Patent Application
20080061917
Manufacturing processes for electrical components have been scrutinized as a way to reduce costs in the highly competitive electronics manufacturing business. Reduction of manufacturing costs are particularly desirable when the components being manufactured are low cost, high volume components. In a high volume component, any reduction in manufacturing costs is, of course, significant. Manufacturing costs as used herein refers to material cost and labor costs, and reduction in manufacturing costs is beneficial to consumers and manufacturers alike. It is therefore desirable to provide a magnetic component of increased efficiency and improved manufacturability for circuit board applications without increasing the size of the components and occupying an undue amount of space on a printed circuit board.
Miniaturization of magnetic components to meet low profile spacing requirements for new products, including but not limited to hand held electronic devices such as cellular phones, personal digital assistant (PDA) devices, and other devices presents a number of challenges and difficulties. Particularly for devices having stacked circuit boards, which is now common to provide added functionality of such devices, a reduced clearance between the boards to meet the overall low profile requirements for the size of the device has imposed practical constraints that either conventional circuit board components may not satisfy at all, or that have rendered conventional techniques for manufacturing conforming devices undesirably expensive.
Such disadvantages in the art are effectively overcome by virtue of the present invention. For a full appreciation of the inventive aspects of exemplary embodiments of the invention described below, the disclosure herein will be segmented into sections, wherein Part I is an introduction to conventional magnetic components and their disadvantages; Part II discloses an exemplary embodiments of a component device according to the present invention and a method of manufacturing the same; and Part III discloses an exemplary embodiments of a modular component device according to the present invention and a method of manufacturing the same.
I. Introduction to Low Profile Magnetic Components
Conventionally, magnetic components, including but not limited to inductors and transformers, utilize a conductive winding disposed about a magnetic core. In existing components for circuit board applications, magnetic components may be fabricated with fine wire that is helically wound on a low profile magnetic core, sometimes referred to as a drum. For small cores, however, winding the wire about the drum is difficult. In an exemplary installation, a magnetic component having a low profile height of less than 0.65 mm is desired. Challenges of applying wire coils to cores of this size tends to increase manufacturing costs of the component and a lower cost solution is desired.
Efforts have been made to fabricate low profile magnetic components, sometimes referred to as chip inductors, using deposited metallization techniques on a high temperature organic dielectric substrate (e.g. FR-4, phenolic or other material) and various etching and formation techniques for forming the coils and the cores on FR4 board, ceramic substrate materials, circuit board materials, phoenlic, and other rigid substrates. Such known techniques for manufacturing such chip inductors, however, involve intricate multi-step manufacturing processes and sophisticated controls. It would be desirable to reduce the complexity of such processes in certain manufacturing steps to accordingly reduce the requisite time and labor associated with such steps. It would further be desirable to eliminate some process steps altogether to reduce manufacturing costs.
II. Magnetic Devices Having Integrated Coil Layers
According to an exemplary embodiment of the invention, the inductor 100 may have a layered construction, described in detail below, that includes a coil layer 102 extending between outer dielectric layers 104, 106. A magnetic core 108 extends above, below and through a center of the coil (not shown in
In an exemplary embodiment, the inductor 100 has a low profile dimension H that is less than 0.65 mm in one example, and more specifically is about 0.15 mm. The low profile dimension H corresponds to a vertical height of the inductor 100 when mounted to the circuit board, measured in a direction perpendicular to the surface of the circuit board. In the plane of the board, the inductor 100 may be approximately square having side edges about 2.5 mm in length in one embodiment. While the inductor 100 is illustrated with a rectangular shape, sometimes referred to as a chip configuration, and also while exemplary dimensions are disclosed, it is understood that other shapes and greater or lesser dimensions may alternatively utilized in alternative embodiments of the invention.
The coil layer 102 further includes termination pads 140A and 142A on the first surface 134 of the base layer 132, and termination pads 140B and 142B on the second surface 135 of the base layer 132. An end 144 of the coil winding portion 130B is connected to the termination pad 140B on the surface 135 (
The base layer 132 may be generally rectangular in shape and may be formed with a central core opening 136 extending between the opposing surfaces 134 and 135 of the base layer 132. The core openings 136 may be formed in a generally circular shape as illustrated, although it is understood that the opening need not be circular in other embodiments. The core opening 136 receives a magnetic material described below to form a magnetic core structure for the coil winding portions 130A and 130B.
