FR2641438A1 - Integrated inductive circuit - Google Patents

Abstract

This planar inductive circuit is noteworthy in that it is monolithically integrated into a single, monolayer or multilayer substrate PC (for example a printed-circuit board), on or in which substrate (or which board) at least one defined turn T1, T2 is formed on the or each conductive layer CLA, CLB, ... CLH. The necessary connections between turns are produced using the technology of plated-through holes and, in particular, of buried holes BUV and of blind holes BLV. Although perfectly adapted for high-frequency use, it can, nevertheless, be used over a wide frequency range, from 50 kHz (at low power) up to 10 MHz (at high power). Application: manufacture of inductive circuits.

Description

DESCRIPTION "Integrated inductive circuit".

 The present invention relates to a planar inductive circuit consisting of windings and possibly a core of magnetic material, the windings being produced by stacking insulating layers on the surface of which are arranged a plurality of flat conductive turns in the form of a spiral, located in parallel or merged planes, the magnetic material core, when it exists, closely surrounding said windings by crossing windows provided in the stack of insulating layers.

 Such an inductive circuit is described in the PCIM publication (August 1986), the title of the article being "1 MHz Resonant Converter Power Transformer is small, efficient, economical". This article describes the problems encountered when designing high frequency inductive circuits around and above 1 MHz. It proposes in particular a power transformer for which the eddy current losses, the skin effect, the leakage inductance and generally the drawbacks which arise during the development of a power supply have been reduced. high frequency power. Thus, the windings of the transformer are produced by means of continuous and flat copper spirals located on independent dielectric substrates. The various printed circuits each consisting of the substrate and the copper coil are stacked while an insulating plate is inserted between two consecutive printed circuits. Such an embodiment, although having the advantages listed above has however various drawbacks. Indeed, for each inductive circuit, it is necessary to develop a series of printed circuits. In addition, the process which consists in stacking the various printed circuits separated by insulating plates does not make it possible to ensure good reproducibility of the inductive circuits and therefore of their characteristics.

 The present invention provides a planar inductive circuit of the aforementioned type which does not have the various drawbacks while retaining the advantages of the known inductive circuit.

 For this, the planar inductive circuit of the kind mentioned in the preamble is remarkable in that it is monolithically integrated on or in a single substrate comprising at least one conductive layer, substrate on or in which on or on each conductive layer is formed at minus a determined turn while the desired transverse connections between turns are made selectively according to the technology of metallized holes and in particular buried holes and blind holes. Thus the choice of an integration of the inductive circuit for example on a monolayer circuit or in a multilayer circuit (although the article in the publication PCIM expressly advises against the choice of such a solution) allows a simple, effective and little realization expensive and this relative to any other known technique. In addition, the inductive circuits thus obtained are perfectly reliable and reproducible, which makes their use practical and safe even at high frequencies (for example up to 10 MHz). Finally, the calculation of the parameters and characteristics relating to circuits thus produced is easy, for example, as regards magnetic coupling, leakage inductance, stray capacitances, leakage flux, insulation and dielectric strength ( 2 to 3 kV between layers), etc ...

 Another important advantage emerges from the choice of such an embodiment. Indeed, such an inductive circuit can be directly integrated into a monolayer or multilayer printed circuit board intended to receive a plurality of discrete components, the connections with said components then being made directly on the conductive layer or between conductive layers. Thus, when inductive circuits must be implanted on a printed circuit board, it suffices to provide for their implantation during the development and manufacture of the printed circuit, which imposes only a very low additional cost for the latter.

The overall cost is significantly reduced since the various inductive circuits are not manufactured independently, moreover no external connection is to be provided for the various connections of the inductive circuits to the other components of the printed circuit, these connections being advantageously performed on the conductive layer or between conductive layers, which has the effect of further improving reliability, reproducibility and behavior at high frequency.

 The following description with reference to the accompanying drawings, all given by way of example, will make it clear how the invention can be implemented.

 Figure la represents a top view of a conductive layer having a set of turns.

 FIG. 1b shows a sectional view of a multilayer printed circuit and of an example of interconnection by buried holes and blind holes.

 FIG. 2 gives an exemplary embodiment of a transformer on a printed circuit.

