Plating permeable cores

Abstract: A shield is applied to a permeable core in a predetermined pattern, where the predetermined pattern covers less than the entire surface area of the permeable core.

Description: This invention relates to plating permeable cores. Electronic transformers, for example, typically have two windings that surround separate portions of a permeable core. Magnetic flux which links both windings through the core is referred to as mutual flux, and flux which links only one winding is referred to as leakage flux. From a circuit viewpoint, the effects of leakage flux are accounted for by associating an equivalent lumped value of leakage inductance with each winding. An increase in the coupling coefficient translates into a reduction in leakage inductance: as the coupling coefficient approaches unity, the leakage inductance of the winding approaches zero. Precise control of leakage inductance is important in many applications, including switching power converters. For example, zero-current switching converters may need a controlled amount of transformer leakage inductance to form part of the power train and govern various converter operating parameters. One known zero-current switching converter is shown in Vinciarelli, U.S. Patent No. 4,415,959. Conductive shields have been used to attenuate and alter the spatial distributions of transformer magnetic fields. For example, Vinciarelli et al., U.S. Patent No. 5,546,065, issued August 13, 1996, describes using a conductive medium to confine and suppress leakage flux. In accordance with a first aspect of the present invention we provide a method comprising: covering a magnetically permeable core with a barrier coating, preferably a plastics material, more preferably Parylene, or a photodefinable epoxy, more preferably a photodefinable epoxy cured using an ultraviolet laser; and plating a conductive shield to the core, wherein the plating step comprises: (1) removing a portion of the barrier coating to expose the surface of the permeable core; or (2) pad-printing a seed layer on the permeable core; or (3) depositing a seed layer in a predetermined pattern defined by a mask and plating an outer layer on the seed layer; or (4) patterning the shield to achieve a controlled leakage inductance; the magnetic property of the core being protected during said plating step by said barrier coating. Implementations of the method may include one or more of the following features. Plating may include removing a portion of a seed layer to leave a predetermined pattern of seed layer on the permeable core and plating an outer layer on the seed layer. Plating a shield may also include electrolessly depositing the seed layer on the permeable core. Removing a portion of the seed layer may include ablating the portion of the seed layer with a laser. The method may further include generating, interactively by computer, pattern data defining the portion of the seed layer to be removed, and transferring the pattern data from a computer aided design station to a computer that controls the removal of the portion of the seed layer. The method may also include identifying a geometric configuration of the permeable core and removing the portion of the seed layer in accordance with the identified geometric configuration. Plating may also include depositing a seed layer on the permeable core in a predetermined pattern defined by a mask and plating an outer layer on the seed layer. The method may also feature identifying a geometric configuration of the permeable core and selecting the mask from a supply of masks in accordance with the geometric configuration of the permeable core. The permeable core may include a permeable core segment, and after plating, the method may feature attaching an end of the permeable core segment to an end of another permeable core segment to form a permeable core. The method may also feature adding windings to the plated permeable core and connecting the plated permeable core to a power converter circuit. The plating step may comprise depositing a seed layer on the permeable core, removing, automatically, a portion of the seed layer, and plating an outer layer on the seed layer. The plating step may comprise depositing a seed layer on the permeable core in a predetermined pattern defined by a mask, and plating an outer layer on the seed layer. Implementations of the method may include one or more of the following features. One feature includes depositing a seed layer on a surface of the permeable core before patterning and plating an outer layer on the seed layer before patterning. Patterning may include forming a pattern in a layer of resist on the outer layer and etching a portion of the outer layer and a portion of the seed layer in accordance with the resist pattern. Forming a pattern may include ablating a portion of the resist layer with a laser beam. The method may also feature identifying a geometric configuration of the permeable core and forming the pattern in the layer of resist in accordance with the identified geometric configuration of the permeable core. The plating step may comprise depositing a seed layer on the permeable core, plating an outer layer on the seed layer, ablating a resist layer on the outer layer with a laser beam to form a predetermined resist pattern on the outer layer, and etching the outer layer and the seed layer in accordance with the resist layer pattern. Before plating the magnetically permeable core, the