METHOD FOR MAKING INDUCTOR COIL STRUCTURE

Abstract

An electrical component is disclosed. The electrical component includes a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit and compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil for magnetically shielding the coil and leaving the terminal ends exposed for connection to the electrical circuit.

Description

FIELD OF INVENTION

The present invention relates to inductor coil structures and methods for making same.

BACKGROUND

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.

Most prior art inductive components are comprised of a magnetic core having a C-shape, and E-shape, a toroidal shape, or other shapes and configurations. Conductive wire coils are then wound around the magnetic core components to create the inductor. These types of prior art inductors require numerous separate parts, including the core, the winding, and some sort of structure to hold the parts together. Also, these inductive coils often have a shell surrounding them. As a result there are many air spaces in the inductor which affect its operation and which prevents the maximization of space.

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.

A further object of the present invention is the provision of a high current, low profile inductor which requires fewer turns of wire in the coil to achieve the same inductance achieved with larger prior art inductors, thus lowering the series resistance of the inductor.

SUMMARY

An electrical component is disclosed. The electrical component includes a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit. According to an embodiment, the electrical component may include compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil for magnetically shielding the coil and leaving the terminal ends exposed for connection to the electrical circuit. According to an embodiment, the electrical component may include compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil that magnetically shields the coil and leaves the terminal ends exposed outside the body. According to an embodiment, the electrical component may include compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil, whereby the terminal ends are exposed outside of the body and the coil is magnetically shielded. According to an embodiment, the electrical component may include compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil and enhances induction and efficiency of the coil.

BRIEF DESCRIPTION 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.

FIG. 14 is a pictorial view of an inductor constructed in accordance with the present invention and mounted upon a circuit board.

FIG. 15 is a pictorial view of the coil of the inductor and the lead frame which is attached to the coil before the molding process.

FIG. 16 is a pictorial view of the inductor of the present invention after the molding process is complete, but before the lead frame is severed from the leads.

FIG. 17 is a flow diagram showing the method for constructing the inductor of the present invention.

FIG. 18A is a sectional view of the lead frame and coil mounted in a press.

FIG. 18B is a top plan view of FIG. 18A.

FIG. 18C is a view similar to FIG. 18A, but showing the powder surrounding the lead frame and coil before pressure is applied.

FIG. 18D is a view similar to 18A, but showing the pressure being applied to the coil, lead frame, and powder.

FIG. 18E is a view similar to 18A, but showing the ejection of the lead frame and the molded inductor from the mold.

FIG. 19 is a perspective view of a modified form of the invention utilizing a coil of wire having a round cross section.

FIG. 20 is an exploded perspective view of the lead frame and coil of the device of FIG. 19 before assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings the numeral 10 generally designates an inductor of the present invention which may be 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% H₃PO₄.

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 unique configuration of the coil 20 reduces its cost of manufacture. Coil 20 may be used in various inductor configurations other than IHLP inductors.

According to a second embodiment, inductor 10 is configured as shown in FIG. 14 to be mounted on a circuit board 12. IHLP 10 includes an inductor body 14 having a first lead 16 and a second lead 18 extending outwardly therefrom. The leads 16 and 18 are bent and folded under the bottom of the inductor body 14 and are shown soldered to a first pad and a second pad 21, 22 respectively.

Referring to FIG. 15 the inductor 10 is constructed by forming a wire coil 24 from a flat wire having a rectangular cross section. An example of a referred wire for coil 24 is an enameled copper flat wire manufactured by H. P. Reid Company, Inc., 1 Commerce Boulevard, P.O. Box 352 440, Palm Coast, Fla. 32135, the wire is made from OFHC Copper 102, 99.95% pure. A polymide enamel, class 220, coats the wire for insulation. An adhesive, epoxy coat bound “E” is coated over the insulation. The wire is formed into a helical coil, and the epoxy adhesive is actuated by dropping acetone on the coil. Activation of the epoxy can also be done by heating the coil. Activation of the adhesive causes the coil to remain in its helical configuration without loosening or unwinding.

Coil 24 includes a plurality of turns 31 and also includes an inner end 27 and an outer end 29.

A lead frame 33 formed of phosphor bronze, 510 alloy, which is one half hardened, includes first lead 16 which has one end 35 welded to the inner end 27 of coil 24. Lead frame 33 also includes a second lead 18 which has one end 38 welded to the outer end 29 of coil 24. Leads 16 and 18 include free ends 37, 40 which are shown to be attached to the lead frame 33 in FIG. 15. The welding of ends 35, 38 to the inner end 27 and the outer end 29 of coil 24 is preferably accomplished by a resistance welding, but other forms of soldering or welding may be used.

Referring to FIGS. 18A and 18B, a pressure molding machine 68 includes a platten 71 having a T-shaped lead frame holder 70 in communication with a rectangular die 72. Platten 71 is slidably mounted for vertical sliding movement on slide posts 74 and is spring mounted on those posts 74 by means of springs 76. A base 78 includes a stationary punch 80 which projects upwardly into the rectangular die 72 as shown in FIG. 18A.

