Abstract:
A magnetic device, method of manufacture therefor and a power supply employing the magnetic device. In one embodiment, the magnetic device includes a metal substrate and a first dielectric layer formed over the metal substrate. The magnetic device further includes a first conductive layer formed over only a portion of the dielectric layer and a magnetic core mounted proximate the first conductive layer adapted to impart a desired magnetic property thereto.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND PATENTS  
       [0001]    This application is related to the following U.S. patents and applications:  
                                           Reference No.   Title   Inventor(s)   Date                   08/908,887   Methods of   Roessler,   Filed       (&#39;887   Manufacturing a   et al.   Aug. 8,       application)   Magnetic Device and       1997           Tool for Manufacturing           the Same       08/940,672   Post-mountable Planar   Pitzele, et   Filed       (&#39;672   Magnetic Device and   al.   Sept. 30,       application)   Method of Manufacture       1997           Thereof       09/045,217   Power Magnetic Device   Pitzele, et   Filed       (&#39;217   Employing a Leadless   al.   Mar. 20,       application)   Connection to a Printed       1998           Circuit Board and           Method of Manufacture           Thereof       09/184,753   Lead-free Solder   Pilukaitis,   Filed       (&#39;753   Process for Printed   et al.   Nov. 2,       application)   Wiring Boards       1998       09/288,749   Inter-substrate   Heinrich,   Filed       (&#39;749   Conductive Mount For a   et al.   April 8,       application)   Circuit Board, Circuit       1999           Board and Power           Magnetic Device           Employing The Same       09/288,750   Surface Mountable Power   Heinrich,   Filed       (&#39;750   Supply Module and   et al.   April 8,       application)   Method of Manufacture       1999           Therefor       09/538,334   Board Mounted Power   Chen, et   Filed       (&#39;334   Supply, Method of   al.   March 29,       application)   Manufacture therefore       2000           and Electronic Device           Employing the Same       5,303,138   Low loss synchronous   Rozman   Issued       (&#39;138   rectifier for       April 12,       patent)   application to clamped-       1994           mode power converters           5,541,828   Multiple Output   Rozman   Issued       (&#39;828   Converter with       July 30,       patent)   Continuous Power       1996           Transfer to an Output           and with Multiple           Output Regulation           5,588,848   Low inductance surface   Law, et al.   Issued       (&#39;848   mount connectors for       Dec. 31,       patent)   interconnecting circuit       1996           devices and method for           using same       5,590,032   Self-synchronized drive   Bowman, et   Issued       (&#39;032   circuit for a   al.   Dec. 31,       patent)   synchronous rectifier       1996           in a clamped-mode power           converter       5,625,541   Low loss synchronous   Rozman   Issued       (&#39;541   rectifier for       April 29,       patent)   application to clamped-       1997           mode power converters       5,724,016   Power Magnetic Device   Roessler,   Issued       (&#39;016   Employing a   et al.   Mar. 3,       patent)   Compression-mounted       1998           Lead to a Printed           Circuit Board               5,750,935   Mounting Device for   Stevens   Issued       (&#39;935   Attaching a Component       May 12,       patent)   Through an Aperture in       1998           a Circuit Board       5,787,569   Encapsulated Package   Lotfi, et   Issued       (&#39;569   for Power Magnetic   al.   Aug. 4,       patent)   Devices and Method of       1998           Manufacture Therefor       5,835,350   Encapsulated,   Stevens   Issued       (&#39;530   Board-mountable Power       Nov. 10,       patent)   Supply and Method of       1998           Manufacture Therefor       5,926,373   Encapsulated, Board-   Stevens   Issued       (&#39;373   mountable Power Supply       July 20,       patent)   and Method of       1999           Manufacture Therefor       5,992,005   Method of Manufacturing   Roessler,   Issued       (&#39;005   a Power Magnetic Device   et al.   Nov. 30,       patent)           1999       6,005,773   Board-mountable Power   Rozman, et   Issued       (&#39;773   Supply Module   al.   Dec. 21,       patent)           1999                  
 
         [0002]    The above-listed applications and patents are commonly assigned with the present invention and are incorporated herein by reference as if reproduced herein in their entirety. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0003]    The present invention is directed, in general, to electronic devices and, more specifically, to a magnetic device, method of manufacture therefor and a power supply employing the magnetic device.  
         BACKGROUND OF THE INVENTION  
         [0004]    A pervasive change in the design and assembly of electronic devices that has been occurring over the last several years, and one that continues to occur, is the development of more compact and, at the same time, more complex electronic devices. Because customers continue to demand smaller and more complex electronic devices, designers of such electronic devices must be more innovative in their product design and configuration.  
