1. Field of the Invention
The present invention relates to embedded magnetic component devices, and in particular to embedded magnetic component devices with improved isolation performance.
2. Description of the Related Art
Power supply devices, such as transformers and converters, involve magnetic components such as transformer windings and often magnetic cores. The magnetic components typically contribute the most to the weight and size of the device, making miniaturization and cost reduction difficult.
In addressing this problem, it is known to provide low-profile transformers and inductors in which the magnetic components are embedded in a cavity in a resin substrate, and the necessary input and output electrical connections for the transformer or inductor are formed on the substrate surface. A printed circuit board (PCB) for a power supply device can then be formed by adding layers of solder resist and copper plating to the top and/or bottom surfaces of the substrate. The necessary electronic components for the device may then be surface mounted on the PCB. This allows a significantly more compact and thinner device to be built.
In US2011/0108317, for example, a packaged structure having a magnetic component that can be integrated into a printed circuit board, and a method for producing the packaged structure, are described. In a first method, illustrated in
Through-holes 106 for forming primary and secondary side transformer windings are then drilled in the solid substrate 105 on the inside and outside circumferences of the toroidal magnetic component 103 (
A solder resist layer can then be added to the top and bottom surfaces of the substrate covering the metallic surface terminal lines, allowing further electronic components to be mounted on the solder resist layer. In the case of power supply converter devices, for example, one or more transistor switching devices and associated control electronics, such as Integrated Circuit (ICs) and passive components, may be mounted on the surface resist layer.
Devices manufactured in this way have a number of associated problems. In particular, air bubbles may form in the epoxy gel 104 as it is solidifying. During reflow soldering of the electronic components on the surface of the substrate, these air bubbles can expand and cause failure in the device.
US2011/0108317 also describes a second technique in which epoxy gel is not used to fill the cavity. This second technique will be described with respect to
As illustrated in
Once the magnetic core 206 has been inserted into the cavity 205 an upper epoxy dielectric layer 207 (such as an adhesive bondply layer) is added to the top of the structure, to cover the cavity 205 and the magnetic core 206. A corresponding layer 207 is also added to the bottom of the structure (
As noted above, where the embedded magnetic components of
In the case of
For many products, safety agency approval is required to certify the isolation characteristics. If the required isolation distance through air is large, there will be a negative impact on product size. For mains reinforced voltages (250 Vrms), for example, a spacing of approximately 5 mm is required across a PCB from the primary windings to the secondary windings in order to meet the insulation requirements of EN/UL60950.
The size and spacing of the vias forming the primary and second windings of the transformer is therefore largely decided by the specifications for the device. Vias have to have a sufficient diameter so that the vias can be successfully plated with metal and so that the metallic traces can be formed in an appropriate winding pattern to connect the vias together. Furthermore, if vias are placed too closely together or too close to other components, such as the magnetic core, the capacitance and isolation characteristics of the device can be adversely affected.
It would be desirable to provide an embedded magnetic component device with improved isolation characteristics, and to provide a method for manufacturing such a device.
According to a preferred embodiment of the present invention, an embedded magnetic component device includes an insulating substrate including a first side and a second side opposite the first side, and including a cavity therein, the toroidal cavity including an inner and an outer periphery; a magnetic core housed in the cavity; an electrical winding, extending through the insulating substrate and around the magnetic core; the electrical winding including: upper conductive traces located on the first side of the insulating substrate; lower conductive traces located on the second side of the insulating substrate; inner conductive connectors extending through the insulating substrate adjacent the inner periphery of the magnetic core, the inner conductive connectors respectively defining electrical connections between respective upper conductive traces and respective lower conductive traces; and outer conductive connectors extending through the insulating substrate adjacent the outer periphery of the magnetic core, the outer conductive connectors respectively defining electrical connections between respective first upper conductive traces and respective first lower conductive traces; wherein the outer conductive connectors include a first set of outer conductive connectors and a second set of outer conductive connectors; the first set of outer conductive connectors are located along the outer periphery of the cavity and are spaced from the outer periphery of the cavity by a first distance; and the second set of the outer conductive connectors are located at a greater distance from the outer periphery of the cavity than the first set; each of the first and second set of outer conductive connectors is electrically connected to an inner conductive connector through one of the upper conductive traces or one of the lower conductive traces.
The first side and the second side of the insulating substrate may be quadrilateral planar in shape, and the second set of outer conductive connectors may be located in a corner of the quadrilateral planar shape.
There may be a region of the device where the connectors in the second set of outer conductive connectors are continuously provided.
The inner conductive connectors may include a plurality of sets of inner conductive connectors, each set located along the inner periphery of the cavity and spaced from the inner periphery of the cavity by a different distance to the other sets.
