Coil transducer with reduced arcing and improved high voltage breakdown performance characteristics

Disclosed herein are various embodiments of coil transducers and galvanic isolators configured to provide high voltage isolation and high voltage breakdown performance characteristics in small packages. A coil transducer is provided across which data or power signals may be transmitted and received by primary and secondary coils disposed on opposing sides thereof without high voltage breakdowns occurring therebetween. At least portions of the coil transducer are formed of an electrically insulating, non-metallic, non-semiconductor, low dielectric loss material. The coil transducer may be formed in a small package using, by way of example, printed circuit board, CMOS-compatible and other fabrication and packaging processes.

FIELD OF THE INVENTION

Various embodiments of the invention described herein relate to the field of data signal and power transformers or galvanic isolators, and more specifically to devices employing inductively coupled magnetic data signal and power transformers.

BACKGROUND

High voltage isolation data signal and power transfer devices (or galvanic isolators) known in the prior art include optical devices, magnetic devices and capacitive devices. Prior art optical devices typically achieve high voltage isolation by employing LEDs and corresponding photodiodes to transmit and receive light signals, usually require high power levels, and suffer from operational and design constraints when multiple communication channels are required.

Prior art magnetic galvanic isolators often achieve voltage isolation by employing opposing inductively-coupled coils, typically require the use of at least three separate integrated circuits or chips, and are often susceptible to electromagnetic interference (“EMI”) and other forms of undesired electrical noise such as transients.

Prior art capacitive galvanic isolators typically achieve high voltage isolation by employing multiple pairs of transmitting and receiving electrodes, where for example a first pair of electrodes is employed to transmit and receive data, and a second pair of electrodes is employed to refresh or maintain the transmitted signals. Such capacitive devices typically exhibit poor high voltage hold-off or breakdown characteristics.

In prior art capacitive and magnetic galvanic isolators, internal and external high voltage breakdowns can occur when disparate voltages on opposing input and output sides of a galvanic isolator cause arcing. Achieving high levels of voltage isolation may require the use of ever more unique and expensive manufacturing and processing methods, which can result in the cost of a product being pushed beyond the boundaries of commercial practicability.

What is needed is a galvanic isolator or isolator package that exhibits improved high voltage internal and external breakdown performance characteristics, is small, consumes reduced power, permits data to be communicated at relatively high data rates, may be built at lower cost, or that has other advantages that will become apparent after having read and understood the specification and drawings hereof.

SUMMARY

In one embodiment, there is provided a coil transducer comprising a generally planar electrically insulating substrate comprising opposing upper and lower surfaces, the substrate forming a dielectric barrier and comprising an electrically insulating, non-metallic, non-semiconductor, low dielectric loss material, a first electrically conductive coil formed in at least a first metalized layer disposed within, upon or near the substrate, and a second electrically conductive coil formed in at least a third metalized layer disposed within, upon or near the substrate, where the first and second coils are spatially arranged and configured respecting one another such that at least one of power and data signals may be transmitted by the first coil to the second coil across the substrate, the first coil is separated from the second coil by a vertical distance exceeding about 1 mil, and a breakdown voltage between the first coil and the second coil exceeds about 2,000 volts RMS.

In another embodiment, there is provided a coil transducer comprising a generally planar electrically insulating substrate comprising opposing upper and lower surfaces, the substrate forming a dielectric barrier and comprising an electrically insulating, non-metallic, non-semiconductor low-dielectric-loss material having a dielectric loss tangent at room temperature that is less than or equal to 0.05, a first electrically conductive coil formed in at least a first metalized layer disposed within, on or near the substrate, and a second electrically conductive coil formed in at least a third metalized layer disposed within, on or near the substrate, where the first and second coils are spatially arranged and configured respecting one another such that at least one of power and data signals may be transmitted by the first coil to the second coil across the substrate, the first metalized layer is separated from the third metalized layer by a vertical distance exceeding about 1 mil, and a breakdown voltage between the first coil and the second coil exceeds about 2,000 volts RMS.

Further embodiments are disclosed herein or will become apparent to those skilled in the art after having read and understood the specification and drawings hereof.

The drawings are not necessarily to scale. Like numbers refer to like parts or steps throughout the drawings, unless otherwise noted.

