US20160268023A1 - Transfer mold compound mixture for fabricating an electronic circuit - Google Patents
Transfer mold compound mixture for fabricating an electronic circuit Download PDFInfo
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- US20160268023A1 US20160268023A1 US15/165,405 US201615165405A US2016268023A1 US 20160268023 A1 US20160268023 A1 US 20160268023A1 US 201615165405 A US201615165405 A US 201615165405A US 2016268023 A1 US2016268023 A1 US 2016268023A1
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- United States
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- mold compound
- ferromagnetic material
- mixed
- transfer mold
- coil
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- 150000001875 compounds Chemical class 0.000 title claims abstract description 91
- 238000012546 transfer Methods 0.000 title claims abstract description 28
- 239000000203 mixture Substances 0.000 title claims abstract description 7
- 239000003302 ferromagnetic material Substances 0.000 claims abstract description 70
- 230000035699 permeability Effects 0.000 claims abstract description 37
- 229910000889 permalloy Inorganic materials 0.000 claims description 7
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 239000011733 molybdenum Substances 0.000 claims description 5
- 229910000702 sendust Inorganic materials 0.000 claims description 4
- 229910000815 supermalloy Inorganic materials 0.000 claims description 4
- 239000004020 conductor Substances 0.000 description 40
- 238000000034 method Methods 0.000 description 28
- 230000008569 process Effects 0.000 description 19
- 239000000758 substrate Substances 0.000 description 18
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 13
- 230000000712 assembly Effects 0.000 description 12
- 238000000429 assembly Methods 0.000 description 12
- 239000002245 particle Substances 0.000 description 11
- 229910052742 iron Inorganic materials 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 239000000843 powder Substances 0.000 description 7
- 229910052759 nickel Inorganic materials 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000005538 encapsulation Methods 0.000 description 4
- 239000012530 fluid Substances 0.000 description 4
- 238000000465 moulding Methods 0.000 description 4
- 208000015943 Coeliac disease Diseases 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 238000009713 electroplating Methods 0.000 description 3
- 239000008393 encapsulating agent Substances 0.000 description 3
- 230000005294 ferromagnetic effect Effects 0.000 description 3
- 230000004907 flux Effects 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 230000005291 magnetic effect Effects 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 238000005453 pelletization Methods 0.000 description 1
- 239000004848 polyfunctional curative Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000001721 transfer moulding Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/0302—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity characterised by unspecified or heterogeneous hardness or specially adapted for magnetic hardness transitions
- H01F1/0306—Metals or alloys, e.g. LAVES phase alloys of the MgCu2-type
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/0001—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor characterised by the choice of material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
- B29C45/14639—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles for obtaining an insulating effect, e.g. for electrical components
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F17/00—Fixed inductances of the signal type
- H01F17/04—Fixed inductances of the signal type with magnetic core
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0003—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds having particular electrical or magnetic properties, e.g. piezoelectric
- B29K2995/0008—Magnetic or paramagnetic
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F17/00—Fixed inductances of the signal type
- H01F17/04—Fixed inductances of the signal type with magnetic core
- H01F2017/048—Fixed inductances of the signal type with magnetic core with encapsulating core, e.g. made of resin and magnetic powder
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/2804—Printed windings
- H01F2027/2814—Printed windings with only part of the coil or of the winding in the printed circuit board, e.g. the remaining coil or winding sections can be made of wires or sheets
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0206—Manufacturing of magnetic cores by mechanical means
- H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
Definitions
- an inductor made of a coil in free space is able to store only a relatively small amount of energy due to the low permeability of free space.
- the inductor can store much more energy.
- an inductor made of a coil in free space is able to store only a relatively small amount of energy due to the low permeability of free space.
- the inductor can store much more energy.
- Encapsulated electronic component assemblies with increased permeability are conventionally produced by placing ferromagnetic materials proximate the electronic components.
- the ferromagnetic materials are typically placed proximate the electronic components by way of a pick and place process or by way of an electroplating process.
- sintered ferromagnetic material is placed in the core of a coil to improve the inductance of the coil.
- the coil, including the ferromagnetic material is then encapsulated.
- the pick and place process and the electroplating process are very time consuming and increase production costs.
- FIG. 1 is an isometric view of a substrate having a plurality of inductors located thereon.
- FIG. 2 is an isometric view of one of the inductors of FIG. 1 .
- FIG. 3 is a side elevation view of the inductor of FIG. 2 .
- FIG. 4 is a flow chart illustrating an embodiment of a method of fabricating a plurality of electronic components.
- FIG. 5 is a cut away, elevation view of an embodiment of a transfer mold system.
- Ferromagnetic materials are sometimes referred to as high permeability materials.
- inductors With regard to inductors, a coil in free space functions as an inductor, but due to the low permeability of free space, the coil cannot store much energy and the resulting inductance is usually low.
- the permeability of the space within the coil increases. It follows that the coil can store more energy. Accordingly, the inductance of the coil with a ferromagnetic core is greater than an identical coil having a free space core.
- Circuits are disclosed herein that are encapsulated with mold compounds having ferromagnetic materials dispersed throughout. These circuits operate in high permeability space and, thus, operate better than conventional circuits that operate in free space. Methods for making such circuits are also disclosed.
