EP0473875B1 - Method for producing a HF-magnetic coil device in chip-construction - Google Patents

Description

The present invention relates to a method for producing an RF magnetic coil arrangement in chip design according to the preamble of claim 1.

With the increasing miniaturization of electrical circuits, which has led in particular to surface-mounted circuits (SMD) with components in the so-called "chip" design, there is a need to also use HF magnet coil arrangements, such as toroidal transformers, with magnet cores Provided chokes, transformers, coils and the like, with very small dimensions in chip design. Annular magnetic cores, which have an outer diameter of less than 6.3 mm and accordingly an inner diameter of the bore of less than 2 mm, can practically no longer be wound with automatic winding machines. With an inner diameter of the bore of 2 mm, winding by hand is still possible, but this is not possible for large quantities due to price reasons and also does not lead to the required tight tolerances of the electrical values. The winding shapes that cannot be observed exactly not only cause deviations in the inductance values, but also lead to very large variations in the capacitance values.

US Pat. No. 4,536,733 describes an HF transformer with a toroidal core made of ferrite material for energy supply, one winding of which consists of wire wound on the toroidal core and the second winding of which consists of individual, correspondingly shaped sheet metal parts which together with printed conductor tracks on a circuit board, which result in turns of the winding.

JP-AS 1-278707, published in Patents Abstracts of Japan, E-882, Jan. 31, 1990, Vol.14 / No.55, describes an induction coil in chip design and a method for its production. At least two parallel rows of holes are created in a flat body made of magnetic material. Between these rows of holes, conductor tracks are formed on the upper flat side of the body parallel to one another and perpendicular to the edge sides and on the lower flat side of the body also parallel to one another, but at an acute angle to the edge sides, that is to say arranged obliquely over this flat side, in such a way that they run helically around the body and adjoin two holes on the lower flat side. The holes are metallized on their inner surfaces, so that a coil-shaped circuit results.

US Pat. No. 3,477,051 describes a magnetic coil arrangement in chip design, which contains an annular magnetic core embedded in plastic material and at least one winding made of at least one turn and guided through the magnetic core, the turns consisting of conductor track parts and which run parallel to the end face of the magnetic core are composed of conductor track parts running parallel to the axis of the magnetic core and inserted in the embedding plastic. The embedding plastic is produced in an injection molding process around the entire ring core, ie both on the two end faces as well as on the outer surface and the inner surface of the interior of the ring core, in one operation. In this process, channels are simultaneously embossed in the embedding plastic in such a way that these channels run helically around the toroid according to the desired coil. The channels are later filled with metal or their surfaces are metallized, so that a magnetic component results which has at least one winding consisting of turns. This component is then placed on a carrier body or in recesses of a carrier body which has the shape of the chip with corresponding connection and contacting surfaces with which the ends of the at least one winding are electrically connected.

US Pat. No. 3,486,149 describes an improved production of the magnetic coil arrangement just illustrated. In the process of reshaping the ring-shaped magnetic core, not only is this core encased in a plastic body with depressions for the coil turns, but at the same time a housing is also produced, which is also provided with corresponding depressions for conductor tracks to connecting surfaces and with plated-through holes in this working step. The housing is preferably rectangular and flat and has pins on one of its narrow side faces for use in holes in printed circuits.

The invention is based on the object of specifying a method for producing an HF magnet coil arrangement, with which constant electrical values can be achieved even in the case of large quantities.

This object is achieved with the features of claim 1. Preferred further developments are specified in the subclaims.

In the context of this invention, the term “annular magnetic core” encompasses all magnetic cores which have at least one through opening surrounded by magnetic material exhibit; the magnetic cores can thus also be rectangular, square or oval and they can also have more than one opening, for example double-hole cores. The recess in the base body is of course adapted to the cross-sectional shape of the magnetic core in these cases.

In the context of this invention, the term "RF magnet coil arrangement" also includes the fact that other electrical components, e.g. Capacitors or resistors, which are integrated on or on the surfaces of the base body or in its interior, can be present. For the sake of simplicity, however, the invention is only described on the basis of individual arrangements with magnetic cores which have a circular cross section.

The invention is explained in more detail below.