 In Figure ta is proposed, as an example, a top view of any conductive layer on which has been formed, by any known method in printed circuit technique, a set of two turns T1 and T2 in the form of a spiral. These two turns which are therefore on the same plane are distinct from each other and are connected when they are integrated in a multilayer circuit (for example by points V1, V2, V3, V4) to other turns formed on an internal conductive layer (lower or upper1 according to buried hole technology or on an external conductive layer (lower or upper) by means of blind holes or finally on several internal and external layers by means of metallized holes. production of two turns is of course not limiting, a single turn or a set of more than two turns which can be formed as required. The calculation makes it possible to determine the necessary width of the turns. The realization by photogravure makes it possible to achieve high precision which allows excellent reproducibility, constant coupling, and guarantees obtaining the desired and calculated characteristics.

 In FIG. 1b is shown a sectional view constituting a stack of a multilayer printed circuit PC which in this example comprises 8 conductive copper layers (CLA, CLB, CLC, CLD, CLE, CLF, CLG, CLH) the interconnections - between layers made by depositing copper on the internal surface of a buried hole BUV between internal layers or of a blind hole BLV between an internal layer and an external layer. A detailed description relating to the definition and manufacture of buried and blind holes is given in the PHILIPS documentation: Philips Components of September 1988, m09398 063 80011. Between each conductive layer is of course an insulation layer '(ILi , IL2, IL3, IL4, ILs, ILs, IL7) for example in laminate.

 In Figure 2 is proposed an embodiment of a transformer according to the invention. This transformer is produced on a printed circuit or a PCB printed circuit board comprising 8 layers with connection of the turns (figure 1) by buried holes and blind holes (figure 2).

In this exemplary embodiment, the transformer is of the type
Forward efficient, it is perfectly suited to high frequency conversion (for example 1 MHz) and allows the transmission of significant powers (for example 75 W.).

 In this exemplary embodiment, this transformer comprises a primary winding of 2 turns, a recovery winding of 2 turns and a secondary winding of 4 turns. The recovery winding serves to drain the magnetizing current by means for example of a freewheeling diode connected to its terminals.

 The magnetic material (3F3) of the core is of type EI42, part E is specially machined to adapt to the thickness of the printed circuit, part I is also of small thickness. Insulating shims Ipi, 1P2 are placed respectively between part E and the PCB circuit and part I and the PCB circuit. In the PCB printed circuit, windows W1, Wz, W3 are arranged so as to allow part E of the magnetic core and an FM fixing means (for example a flange) from said core to the printed circuit. Once fixed, the magnetic core thus tightly surrounds the windings made in the printed circuit.

 According to the invention, the transformer can be manufactured in isolation or be directly integrated into a printed circuit board comprising other components, the connections then being directly and advantageously made between conductive layers. The magnetic circuit can be of any type and of any material, in the same way it can be fixed by gluing or any other means for example by flange, by clip, etc ...

 Such an embodiment of inductive circuits is perfectly suited for use at high frequency (up to 10 MHz) and at high power (around 100 W).

 Such circuits are nevertheless advantageously usable for relatively low frequencies (up to approximately 50 kHz) but this for lower powers (approximately 10 W).

 In addition and obviously, it should be noted that the production of an inductive circuit integrated for example in a hybrid circuit would not depart from the scope of the invention.

Claims (2)

1. Planar inductive circuit consisting of windings and possibly a core of magnetic material, the windings being produced by stacking insulating layers on the surface of which are arranged a plurality of conductive spiral flat turns, located in parallel planes or combined, the magnetic material core, when it exists, closely surrounding said windings by crossing windows provided in the stack of insulating layers, characterized in that it is monolithically integrated on or in a single substrate comprising at least one conductive layer, substrate on or in which on or on each conductive layer is formed at least one determined turn while the desired transverse connections between turns are made selectively according to the technology of metallized holes and in particular buried holes and blind holes. 2. Planar inductive circuit according to claim 1, characterized in that it can be directly integrated into a single-layer or multi-layer printed circuit board intended to receive a plurality of discrete components, the connections with said components then being made directly on the layer. conductive or between conductive layers.