JPH05182850A - Device requiring pressure sensitive adhesive bonding - Google Patents

Abstract

PURPOSE: To provide a high-viscosity adhesive join for forming and holding a continuous magnetic circuit by making a mating surface which is fixed at a specific position depend upon a capillary flow of an applied unset thermosetting adhesive. CONSTITUTION: A winding bobbin 28 surrounds a border formed of center legs 24 and 27. Then an assembly is heated in an oven with a clamp 30 and one drop of an adhesive compound is applied to the mating surface of leg pairs 22 and 25 (forming a border 32) and leg pairs 23 and 26 (forming a border 33) of an exposed join part by using a syringe. This structure is taken out of the oven a sufficiently long setting time, and the clamp 30 is detached. Consequently, inductance is equal to or superior to those of a structure by conventional technology which has surfaces joined together and a permanently clamped structure.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to devices and methods of manufacture that rely on high strength adhesive bonding to create and maintain a continuous magnetic path. A particularly important category is transformers and inductors with windings that rely on the soft magnetic ferrite surface to complete the core structure.

[0002]

BACKGROUND OF THE INVENTION As with the detailed description, discussions of the prior art are made primarily in terms of economic problems that motivated a solution according to the approach of the present invention. The manufacture of devices belonging to the category of windings including transformers and inductors usually involves first winding the wire on a bobbin or other supporting structure and then partially winding it by joining preformed core parts. Forming a magnetic core therein. A particularly important category is the class of devices that rely on soft magnetic ferrite core members. In this regard, for example, Butterworth
erworths), published in 1988 by E. C. EC Snelling and C.I. The book "Soft Magnetic Ferrites, Properties and Applications (Soft Ferrites,
Properties and Applications) ”, 2nd edition.

Currently, the commonly used manufacturing approach relies on permanent mechanical clamping, which keeps the mating surfaces in intimate contact, and thereby the magnetic field within the functional device. Keep reluctance at the required level. This approach is still in use despite its cost, weight and space advantages compared to adhesive bonding.
In this regard, see, for example, pages 160-162 of the above cited reference "Soft Magnetic Ferrites, Properties and Applications".

Ferrite core device (ferrite-core-d
The category of evices) relies on adhesive "bridge bonding" instead of clamping. According to this approach, the temporarily clamped surfaces are joined by coating the outside of the seam with an epoxy or other thermoset resin that leaves a tacky, high strength enclosure as a result of curing. This clamp is removed. Strength requirements require a fairly thick surrounding adhesive layer. Mold costs are avoided by using high viscosity / thixotropic materials to minimize flow before or during curing. This approach is useful for the manufacture of devices with low strength requirements, for example, for joining core sections with relatively large cross-sections, or for joining tevices that may not encounter harsh environmental conditions during use.

The bridging adhesive method is expensive. That is, in order to achieve the maximum strength that can be expected, it is necessary to carefully apply the adhesive to the entire peripheral surface to be wetted.

If there is a larger space / strength requirement such that an extra coating cost can be justified,
Adhesive bonding takes the form of a surface-to-surface bond, i.e. a coating of the individual surfaces to be mated, followed by mating and rubbing to ensure wetting and drive off excess adhesive. Then, clamping is performed.

Despite the many efforts to make up for the various shortcomings of adhesive bonding, this approach has limitations in many respects. That is, mechanical fixation (eg, clamping) is generally required to meet performance / reliability in harsh environments. Further complexity is added due to surface-to-surface adhesive bonding. That is, it is necessary to remove excess adhesive by compressing the seam after curing after mating, which imposes a constraint on the viscosity allowed. In addition, under many conditions voids are formed during high temperature curing, eg, due to loose air and / or moisture, which adversely affects initial strength and strength loss due to cumulative environment. Becomes The constraints thus added limit the adhesive compounds and affect the performance requirements.

