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JP-7857492-B2 - High-frequency connection lines

JP7857492B2JP 7857492 B2JP7857492 B2JP 7857492B2JP-7857492-B2

Inventors

  • 尾崎 常祐
  • 布谷 伸浩
  • 田野辺 博正
  • 福山 裕之

Assignees

  • ＮＴＴ株式会社
  • ＮＴＴイノベーティブデバイス株式会社

Dates

Publication Date
20260512
Application Date
20240222
Priority Date
20230224

Claims (8)

  1. A high-frequency connecting line comprising 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, wherein the two lines 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 substrate comprises a first ground pad formed on the upper surface of the first substrate, 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, A second main line comprising a second grounding ground formed on the upper surface of the second substrate, 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 as to surround the third signal pad, 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, 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, The high-frequency connection line according to claim 1, which is either 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 with the two parallel sides, or a shape including 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 with the two parallel sides.
  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, The first substrate is provided with a ground VIA that penetrates the first substrate for electrically connecting the first lower ground contact ground and the grounding ground layer, 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, The high-frequency connection line according to claim 5 or 6, further comprising at least one half-through hole with a radius of curvature of 0.1 mm or more for improving connection strength, formed in the third signal pad at a position perpendicular to the longitudinal direction of the second high-frequency line.

Description

This disclosure relates to a high-frequency connection line, and more particularly to a high-frequency connection line connecting high-frequency lines having different end structures in the connection region, and which is capable of matching the characteristic impedance of the entire high-frequency line, including not only the characteristic impedance in the connection region at the end of the high-frequency line, but also the characteristic impedance of the portion outside the connection region, to a desired characteristic impedance. In high-frequency transmission lines with a predetermined characteristic impedance, when the ends of separate high-frequency transmission lines are electrically connected facing each other, reducing reflection losses in the connection region is generally considered an important issue. In particular, 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), which are widely used in optical communication systems, heterogeneous substrate bonding is common, where high-frequency lines on a rigid substrate are joined to high-frequency lines on a flexible substrate. In 200 GBd optical communication systems, which use higher baud rates than those used in high-speed broadband optical communication, suppressing reflection losses of high-frequency signals propagating through heterogeneous substrate bonding regions was an urgent issue that needed to be addressed. For example, the metal pads that constitute 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. 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, making them a good choice because they allow for relatively low manufacturing costs and high manufacturing precision (see Patent Document 2). 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). In the rigid substrate (100), a differential microstrip line consisting of two signal lines (101) patterned using the first wiring layer (111) of the rigid substrate is provided on its upper surface. In this case, the ground defining 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. 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 arranged 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