larger total area than the signal layer 431. The ground layer 451 faces the signal layer 431 with the second organic layer 44 of the second surface sandwiched between them. In order to control the characteristic impedance of the signal layer 431 to a desired value that matches the characteristic impedance of the signal layer 331, the ground layer 451 has a predetermined gap d2 in the thickness direction D3 between it and the signal layer 431.

[0084] Manufacturing method of signal transmission board 10 An example of a method for manufacturing the signal transmission board 10 will be described below with reference to Figures 4 to 17.

[0085] (Process for forming the through hole 20) Figure 4 is a cross-sectional view showing a method for manufacturing a signal transmission substrate 10 according to this embodiment. First, a substrate 12 is prepared. Next, a resist layer is provided on at least one of the first surface 13 and the second surface 14. Then, an opening is provided in the resist layer at a position corresponding to the through hole 20. Next, by processing the substrate 12 at the opening in the resist layer, the through hole 20 can be formed in the substrate 12 as shown in Figure 4. As a method for processing the substrate 12, dry etching methods such as reactive ion etching and deep reactive ion etching, or wet etching methods can be used.

[0086] Alternatively, through-holes 20 may be formed in the substrate 12 by irradiating it with a laser. In this case, a resist layer may not be provided. As the laser for laser processing, an excimer laser, Nd:YAG laser, femtosecond laser, etc., can be used. When using an Nd:YAG laser, a fundamental wave with a wavelength of 1064 nm, a second harmonic with a wavelength of 532 nm, a third harmonic with a wavelength of 355 nm, etc., can be used.

[0087] Furthermore, laser irradiation and wet etching can be combined as appropriate. Specifically, first, a modified layer is formed in the area of ​​the substrate 12 where the through-holes 20 are to be formed by laser irradiation. Next, the substrate 12 is immersed in hydrogen fluoride or the like to etch the modified layer. This allows the through-holes 20 to be formed in the substrate 12. Alternatively, the through-holes 20 may be formed in the substrate 12 by blasting, which involves spraying an abrasive material onto the substrate 12.

[0088] By processing the substrate 12 from both the first surface 13 side and the second surface 14 side, a through-hole 20 having a shape that decreases in width towards the center in the thickness direction of the substrate 12, as shown in Figure 4, can be formed.

[0089] (Process for forming the through electrode 22, the first conductive layer 31 on the first surface, and the first conductive layer 41 on the second surface) Figure 5 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 4. After forming the through holes 20, through electrodes 22 are formed on the side walls 21 of the through holes 20, as shown in Figure 5. Specifically, a seed layer 221 is formed on the first surface 13, the second surface 14, and the side walls 21 of the substrate 12 by sputtering, vapor deposition, electroless plating, or the like.

[0090] Figure 6 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 5. After forming the seed layer 221, a resist layer 37 is partially formed on the seed layer 221, as shown in Figure 6.

[0091] Figure 7 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 6. After forming the resist layer 37, as shown in Figure 7, a plating layer 222 is formed on the seed layer 221 that is not covered by the resist layer 37 by electroplating using the resist layer 37 as a mask.

[0092] Figure 8 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 7. After forming the plating layer 222, the resist layer 37 is removed as shown in Figure 8.

[0093] Figure 9 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 8. After removing the resist layer 37, as shown in Figure 9, the portion of the seed layer 221 where the resist layer 37 was formed is removed by wet etching. This makes it possible to form the through electrode 22, the first conductive layer 31 on the first surface including the ground layer 311, and the first conductive layer 41 on the second surface including the ground layer 411. Note that an annealing step of the plating layer 222 may also be performed.

