Patent Publication Number: US-2009231819-A1

Title: Multilayer substrate

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-66245, filed on Mar. 14, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a multilayer substrate which transmits a high frequency signal, for example. 
     DESCRIPTION OF THE BACKGROUND 
     In prior art, layer conversion of a strip conductor and distance conversion between ground conductors in a strip line in a multilayer substrate were designed so that characteristic impedances of lines before and after conversion might become the same. 
     However, even if the characteristic impedances of the lines before conversion and after conversion are designed to coincide, it was difficult to make the characteristic impedance of the layer conversion part completely coincide with a desired value because of design restrictions at the time of manufacturing conductor for interlayer connections, such as a via hole, of the layer conversion part and near the layer conversion part. Because of mismatch of this characteristic impedance, a standing wave occurred in the strip line and the electromagnetic wave propagation characteristic of the strip line was bad. 
     As a method for making characteristic impedances of the lines coincide before and after layer conversion, there is a method in which the pattern widths of the lines are changed before and after layer conversion in consideration of the characteristic impedances of the lines before and after conversion. However, in a high frequency circuit or a circuit of a small area, various problems on a design of the pattern width arise. For example, if pattern width is too small, a problem on which degradation of reliability of performance by a manufacturing process occurs, and a problem on which propagation loss of the line becomes large will arise. In dense patterning, if the pattern width is too large, the problem on which the line comes too close with other lines and a signal quality deteriorates will arise. 
     By forming a cutout part in a ground conductor of the strip line and providing a through hole between the strip lines in a portion which the strip lines are connected by the through hole, a connection structure of the strip line which has good reflective characteristic in high frequency is proposed (for example, refer to JP2003-168903A). However, in a layer conversion of JP2003-168903A, a strip conductor after the layer conversion is located in place more distant from the ground conductor before the layer conversion, viewing from a strip conductor before the layer conversion. From this, this technique is inapplicable to a conversion which each same ground conductor layer is shared before the layer conversion and after the layer conversion. In a layer conversion part shown by JP2003-168903A, since it is necessary to provide the through hole for connection in a ground conductor pattern, an installed position must be designed and it may become a burden in the case of design. 
     As mentioned above, as for a conventional multilayer substrate, electromagnetic wave propagation characteristic of the strip line gets worse easily on the occasion of layer conversion and conversion of distance between ground conductors. When it is tried to avoid aggravation of this electromagnetic wave propagation characteristic, it is necessary to take many design matters into consideration. 
     SUMMARY OF THE INVENTION 
     The present invention was made in order to cope with the above-mentioned situation. An object of the invention is to provide a multilayer substrate which can reduce a burden at the time of a substrate design, and can change a layer of a strip line and a distance between ground conductors without deterioration of the electromagnetic wave propagation characteristic of the strip line. 
     To achieve the above purpose, a multilayer substrate according to the present invention has a plurality of dielectric layers and a plurality of conductor layers laminated via the dielectric layers, respectively, and has a first region, a second region and a third region. The first region has a first strip line including a first strip conductor formed in a first intermediate conductor layer and a first and a second ground conductors formed of conductor layers provided both sides of the first intermediate conductor layer. The second region has a second strip line including a second strip conductor formed in a second intermediate conductor layer which differs from the first intermediate conductor layer, and third ground conductor formed of the same conductor layer as the first ground conductor and the fourth ground conductor formed of a different conductor layer from the second ground conductor. The third region is located between the first and second regions. The third region has a strip line for connection including a strip conductor for connection formed in the first intermediate conductor layer by extending the first strip conductor by ¼ wavelength of a transmission signal with the same pattern width, and a fifth ground conductor formed of the same conductor layer as the first ground conductor and a sixth ground conductor formed of the same conductor layer as the fourth ground conductor. Furthermore, a connection portion for connecting an end portion of the strip conductor for connection of the third region and an end portion of the second strip conductor of the second region is provided. 
     In the multilayer substrate, the first region in which the first strip line was formed, and the second region in which the second strip line having second strip conductor located in a different layer from the first strip conductor is formed, are connected via the third region in which the strip line for connection is formed. 