barrier coating may be applied to prevent the plating chemicals from changing the properties of the core. The barrier coating may comprise plastics or Parylene, and may cover only a portion of the surface area of the core. Plating a conductive shield may include rack plating or barrel plating copper in an acid or alkaline bath. A portion of the barrier coating may be removed to expose the surface of the permeable core by ablating with a laser, or grinding, or using air abrasion. The plating step may comprise pad-printing a seed layer on the permeable core. The seed layer may comprise a conductive material, such as silver ink containing no iron, cobalt, or nickel. The seed layer may be printed on only a fraction of the surface area of the permeable core. The conductive shield is plated on the seed layer. The plating step may comprise coating the permeable core with photodefinable epoxy, curing the epoxy to the core, and plating the shield to the portions of the core not covered with epoxy. Implementations of the method may include one or more of the following features. Curing of the photodefinable epoxy may include using an ultraviolet laser or an ultraviolet oven. The method may also feature washing off the uncured portions of epoxy in an alcohol bath. The plating step may comprise coating the permeable core with photodefinable epoxy, curing the epoxy to the core with an ultraviolet laser, washing off the uncured portions of epoxy in an alcohol bath, further curing the epoxy in an ultraviolet oven, and barrel plating a copper layer on the exposed portion of the core using an alkaline bath. The plating step may comprise coating the permeable core with Parylene, pad-printing a seed layer of iron, cobalt, and nickel-free silver ink on top of the Parylene coating, and rack plating a copper layer on top of the seed layer using an acid bath. Implementations of the method may include one or more of the following features. A portion of the shield may be ablated with a laser to expose the surface of the permeable core. The plating step may comprise coating the permeable core with Parylene, ablating a predetermined pattern of the Parylene coating with a laser, and barrel plating a copper layer on top of the exposed portions of the permeable core using an alkaline bath. According to a second alternative aspect of the invention we provide a method comprising: pad-printing a seed layer of conductive material, preferably of silver ink, more preferably iron, cobalt, and nickel-free silver ink, on a magnetically permeable core, preferably on only a portion of the surface area of the permeable core, and preferably on top of a barrier coating in a predetermined pattern. The invention provides, in a third alternative aspect thereof, a method comprising: depositing a seed layer of conductive material on a magnetically permeable core, preferably a permeable core segment; removing, automatically, a portion of the seed layer; and plating an outer layer on the seed layer. In a fourth alternative aspect thereof, the invention provides a method of processing magnetically permeable cores comprising: for each of a plurality of magnetically permeable cores moving along an automated production line: determining a conductive shield pattern for the said permeable core; and (1) plating the determined conductive shield pattern on the permeable core or (2) patterning a plated conductive shield in accordance with the determined shield pattern to achieve a controlled leakage inductance. We provide, according to a fifth alternative aspect of the invention, a method comprising: barrel plating a conductive shield, preferably copper, to a magnetically permeable core in a predetermined pattern, wherein the barrel plating comprises an alkaline bath to deter changing the magnetic property of the permeable core. Advantages may include one or more of the following. Plating a shield in a predetermined pattern to a permeable core allows precise control over the location, spatial configuration, and amount of leakage flux. Plating also reduces air gaps between the shield and the core which insures high thermal conductivity and further control over leakage flux. A variety of shield patterns may be provided depending upon the application for the core and the core's geometric configuration. Laser ablation minimizes fixture changes and development time and reduces tooling and inventory costs while allowing cores, including cores with varying geometric configurations, to be plated with various patterns. Covering a permeable core with a barrier coating before plating a shield with an acid bath protects the core from the corrosive effects of the plating process. In an acid bath, exposed portions of the core tend to react with the acid resulting in a change in the magnetic characteristics of the core. For example, when a ferrite core containing zinc or zinc compounds is exposed to an acid plating bath there is a measurable degradation in the magnetic and core loss characteristics of the ferrite material. Using an acid bath is advantageous because a higher deposition rate is possible than in an alkaline bath. When plating in an alkaline bath, where the danger of corrosion is not present, the use of a barrier coating simplifies the plating process by allowing the shield to be plated directly to the surface of the core. A partial barrier coating may be applied in a predetermined pattern to define the portions of the core that should not be plated. Pad-printing a seed layer