Patent Publication Number: US-2020286667-A1

Title: Magnetic component structure with thermal conductive filler and method of fabricating the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/816,213, filed on Mar. 10, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a magnetic component structure, and more specifically, to a magnetic component structure with thermal conductive filler. 
     2. Description of the Related Art 
     Magnetic component for example transformer or inductor, also called reactor, is a passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor according to Faraday&#39;s law of electromagnetic induction, which opposes the change in current that created it. Many magnetic components have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. 
     Magnetic components are widely used in alternating current (AC) electronic equipment, particularly in radio equipment, power transfer or power isolation. For example, inductors are used to block the flow of AC current while allowing DC to pass. The inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits. 
     The development and popularity of 5G wireless systems and automotive electronics offer a huge business opportunity to those industries in the field. Extreme demand for passive components like inductors or transformer makes them in quite short supply. Furthermore, 5G wireless systems and automotive electronics need stricter specifications and requirements for the characteristics of magnetic component. For example, how to effectively and quickly dissipate the heat generated by coils and magnetic cores in the magnetic component becomes a critical issue, since increased amount of heat generation and accumulation may rise the temperature of magnetic component in operation and deteriorate their performance, or eventually, burn down the whole device. Accordingly, there is a need for an improved method and construction for dissipating heat from magnetic cores and coils in magnetic component. 
     SUMMARY OF THE INVENTION 
     In order to improve the heat dissipation of magnetic component, the present invention provides a magnetic component structure with thermal conductive fillers between coil and magnetic cores to boost heat conduction therebetween. Unique design for the thermal conductive filler provides improved heat dissipation as well as reducing the manufacturing cost. In addition, the size of coils and magnetic cores may be accordingly reduced to easily achieve desired inductance and facilitate the miniaturization of the magnetic component. 
     One aspect of the present invention is to provide a magnetic component structure with thermal conductive filler, including an upper magnetic core and a lower magnetic core, wherein the upper magnetic core and the lower magnetic core combines to form a casing with a front opening and a rear opening, a coil mounted in the casing, where two terminals of the coil extending outwardly from the front opening, and a thermal conductive filler filling between the casing and the coil in casing. 
     Another aspect of the present invention is to provide a method of fabricating a magnetic component structure with thermal conductive filler, including steps of providing a mold with a coil mounted therein, potting the mold with a thermal conductive material to form a thermal conductive filler encapsulating at least a part of the coil, releasing the thermal conductive filler and the coil from the mold, and combining the thermal conductive filler with magnetic cores to form a magnetic component structure. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute apart of this specification. The drawings illustrate some of the embodiments and, together with the description, serve to explain their principles. In the drawings: 
         FIG. 1  is an exploded view of a magnetic component structure in accordance with one embodiment of the present invention; 
         FIG. 2  is a front perspective view of a magnetic component structure after assembly in accordance with one embodiment of the present invention; 
         FIG. 3  is a rear perspective view of a magnetic component structure in accordance with one embodiment of the present invention; 
         FIG. 4  is a rear perspective view of a magnetic component structure in accordance with another embodiment of the present invention; 
         FIG. 5  is a rear perspective view of a magnetic component structure in accordance with still another embodiment of the present invention; 
         FIG. 6  is a rear perspective view of a magnetic component structure in accordance with still another embodiment of the present invention; 
         FIG. 7  is a bottom perspective view of a magnetic component structure in accordance with one embodiment of the present invention; 
         FIGS. 8 a  and 8 b    are perspective views of lower magnetic cores of the magnetic component structure in accordance with two embodiments of the present invention; 
         FIGS. 9 a  and 9 b    are top views of the lower magnetic cores of magnetic component structure shown in  FIGS. 8 a  and 8 b    in a center-shifted form; 
         FIG. 10  is a perspective view illustrating the assembly of a magnetic component structure in accordance with one embodiment of the present invention; 
         FIG. 11  is a perspective view illustrating the assembly of a magnetic component structure in accordance with another embodiment of the present invention; 
         FIG. 12  is a perspective view illustrating the assembly of a magnetic component structure in accordance with still another embodiment of the present invention; 
         FIG. 13  is a perspective view illustrating the assembly of a magnetic component structure in accordance with still another embodiment of the present invention; and 
         FIGS. 14 a  and 14 b    are perspective views of coils used in the magnetic component structure in accordance with one embodiment of the present invention. 