[0008]

SUMMARY OF THE INVENTION The teachings of the present invention overcome the drawbacks of adhesive bonding outlined in the previous section. The principle of the invention relies on a capillary flow of an uncured thermosetting adhesive applied to a mating surface that is fixed in place with appropriate dimensions. After the capillary flow is performed, hardening is performed to fix the wetted surface of the magnetic member, resulting in the formation of a continuous magnetic flux path including this surface. The usual objective is to minimize or approach the minimum reluctance associated with the seam to approach the performance of continuous (seamless) members. The possibilities of using various epoxies and other adhesive materials are broadened by temperature variations to meet flow and cure requirements. The resulting adhesive and processing flexibility make it economically advantageous in the sense of ease of application and high yields. The adhesive and treatment meet the required performance characteristics when placed in the harsh environment that would be encountered initially and during use. In the context of the latter, for example,
The need for a protective atmosphere due to device capsules or other commonly practiced methods is typically eliminated by the inventive approach.

Many of the constraints associated with bridge junctions are avoided. The disadvantages of prior art surface-to-surface bonding are also overcome. Often such disadvantages result from the tedious task of coating the entire surface to be mated. Generally, in the practice of the present invention, it is sufficient to apply the uncured adhesive to only one location per seam for sufficient wetting of the pre-fixed surface. However, for large seams, it may be more appropriate to apply a plurality of spots or stripes. However, even in this case, it depends on the complete wetting involved in the dispersion by the capillary flow.

The bond strength achieved by the method of the present invention further contributes to the degree of design freedom. An example of this is the manufacture of devices with mating of E-core sections (FIGS. 2 and 3), where reliable bonding is achieved by adhesive bonding of only two of the three mating surfaces.
Reference is made here to the E-core soft magnetic ferrite structure, in which the already wound bibon hides the central seam. This functionally required design is described, for example, on page 281 of the above-referenced document "Soft Magnetic Ferrites, Properties and Applications".

The process of the present invention essentially relies on capillarity which results in the wetting of pre-fixed mating surfaces in contact with each other. It is this aspect that secures many of the advantages associated with the present invention in terms of both ease of application and improved performance. The “Ernegic Considerations” section of the detailed discussion discusses various factors associated with effective application, which influence the spacing between mating surfaces; capillarity and especially viscous drag. Includes adhesive viscosity; contact angle; and temperature. The main purpose of the present invention, namely the goal of magnetic continuity consistent with the required physical properties (strength, resistance to adverse conditions during use, etc.), is the essential weaving provided by capillarity. Depends on the ting.
There is considerable force, including capillary flow, on materials that are otherwise suitable, that is, a broad category of uncured thermosets in relation to the surfaces to be joined. In a preferred aspect of the invention, the required level of continuity is ensured by holding the surfaces to be joined during manufacture in intimate contact by clamping. Soft magnetic ferrites such as those contained within experimentally manufactured devices containing the materials included in the examples of the present invention provide suitable surfaces for such capillary flow. Experimentally, for example, surfaces produced by simple polishing, such as grinding, as well as surfaces produced by polishing to a nearly mirror-like surface were all joined by the technique according to the invention. Clamping pressure to maintain the minimum spacing between mating surfaces, i.e. to maintain intimate contact prior to introduction by capillaries, is not sufficient to prevent the capillary flow wetting of the present invention. It was discovered that there is no.

Various means can be used to initially introduce the uncured resin. Experimentally conducted examples include (1) application of an adhesive to the outer surface of the periphery of the bonding part of an already heated mating pair, and (2) application of the adhesive after application of the adhesive at room temperature. Includes heating of the ting pair. Heating serves a variety of purposes, including one or both to ensure timely wetting of the mated surface and to accelerate subsequent curing. These different purposes can be adequately achieved by maintaining a constant temperature, but as an alternative, the temperature can be raised stepwise so as to most effectively meet the two. Alternatively, various measures can be taken to achieve flow wetting and / or curing without heating.

[0013]

DETAILED DESCRIPTION General The various considerations made clear in this section are useful in identifying various parameters, ie compounds, processing conditions, to meet various immediate needs. More generally, the practice of the invention relies on a wide selection of suitable parameters, which is limited only by widespread common sense. For example, the selection of adhesives based on tack and bond strength necessarily requires a sufficient amount of wetting to ensure capillary flow. Another additional requirement for application relates to viscosity, which is usually met by the use of unfilled thermosets prior to cure. The various functional considerations of capillary flow required in all embodiments of the invention as well as various considerations (temperature,
Viscosity influenced by molecular weight, etc.) is well known.