DETAILED DESCRIPTIONS OF SOME PREFERRED EMBODIMENTS

In the following description, specific details are provided to impart a thorough understanding of the various embodiments of the invention. Upon having read and understood the specification, claims and drawings hereof, however, those skilled in the art will understand that some embodiments of the invention may be practiced without hewing to some of the specific details set forth herein.

In the drawings, some, but not all, possible embodiments of the invention are illustrated, and further may not be shown to scale.

The term “horizontal” as used herein is defined as a plane substantially parallel to the conventional plane or surface of the substrate of the invention, regardless of its actual orientation in space. The term “vertical refers to a direction substantially perpendicular to the horizontal as defined above. Terms such as “on,”, “above,” “below,” “bottom,” “top,” “side,” “sidewall,” “higher,” “lower,” “upper,” “over” and “under” are defined in respect of the horizontal plane discussed above.

Referring toFIGS. 1 and 2, there is shown one embodiment of coil transducer39of the invention.FIG. 1shows a top plan view of coil transducer39, andFIG. 2shows a cross-sectional view of coil transducer39along line2-2ofFIG. 1. Coil transducer39is configured to send data and/or power signals from a transmitter circuit21to a receiver circuit22(not shown inFIGS. 1 and 2) across a dielectric barrier. In one embodiment, such a dielectric barrier comprises substrate33, which is disposed between an input or first transmitting coil23and an output or second receiving coil24. Coil transducer39and substrate33disposed therewithin may comprise any of a number of different non-metallic, non-semiconductor, low dielectric loss materials and/or layers, more about which is said below.

In a preferred embodiment, coil transducer39and substrate33are capable of withstanding several kilovolts of potential difference between the input and output sides of coil transducer39, and thus exhibit high voltage breakdown performance characteristics. In a preferred embodiment, substrate33and coil transducer39have sufficient thicknesses between upper and lower horizontal surfaces thereof, and electrical insulation characteristics appropriate, to withstand the relatively high breakdown voltages.

By way of example, in one embodiment a breakdown voltage between coil23and coil24exceeds about 2,000 volts RMS when applied over a time period of about one minute. In other embodiments, the breakdown voltage between coil23and coil24exceeds about 2,000 volts RMS when applied over six minutes or over 24 hours.

In other embodiments, even higher breakdown voltages can be withstood by coil transducer39, substrate33and galvanic isolator20, such as about 2,500 volts RMS, about 3,000 volts RMS, about 4,000 volts RMS and about 5,000 volts RMS for periods of time of about 1 minute, 6 minutes and/or 24 hour, or over the design lifetime of the device.

These performance characteristics are highly desirable, as the various conductors and coils disposed in coil transducer39often exhibit voltages or potentials that are significantly different from one another. The various embodiments of the invention described and shown herein are thus configured to withstand high breakdown voltages, and may also be configured to transfer signals and power more efficiently than optical isolators of the prior art finding current widespread use.

Substrate33and/or coil transducer39are formed of one or more appropriate electrically insulating, non-metallic, non-semiconductor, low dielectric loss materials. In one embodiment, a suitable material has a dielectric loss tangent at room temperature that is less than about 0.05, less than about 0.01, less than about 0.001 or less than about 0.0001. Further information regarding dielectric loss tangents and the intrinsic and extrinsic losses associated therewith is set forth in “Loss Characteristics of Silicon Substrate with Different Resistivities” to Yang et al., pp. 1773-76, vol. 48, No. 9, September 2006, Microwave and Optical Technology Letters. Yang et al. discuss theoretically and experimentally dividing dielectric losses into an intrinsic loss tangent of silicon and an extrinsic loss associated with substrate leakage losses, and demonstrate that as doping levels in silicon increase, extrinsic losses also increase.

Some examples of suitable materials for forming substrate33and/or various layers included in coil transducer39also include, but are not limited to, one or more of printed circuit board material, FR4 and other printed circuit board materials, fiberglass, glass, ceramic, polyimide, polyimide film, a polymer, an organic material, a combination of an organic filler such as epoxy and an inorganic solid such as glass, a flex circuit material, epoxy, epoxy resin, a printed circuit board material, plastic, DUPONT™ KAPTON™, DUPONT™ PYRALUX AB™ laminate, and a ROGERS™ material (e.g., PTFE—or polytetrafluoroethylene—and glass, PTFE and ceramic, PTFE, glass and ceramic, or thermoset plastic). The particular choice of the material from which substrate33is formed will, in general, depend on cost, the degree or amount of electrical isolation or voltage breakdown protection that is desired, the particular application at hand, and other factors or considerations. For example, glass and ceramic substrates are well suited for applications involving high voltages; to reduce manufacturing and processing costs, flex circuit substrates may be employed.