     
    
    
     It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments. 
     DETAILED DESCRIPTION 
     In following detailed description of the present invention, reference is made to the accompanying drawings which form a part hereof and is shown by way of illustration and specific embodiments in which the invention may be practiced. These embodiments are described in sufficient details to enable those skilled in the art to practice the invention. Dimensions and proportions of certain parts of the drawings may have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     First, please refer to  FIG. 1 , which is an exploded view of a magnetic component structure  100  in accordance with one preferred embodiment of the present invention. This figure shows relative positions and arrangements of elements in the magnetic component structure  100 . The magnetic component structure  100  shown in this embodiment may include, from bottom to top, a lower magnetic core  110 , a bobbin  120 , at least one coil  130 , a thermal conductive filler  140 , an insulating paper or film  150  and an upper magnetic core  160 . The lower magnetic core  110  is provided with a center column  111  extending upwardly from the mounting plane  115  for the bobbin  120  and/or the coil  130  to be mounted thereon. The bobbin  120  may be a bobbin frame with a shape corresponding to the profile of inner sidewalls and the mounting plane of the lower magnetic core  110  and a hollow center cylinder  121  corresponding to and may be mounted on the center column  111  of lower magnetic core  110 . The coil  130  is wound and mounted around the center cylinder  121  of bobbin  120 . In the embodiment of the present invention, the bobbin  120  further includes two cover walls  120   a  conformal with the outer sides of the coil  130  to improve the insulation between the coil  130  and the core  110 ,  160 . The coil  130  is wound independently and then mounted on the bobbin  120  by fitted on the center column  111 . 
     The upper magnetic core  160  has a shape corresponding to the lower magnetic core  110  and, after assembly, it is combined with the lower magnetic core  110  to enclose all aforementioned elements of the magnetic component structure  100 . The thermal conductive filler  140  is filled up and formed in at least a portion of or whole remaining enclosed space between the upper magnetic core  160  and the lower magnetic core  110 . The insulating paper  150  is disposed between the thermal conductive filler  140  and the upper magnetic core  160  to provide better insulating property. Optionally, an elastic tape  170  may be adhered behind the magnetic component structure  100  to seal the rear opening formed by the combined upper magnetic core  160  and lower magnetic core  110 . Please note that the arrangement and configuration identified above is an exemplary preferred embodiment of the present invention. Certain elements like the bobbin  120 , the insulating paper  150  and/or the elastic tape  170  may not be provided in real implementation or may be replaced with other elements. In addition, various modifications and additions relevant to the elements may be made in variant embodiments. In addition, the front opening and the rear opening formed after assembly are opposite to each other respectively in two parallel and opposite directions of expansion stress. The function of openings is to release the expansion stress generated by heat in the operation, so that the stress withstood for the core  110 ,  160  may be significantly reduced. The thermal conductivity of thermal conductive filler and thermal conductive interface material is larger than about 0.3 W/mk (watts per meter-kelvin). In one embodiment, the thermal conductive filler doesn&#39;t encapsulate the outer surfaces of the upper magnetic core  160  and the lower magnetic core  110 . 
