High-frequency connection lines

Abstract

A high-frequency connection line of one embodiment comprises: a first main line having a first signal line and a first ground of a first high-frequency line; and a second main line having a second signal line and a second ground of a second high-frequency line, wherein the first signal line and the second signal line are connected via a junction between a first signal pad and a third signal pad, the first ground and the second ground are connected via a junction between a first ground pad and a third ground pad, a gap between the third signal pad and a ground layer is configured to be smaller than 1 / 4 of a tube wavelength, and a distance between a second signal pad and a second ground pad is configured to be narrower than a distance between the second signal line and the second ground.

Description

Technical Field

[0001] The present disclosure relates to a high-frequency connection line. More specifically, it is a high-frequency connection line that connects high-frequency lines with different end structures in a connection region, and relates to a high-frequency connection line capable of matching the characteristic impedance not only in the connection region of the end of the high-frequency line but also in the whole including parts other than the connection region to a desired characteristic impedance.

Background Art

[0002] In a high-frequency line having a predetermined characteristic impedance, when electrically connecting the line ends of separate high-frequency lines facing each other, reducing reflection loss in the connection region is generally regarded as an important issue.

[0003] Particularly, in optical modules such as TOSA (Transmit Optical Sub-Assembly), ROSA (Receiver Optical Sub-Assembly), BOSA (Bi-directional Optical Sub Assembly), CDM (Coherent Driver Modulators), and ICR (Intradyne Coherent Receiver) widely used in optical communication systems, a case where heterogeneous substrate bonding is performed to bond a high-frequency line on a rigid substrate and a high-frequency line on a flexible substrate having flexibility is common. In a 200GBd optical communication system with a higher baud rate used in high-speed broadband optical communication, suppressing reflection loss of high-frequency signals propagating in the region of heterogeneous substrate bonding has been an urgent issue to be solved.

[0004] For example, the metal pads that form the ends of high-frequency lines on a rigid substrate are located on the surface of the rigid substrate. On the other hand, the metal pads introduced into the flexible substrate for bonding to the rigid substrate are located on the underside of the flexible substrate. However, it is common for high-frequency signal lines to be located on the top surface of the flexible substrate. Therefore, in the region of bonding dissimilar substrates, it becomes necessary to run the signal from the metal pad on the underside of the flexible substrate to the high-frequency signal line on the top surface. As long as such high-frequency connection lines are used, it is considered relatively difficult to achieve characteristic impedance matching for the purpose of reducing reflection loss. Nevertheless, in conventional optical modules, high-frequency connection lines that reduce the change in characteristic impedance after bonding by optimizing the shape of the high-frequency line for both rigid and flexible substrates have been widely adopted.

[0005] Conventional optical modules typically employ a microstrip line structure, where the signal lines are located on the upper surface of the flexible substrate and the ground conductor is located on the lower surface (see, for example, Patent Documents 1 and 2). Microstrip lines are a relatively simple structure among the various types of high-frequency lines, and their adoption was primarily due to the ease with which high manufacturing precision could be achieved at a relatively low cost (see Patent Document 2).

[0006] Referring to Figure 1, the structure of the connection area when joining the ends of a high-frequency line on a rigid substrate (100) and the ends of a high-frequency line on a flexible substrate (200) so that they face each other will be explained. Figure 1(a) is a top view of the connection area, (b) is an Ib-Ib cross-sectional view of the connection area, and (c) is a bottom view of the flexible substrate (200).

[0007] The rigid substrate (100) is provided with a differential microstrip line consisting of two signal lines (101) patterned using the first wiring layer (111) of the rigid substrate on its upper surface. In this case, the ground that defines the ground potential of the differential microstrip line of the rigid substrate (100) is the second wiring layer (112) and the third wiring layer (113) located in the lower layer of the rigid substrate (100), and the ground potential of the first wiring layer (111), the second wiring layer (112), and the third wiring layer (113) is made common by a ground via (not shown) that penetrates the rigid substrate (100). A first insulating layer (114) and a second insulating layer (115) are formed between each wiring layer.

[0008] On the other hand, the flexible substrate (200) is provided with a differential microstrip line consisting of two signal lines (201) that are patterned using the first wiring layer (221) of the flexible substrate (200) on its upper surface. On the second wiring layer (222) located on the back surface of the flexible substrate (200), signal pads (202) and ground pads (211) for joining with the rigid substrate (100) are patterned and placed in predetermined positions. The ends of the first wiring layer (221) of the flexible substrate (200) and the signal pads (212) and ground pads (211) of the newly provided second wiring layer (222) are formed independently on the upper and lower surfaces of the first insulating layer (223) of the flexible substrate (200), respectively, and therefore they are not electrically connected to each other as they are. For this reason, signal vias (202) and ground vias (204) are provided in predetermined positions to penetrate the first insulating layer (223) of the flexible substrate (200) and enable conductivity. In this case, in order to suppress a significant decrease in characteristic impedance at the junction, a ground opening (126) is selectively introduced in the second wiring layer 112 that constitutes the rigid substrate (100).

[0009] Figure 2 is a diagram designed to facilitate a functional discussion of the conventional connection area structure shown in Figure 1. Figure 2(a) is a top view of the connection area of ​​a conventional high-frequency connection line, and (b) is a diagram that virtually divides the connection area on paper according to its function. On the left side of Figure 2(b) is a first high-frequency line formed on the top surface of a rigid substrate (100). On the right side of Figure 2(b) is a second high-frequency line formed on the top surface of a flexible substrate (200). It can be seen that each has different structural characteristics. For example, the line width and line pitch are clearly different. Thus, generally, when using substrates with different materials and thicknesses for the insulating layer, even if the characteristic impedance is the same, the shape and arrangement of the resulting metal pattern that forms the shape of the high-frequency line will not necessarily match. Therefore, when joining one end of two high-frequency lines to the other so that they face each other, a high-frequency connection line with a special structure is required. The structure located in the center of Figure 2(b) corresponds to the high-frequency connection line.

