Abstract:
A surface mount coupler device is provided having a device body with a plurality of terminations located thereon. The coupler device is particularly useful in high frequency circuits to provide coupling between two circuit lines without direct electrical contact. For example, the device may provide coupling between a feedback control loop and an amplifier output section in a RF transmitter. The device body is built up on a rigid insulative substrate. During manufacture, one or more layers of insulative polymer are applied to the insulative substrate. The insulative polymer defines conductor channels in which primary and secondary conductors are located. The primary and secondary conductors are electrically connected to a respective pair of the terminations located on the device body. A sealing cover, preferably glass, is located above the polymeric insulative layers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to small electronic components adapted to be surface mounted on a larger circuit board. More particularly, the invention relates to a surface mount coupler device for use in a variety of applications. 
     Surface mount components are often rectangular, and very small. For example, the component may have length and width dimensions of less than {fraction (1/10)}of an inch. Generally speaking, the component body will include side terminations compatible with mass production soldering techniques. 
     In various types of electronic equipment, it is often necessary to sample the electrical activity in certain conductor lines. For example, electrical activity in the line of interest may be subject to feedback control. Typical coupler devices utilized for this purpose allow sampling without direct galvanic connection. A need exists, however, for novel coupler devices that are compatible with surface mount techniques. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes various disadvantages of prior art constructions and methods. Accordingly, it is an object of the present invention to provide novel surface mount components. 
     It is a more particular object of the present invention to provide various novel structures for a surface mount coupler device. 
     It is a further object of the present invention to provide small coupler devices particularly adapted for use in RF applications. 
     It is also an object of the present invention to provide novel methodology for the production of a coupler device. 
     Some of these objects are achieved by a surface mount coupler device comprising a device body having four electrical terminations located thereon. The device body includes an insulating substrate having a top surface and a bottom surface. A first insulative layer, defining first and second conductor channels therein, is disposed on the top surface of the substrate. First and second conductors are located in the respective first and second conductor channels. The first conductor is electrically connected to first and second terminations on the device body. The second is electrically connected to at least a third termination on the device body. An insulative cover layer disposed above the first insulative layer. 
     In some exemplary embodiments, the second conductor is electrically connected to third and fourth terminations on the device body. The device body may also have at least six terminations thereon, with the first insulative layer further defining a third conductor channel. In this case, a conductor located in the third conductor channel is electrically connected to fifth and sixth terminations on the device body. 
     The respective conductors preferably include respective first and second elongate portions situated in parallel to one another and separated by a predetermined spacing. For example, the first and second elongate portions are substantially straight. Alternatively, the first and second elongate portions may be V-shaped. 
     The four terminations may be located on sides of the device body. For example, the device body may define opposed side faces and opposed end faces. In this case, two of the four terminations may be located on each of the opposed side faces. 
     The coupler device may be configured as a multiple insulative layer structure having a second insulative layer disposed on top of the first insulative layer. For example, a third conductor located directly above the first insulative layer. Preferably, the third conductor is electrically connected to one of the first conductor or the second conductor. Often, the third conductor may be electriclly connected to a fourth termination on the device body. 
     Furthermore, at least one of the conductor channels defined in the first insulative layer may be discontinuous to define at least one crossing bridge for the third conductor. In such cases, a thin conductive element preferably extends under the crossing bridge. 
     In multiple insulative layer embodiments, the first conductor may be U-shaped. In addition, the second conductor and third conductor may be configured to form a spiral. 
     Other objects of the present invention are achieved by a surface mount coupler device comprising a device body having four electrical terminations located thereon. The device body includes an insulating substrate having a top surface and a bottom surface. A first insulative layer, defining a first conductor channel therein, is disposed on the top surface of the substrate. A first conductor, electrically connected to first and second terminations on the device body, is situated in the first conductor channel. 