on the permeable core in a predetermined pattern allows precise control of where plating will be deposited on the core. Using a conductive material for the seed layer, such as silver ink, helps minimize losses attributable to the shield. A barrier coating of photodefinable epoxy allows quick curing to the surface of the permeable core by using an ultraviolet laser. Predetermined laser patterns provide the potential for curing the epoxy to a variety of geometric shapes. Other advantages and features will become apparent from the following description. In the drawings: Fig. 1a is a perspective view of a power converter. Fig. 1b is a schematic diagram of a switching power converter circuit including a transformer. Fig. 2 is a perspective view of a permeable core segment having a plated shield. Fig. 3 is a block diagram of a laser ablation manufacturing line. Figs. 4-7 are cross-sectional side views of a permeable core segment at different stages of manufacture. Fig. 8 is a block diagram of a masking manufacturing line. Fig. 9 is a perspective view of a permeable core segment in a masking fixture. Fig. 10 is a block diagram of an etching manufacturing line. Figs. 11-14 are cross-sectional side views of a permeable core segment at different stages of manufacture. Fig. 15 is a block diagram of a pad-printing manufacturing line. Figs. 16-20 are cross-sectional side views of a permeable core segment at different stages of manufacture. Fig. 21 is a block diagram of another laser ablation manufacturing line. Figs. 22-26 are cross-sectional side views of a permeable core segment at different stages of manufacture. Figs. 27-31 are cross-sectional side views of a permeable core segment at different stages of manufacture. Figs. 32-35 are cross-sectional side views of a permeable core segment at different stages of manufacture. Fig. 36 is a block diagram of a laser curing manufacturing line. Figs. 37-42 are cross-sectional side views of a permeable core segment at different stages of manufacture. Referring to Fig. 1a, a power converter 10 includes a switching power converter circuit 11 (Fig. 1b) including a transformer 14 having two windings 15a, 15b and a switch 13. The windings are wound around a permeable core 16, e.g., ferrite, having a plated shield 18, e.g., copper. Referring also to Fig. 2, permeable core 16 contains, for example, two permeable core segments 20a, 20b. To form core 16, ends 22a and 22b of segments 20a and 20b, respectively, are attached together, for example, by gluing, after shield 18 has been plated in a predetermined pattern to segments 20a and 20b. Referring to Fig. 3, a laser ablation manufacturing line 23 plates shield 18 (Fig. 2) on a series of permeable core segments 20a, 20b in a predetermined pattern by passing the core segments on a conveyor belt 24 through an electroless deposition station 25, a laser patterning station 26, and an electrolytic station 28. Referring also to Figs. 4-7, within electroless deposition station 25, a core segment 20 (Fig. 4) is cleaned at a cleaning station 30 before being passed through electroless deposition station 32 where a conductive seed layer 34 (Fig. 5) of, for example, nickel 36, is electrolessly (i.e., chemically) deposited on the entire surface of core segment 20. Seed layer 34 is approximately 0.04-0.1 mils (0.001 - 0.0025 millimeters) thick, T1. Before being passed through laser patterning station 26, segment 20 including seed layer 34 (i.e., seeded segment 20', Fig. 5) is rinsed and dried at a rinse/dry station 38. Within the laser patterning station, each seeded segment 20' is grasped by a robotic arm 40. A pattern 42 (Fig. 6) within seed layer 34 is ablated (i.e., removed, patterned) by a laser beam (not shown) generated by a laser unit 44. Robotic arm 40 may be a model RV-E2, manufactured by Mitsubishi, Inc.™, and laser unit 44 may be model LME6000 laser system, manufactured by A.B. Laser, Inc™. Pattern 42 exposes ends 22 of segment 20 such that after the shield is plated to the segment, ends 22 remain unplated and may be attached to the ends of another segment to form core 16. The configuration of pattern 42 is determined by the movement of the seeded segment with respect to the laser beam. Laser unit 44 may hold the laser beam in a fixed position while robotic arm 40 moves seeded segment 20' through the path of the laser beam, or robotic arm 40 may hold seeded segment 20' in a fixed position while laser unit 44 moves the laser beam over the surface of the seeded segment. Similarly, laser unit 44 may move the laser beam while robotic arm 40 simultaneously moves the seeded segment. For example, to ablate portions of a plated nickel layer of nominal 0.1 mil (0.0025 millimeter) thickness off of a ferrite core, a model LME6000 laser, referenced above, may be set for a beam spot size of 3.5 mils (0.0089 millimeters), a Q-switch pulse rate of 15 Khz and a lamp power of 16 Amperes. Ablation is performed at a beam scan rate of 98.4 inches/second (2500 mm/sec). A CAD station 48 is used to design pattern 42. The pattern design is then converted by CAD station 48 into pattern data for controlling the movement of either or both the robotic arm and the laser beam and for controlling when, during movement, the laser beam is generated (i.e., the laser beam may be pulsed on and off). CAD station 48 sends the pattern data to a computer 46 which controls the movement of either or both the robotic arm and the laser beam and controls when the laser beam is generated