[0010] In the flexible substrate (200) of the high-frequency connection line in the center of Figure 2(b), a signal line tapered section (203) is introduced in the first wiring layer (221) on the upper surface, and a ground layer tapered section (213) is introduced in the second wiring layer (222) on the lower surface. On the other hand, in the rigid substrate (100) of the high-frequency connection line, a signal line pitch conversion section (102) is introduced in the first wiring layer 111 on the upper surface. Furthermore, directly below the region where the high-frequency connection line of the flexible substrate (200) and the high-frequency connection line of the rigid substrate (100) are joined to each other with solder (300) or the like, a ground opening (126) is selectively introduced in the second wiring layer 112 of the rigid substrate (100).

[0011] Incidentally, unlike conventional optical communications to which Patent Documents 1 and 2 apply, in optical modules used for high-baud rate 200GBd optical communications, the design of high-frequency connection lines implemented inside the optical module undergoes a significant transformation from lumped-parameter treatment to distributed-parameter treatment. In particular, the area in Figure 1 where such treatment is required is the signal line tapered section (203). In order for the signal line tapered section (203) to function as a high-frequency signal line, a reference ground is required in the second wiring layer (222) directly below the first insulating layer (223) of the flexible substrate (200). However, as can be seen from the bottom view of the flexible substrate (200) shown in Figure 1(c), a predetermined gap is provided between the ground layer (210) that provides the reference potential and the signal pad (212) in order to prevent a short circuit with the signal pad (212) provided in the second wiring layer (222).

[0012] If the size of the gap between the ground layer (210) and the signal pad (212) (length in the X-axis direction) is sufficiently smaller than (1 / 16) to (1 / 4) of the in-tube wavelength (wavelength along the signal line (201)) of the high-frequency signal propagating through the signal line tapered section (203) of the second wiring layer (221), then if the gap can be treated as a lumped element and electrically corrected in the flexible substrate (200), reflection of the high-frequency signal in the signal line tapered section (203) will be relatively infrequent. However, in 200GBd optical communication, which has a high baud rate, the frequency of the high-frequency signal used exceeds 100GHz. As a result, the length equivalent to (1 / 16) to (1 / 4) of the in-tube wavelength exceeding 100GHz becomes smaller than the size of the gap, making it difficult to electrically treat the gap as a lumped element, and strong inductivity is exhibited in the gap, i.e., in the signal line tapered section (203). Figure 3 shows the S-parameters and characteristic impedance of a conventional high-frequency connection line with a gap size of 200 μm. Figure 3(a) shows the graph trace of the reflection loss of the S-parameters, (b) shows the graph trace of the transmission loss of the S-parameters, and (c) shows the simulated waveform of the graph trace of the characteristic impedance obtained by TDR (Time-Domain Reflectivity Measurement). It is clear that it exhibits high impedance characteristics due to the emergence of inductance. Therefore, it was difficult to apply conventional high-frequency connection lines, such as those shown in Figures 1 and 2, to high-frequency signals used in 200 GBd optical communication. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2007-123741 [Patent Document 2] Japanese Patent Publication No. 2010-200234 [Overview of the project]

[0014] As mentioned above, in high-frequency connection lines, the increase in characteristic impedance due to the emergence of inductance can lead to mismatches in characteristic impedance, resulting in a degradation of the signal quality of high-frequency signals.

[0015] This disclosure has been made in view of the above problems, and aims to provide a high-frequency connection line with matched characteristic impedance when connecting the ends of high-frequency lines formed on separate substrates in a manner in contact with each other at the ends of each substrate.

[0016] One embodiment of the present invention is a high-frequency connecting line in which a first high-frequency line formed on a first substrate having insulating properties and a second high-frequency line formed on a second substrate having different insulating properties than the first substrate are electrically connected. In one embodiment of a high-frequency connection line, the first high-frequency line is a conductive first main line formed on the upper surface of a first substrate, comprising: the first main line having a first signal line; a first signal pad formed on the upper surface of the first substrate and electrically connected to the end of the first signal line; and a first ground pad formed on the upper surface of the first substrate. In one embodiment of the high-frequency connection line, the second high-frequency line is a conductive second main line formed on the upper surface of the second substrate, comprising: a second signal line and a second ground formed on the upper surface of the second substrate; a second signal pad electrically connected to the end of the second signal line formed on the upper surface of the second substrate; a second ground pad electrically connected to the end of the second ground formed on the upper surface of the second substrate; a third signal pad formed on the lower surface of the second substrate directly below the second signal pad; and a ground layer formed on the lower surface of the second substrate surrounding the third signal pad, including a third ground pad formed on the lower surface of the second substrate directly below the second ground pad. The first signal pad and the third signal pad are joined facing each other, and the first ground pad and the third ground pad are joined facing each other. In one embodiment of a high-frequency connection line, the gap between the third signal pad and the ground layer in the longitudinal direction of the second high-frequency line is smaller than 1 / 4 of the wavelength inside the tube, the width of the second signal pad in the direction perpendicular to the longitudinal direction of the second high-frequency line is wider than the width of the second signal pad in the direction perpendicular to the longitudinal direction of the second high-frequency line, and the distance between the second signal pad and the second ground pad is narrower than the distance between the second signal line and the second ground.

[0017] According to embodiments of the present invention, it is possible to provide a high-frequency connection line with matched characteristic impedances. [Brief explanation of the drawing]