     In the present invention, the material of the upper magnetic core  160  and lower magnetic core  110  may be powder core with lower relative permeability, such Fe—Si based alloy and Fe—Ni based alloy, or ferrite core with higher relative permeability. The material of insulating paper/film  150  may be Dupont Nomex® or Dupont Kapton®, with a thickness enough to achieve insulating requirement and an area larger than the top area of electrified coil  130 . The material of bobbin  120  may be plastics (ex. engineering plastics) that can bear the tension in coil winding process. The material of thermal conductive filler  140  may be inorganic material with good thermal conductivity, such as epoxy, silicon, or polyurethane (PU), or may be materials with thermal conductivity larger than 0.3 W/mk, such as thermoset phenolic resins, thermoplastic polyethylene terephthalate (PET), polyamide (PA), polyphenylene sulfide (PPS) and polyetheretherketone (PEEK). 
     Next, please refer to  FIG. 2 , which is a front perspective view of a magnetic component structure  100  after assembly in accordance with one embodiment of the present invention. The lower magnetic core  110  and the upper magnetic core  160  are combined to form a casing  101  containing the elements of magnetic component structure  100  inside. A front opening  101   a  is formed for terminals  131  of the coil  130  to extend outwardly in front of the casing  101 . The bobbin  120  is mounted along a portion of inner sidewalls of the casing  101 , with the thermal conductive filler  140  filling up inner, at least partial or whole remaining space and encapsulating at least partial or whole coil  130  (two terminals  131  excluded) and the bobbin  120 . The insulating paper  150  is disposed between the shaped thermal conductive filler  140  and the upper magnetic core  130 . 
     In the operation, the heat generated by the coil  130  may be first conducted to the thermal conductive filler  140  encapsulating therearound. The thermal conductive filler  140 , with superior thermal conductive property, may effectively conduct the heat from the coil  130  to the surrounding casing  101 , with the insulating paper  150  facilitating the conduction therebetween. The upper and lower magnetic cores  160  and  110 , which are inherently good thermal conductors, may further conduct the heat to external heat dissipating structures like cooling plates of cellphone or vehicle on which the magnetic component structure  100  is mounted. 
     In one embodiment, the thermal conductive filler  140  is formed by potting the mold consist of an upper magnetic core  160  and a lower magnetic core  110  with a thermal conductive material to form a thermal conductive filler  140  encapsulating fully or partially the coil  130  already mounted therein. 
     Next, please refer to  FIG. 3 , which is a rear perspective view of a magnetic component structure  100  in accordance with one embodiment of the present invention. The rear opening (not shown) formed by the combined lower magnetic core  110  and upper magnetic core  160  may be blocked by a cover  180 . In this embodiment, the cover  180  is a part of casing  101  and may be bonded on the rear side of upper and lower magnetic cores  160  and  110  with a shape flush with the shape of casing  101 . The cover  180  is added in the magnetic component structure  100  to seal the rear opening of casing  101  so that the thermal conductive filler may be retained in the enclosed space until it is cured in a potting process. In this embodiment, the surface of thermal conductive filler may be flush with the rear opening of casing  101 . 
     Next, please refer to  FIG. 4 , is a rear perspective view of a magnetic component structure  100  in accordance with another embodiment of the present invention. In this embodiment, the rear opening  101   b  of casing  101  is not blocked by a cover like the one shown in  FIG. 3 , so that the thermal conductive filler  140  may project outwardly from the inner space of casing  101 . This design is suitable for those magnetic component structures with a portion of the coil out of rear range of the casing  101 . The projecting thermal conductive filler  140  may fully encapsulate this kind of coil even if it is out of rear range of the casing  101 . In the manufacture, this projecting structure is formed by potting the thermal conductive material with a mold made of the upper and lower magnetic cores  160 ,  110  and an additional rear mold piece (not shown) similar to the cover  180  in  FIG. 3 . The rear mold piece provides an inner molding space to shape the projecting portion of the thermal conductive filler  140 . After the thermal conductive filler  140  is cured, the rear mold piece is released from the magnetic cores  110 ,  160  and the thermal conductive filler  140 . This projecting thermal conductive structure may also provide better heat dissipating efficiency if it is contacted with external cooling structures. 