according to the pattern data. Because the movement data is stored in computer 46, seeded segments 20' having different geometric configurations can be patterned one after another on a single manufacturing line 23. When a seeded segment 20' enters laser patterning station 26, an identification (ID) station 50 determines the type of segment configuration and notifies computer 46. Computer 46 then uses pattern data previously received from CAD station 48 and associated with the determined segment configuration type to control the movement of either or both the robotic arm and the laser beam and the generation of the laser beam. Using CAD station 48, the pattern data may be quickly and easily changed such that new patterns are formed in seed layer 34. As a result, the pattern design is flexible and no tooling changes are required before ablating new patterns. Additionally, assembly time and the number of parts required for manufacturing line 23 are reduced because no fixture changes are required to ablate new patterns in the seed layer. After pattern 42 is ablated from seed layer 34, seeded segments 20' with patterned seed layers 34 (i.e., patterned seeded segments 20", Fig. 6) are passed through electrolytic station 28. In electrolytic station 28, a thick (T2, e.g., 4-5 mils or 0.1 to 0.13 mm) layer 52 (Fig. 7) of, for example, copper is electrolytically plated (using, for example, barrel plating) to patterned seed layer 34. As a result, shield 18, consisting of seed layer 34 and copper layer 52, is plated to permeable core segment 20 in a predetermined pattern. Other embodiments are within the scope of the following claims. For example, seed layer 34 (Fig. 5) may be formed from a variety of conductive metals, including, for example, copper 36'. Instead of including a robotic arm 40 in laser ablation manufacturing line 23, seeded segments 20' may be manually positioned by an operator on a tray (not shown) over which laser unit 44 moves the laser beam to ablate seed layer 34 along one or more sides of the seeded segment not resting on the tray. The operator may then manually re-position the partially patterned seeded segment on the tray such that an unpatterned side of the seeded segment may be patterned by the laser unit. Between cleaning station 30 and deposition station 32, manufacturing line 23 may include a masking station 60 where surface areas on segments 20 which are commonly unplated, for instance, ends 22, are masked such that seed layers are not deposited on these surface areas. This reduces the amount of seed layer 34 to be ablated by laser patterning station 26. As an alternative to a two segment permeable core 16, core 16 may be a single solid piece or core 16 may include more than two segments. The shields on each core segment may be identical or different depending upon the final application for core 16. Additionally, the core segments may be glued together before the shields are plated to the segments provided the process for plating the shields on the segments does not reduce the integrity of the bond between the segments. Referring to Fig. 8, an alternative to laser ablation manufacturing line 23 (Fig. 3) is masking manufacturing line 70 which does not require a laser patterning station 26. Similar to laser ablation manufacturing line 23, masking manufacturing line 70 plates shields (18, Fig. 2) on a series of permeable core segments (20, Fig. 4) in a predetermined pattern. Masking manufacturing line 70 includes a cleaning station 72, a masking station 74, an electroless station 76, and an electrolytic station 28. After a segment 20 is cleaned in cleaning station 72, a conveyor belt 79 carries the segment to a mounting station 80 within masking station 74 where the segment is mounted (manually or automatically) in a mechanical masking fixture 82 (Fig. 9). Masking fixture 82 is selected from a fixture supply 84 in accordance with the geometric configuration of the segment. The masking fixture covers portions 86 (Fig. 2) of segment 20 and when the mounted segment 85 and fixture 82 are passed through electroless station 76, a seed layer 34 (Fig. 6) of, for example, copper, is deposited only on the exposed surface area (i.e., the surface area not masked by masking fixture 82) of the mounted segment to form a pattern seeded segment 20". The patterned seeded segment 20" is then removed from fixture 82 and passed through electrolytic station 28 where a thick layer 52 (Fig. 7) of, for example, copper, is electrolytically plated (for example, by barrel plating) to the patterned seed layer. Although masking fixture 82 may be formed from many different materials, preferably masking fixture 82 is injection molded from a thermoplastic elastomer (e.g., Hytrel™, manufactured by Dupont™; Kraton™, manufactured by Shell Oil Company™; Solprene™, manufactured by Phillips Petroleum™), which accommodates the relatively high tolerances of sintered ferrite geometries. A different masking fixture 82 is molded for each different shield 18 pattern 54 (Fig. 2). One or more segments 20 may be mounted in each masking fixture 82. Referring to Fig. 10, another alternative to laser ablation manufacturing line 23 (Fig. 3) is etching manufacturing line 90 which also plates shields (18, Fig. 2) on a series of permeable core segments (20, Fig. 4). Etching manufacturing line 90 includes an electroless deposition station 25, an electrolytic station 28, and a laser patterning station 26 which operate in a manner similar to that