[0018] [Figure 1] This diagram illustrates the structure of the connection region of a conventional high-frequency connection line. (a) is a top view of the connection region, (b) is a cross-sectional view of the Ib-Ib line in (a), and (c) is a bottom view of the flexible substrate (200). [Figure 2] (a) is a top view of the connection area of ​​a conventional high-frequency connection line, and (b) is a diagram divided by function. [Figure 3] This figure shows the S-parameters and characteristic impedance of a conventional high-frequency connection line, where (a) is the graph trace of reflection loss, (b) is the graph trace of pass-through loss, and (c) is the graph trace of characteristic impedance by TDR. [Figure 4] (a) is a top view of a high-frequency connecting line (1) of a first embodiment of the present disclosure, and (b) is a cross-sectional view of the IVb-IVb line in (a). [Figure 5] (a) is a top view of the high-frequency connecting line (1) of the first embodiment corresponding to Figure 4(a), (b) is a top view of the end of the first differential high-frequency line (2), and (c) is a top view of the end of the second differential high-frequency line (3). [Figure 6](a) is a top view of the high-frequency connection line (1) of the first embodiment corresponding to FIG. 4(a), (b) is a top view of the second differential high-frequency line (3) corresponding to FIG. 5(c), and (c) is a bottom view of the second differential high-frequency line (3). [Figure 7] (a) is a top view of the high-frequency connection line (1) of the first embodiment corresponding to FIG. 4(a), and (b) is a diagram (1-1, 1-2, 1-3) in which the regions are divided according to the functions of the high-frequency connection line (1). [Figure 8] It is a diagram showing the S parameters and characteristic impedance of the high-frequency connection line of the first embodiment. (a) is a graph trace of reflection loss, (b) is a graph trace of transmission loss, and (c) is a graph trace of characteristic impedance by TDR. [Figure 9] It is a diagram showing the positions and shapes (3-10-1, 3-10-2, 3-10-3, 3-10-4) of the half-through holes formed on the second substrate on which the second high-frequency line (3) of the first embodiment is formed. [Figure 10] (a) is a top view of the high-frequency connection line (7) of the second embodiment of the present disclosure, and (b) is a cross-sectional view taken along line IXb-IXb in (a). [Figure 11] (a) is a top view of the high-frequency connection line (7) of the second embodiment corresponding to FIG. 10(a), (b) is a top view of the end of the first differential high-frequency line (2), and (c) is a top view of the end of the second differential high-frequency line (8). [Figure 12] (a) is a top view of the high-frequency connection line (1) of the second embodiment corresponding to FIG. 10(a), (b) is a top view of the second differential high-frequency line (8) corresponding to FIG. 11(c), and (c) is a bottom view of the second differential high-frequency line (8). <​​​​This figure shows the S-parameters and characteristic impedance of the high-frequency connection line in the second embodiment, where (a) is a graph trace of the reflection loss, (b) is a graph trace of the pass-through loss, and (c) is a graph trace of the characteristic impedance calculated by TDR. [Figure 15] (a) is a top view of a high-frequency connecting line (9) in a third embodiment of the present disclosure, (b) is a cross-sectional view of the XVb-XVb line in (a), and (c) is a cross-sectional view of the XVc-XVc line in (a). [Modes for carrying out the invention]

[0019] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference numerals in the following description indicate the same or similar elements, and repeated descriptions may be omitted. The numerical values ​​and materials in the following description are illustrative, and the present disclosure can be implemented using different numerical values ​​and materials without departing from the spirit of the work.

[0020] In this embodiment, the material of the first substrate on which the first differential high-frequency line (2) is formed is polyimide (dielectric constant 3.5), and the material of the second substrate on which the second differential high-frequency line (3) is formed is a low-loss resin material (dielectric constant 3.46). However, the material of the first substrate and the material of the second substrate may be quartz glass (dielectric constant 3.8), silicon nitride film (dielectric constant 7), alumina ceramics (dielectric constant 9.8), compound semiconductor InP (dielectric constant 12.4), etc., and it goes without saying that other insulating materials may also be used. Furthermore, in this embodiment, the conductive film is copper foil, but it goes without saying that the material is not limited to this and can also be aluminum foil film, gold foil film, nickel thin film, or palladium thin film, or composite layer metal thin film of one or more of these. Furthermore, although the following embodiment describes joining one pair of differential high-frequency lines (2,3) to form a single differential high-frequency line (1), this can be extended to a configuration in which multiple pairs of differential high-frequency lines are joined. In addition, the configuration of joining one pair of single-phase high-frequency lines may be used as an alternative to one pair of differential high-frequency lines, and this can be further extended to a configuration in which multiple pairs of single-phase high-frequency lines are joined.

[0021] Furthermore, although the first substrate on which the first differential high-frequency line (2) is formed has six conductor layers, the total number of conductor layers is by no means limited to this, and it goes without saying that it can be applied with fewer or more than six layers. Also, although multiple through-holes (3-4) are formed at the ends of the differential high-frequency line on the second substrate on which the second differential high-frequency line is formed, it goes without saying that it can also be applied with conductor-embedded through-holes.

[0022] (First example) Referring to Figures 4 to 9, a high-frequency connection line (1) of a first embodiment of the present disclosure will be described. The high-frequency connection line (1) is formed by joining the end of a first differential high-frequency line (2) formed on a first substrate to the end of a second differential high-frequency line (3) formed on a second substrate. Functionally, the high-frequency connection line (1) is configured such that a first high-frequency line (1-1) formed on the upper surface of the first substrate is located on the left side, a second high-frequency line (1-3) formed on the upper surface of the second substrate is located on the right side, and a high-frequency connection line (1-2) is located in the center (Figure 7(b)). This configuration is the same as the functional configuration of a conventional high-frequency connection line shown in Figure 2(b).

[0023] The first differential high-frequency line (2) has a set of positive line (2-1-1) and negative line (2-1-2) (also called a set of positive signal line and negative signal line, or simply a set of lines) on the upper surface of the first substrate, and grounds (2-1-3, 2-1-4) with earth ground potential on both sides of the set of lines, an earth ground layer (2-2) in the conductor layer directly below the set of lines, and a bottom-contact earth ground layer (2-3) on the lowest surface of the first substrate. Ground vias (2-1-5, 2-1-6) are provided to ensure that the potential of all earth ground layers (2-2) and bottom-contact earth ground layers (2-3) is at earth ground potential. Insulating layers (2-4, 2-5) are introduced between all conductor layers. A portion of the ground (2-1-3, 2-1-4) region of the first differential high-frequency line (2), located below the grounding ground layer (3-1-3, 3-1-4) of the second differential high-frequency line (3) described later, constitutes a ground pad. This ground pad provides a junction region with the ground pad formed by a portion of the grounding ground layer (3-6) of the second differential high-frequency line (3) on the lower surface of the second substrate.