     Next, please refer to  FIG. 5 , which is a rear perspective view of a magnetic component structure in accordance with still another embodiment of the present invention. In this embodiment, instead of using a rear cover  180  blocking the rear opening of casing  101  like the one shown in  FIG. 3 , the rear opening may be sealed by using an adhesive elastic tape  170  adhering on the rear side of the casing  101 . The advantage of this design is it provides flexible space and allowance for the thermal conductive filler formed in the casing  101 . In real manufacture, cured thermal conductive filler may applies a considerable stress to the combined magnetic cores  110 ,  160  and even can crack the magnetic cores  110  if there are not enough space for the thermal conductive filler to expand. The applied elastic tape  170  may serve as a bottom cover to retain the thermal conductive filler in the potting process and, if required, it may be detached by cured, expanding thermal conductive filler to provide an outwardly-expanding space. If not expanding, the surface of thermal conductive filler will be flush with the rear opening of the casing  101 . 
     Next, please refer to  FIG. 6 , which is a rear perspective view of a magnetic component structure  100  in accordance with still another embodiment of the present invention. In another variant of present invention, the thermal conductive filler  140  in the magnetic component structure  100  may be formed in a half-filled or partially-filled mode. As shown in  FIG. 6 , the thermal conductive filler  140  is half-filled from the lower magnetic core  110  toward the upper magnetic core  160 . A portion of the half-filled thermal conductive filler  140  projects outwardly from the rear opening  101   b  of casing  101  like the one shown in  FIG. 4 . It can be seen in  FIG. 6  that portions of the bobbin  120  and the coil  130  are exposed from the thermal conductive filler  140  in the unfilled space. That is, the thermal conductive filler  140  in this embodiment does not fully encapsulate those internal elements. The advantage of this half-filled or partially-filled mode is it can save significant material cost and reduce expansion stress caused by heat in the operation, since nearly only half quantity of the thermal conductive filler  140  is required in this manufacturing process, and at the same time, it maintains appropriate heat conducting property since it has enough thermal conductive contact area between the thermal conductive filler  140  and the lower magnetic core  110 . In the manufacture, this half-filled and projecting structure may be formed by curing the thermal conductive filler  140  in a lateral potting process. Supplementary mold pieces are necessary in front and rear of the casing  101  to retain uncured thermal conductive material until it is cured into the thermal conductive filler  140 . 
     Next, please refer to  FIG. 7 , which is a bottom and inner perspective view of a magnetic component structure  100  in accordance with one embodiment of the present invention. Similar to the embodiment of  FIG. 6 , the thermal conductive filler  140  of this embodiment is also in a half-filled or partially-filled mode. However, in this embodiment, the thermal conductive filler  140  is formed by an upright potting process, with an elastic tape or cover blocking the rear opening  101   b  of the casing  101 . The thermal conductive filler  140  partially fills up the casing  101  from the rear opening  101   b  to the front opening  101   a . In comparison to the embodiment of  FIG. 6 , the contact area between thermal conductive filler  140  and lower magnetic core  110  in this embodiment is much smaller. Although the heat conducting ability is compromised, the advantage of this design is it adopts simple upright potting process. The potting, uncured thermal conductive filler  140  may be easily retained in the formation without the help of supplementary mold pieces. The outer surface of cores  110 ,  160  opposite to the thermal conductive filler  140  would be the cooling surface to contact with a cooler. 