In some embodiments, substrate33and/or coil transducer39has a thickness between the upper and lower horizontal surfaces thereof ranging between about 0.5 mils and about 25 mils. In one embodiment, the thickness of substrate33and/or coil transducer39exceeds about 1.5 mils. In another embodiment, substrate33and/or coil transducer39comprises a plurality of layers, where at least one of the layers comprises a low dielectric loss material.

In one embodiment, the structures illustrated inFIGS. 1 and 2may be fabricated using a conventional printed circuit board fabrication line. As a result, the cost of manufacturing coil transducer39may be much less than that of a coil transducer constructed from silicon on a semiconductor fabrication line. Embodiments of coil transducer39based on flexible organic/inorganic or organic substrates are particularly attractive. Printed circuit boards or circuit carriers are known in the art, and hence need not be discussed in detail here. It is worth noting, however, that substrates33and coil transducers39of the invention that are formed from printed circuit board materials do provide an excellent low-cost alternative to silicon-based fabrication methods and materials. Printed circuit board materials are less expensive, easier to handle, and more amenable to quick design or manufacturing changes than silicon-based materials. For purposes of the present discussion it is sufficient to note that printed circuit boards may be fabricated by depositing a thin metal layer, or attaching a thin metal layer, on a somewhat flexible organic/inorganic substrate formed of fiberglass impregnated with epoxy resin and then converting the layer into a plurality of individual conductors using conventional photolithographic techniques. Additional metal layers may be added atop the thin metal layer after an intervening electrically insulating layer or coating has been laid down on the thin metal layer.

Flex circuit technology may also be employed to form substrate33and/or coil transducer39of galvanic isolator20, where substrate33and/or coil transducer39are made of an organic material such as polyimide. Films and laminates of this type are available commercially from DUPONT™ and utilize substrate materials known as KAPTON™ made from polyimide. In some cases, a plurality of polyimide layers may be laminated with an adhesive to form substrate33and/or coil transducer39. This type of circuit carrier or printed circuit board is significantly less expensive than conventional silicon semiconductor material based approaches and can be employed to provide substrate33and/or coil transducer39having a high breakdown voltage and other desirable high voltage isolation characteristics. Thinner substrates33and/or coil transducers39are preferred in applications where signal losses between primary and secondary coils23and24must be minimized. For example, in one embodiment of substrate33and/or coil transducer39, a PYRALUX AP™ laminate manufactured by DUPONT™ is employed to form a 2 mil thick KAPTON™ substrate33, and electrically conductive copper layers and traces are added to the top and bottom surfaces thereof.

Note that coils23and24may assume any of a number of different structural configurations and nevertheless fall within the scope of the invention. For example, coils23and24may assume the circular or oval spirally-wound shapes illustrated inFIGS. 1 and 2, or may assume myriad other shapes such as rectangularly, squarely, triangularly, pentagonally, hexagonally, heptagonally or octagonally-wound shapes arranged in a horizontal plane, conductors arranged to interleave with one another within a horizontal plane, one or more serpentine conductors arranged in a horizontal plane, and so on. Any suitable structural configuration of coils23and24is permitted so long as the magnetic fields projected by one coil may be received and sufficiently well detected by the other opposing coil.