Section 5, which shows the formulas that are decisive for the application, can be useful for optimization, provided that the person skilled in the art has already identified both the materials and the processing conditions for carrying out the invention. I think I have the right knowledge. Specifications such as pressure difference as well as surface tension values usually relate to the parameters to be optimized. The practicability of the present invention does not depend on such considerations. For example, the spacing between surfaces and the smoothness of the surface can affect performance optimization, but experimentally, even large spacings of 10 mils for capillary flow wetting over a viscosity range of up to 500 centipoise and above. It is known that there is no problem. The nominal spacing of this value is certainly the maximum possible from a performance point of view, provided that the required value of inductance does not suggest a larger spacing between the mating mating surfaces. it is conceivable that. In fact, the 10 mil spacing used only guarantees this minimum, since the surface in this experiment was simply created by polishing, like the area between the spacers and the interlocking protrusions. Variations are also conceivable there, resulting in areas where the spacing is increased by up to 2 mils. All these experiments, and those with seams clamped at 50 psi pressure (no spacing), support the operational certainty of the inventive mechanism for seams encountered in device design. Many magnetic devices have non-magnetic gaps ("
Air gap "). This is typically accomplished by polishing the central leg of the three leg core portion. The length of this gap (and thus the total reluctance of the magnetic path) is required. Tolerances are maintained in the mated structure by clamping during joining to ensure a minimum spacing between mating surfaces of the outer legs. The considerations for magnetic path continuity are therefore
In general, these "without gaps" and "with gaps"
Equal to that for the core structure. Considerations regarding the composition of the adhesive and the choice of treatment include the time required for application;
Requirements due to the composition and size of the surfaces to be joined;
It depends on various factors, including the need due to performance requirements; the design life with attention to the conditions to be trimmed; and considerations regarding overall cost with one or more of these compromises. These considerations are generally discussed by way of example.

As a general overview of the invention, it is helpful to introduce the relevant elements. The summary presented here discusses various factors: adhesive properties, application procedures, and overall performance. This summary is done primarily in the context of the necessary elements, but variations, including both optional procedural and sequential variations, are valid. Some variations are discussed here, but some others are not relevant to this disclosure,
It is up to the person skilled in the art. As is common to the rest of this description, the particular discussion is at least initially in the context of a conventional core structure that requires the joining of core portions to obtain a complete loop. Some considerations, such as those associated with providing an artificially reduced inductance, may consequently be expressed as a specified small spacing of the loop.

1. Surface property wetting Here again, the considerations are fundamental and require consideration of the surface energy, for example based on the composition of the adhesive chosen.

Surface roughness is a concern, whether it is physically flat or other flexible geometry. From the perspective of device functionality,
Some minimum smoothness is required to ensure the required continuity of the magnetic path. From the point of view of the flow of the pressure-sensitive adhesive, the surface shape of the surface which is otherwise appropriate is not a significant problem. In terms of timely wetting of a sufficient portion of the bond, there is no problem with all surfaces that are acceptable from a functional point of view.

Size For the particular effect of the present invention, ie for purposes of "linear" devices such as inductors and transformers in communication circuits, the mating surface is made small. For example, a fraction of a square inch. For so-called "power" devices, the mating surface is usually larger, in the range of square inches or more.

Position mating surfaces are likely to be equalized in size and shape. The general spacing for achieving the most general purpose is usually achieved by pressure by clamping or some other type of mechanical fixation. The latter example relies on magnetic attractive forces that take advantage of the innate soft magnetism of commonly used cores; applying non-uniform magnetic fields; or mere gravity assisted by additional weight. The core structure manufactured by the feasibility study
It consistently showed the maximum achievable inductance for various surface topography used at pressures in the range of 50 to 200 psi.