     The device body further comprises a second insulative layer disposed on top of the first insulative layer. The second insulative layer defines a third conductor channel having a second conductor therein. The second conductor is electrically connected to at least a third termination on the device body. An insulative cover layer is disposed above said third insulative layer. 
     In exemplary embodiments, the insulative layers are constructed of an insulative polymeric material. For example, the insulative polymeric material may be a photoimagable polyimide. The respective conductors may be formed as multilayer planar conductors, such as by electroplating to an initial layer. 
     Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic representation showing a typical application in which a coupler device of the present invention may be utilized; 
     FIG. 2 is a perspective view of a coupler device constructed in accordance with the present invention in position on a printed circuit board; 
     FIG. 3 is an enlarged view from a perspective opposite that of FIG. 2 with the coupler device removed from the circuit board; 
     FIG. 4 is a cross-sectional view as taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG. 4; 
     FIGS. 6A and 6B are views similar to FIG. 5 showing alternative conductor patterns; 
     FIG. 7 is a view similar to FIG. 5 wherein one of the conductor patterns includes a serial resistor; 
     FIG. 8 is a cross-sectional view along a similar plane as the view of FIG. 4 of an alternative structure with conductor patterns on multiple layers; 
     FIG. 9 is a cross-sectional view of the coupler of FIG. 8 as taken along the top surface of the insulating substrate but showing a thin conductive pattern formed thereon; 
     FIG. 10 is a cross-sectional view as taken along line  10 — 10  of FIG. 8; 
     FIG. 11 is a cross-sectional view as taken along line  11 — 11  of FIG. 8; 
     FIG. 12 is a cross sectional view as taken along line  12 — 12  of FIG. 8 showing lower layer conductors in phantom; 
     FIG. 13 is an enlarged cross-sectional view showing interconnection between conductors in the various layers in the coupler device of FIG. 8; 
     FIGS. 14-17 are cross-sectional views similar to FIGS. 9-12 in a further alternative structure with conductor patterns on multiple layers; 
     FIGS. 18-21 are cross-sectional views similar to FIGS. 9-12 in a still further alternative structure with conductor patterns on multiple layers; and 
     FIG. 22 is a view similar to FIG. 5 of an alternative dual-mode coupler device. 
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     It is to be understood by one of skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
     FIG. 1 diagrammatically illustrates a coupler  10  of the present invention employed in a typical application. In this case, coupler  10  is installed in the output section of an RF device, such as a cellular telephone. The output section includes a power amplifier  12  operative to amplify the RF signal received at its input to an appropriate level for transmission via antenna  14 . 
     As can be seen, device  10  has four terminations respectively designated A, B, C and D. Terminations A and B are serially connected into the main line between amplifier  12  and antenna  14 , as shown. Terminations C and D are similarly connected into a feedback loop including a predetermined compensator  16 . Typically, a resistor  18  will be connected between termination D and ground. In many applications, resistor  18  may have a value of about fifty ohms. 
     Due to principles of electromagnetic induction, coupler  10  provides operative coupling between the output of amplifier  12  and the feedback loop. The output of amplifier  12  can be monitored in this manner, and adjusted as desired. For example, it may be desirable to ensure that amplifier  12  delivers a constant level of output power. Alternatively, output power can be selectively varied, such as in proportion to a received signal. 
     Referring now to FIG. 2, coupler  10  is shown as it may appear when surface mounted to a printed circuit board  20 . As shown, terminations A, B, C, and D are attached to the board at respective mounting pad, such as pad  22 . Conductive traces, such as trace  24 , are defined on the top surface of circuit  20  extending from each of the mounting pads. The conductive traces thus provide electrical communication between the respective terminations and the remainder of the circuit into which coupler  10  is connected. 
     In the illustrated example, circuit board  20  includes a conductive ground plane  25  defined on its bottom surface. Circuit board  20  may be made from a low-temperature organic material, with the solder often being a low temperature eutectic solder applied by wave, reflow, vapor phase or manual soldering techniques. 