As described above, substrate33and/or coil transducer39are preferably fabricated to have a thickness between their respective upper and lower surfaces sufficient to prevent high voltage arcing. One advantage of the materials employed to form substrate33and/or coil transducer39of the invention is that substrate33and/or coil transducer39may be substantially thicker than is generally possible or financially feasible in commercial applications which employ conventional semiconductor materials and manufacturing processes. For example, substrate33and/or coil transducer39may have thicknesses ranging between about 1 mil and about 25 mils, between about 1.5 mils and about 25 mils, or between about 2 mils and about 25 mils. Polyimide processes compatible with silicon IC processes are typically much thinner and cannot withstand voltages nearly as high as those capable of being withstood by some embodiments of substrate33and/or coil transducer39. The high distance-through-insulation (DTI) values characteristic of some embodiments of substrate33and coil transducer39provide a desirable performance metric in many electrical isolator applications and easily meet most certification requirements issued by relevant standards organizations. Conversely, substrate33and/or coil transducer39may also be made quite thin, e.g., 0.5 mils or less, and yet still provide relatively high voltage breakdown performance characteristics.

Note further that substrate33and/or coil transducer39of the invention may be formed using any of a number of different manufacturing processes and electrically insulating, non-metallic, non-semiconductor, low dielectric loss materials described above. These processes and materials are amenable to processing bulk electrically insulating materials and do not require the expensive and elaborate procedures required to handle semiconductor materials such as silicon. Moreover, substrate33and coil transducer39of the invention provide superior high voltage breakdown performance characteristics respecting silicon-based devices owing to their increased distances-through-insulation (more about which is said above). Because substrate33and coil transducer39of the invention exhibit substantially increased distances-though-insulation and thicknesses respecting prior art galvanic isolators having silicon substrates (which were generally limited to distances-through-insulation thicknesses of less than 1 mil), substrate33may be configured to impart substantial mechanical rigidity and strength to coil transducer39and galvanic isolator20such that coil transducer39may be handled during normal manufacturing processes without the conductors disposed on, in or near substrate33breaking or fracturing. Unlike the relatively fragile and thin silicon substrates of the prior art, substrate33and coil transducer39of the invention are mechanically robust and strong, may be mounted directly on lead frames, and may be handled without special care.

In addition, although in theory it might be possible to manufacture a substrate or coil transducer from semiconductor-based materials upon opposing surfaces upon which conductors could be formed using metalized layers, such constructions are rarely (if at all) seen in practice owing to the general delicacy of semiconductor-based materials. As a result, substrates or coil transducers formed from semiconductor materials are typically handled in a manner that requires metalized or other layers be formed on one side only of such substrates. Contrariwise, in substrate33and/or coil transducer39of the invention, both sides of substrate33and/or coil transducer39may easily have coils or other components formed or mounted thereon owing to the radically different nature of the manufacturing processes used, and the materials employed, to form substrate33and/or coil transducer39.

Continuing to refer toFIGS. 1 and 2, substrate33separates coils23and24, and forms a portion of coil transducer39, which comprises electrically insulating layers32,34,37and38. In one embodiment, layers34and37are formed of an electrically insulating, non-metallic, non-semiconductor, low dielectric loss material described in greater detail below, while layers32and38are formed of an electrically insulating coating or coverlay material, more about which is also said below. Other embodiments of layers32,34,37and38are also possible.

As shown inFIGS. 1 and 2, coil transducer39comprises first coil23and second coil24. First and second coils23and24are separated from one another by an electrically insulating, non-metallic, non-semiconductor, low dielectric loss material forming substrate33disposed therebetween, which is a dielectric barrier. Upper and lower surfaces of substrate33, and layers32,34,37and38are delineated in the Figures by dashed lines. The same or similar material employed to form substrate33may be used to form dielectric or electrically insulating layers34and37disposed above and below substrate33, and in which electrical conductors23,27,24and28may be embedded or otherwise formed. Alternatively, other suitable materials may be employed to form such layers. In one embodiment, such electrical conductors are spirally or ovally shaped, although many other configurations and shapes for such conductors may be employed. As those skilled in the art will understand, coils23and24may be placed on, in or near substrate33, or on, in, near or under layers34or37. Many other variations and embodiments are also possible.

In addition to providing excellent high voltage breakdown performance characteristics, substrate33and coil transducer39can also be configured to impart substantial structural rigidity and strength to galvanic isolator20, and thereby eliminate the need to include an independent structural member that is separate and apart from a coil transducer, and that is required to impart structural rigidity and strength thereto, such as has been practiced in the prior art by way of, for example, providing a thick (e.g., 25-100 mils) silicon substrate beneath a coil transducer or galvanic isolator.