- Ferromagnetic materials are used in many circuit applications. For example, ferromagnetic materials are commonly placed around conductors in communications circuits to increase the inductance of the conductors. By increasing the inductance of a conductor, the ability of the conductor to transmit signals is enhanced. Ferromagnetic material may also be used proximate conductors in power circuits in order to attenuate voltage spikes.
- Ferromagnetic materials include, the following materials, which are listed with their maximum relative permeability in parenthesis: ferrite M33 (750); nickel (600); ferrite N41 (3000); iron (5000); ferrite T38 (10,000); silicon GO steel (40,000); and supermalloy (1,000,000). It is noted that this is only a partial list.
- the flux density (B) of the above listed ferromagnetic materials are at least ten times higher than the flux density of a conventional mold compound material when exposed to the same field strength (H).
- the flux density of the ferromagnetic material is approximately 0.4 Tesla when in a field of approximately 100 amps/meter.
- the permeability is approximately 0.004 and the relative permeability is approximately 3,200.
- ferromagnetic material may be ground or atomized into powder that is added to a conventional transfer mold compound, referred to herein simply as “mold compound.”
- the addition of ferromagnetic material provides a mixed mold compound, which has an increased permeability over that of the original mold compound.
- the permeability of such mixed mold compound depends on the particle size of the powdered ferromagnetic material, the density of the ferromagnetic material, and many other known factors.
- the permeability of the mixed mold compound can be selected to fit specific design criteria. For example, smaller particle sizes yield lower permeability of the mixed mold compound, but the particles may be more easily dispersed in the mixed mold compound than larger particles.
- the individual powder particles are insulated from one another, which allows the mixed mold compound to have inherently distributed gaps for energy storage, which increases the permeability of the mixed mold compound.
- the relative permeability of the mixed mold compound is at least ten.
- the addition of the ferromagnetic material to the mold compound increases the relative permeability of the resulting mold compound by a factor of at least ten.
- the addition of the ferromagnetic material to the mold compound increases the relative permeability of the resulting mold compound by a factor of at least one hundred.
- the ferromagnetic material is sendust, which is approximately 85% iron, 9% silicon and 6% aluminum and has a relative permeability of up to 140,000.
- the above-described materials are mixed together and then formed into a powder, wherein the particles in the powder can have different sizes depending on the application.
- versions of permalloy may be used as the ferromagnetic material.
- Permalloys may have different concentrations of nickel and iron.
- the permalloy consists of approximately 20% nickle and 80% iron. Variations of permalloy may change the ratios of nickel and iron to 45% nickel and 55% iron.
- ferromagnetic materials include molybdenum permalloy which is an alloy of approximately 81% nickel, 17% iron and 2% molybdenum. Copper may be added to molybdenum permalloy to produce supermalloy which has approximately 77% nickel, 14% iron, 5% copper, and 4% molybdenum.
- circuits and methods of making circuits are described below wherein the circuits are encapsulated with a mold compound having the above-described ferromagnetic material dispersed throughout the mold compound.
- the ferromagnetic material serves to increase the permeability in the space proximate components in the circuit.
- the increased permeability improves the performance of many components on the circuit.
- Many of the improvements come from an increased inductance provided by the proximity of the components to the ferromagnetic material.
- the increased permeability increases the inductance of inductors and conductors.
- Increased permeability also improves signal transmission properties of many conductors.
- FIG. 1 is an isometric view of a partially completed circuit 100 .
- FIGS. 2 and 3 are views of individual components located on the circuit 100 . More specifically, FIG. 2 is an isometric view of an individual inductor assembly 114 and FIG. 3 is a side elevation view of the inductor assembly 114 .
- the inductor assembly 114 includes a coil 106 attached to a substrate 102 .
- FIG. 4 is a flow chart of a method for fabricating individual inductor assemblies 114 .
- the circuit 100 includes a substrate 102 having a surface 104 on which a plurality of electronic components 106 are located.
- the electronic components 106 are coils.
- the coils 106 function as inductors and are sometimes referred to herein as inductors 106 .
- the substrate 102 is encapsulated and singulated to form individual inductor assemblies 114 wherein each of the inductor assemblies 114 includes a portion of the substrate 102 and a coil 106 .
- the process of fabricating the inductor assemblies 114 commences with applying a plurality of conductors 120 to the surface 104 of the substrate 102 as described in step 210 of FIG. 4 .
- the coil 106 has four conductors 120 , which are referred to individually as a first conductor 121 , a second conductor, 123 , a third conductor 125 , and a third conductor 127 .
- the conductors 120 may be applied by any conventional technique for applying conductors to a substrate.
- the conductors 120 may be substantially parallel to each other as shown in FIG. 2 .
- the layout of the conductors 120 forms the boundaries of the coils 106 .
- Each coil 106 has a first end 122 and a second end 124 .
- the first end 122 is defined as the outer edge 128 of the first conductor 121 .
- the second end 124 of the coil 106 is defined by an outer edge 132 of the fourth conductor 127 .
- Each of the conductors 120 has a first end 138 and a second end 140 .
- the ends 138 , 140 also form boundaries of the coil 106 .
- wire bonds 150 are connected to the conductors 120 so as to electrically connect the conductors 120 to each other as described in step 212 of the flow chart 200 .
- the second end 140 of the first conductor 121 is connected to the first end 138 of the second conductor 123 by a first wire bond 156 .
- the second end 140 of the second conductor 154 is electrically connected to the first end 140 of the third conductor 125 by a second wire bond 162 .