The coil portions 130A and 130B extends around the perimeter of the core opening 136 and with each successive turn of the coil winding 130 in each coil winding portion 130A and 130B, the conductive path established in the coil layer 102 extends at an increasing radius from the center of the opening 136. In an exemplary embodiment, the coil winding 130 extends on the base layer 132 for a number of turns in a winding conductive path atop the base layer 132 on the surface 134 in the coil winding portion 130A, and also extends for a number of turns below the base layer 132 on the surface 135 in the coil winding portion 130B. The coil winding 130 may extend on each of the opposing major surfaces 134 and 135 of the base layer 132 for a specified number of turns, such as ten turns on each side of the base layer 132 (resulting in twenty total turns for the series connected coil portions 130A and 130B). In an illustrative embodiment, a twenty turn coil winding 130 produces an inductance value of about 4 to 5 μH, rendering the inductor 100 well suited as a power inductor for low power applications. The coil winding 130 may alternatively be fabricated with any number of turns to customize the coil for a particular application or end use.
As those in the art will appreciate, an inductance value of the inductor 100 depends primarily upon a number of turns of wire in the coil winding 130, the material used to fabricate the coil winding 130, and the manner in which the coil turns are distributed on the base layer 132 (i.e., the cross sectional area of the turns in the coil winding portions 130A and 130B). As such, inductance ratings of the inductor 100 may be varied considerably for different applications by varying the number of coil turns, the arrangement of the turns, and the cross sectional area of the coil turns. Thus, while ten turns in the coil winding portions 130A and 130B are illustrated, more or less turns may be utilized to produce inductors having inductance values of greater or less than 4 to 5 μH as desired. Additionally, while a double sided coil is illustrated, it is understood that a single sided coil that extends on only one of the base layer surfaces 134 or 135 may likewise be utilized in an alternative embodiment.
The coil winding 130 may be, for example, an electro-formed metal foil which is fabricated and formed independently from the upper and lower dielectric layers 104 and 106. Specifically, in an illustrative embodiment, the coil portions 130A and 130B extending on each of the major surfaces 134, 135 of the base layer 132 may be fabricated according to a known additive process, such as an electro-forming process wherein the desired shape and number of turns of the coil winding 130 is plated up, and a negative image is cast on a photo-resist coated base layer 132. A thin layer of metal, such as copper, nickel, zinc, tin, aluminum, silver, alloys thereof (e.g., copper/tin, silver/tin, and copper/silver alloys) may be subsequently plated onto the negative image cast on the base layer 132 to simultaneously form both coil portions 130A and 130B. Various metallic materials, conductive compositions, and alloys may be used to form the coil winding 130 in various embodiments of the invention.
Separate and independent formation of the coil winding 130 from the dielectric layers 104 and 106 is advantageous in comparison to known constructions of chip inductors, for example, that utilize metal deposition techniques on inorganic substrates and subsequently remove or subtract the deposited metal via etching processes and the like to form a coil structure. For example, separate and independent formation of the coil winding 130 permits greater accuracy in the control and position of the coil winding 130 with respect to the dielectric layers 104, 106 when the inductor 100 is constructed. In comparison to etching processes of known such devices, independent formation of the coil winding 130 also permits greater control over the shape of the conductive path of the coil. While etching tends to produce oblique or sloped side edges of the conductive path once formed, substantially perpendicular side edges are possible with electroforming processes, therefore providing a more repeatable performance in the operating characteristics of the inductor 100. Still further, multiple metals or metal alloys may be used in the separate and independent formation process, also to vary performance characteristics of the device.
While electroforming of the coil winding 130 in a manner separate and distinct from the dielectric layers 104 and 106 is believed to be advantageous, it is understood that the coil winding 130 may be alternatively formed by other methods while still obtaining some of the advantages of the present invention. For example, the coil winding 130 may be an electro deposited metal foil applied to the base layer 132 according to known techniques. Other additive techniques such as screen printing and deposition techniques may also be utilized, and subtractive techniques such as chemical etching, plasma etching, laser trimming and the like as known in the art may be utilized to shape the coils.