[0094] (Process for forming the first organic layer 34 on the first surface and the first organic layer 42 on the second surface) Figure 10 is a cross-sectional view showing a method for manufacturing a signal transmission substrate 10 according to this embodiment, following Figure 9. After forming the through-electrode 22, the first conductive layer 31 on the first surface, and the first conductive layer 41 on the second surface, the first organic layer 34 on the first surface 13 or on the first conductive layer 31 on the first surface is formed, as shown in Figure 10. Also, as shown in Figure 10, the first organic layer 42 on the second surface 14 or on the ground layer 411 is formed. The first organic layer 34 on the first surface and the first organic layer 42 on the second surface may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying. In this case, the thickness h4 of the first organic layer 42 on the second surface may be made greater than the thickness h3 of the first organic layer 34 on the first surface, and the elastic modulus of the first organic layer 42 on the second surface may be made less than the elastic modulus of the first organic layer 34 on the first surface.

[0095] (Process for forming the second conductive layer 33 on the first surface and the second conductive layer 43 on the second surface) Figure 11 is a cross-sectional view showing the manufacturing method of the signal transmission substrate 10 according to this embodiment, following Figure 10. After forming the first organic layer 34 on the first surface and the first organic layer 42 on the second surface, as shown in Figure 11, the second conductive layer 33 on the first surface, which includes the signal layer 331, is formed on the first organic layer 34 on the first surface. Also, as shown in Figure 11, the second conductive layer 43 on the second surface, which includes the signal layer 431, is formed on the first organic layer 42 on the second surface. The second conductive layer 33 on the first surface and the second conductive layer 43 on the second surface may be formed by patterning the seed layer 221 and the plating layer 222 by photolithography using the resist layer 37 as a mask, similar to the first conductive layer 31 on the first surface and the first conductive layer 41 on the second surface. At this time, the wiring width W2 of the signal layer 431 shown in Figure 3 is formed to be larger than the wiring width W1 of the signal layer 331 shown in Figure 2.

[0096] (Process for forming the second organic layer 36 on the first surface and the second organic layer 44 on the second surface) Figure 12 is a cross-sectional view showing a method for manufacturing the signal transmission substrate 10 according to this embodiment, following Figure 11. After forming the first surface second conductive layer 33 and the second surface second conductive layer 43, as shown in Figure 12, the first surface second organic layer 36 is formed on the first surface first organic layer 34 or the first surface second conductive layer 33. Also, as shown in Figure 12, the second surface second organic layer 44 is formed on the second surface first organic layer 42 or the second surface second conductive layer 43. The first surface second organic layer 36 and the second surface second organic layer 44 may be formed, for example, by exposure and development treatment using a photosensitive film containing an organic material, or by applying a liquid containing an organic material by spin coating and drying.

[0097] In this case, the thickness h2 of the second organic layer 44 on the second surface is made greater than the thickness h1 of the second organic layer 36 on the first surface, and the elastic modulus of the second organic layer 44 on the second surface is made smaller than the elastic modulus of the second organic layer 36 on the first surface. For example, the second organic layer 44 on the second surface is formed such that the difference in the product of thickness and elastic modulus of the second organic layer 44 on the second surface is less than or equal to a threshold.

[0098] After forming the first surface second organic layer 36 and the second surface second organic layer 44, the first surface third conductive layer 35 is formed on the first surface second organic layer 36, and the second surface third conductive layer 45 is formed on the second surface second organic layer 44, thereby obtaining the signal transmission substrate 10 shown in Figure 1.

[0099] (Example of experiment) Next, an experimental example of the signal transmission board 10 according to this embodiment will be described. Figure 13 is a diagram showing the correspondence between temperature, the stress of the first insulating layer according to temperature, and a parameter correlated with the stress in an experimental example of the signal transmission board 10 according to this embodiment. Figure 14 is a diagram showing the correspondence between temperature, the stress of the second insulating layer according to temperature, and a parameter correlated with the stress in an experimental example of the signal transmission board 10 according to this embodiment. In Figures 13 and 14, the number containing "E" is the number obtained by multiplying the number immediately preceding "E" by a number obtained by exponentiation with base 10 and the number immediately following "E" as the exponent. For example, "6.01E+05" in Figure 13 is 6.01 × 10 5 That is the case.