     Referring now to FIGS. 3-5, a preferred construction of coupler  10  will be explained. In this case, coupler  10  has a rectangular device body  26  defining a longer length dimension and a shorter width dimension. Preferably, device body  26  is sized to conform to a standard size for other small surface mount components, such as multilayer ceramic capacitors. According to industry practice, the size of a such a component is generally expressed as a number “XXYY,” with XX and YY being the length and width, respectively, in hundredths of an inch. A typical size under this practice is 0805. 
     Device body  26  includes a substrate  28  of alumina or similar rigid insulative material. For example, substrate  28  may be made from a glazed alumina. A first insulative layer  30 , disposed above substrate  28 , defines therein a pair of conductor channels. A main line, or primary, conductor  32  fills one of the conductor channels, and extends between terminations A and B. Similarly, a secondary conductor  34  fills the other conductor channel, and extends between terminations C and D. A sealing cover  36 , which may be formed of glass, glass-ceramic, alumina or a similar rigid insulative material, is located above insulative layer  30 . 
     As can be seen most clearly in FIG. 5, conductors  32  and  34  include respective elongate portions  38  and  40  that extend substantially in parallel with one another. The close proximity of elongate portions  38  and  40  provide the desired electromagnetic coupling. For example, elongate portions  38  and  40  may be spaced apart by about 1.7 mils in a preferred embodiment. 
     It will be appreciated that a number of factors will affect the degree of coupling, including the spacing and length of elongate portions  38  and  40 , and the specific materials utilized in the manufacture of coupler  10 . In this case, conductor  32  has a width greater than conductor  34  since it will be required to accommodate greater flow of current. For example, conductor  32  may have a width of about  5  mils, with conductor  34  having a width of about  3  mils in a preferred embodiment. 
     During manufacture of coupler  10 , substrate  28  is appropriately cleaned. A thin layer of metal, such as CrCu, is then deposited over the entire top surface of substrate  28 . The thin metal layer is next etched and stripped by photolithographic techniques to the configuration of conductors  32  and  34 . A photoimagable polyimide is next applied over the substrate to a thickness preferably exceeding 15 microns, and most preferably to a thickness of about 25 microns. 
     The polyimide layer is masked and exposed to UV light and rinsed to define the conductor channels in registry with the metal conductor patterns. The exposed metal is then electroplated, preferably to an overall conductor height of about 25 microns. Various metals may be electroplated in this manner, including copper, silver, gold and the like. Sealing cover  36  is next applied over the surface of the polyimide layer. 
     Often, coupler  10  will be one of many manufactured in a larger sheet. After the larger sheet is diced, terminations A-D are applied according to known techniques. It will be appreciated that, in many respects, the manufacture of coupler  10  is made according to the techniques described in U.S. Pat. No. 5,363,080 to Breen, incorporated herein by reference. 
     FIGS. 6A and 6B illustrate alternative conductor patterns for a coupler device generally as described above. In the embodiment of FIG. 6A, first conductor  42  and second conductor  44  define respective V-shaped elongate portions  46  and  48 . In FIG. 6B, primary conductor  50  and secondary conductor  52  define shorter elongate portions  54  and  56 . The longer parallel length achieved in the embodiment of FIG. 6A generally provides an enhanced coupling factor. 
     A still further alternative is illustrated in FIG.  7 . In this case, a resistive element  58  is located in series with secondary conductor  60 . Resistive element  58  advantageously eliminates the need for providing a separate resistor  18  (FIG. 1) in electrical communication with termination D. Termination D can thus be directly connected to ground. It will be appreciated that any of the various coupler configurations described herein can be equipped with a similar internal resistor. 
     In the embodiments discussed above, the respective conductors are located in a common plane on top of the rigid substrate. According to other embodiments of the invention, at least one of the conductors may partially or wholly be located on a plane above the other conductor with which it will couple. Such embodiments have the advantage of permitting even longer parallel portions of each conductor, with the coupling factor thereby increased. 