The upper and lower dielectric layers 104, 106 overlie and underlie, respectively, the coil layer 102. That is, the coil layer 102 extends between and is intimate contact with the upper and lower dielectric layers 104, 106. In an exemplary embodiment, the upper and lower dielectric layers 104 and 106 sandwich the coil layer 102, and each of the upper and lower dielectric layers 104 and 106 include a central core opening 150, 152 formed therethrough. The core openings 150, 152 may be formed in generally circular shapes as illustrated, although it is understood that the openings need not be circular in other embodiments.
The openings 150, 152 in the respective first and second dielectric layers 104 and 106 expose the coil portions 130A and 130B and respectively define a receptacle above and below the double side coil layer 102 where the coil portions 130A and 130B extend for the introduction of a magnetic material to form the magnetic core 108. That is, the openings 150, 152 provide a confined location for portions 108A and 108B of the magnetic core.
In an exemplary embodiment, the core portions 108A and 108B are applied as a powder or slurry material to fill the openings 150 and 152 in the upper and lower dielectric layers 104 and 106, and also the core opening 136 (
In an illustrative embodiment, the first and second dielectric layers 104 and 106, and the base layer 132 of the coil layer 102 are each fabricated from polymer based dielectric films. The upper and lower insulating layers 104 and 106 may include an adhesive film to secure the layers to one another and to the coil layer 102. Polymer based dielectric films are advantageous for their heat flow characteristics in the layered construction. Heat flow within the inductor 100 is proportional to the thermal conductivity of the materials used, and heat flow may result in power losses in the inductor 100. Thermal conductivity of some exemplary known materials are set forth in the following Table, and it may be seen that by reducing the conductivity of the insulating layers employed, heat flow within the inductor 100 may be considerably reduced. Of particular note is the significantly lower thermal conductivity of polyimide, which may be employed in illustrative embodiments of the invention as insulating material in the layers 104, 106 and 132.
One such polyimide film that is suitable for the layers 104, 106 and 132 is commercially available and sold under the trademark KAPTON® from E. I. du Pont de Nemours and Company of Wilmington, Del. It is appreciated, however, that in alternative embodiments, other suitable electrical insulation materials (polyimide and non-polyimide) such as CIRLEX® adhesiveless polyimide lamination materials, UPILEX® polyimide materials commercially available from Ube Industries, Pyrolux, polyethylene naphthalendicarboxylate (sometimes referred to as PEN), Zyvrex liquid crystal polymer material commercially available from Rogers Corporation, and the like may be employed in lieu of KAPTON®. It is also recognized that adhesiveless materials may be employed in the first and second dielectric layers 104 and 106. Pre-metallized polyimide films and polymer-based films are also available that include, for example, copper foils and films and the like, that may be shaped to form specific circuitry, such as the winding portions and the termination pads, for example, of the coil layers, via a known etching process, for example.
Polymer based films also provide for manufacturing advantages in that they are available in very small thicknesses, on the order of microns, and by stacking the layers a very low profile inductor 100 may result. The layers 104, 106 and 132 may be adhesively laminated together in a straightforward manner, and adhesiveless lamination techniques may alternatively be employed.
The construction of the inductor also lends itself to subassemblies that may be separately provided and assembled to one another according the following method 200 illustrated in
The coil windings 130 may be formed 202 in bulk on a larger piece or sheet of a dielectric base layer 132 to form 202 the coil layers 102 on a larger sheet of dielectric material. The windings 130 may be formed in any manner described above, or via other techniques known in the art. The core openings 136 may be formed in the coil layers 102 before or after forming of the coil windings 130. The coil windings 130 may be double sided or single sided as desired, and may be formed with additive electro-formation techniques or subtractive techniques for defining a metallized surface. The coil winding portions 130A and 130B, together with the termination pads 140, 142 and any interconnections 138 (
The dielectric layers 104 and 106 may likewise be formed 204 from larger pieces or sheets of dielectric material, respectively. The core openings 150, 152 in the dielectric layers may be formed in any known manner, including but not limited to punching techniques, and in an exemplary embodiment, the core openings 150, 152 are formed prior to assembly of the layers 104 and 106 on the coil layer.