[0024] On the other hand, the second differential high-frequency line (3) has a set of positive line (3-1-1) and negative line (3-1-2) (also called a set of positive signal line and negative signal line, or simply a set of lines) on the upper surface of the second substrate, and positive signal pads and negative signal pads formed at the ends of the set of lines. The positive signal pads and negative signal pads have a circular pad (3-3), a through hole (3-4) penetrating the center of the circular pad, and a waist line (3-5) connecting the circular pads. In addition, there are grounds (3-1-3, 3-1-4) with ground potential on both sides of the positive line (3-1-1) and negative line (3-1-2). Furthermore, the second differential high-frequency line (3) includes a positive pad (3-7-1), a negative pad (3-7-2), and a grounding layer (3-6) formed on the same plane as the positive and negative pads on the bottom surface of the second substrate. A portion of the grounding layer (3-6) of the second differential high-frequency line (3), which is located opposite to the ground pad formed by a portion of the ground (2-1-3, 2-1-4) of the first differential high-frequency line (2) described above, constitutes a ground pad. Furthermore, a portion above the ground pad formed by a portion of the grounding layer (3-6) of the ground (3-1-3, 3-1-4) also constitutes a ground pad. A portion of the grounding layer (3-6) is connected to a portion of the grounding layer (3-1-3, 3-1-4) by ground vias (3-1-5, 3-1-6). In addition, an insulating layer (3-8) is introduced between the upper conductor layer and the lower conductor layer.

[0025] The width of the waist lines (3-5) constituting the second differential high-frequency line (3) is sufficiently narrower than the width of the positive pad (3-7-1) and negative pad (3-7-2) on the bottom side. For example, regarding the pad width (represented by the dashed rectangle) excluding the land portion forming the via on the bottom side, it is important to suppress the emergence of electrical capacitiveness at the connection point as much as possible, considering the high-speed signal velocity of the propagating high-frequency signal. Assuming compatibility with 200GBd, it is desirable that the width (length in the Y-axis direction) be 200 μm or less, and the length (length in the X-axis direction) be 1 mm or less (Figure 6(c)). The line width on the bottom side of the second substrate is unsuitable to be 100 μm or less because it limits the connection strength. On the other hand, the width (length in the Y-axis direction) of the waist line portion on the top side has almost no effect on the connection strength, so it is better to make it as small as possible as it affects capacitiveness, but considering the risk of disconnection, it is good to make it, for example, around 50 to 100 μm (Figure 6(b)).

[0026] Furthermore, if the through-holes (3-4) on the top and bottom surfaces of the second substrate that provide electrical connections are made into embedded vias, a waistline is not necessarily required (for example, a straight line can be used), and it is possible to form only via lands. By using an embedded via shape, the solder used for the connection does not wet onto the top surface of the pattern, and in principle, wetting and spreading cannot occur, thus suppressing the emergence of electrical capacitiveness and, as a result, preventing low impedance.

[0027] The size of the connection area relative to the entire substrate is very small. Therefore, it goes without saying that the alignment accuracy between the patterns on the first substrate and the patterns on the second substrate is important. Accordingly, in this embodiment, as shown in Figure 9, the second substrate is provided with half-through holes (3-10-3, 3-10-4) on both sides (in the direction perpendicular to the signal propagation direction) that allow the use of positioning pins. Considering the diameter size that can ensure sufficient strength and accuracy as positioning pins, and the influence of the half-through holes on the patterns of the positive line (3-1-1) and negative line (3-1-2) on the second substrate such as a flexible substrate, it is preferable that the radius of curvature of the half-through holes be about 0.3 mm to 0.5 mm. For example, if the size of the half-through holes (3-10-3, 3-10-4) becomes too large, it may be necessary to remove the ground (3-1-3, 3-1-4) and ground layer (3-6) of the second board, and it may also become difficult to route the positive line (3-1-1) and negative line (3-1-2) patterns. By providing the positioning pins on the first board, precise alignment is possible. In addition, for example, the half-through holes (3-10-3, 3-10-4) can also be applied to applications where the second board is mechanically picked up or positioned using equipment, thus providing greater versatility. However, when considering connections using solder or conductive adhesive with a hotbar, if the positioning pins are placed in the same row as the connection point, it will reduce work efficiency, such as making it impossible to drop the hotbar tool. In that case, it is necessary to keep them at least 500 μm away from the connection point in the direction of signal propagation. Furthermore, after connection, the connection strength can be strengthened by connecting the half-through holes (3-10-3, 3-10-4) to the first substrate with solder or conductive adhesive. When soldering the half-through holes (3-10-3, 3-10-4), the areas on the sides, top, and bottom surfaces of the half-through holes (3-10-3, 3-10-4) with a radius of curvature of +100 μm or more must be metallized.Furthermore, if the region is metallized, it is desirable, from the viewpoint of minimizing the impact on the second differential high-frequency line (3) of the second substrate and ease of soldering, that the metallization of the region on the upper and lower surfaces of the half-through hole be separated as much as possible from the metallization of the ground (3-1-3, 3-1-4) and grounding ground layer (3-6) of the second substrate.

[0028] Similarly, from the viewpoint of improving connection strength, it is possible to improve connection strength by placing at least one half-through hole (3-10-1, 3-10-2) with a radius of curvature of 0.1 mm or more (the larger the half-through hole, the more effective it is in improving connection strength) on the edge side of the second substrate parallel to the connection part (both sides of the second substrate as described above) and connecting and fixing it to the first substrate.

[0029] The first differential high-frequency line (2) formed on the first substrate and the second differential high-frequency line (3) formed on the second substrate are electrically permanently connected. In this embodiment, solder is used. The positive pad (2-7-1) formed at the end of the positive line (2-1-1) and the negative pad (2-7-2) formed at the end of the negative line (2-1-2) of the first differential high-frequency line (2) formed on the first substrate are connected to the positive pad (3-7-1) formed at the end of the positive line (3-1-1) and the negative pad (3-7-2) formed at the end of the negative line (3-1-2) of the second differential high-frequency line (3) formed on the second substrate by a bottom solder layer (3-9-3) (Figure 4(b)). Furthermore, when the solder is heated during connection, its fluidity is revealed, causing the solder to wet and spread inside the through-holes (3-4) formed on the second substrate and on the upper surface of the ends of the second differential high-frequency lines (3) formed on the second substrate, resulting in the formation of through-hole solder (3-9-1) and upper surface solder (3-9-2), respectively (Figure 4(b)).

[0030] In this embodiment, a region (2-6) is provided in the ground layer (2-2), which is a conductor layer in the first substrate directly beneath the soldered region, where the conductor layer has been selectively removed. This is a basic structure introduced to suppress the increase in capacitance and subsequent decrease in impedance that can occur when the end of the first differential high-frequency line (2) formed on the first substrate and the end of the second differential high-frequency line (3) formed on the second substrate are soldered together, causing the size of the conductor in the joint region to become larger than before the joint.