- This electrical connection scheme continues for the length of the coil 106 .
- the conductors 120 and the wire bonds 150 at least partially define the coil 106 .
- the wire bonds 150 form arcs spaced a distance 170 from the surface 104 of the substrate 110 .
- the arcs each form a space between the wire bonds 150 and the conductors 120 .
- the distance 170 is approximately 120 mils (0.12 inches) or approximately 3.1 millimeters.
- a mold compound with the above-described ferromagnetic material dispersed throughout encapsulates the coil 105 . Accordingly, the distance 170 has to be great enough to allow the mold compound with the ferromagnetic material dispersed throughout to pass between the wire bonds 150 and the conductors 120 .
- the inductance of the coil 106 and thus, the inductor assembly 114 is dependent on the length and width of the coil 106 , the distance 170 between the conductors 120 and the wire bonds 150 , the number of wire bonds 150 or windings in the coil 106 , and several other factors, including the mold compound and the ferromagnetic material dispersed throughout the mold compound.
- the mixed mold compound is able to be located between the wire bonds 150 and the conductors 120 . Because the mixed mold compound includes ferromagnetic material, the permeability of the space proximate the coil 106 is improved over a coil having air or just a mold compound located therein.
- the substrate 102 has a plurality of coils 106 located thereon. Components in addition to the coils 106 or instead of the coils 106 may be located on the substrate 102 . There is a space between the wire bonds 150 and the conductors 120 on the surface 104 of the substrate 102 . If other discrete components are located on the surface 104 of the substrate 102 , they may be electrically connected to the substrate 102 by way of wire bonds, traces, and/or other conductors located on the substrate 102 . Accordingly, the aforementioned mixed mold compound having ferromagnetic material dispersed throughout is able to encapsulate such conductors and increase the inductance associated with all the conductors and components located on the substrate 102 .
- a ferromagnetic material as described above is mixed into a conventional mold compound that is used to encapsulate the circuit 100 of FIG. 1 .
- the mixed mold compound has at least two components, one component is a conventional encapsulant or mold compound and another component is the ferromagnetic material that has a higher permeability than the conventional mold compound.
- the ferromagnetic material is fifteen percent of the overall weight of the mixed mold compound. In other embodiments, the ferromagnetic material is ten percent of the weight of the mixed mold compound.
- the conventional mold compound may be a polymer, monomer, or other conventional material and may be made by pelletizing fine powder of a mixture of resin, filler, hardener, catalyst, carbon black, and other materials.
- the transfer mold compound is in a powdered or solid form and is placed in a pot where heat and pressure are applied to the transfer mold compound. The heat and pressure cause the transfer mold compound to change to a fluid state. In the fluid state, the transfer mold compound may be injected into a cavity to encapsulate a circuit. The transfer mold compound eventually solidifies to form a hard casing around the circuit.
- the conventional mold compound serves to keep contaminants from the components 106 on the substrate 102 and to insulate the components 106 from other electronic devices and may also serve to dissipate heat from the circuit 100 .
- the ferromagnetic material may be ground or atomized into powder that is added to the conventional mold compound, typically when the conventional mold compound is in a powered state and before it is placed into the pot.
- the ferromagnetic material is in the form of particles that are dispersed throughout the mold compound.
- the above-described sendust may be used as the ferromagnetic material.
- the use of fine particles of sendust or other ferromagnetic powder materials enables the ferromagnetic materials to flow with the molten mold compound around the bond wires 150 of the inductors 114 or other electronic components that are encapsulated during the molding process. The particles are fine enough to fit within the space between the wire bonds 150 and the conductors 120 .
- the circuit 100 is encapsulated per a transfer mold process as described in step 216 of the flow chart 200 .
- Examples of transfer molds and processes of transfer molding are described in U.S. Pat. No. 7,871,864 and United States published patent application 2007/0087079, both of which are incorporated herein.
- FIG. 5 A simplified embodiment of a transfer mold device 300 is shown in FIG. 5 .
- the device 300 includes three plates that are referred to individually as a top plate 306 , an intermediate plate 308 , and a bottom plate 310 .
- the top plate 306 has a plunger portion 314 that is sized to be received in a cavity or pot 316 in the intermediate plate 308 as described below.
- the top plate 306 may be connected to a press (not shown) such as a hydraulic press that forces the plunger portion 314 into the pot 316 .
- the intermediate plate 308 includes the pot 316 that receives the plunger portion 314 .
- the pot 316 receives an uncured mixed mold compound 322 , which is usually in a powdered or solid form.
- the uncured mixed mold compound 322 has been mixed to include the ferromagnetic material as described above.
- the intermediate plate 308 may have a plurality of heating elements (not shown) that serve to heat the mixed mold compound 322 in a conventional manner.
- a plurality of sprues 326 extend from the pot 316 to the bottom plate 310 .
- the sprues 326 are channels or other passages that transfer the mixed mold compound 322 to a mold cavity 328 in the bottom plate 310 .
- the bottom plate 310 is configured to be removably attached to the intermediate plate 308 .
- the bottom plate 310 is securely attached to the intermediate plate 308 using conventional mechanisms.
- the bottom plate 310 is removed from the intermediate plate 308 in order to remove the molded pieces.
- the mold cavity 328 is located in the bottom plate 310 .
