Patent Publication Number: US-2023164909-A1

Title: Circuit board having complementary signal conducting patterns

Description:
BACKGROUND 
     1. Field 
     The present disclosure generally relates to a conductive pattern, and more particularly, a conductive pattern having a pair of terminal portions having a pair of circular arc profile with a pair of complementary notches. 
     2. Related Art 
     High frequency signals transmitted through transmission lines may suffer from insertion losses. The magnitude of the insertion loss depends on the signal frequency, the transmission line geometry, and the material properties of the signal carrying medium. Further, transmission lines arranged close to each other may exhibit signal cross talk. Thus, the provision of improved transmission structure for high frequency signals is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    illustrates a 3D representation view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  2    illustrates a 3D representation view of a substrate according to some embodiments of the instant disclosure; 
         FIG.  3    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  4    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  5    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  6    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  7    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  8    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  9    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  10    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure; 
         FIG.  11    illustrates a flowchart of a method of forming an inter-surface junction of a substrate according to some embodiments of the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout. 
     The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having” when used herein, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG.  1    illustrates a 3D representation view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. In some embodiments, the inter-surface junction is formed within a substrate. In some embodiments, the substrate comprises a generally planar structure that provides mechanical support for a plurality layers of conductive traces (e.g., circuit/interconnecting components). In some embodiments, the substrate can be a printed circuit board (PCB) such as Single-layer PCBs, Double-layer PCBs, Multi-layer PCBs, Rigid PCBs, Flexible PCBs, Rigid-Flex PCBs, High-frequency PCBs, Aluminum-backed PCBs. 
     The inter-surface junction allows electrical connection between the conductive paths on the first surface and the conductive paths on second surface of the substrate. In some embodiments, the inter-surface junction includes a first conductive trace, a second conductive trace, and a conductive via  30 . The first conductive trace formed on the first surface includes a linear portion  12  and a terminal portion  11 . The second conductive trace formed on the second surface includes a linear portion  22  and a terminal portion  21 . The conductive via  30  penetrates through the central area of the terminal portions  11 ,  21  of the first conductive trace and the second conductive trace. In this way, the conductive via  30  may electrically connect the first conductive trace and the second conductive trace. 
     In some other embodiments, a third conductive trace having a terminal portion  41  is disposed in a level between the first conductive trace and the second conductive trace (e.g., in a middle layer of a multilayered, stacked laminate structure). In some embodiments, the conductive via  30  penetrates through the central area of the terminal portion  41  of the third conductive trace. In this way, the third conductive trace may be electrically connected to the first conductive trace and the second conductive trace. 
     In some embodiments, conductive via  30  is formed by forming a through hole through the central area of the terminal portions  11 ,  21  of the first conductive trace and the second conductive trace. Subsequently, a conductive material may be plated onto the sidewall surface exposed by the through holes. The terminal portions  11 ,  21  of the first conductive trace and the second conductive trace are electrically coupled through the conductive plating in the through hole. In some embodiments, the through hole of the conductive via  30  may be further filled with fillings such as dielectric material or conductive material. 
     When two of the inter-surface junctions such as shown in  FIG.  1    are placed in close vicinity of each other, problems may occur during device operation.  FIG.  2    illustrates a 3D representation view of a substrate according to some embodiments of the instant disclosure. In some embodiments, an inter-surface junction having two signal paths is formed within the substrate  1 . The substrate  1  have a first surface and a second surface opposite the first surface. In some embodiments, the inter-surface junction includes a pair of conductive vias  30 A and  30 B adjacent to each other and a gap AG (i.e. air gap) formed between the pair of conductive vias  30 A and  30 B. The gap AG is configured to enable access between the first surface and the second surface. The absence of material in the gap AG helps to reduce the overall dielectric constant at the trace terminal/vias region, thus alleviating parasitic capacitance that may lead to undesirable problems such as signal delay and crosstalk. It is to be noted that, the term “air gap” generally refers to the absence of material filling in a particular region (thereby forming a structure with void), and does not necessarily imply the gaseous content therein. 
     In some embodiments, the gap AG defines a substantially elliptical air gap. In some other embodiments, the gap AG defines a substantially circular air gap. In some embodiments, the conductive vias  30 A and  30 B enables signal communication between the first surface and the second surface of the substrate  1 . 