     Next, please refer to  FIGS. 8 a  and 8 b   , which are perspective views of the lower magnetic cores  110  of magnetic component structure in accordance with two embodiments of the present invention. The magnetic component structure in the present invention may adopt various types of lower magnetic cores  110 , such as EQ-core shown in  FIG. 8 a    and E-core shown  FIG. 8 b   . The EQ-type lower magnetic core  110  is provided with a center column  111  for coil or bobbin to be mounted thereon. The E-type lower magnetic core  110 , unlike the aforementioned one, is provided with a center bar  113  for the coil to be wound therearound. Both of these two types of lower magnetic core  110  are provided with front openings  101   a  and rear openings  101   b  for internal elements to extend outwardly therefrom. Please note that the types of lower magnetic cores  110  identified above are merely exemplary embodiments, other types of lower magnetic cores  110  like EP-core, ER-core, ETD-core, PM-core and PQ-core may also be well applied in the present invention, to combine and bonded with a matching upper magnetic core  160  with the same core type or just using a simple I-core. 
     Next, please refer to  FIGS. 9 a  and 9 b   , which are top views of the lower magnetic cores  110  of magnetic component structure shown in  FIGS. 8 a  and 8 b    respectively in a center-shifted form. As shown in the figures, the center column  111  and the center bar  113  of lower magnetic cores  110  in these two embodiments may be shifted in a distance from the center C of mounting plane  115  on the lower magnetic cores  110  toward the front opening  101   a . The purpose of this design is to prevent the coil mounted on the center column  111  or the center bar  113  out of the rear range of lower magnetic core  110 . In this way, the coil wound around the column and the bar may also be shifted toward the front opening  101   a  and the rear opening  101   b  may be sealed with an elastic tape that may be easily removed after potting and provide better flexibility in the process. The molded thermal conductive filler  140  in these two embodiment may be flush with the rear opening  101   b  rather than projecting therefrom like the one shown in  FIG. 4 . 
     After describing various structural embodiments above, now please refer to  FIGS. 10-13 , which are perspective views illustrating the assembly of a magnetic component structure in accordance with various embodiments of the present invention. The thermal conductive filler  140  of the present invention may be molded in various form. First, please refer to  FIG. 10 . In this embodiment, the thermal conductive filler  140  is formed partially encapsulating the coil  130  and nearly encapsulating entire lower magnetic core  110 . In the manufacture, the thermal conductive material is potted into the mold (not shown) containing the lower magnetic core  110  and the coil  130  mounted thereon. The potted thermal conductive material is cured and takes shape into the thermal conductive filler  140  that encapsulates the lower magnetic core  110  and the lower portion of coil  130 . After released from the mold, the lower magnetic core  110 , including the encapsulated coil  130 , are combined and bonded with the upper magnetic core  160  to form the magnetic component structure. The advantage of this design is its manufacturing process is very simple, and the fully-encapsulating thermal conductive filler  140  may provide better heat dissipating efficiency and low thermal expansion stress for the magnetic component structure in comparison to those with un-encapsulated lower magnetic core  110 . 
     Next, please refer to  FIG. 11 . The thermal conductive filler  140  in this embodiment may be formed together with the lower magnetic core  110  in another form. As shown in  FIG. 11 , the thermal conductive filler  140  is formed on the mounting plane  115  of lower magnetic core  110  with its shape conformal to at least partial or whole inner sidewalls and its rear surface flush with the rear opening of the lower magnetic core  110 . The thermal conductive filler  140  in this embodiment may be formed by potting thermal conductive material into a mold made of combining lower magnetic core  110  and an upper mold piece (not shown) with predetermined shape and sidewall profiles. After the thermal conductive filler  140  is cured and released from the upper mold piece, the thermal conductive filler  140 , including the lower magnetic core  110  and the coil  130  fully or partially encapsulated therein, may be combined and bonded with the upper magnetic core  160  to form the magnetic component structure. Similarly, the advantage of this design is its manufacturing process is very simple, and the thermal conductive filler  140  may be formed together with the lower magnetic core  110  to prevent engineering tolerance between shaped thermal conductive filler  140  and the magnetic cores in the assembly, especially for those sintered ferrite cores with unexpected shrunken dimension. 