[0100] In the experimental example, a sample was prepared that simulated the signal transmission substrate 10 shown in Figure 1, with a first insulating layer on the first surface 13 of the substrate 12 and a second insulating layer on the second surface 14 of the substrate 12. The stress balance between the first insulating layer and the second insulating layer was evaluated for this sample. As shown in Figure 13, the first insulating layer was made of PN, a photosensitive polyimide coating agent manufactured by Toray Industries, Inc., with a thickness of 10 μm. As shown in Figure 14, the second insulating layer was made of LPA, a photosensitive polyimide adhesive sheet manufactured by Toray Industries, Inc., with a thickness of 19 μm.

[0101] As shown in Figures 13 and 14, the curing temperature, or thermosetting temperature, of both the first and second insulating layers is 200°C.

[0102] As shown in Figures 13 and 14, the difference in the product of the indentation modulus and thickness between the first and second insulating layers was 15% or less at temperatures below the curing temperature. For example, at room temperature (25°C), the product of the indentation modulus and thickness of the first insulating layer was 37, while the product of the indentation modulus and thickness of the second insulating layer was 39.9. Therefore, at 25°C, the difference in the product of the indentation modulus and thickness between the first and second insulating layers is 2.9. Dividing this difference of 2.9 by the product of the indentation modulus and thickness of the second insulating layer (39.9) and multiplying by 100 gives a percentage of 2.9, which is 15% or less, and is 7.27%.

[0103] Furthermore, as shown in Figures 13 and 14, the ratio of the difference between the thermal expansion coefficient α, the temperature change ΔT relative to the curing temperature, the elastic modulus E, and the thickness h (α × ΔT × E × h) between the first and second insulating layers in the temperature range from a curing temperature of 200°C (an example of the first temperature) to room temperature of 25°C (an example of the second temperature after curing) was 6.25%, calculated by {(4.08E+05-3.84E+05) / 3.84+E05}×100. The denominator of the ratio is the product of the thermal expansion coefficient α, the temperature change ΔT, the elastic modulus E, and the thickness h of the second insulating layer. Also, α × ΔT × E is the stress acting on the first and second insulating layers in response to the temperature change from the curing temperature. The stress at the curing temperature is zero. The ratio of 6.25% obtained from Figures 13 and 14 is a sufficiently low value when the ratio threshold is set to 15%.

[0104] Experimental examples show that by reducing the difference in the product of the elastic modulus and thickness between the first insulating layer and the second insulating layer to 15% or less, the difference in stress between the first surface 13 and the second surface 14 can be sufficiently suppressed. In other words, experimental examples show that warping of the substrate 12 during the cooling period after the curing process can be effectively suppressed.

[0105] Figure 15 is a perspective view of an indenter I that can be used to measure the indentation modulus correlated with the stress of the first and second insulating layers in an experimental example of the signal transmission substrate 10 according to this embodiment. Figure 16 is a cross-sectional view showing an example of measuring the indentation modulus of the first and second insulating layers in an experimental example of the signal transmission substrate 10 according to this embodiment. Figure 17 is a graph showing an example of measuring the indentation modulus of the first and second insulating layers in an experimental example of the signal transmission substrate 10 according to this embodiment. In Figure 17, the horizontal axis shows the indentation depth of the indenter I, and the vertical axis shows the load applied to the first and second insulating layers by the indenter I. Hereinafter, the first and second insulating layers will also be simply referred to as insulating layers.