           [0005]    One of the essential circuits found in many electronic devices is a power supply. The power supplies typically receive electrical power from an external power source and condition the power to meet the requirements of the components of the electronic device. For example, many electronic devices require DC power to operate. The external power source, however, may only provide AC power. The power supply is therefore required to convert the AC power to the DC power to operate the components of the electronic device.  
           [0006]    The use of more efficient power supplies is one way that the electronic devices can be made more compact. This must be done while preserving the functional capabilities of the power supply. If a power supply can be made smaller and more efficient, more space on the circuit boards of the electronic device may be made available for other electronic components or, if additional components are not required, the size and weight of the circuit boards and, accordingly, the electronic device itself, can be reduced.  
           [0007]    Board-mounted power supplies currently being used in many electronic devices frequently require a transformer to convert AC power to DC power. In one conventional approach, the transformer is physically mounted on a surface of the circuit board and projects into the adjacent space, thereby transferring generated heat to the surrounding air in the environment of the circuit board. While functional, this configuration places a major heat generating device on one side of the board. Alternatively, the transformer may be constructed by building up the transformer windings on either side of the circuit board, and placing the core physically about the windings with the core centered on the circuit board.  
           [0008]    Traditionally, board mounted power supplies have not been without problems. For example, it is in the very nature of power supplies that they generate a considerable amount of heat. Full load operation at 85° C. ambient air is becoming the norm as systems become more compact. Conventional circuit boards, such as a multi-layer FR-4 board manufactured by Photocircuits Corporation of Glen Cove, N.Y., have difficulty dissipating the heat because of poor thermal conductivity. Alternatively, insulated metal substrate boards, with improved thermal conductivity, have been used except presently there is no configuration for integrating components, such as magnetic devices (e.g., a transformer), on to the board to take proper advantage of the such attributes. Therefore, discrete magnetic devices have been employed with power supplies constructed on the insulated metal substrate boards.  
           [0009]    Accordingly, what is needed in the art is a magnetic device configuration that may be integrated into a circuit board such as an insulated metal substrate board.  
         SUMMARY OF THE INVENTION  
         [0010]    To address the above-discussed deficiencies of the prior art, the present invention provides a magnetic device, method of manufacture therefor and a power supply employing the magnetic device. In one embodiment, the magnetic device includes a metal substrate and a first dielectric layer formed over the metal substrate. The magnetic device further includes a first conductive layer formed over only a portion of the dielectric layer and a magnetic core mounted proximate the first conductive layer adapted to impart a desired magnetic property thereto.  
           [0011]    The present invention introduces, in one aspect, a magnetic device that may be formed as an integral part of an insulated metal substrate. As a result, the magnetic device may assume a reduced overall profile.  
           [0012]    The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The invention is best understood from the following detailed description when read with the accompanying FIGURES. It is emphasized that in accordance with the standard practice in the electronics industry, various features may not be drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 illustrates an isometric view of an embodiment of an electrical device constructed according to the principles of the present invention;  
         [0015]    [0015]FIG. 2 illustrates an exploded isometric view of an embodiment of a multilayer subassembly constructed according to the principles of the present invention;  
         [0016]    [0016]FIG. 3A illustrates an exploded isometric view of an embodiment of a magnetic device constructed according to the principles of the present invention;  
         [0017]    [0017]FIG. 3B illustrates a partial sectional view of the magnetic device of FIG. 3A along a plane  3 B- 3 B;  
         [0018]    [0018]FIG. 4 illustrates an isometric view of an embodiment of a power supply constructed according to the principles of the present invention; and  
         [0019]    [0019]FIG. 5 illustrates a schematic diagram of an embodiment of a power supply constructed according to the principles of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0020]    Referring initially to FIG. 1, illustrated is an isometric view of an embodiment of an electrical device  100  constructed according to the principles of the present invention. The electrical device  100  includes a metal substrate  110 , a dielectric layer  120 , a conductive layer  130  and an aperture  140 . The dielectric layer  120  is formed over and, in the illustrated embodiment, completely covers the metal substrate  110 . However, those skilled in the art will realize that the dielectric layer  120  need not necessarily cover the entire metal substrate  110 .  
         [0021]    The metal substrate  110  and dielectric layer  120  form an insulated metal substrate  125 . The insulated metal substrate  125  is thermally conductive with the metal substrate  110  formed from a metal sheet material and the dielectric layer  120  formed from a thermally conductive insulated adhesive material. The metal sheet material is selected based upon the coefficient of thermal expansion (CTE), thermal conductivity, heat capacity, cost, and other criteria specific to the end application. The metal substrate  110  may be treated with a surface treatment to promote adequate adhesion between the metal substrate  110  and the dielectric layer  120 . In an exemplary embodiment, the insulated metal substrate  125  may be an insulated metal substrate provided by the Bergquist Company of Chanhassen, Minnesota as disclosed, in pertinent part, in U.S. Pat. No. 4,810,563, entitled “Thermally Conductive, Electrically Insulative Laminate,” by David G. DeGree, et al., issued Mar. 7, 1989, which is incorporated herein by reference. In accordance therewith, the thermally conductive insulated adhesive material may be a Thermal Clad® thermally conductive dielectric adhesive designed by the Bergquist Company.  