The outer otherwise exposed metalized layers of coil transducer39are preferably protected by an electrically insulating or dielectric coating or coverlay layers32and38. In preferred embodiments, coating or coverlay layers32and38are relatively thin and conform to the pattern of etched metal spiral conductors27and28disposed therebeneath. Coating or coverlay layers32and38should have few or no empty regions or voids disposed therebeneath or therein so as to prevent high voltage breakdown thereacross owing to the reduced ability of the empty region or void to withstand high voltages compared to, for example, polyimide. To prevent the formation of voids in such a coating or coverlay material, a vacuum may be drawn while laminating the different layers of coil transducer39together, or by degassing liquid photo-imageable coverlay materials before they are applied. Since an electrically insulating, non-metallic, non-semiconductor, low dielectric loss material such as polyimide disposed beneath the coating or coverlay material may be relatively thin, the ability to withstand high voltages may not be as good through coating or coverlay layers32and38as through substrate33(regardless of whether or not voids are present in or adjacent to coating or coverlay layers32and38).

In the embodiment illustrated inFIGS. 1 and 2, first coil23comprises a first spiral electrical conductor23and a second spiral electrical conductor27. Second spiral conductor27is located above first spiral conductor23and is disposed in a second metalized layer, while first spiral conductor23is located below second spiral conductor27and is disposed in a first metalized layer. First and second spiral conductors23and27are electrically connected to one another by vertical metal via35, which electrically interconnects the first and second metalized layers and first and second spiral conductors23and27disposed therein. The first and second metalized layers, and first and second spiral conductors23and27, are configured and positioned respecting one another such that electrical current rotates in the same direction through first and second spiral conductors23and27. Maintaining the same sense of rotation causes the magnetic fields generated by first and second spiral conductors23and27to add constructively to one another instead of cancelling one another.

Referring now toFIG. 2, second coil24comprises third spiral electrical conductor24and fourth spiral electrical conductor28. Third spiral conductor24is located above fourth spiral conductor28and is disposed in a third metalized layer, while fourth spiral conductor28is located below third spiral conductor24and is disposed in a fourth metalized layer. Third and fourth spiral conductors24and28are electrically connected to one another by vertical metal via31, which electrically interconnects the third and fourth metalized layers and spiral conductors24and28disposed therein. The third and fourth metalized layers, and third and fourth spiral conductors24and28, are configured and positioned respecting one another such that electrical current rotates in the same direction through third and fourth spiral conductors24and28. Maintaining the same sense of rotation causes the magnetic fields generated by third and fourth spiral conductors24and28to add constructively to one another instead of cancelling one another.

Continuing to refer toFIG. 2, regions11and12in coil transducer39represent those portions of coil transducer39where internal high voltage breakdown may be most likely to occur. This is due to distance D1between spiral conductors24and28(which are held at a first voltage) and vertical metal via36(which is held a second voltage different from the first voltage) being relatively small. Furthermore, voids or adhesives which may be present in this region do not withstand as high voltages per unit distance as solid insulators such as KAPTON.™ By way of example, in some embodiments of the invention distance D1may range between about 2 mils and about 10 mils. In contrast, internal high voltage breakdown is less likely to occur between first spiral conductor23and third spiral conductor24, where distance D2between first spiral conductor23(which is held at a first voltage) and third spiral conductor24(which is held at a second voltage different from the first voltage) can be relatively large. Note further that the gaps shown inFIG. 2between vertical vias30and36on the one hand, and conductors27,23,24and28on the other hand, need not be all be restricted to the same distance D1, and indeed may assume any of a number different suitable values. Moreover, in preferred embodiments of the invention, distance D1is greater than or equal to distance D2, since high voltage breakdowns may occur at horizontally opposed internal interfaces more easily than through vertically opposed internal interfaces (where bulk material must generally be traversed to effect a voltage breakdown) owing to the lower critical electric field potentials typically associated with horizontally opposed interfaces, voids or adhesives.

As shown inFIG. 2, in one embodiment distance D2corresponds to the distance or separation between the lower surface of first spiral conductor23and the upper surface of third spiral conductor24, and also corresponds to a distance extending vertically across substrate33forming the dielectric barrier and comprising the special non-metallic, non-semiconductor, low dielectric loss materials discussed above. That is, in the embodiment shown inFIG. 2, distance D2corresponds to the thickness of substrate33and in some preferred embodiments exceeds about 0.5 mils, about 1 mil, about 2 mils, about 3, mils, about 4 mils, about 5 mils, about 6 mils, about 7 mils, about 8 mils, about 9 mils and about 10 mils.