The sheets including the coil layers 102 from step 202 and the sheets including the dielectric layers 104, 106 formed in step 204 may then be stacked 206 and laminated 208 to form an assembly as shown in
With the above-described layered construction and methodology, magnetic components such as inductors may be provided quickly and efficiently, while still retaining a high degree of control and reliability over the finished product. By pre-forming the coil layers and the dielectric layers, greater accuracy in the formation of the coils and quicker assembly results in comparison to known methods of manufacture. By forming the core over the coils in the core openings once the layers are assembled, separately provided core structures, and manufacturing time and expense, is avoided. By embedding the coils into the core, separately applying a winding to the surface of the core in conventional component constructions is also avoided. Low profile inductor components may therefore be manufactured at lower cost and with less difficulty than known methods for manufacturing magnetic devices.
It is contemplated that greater or fewer layers may be fabricated and assembled into the component 100 without departing from the basic methodology described above. Using the above described methodology, magnetic components for inductors and the like may be efficiently formed using low cost, widely available materials in a batch process using relatively inexpensive techniques and processes. Additionally, the methodology provides greater process control in fewer manufacturing steps than conventional component constructions. As such, higher manufacturing yields may be obtained at a lower cost.
III. A Modular Approach
Like the component 100 described above, the upper and lower dielectric layers 304 and 306 include pre-formed openings 310, 312 defining receptacles for magnetic core portions 308A and 308B in a similar manner as that described above for the component 100.
Each of the coil layers 302A, 302B, 302C, 302D, 302E, 302F, 302G, 302H, 302I and 302J includes a respective dielectric base layer 314A, 314B, 314C, 314D, 314E, 314F, 314G, 314H, 314I and 314J and a generally planar coil winding portion 316A, 316B, 316C, 316D, 316E, 316F, 316G, 316H, 316I and 316J. Each of the coil winding portions 316A, 316B, 316C, 316D, 316E, 316F, 316G, 316H, 316I and 316J includes a number of turns, such as two in the illustrated embodiment, although greater and lesser numbers of turns may be utilized in another embodiment. Each of the coil winding portions 316 may be single-sided in one embodiment. That is, unlike the coil layer 102 described above, the coil layers 302 may include coil winding portions 316 extending on only one of the major surfaces of the base layers 314, and the coil winding portions 316 in adjacent coil layers 302 may be electrically isolated from one another by the dielectric base layers 314. In another embodiment, double sided coil windings may be utilized, provided that the coil portions are properly isolated from one another when stacked to avoid electrical shorting issues.
Additionally, each of the coil layers 302 includes termination openings 318 that may be selectively filled with a conductive material to interconnect the coil windings 316 of the coil layers 302 in series with one another in the manner explained below. The openings 318 may, for example, be punched, drilled or otherwise formed in the coil layer 402 proximate the outer periphery of the winding 316. As schematically illustrated in
Likewise, each coil layer 302 includes a number of inner coil termination openings 320A, 320B, 320C, 320D, 320E, 320F, 320G, 320H, 320I, 320J, that likewise may be punched, drilled or otherwise formed in the coil layers 302. The number of inner termination openings 320 is the same as the number of outer termination openings 318 in an exemplary embodiment, although the relative numbers of inner and outer termination openings 320 and 318 may varied in other embodiments. Each of the outer termination openings 318 is connectable to an outer region of the coil 316 by an associated circuit trace 322A, 322B, 322C, 322D, 322E, 322F, 322G, 322H, 322I, and 322J. Each of the inner termination openings 320 is also connectable to an inner region of the coil 316 by an associated circuit trace 324A, 324B, 324C, 324D, 324E, 324F, 324G, 324H, 324I, and 324J. Each coil layer 302 also includes termination pads 326, 328 and a central core opening 330.
In an exemplary embodiment, for each of the coil layers 302, one of the traces 322 associated with one of the outer termination openings 318 is actually present, and one of the traces 324 associated with one of the inner termination openings 322 is actually present, while all of the outer and inner termination openings 318 and 320 are present in each layer. As such, while a plurality of outer and inner termination openings 318, 320 are provided in each layer, only a single termination opening 318 for the outer region of the coil winding 316 in each layer 302 and a single termination opening 320 for the inner region of each coil winding 316 is actually utilized by forming the associated traces 322 and 324 for the specific termination openings 318, 320 to be utilized. For the other termination openings 318, 320 that are not to be utilized, connecting traces are not formed in each coil layer 302.