The outer conductive connectors in the second set of outer conductive connectors may have a greater cross-sectional area than the outer conductive connectors in the first set of outer conductive connectors.
Electronic components may be mounted on the first side and/or the second side of the insulating substrate.
The magnetic core may include a first section and a second section, and the electrical winding may include a primary electrical winding disposed around the first section and a secondary electrical winding disposed around the second section, wherein the primary electrical winding and the secondary electrical winding are isolated from one another, and the primary electrical winding and the secondary electrical winding respectively include the upper conductive traces, the lower conductive traces, the inner conductive connectors, and the outer conductive connectors.
The device may further include: a first isolation barrier located on the first side of the insulating substrate, covering at least the portion of the first side between the primary electrical winding and the second electrical winding where the primary electrical winding and the second electrical winding are closest, and defining a solid bonded joint with the first side of the insulating substrate; and a second isolation barrier located on the second side of the insulating substrate, covering at least a portion of the second side between the primary electrical winding and the second electrical winding, where the primary electrical winding and the second electrical winding are closest, and defining a solid bonded joint with the second side of the insulating substrate.
The first isolation barrier and/or the second isolation barrier may include only a single layer. Alternatively, the first isolation barrier and/or the second isolation barrier may include a plurality of layers.
Electronic components may be mounted on the first isolation barrier and/or the second isolation barrier.
The magnetic core may be an elongated toroid a circular toroid, a gapped circular or elongate toroid, or has an EE, EI, I, EFD, EP, UI or UR toroidal core shape.
The inner conductive connectors and the outer conductive connectors may be conductive wires, pins or filaments extending through the insulating substrate.
A preferred embodiment of the present invention provides a method of manufacturing the above device. The method for manufacturing an embedded magnetic component device, includes a) preparing an insulating substrate including a first side and a second side opposite the first side, and including a toroidal cavity therein, the toroidal cavity including an inner and an outer periphery; b) installing a magnetic core in the toroidal cavity; c) forming an electrical winding extending through the insulating substrate and around the magnetic core, the electrical winding including: upper conductive traces located on the first side of the insulating substrate; lower conductive traces located on the second side of the insulating substrate; inner conductive connectors extending through the insulating substrate adjacent the inner periphery of the magnetic core, the inner conductive connectors respectively defining electrical connections between respective upper conductive traces and respective lower conductive traces; and outer conductive connectors extending through the insulating substrate adjacent the outer periphery of the magnetic core, the outer conductive connectors respectively defining electrical connections between respective first upper conductive traces and respective first lower conductive traces; d) in step c) forming the outer conductive connectors to include a first set of outer conductive connectors and a second set of outer conductive connectors; wherein the first set of outer conductive connectors are located along the outer periphery of the toroidal cavity and are spaced from the outer periphery of the toroidal cavity by a first distance; and the second set of the outer conductive connectors are located at a greater distance from the outer periphery of the toroidal cavity than the first set; and each one of the first and second set of outer conductive connectors is electrically connected to one of the inner conductive connectors through one of the upper conductive traces or one of the lower conductive traces.
The first side and the second side of the insulating substrate may be quadrilateral planar in shape, and the second set of outer conductive connectors may be located in a corner of the quadrilateral planar shape.
The second set of outer conductive connectors may be formed continuously in a region.
The inner conductive connectors may include a plurality of sets of inner conductive connectors, each set located along the inner periphery of the toroidal cavity and spaced from the inner periphery of the toroidal cavity by a different distance to the other sets.
The outer conductive connectors in the second set of outer conductive connectors may have a greater cross-sectional area than outer conductive connectors in the first set of outer conductive connectors.
The method may include mounting electronic components on the first side and/or the second side of the insulating substrate.
The magnetic core may include a first section and a second section, and the electrical winding may include a primary electrical winding disposed around the first section and a secondary electrical winding disposed around the second section, wherein the primary electrical winding and the secondary electrical winding are isolated from one another, and the primary electrical winding and the secondary electrical winding respectively include the upper conductive traces, the lower conductive traces, the inner conductive connectors, and the outer conductive connectors.
The method may also include: forming a first isolation barrier on the first side of the insulating substrate, covering at least the portion of the first side between the primary electrical winding and the second electrical winding where the primary electrical winding and the second electrical winding are closest, the first insulation barrier defining a solid bonded joint with the first side of the insulating substrate; forming a second isolation barrier on the second side of the insulating substrate, covering at least a portion of the second side between the primary electrical winding and the second electrical winding, where the primary electrical winding and the second electrical winding are closest, the second isolation barrier defining a solid bonded joint with the second side of the insulating substrate.