     In some embodiments, a pair of first complementary conductive traces formed on the first surface are correspondingly coupled to the conductive vias  30 A and  30 B. In some embodiments, the conductive vias  30 A and  30 B are tubular structures having a conductive sidewall and a channel in the central area surrounded by the sidewall. In some embodiments, the central area has no filling. In some other embodiments, the central area has fillings including at least one of conductive material and dielectric material. Each of the first complementary conductive traces correspondingly includes a linear portion  12 A,  12 B and a terminal portion  11 A,  11 B. The linear portions  12 A and  12 B extend linearly abreast each other. The terminal portions  11 A and  11 B are arranged adjacent to each other. The terminal portions  11 A and  11 B each have a circular arc profile. The circular arc profile can be curved profile resembling a part of the circumference of a circle. Further, the terminal portions  11 A and  11 B have a pair of complementary notches facing towards each other. In some embodiments, the pair of complementary notches conforms to the profile of the gap AG. The complementary notches of the terminal portions  11 A and  11 B are substantially mirror symmetrical. In some embodiments, the gap AG exposes the conductive vias  30 A and  30 B at the complementary notches of the terminal portions  11 A and  11 B. 
     In some embodiments, a pair of second complementary conductive traces formed on the second surface are correspondingly coupled to the conductive vias  30 A and  30 B. Each of the second complementary conductive traces correspondingly includes a linear portion  22 A,  22 B and a terminal portion  21 A,  21 B. The linear portions  22 A and  22 B extend linearly abreast each other. The terminal portions  21 A and  21 B are arranged adjacent to each other. The terminal portions  21 A and  21 B each have a circular arc profile. Further, the terminal portions  21 A and  21 B have a pair of complementary notches facing towards each other. The complementary notches of the terminal portions  21 A and  21 B are substantially mirror symmetrical. In some embodiments, the gap AG exposes the conductive vias  30 A and  30 B at the complementary notches of the terminal portions  21 A and  21 B. 
     In some embodiments, the terminal portions  11 A is electrically coupled to the terminal portions  21 A through the conductive via  30 A. In some embodiments, the terminal portions  11 B is electrically coupled to the terminal portions  21 B through the conductive via  30 B. 
     In some embodiments, the inter-surface junction is formed between a pair of power junctions  70 . In some embodiments, the power junctions  70  may include at least one of a power supply via or a ground via. 
     In some embodiments, the substrate  1  further includes a solder mask material  60  disposed on at least one surface of the substrate  1 . The solder mask layer  60  exposes at least a portion of the conductive traces. In an exemplary embodiment of  FIG.  2   , the terminal portions  11 A and  11 B are exposed through the solder mask layer  60 . 
     Further, the solder mask layer  60  exposes a dielectric region  50  of the substrate  1 . In some embodiments, the dielectric region  50  have a rounded annular profile. A portion of the annular profile conforms to the profile of the terminal portions  11 A and  11 B. Further, another portion of the annular profile conforms to the profile of the gap between the complementary notches of the terminal portions  11 A and  11 B. 
       FIG.  3    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction disposed in a substrate  100  comprises a pair of conductive vias  130 A and  130 B arranged adjacent to each other, a pair of terminal portions  111 A and  111 B formed on the first surface of the substrate  100  and correspondingly coupled to the conductive vias  130 A and  130 B, a pair of linear portions  112 A and  112 B correspondingly coupled to the terminal portions  111 A and  111 B, and a pair of terminal portions  121 A and  121 B formed on the second surface of the substrate  100  and correspondingly coupled to the conductive vias  130 A and  130 B. 
     In some embodiments, the inter-surface junction further comprises a pair of terminal portions  141 A and  141 B formed between the first surface and the second surface of the substrate  100  and correspondingly coupled to the conductive vias  130 A and  130 B. 
     In some embodiments, the terminal portions  111 A,  111 B,  121 A and  121 B correspondingly have an annular profile (i.e. circular profile). Further, terminal portions  141 A and  141 B correspondingly have an annular profile (i.e. circular profile). In some embodiments the terminal portions  111 A and  121 A electrically coupled to the conductive via  130 A projectively overlap each other. In some embodiments the terminal portions  111 B and  121 B electrically coupled to the conductive via  130 B projectively overlap each other. 
     In some other embodiments the terminal portion  141 A electrically coupled to the conductive via  130 A is projectively overlapping with the terminal portions  111 A and  121 A. In some other embodiments the terminal portion  141 B electrically coupled to the conductive via  130 B is projectively overlapping with the terminal portions  111 B and  121 B. 
     In some embodiments, the substrate  100  comprises dielectric material (e.g., glass-reinforced epoxy laminate material such as FR4). The conductive vias  130 A and  130 B and the terminal portions  111 A,  111 B,  121 A and  121 B are surrounded by the dielectric material. During operation, the dielectric material between the conductive vias  130 A and  130 B may cause insertion loss causing a slower propagation speed. 
       FIG.  4    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction disposed in a substrate  200  comprises a pair of conductive vias  230 A and  230 B arranged adjacent to each other, a pair of terminal portions  211 A and  211 B formed on the first surface of the substrate  200  and correspondingly coupled to the conductive vias  230 A and  230 B, a pair of linear portions  212 A and  212 B correspondingly coupled to the terminal portions  211 A and  211 B, and a pair of terminal portions  221 A and  221 B formed on the second surface of the substrate  200  and correspondingly coupled to the conductive vias  230 A and  230 B. 