As illustrated in
When the coil layers 302 are stacked, the inner and outer termination openings 318 and 320 formed in each of the base layers 314 are aligned with another, forming continuous openings throughout the stacked coil layers 302. Each of the continuous openings may be filled with a conductive material, but because only selected ones of the openings 318 and 320 include a respective conductive trace 322 and 324, electrical connections are established between the coil winding portions 316 in the coil layers 302 only where the traces 322 and 324 are present, and fail to establish electrical connections where the traces 322 and 324 are not present.
In the embodiment illustrated in
The upper and lower dielectric layers 304, 306, and the base dielectric layers 314 may be fabricated from polymer based metal foil materials as described above with similar advantages. The coil winding portions 316 may be formed any manner desired, including the techniques described above, also providing similar advantages and effects. The coil layers 302 may be provided in module form, and depending on the number of coil layers 302 used in the stack, inductors of various ratings and characteristics may be provided. Because of the stacked coil layers 302, the inductor 300 has a greater low profile dimension H (about 0.5 mm in an exemplary embodiment) in comparison to the dimension H of the component 100 (about 0.15 mm in an exemplary embodiment), but is still small enough to satisfy many low profile applications for use on stacked circuit boards and the like.
The construction of the component 300 also lends itself to subassemblies that may be separately provided and assembled to one another according the following method 350 illustrated in
The coil windings may be formed in bulk on a larger piece of a dielectric base layer to form 352 the coil layers 302 on a larger sheet of dielectric material. The coil windings may be formed in any manner described above or according to other techniques known in the art. The core openings 330 may be formed into the sheet of material before or after forming of the coil windings. The coil windings may be double sided or single sided as desired, and may be formed with additive electro-formation techniques or subtractive techniques on a metallized surface. The coil winding portions 316, together with the termination traces 322, 324 and termination pads 326, 328 are provided on the base layer 314 in each of the coil layers 302. Once the coil layers 302 are formed in step 352, the coil layers 302 may be stacked 354 and laminated 356 to form coil layer modules. The termination openings 318, 320 may be provided before or after the coil layers 302 are stacked and laminated. After they are laminated 356, the termination openings 318, 320 of the layers may be filled 358 to interconnect the coils of the coil layers in series in the manner described above.
The dielectric layers 304 and 306 may also be formed 360 from larger pieces or sheets of dielectric material, respectively. The core openings 310, 312 in the dielectric layers 304, 306 may be formed in any known manner, including but not limited to punching or drilling techniques, and in an exemplary embodiment the core openings 310, 312 are formed prior to assembly of the dielectric layers 304 and 306 to the coil layer modules.
The outer dielectric layers 304 and 306 may then be stacked and laminated 362 to the coil layer module. Magnetic core material may be applied 364 to the laminated stack to form the magnetic cores. After curing the magnetic material, the stacked sheets may be cut, diced, or otherwise singulated 366 into individual inductor components 300. Before or after singulation of the components, vertical surfaces of the terminations 305, 307 (
With the layered construction and the method 350, magnetic components such as inductors and the like may be provided quickly and efficiently, while still retaining a high degree of control and reliability over the finished product. By pre-forming the coil layers and the dielectric layers, greater accuracy in the formation of the coils and quicker assembly results in comparison to known methods of manufacture. By forming the core over the coils in the core openings once the layers are assembled, separately provided core structures, and manufacturing time and expense, is avoided. By embedding the coils into the core, a separate application of a winding to the surface of the core is also avoided. Low profile inductor devices may therefore be manufactured at lower cost and with less difficulty than known methods for manufacturing magnetic devices.
It is contemplated that greater or fewer layers may be fabricated and assembled into the component 300 without departing from the basic methodology described above. Using the above described methodology, magnetic components may be efficiently formed using low cost, widely available materials in a batch process using relatively inexpensive known techniques and processes. Additionally, the methodology provides greater process control in fewer manufacturing steps than conventional component constructions. As such, higher manufacturing yields may be obtained at a lower cost.
For the reasons set forth above, the inductor 300 and method 350 is believed to be avoid manufacturing challenges and difficulties of known constructions and is therefore manufacturable at a lower cost than conventional magnetic components while providing higher production yields of satisfactory devices.
IV. Conclusion
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