A preferred embodiment of the present invention provides a power electronics device including the embedded magnetic component device.
The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
A first preferred embodiment of the present invention of an embedded magnetic component device will now be described with reference to
In a first step, illustrated in
As shown in
In the next step, illustrated in
In the next step illustrated in
As shown in
Metallic traces 308 are also formed on the bottom surface of the insulating substrate 301 to define a lower winding layer also connecting the respective conductive via holes 307 to partly form the windings of the transformer. The upper and lower winding layers 308 and the via holes 307 together define the primary and secondary windings of the transformer.
Lastly, as shown in
Through holes and via conductors can be formed through the second and third insulating layers, i.e., first isolation barrier 309a and second isolation barrier 309b, in order to connect to the input and output terminals of the primary and second transformer windings (not shown). Where the conductive vias holes through the second and third insulating layers, i.e., first isolation barrier 309a and second isolation barrier 309b, are located apart from the vias through the substrate 301 and the cover layer 305, a metallic trace will be needed on the upper winding layer connecting the input and output vias to the first and last via in each of the primary and secondary windings. Where the input and output vias are formed in overlapping positions, then conductive or metallic caps could be added to the first and last via in each of the primary and secondary windings.
To meet the insulation requirements of EN/UL60950 only 0.4 mm is required through a solid insulator for mains referenced voltages (250 Vrms), for example.
The first and second isolation barriers 309a and 309b are formed on the substrate 301 and cover layer 305 without any air gap between the layers. If there is an air gap in the device, such as above or below the winding layers, then there would be a risk of arcing and failure of the device. The first and second isolation barriers 309a and 309b, the cover layer 305 and the substrate 301, therefore define a solid block of insulating material.
In the above-described figures, the first and second isolation barriers 309a and 309b are illustrated preferably as covering the whole of the cover layer 305 and the bottom surface of the substrate 301 of the embedded magnetic component device 300. In alternative preferred embodiments, however, it may be sufficient if the first and second isolation barriers are applied to the cover layer 305 and the bottom of the substrate 301 so that they at least cover only the portion of the surface of the cover layer 305 and substrate 301 surface between the primary and secondary windings, where the primary and secondary windings are closest. In
The pattern of through holes 306, conductive vias 307, and metallic traces 308 defining the upper and lower winding layers of the transformer will now be described in more detail with reference to
The primary winding of the transformer 410 includes outer conductive connectors or vias 411 arranged around the outer periphery of the cavity 302 containing the magnetic core 304. As illustrated in
Inner conductive connectors or vias 412 are provided in the inner or central isolation region of the substrate 301 and are arranged in rows adjacent the inner circumference of the cavity 302 containing the magnetic core 304. Owing to the smaller radius circumscribed by the inner cavity wall compared to the outer cavity wall, there is less space to arrange the inner conductive vias 412 compared to the outer conductive vias 411. As a result, the inner conductive vias 412 are staggered and arranged broadly in two or more rows having different radii. Some of the inner conductive vias 412 in the primary winding are therefore located closer to the wall of the cavity 302 than the other inner conductive vias 412, which are located closer to the central portion of the device. In
Each outer conductive via 411 in the upper winding layer 308 is connected to a single inner conductive via 412 by a metallic trace 413. The metallic traces 413 are formed on the surface of the cover layer 305 and so cannot overlap with one another. Although, the inner conductive vias 412 need not be arranged in rows, it is helpful to do so, as an ordered arrangement of the inner conductive vias 412 assists in arranging the metallic traces 413 so that they connect the outer conductive vias 411 to the inner conductive vias 412.
In at least one region, the outer conductive vias 411a of the primary winding are spaced farther away from the periphery of the cavity than the other outer conductive vias 411. For example, in
The larger circumference of the via holes 411a also means that the cross-sectional area of via holes 411a may be greater than the other via holes 411 spaced around the periphery of the magnetic core. Overall, the conductive vias 411a in region 410a may therefore present less electrical resistance to the current flowing through the primary winding and improves the electrical characteristics of the device.
In
The secondary winding of the transformer 420 also includes outer conductive vias 421 and inner conductive vias 422 connected to each other by respective metallic traces 423 in the same way as for the primary winding. As with the primary winding, in at least one region 420a, the outer conductive vias 421a of the secondary primary winding are located farther away or stepped-out from the periphery of the cavity 302 than the other outer conductive vias 421, and have larger circumferences and cross-sectional area to thereby present less electrical resistance to the current flowing through the windings. Despite the increase in diameter of the outer conductive vias 411a and 421a in regions 410a and 420a, the overall size of the device is unaffected.