     In some embodiments, the inter-surface junction further comprises a pair of terminal portions  241 A and  241 B formed between the first surface and the second surface of the substrate  200  and correspondingly coupled to the conductive vias  230 A and  230 B. 
     In some embodiments, the terminal portions  211 A,  211 B,  221 A and  221 B correspondingly have an annular profile (i.e. circular profile). Further, terminal portions  241 A and  241 B correspondingly have an annular profile (i.e. circular profile). In some embodiments the terminal portions  211 A and  221 A electrically coupled to the conductive via  230 A projectively overlap each other. In some embodiments the terminal portions  211 B and  221 B electrically coupled to the conductive via  230 B projectively overlap each other. 
     In some other embodiments the terminal portion  241 A electrically coupled to the conductive via  230 A is projectively overlapping with the terminal portions  211 A and  221 A. In some other embodiments the terminal portion  241 B electrically coupled to the conductive via  230 B is projectively overlapping with the terminal portions  211 B and  221 B. 
     In some embodiments, the substrate  200  comprises dielectric material (i.e. glass-reinforced epoxy laminate material such as FR4). The conductive vias  230 A and  230 B and the terminal portions  211 A,  211 B,  221 A and  221 B are surrounded by the dielectric material. 
     In some embodiments, a portion of the dielectric material between the conductive vias  230 A and  230 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  211 A and  211 B. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     In some embodiments, a portion of the dielectric material between the conductive vias  230 A and  230 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  221 A and  221 B. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     Although there is a layer of dielectric material between the conductive vias  230 A and  230 B, a gap AG between the conductive vias  230 A and  230 B is formed. The gap AG may be an air gap having a relative dielectric constant of 1. In some embodiments, the wall within the air gap is not coated with any material. Thus, during operation, the gap AG may lower insertion loss causing a higher propagation speed. 
       FIG.  5    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction disposed in a substrate  300  comprises a pair of conductive vias  330 A and  330 B arranged adjacent to each other, a pair of terminal portions  311 A and  311 B formed on the first surface of the substrate  300  and correspondingly coupled to the conductive vias  230 A and  330 B, a pair of linear portions  312 A and  312 B correspondingly coupled to the terminal portions  311 A and  311 B, and a pair of terminal portions  321 A and  321 B formed on the second surface of the substrate  300  and correspondingly coupled to the conductive vias  330 A and  330 B. 
     In some embodiments, the inter-surface junction further comprises a pair of terminal portions  341 A and  341 B formed between the first surface and the second surface of the substrate  300  and correspondingly coupled to the conductive vias  330 A and  330 B. 
     In some embodiments, the terminal portions  311 A,  311 B,  321 A and  321 B correspondingly have an annular profile (i.e. circular profile). Further, terminal portions  341 A and  341 B correspondingly have an annular profile (i.e. circular profile). In some embodiments the terminal portions  311 A and  321 A electrically coupled to the conductive via  330 A projectively overlap each other. In some embodiments the terminal portions  311 B and  321 B electrically coupled to the conductive via  330 B projectively overlap each other. 
     In some other embodiments the terminal portion  341 A electrically coupled to the conductive via  330 A is projectively overlapping with the terminal portions  311 A and  321 A. In some other embodiments the terminal portion  341 B electrically coupled to the conductive via  330 B is projectively overlapping with the terminal portions  311 B and  321 B. 
     In some embodiments, the substrate  300  comprises dielectric material (i.e. glass-reinforced epoxy laminate material such as FR4). The conductive vias  330 A and  330 B and the terminal portions  311 A,  311 B,  321 A and  321 B are surrounded by the dielectric material. 
     In some embodiments, a portion of the dielectric material between the conductive vias  330 A and  330 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  311 A and  311 B. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     In some embodiments, a portion of the dielectric material between the conductive vias  330 A and  330 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  321 A and  321 B. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     A gap AG between the conductive vias  330 A and  330 B is formed. A portion of the conductive vias  330 A and  330 B are exposed in the gap AG. The gap AG may be an air gap having a relative dielectric constant of 1. In some embodiments, the wall within the air gap is not coated with any material. Thus, during operation, the gap AG may lower insertion loss causing a higher propagation speed. 
       FIG.  6    illustrates a cross sectional view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction disposed in a substrate  400  comprises a pair of conductive vias  430 A and  430 B arranged adjacent to each other, a pair of terminal portions  411 A and  411 B formed on the first surface of the substrate  400  and correspondingly coupled to the conductive vias  430 A and  430 B, a pair of linear portions  412 A and  412 B correspondingly coupled to the terminal portions  411 A and  411 B, and a pair of terminal portions  421 A and  421 B formed on the second surface of the substrate  400  and correspondingly coupled to the conductive vias  430 A and  430 B. 