The basic idea of the invention is to assemble the individual windings of the at least one winding both by surface-mounted conductor track parts and by through-holes located in bores in order to achieve a completely or largely complete mechanical, but also inexpensive series production with a consistently high quality to achieve the electrical properties. An essential aspect of the invention is seen in the fact that a base body is used in which the toroidal core is inserted and that the sections of the individual turns running parallel to the axis of the toroidal core are accommodated in bores of this base body. Depending on the material used and its thickness, holes with diameters of up to 0.1 mm can still be mastered with metal drills. Laser drilling is recommended for even smaller bore diameters. These holes are then plated through, depending on the material and Offer dimensions different processes. With larger diameters in the region of 0.3 mm, you can either press electrically conductive paste into these holes or press in liquid solder. An electroplating process is of particular importance here. The surface electroplating of plastic bodies with electrically conductive coatings is well known. With very small bore diameters, however, there is a risk that the electroplating liquid will no longer penetrate into the bore by itself. In this case, it is possible to create a vacuum above the electroplating bath that receives the base body, at least for a short time or also pulsatingly, whereby the electroplating liquid is sucked into the capillary-shaped bore. By using ultrasound, high penetration depths can be achieved even in narrow bores.

The base body used, which receives the magnetic core, is either laminated on its one side, called the base side, either before contacting through the bores with the corresponding portions of the turns running perpendicular to the bores, or this lamination is carried out only subsequently. This lamination can be done either by providing the entire surface with an electrically conductive coating and etching off the parts that are not required, or by printing or vapor-coating the corresponding conductor tracks separately. The then still missing parts for completing the coils are achieved by a cover part which is applied to the base body on the side opposite the base part and which contains conductor tracks laminated on similarly to the base part. Depending on the technology used, this cover part can be applied before or after the drilling process.

The through-contacting of conductor tracks is known. If this technology is used, the lid can be retrofitted. The other possibility is to apply the cover before drilling and at the same time to drill through the base body and to make contact with one of the methods specified.

Since all of these process steps can be carried out by machine, a large number of such coils or toroidal core transformers can be produced simultaneously in a grid of, for example, 100 x 100 elements, and the finished components are subsequently, as is known from wafers, by sawing or another separation process isolated.

Instead of providing a base body in which the metallic connections parallel to the axis of the magnetic core are subsequently realized via bores, one can also proceed in such a way that these conductor webs are formed by layer-by-layer application of electrically conductive material. In this case, a base plate is used, on which electrically conductive material, for example silver, is applied, for example vapor-deposited or printed, at locations where these conductor tracks are to be produced. This method can be used to produce metallic columns of the desired order of magnitude of several millimeters in length and diameters of approximately 0.1 mm, it being possible to carry out the application process in several stages in order to harden or mechanically harden the material already applied stabilize. With this method, it is advisable to arrange the magnetic cores on this base plate before the columnar conductor tracks are applied and to fix them firmly with this plate, so that these columnar conductor webs are then in close proximity can bring up to the magnetic cores. The space between the surface and the upper edge of the magnetic cores, which has not yet been filled, is then filled by electrically insulating material, for example plastic, using an immersion bath or a spraying or printing process.

A similar method of forming columnar traces can be achieved using whisker technology. It is a process that has been known for years, in which, by electrolytic deposition and in particular by condensation from the gas phase, metals can also be formed by germ growth, usually in a hydrocarbon atmosphere, material rods with diameters up to 1 µm and lengths up to several millimeters.

