JP2013172128A - Flexible substrate and optical module including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the deterioration of transmission characteristics at a connection region between a signal electrode and a signal path in a signal line.SOLUTION: A flexible substrate includes: a plate dielectric; a signal line provided on a first surface of the dielectric; multiple first ground electrodes provided on the first surface of the dielectric; and a ground conductor pattern provided on a second surface of the dielectric that faces the first surface. The signal line includes: a signal path provided along the ground conductor pattern; a first signal electrode provided between the multiple first ground electrodes; and a taper part that widens from the signal path toward the first signal electrode in a tapered manner. The ground conductor pattern includes: a slit part forming an opening according to a shape of the taper part; and multiple second ground electrode parts that extend from the slit part and are provided so as to face the first ground electrodes.

Description

  The present invention relates to a flexible substrate and an optical module including the flexible substrate.

  For example, as represented by X2 and XFP (10 Gigabit Small Form Factor Pluggable), which are 10 Gbps optical transceivers, downsizing of optical transceivers used in optical communication systems has been progressing rapidly in recent years. Accordingly, in the electro-optical conversion unit and the photoelectric conversion unit used in the optical transceiver, TOSA (Transmitter Optical Subsymbol) called XMD-MSA (10 Gigabit / s Miniature Device Multi Source Agreement) is also used. Standards such as ROSA (Receiver Optical SubAssembly) have become common. Here, in XMD-MSA, it is assumed that a flexible substrate is used for connection between TOSA, ROSA and a rigid substrate of an optical transceiver. In the connection portion between the flexible substrate and the rigid substrate, signal reflection occurs due to the discontinuous cross-sectional structure of the transmission line, which is a cause of deterioration in transmission characteristics.

  Therefore, a flexible substrate 600 shown in FIG. 6 is known for the purpose of preventing deterioration of high-frequency signal transmission characteristics at the connection point between the flexible substrate and the rigid substrate (see Patent Document 1). As shown in FIG. 6, the flexible substrate 600 includes a plate-shaped dielectric 601, a signal line 603 and a pair of signal electrodes 602 formed on the upper surface of the dielectric 601, and a ground formed on the lower surface of the dielectric 601. A conductor pattern 604 is included.

  The signal line 603 includes a signal path 605, a signal electrode 606, and a wiring region 607 formed between the signal path 605 and the signal electrode 606. Here, the width of the signal electrode 606 is larger than the width of the signal path 605, and the width of the signal electrode 606 and the wiring region 607 is substantially the same. Further, the width of the wiring region 607 is larger than the width of the signal path 605.

  Here, the ground conductor pattern 604 is disposed on the lower surface of the dielectric 601 so that the half region on the signal path 605 side of the wiring region 607 covers the ground conductor pattern 604 when viewed from the upper surface of FIG. Thus, in the region where the ground conductor pattern 604 is disposed on the lower surface, the width of the wiring region 607 is increased, so that in the region where the ground conductor pattern 604 is present on the lower surface, the wiring region 607 and the ground conductor pattern 604 on the lower surface The capacitance component between them becomes larger than that of the signal path 605. Therefore, the characteristic impedance is lower than that of the signal path 605 in this region. On the other hand, in a region where the ground conductor pattern 604 is not provided on the lower surface, the capacitance component between the wiring region 607 and the ground conductor pattern 604 is smaller than that of the signal path 605, so that the characteristic impedance is higher than that of the signal path 605. Then, the width of the wiring region 607 is adjusted so that the average of the characteristic impedances of the high and low characteristic impedances matches the characteristic impedance of the signal path 605. As a result, the amount of reflection that occurs in the entire wiring region 607 is suppressed, and as a result, deterioration of the transmission characteristics of the high-frequency signal at the joint portion between the flexible substrate 600 and the rigid substrate (not shown) is prevented.

JP 2010-212617 A

  However, in the flexible substrate 600, the reflection generated in the wiring region 607 cannot be completely eliminated. In addition, discontinuous points of the transmission line are generated and the reflection is caused by alternately arranging the high and low characteristic impedance regions. In addition, when the length of the wiring region 607 is not negligible with respect to the wavelength of the transmission signal, the magnitude of reflection becomes more prominent. Therefore, it is necessary to shorten the length of the wiring region 607. Further, when a discontinuity of impedance different from the wiring region 607 occurs, resonance may occur and lead to a large waveform deterioration even if the amount of reflection generated in the wiring region 607 is kept low.

  In view of the above problems, an object of the present invention is to realize a flexible substrate that can improve transmission characteristics of signal wiring and an optical module that includes the flexible substrate.