     Referring now to FIGS. 8-12, one such coupler  62  is illustrated. Like coupler  10 , coupler  62  includes a substrate  64  of alumina or similar rigid insulative material. In this case, however, a plurality of polymeric insulative layers are disposed above substrate  64 . In particular, coupler  62  includes first insulative layer  66  and second insulative layer  68 . It will be appreciated that such a device may be made using photoimagable polyimide by repeating the processing steps described above for each successive layer. A sealing cover  70  is located above second insulative layer  70 . 
     As shown in FIG. 9, the thin metallic pattern formed on the top surface of substrate  64  defines the entire outline  72  of the primary conductor as well as a portion  74  of the secondary conductor. As illustrated in FIG. 10, the conductor channels in first insulative layer  66  are generally in register with the thin metallic pattern. It should be noted, however, that discontinuities are formed in the conductor channel at several locations. Despite the discontinuities, the conductors formed within the conductor channels of first insulative layer  66  will remain in electrical communication by virtue of the thin conductor pattern underneath. 
     The discontinuities in the conductor channels of insulative layer  68  provide insulated crossing bridges for subsequently formed conductors. As shown in FIG. 11, conductor portion  76  of second insulative layer  68  crosses the conductors of first insulative layer  66  without shorting. The particular crossing locations  78   a-c  are most readily seen in FIG.  12 . 
     Referring now to FIG. 13, electrical connection between the conductors of insulative layers  66  and  68  is achieved through an aperture  80  defined in insulative layer  66 . In particular, second insulative layer  66  defines aperture  80  at a location in registry with an end of the secondary conductor portion formed therein. As a result, electrical connection with conductor portion  76  can be achieved. Because FIG. 13 is enlarged in comparison with previous figures, the multilayer structure of the conductors, due to the electroplating process described above, can be easily seen. 
     FIGS. 14 through 17 illustrate a further multilayer embodiment that is similar in many respects to the embodiment of FIGS. 9 through 12. This embodiment will not be described in detail since its construction will thus be readily apparent to one skilled in the art. Analogous elements to the embodiment of FIGS. 9 through 12 have reference numbers augmented by one hundred. 
     FIGS. 18 through 22 illustrate a coupler device  210  in which a multiturn secondary conductor is predominantly located on the same planar level with the primary conductor. As shown in FIG. 18, the thin metallic pattern defined on insulating substrate  212  forms a plurality of interconnects  214   a-d . Next, as shown in FIG. 19, polymeric insulators  216   a-c  are formed over the interconnects. An aperture  218  is formed in insulator  216   a  at a location in registry with an end of interconnect  214   b.    
     Referring now to FIG. 20, an insulative polymer layer  220  is then formed as described above to define a plurality of conductor channels. As shown, primary conductor  222  extends between terminations A and B. Various secondary line segments are located to be electrically connected by the interconnects defined on substrate  212 . The resulting secondary conductor  224  is clearly shown in FIG. 21, and loops both inside and outside of primary conductor  222 . 
     In accordance with the present invention, devices can also be provided that incorporate more than one coupler in one body. For example, FIG. 22 illustrates a dual-mode coupler device  250  that can be utilized to sample, for example, signals at two different frequencies. Toward this end, coupler device  250  includes six terminations (designated A-F). As can be seen, a secondary conductor  252  extends between terminations C and D. Dual primary conductors  254  and  256  extend between termination pairs A-B and A′-B′, respectively. 
     It can be seen that the present invention provides various novel coupler structures adapted for use as surface mount components. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art. For example, primary and secondary conductors could be located in entirely in different polymer layers. While the primary conductor has been described above in the lower layer of multilayer embodiments, the primary conductor could be located in an upper layer. In addition, respective polymer layers may be separated by an intermediate polymer layer, with interconnection through a via. 
     Accordingly, it should be understood that these and other variations of the disclosed embodiments are intended to be included within the scope of the appended claims. In addition, aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention so further described in such appended claims.