- the mold cavity 328 is in the shape of the final product, which in the embodiments described herein may be a substantially box-shaped electronic component.
- vent holes may extend to the cavity 328 in order to vent air pockets located in the cavity 328 during the mold process.
- the circuit 100 is encapsulated at step 216 as described below.
- the molding process for applying an encapsulant to the circuit 100 commences with separating the bottom plate 310 from the intermediate plate 308 .
- the circuit 100 is placed into the cavity 328 and the intermediate plate 308 is attached to the bottom plate 310 .
- the uncured mixed mold compound 322 with the ferromagnetic material dispersed throughout is placed into the pot 316 .
- the mixed mold compound 322 in the pot 316 is not cured.
- the pot 316 is heated by conventional mechanisms, which heats the mixed mold compound 322 .
- the top plate 306 is applied to the intermediate plate 308 so that the plunger portion 314 extends into the pot 316 .
- Pressure is then applied to the top plate 306 in a direction 330 to compress the mixed mold compound 322 .
- the combination of heat and compression causes the mixed mold compound 322 to enter a relatively low viscosity fluid state and flow through the sprues 326 and into the cavity 328 where it eventually cures and solidifies.
- the low viscosity of the mixed mold compound in its heated fluid state enables it to fully encapsulate the coils 106 , FIG.
- the method described above encapsulates the entire circuit 100 , which contains several individual inductor assemblies 114 .
- the individual inductor assemblies 114 are then separated or singulated in a conventional manner as described in step 218 of FIG. 4 .
- the individual inductor assemblies 114 may be singulated prior to encapsulation. Accordingly, the singulation process after encapsulation is not always required.
- the use of the above-described transfer mold process enables a plurality of components to be simultaneously encapsulated with a mold compound having a high permeability.
- the low viscosity of the mixed mold compound enables the several components to be simultaneously encapsulated wherein the mixed mold compound disperses into the coils 106 .
- the resulting fabrication yields a plurality of inductor assemblies 114 .
- the inductor assemblies 114 are able to be mass produced from a single substrate 102 and are able to have higher inductance due to the ferromagnetic material in the encapsulant.
- the inductance of the inductor assemblies 114 is greatly enhanced over conventional mass produced inductors. It is noted that the inductance of the inductor assemblies 114 is dependent on the characteristics of the coils 106 in addition to the type of ferromagnetic material used, the density of the ferromagnetic material, the size of the particles used as ferromagnetic material, and other known variables affecting permeability of the ferromagnetic material.
- sufficient ferromagnetic material is added to the mold compound to increase the relative permeability of the mold compound mixture over that of the mold compound before addition of the ferromagnetic material by at least five hundred percent.
- the relative permeability of the mold compound after addition of the ferromagnetic material is increased by at least one thousand percent.
- the relative permeability of the mold compound with the ferromagnetic material added thereto is at least ten.
- the ferromagnetic material comprises at least ten percent of the weight of the mixed mold compound.
- the ferromagnetic material comprises at least fifteen percent of the weight of the mixed mold compound.
- the ferromagnetic materials encompass various conductors and wire bonds that where conventional fabrication techniques could not locate ferromagnetic materials.
- ferromagnetic materials may be quickly and efficiently placed around encapsulated electronic components through the use of the encapsulation process itself.
Abstract
A transfer mold compound mixture for use in a transfer mold device to encapsulate electronic components. A ferromagnetic material is mixed into a mold compound to produce a mixed mold compound having an increased permeability over the mold compound.
Description
- This Application is a Divisional of and claims benefit to U.S. patent application Ser. No. 13/328,665 filed on Dec. 16, 2011. Said Application incorporated herein by reference.
- Many electronic components function better when they are located in the proximity of a magnetic or ferromagnetic material. For example, an inductor made of a coil in free space is able to store only a relatively small amount of energy due to the low permeability of free space. However, when a ferromagnetic material, which has a much greater permeability than free space, is placed within the coil, the inductor can store much more energy.
- Many electronic components function better when they are located in the proximity of a magnetic or ferromagnetic material. For example, an inductor made of a coil in free space is able to store only a relatively small amount of energy due to the low permeability of free space. However, when a ferromagnetic material, which has a much greater permeability than free space, is placed within the coil, the inductor can store much more energy.
- Encapsulated electronic component assemblies with increased permeability are conventionally produced by placing ferromagnetic materials proximate the electronic components. The ferromagnetic materials are typically placed proximate the electronic components by way of a pick and place process or by way of an electroplating process. For example, sintered ferromagnetic material is placed in the core of a coil to improve the inductance of the coil. The coil, including the ferromagnetic material is then encapsulated. The pick and place process and the electroplating process are very time consuming and increase production costs.
-
FIG. 1 is an isometric view of a substrate having a plurality of inductors located thereon. -
FIG. 2 is an isometric view of one of the inductors ofFIG. 1 . -
FIG. 3 is a side elevation view of the inductor ofFIG. 2 . -
FIG. 4 is a flow chart illustrating an embodiment of a method of fabricating a plurality of electronic components. -
FIG. 5 is a cut away, elevation view of an embodiment of a transfer mold system. - Many circuits and electronic devices function better in the presence of ferromagnetic materials. Ferromagnetic materials are sometimes referred to as high permeability materials. With regard to inductors, a coil in free space functions as an inductor, but due to the low permeability of free space, the coil cannot store much energy and the resulting inductance is usually low. However, when a ferromagnetic material is inserted into the coil, the permeability of the space within the coil increases. It follows that the coil can store more energy. Accordingly, the inductance of the coil with a ferromagnetic core is greater than an identical coil having a free space core. Circuits are disclosed herein that are encapsulated with mold compounds having ferromagnetic materials dispersed throughout. These circuits operate in high permeability space and, thus, operate better than conventional circuits that operate in free space. Methods for making such circuits are also disclosed.