  (1) A flexible substrate according to the present invention includes a plate-shaped dielectric, a signal line provided on the first surface of the dielectric, and a plurality of first grounds provided on the first surface of the dielectric. A flexible substrate having an electrode and a ground conductor pattern provided on a second surface opposite to the first surface of the dielectric, wherein the signal line is provided along the ground conductor pattern. A signal path, a first signal electrode provided between the plurality of first ground electrodes, and a tapered portion having a tapered width in a direction from the signal path portion toward the signal electrode portion. The ground conductor pattern includes a slit portion that forms an opening corresponding to the shape of the tapered portion, and a plurality of second ground electrodes that extend from the slit portion and that are provided to face the first ground electrode. And a portion.

  (2) The flexible substrate according to (1), wherein the width of the opening of the slit portion is in a range of 0.6 to 1.2 times the width of the tapered portion. .

  (3) The flexible substrate according to the above (1) or (2), wherein the flexible substrate further includes a plurality of second signals opposed to the plurality of first signal electrodes on the second surface. It has an electrode.

  (4) The flexible substrate according to any one of (1) to (3), wherein each of the first signal electrodes and each of the second signal electrodes has a first through hole provided in the dielectric. It is characterized in that it is electrically connected.

  (5) The flexible substrate according to any one of (1) to (4), wherein each of the first ground electrodes and each of the second ground electrodes has a first through hole provided in the dielectric. It is characterized in that it is electrically connected.

  (6) The flexible substrate according to any one of (1) to (5), wherein the flexible substrate includes a plurality of the signal lines.

  (7) An optical module comprising the flexible substrate according to any one of (1) to (6).

It is a figure for demonstrating the outline of the optical module in embodiment of this invention. It is a figure for demonstrating the outline of the flexible substrate shown in FIG. It is a figure which shows the III-III cross section of FIG. It is a figure which shows the relationship between Ws and Wg. It is a figure for demonstrating the outline of the flexible substrate in a modification. It is a figure which shows the flexible substrate in related technology.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, about drawing, the same code | symbol is attached | subjected to the same or equivalent element, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a diagram for explaining an outline of an optical module according to the present embodiment. As shown in FIG. 1, the optical module 100 including a flexible substrate includes an optical module 120 and a flexible substrate 110 connected to the optical module 120.

  The optical module 120 corresponds to, for example, an optical transmission module that converts an electrical signal into an optical signal, an optical reception module that converts a received optical signal into an electrical signal, or an optical transmission / reception module. More specifically, for example, as the optical module 120, an XFP (10-Gigabit Small Form Factor Pluggable) or SFP + (Small Form Factor Pluggable Plus) module is used. Note that the details of the configuration of the optical module 120 are well known, and a description thereof will be omitted. Further, the flexible substrate 110 is connected to a rigid substrate (not shown) at the end opposite to the side connected to the optical module 120 via a ground electrode and a signal electrode of the flexible substrate 110 described later.

  FIG. 2 is a diagram for explaining the outline of the flexible substrate shown in FIG. As shown in FIG. 2, the flexible substrate 110 includes a plate-shaped dielectric 201, a pair of first ground electrodes 202 and a signal line 203 disposed on the upper surface of the dielectric 201, and a lower surface of the dielectric 201. The ground conductor pattern 204 is included.

  The dielectric 201 has a plate shape and is formed of, for example, a flexible insulating material. More specifically, for example, a material such as polyimide or a liquid crystal polymer may be used as the material of the dielectric 201.

  The signal line 203 includes a signal path 205, a signal electrode 206, and a tapered portion 207. Moreover, the signal line 203 is arrange | positioned in the approximate center of the dielectric material 201 along the longitudinal direction of the dielectric material 201, for example, as shown in FIG.

  The signal path 205 constitutes a so-called microstrip line together with a ground conductor portion of a ground conductor pattern 204 described later. Then, the width of the signal line 203 is adjusted according to the thickness of the dielectric 201 and the relative dielectric constant so as to have a desired characteristic impedance. Specifically, for example, since the characteristic impedance of other devices is generally set to 50Ω, the characteristic impedance is set to 50Ω in consideration of connectivity with other devices.

  The signal electrode 206 is disposed at the end of the plate-like dielectric 201. The signal electrode 206 has a rectangular shape. In order to ensure the reliability of electrical connection with a rigid substrate (not shown), the width of the signal electrode 206 and the first ground electrode 202 described later is made wider than the width of the signal path 205. For example, in XMD-MSA, the pitch between the electrodes is set to 0.79 mm. Therefore, in this case, considering the gap between the electrodes, the widths of the first and second signal electrodes 206 and 213 and the first and second ground electrodes 202 and 211 are approximately 0.3 to 0.6 mm. . The second signal electrode 213 and the first and second ground electrodes 202 and 211 will be described later. The rigid board and the first and second signal electrodes 206 and 213 and the first and second ground electrodes 202 and 211 are electrically and mechanically connected using, for example, solder or a conductive adhesive. .