     In some embodiments, the inter-surface junction further comprises a pair of terminal portions  441 A and  441 B formed between the first surface and the second surface of the substrate  400  and correspondingly coupled to the conductive vias  430 A and  430 B. 
     In some embodiments, the terminal portions  411 A,  411 B,  421 A and  421 B correspondingly have an annular profile (i.e. circular profile). Further, terminal portions  441 A and  441 B correspondingly have an annular profile (i.e. circular profile). In some embodiments the terminal portions  411 A and  421 A electrically coupled to the conductive via  430 A projectively overlap each other. In some embodiments the terminal portions  411 B and  421 B electrically coupled to the conductive via  430 B projectively overlap each other. 
     In some other embodiments the terminal portion  441 A electrically coupled to the conductive via  430 A is projectively overlapping with the terminal portions  411 A and  421 A. In some other embodiments the terminal portion  441 B electrically coupled to the conductive via  330 B is projectively overlapping with the terminal portions  411 B and  421 B. 
     In some embodiments, the substrate  400  comprises dielectric material (i.e. glass-reinforced epoxy laminate material such as FR4). The conductive vias  430 A and  430 B and the terminal portions  411 A,  411 B,  421 A and  421 B are surrounded by the dielectric material. 
     In some embodiments, a portion of the dielectric material between the conductive vias  430 A and  430 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  411 A and  411 B. The terminal portions  411 A and  411 B is formed to have circular arc profile. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     In some embodiments, a portion of the dielectric material between the conductive vias  430 A and  430 B is removed. In this way, a pair of complementary notches are formed on the pair of terminal portions  421 A and  421 B. The terminal portions  421 A and  421 B is formed to have circular arc profile. In some embodiments, the complementary notches are mirror symmetrical to each other. 
     A gap AG between the conductive vias  430 A and  430 B is formed. A portion of the conductive vias  430 A and  430 B are exposed in the gap AG. Further, a portion of the conductive vias  430 A and  430 B are removed during forming of the gap AG. In some embodiments, to preserve the structural integrity of the conductive vias  430 A and  430 B, the conductive vias  430 A and  430 B may be a solid structure of conductive material. In some other embodiments, the structural integrity of the conductive vias  430 A and  430 B are strong enough such that no filling is required in the central area of the conductive vias  430 A and  430 B to support the formation of the gap AG. 
     In some other embodiments, the conductive vias  430 A and  430 B includes a conductive material plating formed within a through holes correspondingly penetrating the central areas of the terminal portions  411 A,  411 B,  421 A and  421 B. And, a filling  431 A and  431 B such a dielectric material or conductive epoxy may disposed within the central area of the through holes to support the conductive material plating and prevent peeling during formation of the gap AG. 
     The gap AG may be an air gap having a relative dielectric constant of 1. In some embodiments, the wall within the air gap is not coated with any material. Thus, during operation, the gap AG may lower insertion loss causing a higher propagation speed. 
       FIG.  7    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction comprises a pair of terminal portions  511 A and  511 B arranged adjacent to each other, and a pair of linear portions  512 A and  512 B correspondingly extending away from the pair of terminal portions  511 A and  511 B and arranged to be linearly abreast each other. In some embodiments, the pair of terminal portions  511 A and  511 B and the pair of linear portions  512 A and  512 B are formed on the first surface of a substrate. In some embodiments, a buffer section may be arranged between the linear portions  512 A and  512 B and the terminal portions  511 A and  511 B. The buffer section defines a gradually increasing separation from the linear portions  512 A and  512 B to the terminal portions  511 A and  511 B. 
     In some embodiments, the inter-surface junction further comprises another pair of terminal portions (not shown in  FIG.  7   ) formed on the second surface of the substrate and arranged adjacent to each other, and a pair of linear portions  522 A and  522 B correspondingly extending away from the pair of terminal portions on the second surface and arranged to be linearly abreast each other. In some embodiments, a buffer section may be arranged between the linear portions  522 A and  522 B and the terminal portions on the second surface. The buffer section defines a gradually increasing separation from the linear portions  522 A and  522 B to the terminal portions on the second surface. 
     In some embodiments, a pair of complementary conductive vias  530 A and  530 B are formed correspondingly in the central area of the pair of terminal portions  511 A and  511 B. The conductive vias  530 A and  530 B enable signal communication between the first surface and the second surface. In an exemplary embodiment, a diameter of projective profile of the conductive vias  530 A and  530 B ranges between 10 mil to 12 mil. Though, the diameter of the conductive vias  530 A and  530 B may vary according to the design rule used in forming the conductive pattern. In some embodiments, the dimeter of the conductive vias  530 A and  530 B may be reduced when terminal portions  511 A and  511 B having a larger profile area is needed. 