- Ferromagnetic materials are used in many circuit applications. For example, ferromagnetic materials are commonly placed around conductors in communications circuits to increase the inductance of the conductors. By increasing the inductance of a conductor, the ability of the conductor to transmit signals is enhanced. Ferromagnetic material may also be used proximate conductors in power circuits in order to attenuate voltage spikes.
- Ferromagnetic materials include, the following materials, which are listed with their maximum relative permeability in parenthesis: ferrite M33 (750); nickel (600); ferrite N41 (3000); iron (5000); ferrite T38 (10,000); silicon GO steel (40,000); and supermalloy (1,000,000). It is noted that this is only a partial list.
- The flux density (B) of the above listed ferromagnetic materials are at least ten times higher than the flux density of a conventional mold compound material when exposed to the same field strength (H). For example, in one embodiment the flux density of the ferromagnetic material is approximately 0.4 Tesla when in a field of approximately 100 amps/meter. The permeability is approximately 0.004 and the relative permeability is approximately 3,200.
- As described in greater detail below, ferromagnetic material may be ground or atomized into powder that is added to a conventional transfer mold compound, referred to herein simply as “mold compound.” The addition of ferromagnetic material provides a mixed mold compound, which has an increased permeability over that of the original mold compound. The permeability of such mixed mold compound depends on the particle size of the powdered ferromagnetic material, the density of the ferromagnetic material, and many other known factors. By changing the particle size and density of the ferromagnetic material, the permeability of the mixed mold compound can be selected to fit specific design criteria. For example, smaller particle sizes yield lower permeability of the mixed mold compound, but the particles may be more easily dispersed in the mixed mold compound than larger particles. In some embodiments, the individual powder particles are insulated from one another, which allows the mixed mold compound to have inherently distributed gaps for energy storage, which increases the permeability of the mixed mold compound. In one embodiment, the relative permeability of the mixed mold compound is at least ten. In other embodiments, the addition of the ferromagnetic material to the mold compound increases the relative permeability of the resulting mold compound by a factor of at least ten. In yet another embodiment, the addition of the ferromagnetic material to the mold compound increases the relative permeability of the resulting mold compound by a factor of at least one hundred.
- In one embodiment, the ferromagnetic material is sendust, which is approximately 85% iron, 9% silicon and 6% aluminum and has a relative permeability of up to 140,000. The above-described materials are mixed together and then formed into a powder, wherein the particles in the powder can have different sizes depending on the application. In other embodiments, versions of permalloy may be used as the ferromagnetic material. Permalloys may have different concentrations of nickel and iron. In one embodiment, the permalloy consists of approximately 20% nickle and 80% iron. Variations of permalloy may change the ratios of nickel and iron to 45% nickel and 55% iron. Other ferromagnetic materials include molybdenum permalloy which is an alloy of approximately 81% nickel, 17% iron and 2% molybdenum. Copper may be added to molybdenum permalloy to produce supermalloy which has approximately 77% nickel, 14% iron, 5% copper, and 4% molybdenum.
- Having described some of the ferromagnetic materials that may be used in a mixture with the mold compounds, the circuits which may be encapsulated with such mold compounds will now be described.
- Circuits and methods of making circuits are described below wherein the circuits are encapsulated with a mold compound having the above-described ferromagnetic material dispersed throughout the mold compound. The ferromagnetic material serves to increase the permeability in the space proximate components in the circuit. The increased permeability improves the performance of many components on the circuit. Many of the improvements come from an increased inductance provided by the proximity of the components to the ferromagnetic material. For example, the increased permeability increases the inductance of inductors and conductors. Increased permeability also improves signal transmission properties of many conductors.