• a) eine vorgefertigte Platte aus Gießharz wird mit einer Matrix einer Vielzahl von die Ausnehmung ergebenden, durchgehenden Öffnungen und wenigstens zwei Referenzöffnungen versehen und auf eine ebene, geheizte Unterlage gelegt, wonach in jede Ausnehmung Gießharz in einer Menge gefüllt wird, die das Volumen des später einzusetzenden Magnetkernes berücksichtigt,
• b) in die Öffnungen werden elektrisch und auf Maßhaltigkeit geprüfte Ringmagnetkerne aus Ferritmaterial eingesetzt, gegebenenfalls noch vorhandene Leerräume insbesondere im Innenraum der Magnetkerne werden mit Gießharz gefüllt,
• c) Trocknen der so vorbereiteten Platte bei 60°C und danach Aushärten bei 120°C,
• d) erforderlichenfalls werden die großen Flächen der Platten planparallel geschliffen,
• e) Aufbringen von je einer gereinigten Verbundfolie (Dicke 25 µm) aus einer Folie aus Polyimid, das hochwarmfest ist und keine Schmelztemperatur besitzt (Kapton-Folie), und Kupfer (Dicke 17 µm) auf die planparallelen Flächen der Platte,
• f) erneutes Trocknen der so vorbereiteten Platte, eingespannt zwischen zwei Heizplatten, bei 60°C und danach Aushärten bei 120°C,
• g) definiertes Anordnen der Platte auf einer Vorrichtung unter Ausnutzung der Referenzöffnungen als Zentrierhilfe und rechnergesteuertes Erzeugen der Bohrungen für die Durchkontaktierungen entsprechend einem vorgegebenen, die gewünschten Windungszahlen berücksichtigenden Muster,
• h) Erzeugen der Durchkontaktierungen in den Bohrungen durch galvanisches Abscheiden von Metall (Kupfer) an den Innenwänden der Bohrungen nach an sich bekannten Verfahren,
• i) Erzeugen
  • der Leiterbahnen, die die Metallisierungen in den Bohrungen entsprechend der für die Windungen der Wicklungen erforderlichen Führung verbinden,
  • der Kontaktflächen für die Verbindung der Wicklungen mit der gedruckten SMD-Schaltung,
  • und der Leiterbahnen, die die Enden der jeweiligen Wicklungen mit den Kontaktflächen verbinden, entsprechend dem gleichzeitig für den Verfahrensschritt g) gültigen vorgegebenen Muster durch Ätzen der Kupferfolie nach für die Herstellung gedruckter Schaltungen bekannten Verfahren,
• j) automatische elektrische Prüfung der fertigen Übertrager und davor oder danach Aufteilen der Platte in die einzelnen Ubertrager insbesondere durch Sägen längs vorgegebener Trennlinien,

A preferred further process consists of the following process steps:

• a) a prefabricated plate made of casting resin is provided with a matrix of a plurality of through openings and at least two reference openings resulting in the recess and placed on a flat, heated surface, after which casting resin is filled into each recess in an amount which corresponds to the volume of the later magnetic core to be used,
• b) electrical and magnetically tested ring magnetic cores made of ferrite material are inserted into the openings, empty spaces which may still be present, in particular in the interior of the magnetic cores, are filled with casting resin,
• c) drying the prepared plate at 60 ° C and then curing at 120 ° C,
• d) if necessary, the large areas of the plates are ground plane-parallel,
• e) applying a cleaned composite film (thickness 25 µm) made of a film made of polyimide, which is highly heat-resistant and has no melting temperature (Kapton film), and copper (thickness 17 µm) on the plane-parallel surfaces of the plate,
• f) drying the plate prepared in this way, clamped between two heating plates, at 60 ° C. and then curing at 120 ° C.,
• g) defined arrangement of the plate on a device using the reference openings as a centering aid and computer-controlled creation of the holes for the through-plating in accordance with a predetermined pattern, taking into account the desired number of turns,
• h) generation of the plated-through holes in the bores by galvanic deposition of metal (copper) on the inner walls of the bores by methods known per se,
• i) Generate
  • the conductor tracks that connect the metallizations in the bores in accordance with the guidance required for the windings of the windings,
  • the contact surfaces for connecting the windings to the printed SMD circuit,
  • and the conductor tracks that connect the ends of the respective windings to the contact areas, in accordance with the predetermined pattern that is also valid for process step g), by etching the copper foil according to methods known for the production of printed circuits,
• j) automatic electrical testing of the finished transducers and before or after dividing the plate into the individual transducers, in particular by sawing along predetermined dividing lines,

A modification of this method provides that instead of a plate made of casting resin, a plate made of thermoplastic is used and the spaces in the openings between the magnetic cores and the plate are filled with hardenable casting resin.

On the basis of the embodiments shown in the figures, the invention is explained together with exemplary embodiments.