         [0022]    The dielectric layer  120 , also being an adhesive in the present embodiment, physically bonds the metal substrate  110  to the conductive layer  130  as well as insulating the metal substrate  110  from the conductive layer  130 . The conductive layer  130  may be formed from any suitable conductive material (e.g., aluminum, copper, gold) and is formed over only a portion (i.e., area  150 ) of the dielectric layer  120 . In the illustrated embodiment, the conductive layer  130  is formed as a trace proximate the aperture  140 . Of course, the conductive layer  130  may take any required form. The aperture  140  is formed in and passes through both the dielectric layer  120  and the metal substrate  110  proximate the area  150  of the dielectric layer  120 . Those skilled in the art will recognize that the conductive layer  130  and aperture  140  form a two-turn air coil, a basic form of an electrical inductive device. Of course, single turns or additional turns may be formed as needed. Additionally, a magnetic material may also be used as a magnetic core thereby forming a solenoid.  
         [0023]    Turning now to FIG. 2, illustrated is an exploded isometric view of an embodiment of a multilayer subassembly constructed according to the principles of the present invention. The multilayer subassembly includes first, second, and third conductive layers  211 ,  212 ,  213 , first and second dielectric layers  221 ,  222 , conductive vias (collectively designated  230 ) and apertures (collectively designated  240 ).  
         [0024]    The first and second conductive layers  211 ,  212  may be formed of a metal foil of appropriately selected weight about two faces  221   a,    221   b  of the first dielectric layer  221  using external registration  250  or registration vias  260 . Those skilled in the art are familiar with the registration of layered electrical components. Exposed faces of the first, second, and third conductive layers  211 ,  212 ,  213  are conditioned as required. A bond is formed between the respective layers in a manner as described in DeGree, et al. The conductive vias  230  may be formed by drilling or routing with the addition of electrical connectivity via isolation material (not shown), if necessary.  
         [0025]    Turning now to FIG. 3A, illustrated is an exploded isometric view of an embodiment of a magnetic device  310  constructed according to the principles of the present invention. The magnetic device  310  includes a metal substrate  320 , a first dielectric layer  331 , first conductive layers or windings  341   a,    341   b,  second dielectric layers  332   a,    332   b,  second conductive layers or windings  342   a,    342   b,  third dielectric layers  333   a,    333   b,  third conductive layers or windings  343   a,    343   b,  fourth dielectric layers  334   a,    334   b,  a fourth conductive layer or winding  344   a,  a fifth dielectric layer  335   a,  apertures (collectively designated  350 ), first and second magnetic core halves  361 ,  362  (forming a magnetic core), and conductive vias (collectively designated  370 ). The first and second magnetic core halves  361 ,  362  are placed through in the apertures  350  and retained therein. The metal substrate  320  has an extended aperture  321  between the apertures  350  in the first dielectric layer  331  so as to prevent core half  362  from shorting between a pole A and a pole B of the magnetic core  361 ,  362 . Of course, other configurations including insulated standoffs, etc., may also be incorporated in the core halves  361 ,  362  to accomplish the same objective. Those skilled in the art are familiar with such standoffs.  
         [0026]    In the illustrated embodiment, the magnetic device  310  is a transformer having four windings  341   a,    342   a,    343   a,    344   a  about one pole A of the magnetic core  361 ,  362  and three windings  341   b,    342   b,    343   b  about the other pole B of the magnetic core  361 ,  362 . Fourth dielectric layer  334   b  and fifth dielectric layer  335   a  assure that magnetic core half  361  does not create a short between pole A and pole B. Thus, with the present invention, the magnetic device  310  may be constructed as an integral part of an insulated metal substrate having any desired number of windings per pole of the core. Of course, an application for the magnetic device  310  is in a power supply and, therefore, the windings  341   a,    342   a,    343   a,    344   a  about the one pole A of the magnetic core  361 ,  362  and the windings  341   b,    342   b,    343   b  about the other pole B of the magnetic core  361 ,  362  may be connected to separate stages of the power supply. Those skilled in the art are familiar with the use of transformers in power supplies.  