     As for the strip line for connection, the first strip conductor is extended by a length equivalent to ¼ wavelength of a transmission signal with the same pattern width. At this time, the end of the strip conductor for connection and the end of the second strip conductor are electrically connected by a connection portion for connecting. Thus, as for the multilayer substrate, by connecting the first and second regions via the third region, a difference in characteristic impedances will be matched in the strip conductor for connection of the third region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a multilayer substrate according to first embodiment according to the present invention. 
         FIG. 2  is a cross-sectional view taken along an A-A line in  FIG. 1 . 
         FIG. 3  is a perspective view of a multilayer substrate according to second embodiment according to the present invention. 
         FIG. 4  is a cross-sectional view taken along a B-B line in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments according to the present invention are explained in detail with reference to the drawings. 
     Embodiment 1 
       FIG. 1  is a perspective view of a multilayer substrate according to the first embodiment of the present invention.  FIG. 2  is a cross-sectional view taken along an A-A line in  FIG. 1 . Multilayer substrate  1  shown in  FIG. 1  has a five-layer substrate structure which has five conductor layers laminated via four dielectric layers  15 , respectively. In  FIG. 1 , since one conductor layer between upper dielectric layers  15  was removed, only four conductor layers are shown. Multilayer substrate  1  possesses region  10 , region  20 , and region  30  located between region  10  and region  20 , and strip line is formed in each region. 
     Strip line  11  is formed in region  10 . Strip line  11  has strip conductor  12  formed of a first intermediate conductor layer, and has ground conductors  13  and  14  formed of conductor layers provided both sides of strip conductor  12 . A distance between strip conductor  12  and ground conductor  13  and a distance between strip conductor  12  and ground conductor  14  are equal. 
     Strip line  31  is formed in region  30 . Strip line  31  has strip conductor  32  formed of a second intermediate conductor layer different from the first intermediate conductor layer, and has ground conductors  33  and  34  formed of conductor layers provided both sides of strip conductor  32 . Strip conductor  32  is in the same pattern width as strip conductor  12 , and is located in a layer which is different from strip conductor  12 . Ground conductor  33  is the same layer as ground conductor  13 , and ground conductor  34  is a different layer from ground conductor  14 . Strip conductor  32  is formed in the same conductor layer as ground conductor  14 . A distance between strip conductor  32  and ground conductor  33  and a distance between strip conductor  32  and ground conductor  34  are equal. 
     Strip line  21  is formed in region  20 . Strip line  21  has strip conductor  22  formed of the first intermediate conductor layer and has ground conductors  23  and  24  formed of conductor layers provided both sides of strip conductor  22 . Strip conductor  22  is the same pattern width as strip conductor  12 , and is formed by extending strip conductor  12  by a length equivalent to ¼ wavelength of a transmission signal. Ground conductor  23  is the same layer as ground conductor  13 , and ground conductor  24  is the same layer as ground conductor  34 . At this time, a distance between strip conductor  22  and ground conductor  23  is smaller than a distance between strip conductor  22  and ground conductor  24 . 
     Via hole, for example through hole  16 - 1 , is arranged between region  20  and region  30 , and it is provided in parallel to a lamination up-and-down direction of multilayer substrate  1 . Through hole  16 - 1  electrically connects an end portion of strip conductor  22  and an end portion of strip conductor  32 . 
     Transmission of a signal in multilayer substrate  1  of above-mentioned composition is explained in detail. 
     Multilayer substrate  1  transmits a transmission signal to strip conductor  32  connected by through hole  16 - 1  via strip conductor  22  from strip conductor  12 . At this time, a characteristic impedance of strip line  11  and a characteristic impedance of strip line  31  differ mutually. Strip line  21  almost fulfills conditions to match these characteristic impedances. The conditions to match different characteristic impedances are that a characteristic impedance of strip line  21  is almost square root of a product of the characteristic impedance of strip line  11  and the characteristic impedance of strip line  31 , and a length of strip line  21  is (2n−1)×¼ (n is an integer) of a wavelength of the transmission signal. In this embodiment, the above-mentioned conditions is fulfilled by extending strip conductor  12  by a length equivalent to ¼ wavelength of the transmission signal to form strip conductor  22  by an extended part, and letting ground conductor  23  and ground conductor  13  be the same layer, and letting ground conductor  24  and ground conductor  34  be the same layer. 