described for laser ablation manufacturing line 23. In addition, etching manufacturing line 90 includes a resist station 94, an etching station 96, and a stripping station 98. Segment 20 (Fig. 4) is first passed, on a conveyor belt 92, through electroless deposition station 25 in which a seed layer 34 (Fig. 5) of, for example, copper, is deposited on the entire surface area of the segment to form a seeded segment 20'. The seeded segment is then passed through electrolytic plating station 28 to plate a thick layer 52 (Fig. 11) of, for example, copper, on the seed layer to form a fully plated segment 100. From the electrolytic plating station, the fully plated segment is passed through resist station 94. At a resist applying station 104, a layer 102 of resist, for example, an epoxy based polymer (e.g., KTFR or KPR, manufactured by Eastman Kodak Co.™; AZ photoresist, manufactured by Shipley Co., Inc.™, Newton, MA, USA), is applied, for instance, through spraying or dipping, on the entire surface area of the fully plated segment. The resist coated, fully plated segment 100' is then passed through a resist curing station 106 where the resist layer is cured by, for example, applying heat or ultra violet light. Laser patterning station 26 then removes a pattern 108 (Fig. 13) of resist using the techniques described above for removing a pattern 42 (Fig. 6) from seed layer 34. Conveyor belt 92 then carries the patterned resist, fully plated segment 100" (Fig. 13) to etching station 96 where the copper exposed by the removal of resist pattern 108 is chemically etched/removed (Fig. 14) from the surface (including ends 22) of segment 20. Preferably, both seed layer 34 and the thicker electrolytically plated layer 52 are of the same material, for example, copper, such that a single etching station can be used to remove both layers simultaneously. Where seed layer 34 is different from layer 52, separate chemical baths (i.e., separate etching stations) may be required. The etched segment 100''' is then passed through stripper 98 where the remaining resist layer 102 is removed to provide a permeable core segment 20 with a patterned shield 18 (Fig. 2). Using laser patterning station 26 (Fig. 3) to remove the seed layer from the permeable core segment 20 may cause localized heating in the surface of the segment that is exposed to the laser beam. Such localized heating may cause the core material, e.g., ferrite, to expand which may cause cracking or exfoliation. Etching manufacturing line 90 uses laser patterning station 26 to remove a pattern 108 within resist layer 102, not a pattern 42 (Fig. 6) within seed layer 34. As a result, laser patterning station 26 of etching manufacturing line 90 does not cause localized heating along a surface of segment 20. Referring to Fig. 15, a pad-printing manufacturing line 114 plates a shield on permeable core segment 20 in predetermined patterns by passing the core segments on a conveyor belt 24 through a cleaning station 30, a barrier coating station 109, a pad-printing station 110, a rack or barrel plating station 28, and, in some cases, a laser ablation station 26. Referring also to Figs. 16-20, permeable core segment 20 of, e.g., ferrite (Fig. 16) is cleaned at a cleaning station 30 by being dipped in a cleaning solvent of 99% isopropyl alcohol. The cleaned core segment 20 is then passed through barrier coating station 109 where a barrier coating 111 (Fig. 17) of, for example, Parylene (available from Paratronix, Attleboro, MA) is deposited on the entire surface of core segment 20 using a vacuum coating process. The barrier coating 111 typically is less than 0.001 inch (0.025 mm) thick, T3, but could range from 0.0002 inch (0.005 mm) to more than 0.001 (0.025 mm) inch in thickness. In pad-printing station 110, a conductive seed layer 34 (Fig. 18) of, for example, silver ink (available from, for example, Creative Materials, Tyngsborough, MA, USA) is pad-printed on the surface of the barrier coating of segment 112b according to a predetermined pattern using, e.g., model TP100 pad-printer available from Teca-Print U.S.A., Billerica, MA, USA. The pattern of pad-printing on each core depends upon the geometric shape of the permeable core and the desired arrangement of shielding. Multiple interrelated impressions may be required to pad-print the entire predetermined pattern on core segment 20. Seed layer 34 is approximately 0.0002 inch (0.005 mm) thick, T4. To keep uncontrolled traces of magnetic material away from the core, a silver ink, formulated to be free of magnetic materials, such as iron, cobalt and nickel (available from Creative Materials, Tyngsborough, MA) may be used in the pad-printing process. After coated segment 112b has been seeded, the seeded segment 112c (Fig. 18) is passed through plating station 28, where a layer 52 of, for example, copper is electrolytically plated to patterned seed layer 34. Plating station 28 may perform rack plating in an acid bath (not shown) that deposits a relatively thick layer T5, e.g., 4-5 mils (0.1 to 0.13 mm), of copper on seeded segment 112c. As a result, shield 18, comprising barrier coating 111, seed layer 34, and copper layer 52, is plated to permeable core segment 20 in a predetermined pattern. An acid bath gives a higher deposition rate than an alkaline bath. If barrel plating instead of rack plating were used, the barrier coating may be abraded from the edges and ends 22 of the cores during tumbling, thereby causing unwanted plating at the