[0106] The indentation modulus shown in Figures 13 and 14 can be measured by a nanoindentation test using a Berkovich-type indenter I shown in Figure 15. The indenter I shown in Figure 15 has a pyramidal face apex angle of 115°. As shown in Figure 16, in the nanoindentation test, the indenter I, mounted on a transducer, is pressed into the insulating layer placed on the stage while applying a load with the transducer. As shown in Figure 17, the load applied to the insulating layer from the indenter I increases following a quadratic load curve A as the indentation depth h of the indenter I increases. Also, as shown in Figure 16, the surface of the insulating layer deforms from the initial surface to the surface under load due to the indentation load of the indenter I. This deformation is due to both elastic and plastic deformation. As shown in Figures 16 and 17, when the indentation is complete, the indentation depth of the indenter I reaches its maximum value h. max As a result, the load also reaches its maximum value P. max This is the result. After the indentation of the indenter I is complete, the indenter I is moved in the opposite direction to the indentation direction. As a result, as shown in Figure 17, the load applied to the insulating layer by the indenter I decreases by following a quadratic load-unloading curve B that is steeper than the load-loading curve A. Also, as shown in Figure 16, due to the elastic recovery accompanying the unloading of the indenter I, the surface of the insulating layer deforms from the surface under load to the surface after unloading. Note that the surface after unloading exhibits a deformation mark that is more recessed than the initial surface due to the effect of plastic deformation under load. In Figures 16 and 17, the depth of the surface after unloading is hf It is.

[0107] In the above nanoindentation test, the indentation elastic modulus E of the insulating layer IT can be obtained by the following formula. E IT ={1-(V S ) 2} / [(1 / E r )-{1-(V i ) 2} / E i (1) <00已发送00470>However, in Equation (1), V S is the Poisson's ratio of the insulating layer. V i is the Poisson's ratio of the indenter I. E i is the elastic modulus of the indenter I. E r is the reduced elastic modulus of the indentation contact point.

[0108] The reduced elastic modulus E of the indentation contact point in Equation (1) r can be obtained by the following formula. E r =π 1 / 2 / 2CA p <00000已发送1>(2) [[ID=已发送0]] However, in Equation (2), C is the slope dP / dh of the tangent line of the load unloading curve B at the maximum value P of the load shown in Fig. 17 max . A p is the projected area where the indenter I contacts the insulating layer.

[0109] A in Equation (2) p can be obtained by the following formula. A p =23.96×{h max -ε(h max -h C )} (3) However, in Equation (3), h max is the maximum value of the indentation depth described above. ε is a correction coefficient depending on the geometric shape of the indenter I, and is 0.75 in the case of a diamond Vickers indenter. h C is the maximum value P of the load described above maxThis is the intersection point of the tangent line to the load-unloading curve B and the horizontal axis in Figure 17.

[0110] The effects brought about by this embodiment will be described below.

[0111] In this embodiment, the signal transmission substrate 10 has a signal layer 431 on the second surface 14 with a width dimension W2 greater than the signal layer 331 on the first surface 13 with a width dimension W1. Furthermore, the second organic layer 44 on the second surface has a greater thickness and a smaller modulus of elasticity than the second organic layer 36 on the first surface.

[0112] If the thickness of the second organic layer 44 on the second surface is simply made greater than the thickness of the second organic layer 36 on the first surface, considering only impedance matching between the first surface 13 and the second surface 14, the stress on the second surface 14 due to the second organic layer 44 will be greater than the stress on the first surface 13 due to the second organic layer 36 on the first surface, and there is a risk that the substrate 12 will warp toward the second surface 14 side where the stress is greater. In contrast, in this embodiment, by making the elastic modulus of the thicker second organic layer 44 less elastic than the elastic modulus of the thinner second organic layer 36 on the first surface, both impedance matching and stress balance can be ensured between the first surface 13 and the second surface 14. This makes it possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0113] Furthermore, in this embodiment, improved signal transmission efficiency and suppression of substrate warping 12 can be achieved in a strip line, which has superior noise characteristics compared to a coplanar line.