     As mentioned above, in multilayer substrate  1  according to the first embodiment, strip line  11  of region  10  is electrically connected with strip line  31  of region  30  via strip line  21  of region  20 . At this time, strip line  21  fulfills conditions to match the characteristic impedance of strip line  11  with the characteristic impedance of strip line  31 . 
     By this, when multilayer substrate  1  transmits a transmission signal of which quarter-wavelength corresponds to the length of strip line  21 , a difference between a characteristic impedance of strip line  11  and a characteristic impedance of strip line  31  will be matched by strip line  21 . That is, a reflection of electromagnetic wave in line propagation in an operating frequency will be reduced. 
     From the above-mentioned conditions, with a high frequency signal of frequency other than the operating frequency, since matching of characteristic impedances does not take place in many cases, reflection of electromagnetic waves has an increasing tendency. That is, it becomes possible to suppress electromagnetic wave propagation of frequency other than the operating frequency. Thereby, an effect of a frequency filter can be added in the case of the layer conversion in the strip line. 
     Since generating of reflection of electromagnetic waves can be suppressed by forming strip line  21  between strip line  11  and strip line  31 , it becomes unnecessary to perform strict adjustment of characteristic impedance in a layer conversion part. That is, it is restricted to neither design conditions of a conductor for a interlayer connection, such as a via hole, nor design conditions of its neighborhood, and it becomes possible to design the layer conversion of the strip line freely more. 
     Furthermore, it becomes unnecessary to make the characteristic impedance of strip line  11  and the characteristic impedance of strip line  31  coincide by forming strip line  21  between strip line  11  and strip line  31 . Thereby, pattern width of all the strip conductors can be made the same. That is, multilayer substrate  1  according to the embodiment can solve a problem of the design matter about pattern width. 
     In a line on which structure of a ground conductor in the strip line changes, the necessity of newly providing a design factor for realizing matching over this structural change decrease. For this reason, in the state with few elements which may generate mismatching, with a simpler structure, a good electromagnetic wave propagation characteristic which does not generate reflection of electromagnetic waves can be obtained. 
     Therefore, the multilayer substrate according to the first embodiment can reduce a burden at the time of the substrate design, and can change the layer of the strip line and distance between ground conductors without deterioration of the electromagnetic wave propagation characteristic of the strip line. 
     Embodiment 2 
       FIG. 3  shows a perspective view of a multilayer substrate according to the embodiment 2 of the present invention.  FIG. 4  shows a cross-sectional view taken along B-B line in  FIG. 3 . Multilayer substrate  2 , shown in  FIG. 3 , has a five-layer substrate structure which has five conductor layers laminated via four dielectric layers  15 , respectively. In addition to the multilayer substrate of  FIG. 1 , multilayer substrate  2  has regions  40  and  50 , and there are two layer conversions. A length of strip line  31  in region  30  is set up arbitrarily. 
     Strip line  51  is formed in region  50 . Strip line  51  has strip conductor  52  formed of a third conductor layer and ground conductors  53  and  54  formed of conductor layers provided both sides of strip conductor  52 . Here, strip conductor  52  is the same pattern width as strip conductor  32 , and is located in a layer which is different from strip conductor  32 . Ground conductor  54  is the same layer as ground conductor  34 , and ground conductor  53  is a different layer from ground conductor  33 . Ground conductor  53  is formed in the same conductor layer as strip conductor  32 . A distance between strip conductor  52  and ground conductor  53  and a distance between strip conductor  52  and ground conductor  54  are equal. 
     Strip line  41  is formed in region  40 . Strip line  41  has strip conductor  42  formed of a third conductor layer and ground conductors  43  and  44  formed of conductor layers provided both sides of strip conductor  42 . Here, strip conductor  42  is the same pattern width as strip conductor  52 , and is formed by extending strip conductor  52  by a length equivalent to ¼ wavelength of a transmission signal. Ground conductor  43  is the same layer as ground conductor  33 , and ground conductor  44  is the same layer as ground conductor  54 . At this time, a distance between strip conductor  42  and ground conductor  44  is smaller than a distance between strip conductor  42  and ground conductor  43 . 