Electrical connections must be established between coil transducer39and devices external thereto, such as transmitter circuit21and receiver circuit22(not shown inFIGS. 1 and 2). In one configuration, and as shown inFIG. 1, wirebond pads59,60,62and63are located on the top surface of coil transducer39. In such a configuration, access to the third and fourth metalized layers must somehow be provided from the top surface of coil transducer39, such as by disposing conductive via30between such layers and wirebond contact59. Wirebond pads59,60,62and63are preferably electroplated to facilitate the establishment of electrical connections. Holes can be formed in the top coating or coverlay material to permit access to wirebond pads59,60,62and63. Alternatively, by way of example, two via holes can be formed that extend from locations52and53disposed atop coil transducer39down to the third and fourth metalized layers, respectively (and which contain third and fourth spiral conductors24and28). Conductive via31can be configured to route a signal between the fourth metalized layer and the third metalized layer, and wirebond pads59and63can be electroplated to permit the third and fourth metalized layers to be accessed electrically therethrough. The embodiment illustrated inFIGS. 1 and 2offers the convenience of easy topside wirebonding access to each of the first, second, third and fourth metalized layers. It will be appreciated, however, that full through vias30and36(as well as the via disposed beneath location53) consume a relatively large amount of “real estate” in coil transducer39, and consequently result in the size or volume of coil transducer39becoming relatively large. The embodiment shown inFIGS. 1 and 2also features an increased risk of internal high voltage breakdown between such full through vias and coils23and24, especially if voids have formed between any of the various layers of coil transducer39during manufacturing, more about is said below.

Referring now toFIG. 3, there is shown a cross-sectional view of another embodiment of coil transducer39of the invention, where portions of vertical via36extending downwardly beyond the first metalized layer, and portions of vertical via30extending upwardly beyond the third metalized layer, have been eliminated therefrom. Such a configuration eliminates the potential high voltage breakdown problems arising from the horizontal proximities of via36to the third and fourth metalized layers, and via30to the second and first metalized layers (as shown inFIG. 2and denoted by distances D1). Instead, the embodiment illustrated inFIG. 3features distance D2as the closet dimension between the various components of coil23on the one hand, and coil24on the other hand, which as described above are often at very different electrical potentials respecting one another. Thus, at least in respect of reducing the probability or possibility of arcing between various portions of coil23and coil24, it will be appreciated that the embodiment illustrated inFIG. 3provides improved performance compared to the embodiment shown inFIG. 2. Note further that the embodiment illustrated inFIG. 3also eliminates major portions of vertical vias30and36in respect of the embodiment shown inFIG. 2.

As in the embodiment shown inFIG. 2, coating or coverlay material32and38is disposed over otherwise exposed coils23and24. In addition, electrical connections to transmitter circuit21and receiver circuit22(not shown inFIG. 3) are established through wirebond pads60and62(see, for example,FIG. 1), and through wirebond pads61and an additional wirebond pad (not shown inFIG. 3), and which are located on opposing respective top and bottom sides of coil transducer39. In such a wirebond pad configuration, conductive vias36and30need only penetrate two metalized layers so that, for example, electrical signals need only be routed from wirebond pad62to spiral conductor27, then through via35to coil23, and then up through via36to wirebond pad60. Similarly, electrical signals need only be routed between the third and fourth metalized layers and then to wirebond pad61. Because lithographic alignment is much easier when blind or partial vias36and30ofFIG. 3are employed instead of full or through vias, metal landing pads51,54,57and58can be made smaller. As a result, vias36and30do not consume as much real estate or volume in coil transducer39ofFIG. 3as in the embodiments illustrated inFIGS. 1 and 2, which in turn permits coil transducer39to be made smaller. Because no penetrations of substrate33are required to accommodate full or through vias in the embodiment shown inFIG. 3, internal high voltage breakdown performance is improved in the embodiment shown inFIG. 3respecting the embodiment ofFIGS. 1 and 2. On the other hand, during manufacturing the embodiment ofFIG. 3must be turned over to complete wirebonding, while all wirebonding can be carried out in the embodiment ofFIGS. 1 and 2without turning over coil transducer39.