  The tapered portion 207 corresponds to a part of the signal line 203 provided between the first signal electrode 206 and the signal line 203. The tapered portion 207 has a so-called tapered shape in which the width gradually increases from the signal line 203 toward the first signal electrode 206. That is, the taper portion 207 has a shape similar to, for example, an isosceles triangle as viewed from the upper surface of FIG. Further, the end of the tapered portion 207 has an angle toward the signal path 205 so as not to interfere with the first ground electrode 202.

  A ground conductor pattern 204 is disposed on the lower surface of the dielectric 201. The ground conductor pattern 204 includes a rectangular ground conductor portion 208 disposed along the signal path 205, and a region 210 (hereinafter referred to as “slit”) where the ground conductor pattern 204 is not disposed along the taper portion 207. The slit part 209 is included. The ground conductor pattern 204 includes a pair of second ground electrodes 211 provided to face the pair of first ground electrodes 202.

  Specifically, as shown in FIG. 3, the ground conductor pattern 204 is arranged so that slits are arranged along the width (Ws) of the tapered portion 207 arranged on the upper surface of the dielectric 201. FIG. 3 is a view showing a cross section taken along the line III-III in FIG. Here, as shown in FIG. 3, the width of the tapered portion 207 is Ws, and the width of the slit formed in the slit portion 209 is Wg. Details of the relationship between Ws and Wg will be described later.

  The pair of second ground electrodes 211 is disposed on the lower surface of the dielectric 201 so as to face the pair of first ground electrodes 202 disposed on the upper surface of the dielectric 201. Further, the second ground electrode 211 and the first ground electrode 202 are electrically connected through one or a plurality of through holes 212 formed in the dielectric 201.

  Further, the second signal electrode 213 is disposed on the lower surface of the dielectric 201 so as to face the first signal electrode 206. The first signal electrode 206 and the second signal electrode 213 are electrically connected through one or more through holes 212 formed in the dielectric 201. The width of the second signal electrode 213 is substantially equal to the width of the first signal electrode 206. Further, the second signal electrode 213 and the ground conductor pattern 204 are installed at a predetermined interval so as not to be electrically short-circuited even when the bonding agent protrudes. Specifically, it is desirable to arrange them with an interval of about 0.2 mm or more. In other words, in the present embodiment, as described above, a region (slit) in which the ground conductor pattern 204 does not exist is provided in a region where the tapered portion 207 faces via the dielectric 201.

  As described above, the shape of the slit is a shape corresponding to the shape of the tapered portion 207. Specifically, as illustrated in FIG. 3, the width of the taper portion 207 is set so as to be along the width of the slit when viewed from the cross section of the flexible substrate 110 illustrated in FIG. 3. Then, the width of the taper portion 207 with respect to the width of the slit is adjusted so as to have a desired characteristic impedance. Thereby, it is possible to form the signal line 203 that can prevent the occurrence of reflection in the region (tapered portion 207) where the signal line 203 and the first signal electrode 206 are connected.

  Here, the width (Wg) of the slit and the width (Ws) of the tapered portion 207 for obtaining a desired characteristic impedance are obtained based on the relative dielectric constant and thickness of the dielectric 201. FIG. 4 shows, as an example, the relationship between Ws and Wg for setting the characteristic impedance to 50Ω when the relative permittivity of the dielectric 201 is 3 and the thickness of the dielectric 201 is 25 μm, 50 μm, and 100 μm. . As shown in FIG. 4, the characteristic impedance can be set to 50Ω by setting Wg in the range of 0.6 to 1.2 times Ws. That is, by connecting the microstrip line having a characteristic impedance of 50Ω by setting the width of the taper portion 207 and the slit so as to maintain the relationship between Ws and Wg in the region surrounded by the broken line shown in FIG. A signal line 203 in which no reflection occurs can be realized.

  The present invention is not limited to the above-described embodiment, and is substantially the same configuration as the configuration shown in the above-described embodiment, a configuration that exhibits the same operational effects, or a configuration that can achieve the same purpose. May be replaced. For example, the wiring patterns such as the tapered portion 207, the signal path 205, and the ground conductor pattern 204 are protected except for the region where the first and second signal electrodes 206 and 213 and the first and second ground electrodes 202 and 211 are disposed. Therefore, you may comprise so that a coverlay may be covered.

[Modification]
Next, a modification of the present invention will be described. FIG. 5 is a diagram for explaining the outline of the flexible substrate in the modification. As shown in FIG. 5, the present modification is mainly different from the first embodiment in that two signal lines 203 are arranged and a slit portion 209 corresponding to them is formed. In the following, description of points that are the same as those of the first embodiment will be omitted.