         [0027]    Turning now to FIG. 3B, illustrated is a partial sectional view of the magnetic device  310  of FIG. 3A along a plane  3 B- 3 B. The sectional view illustrates the metal substrate  320 , the first dielectric layer  331 , the apertures  350 , the second magnetic core half  362  and relieved areas (collectively designated  380 ). The relieved areas  380  are removed from the metal substrate  320  proximate the apertures  350  to prevent shorting by the second magnetic core half  362 . An additional insulative spacer  383  may also be employed as shown.  
         [0028]    Referring now to FIG. 4, illustrated is an embodiment of a power supply constructed according to the principles of the present invention. The power supply is constructed on a circuit board  400  having multi-layered magnetic devices  410  constructed according to the principles of the present invention on only portions  420  of the circuit board  400 . It should be noted that the circuit board  400  is primarily a conventional circuit board having a metal layer  401  that extends entirely across a surface  402  of the circuit board  400 . Of course, that metal layer  401  need not, in its finished state, be contiguous across the circuit board  400 , but may be formed by masking and etching into simple or complex traces that interconnect components, some representative components designated  430 , on an opposing surface  407  thereof. One who is skilled in the art is familiar with the formation of interconnecting traces on printed circuit boards.  
         [0029]    Only portions  420  of the circuit board  400  are multi-layered having alternating conductive and dielectric layers as described above. The portions  420  may have a plurality of layers as required for a particular application while the rest of the circuit board  400  has only a single layer. Of course, provisions to avoid shorting by the cores as discussed with respect to FIGS. 3A and 3B should be addressed in any such design.  
         [0030]    Referring now to the preceding FIGURES in general, a method of manufacturing will hereinafter be described. To manufacture a multi-layered magnetic device, a metal sheet material acting as a metal substrate is selected based on its coefficient of thermal expansion, thermal conductivity, heat capacity, cost, and other appropriate criteria in accordance with the end application. Surfaces of the metal sheet material are given a surface treatment to promote adequate adhesion between the metal sheet material and a dielectric layer such as a thermally conductive insulated adhesive material. The dielectric layer is bonded to the metal substrate in a manner as described in Degree, et al.  
         [0031]    Subassemblies formed of alternating conductive layers (e.g., windings) and dielectric layers are progressively formed together using the bonding process and conventional masking, developing and etching techniques as required until the desired number of conductive layers has been achieved. Interconnecting conducting vias and the metal interconnects (not shown) filling them between conducting layers are formed conventionally as the subassemblies are manufactured. A plurality of relieved areas are concurrently formed in a similar manner by masking and etching.  
         [0032]    A pair of apertures are then formed in the respective layers of the subassemblies and the metal substrate. If necessary, additional registration vias or conductive vias may be drilled during the winding build-up. Using a layer registration system as above along with heat and pressure, the conductive layers are mated to the dielectric layers about the apertures therethrough. When appropriate, a plurality of the subassemblies may be formed to the required layers/thickness on a single sheet and then separated by cutting or routing. These subassemblies are then affixed to the metal substrate using heat and pressure in accordance with Degree, et al. Finally, first and second magnetic core halves are inserted into the apertures and fastened to each other with an appropriate adhesive. Final connections to the contacts for each winding and the remainder of the circuit are formed by conventional means.  
         [0033]    Thus, a magnetic device and method of manufacturing a multi-layered magnetic device integrally on an insulated metal substrate board has been described. It should be clear to those skilled in the art that the present invention, may be used to manufacture any of the variety of magnetic devices (e.g., transformers, inductors, etc.) integrally with an insulated metal substrate.  
         [0034]    Turning now to FIG. 5, illustrated is a schematic diagram of an embodiment of a power supply  500  constructed according to the principles of the present invention. The power supply  500  includes a power train having a conversion stage including a power switching device  510  for receiving input electrical power V IN  and producing therefrom switched electrical power. The power supply  500  further includes a filter stage (including an output inductor  550  and output capacitor  560 ) for filtering the switched electrical power to produce output electrical power (represented as an output voltage V OUT ). The power supply  500  still further includes a transformer  520 , having a primary winding  523  and a secondary winding  526 ) and a rectification stage (including rectifying diodes  520 ,  530 ) coupled between the power conversion stage and the filter stage. The transformer  520  is constructed according to the principles of the present invention as previously described. Of course, the magnetic device constructed according to the principles of the present may be employed in other electronic circuits such as transmission circuits.  
         [0035]    For a better understanding of power electronics including power supplies and conversion technologies see “Principles of Power Electronics,” by J. G. Kassakian, M. F. Schlecht and G. C. Verghese, Addison-Wesley (1991). For a better understanding of magnetic devices and construction techniques therefor see “Printed Circuits Handbook,” by Clyde Coombs, Jr., McGraw Hill Book Co., 4th Edition (1995). The aforementioned references are incorporated herein by reference.  
         [0036]    Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.