[0031] On the other hand, at the ends of the positive line (3-1-1) and negative line (3-1-2) of the second differential high-frequency line (3) formed on the second substrate, the bottom-side conductor layer (positive pad (3-7-1) and negative pad (3-7-2)) are electrically joined by through-holes. The second differential high-frequency line (3) also has a ground layer (3-6) on the bottom-side conductor layer. As described above, in order to prevent a short circuit between the ground layer (3-6) and the positive pad (3-7-1) and negative pad (3-7-2), the ground layer (3-6) is formed at the edge of the plate so as to surround the positive pad (3-7-1) and negative pad (3-7-2). In this way, a predetermined gap is formed between the ground layer (3-6) and the positive pad (3-7-1) and negative pad (3-7-2), similar to the conventional example in Figure 1 (Figure 6(c)). In this case, when the positive line (3-1-1) and negative line (3-1-2) constituting the second differential high-frequency line (3) formed on the second substrate move toward the edge of the plate in the extension direction (X-axis direction), they lose capacitance with the ground layer (3-6) in the region of the gap, causing the characteristic impedance to rise significantly and resulting in a high-impedance line. As a result, the high-frequency signal suffers a large reflection loss, leading to a deterioration of the bandwidth characteristics. In this embodiment, the gap is set to 100 μm or less, which is sufficiently smaller than 1 / 4 the length of the tube wavelength corresponding to 100 GHz on the second substrate. Furthermore, when the positive line (3-1-1) and negative line (3-1-2) constituting the second differential high-frequency line (3) formed on the second substrate move toward the edge of the plate, their line width is set to a shape (3-2-1) that is wider than the positive line (3-1-1) and negative line (3-1-2), thereby providing electrical capacitance (Figure 6(c)). This makes it possible to counteract the inductance that is the source of the high impedance characteristics in the gap region of 100 μm or less mentioned above. In this embodiment, a differential high-frequency transmission line is treated as one example, in a differential high-frequency transmission line, a capacitive junction occurs between the positive and negative transmission lines in the differential signal, and electric field lines are generated between the transmission lines.To maintain the distribution shape of electric field lines between these lines, to maintain the coupling mode of the electromagnetic field, and to reduce reflection due to changes in the electromagnetic field mode, the gap between the positive line (3-1-1) and the negative line (3-1-2) is the same even in the line (3-2-1) which has the aforementioned wider line width.

[0032] Figure 8 shows the S-parameters and characteristic impedance of the high-frequency connection line of the first embodiment, along with the characteristics of the conventional high-frequency connection line. Figure 8(a) shows the graph trace of the reflection loss of the S-parameters, (b) shows the graph trace of the pass-through loss of the S-parameters, and (c) shows the simulated waveform of the graph trace of the characteristic impedance obtained by TDR (Time Domain Reflectivity Measurement). In Figure 8, the dashed graph traces (4-1, 5-1, 6-1) represent the characteristics of the conventional example, and the solid graph traces (4-2, 5-2, 6-2) represent the characteristics of this embodiment. The simulation model was designed to match a differential impedance of 100Ω. When the target levels for the reflection loss and pass-through loss at the junction between the first differential high-frequency line (2) and the second high-frequency signal line (3) are set to -10dB (10% of the power is reflected) and 1dB (0.2 times the power loss), respectively, it is clear that this embodiment is superior. In fact, the graph trace of the characteristic impedance using TDR shows that the peak characteristic impedance that occurred in the aforementioned gap area in the conventional example has been improved.

[0033] (Second example) Referring to Figures 10 to 13, a high-frequency connection line (7) of a second embodiment of the present disclosure will be described. The high-frequency connection line (7) is formed by joining the end of a first differential high-frequency line (2) formed on a first substrate to the end of a second differential high-frequency line (8) formed on a second substrate. Functionally, the high-frequency connection line (7) is configured such that the first high-frequency line (7-1) formed on the upper surface of the first substrate is located on the left side, the second high-frequency line (7-3) formed on the upper surface of the second substrate is located on the right side, and the high-frequency connection line (7-2) is located in the center (Figure 13(b)). This configuration is the same as the functional configuration of a conventional high-frequency connection line shown in Figure 2(b).

[0034] The first differential high-frequency line (2) formed on the first substrate includes a set of positive lines (2-1-1) and negative lines (2-1-2) (i.e., a set of lines) on the upper surface of the first substrate, and grounds (2-1-3, 2-1-4) with ground potential on both sides of the set of lines, a ground layer (2-2) in the conductor layer directly below the set of lines, and a bottom-contact ground layer (2-3) on the lowest surface of the first substrate. Ground vias (2-1-5, 2-1-6) are provided to bring the potential of all ground layers (2-2) and bottom-contact ground layers (2-3) to ground potential. Insulating layers (2-4, 2-5) are introduced between all conductor layers.

[0035] On the other hand, the second differential high-frequency line (8) has a set of positive line (8-1-1) and negative line (8-1-2) (also called a set of positive signal line and negative signal line, or simply a set of lines) on the upper surface of the second substrate, and positive signal pads and negative signal pads formed at the ends of the set of lines. The positive signal pads and negative signal pads have a circular pad (8-3) formed at the end of the set of lines, a through-hole (8-4) that penetrates the center of the circular pad (8-3), and a waist line (8-5) connecting the circular pads. In addition, there are grounds (8-1-3, 8-1-4) with ground potential on both sides of the positive line (8-1-1) and negative line (8-1-2). Furthermore, the second differential high-frequency line (8) includes a positive pad (8-7-1), a negative pad (8-7-2), and a grounding layer (8-6) formed on the same plane as the positive and negative pads on the bottom surface of the second substrate. A portion of the grounding layer (8-6) of the second differential high-frequency line (8), which is located opposite to the ground pad formed by a portion of the ground (2-1-3, 2-1-4) of the first differential high-frequency line (2) described above, constitutes a ground pad. Furthermore, a portion above the ground pad formed by a portion of the grounding layer (8-6) of the ground (8-1-3, 8-1-4) also constitutes a ground pad. The grounding layer (8-6) is connected to the grounding layers (8-1-3, 8-1-4) by ground vias (8-1-5, 8-1-6). In addition, an insulating layer (8-8) is introduced between the upper conductor layer and the lower conductor layer. The width of the aforementioned waist track (8-5) is considerably narrower than the width of the positive pad (8-7-1) and negative pad (8-7-2) located on the bottom side.