  As shown in FIG. 5, the flexible substrate 110 in this modification includes a plate-like dielectric 201, three first ground electrodes 202, two signal lines 203, and a ground conductor disposed on the lower surface of the dielectric 201. Pattern 204. The signal lines 203 of the third first ground electrodes 202 and 2 are disposed on the upper surface of the dielectric 201.

  Here, of the two signal lines 203, one signal line 203 transmits a normal phase signal, and the other signal line 203 transmits a reverse phase signal whose polarity is reversed from that of the normal phase. That is, according to the flexible substrate 110 in this modification, a differential signal can be transmitted.

  As shown in FIG. 5, the three first ground electrodes 202 are arranged at predetermined intervals at the end of the dielectric 201. Further, the second ground electrode 211 is disposed on the lower surface of the dielectric 201 so as to face the three first ground electrodes 202. The first ground electrode 202 and the corresponding second ground electrode 211 are electrically connected through one or more through holes 212 formed in the dielectric 201 in the same manner as in the above embodiment. is there.

  The two signal lines 203 are respectively disposed between the first ground electrodes 202. The configuration of each signal line 203 is the same as that in the above embodiment. Similarly to the above embodiment, the ground conductor pattern 204 is provided with a slit portion 209 having a shape along the tapered portion 207 of each signal line 203. That is, the slit portion 207 in the present modification includes two slits.

  According to this modification, by adjusting the width of the tapered portion 207 and the slit of each signal line 203, the characteristic impedance of the connection region (tapered portion 207) is substantially the same value as the region where the signal path 203 is formed, For example, it can be 50Ω. Thereby, the transmission line which does not produce reflection can be formed.

  Note that the present invention is not limited to the above-described embodiments and modifications, and achieves substantially the same configuration, the same operational effect, or the same object as the configuration shown in the above-described embodiments. A configuration that can be used may be replaced.

  Specifically, for example, in the above-described modification, between the first signal electrode 206, the first and second ground electrodes 202 and 211, and the slit portion 204 of the ground conductor pattern 208, the ground conductor portion 208 to the second ground You may comprise so that the part (for example, the part regarding the 1st ground electrode 202 shown in FIG. 5) which reaches to the electrode 211 may not be provided. In this case, the width and interval of the signal line 205 are set so that the differential impedance of the two signal paths 205 is twice a desired value, for example, 100Ω, and the width of each taper portion 207 and each taper The interval between the portions 207 and the width of the slit provided corresponding to each tapered portion 207 are adjusted. As a result, the characteristic impedance of the taper portion 207 can be made substantially the same value as the characteristic impedance of the signal path 205, and as a result, the signal line 203 without reflection can be realized.

  110, 600 Flexible substrate, 120 Optical module, 201, 601 Dielectric, 202 First ground electrode, 203, 605 Signal line, 204, 604 Ground conductor pattern, 205 Signal path, 206 First signal electrode, 207 Tapered portion, 208 Ground conductor pattern, 209 slit portion, 211 second ground electrode, 212 through hole, 602, 606 signal electrode, 607 wiring region.

Claims (7)

A plate-like dielectric;
A signal line provided on the first surface of the dielectric;
A plurality of first ground electrodes provided on the first surface of the dielectric;
A grounding conductor pattern provided on a second surface opposite to the first surface of the dielectric,
The signal line includes a signal path provided along the ground conductor pattern, a first signal electrode provided between the plurality of first ground electrodes, and a direction from the signal path section toward the signal electrode section. And a taper portion having a taper-like width.
The ground conductor pattern includes a slit portion that forms an opening corresponding to the shape of the tapered portion, and a plurality of second ground electrode portions that extend from the slit portion and are provided to face the first ground electrode. And a flexible substrate. The flexible substrate according to claim 1,
The width of the opening of the slit portion is in the range of 0.6 to 1.2 times the width of the tapered portion. The flexible substrate according to claim 1 or 2,
The flexible substrate further includes a plurality of second signal electrodes respectively opposed to the plurality of first signal electrodes on the second surface. A flexible substrate according to any one of claims 1 to 3,
Each of the first signal electrodes and each of the second signal electrodes is electrically connected through a first through hole provided in the dielectric. A flexible substrate according to any one of claims 1 to 4,
Each of the first ground electrodes and each of the second ground electrodes is electrically connected through a first through hole provided in the dielectric. A flexible substrate according to any one of claims 1 to 5,
A flexible substrate comprising a plurality of the signal lines.   An optical module comprising the flexible substrate according to claim 1.

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