     In some embodiments, a solder mask material  560  disposed on at least one surface of the substrate. The terminal portions  511 A and  511 B are exposed through the solder mask layer  560 . Further, the solder mask layer  560  exposes a dielectric region  550  of the substrate. In some embodiments, the dielectric region  550  have a rounded annular profile. A portion of the annular profile conforms to the profile of the terminal portions  511 A and  511 B. 
       FIG.  8    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction comprises a pair of terminal portions  611 A and  611 B arranged adjacent to each other, and a pair of linear portions  612 A and  612 B correspondingly extending away from the pair of terminal portions  611 A and  611 B and arranged to be linearly abreast each other. A first separation is formed between the linear portions  612 A and  612 B. The first separation have a width W 61 . In some embodiments, the pair of terminal portions  611 A and  611 B and the pair of linear portions  612 A and  612 B are formed on the first surface of a substrate. In some embodiments, a buffer section may be arranged between the linear portions  612 A and  612 B and the terminal portions  611 A and  611 B. The buffer section defines a gradually increasing separation from the linear portions  612 A and  612 B to the terminal portions  611 A and  611 B. 
     In some embodiments, the inter-surface junction further comprises another pair of terminal portions (not shown in  FIG.  8   ) formed on the second surface of the substrate and arranged adjacent to each other, and a pair of linear portions  622 A and  622 B correspondingly extending away from the pair of terminal portions on the second surface and arranged to be linearly abreast each other. In some embodiments, a buffer section may be arranged between the linear portions  622 A and  622 B and the terminal portions on the second surface. The buffer section defines a gradually increasing separation from the linear portions  622 A and  622 B to the terminal portions on the second surface. 
     In some embodiments, a pair of complementary conductive vias  630 A and  630 B are formed correspondingly in the central area of the pair of terminal portions  611 A and  611 B. The conductive vias  630 A and  630 B enable signal communication between the first surface and the second surface. In an exemplary embodiment, a diameter of projective profile of the conductive vias  630 A and  630 B ranges between 10 mil to 12 mil. Though, the diameter of the conductive vias  630 A and  630 B may vary according to the design rule used in forming the conductive pattern. In some embodiments, the dimeter of the conductive vias  630 A and  630 B may be reduced when terminal portions  611 A and  611 B having a larger profile area is needed. 
     In some embodiments, a solder mask material  660  disposed on at least one surface of the substrate. The terminal portions  611 A and  611 B are exposed through the solder mask layer  660 . Further, the solder mask layer  660  exposes a dielectric region  650  of the substrate. In some embodiments, the dielectric region  650  have a rounded annular profile. A portion of the annular profile conforms to the profile of the terminal portions  611 A and  611 B. 
     In some embodiments, a gap AG is formed between the terminal portions  611 A and  611 B. In some embodiments, the gap AG defines a substantially circular profile. The dielectric region  650  of the substrate further conforms to the profile of the gap AG. 
     A second separation is formed between the terminal portions  611 A and  611 B by the gap AG. The second separation have a width W 62 . In some embodiments, the width W 62  of the second separation is greater than the width W 61  of the first separation. 
     In some embodiments, the gap AG forms complementary notches between the terminal portions  611 A and  611 B. The width W 62  of the gap AG between the complementary notches ranges between 30 mil to 40 mil. In some embodiments, the width W 62  is 30 mil. Further, the notches on the formed on terminal portions  611 A and  611 B by the gap AG are mirror symmetrical to each other. 
       FIG.  9    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction comprises a pair of terminal portions  711 A and  711 B arranged adjacent to each other, and a pair of linear portions  712 A and  712 B correspondingly extending away from the pair of terminal portions  711 A and  711 B and arranged to be linearly abreast each other. A first separation is formed between the linear portions  712 A and  712 B. The first separation have a width W 71 . In some embodiments, the pair of terminal portions  711 A and  711 B and the pair of linear portions  712 A and  712 B are formed on the first surface of a substrate. In some embodiments, a buffer section may be arranged between the linear portions  712 A and  712 B and the terminal portions  711 A and  711 B. The buffer section defines a gradually increasing separation from the linear portions  712 A and  712 B to the terminal portions  711 A and  711 B. 
     In some embodiments, the inter-surface junction further comprises another pair of terminal portions (not shown in  FIG.  9   ) formed on the second surface of the substrate and arranged adjacent to each other, and a pair of linear portions  722 A and  722 B correspondingly extending away from the pair of terminal portions on the second surface and arranged to be linearly abreast each other. In some embodiments, a buffer section may be arranged between the linear portions  722 A and  722 B and the terminal portions on the second surface. The buffer section defines a gradually increasing separation from the linear portions  722 A and  722 B to the terminal portions on the second surface. 