[0114] (First variation) Next, a first modified example in which the second conductive layer 33 on the first surface and the second conductive layer 43 on the second surface constitute a coplanar line will be described. Figure 18 is a cross-sectional view of the signal layer 331 side on the first surface 13 showing the signal transmission substrate 10 according to the first modified example of this embodiment. Figure 18 corresponds in position to the cross-sectional view in Figure 2. Figure 19 is a cross-sectional view of the signal layer 431 side on the second surface 14 showing the signal transmission substrate 10 according to the first modified example of this embodiment. Figure 19 corresponds in position to the cross-sectional view in Figure 3.

[0115] Figures 1 to 17 illustrate an example in which the second conductive layer 33 of the first surface forms a strip line on the first surface 13 side between the first conductive layer 31 of the first surface and the third conductive layer 35 of the first surface, and the second conductive layer 43 of the second surface forms a strip line on the second surface 14 side between the first conductive layer 41 of the second surface and the third conductive layer 45 of the second surface.

[0116] In contrast, in the first modified example, the second conductive layer 33 on the first surface constitutes the coplanar line on the first surface 13 side, and the second conductive layer 43 on the second surface constitutes the coplanar line on the second surface 14 side.

[0117] Specifically, as shown in Figure 18, the second conductive layer 33 on the first surface has a signal layer 331 and a ground layer 332 adjacent to the signal layer 331 with a gap in the width direction D2, as an example of a third ground layer. Also, as shown in Figure 19, the second conductive layer 43 on the second surface has a signal layer 431 and a ground layer 432 adjacent to the signal layer 431 with a gap in the width direction D2, as an example of a fourth ground layer.

[0118] According to the first modification, even in a coplanar transmission line, the wiring width W2 of the signal layer 431 on the second surface 14 is greater than the wiring width W1 of the signal layer 331 on the first surface 13, and the second organic layer 44 on the second surface has a greater thickness and a smaller modulus of elasticity than the second organic layer 36 on the first surface. This ensures both impedance matching and stress balance between the first surface 13 side and the second surface 14 side. This makes it possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0119] (Second variation) Next, a second modification will be described, which has a differential transmission line that transmits one data using two signal lines. Figure 20 is a cross-sectional view of the signal layer 331 side on the first surface 13 showing the signal transmission board 10 according to the second modification of this embodiment. Figure 20 corresponds in position to the cross-sectional view in Figure 2. Figure 21 is a cross-sectional view of the signal layer 431 side on the second surface 14 showing the signal transmission board 10 according to the second modification of this embodiment. Figure 21 corresponds in position to the cross-sectional view in Figure 3.

[0120] Up to this point, we have described an example of a signal transmission board 10 equipped with a single-ended coplanar line or strip line that transmits one data signal per signal line. In contrast, the second modified signal transmission board 10 has a differential transmission line.

[0121] Specifically, as shown in Figure 20, the second conductive layer 33 on the first surface has two signal layers 331a and 331b spaced apart in the width direction D2, and a ground layer 332 spaced outward in the width direction D2 relative to the signal layers 331a and 331b. The two signal layers 331a and 331b divide and transmit a single electrical signal. As shown in Figure 21, the second conductive layer 43 on the second surface has two signal layers 431a and 431b spaced apart in the width direction D2, and a ground layer 432 spaced outward in the width direction D2 relative to the signal layers 431a and 431b. Each of the two signal layers 431a and 431b is electrically connected to each of the two signal layers 331a and 331b via through electrodes 22. The two signal layers 431a and 431b transmit the same electrical signals as those transmitted by the two signal layers 331a and 331b, respectively.

[0122] According to the second modification, by having a differential transmission line, a signal waveform can be formed with a small voltage. Since a signal waveform can be formed with a small voltage, the signal rise time can be shortened. Since the signal rise time can be shortened, high-frequency electrical signals can be transmitted appropriately compared to the single-ended method. Furthermore, according to the second modification, even in the differential transmission line, the wiring width W2 of the signal layers 431a and 431b on the second surface 14 is larger than the wiring width W1 of the signal layers 331a and 331b on the first surface 13, and the second organic layer 44 on the second surface has a greater thickness and a smaller modulus of elasticity than the second organic layer 36 on the first surface, thereby ensuring both impedance matching and stress balance between the first surface 13 side and the second surface 14 side. This makes it possible to achieve both improved signal transmission efficiency and suppression of warping of the substrate 12.

