Abstract:
A high current, low profile inductor (IHLP) includes a conductive coil molded within an inductor body substantially free from ferrite materials and comprising powdered iron materials. The method comprises pressure molding the inductor body substantially free from ferrite materials and comprising a powdered magnetic material within the hollow core of the coil and completely around the coil so that the magnetic material is substantially free from voids therein without shorting out the coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 09/546,859, filed on Apr. 10, 2000 and issuing on Sep. 17, 2002 as U.S. Pat. No. 6,449,829, which is a divisional of Ser. No. 09/271,748, filed on Mar. 18, 1999, and issuing as U.S. Pat. No. 6,198,375 on Mar. 6, 2001. This application is also a continuation of application Ser. No. 09/547,155, filed Apr. 11, 2002, now U.S. Pat. No. 6,460,244 issued Oct. 8, 2002, which is a divisional of application Ser. No. 08/963,224 filed Nov. 3, 1997, now U.S. Pat. No. 6,204,744, which is a continuation of application Ser. No. 08/503,655 filed Jul. 18, 1995, now abandoned. The Specification and Drawings of application Ser. No. 09/547,155, now U.S. Pat. No. 6,460,244, are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an inductor coil structure and method for making same. The coil structure of the present invention is preferably for use in a high current low profile inductor commonly referred to by the designation IHLP. However, the particular coil structure may be used in other types of inductors. 
     Inductor coils have in the prior art been constructed from various shapes of materials formed into various helical shapes. However, there is a need for an improved inductor coil structure which is simple to manufacture and which provides an efficient and reliable inductance coil. 
     Therefore, a primary object of the present invention is the provision of an improved inductor coil structure and method for making same. 
     A further object of the present invention is the provision of an inductor coil structure which can be used in a high current low profile inductor having no air spaces in the inductor, and which includes a magnetic material completely surrounding the coil. 
     A further object of the present invention is the provision of an inductor coil structure which includes a closed magnetic system which has self-shielding capability. 
     A further object of the present invention is the provision of an inductor coil structure which maximizes the utilization of space needed for a given inductance performance so that the inductor can be of a minimum size. 
     A further object of the present invention is the provision of an improved inductor coil structure which is smaller, less expensive to manufacture, and is capable of accepting more current without saturation than previous inductor coil structures. 
     A further object of the present invention is the provision of an inductor coil structure which lowers the series resistance of the inductor. 
     SUMMARY OF THE INVENTION 
     The foregoing objects may be achieved by a high current low profile inductor comprising a conductor coil having first and second coil ends. A magnetic material surrounds the conductor coil to form an inductor body. The inductor coil comprises a plurality of coil turns extending around a longitudinal coil axis in an approximately helical path which progresses axially along the coil axis. The coil turns are formed from a flat plate having first and second opposite flat surfaces, at least a portion of each of the flat surfaces of the coil turns facing in a axial direction with respect to the coil axis. 
     The method for making the inductor includes taking an elongated plate conductor having a first end, a second end, opposite side edges, opposite flat surfaces, and a longitudinal plate axis. A plurality of slots are cut in each of the opposite side edges of the plate conductor so as to form the plate conductor into a plurality of cross segments extending transversely with respect to the plate axis and a plurality of connecting segments extending approximately axially with respect to the plate axis. The connecting segments connect the cross segments together into a continuous conductor which extends in a sine shaped path. As used herein the term “sine shaped” refers to any shape which generally conforms to a sine curve, but which is not limited to a continuous curve and may include apexes, squared off corners or other various shapes. 
     After cutting the slots in the opposite side edges of the plate conductor the connecting segments are bent along one or more bend axes extending transversely with respect to the plate axis so as to form the plate conductor into a plurality of accordion folds, each of which comprise one of the cross segments and a portion of one of the connecting segments. In the resulting structure, the cross segments and the connecting segments form a continuous conductor coil of approximate helical shape having first and second opposite ends. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
         FIG. 1  is a perspective view of the inductor constructed in accordance with the present invention and mounted upon a circuit board. 
         FIG. 2  is a pictorial view of the coil of the inductor before the molding process. 
         FIG. 3  is a pictorial view of the inductor of the present invention after the molding process is complete, but before the leads have been formed. 
         FIG. 4  is an end elevational view taken along line  4 — 4  of FIG.  2 . 
         FIG. 5  is an elevational view taken along lines  5 — 5  of FIG.  4 . 
         FIG. 6  is a perspective view of an elongated conductor blank from which the inductor coil is formed. 
         FIG. 7  shows the blank of  FIG. 6  after the formation of slots extending inwardly from the opposite edges thereof. 
         FIG. 8  is a view similar to  FIG. 7 , showing the first folding step in the formation of the inductor coil of the present invention. 
         FIG. 9  is a side elevational view showing the same folding step shown in FIG.  8 . 
         FIG. 10  is a view similar to  8  and showing a second folding step in the process for making the inductor coil of the present invention. 
         FIG. 11  is an inverted pictorial view of the inductor after it has been pressed, but before the leads have been formed. 
         FIG. 12  is a view similar to  FIG. 11  showing the inductor after partial forming of the leads. 
         FIG. 13  is a view similar to  FIGS. 11 and 12  showing the final forming of the leads. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings the numeral  10  generally designates an inductor of the present invention mounted upon a circuit board  12 . Inductor  10  includes an inductor body  14  having a first lead  16  and a second lead  18  extending therefrom and being folded over the opposite ends of body  14 . Leads  16 ,  18  are soldered or otherwise electrically connected on the circuit board  12 . 