     In some embodiments, a pair of complementary conductive vias  730 A and  730 B are formed correspondingly in the central area of the pair of terminal portions  711 A and  711 B. The conductive vias  730 A and  730 B enable signal communication between the first surface and the second surface. In an exemplary embodiment, a diameter of projective profile of the conductive vias  730 A and  730 B ranges between 10 mil to 12 mil. Though, the diameter of the conductive vias  730 A and  730 B may vary according to the design rule used in forming the conductive pattern. In some embodiments, the dimeter of the conductive vias  730 A and  730 B may be reduced when terminal portions  711 A and  711 B having a larger profile area is needed. 
     In some embodiments, a solder mask material  760  disposed on at least one surface of the substrate. The terminal portions  711 A and  711 B are exposed through the solder mask layer  760 . Further, the solder mask layer  760  exposes a dielectric region  750  of the substrate. In some embodiments, the dielectric region  750  have a rounded annular profile. A portion of the annular profile conforms to the profile of the terminal portions  711 A and  711 B. 
     In some embodiments, a gap AG is formed between the terminal portions  711 A and  711 B. In some embodiments, the gap AG defines a substantially elliptical profile. The dielectric region  650  of the substrate further conforms to the profile of the gap AG. 
     A second separation is formed between the terminal portions  711 A and  711 B by the gap AG. The second separation have a width W 72 . In some embodiments, the width W 72  of the second separation is greater than the width W 71  of the first separation. 
     In some embodiments, the gap AG forms complementary notches between the terminal portions  711 A and  711 B. The width W 72  of the gap AG between the complementary notches ranges between 30 mil to 40 mil. In some embodiments, the width W 72  is 40 mil. Further, the notches on the formed on terminal portions  711 A and  711 B by the gap AG are mirror symmetrical to each other. When a width W 72  of a gap AG is increased, the area of the terminal portions  711 A and  711 B are decreased. In this way, the insertion loss during operation decreases as the width W 72  of the gap AG increases. In some embodiments, the width W 72  to length L 72  ratio of the gap AG may be 3:8. In some embodiments, when the length L 72  of the gap AG is 32 mil, the width W 72  of the gap AG is 12 mil. 
       FIG.  10    illustrates a projective view of an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The inter-surface junction comprises a pair of terminal portions  811 A and  811 B arranged adjacent to each other, and a pair of linear portions  812 A and  812 B correspondingly extending away from the pair of terminal portions  811 A and  811 B and arranged to be linearly abreast each other. A first separation is formed between the linear portions  812 A and  812 B. The first separation have a width W 81 . In some embodiments, the pair of terminal portions  811 A and  811 B and the pair of linear portions  812 A and  812 B are formed on the first surface of a substrate. In some embodiments, a buffer section may be arranged between the linear portions  812 A and  812 B and the terminal portions  811 A and  811 B. The buffer section defines a gradually increasing separation from the linear portions  812 A and  812 B to the terminal portions  811 A and  811 B. 
     In some embodiments, the inter-surface junction further comprises another pair of terminal portions (not shown in  FIG.  10   ) formed on the second surface of the substrate and arranged adjacent to each other, and a pair of linear portions  822 A and  822 B correspondingly extending away from the pair of terminal portions on the second surface and arranged to be linearly abreast each other. In some embodiments, a buffer section may be arranged between the linear portions  822 A and  822 B and the terminal portions on the second surface. The buffer section defines a gradually increasing separation from the linear portions  822 A and  822 B to the terminal portions on the second surface. 
     In some embodiments, a pair of complementary conductive vias  830 A and  830 B are formed correspondingly in the central area of the pair of terminal portions  811 A and  811 B. The conductive vias  830 A and  830 B enable signal communication between the first surface and the second surface. In some embodiments, the diameter of the terminal portions  811 A and  811 B is 20 mil. In an exemplary embodiment, a diameter of projective profile of the conductive vias  830 A and  830 B ranges between 10 mil to 12 mil. Though, the diameter of the conductive vias  830 A and  830 B and the terminal portions  811 A and  811 B may vary according to the design rule used in forming the conductive pattern. In some embodiments, the diameter of the conductive vias  830 A and  830 B may be reduced when terminal portions  811 A and  811 B having a larger profile area is needed. In some other embodiments, the diameter of the terminal portions  811 A and  811 B may be increased when conductive vias  830 A and  830 B having a larger projective profile is needed. 
     In some embodiments, a solder mask material  860  disposed on at least one surface of the substrate. The terminal portions  811 A and  811 B are exposed through the solder mask layer  860 . Further, the solder mask layer  860  exposes a dielectric region  850  of the substrate. In some embodiments, the dielectric region  850  have a rounded annular profile. A portion of the annular profile conforms to the profile of the terminal portions  811 A and  811 B. 