- A circuit and a process of fabricating a circuit encapsulated with the above-described mixed mold compound will now be described. Reference is made to
FIGS. 1-4 .FIG. 1 is an isometric view of a partially completedcircuit 100.FIGS. 2 and 3 are views of individual components located on thecircuit 100. More specifically,FIG. 2 is an isometric view of anindividual inductor assembly 114 andFIG. 3 is a side elevation view of theinductor assembly 114. Theinductor assembly 114 includes acoil 106 attached to asubstrate 102.FIG. 4 is a flow chart of a method for fabricatingindividual inductor assemblies 114. - The
circuit 100 includes asubstrate 102 having asurface 104 on which a plurality ofelectronic components 106 are located. In the embodiment ofFIG. 1 , theelectronic components 106 are coils. Thecoils 106 function as inductors and are sometimes referred to herein asinductors 106. As described in greater detail below, thesubstrate 102 is encapsulated and singulated to formindividual inductor assemblies 114 wherein each of theinductor assemblies 114 includes a portion of thesubstrate 102 and acoil 106. - Referring to
FIG. 2 , the process of fabricating theinductor assemblies 114 commences with applying a plurality ofconductors 120 to thesurface 104 of thesubstrate 102 as described instep 210 ofFIG. 4 . In the embodiments of theinductor assembly 114 described herein, thecoil 106 has fourconductors 120, which are referred to individually as afirst conductor 121, a second conductor, 123, athird conductor 125, and athird conductor 127. Theconductors 120 may be applied by any conventional technique for applying conductors to a substrate. Theconductors 120 may be substantially parallel to each other as shown inFIG. 2 . The layout of theconductors 120 forms the boundaries of thecoils 106. Eachcoil 106 has afirst end 122 and asecond end 124. Thefirst end 122 is defined as theouter edge 128 of thefirst conductor 121. In the embodiment ofFIGS. 2 and 3 where eachcoil 106 has fourconductors 120, thesecond end 124 of thecoil 106 is defined by anouter edge 132 of thefourth conductor 127. Each of theconductors 120 has afirst end 138 and asecond end 140. The ends 138, 140 also form boundaries of thecoil 106. - After the
conductors 120 are applied to thesubstrate 102,wire bonds 150 are connected to theconductors 120 so as to electrically connect theconductors 120 to each other as described instep 212 of theflow chart 200. As shown inFIG. 2 , thesecond end 140 of thefirst conductor 121 is connected to thefirst end 138 of thesecond conductor 123 by afirst wire bond 156. Thesecond end 140 of the second conductor 154 is electrically connected to thefirst end 140 of thethird conductor 125 by asecond wire bond 162. This electrical connection scheme continues for the length of thecoil 106. Theconductors 120 and thewire bonds 150 at least partially define thecoil 106. - As shown in
FIG. 3 , thewire bonds 150 form arcs spaced adistance 170 from thesurface 104 of the substrate 110. The arcs each form a space between thewire bonds 150 and theconductors 120. In some embodiments, thedistance 170 is approximately 120 mils (0.12 inches) or approximately 3.1 millimeters. As briefly described above, a mold compound with the above-described ferromagnetic material dispersed throughout encapsulates the coil 105. Accordingly, thedistance 170 has to be great enough to allow the mold compound with the ferromagnetic material dispersed throughout to pass between thewire bonds 150 and theconductors 120. - It is noted that the inductance of the
coil 106 and thus, theinductor assembly 114, is dependent on the length and width of thecoil 106, thedistance 170 between theconductors 120 and thewire bonds 150, the number ofwire bonds 150 or windings in thecoil 106, and several other factors, including the mold compound and the ferromagnetic material dispersed throughout the mold compound. The mixed mold compound is able to be located between thewire bonds 150 and theconductors 120. Because the mixed mold compound includes ferromagnetic material, the permeability of the space proximate thecoil 106 is improved over a coil having air or just a mold compound located therein. - With additional reference to
FIG. 1 , at this point in the fabrication process, thesubstrate 102 has a plurality ofcoils 106 located thereon. Components in addition to thecoils 106 or instead of thecoils 106 may be located on thesubstrate 102. There is a space between thewire bonds 150 and theconductors 120 on thesurface 104 of thesubstrate 102. If other discrete components are located on thesurface 104 of thesubstrate 102, they may be electrically connected to thesubstrate 102 by way of wire bonds, traces, and/or other conductors located on thesubstrate 102. Accordingly, the aforementioned mixed mold compound having ferromagnetic material dispersed throughout is able to encapsulate such conductors and increase the inductance associated with all the conductors and components located on thesubstrate 102. - As indicated at
step 214 ofFIG. 4 , a ferromagnetic material as described above is mixed into a conventional mold compound that is used to encapsulate thecircuit 100 ofFIG. 1 . The mixed mold compound has at least two components, one component is a conventional encapsulant or mold compound and another component is the ferromagnetic material that has a higher permeability than the conventional mold compound. In some embodiments, the ferromagnetic material is fifteen percent of the overall weight of the mixed mold compound. In other embodiments, the ferromagnetic material is ten percent of the weight of the mixed mold compound. - The conventional mold compound may be a polymer, monomer, or other conventional material and may be made by pelletizing fine powder of a mixture of resin, filler, hardener, catalyst, carbon black, and other materials. Conventionally, the transfer mold compound is in a powdered or solid form and is placed in a pot where heat and pressure are applied to the transfer mold compound. The heat and pressure cause the transfer mold compound to change to a fluid state. In the fluid state, the transfer mold compound may be injected into a cavity to encapsulate a circuit. The transfer mold compound eventually solidifies to form a hard casing around the circuit. The conventional mold compound serves to keep contaminants from the
components 106 on thesubstrate 102 and to insulate thecomponents 106 from other electronic devices and may also serve to dissipate heat from thecircuit 100. - The ferromagnetic material may be ground or atomized into powder that is added to the conventional mold compound, typically when the conventional mold compound is in a powered state and before it is placed into the pot. In some embodiments, the ferromagnetic material is in the form of particles that are dispersed throughout the mold compound. For example, the above-described sendust may be used as the ferromagnetic material. The use of fine particles of sendust or other ferromagnetic powder materials enables the ferromagnetic materials to flow with the molten mold compound around the