The cured regardless of whether with or without an increase in the other temperature; prior to application, during, or regardless of whether used in either after the pressure
Thermal means; and Te regardless of whether only all or selected product
Strikes are some of the many usual considerations for manufacturing specifications. Regarding this, "Adhesive Handbook"
(Handbook of Adhesives), Irving Skeist, 197
7 years, see New York Publishing. These are relevant only to the present invention in that they affect the criteria set forth above.

Bad Conditions Reliability, mainly in the context of aging, is ensured by proper selection of the parameters indicated above. The introduction of the adhesive by capillarity according to the invention makes it possible to maximize the properties which are specific to both the adhesive and the surface to be bonded. Depending on the materials and processes currently available,
Temperature cycling both during manufacture and use; moisture aging; and mechanical conditions encountered, such as impact,
Can cope with vibration sufficiently.

Adhesives The central thrust of the teachings of the present invention depends on the flow of the adhesive induced by capillary action. The timely flow of the adhesive, on the other hand, depends on the spacing, surface regularity, required path length and surface energy. These considerations suggest the required adhesive properties to meet these requirements. Adhesive properties that are important in this respect are viscosity and surface tension under flow and other conditions during flow.

All of these requirements in connection with application are satisfactory for a wide range of epoxies and other adhesives, so the choice is not greatly constrained by such considerations.

Viscosity An important physical property relates to this property. A timely flow of about 500 centipoise (about 500) for a likely flow path length (eg, seconds / centimeter) for the most demanding use in relation to temperature in the flow.
All were achieved at viscosities below cps). Greater viscosities, which are generally unfavorable from a flow standpoint, may also be tolerated due to the use of self-adhesive materials with other required properties / costs. Meaningful viscosity is defined as being applied at the time of application or after being applied at low temperature (eg
Measured at the temperature at which the mated surface is heated (after being applied at room temperature). For most magnetic core assemblies, the choice of temperature is simply to ensure flow before significant flow impeding cure occurs. On the other hand, weakness to heat limits the maximum temperature. For many other suitable adhesives, such as the epoxy adhesives used in the examples herein, suitable flow is achieved at temperatures below about 200 ° C. In some cases, heat sensitivity may require selection of adhesives from a more restricted class. Alternatively, as a result of this consideration,
It is also possible to redesign the assembly during manufacture.

[0025] Detailed Description of composition suitable adhesive composition is not appropriate here.
Certainly, the present invention depends to a large extent on how adhesives with suitable viscosity and strength properties are available. However, beyond these considerations, suitability depends on the particular needs imposed by the present invention. The composition to be considered is thermal cure (required for both the initial low viscosity required for the flow and the tack and strength properties obtained after cure). As discussed in detail under "Application-Theory", flow properties include viscosity, surface tension,
It involves physical properties such as contact angles, as well as the dependence of these properties on temperature. There is a very broad category of adhesive compounds, including hardeners, modifiers, and adhesive polymers themselves, from which one can select materials that meet the requirements of the present invention. Variations concern both the choice of the compound in the general sense shown and the choice of the uncured polymer with the appropriate molecular weight for the properties which give particular results to the invention, eg the viscosity required.

"Adhesive Handbook" (cited above)
Identifies and characterizes multiple categories of adhesives, from which an appropriate adhesive can be selected.
These include epoxies, an aerobics (eg, acrylates and diacrylates, both containing dispersed hardeners), acrylates, urethanes, polyesters,
As well as other materials with the required properties that are currently commercially available or that will be developed in the future. Curing agents are also selected in relation to their impact on the requirements of the present invention, eg, flow rate, time to the onset of cure to allow dispersion before cure that significantly inhibits flow. The required cure temperature is also a factor in these choices. Effective adhesive compositions desirably include one or more modifiers, eg, to reduce viscosity. Other components are functions that promote tackiness (eg, organofunctional silanes that are incorporated into some epoxies); function that varies surface tension (surfactants); and
It serves a variety of ancillary purposes, such as colorants. In general, granule fillers, thixotropes, and other non-essential ingredients to improve viscosity should not be included. However, again, under special circumstances it may be necessary to include them. Although not desirable under normal circumstances, if the objective involves surface-to-surface continuity (in terms of magnetic reluctance), or near continuity,
These may limit flow losses, for example for large spacings between vertically located surfaces. This is required to modify the inductance to some value below the maximum achievable value.

The adhesive used in the examples herein is an epoxy. Compositionally, these are diglycidyl ethers of bisphenol-A (epoxy equivalent = about 18
0), containing a heterocyclic amine curing agent.

Treatment Application The uncured adhesive is applied by any suitable method, such as a dropper, eyedropper, nozzle, toothpick and the like.
The amount is sufficient to wet at least a majority of the mated surface, preferably the entire surface is wetted. Unlike conventional surface-to-surface bonding,
Excess adhesive is prevented from entering the joint from the beginning in the preferred embodiment of clamping, thus
No undesired surface-to-surface spacing is provided. If required by size strictness and other considerations, excess material is allowed to remain outside the joint.

Application-Theory This section describes the factors associated with the introduction of uncured thermoset adhesive.

As with normal use, the flow that ensures wetting between mated surfaces is called "wicking". This term is used in another sense, meaning "capillary flow".
synonymous with w) ”. Capillary force causes the flow of adhesive between mated surfaces, which is resisted by viscous drag. It wicks between surfaces through a flow path distance L. The time t required for is given by:

[0031]

[Equation 1]

Where g is the spacing between mated surfaces, μ is the viscosity, δ is the surface tension, and θ is the dynamic (advancing) contact angle of the adhesive to the surface, all of which are interchangeable. It is expressed in units of holding.

It can be seen that increasing the viscosity and flow path increases the time required, and increasing the space size, surface tension and cosine of the contact angle decreases the time required.

It is common to measure the contact angle θ statically, but in practice this depends on the wetting dynamics (the instantaneous value of θ). As expected, wicking is slowed down by dynamic effects.

The flow mechanism will be discussed in more detail in connection with FIG. This figure schematically shows the bodies 10 and 11 providing pre-positioned mating surfaces 12 and 13 which define the spacing g. The advancing menisc starting with the adhesive component first applied at 14 points.
us) The surface 15 should fill the entire path length L. The symbol 1 (t) represents the instantaneous length of the path defined by the advancing meniscus 15 at time t.

The positive force causing the flow ("wicking") is due to the pressure difference Δp across the meniscus 15 in the direction of movement. This pressure difference, for example p _liquid −p
_air has the following values.

[0037]

[Equation 2]

Here, the parameters are as defined above. The instantaneous velocity V in the region near the entrance at 14 (away from the meniscus 15 at the position shown) is calculated as the balance between this positive force and the viscous drag:

[0039]

[Equation 3]

Where y represents the distance measured from the center of the gap.

The flow velocity at the advancing meniscus 15 (the velocity of the advancing front represented by the meniscus 15 itself) is given by:

[0042]

[Equation 4]

In developing the above equation, the following approximation is performed. g << L and

[0044]

[Equation 5]

Here, g ₂ is gravity acceleration. Both assumptions have sufficient justification in the normally assumed geometry.

Constraints The general nature of the progress of the present invention is clear. The most important implication of the present invention is that economics are realized, mainly in terms of achieving excellent products both early and in use. For many purposes, excellence must take into account performance characteristics. That is, for many purposes, such as magnetic reluctance, this requires a defined spacing between the joined surfaces. The latter is usually optimized by the minimum surface-to-surface spacing ensured by mechanical clamping.

The driving force of the present invention relates to the perfect surface wetting inherent in the capillary flow mechanism.
Commercial advantages are expected in terms of optimizing this approach. Traditional bridge joints presume sufficient viscosity before and during cure, which is generally ensured by the deliberate addition of thixotropes, which results in both capillary and viscous flow. Be pushed down. Practical changes to comply with the present disclosure are generally necessary for the practice of the present invention, and thixotropes, and other similar considerations to ensure a reduction in viscosity that is undesirable from a bridge junction perspective. Takes the form of avoidance.