     In some embodiments, a gap AG is formed between the terminal portions  811 A and  711 B. In some embodiments, the gap AG defines a substantially elliptical profile. The dielectric region  650  of the substrate further conforms to the profile of the gap AG. 
     A second separation is formed between the terminal portions  811 A and  811 B by the gap AG. The second separation have a width W 82 . In some embodiments, the width W 82  of the second separation is greater than the width W 81  of the first separation. 
     In some embodiments, the gap AG forms complementary notches between the terminal portions  811 A and  811 B. The width W 82  of the gap AG between the complementary notches ranges between 30 mil to 40 mil. In some embodiments, the width W 82  is 35 mil. Further, the notches on the formed on terminal portions  811 A and  811 B by the gap AG are non-symmetrical. In some embodiments, the area of one of the terminal portions  811 A and  811 B is greater than the other depending on the need of the operation. In this way, the insertion loss during operation decreases as the width W 82  of the gap increases. 
       FIG.  11    illustrates a flowchart of a method of forming an inter-surface junction of a substrate according to some embodiments of the instant disclosure. The method of forming an inter-surface junction of a substrate includes receiving a substrate, forming a pair of first complementary conductive traces, and removing a portion the pair of complementary conductive traces. The substrate has a first surface and an opposite second surface. The first complementary conductive traces are formed on the first surface. Each of the first traces comprises a linear portion and a terminal portion. A portion of the terminal portions of the first traces are removed to form a pair of complementary notches facing toward each other on the terminal portions of the first traces. 
     When the terminal portions of the first traces are initially formed on the substrate, the terminal portions each have an annular profile. After removing a portion of the terminal portions of the first traces, the terminal portions each have a circular arc profile. The notches on the terminal portions are complementary to each other. And, a gap is formed between the notches. The gap is used to decrease the insertion loss during operation. Thus, the propagation speed is increased, and the threshold trace length is increased. 
     In some embodiments, a pair of second complementary conductive traces are formed on the second surface of the substrate. Each of the second complementary conductive traces comprises a linear portion and a terminal portion. A portion of the terminal portions of the second traces are removed to form a pair of complementary notches facing toward each other on the terminal portions of the second traces. 
     In some embodiments, the terminal portions on the first surface projectively overlaps the terminal portions on the second surface. the terminal portions of the conductive traces on the first and the second surfaces of the substrate substantially align to each other. On the other hand, the linear portions on the first surface extends in an opposite direction of the linear portions on the second surface as shown in  FIGS.  7 - 10   . 
     In some embodiments, a pair of conductive vias are formed adjacent to each other to correspondingly electrically couple the terminal portions on the first surface to the terminal portions on the second surface. In some embodiments, the conductive vias before forming the notches on the terminal portions of the first surface and the terminal portions of the second surface. 
     In some embodiments, the conductive vias are formed by forming a through hole on the central area of the terminal portions and plating the wall of the through hole with a layer of conductive material to electrically connect the terminal portions formed within the different layers of the substrate. In an exemplary embodiment shown in  FIG.  2   , the terminal portions on the first surface is electrically connected to the terminal portions on the second surface through the conductive vias. 
     Further, to increase the structural integrity of the conductive vias, a filling is further disposed within the conductive vias. The material of the filling includes at least one of dielectric material and conductive epoxy material. 
     In some other embodiments, the conductive vias are formed by stacking a plurality of sectional vias on top of each other. The sectional vias are formed on plurality of dielectric layers stacked together to form the substrate. 
     When forming the gap between the pair of complementary traces, drilling process may be utilized. Drilling through the substrate between the terminal portions removes a portion of the terminal portions to form pairs of circular arc profiles on both the first surface and the second surface of the substrate. A pair of complementary notches facing toward each other is defined on the first surface and the second surface. In some embodiments, the width of the hole formed by the drill is at 30 mil. To increase the width of the gap, the number of times the drilling process is increased. In some embodiments, when the conductive vias are plugged vias or filled vias, the through holes of the conductive vias may be formed in the same process as forming the gap. In some embodiments, the through holes of the conductive vias and the gap are formed sequentially. In some other embodiments, the through holes of the conductive vias and the gap are formed simultaneously. 
     In some embodiments, to form the gap in  FIG.  8   , one time drilling is utilized. In some other embodiments, to form the gap in  FIG.  10   , two times drilling is utilized. In some other embodiments, to form the gap in  FIG.  9   , three times drilling is utilized. The increase in the air gap separation of between the complementary traces decreases the insertion loss during operation. 
     In some embodiments, after the gap is formed between the complementary traces, a layer of dielectric material is left between the pair of complementary conductive vias as shown in  FIG.  4   . In some other embodiments, after the gap is formed between the complementary traces, a portion of the pair of complementary conductive vias are exposed through the gap as shown in  FIG.  5   . Further, after the gap is formed between the complementary traces, a portion of the pair of complementary conductive vias are removed as shown in  FIG.  6   . 