Another consideration in packaging is whether to provide one or more metal shield planes. A metal shield plane can help reduce undesired outside electromagnetic interference from interfering with the operation of coil transducer39or galvanic isolator20. If such a metal shield plane is located too close to coils23or24, however, the metal shield plane may attenuate the magnetic fields generated by coil transducer39.FIG. 5shows electromagnetic modeling results generated using software from Computer Simulation Technology™ (“CST”) for a galvanic isolator having a metal shield plane located about 10 mils from a coil transducer (circles), about 100 mils from a coil transducer (triangles), and with no metal shield (upside-down triangles). As shown inFIG. 5, S21signal through-parameter performance degrades substantially when a metal shield plane is brought too close to a coil transducer (e.g., a separation of only 10 mils). Related modeling work indicates that a 50 mil thickness of silicone or other suitable electrically insulating material or molding compound may also function as an effective shield, even when no metal is disposed therein. Because high throughput is desired for both signal and power applications, locating any metal—even a metal shield plane held at approximately the same potential as nearby coils23or24—over or near such coils at a separation distance of 50 mils or less may degrade throughput performance top an unacceptable degree.

To avoid high voltage breakdown through the coating or coverlay layers32and38, it is preferred not to place coil23and coil24of coil transducer39such that they are located directly over (in respect of a vertical direction) a metal lead frame, which is typically at a very different potential. For example, at any given time transmitter circuit21might be running at a potential 5 kV different from receiver circuit22. Thus, if the first and second metalized layers are used to form input coil23and the third and fourth metalized layers are used to form output coil24, then an input lead frame for galvanic isolator20which is at a similar potential to coil23should not extend directly beneath coil24.

Accordingly, galvanic isolator20is preferably configured such that input lead frame71extends beneath input wirebond pads to facilitate wirebonding and provide firm structural support thereunder, but terminates before extending directly beneath coil24. Similarly, output lead frame73preferably extends beneath output wirebond pads to facilitate wirebonding and provide firm structural support thereunder, but terminates before extending directly beneath either via30or the via under53. A cross-sectional view of one embodiment of galvanic isolator20satisfying such design criteria is shown inFIG. 5. In the embodiment shown inFIG. 5, wirebond pads59and60are located on the top surface of coil transducer39, and are operably connected to transmitter IC21through wirebonds41, and receiver IC22through wirebonds42, respectively. In such a configuration, and as in the embodiment shown inFIGS. 1 and 2, access to the third and fourth metalized layers is provided from the top surface of coil transducer39by conductive vias30.36and a via disposed beneath location53(seeFIG. 1).

A top view of another embodiment of galvanic isolator20comprising a plurality of coil transducers39a-39esatisfying the design criteria discussed hereinabove is shown inFIG. 6.

Yet another consideration in galvanic isolator packaging is where busbars should be located so that a bias voltage may be provided to wirebond pads during electroplating, thereby to facilitate the establishment of reliable wirebonded connections. The busbars must reach to the edges of coil transducer39so that a bias voltage may be applied during an electroplating process. In one embodiment, a first busbar is operably connected to first coil23, while a second busbar is operably connected to second coil24. If a busbar end is located directly over a lead frame operating at a significantly different electrical potential than the busbar, an external high voltage breakdown can occur along the edge of coil transducer39between the end of the busbar and the lead frame. External high voltage breakdowns can also occur between busbar ends that are located too close to one another, especially since the process used to separate coil transducer die from one another can smear the metal along the cut sides of the coil transducers. Busbars and busbar ends are therefore preferably spaced far enough apart that external high voltage breakdowns cannot occur between them, and not directly above or below a lead frame at a significantly different potential. In one embodiment, a first busbar for coil23is located relatively close to an input lead frame, while a second busbar for coil24is located relatively close to an output lead frame. In preferred embodiments of the invention, busbars or portions of busbars are separated from one another, as well as from lead frames, by at least about 75 mils.