     Referring to  FIG. 2 , the inductor coil of the present invention is generally designated by the numeral  20 . Leads  16 ,  18  form the ends of coil  22 . Between leads  16 ,  18  are a plurality of L-shaped coil segments  26  each comprising a horizontal leg  28  and a vertical leg  30 . Vertical leg  30  terminates at a connecting segment  32  which is folded over at approximately 180° so as to create an accordion like configuration for inductor coil  20 . The L-shaped coil segments are connected together to form a helical coil having an open coil center  34  extending along a longitudinal coil axis  36 . 
       FIGS. 6-10  show the process for making the coil  20 . Initially as shown in  FIG. 6  a blank flat conductor plate  50  formed of copper or other electrically conductive material includes: first and second ends  52 ,  54 ; a pair of opposite flat surfaces  56 ; and a pair of opposite side edges  58 ,  60 . 
       FIG. 7  shows the first step in forming the coil  20 . In this step a plurality of slots  62 ,  64  are cut in the opposite edges  58 ,  60  respectively of the blank flat plate  50 . Various cutting methods may be used such as stamping or actual cutting by laser or other cutting tools known in the art. 
     Upon completion of the cutting operation, the blank  50  is transformed into an elongated sine shaped body formed from a plurality of cross segments  66  extending transversely to the longitudinal axis of plate  50  and a plurality of connecting segments  67  extending axially with respect to the longitudinal axis of plate  50 . The segments  66 ,  67  form a continuous sine shaped configuration as shown in FIG.  7 . 
       FIG. 8  shows the next step in forming the coil  20 . The end  52  is folded over at an angle of 180° to form the 180° angle bend  63  in the first connecting segment  67 .  FIG. 10  shows a second bend  65  which is in the next connecting segment  67 . Bends  63 ,  65  are in opposite directions, and are repeated until an accordion like structure is provided similar to that shown in FIG.  5 . 
     In  FIG. 5  the coil  20  includes opposite ends  16 ,  18  which are formed from the opposite ends  52 ,  54  of blank  50 . The cross segments  66  of blank  50  form the first horizontal legs  28  of coil  20 , and the connecting segments  67  of blank  50  form the second vertical legs  30  and the connecting segments  32  of coil  20 . 
     An example of a preferred material for coil  20  is a copper flat plate made from OFHC copper  102 , 99.95% pure. 
     The magnetic molding material of body  14  is comprised of a powdered iron, a filler, a resin, and a lubricant. The preferred powdered material is manufactured by BASF Corporation, 100 Cherryhill Road, Parsippany, N.J. under the trade designation Carbonyl Iron, Grade SQ. This SQ material is insulated with 0.875% mass fraction with 75% H 3 PO4. 
     An epoxy resin is also added to the mixture, and the preferred resin for this purpose is manufactured by Morton International, Post Office Box 15240, Reading, Pa. under the trade designation Corvel Black, Number 10-7086. 
     In addition a lubricant is added to the mixture. The lubricant is a zinc stearate manufactured by Witco Corporation, Box 45296, Houston Tex. under the product designation Lubrazinc W. 
     Various combinations of the above ingredients may be mixed together, but the preferred mixture is as follows:
         1,000 grams of the powdered iron.   3.3% by weight of the resin.   0.3% by weight of the lubricant.
 
The above materials (other than the lubricant) are mixed together and then acetone is added to wet the material to a mud-like consistency. The material is then permitted to dry and is screened to a particle size of −50 mesh. The lubricant is then added to complete the material  82 . The material  82  is then ready for pressure molding.
       

     The next step in the process involves compressing the material completely around the coil  20  so that it has a density produced by exposure to pressure of from 15 to 25 tons per square inch. This causes the powdered material  82  to be compressed and molded tightly completely around the coil so as to form the inductor body  14  shown in FIG.  1  and in  FIGS. 11-13 . 
     At this stage of the production the molded assembly is in the form which is shown in FIG.  11 . After baking, the leads  16 ,  18  are formed or bent as shown in  FIGS. 12 and 13 . The molded assemblies are then baked at 325° F. for one hour and forty-five minutes to set the resin. 
     When compared to other inductive components the IHLP inductor of the present invention has several unique attributes. The conductive coil, lead frame, magnetic core material, and protective enclosure are molded as a single integral low profile unitized body that has termination leads suitable for surface mounting. The construction allows for maximum utilization of available space for magnetic performance and is magnetically self-shielding. 
     The unitary construction eliminates the need for two core halves as was the case with prior art E cores or other core shapes, and also eliminates the associated assembly labor. 
     The unique conductor winding of the present invention allows for high current operation and also optimizes magnetic parameters within the inductor&#39;s footprint. 
     The manufacturing process of the present invention provides a low cost, high performance package without the dependence on expensive, tight tolerance core materials and special winding techniques. 
     The magnetic core material has high resistivity (exceeding 3 mega ohms) that enables the inductor as it is manufactured to perform without a conductive path between the surface mount leads. The magnetic material also allows efficient operation up to 1 MHz. The inductor package performance yields a low DC resistance to inductance ratio of two milliOhms per microHenry. A ratio of 5 or below is considered very good. 
     The unique configuration of the coil  20  reduces its cost of manufacture. Coil  20  may be used in various inductor configurations other than IHLP inductors. 
     In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in the form and the proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims.