GB2087656A - Miniaturized transformer construction - Google Patents

Abstract

A minaturized transformer comprises two rectangular substrates (10, 12) each carrying successive screen-printed thick-film layers (14, 16) of dielectric with spiral planar windings (18) embedded therein. The substrates (10, 12) and the dielectric layers (14, 16) are formed with a central opening (24) in which is positioned the central leg (22) of a three-legged solid magnetic core (20). The remaining portions (26, 28) of the core (20) surround the two substrates (10, 12) to form a compact rugged construction especially suitable for assembly with hybrid integrated circuit components. The thick film layer may be conductive particles and the dielectric may be glass, these being sintered separately or together. <IMAGE>

Description

SPECIFICATION Miniaturized transformer construction This invention relates to transformers. More particularly, this invention relates to miniaturized transformers suitable for use in small-sized electrical devices such as hybrid integrated circuit components, or smali-sized modular components.

As demand for small-sized electrical components has increased over the years, there has been a corresponding need to provide miniaturized transformers for components requiring such elements. Generally speaking, the probiem of transformer miniaturization has been quite difficult relative to miniaturization of other kinds of electrical elements, and this has particularly been true where low-frequency applications are involved.

For a number of reasons, traditional transformer design concepts have not provided a suitable basis for making such miniaturized transformers. For example, conventional wound transformers are difficult to make in small sizes, especially because the windings typically must be made of very tiny wire. The cost of manufacture also is considerabie, due to the large amount of painstaking labor required. Moreover, it has been difficult to achieve high performance with such small-sized devices of conventional design.

Various proposals have been made from time to time seeking a solution to the problem of making miniaturized transformers, but none of these proposals has resulted in a truly satisfactory transformer construction.

in a preferred embodiment of the present invention to be described hereinafter in detail, a compact transformer construction is provided wherein the transformer windings are arranged in planar spiral configuration, with each winding embedded in a layer of solid insulating dielectric securely attached to a rigid substrate. Both the substrate and the insulating dielectric are formed with a common opening about which the windings are disposed, and a solid magnetic core extends through that opening to form a low-reluctance closed magnetic circuit for the transformer windings. Advantageously, a transformer embodying this invention may comprise two such rigid substrates carrying identical sets of planar spiral windings disposed about the common solid magnetic core.

The layers of insulating dielectric and windings embedded therein preferably are laid down on the substrate by well-established thick-film deposition processes. It thus is possible to make, at iow cost, a rugged multi-layered transformer structure combining small size, excellent performance, high reliability, and ready adaptability to standard component assembly techniques.

The transformer embodying this invention can be used for low-frequency applications-and has high performance capabilities including excellent magnetic coupling, good linearity, and the ability to withstand high voltages between windings.

In order that the invention may be more readily understood, a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which: FIGURE 1 is a plan view of a transformer constructed in accordance with one embodiment of the present invention. (Note:The opaque layers of insulating dielectric are not shown in this view in order to present the general configuration of the metallized windings embedded in the dielectric); FIGURE 2 is a side elevation view of the transformer shown in Figure 1; FIGURE 3 is a vertical section taken along line 3-3 of Figure 1; FIGURE 4 is an enlarged plan view of one substrate of the transformer, showing the three transformer windings as though the insulating dielectric were transparent; FIGURE 5 is a detail section taken along line 5-5 of Figure 4; and FIGURE 6 is a detail section taken along line 6-6 of Figure 4.

Referring now to Figures 1-3, the transformer embodying the present invention comprises first and second rigid rectangular substrates 10 and 12 of alumina, held together in overlying position, and offset a short distance longitudinally. Each substrate carries on one flat surface thereof a film as generally indicated at 14 and 16. These films comprise a series of distinct layers of an insulating dielectric, with each layer having embedded therein a corresponding planar spiral winding in the form generally illustrated at 1 8 in Figure 1. In the present embodiment. each of the two substrates 10 and 12 carries three such winding layers, for a total of six transformer windings.

The multi-layered films 14 and 1 6 preferably are formed by well-known thick-film processing techniques. In one such process, each individual winding layer of the film is developed by screenprinting a metallization pattern, comprising a matrix of conductive particles arranged (in this case) in a spiral configuration, and an overlay of insulating dielectric material such as a hightemperature crystallizable glass dielectric. The screen-printed material then is either singly or cofired at high temperature to complete the process.

Firing of the screen-printed material causes the conductive particles of the metallization pattern to be sintered and fused into a continuous conductor forming a planar spiral winding such as is generally indicated at 18 in Figure 1. Firing also solidifies the glass insulating dielectric to form a rigid pancake-like structure with the planar spiral winding embedded therein.

As noted above, each substrate 1 0, 12 carries three such winding layers. As will be described in more detail hereinbelow, a fourth layer also is laid over the top winding layer to provide cross-over electrical conductors for making connections from the inner ends of the three windings to corresponding termination points at the edge of each substrate. The screen-printing and firing procedure is carried out for each winding layer, and also for the fourth layer establishing the crossover electrical connections. Each of the four screen-printed layers ordinarily will be about 1 mil thick (0.001"), whereas the supporting alumina substrate may have a thickness of about .015".

The central portions of the substrates 10, 12 are enclosed within a three-legged magnetic core 20, preferably composed of facing, mated E-l cores adhesively secured together at the regions of joinder. These E-l cores are assembled to the completed substrates with the central leg 22 of the E-core fitted into aligned rectangular holes 24 (see also Figure 4) cut in the substrates prior to the thick-film processing. The side legs 26, 28 of the E-core extend down along the sides of the substrates to the regions of joinder with the flat I-core, to establish closed magnetic circuits passing through the substrate openings 24.

The screen-printed films 14, 1 6 applied to the substrates 10, 12 extend substantially to the edges of the central openings 24 cut in the substrates. The magnetic core leg 22 is dimensioned to provide a reasonably close fit with the openings 24, and serves to aid in holding the substrates in position.

As shown in Figure 1, each substrate 1 0, 12 is provided at one end thereof with a set of termination pads 30, 32 for making electrical connections to the spiral windings generally indicated at 1 8. With the longitudinally offset arrangement of the substrates, both termination pads, 30, 32 are readily accessible from the same side of the transformer for establishing connections thereto.

It will be seen that the transformer of this invention is especially suitable for adaptation to hybrid integrated circuit components, and can readily be mounted on a mother substrate together with other elements. Conventional connection techniques such as wire-bonding advantageously can be used to make electrical connection to the termination pads 30, 32. As noted above, each substrate in the present embodiment carries three separate windings (in corresponding layers of the thick films 14, 1 6) requiring six terminals on each substrate. Such a transformer is particularly adapted for use in a single-transformer isolator of the type disclosed in our copending patent application No. 8041517.

In this embodiment, both substrates 10 and 12 are identical, with essentially identical multilayered films 14 and 16 containing the sets of three spiral transformer windings. Since the winding arrangements are essentially identical, only one set of windings will be described hereinbelow.

Referring now to the plan view of Figure 4 and the sectional views of Figures 5 and 6, it can be seen that the spiral conductors of each of the three windings 34, 36, 38 are planar, with adjacent turns of the spiral being uniformly spaced apart. The conductors of the bottom and top windings 34, 38 are aligned vertically, while the conductors of the middle winding are offset laterally from those of the other two windings, to assure optimum spacing. Insulating dielectric 40 is laid down for each layer including the fourth layer 42 for the cross-over conductors. The dielectric material extends between and around the metallization layers, and includes an outer layer 40a.

Referring particularly to Figures 4 and 6, the fourth thick-film layer 42 comprises a set of crossover return conductors such as the conductor illustrated at 44. That cross-over conductor is connected at its inner end 44a to the inner end of the corresponding spiral winding 36 by means of a vertical conductor 46. This conductor is formed in staircase fashion by a series of metallizations carried out during formation of the winding layers 34, 36, 38. Such vertical staircase conductor is located in a corresponding rectangular vertical opening 50 (Figure 4) formed in the insulating dielectric 40 during screen-printing of the winding layers.The outer end 44b of the cross-over conductor 44 is connected to the corresponding terminal point 52 of the termination pad 26 by means of a vertical conductor 54 which also is formed in staircase fashion by a series of metallizations, just as in making the inner vertical conductor 46.

The formation of the multiple winding layers as described above, including the vertical conductors 46 and 54, is carried out using well-known and frequently used multi-layer thick-film techniques which are part of the established prior art in that area of technology. Thus detailed discussion of these techniques has been omitted, in order to simplify the present disclosure.

Although a specific preferred embodiment of the novel transformer construction of the present invention has been described hereinabove in detail, it is desired to emphasize that this detailed description is solely for the purpose of illustrating the invention, and is not to be considered as limiting the scope of the invention since it is clear that many variations and modifications can be made by those oi skill in the art in order to meet the requirements of particular applications. For example, transformers in accordance with the invention can be provided with different numbers of windings, and various kinds of conductive materials and techniques can be used to form the windings. Different types of insulating dielectric can be employed. Also, although the described arrangement provides a single winding in each layer, other arrangements are possible. For example, each of two layers could carry one-half of a spiral winding, with the complete winding being established by making vertical connection between the inner ends of the two half-windings.

Additionally, each layer could be formed with more than a single winding (or half-winding) by using spiral interlace arrangements. Thus it is clear that there are many ways in which to carry out the invention to obtain the important advantages thereof.

Claims (12)

1. A transformer comprising: first and second winding means each including at least one spiral turn disposed about a central region: said spiral turns being generally planar with the planes thereof parallel; said winding means being embedded in rigid insulating dielectric means of generally flat configuration with the lateral dimensions thereof parallel to said planar winding means; substrate means supporting said dielectric insulation means; said substrate means and said insulating dielectric means being formed with an opening therethrough centrally located to correspond to said central region of said spiral winding means; a solid magnetic core extending through said opening and linking both said first and second winding means; and termination means connected to the ends of said winding means to provide for making electrical connection thereto.

2. Apparatus as claimed in Claim 1, wherein said winding means comprises a matrix of conductive particles within said dielectric means and fired at high temperature so that said conductive particles are sintered together to form continuous conductors for said winding means.

3. Apparatus as claimed in Claim 1 or 2, wherein said insulating dielectric means comprises at least first and second adjacent layers on a single substrate, each such layer having embedded therein a corresponding spiral winding.

4. Apparatus as claimed in Claim 3, including a further layer of insulating dielectric providing cross-over conductors for making connection to the inner ends of at least one of said windings.

5. Apparatus as claimed in any preceding claim, wherein said magnetic core is a three-legged structure with the center leg thereof passing through said opening and the remainder of the core surrounding said substrate means.

6. Apparatus as claimed in Claim 5, wherein said magnetic core comprises mated E--l cores.

7. Apparatus as claimed in any preceding claim, wherein said substrate means comprises first and second substrates each carrying at least one layer of insulating dielectric with a spiral winding embedded therein.

8. Apparatus as claimed in Claim 7, wherein each of said first and second substrates includes a plurality of layers of dielectric with planar spiral windings embedded therein.

9. Apparatus as claimed in Claim 7 or 8, wherein said magnetic core is a three-legged structure with the center leg thereof passing through said opening; said two substrates being secured together in parallel closely-adjacent positions passing through the spaces between said center leg and the outer legs of said core structure.

10. Apparatus as claimed in Claim 7, 8 or 9, wherein said substrates are elongate members secured together in parallel overlying relationship, offset a short distance longitudinally; said substrates being provided at opposite ends thereof with termination means accessible from the same side as a result of said longitudinal offset.

11. A transformer comprising: first and second substrates secured together in parallel configuration; each of said substrates carrying at least one layer of insulating dielectric surrounding a corresponding winding in the form of a spiral conductor; said spiral windings being positioned so that the central regions thereof are vertically aligned; said layers of insulating dielectric and said substrates all being formed with a common opening passing therethrough in a direction perpendicular to the planes of said substrates and through said central regions of both of said spiral windings; a solid magnetic core extending through said opening to link both said first and second windings; and termination means connected to the ends of said winding means to provide for making electrical connection thereto.

12. A transformer constructed substantially as hereinbefore described with reference to the accompanying drawings.