abraded areas. Adjustment of the tumbling speed may, in certain cases, reduce the abrasion. In some cases, plated segment 112d is passed through laser ablation station 26 (described above) where a predetermined pattern 42 (Fig. 20) is ablated by a laser beam to expose ends 22 of segment 20, resulting in ablated segment 112e. Pairs of plated segments 112d or ablated segments 112e may be mated to form permeable core 16 (Fig. 2). Referring to Fig. 21, in a laser ablation manufacturing line 115, after passing through cleaning station 30 and applying a barrier coating 111, segment 113b is then passed through laser ablation station 26 (described above) where a predetermined pattern 116 (Fig. 24) is ablated by a laser beam, resulting in pattern coated segment 113c. After ablating part of the barrier coating, a layer 52 of, for example, copper is deposited on the uncoated portions of segment 113c (Fig. 25) by passing it through an electrolytic plating station 28. Plating station 28 may include rack or barrel plating in an alkaline bath (not shown) that deposits a relatively thick layer T7, e.g., 4-5 mils (0.1 to 0.13 mm), of copper on segment 113c, resulting in plated segment 113d. An alkaline bath is preferable to an acid bath for plating copper directly onto the surface of a ferrite core because acid tends to react with the exposed portions of the core 116 (i.e., where the barrier coating has been ablated), resulting in a change in the magnetic characteristics of the core. For example, when ferrites containing zinc or zinc compounds are exposed to acid plating baths, there is a measurable degradation in the magnetic and core loss characteristics of the ferrite material. In some cases, plated segment 113d is passed through laser ablation station 26, as described above, to expose ends 22 of segment 20. Alternatively, the ends may be exposed by grinding or air abrasion. Referring to Figs. 27-31, in another manufacturing line (similar to 114, Fig. 15), after passing through cleaning station 30, core segment 20 (Fig. 27) is partially coated with a barrier coating 111 by either dipping a portion of the core in the barrier bath or pad-printing the barrier coating, such that the large end 115 of the core is left uncovered with the barrier coating (Fig. 28). Coated segment 114b is then passed through pad-printing station 110, where a conductive seed layer 34 is pad-printed on the core in a predetermined pattern 116 (Fig. 29), depending upon the geometric configuration of core segment 20. Seeded segment 114c (Fig. 29) is then passed through barrel or rack plating station 28 where a layer 52 of copper is deposited on both the seeded portions of the core as well as the portions of the core that are not covered with a barrier coating (e.g., 115) using an alkaline bath. Plated segment 114d (Fig. 30) may then be passed through laser ablation station 26, as described above. Referring to Figs. 32-35, in another manufacturing line (similar to 115, Fig. 21), after passing through cleaning station 30, core segment 20 (Fig. 32) is pad-printed with a barrier coating 111 on the ends 22 and in the interior section 118 between the legs (Fig. 33). Instead of seed coating the core, a layer 52 of, for example, copper is barrel plated 28 onto the exposed portions of segment 117b using an alkaline bath. Resulting segment 117c may then be laser ablated 26 to expose ends 22. (Fig. 35). Referring to Fig. 36, a laser curing manufacturing line 119 plates shield 18 (Fig. 2) on permeable core segments 20a, 20b (Fig. 2) in predetermined patterns by passing the core segments through a cleaning station 30, a barrier coating station 109, a laser curing station 120, a second cleaning station 30, an oven curing station 121, and a plating station 28. Referring also to Figs. 37-42, after passing through cleaning station 30, core segment 20 (Fig. 37) is partially coated with a barrier coating 111 by dipping a portion of the core in a bath of photodefinable epoxy, such as Cibatool SL 5170 (available from 3D Systems, Valencia, CA). The large end 115 of core segment 20 is left uncovered with the barrier coating 111, as shown in Fig. 38. Coated segment 122b is then passed through laser curing station 120 where a low-power ultraviolet (UV) laser 124 (HeCd laser available from omnichrome, Chino, CA) cures a predetermined pattern 123 (Fig. 39) of epoxy on the surface of core segment 20. The liquid epoxy solidifies when the laser beam (not shown) comes in contact with it. Laser-cured segment 122c is then cleaned a second time in cleaning station 30, where any uncured epoxy is washed off core segment 20. Before plating the core, the epoxy is fully cured by passing it through oven curing station 121, where a UV oven (not shown) further hardens the epoxy and drives off any remaining moisture. Typically, full curing requires approximately twenty minutes in the UV oven. Finally, in plating station 28 a layer 52 of, for example, copper is deposited on the uncoated portions of segment 122e (Fig. 41) by barrel plating the core in an alkaline bath (not shown). Barrel plating deposits) a relatively thick layer, e.g., 4-5 mils (0.1 to 0.13 mm), of copper on segment 122e, resulting in plated segment 122f. An alkaline bath is preferable to an acid bath for plating copper directly onto the surface of a ferrite core because acid tends to react with the exposed portions of the core 124 (i.e., where there is no epoxy), resulting in a change in the magnetic characteristics of the core.