     In addition, the layer of strip conductor  12  of strip line  11  into which the transmission signal is inputted, and the layer of strip conductor  52  of strip line  51  from which the transmission signal is outputted are different, respectively. 
     Through hole  16 - 2  is arranged between region  30  and region  40 , and is provided in parallel to a lamination up-and-down direction of multilayer substrate  2 . Through hole  16 - 1  electrically connects an end portion of strip conductor  32  and an end portion of strip conductor  42 . 
     As mentioned above, in the multilayer substrate according to the embodiment 2, strip line  11  of region  10  is electrically connected with strip line  31  of region  30  via strip line  21  of region  20 , and strip line  31  of region  30  is electrically connected with strip line  51  of region  50  via strip line  41  of region  40 . At this time, strip line  21  fulfills the conditions to match the characteristic impedance of strip line  11  and the characteristic impedance of strip line  31 , and strip line  41  fulfills conditions to match a characteristic impedance of strip line  31  and a characteristic impedance of strip line  51 . 
     Thereby, when transmitting a high frequency signal of which quarter-wavelength corresponds to each length of strip lines  21  and  41 , a difference between the characteristic impedance of strip line  11  and the characteristic impedance of strip line  31  is matched by strip line  21 . Furthermore, a difference between the characteristic impedance of strip line  31  and the characteristic impedance of strip line  51  is matched by strip line  41 . That is, a reflection of electromagnetic waves in line propagation in an operating frequency will be reduced. 
     In a high frequency signal of frequency other than the operating frequency, since matching of the characteristic impedances does not take place in many cases, electromagnetic wave propagation of the frequency other than the operating frequency can be suppressed. Thereby, an effect of a frequency filter can be added in the case of layer conversion in the strip line. 
     Since multilayer substrate  2  performs the layer conversion twice, a high frequency signal passes these frequency filters twice in this embodiment. Thereby, multilayer substrate  2  can make more remarkable the effect which suppresses electromagnetic wave propagation of the frequency other than the operating frequency. 
     Furthermore, by forming strip line  21  between strip line  11  and strip line  31 , and by forming strip line  41  between strip line  31  and strip line  51 , generating of reflection of electromagnetic waves can be suppressed. Thereby, it becomes unnecessary to perform strict adjustment of characteristic impedance in a layer conversion part. That is, it is restricted to neither design conditions of a conductor for a interlayer connection, such as a via hole, nor design conditions of its neighborhood, and it becomes possible to design the layer conversion of the strip line freely more. 
     By forming strip line  21  between strip line  11  and strip line  31 , it becomes unnecessary to make the characteristic impedance of strip line  11  and the characteristic impedance of strip line  31  coincide. And forming strip line  41  between strip line  31  and strip line  51 , it becomes unnecessary to make the characteristic impedance of strip line  31  and the characteristic impedance of strip line  51  coincide. Thereby, it becomes possible to make the pattern width of all the strip conductors the same. That is, multilayer substrate  2  according to this embodiment can solve the problem of the design matter about the pattern width. 
     Furthermore, in a line in which a structure of the ground conductors in the strip line changes, the necessity of newly providing a design factor for realizing matching over this structural change decreases. For this reason, in the state with few elements which may generate mismatching, with a simpler structure, good electromagnetic wave propagation characteristic which does not generate reflection of electromagnetic waves can be obtained. 
     Therefore, multilayer substrate  2  according to the embodiment 2 can reduce a burden at the time of the substrate design, and can change the layer of the strip line, and change the distance between ground conductors without aggravation of the electromagnetic wave propagation characteristic of the strip line. 
     (Modification) 
     The multilayer substrate according to the present invention is not necessarily limited to the embodiments mentioned above. For example, in each above-mentioned embodiment, an example of the multilayer substrate of five-layer substrate structure is explained, but the present invention is not necessarily restricted to the multilayer substrate of five-layer substrate structure. 
     Although each above-mentioned embodiment explained the example which performs the layer conversion once or twice, the number of times of conversion does not necessarily have restrictions. In addition, increasing the number of times of this layer conversion makes more remarkable the effect which the electromagnetic wave of only the operating frequency propagates. 
     Other embodiments or modifications of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and example embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following.