The lower winding layer 308 of the transformer is arranged in the same way, and is illustrated in
In
Additionally, input and output connections to the transformer windings are illustrated by vias 415, 416, 417, and 418.
In an isolated DC-DC converter, for example, the primary winding 410 and the secondary winding 412 of the transformer must be sufficiently isolated from one another. In
Due to first and second isolation barriers 309a and 309b, the second and the third insulating layers, provided in the present preferred embodiment, the distance 432 between the primary and secondary side can be reduced to about 0.4 mm, for example, allowing significantly smaller devices to be produced, as well as devices with a higher number of transformer windings.
The second and third insulating layers need only be on the top and bottom of the device in the central region between the primary and secondary windings. However, in practice it is advantageous to make the second and third insulating layers cover the same area as that of the cover layer 305 and substrate 301 on which they are formed. As will be described below, this provides a support layer for a mounting board on top, and provides additional insulation between the components on that board, and the transformer windings underneath.
The preferred thickness of the first and second isolation barriers 309a and 309b may depend on the safety approval required for the device as well as the expected operating conditions. For example, FR4 has a dielectric strength of around 750 V/mm, and if the associated magnitude of the electric field used in an electric field strength test were to be 3000 V, such as that which might be prescribed by the UL60950-1 standard, a minimum thickness of 0.102 mm would be required for the first and second isolation barriers 309a and 309b. The thickness of the first and second isolation barriers 309a and 309b could be greater than this, subject to the desired dimensions of the final device. Similarly, for test voltages of 1500 V and 2000 V, the minimum thickness of the first and second isolation barriers 309a and 309b, if formed of FR4 would be 0.051 mm and 0.068 mm respectively, for example.
Although solder resist may be added to the exterior surfaces of the second and third insulating layers, i.e., the first and second isolation barriers 309a and 309b, this is optional in view of the insulation provided by the layers themselves.
Although in the preferred embodiment described above, the substrate 301, the cover layer 305, and the first and second isolation barriers 309a and 309b are made of FR4, any suitable PCB laminate system having a sufficient dielectric strength to provide the desired insulation may be included. Non-limiting examples include FR4-08, G11, and FR5.
As well as the insulating properties of the materials themselves, the cover layer 305 and the insulating layer 309 must bond well with the substrate 301 to form a solid bonded joint. The term solid bonded joint means a solid consistent bonded joint or interface between two materials with little voiding. Such joint should keep its integrity after relevant environmental conditions, for example, high or low temperature, thermal shock, humidity, and so on. Well-known solder resist layers on PCB substrates cannot form such solid bonded joint, and therefore the cover layer 305 and insulating layer 309 are different from such solder resist layers. For this reason, the material for the extra layers is preferably the same as the substrate 301, as this improves bonding between them. The cover layer 305, the insulating layer 309, and the substrate 301 could however be made of different materials providing there is sufficient bonding between them to form a solid body. Any material chosen preferably has good thermal cycling properties so as not to crack during use and would preferably be hydrophobic so that water would not affect the properties of the device.
In other preferred embodiments, the insulating substrate 301 could be formed from other insulating materials, such as ceramics, thermoplastics, and epoxies. These may be formed as a solid block with the magnetic core 304 embedded inside. As before, cover layer 305 and first and second isolation barriers 309a and 309b would then be laminated onto the substrate 301 to provide the additional insulation.
The magnetic core 304 is preferably a ferrite core as this provides the device with the desired inductance. Other types of magnetic materials, and even air cores, that is an unfilled cavity formed between the windings of the transformer are also possible in alternative preferred embodiments. Although, in the examples above, the magnetic core is toroidal in shape, it may have a different shape in other preferred embodiments. Non-limiting examples include, an oval or elongate toroidal shape, a circular shape having a gap, EE, EI, I, EFD, EP, UI and UR core shapes. In the present example, a round or an oval toroid shape was found to be the most robust and to provide sufficient space to locate the conductive vias around the magnetic core. The magnetic core 304 may be coated with an insulating material to reduce the possibility of breakdown occurring between the conductive magnetic core 304 and the conductive vias 307 or metallic traces 308. The magnetic core 304 may also have chamfered edges providing a profile or cross section that is rounded.