Claims: A method comprising: covering a magnetically permeable core with a barrier coating, preferably a plastics material, more preferably Parylene, or a photodefinable epoxy, more preferably a photodefinable epoxy cured using an ultraviolet laser; and plating a conductive shield to the core, wherein the plating step comprises: (1) removing a portion of the barrier coating to expose the surface of the permeable core; or (2) pad-printing a seed layer on the permeable core; or (3) depositing a seed layer in a predetermined pattern defined by a mask and plating an outer layer on the seed layer, or (4) patterning the shield to achieve a controlled leakage inductance; the magnetic property of the core being protected during said plating step by said barrier coating. A method according to Claim 1, in which the barrier coating is applied to only a portion of the surface area of the core. A method according to Claim 1, in which the removing step includes: ablating a portion of the barrier coating with a laser, or grinding a portion of the barrier coating off the permeable core; or using air abrasion to remove a portion of the barrier coating. A method according to Claim 1, wherein the plating step comprises pad-printing a seed layer, preferably of conductive material, more preferably of silver ink, most preferably iron, cobalt, and nickel-free silver ink, on the permeable core, preferably on only a fraction of the surface area of the permeable core. A method according to Claim 4, wherein the plating step further comprises: plating a shield on the seed layer. A method according to Claim 1, wherein the plating step leaves the shield in a predetermined pattern, preferably configured to achieve a controlled leakage inductance, wherein the predetermined pattern covers less than the entire surface area of the permeable core. A method according to Claim 6, wherein the plating step includes: removing a portion of a seed layer to leave a predetermined pattern of seed layer; and plating an outer layer on the seed layer. A method according to Claim 7, wherein the plating step further includes: electrolessly depositing the seed layer. A method according to Claims 7 or 8, wherein the removing step includes: ablating the portion of the seed layer with a laser. A method according to any of Claims 1, or 6 to 9, further comprising: generating, interactively by computer, pattern data defining the predetermined pattern or the portion of the seed layer to be removed. A method according to Claim 10, further comprising: transferring the pattern data from a computer aided design station to a computer that controls the removal of the portion of the seed layer. A method according to any of Claims 7 to 11, further comprising: identifying a geometric configuration of the permeable core, and wherein removing is in accordance with the identified geometric configuration. A method according to Claim 6, wherein the plating step includes: depositing a seed layer in a predetermined pattern defined by a mask; and plating an outer layer on the seed layer. A method according to Claim 13, further comprising: identifying a geometric configuration of the permeable core; and selecting the mask from a supply of masks in accordance with the geometric configuration of the permeable core. A method according to Claim 1, wherein the plating step comprises: depositing a seed layer in a predetermined pattern defined by a mask; and plating an outer layer on the seed layer. A method according to Claim 1, further comprising: depositing a seed layer before patterning; and plating an outer layer on the seed layer before patterning. A method according to Claims 10 or 16, wherein patterning includes: forming a pattern in a layer of resist on the outer layer, and etching a portion of the outer layer and a portion of the seed layer in accordance with the resist pattern. A method according to Claim 17, wherein forming includes: ablating a portion of the resist layer with a laser beam. A method according to Claims 17 or 18, further comprising: identifying a geometric configuration of the permeable core, and wherein forming is in accordance with the identified geometric configuration of the permeable core. A method comprising: pad-printing a seed layer of conductive material, preferably of silver ink, more preferably iron, cobalt, and nickel-free silver ink, on a magnetically permeable core, preferably on only a portion of the surface area of the permeable core, and preferably on top of a barrier coating in a predetermined pattern. A method comprising: depositing a seed layer of conductive material on a magnetically permeable core, preferably a permeable core segment; removing, automatically, a portion of the seed layer; and plating an outer layer on the seed layer. A method of processing magnetically permeable cores comprising: for each of a plurality of magnetically permeable cores moving along an automated production line: determining a conductive shield pattern for the said permeable core; and (1) plating the determined conductive shield pattern on the permeable core or (2) patterning a plated conductive shield in accordance with the determined shield pattern to achieve a controlled leakage inductance. A method according to Claim 22, wherein the permeable cores are identical. A method according to Claim 22, wherein the plating step further comprises: depositing a seed layer on the permeable core; plating an outer layer on the seed layer; ablating a resist layer on the outer layer with a laser beam to form a resist pattern on the outer layer; and etching the outer layer and the seed layer in accordance with the resist pattern. A method according to Claim 