Referring now toFIGS. 7(a) and7(b), there is shown an embodiment of galvanic isolator20where wirebond connections to the input and output sides of coil transducer39are disposed on opposing sides thereof.FIGS. 7(a) and7(b) show cross-sectional views of galvanic isolator20in different stages of package assembly. InFIG. 7(a), transmitter circuit21is attached to input lead frame71by, for example, electrically non-conductive epoxy, and then operably connected to the input side of coil transducer39through wirebond41and wirebond pad60. Next, isolator20is flipped over and receiver circuit22is attached to output lead frame73by, for example, electrically non-conductive epoxy, and then operably connected to the output side of coil transducer39through wirebond42and wirebond pad61(seeFIG. 7(b)). As discussed above in respect ofFIG. 3, the configuration of galvanic isolator20shown inFIGS. 7(a) and7(b) eliminates the potential high voltage breakdown problems arising from the horizontal proximities of via36to the third and fourth metalized layers, and of via30to the second and first metalized layers shown inFIG. 2and denoted by distances D1. Instead, the embodiment illustrated inFIGS. 7(a) and7(b) features increased distance D2as the closet dimension between the various components of coil23on the one hand, and coil24on the other hand, which as described above are often operating at very different electrical potentials respecting one another. Moreover, galvanic isolator20ofFIGS. 7(a) and7(b) features input lead frame71and output lead frame73positioned in respect of galvanic isolator20such that structural support is provided thereto by lead frames71and73. This reduces the probability or possibility of external arcing because lead frames71and73do not extend beneath isolator20or coil transducer39sufficiently far so as to be located directly beneath coils23or24.

Once coil transducer39has been attached to lead frames71and73and wirebonds have operably attached transmitter circuit21and receiver22thereto, isolator20is preferably potted in a dielectric potting material that inhibits or prevents the occurrence of external high voltage breakdown (not shown in the Figures). This dielectric material should wet or adhere to the surfaces of coil transducer39, lead frames71and73, and ICs21and22such that no or few voids form or are included in the potting material after it has cured or dried. The dielectric potting material preferably exhibits high voltage hold-off and low dielectric loss performance characteristics so that the magnetic fields generated by isolator20are not attenuated. The dielectric potting material should also have a coefficient of thermal expansion similar to that of coil transducer39so that excessive stress is not placed on layers disposed within coil transducer39; otherwise, spiral conductors23,27,24or28may break or fracture. In another embodiment, a first dielectric potting material may be placed around various or all portions of isolator20, followed by placing a second dielectric potting material around the first dielectric potting material, the second dielectric potting material forming an external surface of isolator20. Examples of suitable dielectric potting materials include silicone, electrically non-conductive epoxy, polyimide, glass-filled epoxy and glass- and carbon-filled epoxy.

In another embodiment, galvanic isolator20is overmolded. In one embodiment, lead frame71with transmitter integrated circuit21, and coil transducer39attached thereto, and lead frame73with receiver integrated circuit22and coil transducer39attached thereto, are wirebonded, placed in a mold, and a melted appropriate electrically insulating molding material such as glass-filled epoxy is forced into the mold to encapsulate at least portions of the package. The molding material is then allowed to cool and harden, thereby providing electrical insulation and imparting substantial additional structural rigidity to the resulting package. The molding material preferably has an appropriate dielectric constant and low dielectric loss such that the electrical performance of galvanic isolator20is not degraded. The leads are then trimmed and bent.

Any one or more of the first, second, third, and fourth metalized layers, and vias30,31,35and36may be formed of one or more of gold, silver, copper, tungsten, nickel, tin, aluminum, aluminum-copper, and alloys, combinations or mixtures thereof.

In addition, in one embodiment coil transducer39may be mounted on a printed circuit board or a flex circuit substrate instead of being mounted on one or more lead frames. Thus, the packaging examples described and shown herein are not meant to cover all possibilities for packaging coil transducer39of the invention, and many different variations and permutations are contemplated.

Note that included within the scope of the present invention are methods of making and having made the various components, devices and systems described herein.

The above-described embodiments should be considered as examples of the present invention, rather than as limiting the scope of the invention. In addition to the foregoing embodiments of the invention, review of the detailed description and accompanying drawings will show that there are other embodiments of the invention. Accordingly, many combinations, permutations, variations and modifications of the foregoing embodiments of the invention not set forth explicitly herein will nevertheless fall within the scope of the invention.