[0036] The first differential high-frequency line (2) formed on the first substrate and the second differential high-frequency line (8) formed on the second substrate are electrically permanently connected. In this embodiment, solder is used. The positive pad (2-7-1) formed at the end of the positive line (8-1-1) and the negative pad (2-7-2) formed at the end of the negative line (2-1-2) of the first differential high-frequency line (2) formed on the first substrate are connected to the positive pad (8-7-1) formed at the end of the positive line (8-1-1) and the negative pad (8-7-2) formed at the end of the negative line (8-1-2) of the second differential high-frequency line (8) formed on the second substrate by a bottom solder layer (8-9-3) (Figure 10(b)). Furthermore, when the solder is heated during connection, its fluidity is revealed, causing the solder to wet and spread inside the through-hole (8-4) formed on the second substrate and on the upper surface of the end of the second differential high-frequency line (8) formed on the second substrate, resulting in the formation of through-hole solder (8-9-1) and upper surface solder (8-9-2), respectively (Figure 10(b)).

[0037] In this embodiment, a region (2-6) is provided in the ground layer (2-2), which is a conductor layer in the first substrate directly beneath the soldered region, where the conductor layer has been selectively removed. This is a basic structure introduced to suppress the increase in capacitance that occurs when the end of the first differential high-frequency line (2) formed on the first substrate and the end of the second differential high-frequency line (8) formed on the second substrate are soldered together, causing the size of the conductor in the joint region to become larger than before the joint.

[0038] On the other hand, at the ends of the positive line (8-1-1) and negative line (8-1-2) of the second high-frequency line (3) provided on the second substrate, the bottom and top conductor layers (positive pad (8-7-1) and negative pad (8-7-2)) are electrically joined by through-holes. The second differential high-frequency line (8) is also provided with a ground layer (8-6) on the bottom conductor layer. As described above, in order to prevent a short circuit between the ground layer (8-6) and the positive pad (8-7-1) and negative pad (8-7-2), the ground layer (8-6) is formed at the edge of the plate so as to surround the positive pad (8-7-1) and negative pad (8-7-2). In this way, a predetermined gap is formed between the ground layer (8-6) and the positive pad (8-7-1) and negative pad (8-7-2) (Figure 12(c)). In this case, when the positive line (8-1-1) and negative line (8-1-2) constituting the second differential high-frequency line (8) formed on the second substrate extend toward the edge of the plate in the extension direction (X-axis direction), they lose capacitance with the ground in the region of the gap, causing the characteristic impedance to rise significantly and resulting in a high-impedance line. As a result, the high-frequency signal suffers a large reflection loss, leading to a deterioration of the bandwidth characteristics. In this embodiment, the gap is set to 100 μm or less, and furthermore, when the positive line (8-1-1) and negative line (8-1-2) constituting the second differential high-frequency line (8) formed on the second substrate extend toward the edge of the plate in the extension direction (X-axis direction), the line width is wider than the width of the positive line (8-1-1) and negative line (8-1-2), and the line shape (8-2) is wider than the diameter of the circular pad (8-3) provided on the second substrate. In this embodiment, since it is a differential transmission line, the aforementioned transmission line shape (8-2) further improves the capacitiveness between the positive transmission line (8-1-1) and the negative transmission line (8-1-2). While the aforementioned transmission line shape (8-2) is described as having multiple vertices, it is by no means limited to this. The outer shape may also be curved.By adopting the line shape (8-2) of this embodiment, it becomes possible to further cancel the inductance that is the source of the high impedance characteristics in the gap region of 100 μm or less mentioned above.

[0039] In the first embodiment, the shape of the portion surrounding the positive pad (8-7-1) and the negative pad (8-7-2) was a rectangle having two sides parallel to the longitudinal direction of the second high-frequency line and two sides perpendicular to the longitudinal direction of the second high-frequency line. In this embodiment, it is a hexagon. The hexagon has two sides parallel to the longitudinal direction of the second high-frequency line, two sides perpendicular to the longitudinal direction of the second high-frequency line, and two sides connecting the positive line (8-1-1) and negative line (8-1-2) side of the two sides perpendicular to the longitudinal direction of the second high-frequency line with the two sides parallel to the longitudinal direction of the second high-frequency line. The interior angles of the hexagon on the positive line (8-1-1) and negative line (8-1-2) side are obtuse angles. The shape of the portion surrounding the positive pad (8-7-1) and the negative pad (8-7-2) may be such that the two sides connecting the positive line (8-1-1) and the negative line (8-1-2) side of the two sides perpendicular to the longitudinal direction of the second high-frequency line of the hexagon in this embodiment are curved.

[0040] Figure 14 shows the S-parameters and characteristic impedance of the high-frequency connection line of the second embodiment, along with the characteristics of the conventional high-frequency connection line and the high-frequency connection line of the first embodiment. Figure 14(a) shows the graph trace of the reflection loss of the S-parameters, (b) shows the graph trace of the pass-through loss of the S-parameters, and (c) shows the simulated waveform of the graph trace of the characteristic impedance obtained by TDR (Time Domain Reflectivity Measurement). In Figure 14, the dashed graph traces (4-1, 5-1, 6-1) represent the characteristics of the conventional example, the single-dot dashed graph traces (4-2, 5-2, 6-2) represent the characteristics of the first embodiment, and the solid graph traces (4-3, 5-3, 6-3) represent the characteristics of this embodiment. For the simulation, the design was made to match a differential impedance of 100Ω. In the high-frequency connection line (7) of this embodiment, when the target levels for reflection loss and transmission loss at the junction between the first high-frequency line (2) and the second high-frequency line (8) are set to -10 dB (10% of the power is reflected) and 1 dB (0.2 times the power loss), respectively, it can be seen that this embodiment shows further improvement in the reflection loss characteristics compared to the first embodiment. In fact, the graph trace of the characteristic impedance by TDR also shows that the peak characteristic impedance that occurred in the gap area in the conventional rigid substrate has been further improved.