• Fig. 1 einen Schnitt durch einen Ringkernübertrager mit Deckel und Bodenteil,
• Fig. 2 einen aufgeschnittenen Ringkernübertrager nach Fig. 1,
• Fig. 3 eine gegenüber den Fig. 1 und 2 verbesserte Ausführungsform eines Ringkernübertragers mit durchgehender Ausnehmung, perspektivisch,
• Fig. 4 einen Schnitt durch den Ringkernübertrager nach Fig. 3.

Show it:

• 1 shows a section through a toroidal core transformer with cover and base part,
• 2 shows a cut toroidal transformer according to FIG. 1,
• 3 an improved embodiment of a toroidal core transformer with a continuous recess compared to FIGS. 1 and 2, in perspective,
• 4 shows a section through the toroidal core transformer according to FIG. 3.

1 consists of a base body 1, an annular magnetic core 2 inserted therein and a cover 3. The base body 1 is designed, for example, as a thermoplastic body and has a recess the size of the magnetic core 2. The magnetic core 2 is inserted into this recess. The magnetic core 2 has an outer diameter of approximately 4 mm and an inner diameter of approximately 1.5 mm. The base body 1 consists, for example, of thermoplastic material, in which the recess for the magnetic core is already provided in the production, or of a material in which this recess is subsequently, e.g. is produced by drilling.

The magnetic core 2 inserted into the base body 1 is flush with the surface of the base body 1. The height of the base body 1 is approximately 0.5 mm greater than the height of the magnetic core, so that the base body 1 has a closed, non-perforated bottom surface 4. The cover 3 has a layer thickness of approximately 1 mm. The outer surface of the cover 3 and the bottom surface of the base body 1 have vapor-deposited or printed electrical conductor tracks 5, the ends of which each connect a point above or below the core bore of the magnetic core 2 with a point outside the magnetic core 2.

Fig. 2 shows very clearly the conductor routing in a toroidal core transformer with two coils 6 and 7. The respectively horizontal conductor parts of the turns are formed by the already mentioned conductor paths 5 on the cover 3 or the bottom surface 4 of the base body 1. The vertical sections 8 of each Windings of the coils 6 and 7 are realized through bores which run through the base body 1 in the axial direction of the magnetic core 2. In the exemplary embodiment shown, these bores have a bore diameter of 0.3 mm. They are filled with electrically conductive material and each connect an electrical conductor track on the bottom surface 4 with a conductor track on the cover 3.

A production method for a toroidal core transformer is described below, in which the recess in the base body is not continuous, according to FIGS. 1 and 2.

In a matrix plate made of thermoplastic plastic of 16 cm x 16 cm, 20 x 20 = 400 recesses for 400 ring cores are provided at intervals of 8 mm. This matrix plate is equipped with 400 magnetic cores 2 of the dimensions given above. The matrix plate has on its bottom surface a thin copper layer, as is known from printed circuits; if necessary, it can also be underlaid with a thin polylimide film (Kapton film). Then the cover part 3 is glued or welded onto the assembled matrix plate. The cover part 3 also has a continuous conductor layer on its outside. Then the individual holes are drilled through the cover part 3 and the matrix plate in an automatic process, which holes are to form the already mentioned vertical sections 8 of the coils 6 and 7. A laser drilling method or a mechanical drilling method is suitable for this method, for example. Mechanical drilling can handle bore diameters of up to 0.1 mm, while laser drilling can reproduce even smaller ones.

The holes are then completely or partially filled with electrically conductive material so that a Through-contacting between the electrical conductor tracks of the bottom surface 4 and the cover 3 results. Either electrically conductive paste can be used for this purpose, which is injected under very small bore diameters under pressure, or a process of galvanic metallization of plastic surfaces is used. In the case of very small bore diameters, it is advisable to expel the air contained in the bore by using a vacuum. Since the bottom surface 4 of the matrix plate is completely closed except for the bores, this surface can also be pressurized and the plating liquid can be pushed through the bores from this side or processed with negative pressure on this side in order to suck it through from the other side until the bores are completely or are partially closed.

Suitable processes are described, for example, in the magazine "productronic 1/2 - 1988, pages 80-82" in connection with the through-contacting of printed circuit boards. In particular, the squeeze-rolling process mentioned there for forced flooding of the holes appears relevant for the present purpose.