     Next, please refer to  FIG. 12 . In this embodiment, like the one shown in  FIG. 10 , the thermal conductive filler  140  is formed together with the lower magnetic core  110 . However, in this embodiment, the bobbin  120  is included in the formation of thermal conductive filler  140 . In the manufacture, the coil  130  is first wound on the bobbin  120 , and the bobbin  120  is further mounted on the lower magnetic core  110 . After these three pieces are assembled, the whole piece is potted with thermal conductive material in a mold (not shown) having predetermined shape and inner profile. The coil  130  may be fully or at least partially encapsulated on the bobbin  120  and the lower magnetic core  110  by thermal conductive filler  140 . Only the top surface of bobbin  120  is exposed. After released from the mold, the lower magnetic core  110 , including the encapsulating thermal conductive filler  140 , bobbin  120  and coil  130  mounted thereon, is combined and bonded with the upper magnetic core  160  to form the magnetic component structure. The advantage of this design is it includes bobbin  120  in the formation of thermal conductive filler  140 , which is more suitable for complex structural design, such as complex coil structures or complex internal assembly. Optionally, a flexible thermal conductive interface material  190  may be disposed between the thermal conductive filler  140  and the upper magnetic core  160  or between the thermal conductive filler  140  and the lower magnetic core  110 , to absorb stress caused by the thermal conductive filler  140 , to fill possible gap between the bobbin  120  and the upper magnetic core  160 , and to provide better insulating and heat conductive property. The flexible thermal conductive interface material  190  may be thermal adhesive, thermal grease, thermal pad or thermal gap filler, etc, with a hardness smaller than the one of thermal conductive filler  140  or/and cores  110 ,  160  to further lower the thermal stress and assembly tolerance. 
     Next, please refer to  FIG. 13 . In this embodiment, unlike the one shown in  FIG. 12 , the thermal conductive filler  140  is not formed together with the lower magnetic core  110 . It is formed individually by using a mold (not shown) with predetermined inner profile corresponding to the one of magnetic cores  110  and  160 . The cured and shaped thermal conductive filler  140  would encapsulate the coil  130 , and may be combined and well-fitted between the lower magnetic core  110  and the upper magnetic core  160  to form magnetic component structure. Similarly, a flexible thermal conductive interface material  190  may be disposed between the thermal conductive filler  140  and the upper magnetic core  160  or between the thermal conductive filler  140  and the lower magnetic core  110  to absorb the stress applied on the magnetic cores, fill possible gap between the thermal conductive filler  140  and the upper magnetic core  160 , and provide better heat conductive property. The advantage of this embodiment is it provides better flexibility and design for assembly since the thermal conductive filler  140  and the magnetic cores  110 ,  160  are formed individually and may be assembled in adequate timing. 
     Lastly, please refer to  FIGS. 14 a  and 14 b   , which are perspective views of two types of coils  130  used in the magnetic component structure in accordance with one embodiment of the present invention.  FIG. 14 a    shows a coil  130  in a round wire type, while  FIG. 14 b    shows a coil in a copper sheet type. Please note that the types of coil  130  identified above are merely exemplary embodiments, other types of coil, such as flat wire, stranded wire, stranded self-bonding wire or the combination thereof, may also be well applied in the present invention. If the coil is in a type of flat wire, copper sheet, or thick heavy round wire, the coil may be molded directly with the thermal conductive filler  140  without using bobbin. If the coil is in a type of round wire, stranded wire or composite wire, bobbin is required to fix the coil in the potting process like the one shown in  FIG. 12 . 
     In the present invention, the thermal conductive filler made by potting and curing thermal conductive material between the coil and the magnetic cores significant improves the heat dissipating efficiency of the magnetic component structure. Therefore, diameter of the coil, volume of the magnetic cores and total magnetic path may be further reduced to increase the inductance. The desired inductance may be obtained with smaller number of coils and smaller magnetic cores in this design and is advantageous to the electrical properties and manufacturing cost of the magnetic component structure. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.