22, wherein the plating step includes: depositing a seed layer on the permeable core; removing a portion of the seed layer in accordance with the predetermined shield pattern; and plating an outer layer on the seed layer. A method according to Claim 22, wherein the plating step includes: selecting a mask from a supply of masks in accordance with the determined shield pattern; depositing a seed layer on the permeable core in accordance with the determined shield pattern defined by the mask; and plating an outer layer on the seed layer. A method according to Claim 22, wherein patterning includes: forming a layer of resist on the plated shield in accordance with the determined shield pattern; and etching the plated shield in accordance with the determined shield pattern defined by the resist layer. A method according to Claim 22, further comprising plating the shield on the permeable core. A method according to Claim 22, wherein the permeable cores are identical. A method according to any of Claims 20 to 29, further comprising covering the magnetically permeable core with a barrier coating to protect a magnetic property of the core. A method according to Claim 30, wherein the barrier coating comprises a photodefinable epoxy. A method according to any of Claims 1 to 19, 21 to 29, or Claims 30 or 31 as appendant to any of these claims, in which the plating step comprises rack plating. A method according to Claim 32, in which the rack plating comprises plating a shield on top of a seed layer. A method according to any of Claims 1 to 19, 21 to 29, or Claims 30 or 31 as appendant to any of these claims, in which the plating includes barrel plating. A method according to Claims 32 or 34, in which the plating is performed in an alkaline bath. A method according to Claims 32 or 34, in which the plating is performed in an acid bath. A method according to any of Claims 32, 34 or 35, in which the plating comprises applying copper to the permeable core.. A method comprising: barrel plating a conductive shield, preferably copper, to a magnetically permeable core in a predetermined pattern, wherein the barrel plating comprises an alkaline bath to deter changing the magnetic property of the permeable core. A method according to Claim 38, in which the shield is plated on top of a barrier coating. A method according to Claim 38, in which the shield is plated on top of a seed layer. A method according to Claim 1 comprising the following steps in order: coating said magnetically permeable core with photodefinable epoxy; curing the epoxy to the core, preferably by an ultraviolet laser or by an ultraviolet oven; and plating said conductive shield to the portions of the core not covered with epoxy, preferably by barrel plating, preferably with copper, and preferably in an alkaline bath; the magnetic property of the permeable core being protected from alteration by said epoxy during said plating in the regions covered by epoxy. A method according to Claim 41, further comprising: washing off the uncured portions of epoxy in an alcohol bath. A method according to claim 1, wherein the plating step comprises: coating the magnetically permeable core with photodefinable epoxy, curing the epoxy to the core with an ultraviolet laser; washing off the uncured portions of epoxy in an alcohol bath; further curing the epoxy in an ultraviolet oven; and barrel plating a copper layer on the exposed portion of the core using an alkaline bath to deter changing the magnetic property of the permeable core. A method according to both Claim 5 and Claim 36, comprising the following steps in order: coating said magnetically permeable core with Parylene; pad-printing said seed layer of iron, cobalt, and nickel-free silver ink on top of the Parylene coating; and rack plating a copper layer on top of the seed layer using an acid bath, the magnetic property of the permeable core being protected from alteration by said Parylene coating during said rack plating. A method according to Claim 44, further comprising: ablating a portion of the shield with a laser to expose the surface of the permeable core. A method according to Claim 1, wherein the plating step comprises: coating the magnetically permeable core with Parylene; ablating a predetermined pattern of the Parylene coating with a laser; and barrel plating a copper layer on top of the exposed portions of the permeable core using an alkaline bath to deter changing a magnetic property of the permeable core. A method according to Claim 46, further comprising: ablating a portion of the Parylene coating to expose the surface of the permeable core. A method according to any preceding claim, wherein the permeable core comprises a permeable core segment, the method further comprising: attaching an end of the permeable core segment to an end of another permeable core segment to form a permeable core. A method according to any of Claims 1 to 19, 21 to 29, Claims 30 or 31 as appendant to any of these claims, Claims 32 to 47, or Claim 48 as appendant to any of the foregoing claims, further comprising: adding windings to the plated permeable core. A method according to any of Claims 1 to 19, 21 to 29, Claims 30 or 31 as appendant to any of these claims, Claims 32 to 47, or Claim 48 as appendant to any of the foregoing claims, further comprising: connecting the plated permeable core to a power converter circuit.

Inventors: ANDRUS LANCE L, CALDERON CRUZ R, DAVIDSON CRAIG R, VINCIARELLI PATRIZIO, ANDRUS, LANCE L., CALDERON, CRUZ R., DAVIDSON, CRAIG R., VINCIARELLI, PATRIZIO
Applicants: VLT CORP, VLT CORPORATION
Application year: 1996
Main classification: C25D5
IPC codes: C23C18, C25D5, H01F3, H01F27, H01F41