[0041] (Third example) Referring to Figure 15, a high-frequency connection line (9) of a third embodiment of the present disclosure will be described. The high-frequency connection line (9) is formed by joining the ends of the first differential high-frequency lines (13-1-1, 13-1-2, 13-2-1, 13-2-2) formed on a first substrate to the ends of the second differential high-frequency lines (14-0-1, 14-0-2) formed on a second substrate. The first differential high-frequency lines (13-1-1, 13-1-2, 13-2-1, 13-2-2) are formed within the first differential high-frequency circuit (10) on the first substrate (for example, an IC or LSI substrate). The second differential high-frequency lines (14-0-1, 14-0-2) are formed on the line substrate (11) which serves as the second substrate.

[0042] The differential high-frequency circuit (10) formed on the first substrate is provided with a plurality of DC power pads and DC ground pads (13-3) at the right edge of the insulating layer (15) on the upper surface of the first substrate, and differential signal pads (13-2-3 and 13-2-4) and high-frequency ground pads (13-2-5 and 13-2-6) at the left edge.

[0043] Furthermore, the differential high-frequency circuit (10) includes a differential gain circuit (12) on an insulating layer (15) on the upper surface of the first substrate, and first differential high-frequency lines (13-1-1, 13-1-2, 13-2-1, 13-2-2) for high-frequency signal input and output that are electrically connected to the differential gain circuit (12). Positive pads (13-1-3) and negative pads (13-1-4) are formed at the ends of the first differential high-frequency lines.

[0044] The second circuit board (11), which serves as the second substrate, comprises a second differential signal pad, a second differential high-frequency line (14-0-1, 14-0-2), and a plurality of pads (14-2) having through-holes. The plurality of pads (14-2) are electrically connected to the DC power line and the DC ground line (14-1). The second differential signal pad has the same configuration as in Embodiment 2, and at the ends of the second differential high-frequency lines (14-0-1, 14-0-2), the upper surface side of the second substrate is provided with a circular pad (8-3), a waist line (8-5) connecting the circular pads, and a line shape (8-2) with a width greater (wider) than the diameter of the circular pad (8-3). The circular pad (8-3) is connected to the positive pad (13-1-3) and negative pad (13-1-4) formed at the end of the first differential high-frequency line via through-holes (not shown) and pads on the underside (not shown). Ground layers (8-1-3, 8-1-4) are also provided on both sides of the second differential signal pad. The ground layers (8-1-3, 8-1-4) are connected to the ground of the first substrate (13-1-5, 13-1-6) via through-holes (not shown) and pads on the underside (not shown).

[0045] The conductor cross-sectional size of high-frequency lines provided on IC and LSI substrates is generally only a few microns square. Furthermore, the insulating layer is also known to be only a few microns thick. High-frequency lines with these dimensions experience greater propagation loss as the frequency of the high-frequency signal increases, particularly limiting the length of the transmission line in 200 Gbd applications. In this embodiment, instead of providing high-frequency signal pads and high-frequency ground pads handling such high frequencies at the edge of the IC or LSI substrate, away from the high-frequency gain circuit (12), a structure is provided in which these are connected to a second differential high-frequency line on a second substrate (11) with lower propagation loss, located inside the substrate. This makes it relatively easy to realize 200 Gbd ICs and LSIs without degrading the signal level of the high-frequency signal. [Industrial applicability]

[0046] This invention provides a high-frequency connection line with matched characteristic impedances when connecting the ends of high-frequency lines formed on separate substrates in a manner in contact with each other at the ends of the respective substrates. [Explanation of Symbols]

[0047] 1. High-frequency connecting line 2 Differential high-frequency transmission lines 2-1-1 Positive Line (Conductor Layer) 2-1-2 Negative Line (Conductor Layer) 2-1-3, 2-1-4 Ground (Conductor Layer) 2-1-5, 2-1-6 Grand VIA 2-2 Grounding layer (conductor layer) 2-3 Ground contact layer (conductor layer) 2-4, 2-5 Insulating layer 2-6 Region from which the conductive layer has been removed 2-7-1 Positive Pad 2-7-2 Negative Pad 3. Differential high-frequency transmission lines 3-1-1 Positive Line (Conductor Layer) 3-1-2 Negative Line (Conductor Layer) 3-1-3, 3-1-4 Grounding (Conductor Layer) 3-1-5, 3-1-6 Grand VIA 3-2-1 Wide shape 3-3 Circular Pads 3-4 Through Hole 3-5 West Track 3-6 Grounding layer (conductor layer) 3-7-1 Positive Pad 3-7-2 Negative Pad 3-8 Insulating layer 3-9-1 Soldering inside through-holes 3-9-2 Top solder 3-9-3 Bottom solder layer 3-10-1, 3-10-2, 3-10-3, 3-10-4 Half-through holes 7. High-frequency connecting lines 8 Differential high-frequency transmission lines 8-1-1 Positive track 8-1-2 Negative track 8-1-3, 8-1-4 Grounding (Conductor Layer) 8-1-5, 8-1-6 Grand VIA 8-2 Wide track shape 8-3 Circular Pad 8-4 Through Hole 8-5 West Track 8-6 Grounding layer (conductor layer) 8-7-1 Positive Pad 8-7-2 Negative Pad 8-8 Insulating layer 8-9-1 Soldering inside through-holes 8-9-2 Top solder 8-9-3 Bottom solder layer 9. High-frequency connection lines 10 Differential High-Frequency Circuits 11 Track base 14-2 Pad 13-1-1, 13-1-2 Differential High-Frequency Transmission Lines 13-1-3 Positive Pad 13-1-4 Negative Pad 13-1-5, 13-1-6 Ground (conductor layer) 13-2-1, 13-2-2 Differential High-Frequency Transmission Lines 13-2-3, 13-2-4 Differential Signal Pads 13-2-5, 13-2-6 High-Frequency Grounding Pads 13-3 DC Power Pad, DC Grounding Pad 14-0-1, 14-0-2 Differential High-Frequency Transmission Lines 14-1 DC power lines, DC grounded lines 14-2 Pad 15. Insulating layer 100 Rigid substrates 101 Signal Line 102 Signal line pitch conversion unit 111 1st wiring layer 112 2nd wiring layer 113 3rd wiring layer 114 First insulating layer 115 Second insulating layer 126 Grand opening 200 Flexible circuit boards 201 Signal Line 202 Signal VIA 203 Signal line tapered section 204 Grand VIA 210 Ground Layer 211 Ground Pad 212 Signal Pad 213 Ground layer tapered section 221 1st wiring layer 222 2nd wiring layer 223 First insulating layer 300 solder