As soon as the electrically conductive connections have been reached through the bores to the corresponding conductor tracks 5 on the cover 3 and the bottom surface 4, the electrical conductor tracks are produced on these latter two parts by a customary photo-etching process by placing the unnecessary conductive areas on them be removed from both surfaces. The conductor tracks can also be selectively printed or stamped on. Then the two surfaces of the cover 3 and the bottom surface 4 carrying the conductor tracks are provided with a synthetic resin coating in order to mechanically protect these surfaces, which can be done in an immersion bath. It is However, make sure that the contact surfaces 9 (connection pads) for the coils 6 and 7 remain free of plastic coating, which is achieved for example by a previous lamination. This lamination is then removed and the entire plate is drawn through a soldering bath, as a result of which these connecting pads 9 protrude slightly as tin soldering feet, so that the later toroidal transformer is designed as an SMD module.

Then the 400 toroidal transformers, which are still connected in the matrix plate, are tested electrically, whereby any defective transmitters are given a color dot.

After testing, the matrix plate is sawn to separate the toroidal core transformers.

Depending on the hole diameter used for the plated-through holes, it may be necessary to clean the holes before inserting the electrical conductor. For this purpose, for example, a plasma cleaning process is available, as described, for example, in the magazine "productronic 1/2 - 1988, pages 71-72".

The embodiment shown in FIG. 3 differs from the embodiment of FIGS. 1 and 2 in that the cover 3 has been omitted. As is clear from the explanation of FIG. 4, the bottom part 4 is also configured differently; it has a continuous opening for the magnetic core, which is filled with casting resin. Otherwise, the same reference numerals are used for the same parts as in FIGS. 1 and 2. The conductor tracks 5 on the top 10 and the bottom 11 of the base body 1 are located on foils 12 made of polyimide.

Polyimide films are sold under the trademark "Kapton". These foils are highly heat-resistant, so they can withstand high temperatures, have no melting temperature, they only carbonize at approx. 800 ° C, and have a very high electrical resistance. With these properties, they serve as a heat buffer during the hardening of the casting resin and the subsequent cooling.

A manufacturing method for a toroidal core transformer according to FIG. 3 is described below with reference to FIG. 4. If the same or corresponding procedural measures as for core transformers according to FIGS. 1 and 2 are to be used, e.g. The explanation is not repeated for the production of the bores, the conductor tracks on the surfaces of the base body, the metallizations in the bores or the end pads.

First, one or more sheets of castable epoxy resin with the desired dimensions (length, width, thickness) are cast in a vacuum and cured at approx. 120 ° C. The recesses 13 is shown in the drawing by dashed lines, because due to the subsequent joint curing of the base body 1 and the filling 15 made of the same cast resin, a transition is practically no longer recognizable. The recesses 13 for the magnetic cores 2 (for example made of ferromagnetic ceramic material) are positioned exactly in accordance with the number of transmitters to be manufactured. Such a matrix has, for example, a plate with the dimensions 16 cm × 16 cm and contains 400 recesses 13. Then holes are drilled or milled through the plate. In addition, two holes for reference holes are drilled at defined locations. The plate can also be made of thermoplastic material consist, for example, of polyamide, which has a particularly low epsilon value.

The magnetic cores 2 to be inserted into the recesses 13 are checked electrically and for dimensional accuracy and then inserted into the recesses 13 of the plate, which are placed on a flat, heated surface, e.g. a glass plate, after a small amount of casting resin has been filled into the recesses 13 beforehand, which can in particular be carried out fully automatically. The interior of the magnetic cores 2 is then filled with the same casting resin. Since the thickness of the plate is slightly, e.g. 0.5 mm, larger than the height of the magnetic cores 2, thin insulating layers 14 are formed from the same casting resin as the filling 15 in the interior of the magnetic cores 2. The casting resin for the interior of the magnetic cores 2 can also be filled with ferrite powder, in order to influence the electrical properties of the entire structure in the desired manner.

The plate prepared in this way is then dried at 60 ° C. and then cured at 120 ° C. If necessary, the hardened plate is subjected to a grinding process to ensure the plane parallelism required for further processing.

After cleaning with grease-removing and dirt-removing agents, it is advisable to dry the plate in an oven at 100 ° C. Then composite films are applied to each side, which have also been cleaned well and which consist of polyimide film of the type described above (25 µm thick) and copper coating (17 µm thick). This is done by rolling the composite films.