[0123] (Third variation) Next, a third modification having a capacitor will be described. Figure 22 is a cross-sectional view showing the signal transmission board 10 according to the third modification of this embodiment.

[0124] As shown in Figure 22, in the third modified example, a portion of the signal layer 311, together with the dielectric 32 located on the signal layer 311 and the first-surface second conductive layer 33 located on the dielectric 32, constitutes a MIM (Metal-Insulator-Metal) structure capacitor 15. The dielectric 32 contains, for example, a silicon nitride such as SiN.

[0125] The signal transmission board 10 of this disclosure can also be applied to transmission lines other than the various transmission lines described above. For example, the signal transmission board 10 may be applied to a microstrip line.

[0126] It is possible to make various modifications to the embodiments described above. Hereinafter, modifications will be described with reference to the drawings as necessary. In the following description and the drawings used therein, parts that can be configured similarly to the embodiments described above will be given the same reference numerals as those used for the corresponding parts in the embodiments described above, and redundant explanations will be omitted. Furthermore, if it is clear that the effects and advantages obtained in the embodiments described above can also be obtained in the modifications, the explanation may be omitted.

[0127] Examples of products that incorporate electrode substrates Figure 23 shows an example of a product on which the signal transmission board 10 according to the embodiment of this disclosure can be mounted. The signal transmission board 10 according to the embodiment of this disclosure can be used in a variety of products. For example, it can be mounted in a notebook personal computer 110, a tablet terminal 120, a mobile phone 130, a smartphone 140, a digital video camera 150, a digital camera 160, a digital clock 170, a server 180, etc. [Explanation of Symbols]

[0128] 10 Signal transmission board 12 circuit boards 331 Signal Layer 34 1st surface 1st organic layer 351 Ground Layer 431 Signal Layer 44 2nd side 2nd organic layer 451 Ground Layer

Claims

1. A substrate having a first surface and a second surface opposite to the first surface, A first signal layer located on the first surface, A first insulating layer located on the first signal layer, A first ground layer located on the first insulating layer, A second signal layer located on the second surface and electrically connected to the first signal layer, A second insulating layer located on the second signal layer, A second ground layer located on the second insulating layer, A fifth ground layer located between the first surface and the first signal layer, It comprises a sixth ground layer located between the second surface and the second signal layer, The ratio (S2 / d2) of the area of ​​the second signal layer (S2) to the distance (d2) between the second signal layer and the second ground layer is equal to the ratio (S1 / d1) of the area of ​​the first signal layer (S1) to the distance (d1) between the first signal layer and the first ground layer. A signal transmission path in which the ratio (S2 / d4) of the area of ​​the second signal layer (S2) to the distance (d4) between the second signal layer and the sixth ground layer is equal to the ratio (S1 / d3) of the area of ​​the first signal layer (S1) to the distance (d3) between the first signal layer and the fifth ground layer.

2. The second signal layer has a larger dimension in the width direction intersecting the signal transmission direction than the first signal layer. The signal transmission path according to claim 1, wherein the second insulating layer has a larger dimension in the thickness direction intersecting the signal transmission direction and the width direction than the first insulating layer, and has a smaller modulus of elasticity.

3. The signal transmission path according to claim 2, wherein the difference between the product of the thickness direction dimension and the elastic modulus of the first insulating layer and the product of the thickness direction dimension and the elastic modulus of the second insulating layer is a ratio less than or equal to a threshold value with respect to the product of the thickness direction dimension and the elastic modulus of the second insulating layer.