Claims

1. A high-frequency connecting line in which a first high-frequency line formed on a first substrate having insulating properties and a second high-frequency line formed on a second substrate having different insulating properties than the first substrate are electrically connected, The first high-frequency transmission line is, A conductive first main line formed on the upper surface of the first substrate, comprising a first main line with a first signal line, A first signal pad is electrically connected to the end of the first signal line formed on the upper surface of the first substrate, The first ground pad formed on the upper surface of the first substrate and Equipped with, The second high-frequency transmission line is A conductive second main line formed on the upper surface of the second substrate, The second signal track, The second grounding ground formed on the upper surface of the second substrate and A second main track equipped with, A second signal pad is electrically connected to the end of the second signal line formed on the upper surface of the second substrate, A second ground pad electrically connected to the end of the second ground ground formed on the upper surface of the second substrate, A third signal pad is formed on the lower surface of the second substrate, directly below the second signal pad, A grounding ground layer formed on the lower surface of the second substrate in such a manner that it surrounds the third signal pad, and the grounding ground layer includes a third ground pad formed at a position directly below the second ground pad on the lower surface of the second substrate. Equipped with, The first signal pad and the third signal pad are joined facing each other, The first ground pad and the third ground pad are joined facing each other. The gap between the third signal pad and the ground layer in the longitudinal direction of the second high-frequency line is smaller than 1 / 4 of the wavelength inside the pipe. A high-frequency connection line wherein the width of the second signal pad in the direction perpendicular to the longitudinal direction of the second high-frequency line is wider than the width of the second signal pad in the direction perpendicular to the longitudinal direction of the second high-frequency line, and the distance between the second signal pad and the second ground pad is narrower than the distance between the second signal line and the second ground.

2. The shape of the grounding layer surrounding the third signal pad is, A rectangle comprising two sides parallel to the longitudinal direction of the second high-frequency line and two sides perpendicular to the longitudinal direction of the second high-frequency line, A hexagon including the two parallel sides, the two perpendicular sides, and two sides connecting the side of the two perpendicular sides that is on the second signal line side to the two parallel sides, or The shape includes the two parallel sides, the two perpendicular sides, and two curves connecting the side of the two perpendicular sides that is on the second signal line side to the two parallel sides. A high-frequency connecting line according to claim 1, which is any of the following.

3. The high-frequency connection line according to claim 2, comprising at least one signal via consisting of a conductor penetrating the second substrate for electrically connecting the second signal pad and the third signal pad, wherein the signal via is a conductor embedded via.

4. The device comprises at least one signal VIA consisting of a conductor penetrating the second substrate for electrically connecting the second signal pad and the third signal pad, The high-frequency connection line according to claim 1, wherein the line connecting the region connected to the signal VIA in the second signal pad has a line shape with a width narrower than the line connecting the region connected to the signal VIA in the third signal pad.

5. The first high-frequency transmission line includes a first grounding ground formed on the upper surface of the first substrate. The first signal line is a differential signal line in which a differential signal consisting of a pair of positive and negative signals propagates, and a first positive signal line and a first negative signal line are arranged adjacent to each other at a predetermined first interval, with the first grounding grounds arranged on both sides. The second signal line is a differential signal line in which a differential signal consisting of a pair of positive and negative signals propagates, and a second positive signal line and a second negative signal line are arranged adjacent to each other at a predetermined second interval different from the first interval, and the second ground is provided on both sides. The high-frequency connection line according to claim 4, wherein the first positive signal line and the first negative signal line and the second positive signal line and the second negative signal line are each connected via the second signal pad, the signal VIA, and the third signal pad, respectively.

6. The first high-frequency transmission line includes a first grounding ground formed on the upper surface of the first substrate. The first signal line is a differential signal line in which a differential signal consisting of a pair of positive and negative signals propagates, and a first positive signal line and a first negative signal line are arranged adjacent to each other at a predetermined first interval, with the first grounding grounds arranged on both sides. The second signal line is a differential signal line in which a differential signal consisting of a pair of positive and negative signals propagates, and a second positive signal line and a second negative signal line are arranged adjacent to each other at a predetermined second interval different from the first interval, and the second ground is provided on both sides. The first positive signal line and the first negative signal line are configured to be connected to the second positive signal line and the second negative signal line via the second signal pad, the signal VIA, and the third signal pad, respectively. The high-frequency connection line according to claim 4, wherein the line at the connection portion with the second positive signal line in the second signal pad has a line shape with a width wider than the width of the second signal pad, the width of the third signal pad, and the width of the second main line.

7. The first substrate is A first lower ground contact ground (2-3) formed on the lower surface of the first substrate, directly below the first signal line and the first ground contact ground, A grounding ground layer formed between the upper surface on which the conductive first main line is formed and the first lower ground contact ground, The insulating layers formed in the upper and lower layers of the grounding ground layer, A ground VIA penetrating the first substrate for electrically connecting the first lower ground contact and the grounding ground layer Equipped with, The high-frequency connection line according to claim 5 or 6, wherein the grounding layer is not formed in the region directly beneath the first signal pad.

8. The width of the third signal pad is 100 to 200 μm, the width of the second signal pad is 50 to 100 μm, and the longitudinal length of the second high-frequency line of the third signal pad, which is joined in correspondence with the first signal pad, is 1 mm or less. A half-through hole with a radius of curvature of 0.3 mm to 0.5 mm is formed at a position 500 μm or more away from the third signal pad in the longitudinal direction of the second high-frequency line, At least one half-through hole with a radius of curvature of 0.1 mm or more for improving connection strength is formed in the third signal pad at a position perpendicular to the longitudinal direction of the second high-frequency line, and The high-frequency connecting line according to claim 5 or 6, further comprising the above.

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