Finally, the structure is clamped between two plates, dried and hardened again.

The plate is then clamped with its reference holes onto a device with which the holes 16 for the plated-through holes are produced, in particular drilled, in accordance with the predetermined pattern, taking into account the number and position of the turns and windings of the individual coils.

This predetermined pattern, which is to be referred to as a layout, is produced in a computer-controlled manner and has the taps required for the required number of turns of the desired windings and also contains the masks for the later production of the conductor tracks 5.

The plates are then plated through by galvanically producing 16 metal coatings on the inner surfaces of the holes. Photoresist is then applied to the copper layers of the upper side 10 and the lower side 11, the pattern for the conductor tracks is generated using the layout, exposed and etched in a manner known per se, so that the conductor tracks 5 are formed.

In this way, a plate is created with a large number of RF magnet coil arrangements, which can already be tested electrically in this state. The individual arrangements are then separated by means of a circular saw by cuts along predetermined lines.

If necessary, the individual components can also be soldered to a body specially manufactured for SMD circuits and also provided with a protective cap and are then ready for the final test.

Claims (14)

1. Process for manufacturing a high frequency magnetic coil arrangement in a chip construction, with a magentic core (2) bedded in a body made of insulating material and at least one coil (6, 7), which is assembled from individual conducting members running parallel to the axis of the magnetic core and individual conducting members running at right-angles to the axis of the magnetic core, gripping around the magnetic core, wherein a casing (1) with a number of recesses (13) for the uptake of a corresponding number of magnetic cores (2) is formed, and the magnetic core is inserted into the recesses, and layers with the necessary conducting members running at right-angles to the axis of the magnetic core are applied on the upper and/or the underside of the casing (1), the said layers also having connections for the coil(s), and the necessary borings for the conducting members are formed running parallel to the axis of the magnetic core, and the borings are filled with conductive material, and the chips are then separated by sawing or another separation process.
2. Process in accordance with claim 1 wherein the recesses (13) in the casing (1) for the uptake of the magnetic coil (2) do not fully pass through the casing so that there is a closed surface onto which the layer with conducting members is applied.
3. Process in accordance with either claim 1 or 2 wherein a covering member (3) and/or a base member (4) which contains the layer with the conducting members, are or is attached, on the side of the casing (1) with the recesses (13) for the magnetic coil.
4. Process in accordance with either claim 2 or 3 wherein a copper sheet is employed for the formation of the layer with the conducting members and from which the unrequired surfaces are etched out.
5. Process in accordance with either claim 2 or 3 wherein the conducting members are pressed or steamed on to form the layer with the conducting members.
6. Process in accordance with any one of claims 1 to 5 wherein the filling of the borings with conductive material occurs by means of one of the following alternatives:

   a) Pressing in soldering tin;

   b) Pressing in conductive paste;

   c) An electroplating process by means of which conductive material is deposited.
7. Process in accordance with any one of claims 4 to 6 wherein the layer with conducting members is made of a sheet of polyamide onto which the copper layer is applied.
8. Process in accordance with claim 3 wherein the layer is applied on the outside of the covering member (3) or of the base member (4) and that the electrical connection with the conducting members running parallel to the axis of the magnetic core (2) is achieved with a soldered through-connection.
9. Process in accordance with claim 10 wherein the soldering material employed has a melting point of at least 300°C.
10. Process in accordance with any one of claims 1 to 9 wherein a thermoplast or hardening liquid resin is employed as material for the casing (1).
11. Process in accordance with claim 10 wherein an epoxy resin which hardens at preferably 120°C is employed as a liquid resin.
12. Process in accordance with any one of claims 1 to 11 wherein recesses (13) are formed in the casing (1) which also recess the space inside the magnetic core (2), and magnetic cores are employed the axial measurements of which are less than the inner height of the recesses (13), and the volume of the recesses is filled with insulating material such that a closed surface for the uptake of the layer with the conducting members exists.
13. Process in accordance with claim 12 wherein the material, with which the recesses (13) are filled, contains an actively magnetic content.
14. Process in accordance with any one of claims 1 to 13 wherein at least two openings are developed in the casing (1) and with which the part can be held under an exact tension on a base for the separate stages of processing.

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