bond wires 150 of theinductors 114 or other electronic components that are encapsulated during the molding process. The particles are fine enough to fit within the space between thewire bonds 150 and theconductors 120. - In the embodiments described herein, the
circuit 100 is encapsulated per a transfer mold process as described instep 216 of theflow chart 200. Examples of transfer molds and processes of transfer molding are described in U.S. Pat. No. 7,871,864 and United States published patent application 2007/0087079, both of which are incorporated herein. - A simplified embodiment of a
transfer mold device 300 is shown inFIG. 5 . Thedevice 300 includes three plates that are referred to individually as atop plate 306, anintermediate plate 308, and abottom plate 310. Thetop plate 306 has aplunger portion 314 that is sized to be received in a cavity orpot 316 in theintermediate plate 308 as described below. Thetop plate 306 may be connected to a press (not shown) such as a hydraulic press that forces theplunger portion 314 into thepot 316. - The
intermediate plate 308 includes thepot 316 that receives theplunger portion 314. In addition, thepot 316 receives an uncuredmixed mold compound 322, which is usually in a powdered or solid form. The uncuredmixed mold compound 322 has been mixed to include the ferromagnetic material as described above. Theintermediate plate 308 may have a plurality of heating elements (not shown) that serve to heat themixed mold compound 322 in a conventional manner. A plurality ofsprues 326 extend from thepot 316 to thebottom plate 310. Thesprues 326 are channels or other passages that transfer themixed mold compound 322 to amold cavity 328 in thebottom plate 310. - The
bottom plate 310 is configured to be removably attached to theintermediate plate 308. During the molding process, thebottom plate 310 is securely attached to theintermediate plate 308 using conventional mechanisms. After the molding process, thebottom plate 310 is removed from theintermediate plate 308 in order to remove the molded pieces. As briefly described above, themold cavity 328 is located in thebottom plate 310. Themold cavity 328 is in the shape of the final product, which in the embodiments described herein may be a substantially box-shaped electronic component. In some embodiments, vent holes may extend to thecavity 328 in order to vent air pockets located in thecavity 328 during the mold process. - Referring briefly to
FIG. 4 , thecircuit 100 is encapsulated atstep 216 as described below. The molding process for applying an encapsulant to thecircuit 100 commences with separating thebottom plate 310 from theintermediate plate 308. Thecircuit 100 is placed into thecavity 328 and theintermediate plate 308 is attached to thebottom plate 310. The uncuredmixed mold compound 322 with the ferromagnetic material dispersed throughout is placed into thepot 316. - As described above, the
mixed mold compound 322 in thepot 316 is not cured. Thepot 316 is heated by conventional mechanisms, which heats themixed mold compound 322. Thetop plate 306 is applied to theintermediate plate 308 so that theplunger portion 314 extends into thepot 316. Pressure is then applied to thetop plate 306 in adirection 330 to compress themixed mold compound 322. The combination of heat and compression causes themixed mold compound 322 to enter a relatively low viscosity fluid state and flow through thesprues 326 and into thecavity 328 where it eventually cures and solidifies. The low viscosity of the mixed mold compound in its heated fluid state enables it to fully encapsulate thecoils 106,FIG. 3 , including the region between theconductors 120 and the wire bonds 150. When the mixed mold compound in the cavity 338 cures, thecircuit 100 within thecavity 328 is encapsulated. Upon completion of the curing, theintermediate plate 308 is separated from thelower plate 310 and the encapsulatedcircuit 100 is removed. Although a basic transfer mold process has been described herein, many variations of this basic transfer mold process may be used to encapsulate circuits with mold compounds mixed with ferromagnetic particles, as will be obvious to those with ordinary skill in the art who have read this disclosure. - The method described above encapsulates the
entire circuit 100, which contains severalindividual inductor assemblies 114. Theindividual inductor assemblies 114 are then separated or singulated in a conventional manner as described instep 218 ofFIG. 4 . In other embodiments, theindividual inductor assemblies 114 may be singulated prior to encapsulation. Accordingly, the singulation process after encapsulation is not always required. - The use of the above-described transfer mold process enables a plurality of components to be simultaneously encapsulated with a mold compound having a high permeability. The low viscosity of the mixed mold compound enables the several components to be simultaneously encapsulated wherein the mixed mold compound disperses into the
coils 106. - In the embodiments described above, the resulting fabrication yields a plurality of
inductor assemblies 114. Theinductor assemblies 114 are able to be mass produced from asingle substrate 102 and are able to have higher inductance due to the ferromagnetic material in the encapsulant. The inductance of theinductor assemblies 114 is greatly enhanced over conventional mass produced inductors. It is noted that the inductance of theinductor assemblies 114 is dependent on the characteristics of thecoils 106 in addition to the type of ferromagnetic material used, the density of the ferromagnetic material, the size of the particles used as ferromagnetic material, and other known variables affecting permeability of the ferromagnetic material. - In one embodiment, sufficient ferromagnetic material is added to the mold compound to increase the relative permeability of the mold compound mixture over that of the mold compound before addition of the ferromagnetic material by at least five hundred percent. In another embodiment, the relative permeability of the mold compound after addition of the ferromagnetic material is increased by at least one thousand percent. In another embodiment, the relative permeability of the mold compound with the ferromagnetic material added thereto is at least ten. In one embodiment the ferromagnetic material comprises at least ten percent of the weight of the mixed mold compound. In another embodiment the ferromagnetic material comprises at least fifteen percent of the weight of the mixed mold compound.