     In some embodiments, a solder mask layer is formed on a surface of the substrate. A dielectric region defining the inter-surface junction is exposed through the solder mask layer. The dielectric region has an annular profile conforming to the terminal portions of the complementary traces and the gap between the terminal portions. 
     Accordingly, one aspect of the instant disclosure provides a conductive pattern over a substrate that comprises a pair of complementary conductive traces, each comprising a linear portion and a terminal portion. The linear portions of the pair of traces extend linearly abreast each other at a first separation. The terminal portions of the pair of traces are arranged adjacent to each other. The terminal portions of the pair of traces comprises a pair of circular arc profile with a pair of complementary notches facing toward each other. A gap between the complementary notches of the terminal portions is wider than the first separation. 
     In some embodiments, the pattern comprises a dielectric region having a rounded annular profile. The terminal portions of the pair of traces are arranged in the dielectric region. 
     In some embodiments, the annular profile of the dielectric region partially conforms to the gap between the complementary notches of the pair of terminal portions, and defines a substantially elliptical air gap. 
     In some embodiments, the complementary notches are substantially mirror symmetrical. 
     In some embodiments, a width of the gap between the pair of complementary notches ranges between 30 mil to 40 mil. 
     In some embodiments, the complementary conductive traces and the dielectric region are exposed from a solder mask layer disposed over the substrate. 
     In some embodiments, the complementary conductive traces further comprise an buffer section arranged between the linear portions and the terminal portions. The buffer section defines a gradually increasing separation from the linear portions toward the terminal portions. 
     Accordingly, another aspect of the instant disclosure provides a conductive structure that comprises a substrate having a first surface and an opposite second surface, an inter-surface junction having an air gap formed in the substrate, a pair of first complementary conductive traces arranged on the first surface of the substrate, and a pair of second complementary conductive traces arranged on the second surface of the substrate. The air gap enabling access between the first surface and the second surface. Each of the first complementary conductive traces comprising a linear portion and a terminal portion. The terminal portions of the pair of first traces comprise a pair of circular arc profile with a pair of complementary notches facing toward the air gap. Each of second complementary conductive traces comprising a linear portion and a terminal portion. The terminal portions of the pair of second traces comprise a pair of circular arc profile with a pair of complementary notches facing toward the air gap. 
     In some embodiments, the air gap exposes conductive vias that enable signal communication between the first surface and the second surface at the complementary notches. 
     In some embodiments, the terminal portions of the pair of first traces and the terminal portions of the pair of second traces are electrically connected through the conductive vias exposed from the air gap. 
     In some embodiments, the pattern further comprises a dielectric region having a rounded annular profile. The terminal portions of the pair of first trances are arranged in the dielectric region. 
     In some embodiments, the annular profile of the dielectric region partially conforms to the sectional profile of the air gap between the complementary notches of the pair of terminal portions of the first traces, and defines a substantially elliptical air gap. 
     In some embodiments, the complementary notches are substantially mirror symmetrical. 
     In some embodiments, a width of the air gap ranges between 30 mil to 40 mil. 
     In some embodiments, the complementary conductive traces and the dielectric region are exposed from solder mask material disposed over the substrate. The side wall that defines the air gap is free from solder mask material. 
     In some embodiments, at least one of the first or the second complementary conductive traces further comprise an buffer section arranged between the linear portions and the terminal portions. The buffer section defines a gradually increasing separation from the linear portions toward the air gap. 
     Accordingly, another aspect of the instant disclosure provides a method of forming a circuit board that comprises receiving a substrate, the substrate having a first surface and an opposite second surface; forming a pair of complementary conductive traces on the first surface, each comprising a linear portion and a terminal portion having an annular profile; and removing a portion of the terminal portions to form a pair of circular arc profile with a pair of complementary notches facing toward each other. 
     In some embodiments, the method further comprises forming another pair of complementary conductive traces on the second surface, each comprising a linear portion and a terminal portion having an annular profile. The terminal portions of the conductive traces on the first and the second surfaces of the substrate substantially align to each other. The removing of a portion of the terminal portions comprising drilling through the substrate between the terminal portions to form pairs of circular arc profiles on both the first and the second surfaces of the substrate, each defining a pair of complementary notches facing toward each other. 
     In some embodiments, the method further comprises forming conductive vias electrically coupling the pair of terminal portions on the first surface and the pair of terminal portions on the second surface. The conductive vias are formed before forming the notches on the first surface and the second surface. 
     In some embodiments, the drilling though the substrate between the terminal portions forms an air gap that exposes conductive vias that enable signal communication between the first surface and the second surface at the complementary notches. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.