4. The signal transmission path according to claim 3, wherein the threshold is 15%.

5. The signal transmission path according to claim 3 or 4, wherein the difference between the product of the thermal expansion coefficient, thickness dimension, and elastic modulus of the first insulating layer and the product of the thermal expansion coefficient, thickness dimension, and elastic modulus of the second insulating layer is less than or equal to a threshold ratio with respect to the product of the thermal expansion coefficient, thickness dimension, and elastic modulus of the second insulating layer.

6. At least one third insulating layer located on the first signal layer and at least one on the side opposite to the first signal layer, The system further comprises at least one fourth insulating layer located on the second signal layer and at least one on the side opposite to the second signal layer, The signal transmission path according to any one of claims 1 to 5, wherein the difference between the sum of the product of the thickness direction dimension and elastic modulus of the first insulating layer and the product of the thickness direction dimension and elastic modulus of the third insulating layer, and the sum of the product of the thickness direction dimension and elastic modulus of the second insulating layer and the product of the thickness direction dimension and elastic modulus of the fourth insulating layer, is a ratio less than or equal to a threshold value with respect to the sum of the product of the thickness direction dimension and elastic modulus of the second insulating layer and the product of the thickness direction dimension and elastic modulus of the fourth insulating layer.

7. The signal transmission path according to any one of claims 1 to 6, further comprising through electrodes electrically connected to the first signal layer and the second signal layer.

8. The signal transmission path according to any one of claims 1 to 7, further comprising a capacitor electrically connected to the first signal layer or to the second signal layer.

9. The signal transmission path according to any one of claims 1 to 8, wherein the second signal layer can be mounted on a wiring board and an integrated circuit can be mounted on the first signal layer.

10. A step of preparing a substrate having a first surface and a second surface opposite to the first surface, The process involves forming a first signal layer on the first surface, The process involves forming a first insulating layer on the first signal layer, The process involves forming a first ground layer on the first insulating layer, A step of forming a second signal layer electrically connected to the first signal layer on the second surface, The process involves forming a second insulating layer on the second signal layer, The process involves forming a second ground layer on the second insulating layer, A step of forming a fifth ground layer between the first surface and the first signal layer, The process includes the step of forming a sixth ground layer between the second surface and the second signal layer, The ratio (S2 / d2) of the area of ​​the second signal layer (S2) to the distance (d2) between the second signal layer and the second ground layer is formed to be equal to the ratio (S1 / d1) of the area of ​​the first signal layer (S1) to the distance (d1) between the first signal layer and the first ground layer. A method for manufacturing a signal transmission line, wherein the ratio (S2 / d4) of the area of ​​the second signal layer (S2) to the distance (d4) between the second signal layer and the sixth ground layer is formed to match the ratio (S1 / d3) of the area of ​​the first signal layer (S1) to the distance (d3) between the first signal layer and the fifth ground layer.

11. The step of forming the first insulating layer includes thermal curing the first insulating layer at a first temperature. The step of forming the second insulating layer includes thermal curing the second insulating layer at the first temperature when thermal curing the first insulating layer. A method for manufacturing a signal transmission line according to claim 10, wherein, in a temperature range from the first temperature to the second temperature after heat curing, the difference between the product of the thermal expansion coefficient of the first insulating layer, the temperature change with respect to the first temperature, the dimension in the thickness direction of the first insulating layer, and the elastic modulus of the first insulating layer, and the product of the thermal expansion coefficient of the second insulating layer, the temperature change with respect to the first temperature, the dimension in the thickness direction of the second insulating layer, and the elastic modulus of the second insulating layer, is less than or equal to a threshold ratio with respect to the product of the thermal expansion coefficient of the second insulating layer, the temperature change with respect to the first temperature, the dimension in the thickness direction of the second insulating layer, and the elastic modulus of the second insulating layer, in a temperature range from the first temperature to the second temperature after heat curing.

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