- It will be appreciated from the above description that a method of encapsulating electronic circuit components has been disclosed that has several significant advantages over prior art encapsulation methods. One advantage is that the disclosed method is much less labor intensive. Electroplating of circuit components with ferromagnetic materials and picking and placing ferromagnetic materials proximate electronic components is completely eliminated. Instead, ferromagnetic materials are placed proximate circuit components by mixing the materials with mold compounds before they are used to encapsulate components. Also, since the ferromagnetic materials are dispersed in a molten transfer mold compound, they flow with the mixed mold compound into small and otherwise hard to access areas on the circuit. For example, the ferromagnetic materials encompass various conductors and wire bonds that where conventional fabrication techniques could not locate ferromagnetic materials. Thus, using the disclosed methodology, ferromagnetic materials may be quickly and efficiently placed around encapsulated electronic components through the use of the encapsulation process itself.
- While illustrative and presently preferred embodiments of the invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.
Claims (7)
1-20. (canceled)
21. A transfer mold compound mixture for use in a transfer mold device to encapsulate electronic components, said transfer mold compound mixture comprising a mold compound and at least one ferromagnetic material.
22. The transfer mold compound of claim 21 , wherein said ferromagnetic material comprises at least one of sendust, permalloy, supermalloy, and molybdenum supermalloy.
23. The transfer mold compound of claim 21 , wherein the relative permeability of the mixed transfer mold compound is at least five hundred percent greater than the relative permeability of said mold compound.
24. The transfer mold compound of claim 21 , wherein the relative permeability of the mixed transfer mold compound is at least one thousand percent greater than the relative permeability of said mold compound.
25. The transfer mold compound of claim 21 , wherein said ferromagnetic material comprises at least ten percent of the weight of said mixed mold compound.
26. The transfer mold compound of claim 21 , wherein said ferromagnetic material comprises at least fifteen percent of the weight of said mixed mold compound.
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US15/165,405 US20160268023A1 (en) | 2011-12-16 | 2016-05-26 | Transfer mold compound mixture for fabricating an electronic circuit |
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US13/328,665 US9378882B2 (en) | 2011-12-16 | 2011-12-16 | Method of fabricating an electronic circuit |
US15/165,405 US20160268023A1 (en) | 2011-12-16 | 2016-05-26 | Transfer mold compound mixture for fabricating an electronic circuit |
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US13/328,665 Division US9378882B2 (en) | 2011-12-16 | 2011-12-16 | Method of fabricating an electronic circuit |
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US15/165,405 Abandoned US20160268023A1 (en) | 2011-12-16 | 2016-05-26 | Transfer mold compound mixture for fabricating an electronic circuit |
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US10593566B2 (en) | 2017-12-27 | 2020-03-17 | Texas Instruments Incorporated | Switch-mode converter module |
US11855540B2 (en) | 2019-03-26 | 2023-12-26 | Texas Instruments Incorporated | Leadframe for conductive winding |
US11456262B2 (en) | 2020-04-30 | 2022-09-27 | Texas Instruments Incorporated | Integrated circuit |
Family Cites Families (15)
Publication number | Priority date | Publication date | Assignee | Title |
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US3243752A (en) * | 1962-03-07 | 1966-03-29 | Allen Bradley Co | Encapsulated supported coils |
US3255512A (en) * | 1962-08-17 | 1966-06-14 | Trident Engineering Associates | Molding a ferromagnetic casing upon an electrical component |
US3675174A (en) * | 1970-11-09 | 1972-07-04 | Electronic Associates | Electrical coil and method of manufacturing same |
US3824518A (en) * | 1973-03-05 | 1974-07-16 | Piconics Inc | Miniaturized inductive component |
US3848208A (en) * | 1973-10-19 | 1974-11-12 | Gen Electric | Encapsulated coil assembly |
US5589808A (en) * | 1993-07-28 | 1996-12-31 | Cooper Industries, Inc. | Encapsulated transformer |
US5846477A (en) * | 1994-12-08 | 1998-12-08 | Nitto Denko Corporation | Production method for encapsulating a semiconductor device |
US6103157A (en) * | 1997-07-02 | 2000-08-15 | Ciba Specialty Chemicals Corp. | Process for impregnating electrical coils |
JP4684461B2 (en) * | 2000-04-28 | 2011-05-18 | パナソニック株式会社 | Method for manufacturing magnetic element |
DE10024824A1 (en) * | 2000-05-19 | 2001-11-29 | Vacuumschmelze Gmbh | Inductive component and method for its production |
DE10128004A1 (en) * | 2001-06-08 | 2002-12-19 | Vacuumschmelze Gmbh | Wound inductive device has soft magnetic core of ferromagnetic powder composite of amorphous or nanocrystalline ferromagnetic alloy powder, ferromagnetic dielectric powder and polymer |
US6873241B1 (en) * | 2003-03-24 | 2005-03-29 | Robert O. Sanchez | High frequency transformers and high Q factor inductors formed using epoxy-based magnetic polymer materials |
US7169345B2 (en) * | 2003-08-27 | 2007-01-30 | Texas Instruments Incorporated | Method for integrated circuit packaging |
US8466764B2 (en) * | 2006-09-12 | 2013-06-18 | Cooper Technologies Company | Low profile layered coil and cores for magnetic components |
US7701073B2 (en) * | 2006-09-19 | 2010-04-20 | Texas Instruments Incorporated | Locking feature and method for manufacturing transfer molded IC packages |
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