The lead frame and coil assembly shown in FIG. 15 is placed in the T-shaped lead frame holder 70 as shown in FIGS. 18A and 18B. In this position the coil is spaced slightly above the upper end of stationary punch 80.

Referring to FIG. 18C a powdered molding material 82 is poured into the die 72 in such a manner as to completely surround the coil 24. The leads 16, 18 extend outwardly from the powdered material 82 where they are connected to the lead frame 33.

The magnetic molding material is comprised of a first powdered iron, a second powdered iron, a filler, a resin, and a lubricant. The first and second powdered irons have differing electrical characteristics that allow the device to have a high inductance yet low core losses so as to maximize its efficiency. Examples of preferred powdered irons to use in this mixture are as follows: a powdered iron manufactured by Hoeganaes Company, River Road and Taylors Lane, Riverton, N.J., under the trade designation Ancorsteel 1000C. This 1000 C material is insulated with 0.48% mass fraction with 75% H₃PO₄. The second 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% H₃PO₄.

The powdered magnetic material also includes a filler, and the preferred filler is manufactured by Cyprus Industrial Minerals Company, Box 3299, Ingelwood, Calif. 80155 under the trade designation Snowflake PE. This is a calcium carbonate powder.

A polyester 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 Flat Black, Number 21-7001.

In addition a lubricant is added to the mixture. The lubricant is a zinc stearate manufactured by Witco Corporation, Box 45296, Huston, 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 first powdered iron. 1,000 grams of the second powdered iron. 36 grams of the filler. 74 grams 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 added to the die 72 as shown in FIG. 18C.

The next step in the process involves the forcing of a movable ram 87 downwardly onto the removable punch 84 so as to force the punch 84 into the die 72. The force exerted by the removable punch 84 should be approximately 15 tons per square inch to 20 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. 14 and in FIG. 18E.

Referring to FIG. 18E an ejection ram 86 is lowered on to platten 71 so as to force platten 71 downwardly against the bias of springs 76. This causes the stationary ram 80 to eject the molded assembly from the die 72. At this stage of the production the molded assembly is in the form which is shown in FIG. 16. The molded assemblies are then baked at 325° F. for one hour and forty-five minutes to set the polyester resin.

The next step in the manufacturing process is to severe the lead frame 33 from the leads 16, 18 along the cut lines 42, 44. The leads 16, 18 are then bent downwardly and inwardly so as to be folded against the bottom surface of the inductor body 14.

The various steps for forming the inductor are shown in block diagram in FIG. 17. Initially one of the wire ends 27, 29 is welded to its corresponding end 35, 37 of leads 16, 18 as represented by block 145. Next the coil is wound into a helix as shown by block 146. Block 150 represents the step of welding the other end 27, 29 to its corresponding lead 16, 18. The coil wire includes an epoxy coat of bonding material described above. A bonding step 149 is achieved by applying the acetone 148 or heat to cause the bonding material to bind or adhere the various turns 31 of coil 24 together.

Next, at step 152 the powdered magnetic material is mixed together adding ingredients 154, 156, 158, 160, and 162.

The pressure molding step 64 involves the application of pressure as shown in FIGS. 18A through 18E. The parts are then heated to cure the resin as shown in box 165.

Finally after the curing is complete the bending and cutting step involves cutting off the lead frame 25 and folding the leads 16, 18 against the bottom surface of the inductor body 14.

Then compared to other inductive components the IHLP inductor of the present invention has several unique attributes. The conductive winding, 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's footprint.

The manufacturing processes of the embodiments provide 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.

Referring to FIGS. 19 and 20 a modified form of the invention is designated by the numeral 88. Inductor 88 is formed from a coil 90 of wire having round cross section. The coil 90 includes a first coil end 92 and a second coil end 94. A lead frame 96 includes a first lead 98 and a second lead 100 having first and second lead ends 102, 104.

The method of assembly of device 90 is different from the device 10 shown in FIGS. 14-18. With device 90, the coil is wound first and is heat bonded during winding. Then the coil ends 92, 94 are welded to the lead ends 102, 104 respectively. The mixed powdered material is then applied and the pressure molding process is accomplished in the same fashion as described before. Finally the leads 98, 100 are cut off and bent downwardly under the bottom of the device 10.

The position of the leads 98, 100 can be varied without detracting from the invention. Also, it is possible to put more than one coil within a molded part. For example, it would be possible to put two or more coils 24 within the molded body 10 or two or more coils 90 within the molded body 89.

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.

Claims

1. An electrical component comprising: a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit; and,compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil for magnetically shielding the coil and leaving the terminal ends exposed for connection to the electrical circuit.

2. An electrical component comprising: a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit; and,compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil that magnetically shields the coil and leaves the terminal ends exposed outside the body.

3. An electrical component comprising: a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit; and,compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil,whereby the terminal ends are exposed outside of the body and the coil is magnetically shielded.

4. An electrical component comprising: a current conducting coil having inside and outside surface and terminal ends that are configured for connection to an electrical circuit; and, compressed iron particles that form a body which completely contacts the inside and outside surfaces of the coil and enhances induction and efficiency of the coil.