Furthermore, although the embedded magnetic component device illustrated above uses conductive vias 307 to connect the upper and lower winding layers 308, in alternative preferred embodiments, other connections could be used, such as conductive pins, wires, or filaments. The conductive pins could be inserted into the through holes 306 or could be preformed at appropriate locations in the insulating substrate 301 and cover layer 305. In this sense, the conductive vias 307 or indeed their equivalents if provided as pins, wires, or filaments may be referred to more generally as interlayer conductive winding sections, while the metallic traces 308 or their equivalent as a pin, wire or filament may be referred to more generally as an intra-layer conductive sections. The term intra-layer is used to indicate that the conductive winding sections of the upper and lower winding layers occur substantially on the same layer or layers of the device, while the term interlayer is used to indicate that the conductive winding sections cut through the device passing from the upper winding layer to the lower winding layer.
In this description, the terms top, bottom, upper, and lower are used only to define the relative positions of features of the device with respect to each other and in accordance with the orientation shown in the drawings, that is with a notional z axis extending from the bottom of the page to the top of the page. These terms are not therefore intended to indicate the necessary positions of the device features in use, or to limit the position of the features in a general sense.
A second preferred embodiment of the present invention will be described with reference to
In the first preferred embodiment, the lower winding layer of the transformer primary windings 410 and secondary windings 412 preferably is formed directly on the lower side of the insulating substrate 301, and the second isolation barrier 309b is subsequently laminated onto the insulating substrate 301 over the lower winding layer 308.
In the second preferred embodiment, the structure of the device 300a preferably is identical to that described in
The second cover layer 305b provides additional insulation for the lower winding layer 308.
In addition to significantly improving the electrical insulation between the primary and secondary side windings of the transformer, the first and second isolation barriers 309a and 309b usefully define and function as the mounting board on which additional electronic components can be mounted. This allows insulating substrate 301 of the embedded magnetic component device to act as the PCB of more complex devices, such as power supply devices. In this regard, power supply devices may include DC-DC converters, LED driver circuits, AC-DC converters, inverters, power transformers, pulse transformers, and common mode chokes, for example. As the transformer component is embedded in the substrate 301, more board space on the PCB is available for the other components, and the size of the device can be made small.
A third preferred embodiment of the present invention will therefore now be described with reference to
Before the electronic components 501, 502, 503, and 504 are mounted on the mounting surface, a plurality of metallic traces are formed on the surfaces of the first and second isolation barriers 309a and 309b to make suitable electrical connections with the components. The metallic traces 505, 506, 507, 508, and 509 are formed in suitable positions for the desired circuit configuration of the device. The electronic components 501, 502, 503, and 504 can then be surface mounted on the device and secured in place by reflow soldering, for example. One or more of the surface mounted components 501, 502, 503, and 504 preferably connects to the primary windings 410 of the transformer, while one or more further components 501, 502, 503, and 504 preferably connects to the secondary windings 420 of the transformer.
The resulting power supply device 500 shown in
A fourth preferred embodiment of the present invention will now be described with reference to
The fifth and sixth insulating layers 610a and 610b provide additional depth in which circuit lines can be constructed. For example, the metallic traces 612 can be an additional layer of metallic traces to metallic traces 505, 506, 507, 508, and 509, allowing more complicated circuit patterns to be formed. Metallic traces 505, 506, 507, 508, and 509 on the outer surface can be taken into the inner fifth and sixth insulating layers 610a and 610b of the device and back from it, using conductive vias. The metallic traces 505, 506, 507, 508, and 509 can then cross under metallic traces appearing on the surface without interference. The inner fifth and sixth insulating layers 610a and 610b therefore allow extra tracking for the PCB design to aid thermal performance, or more complex PCB designs. The device shown in
Alternatively, or in addition, the metallic traces of the fifth and sixth insulating layers 610a and 610b may be used to provide additional winding layers for the primary and secondary transformer windings. In the examples discussed above, the upper and lower windings 308 are formed on a single level. By forming the upper and lower winding layers 308 on more than one layer it is possible to put the metallic traces of one layer in an overlapping position with another layer. This means that it is more straightforward to take the metallic traces to conductive vias in the interior section of the magnetic core, and potentially more conductive vias can be incorporated into the device.
Only one of two additional insulating layers 610a or 610b may be necessary in practice. Alternatively, more than one additional insulating layer 610a or 610b may be provided on the upper or lower side of the device. The additional insulating layers 610a and 610b may be used with any of the first, second, or third preferred embodiments.
In practice, for
In all of the devices described, an optional solder resist cover may be added to the exterior surfaces of the device, either the first and second isolation barriers 309a and 309b or the fifth and sixth insulating layers 610a and 610b.
Example preferred embodiments of the present invention have been described for the purposes of illustration only. These are not intended to limit the scope of protection as defined by the attached claims. Features of one preferred embodiment may be used together with features of another preferred embodiment.
It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.
Number | Date | Country | Kind |
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1418482.4 | Oct 2014 | GB | national |