The present invention is distinctly different from the first prior art bridge junction. Approximately 50 (for temperature and other conditions during capillary flow wetting) for many purposes
The viscosities below 0 centipoise are very low compared to thousands of bridge joints and even 50,000 centipoises or more.

Drawings In connection with FIG . 1, the "wicking" mechanism which constitutes the main thrust of the present invention is described. The remaining figures relate to the manufacture of an example class of magnetic devices. Note that the devices in question generally rely on the fabrication of mechanically reliable low magnetic reluctance paths. 2 and 3 are consistent with the rest of this description, with emphasis on winding devices whose function requires induction, for example, via a core loop of a soft magnetic ferrite composition. Placed. Specific configurations used in the examples contained in Section 8 are shown. This device is an inductor with a magnetic "E-core" structure as commonly used in communication and power conversion devices. Various magnetic structures are known which are desirable to manufacture in accordance with the present invention. In this regard,
For example, U, Pot, RM, PM, PQ, ETD, E
References above to describe suitable standard core structures including C, EI, LP and others as well as E-cores, "SoftFerrites", pages 162,2.
81-284 and 288.

FIG. 2 shows that each has two outer and middle legs 22, 23, 24 and 25, 26, 27, respectively.
2 illustrates an unassembled E-core structure including E-shaped core portions 20 and 21 including. At the stage of manufacture shown, wire is wound around the bibon 28 to obtain the inductor winding 29.

The structures of the type shown belong to the type manufactured according to the examples in the following sections. In Example 1, the structure is assembled and held by clamps 30 as shown in FIG. As shown here, the winding bobbin 28 surrounds the boundary formed by the central legs 24 and 27 (hidden by the boundary within the bibon 28 and not shown). (The particular structure shown here is an inductor and therefore has only two terminals 34, 35. Clamp 30
Are in place, leg pairs 22 and 25 (forming boundary 32) and leg pair 23 (forming boundary 33)
And 26 mating surfaces are adhesively joined in accordance with the teachings of the present invention (see, for example, the description of FIG. 1). The clamp 30 is usually removed after curing the thermosetting resin.

Examples A considerable amount of experimental work is the basis for the above explanations and constraints. The manufactured device provides various magnetic functions. The manufacture of such devices involves joining according to the invention in the magnetic path, for example in the core loop in the case of common inductors and transformers. All structures have advantages in achieving reliability in various respects. That is, the integrity of the joint is found both under the initial conditions and under various conditions encountered throughout service life. In some cases, a suitable adhesive composition is consistent with other requirements, such as attacking resistance by moisture, and provides long-term resistance to vapor permeation as verified by accelerated life tests with water immersion tests. .

The applicability of the process according to the invention from the point of view described is justified by the hundreds of experiments carried out to determine the quality level of the manufacturer. The following example has been chosen as a suitable example to represent the near future production of inductors and converters with characteristics typical of devices used in the telephone industry today and similar devices used in power conversion. It was

Example 1 This example illustrates the manufacture of the E-core inductor shown in FIGS. The overall dimensions of the completed device is approximately 1x1 inch in the major surface of the core. The joined leg surface is about a quarter square inch. Clamping with a force of about 10 pounds (about 50 psi) was used for manufacturing. Thus, the clamped assembly was heated to about 150 ° C. in an oven and a drop of adhesive compound was applied to each side of the exposed joint using a syringe (the middle leg joint was Inaccessible). This particular adhesive compound is based on an epoxy resin, a diglycidyl ether of bisphenol-A ("DGEBA") with an epoxy equivalent of 180-190. To this compound was added about 10 phr (1 part per 100 parts by weight) hardener, ie 2 ethyl-4 methylimidizole (2,4-EM).
I) was mixed. After sufficient cure time (within 5 minutes), the structure was removed from the oven, unclamped, and the resulting structure was tested. Mechanically, in both tension and torsion tests, damage to the core material occurred before adhesive damage to the joint. Similar results were obtained after an accelerated endurance test involving one hour of immersion in boiling water. Also in terms of performance,
We were able to meet normal specifications. In other words, the inductance has shown results equal to or better than bridge-bonded or surface-bonded prior art structures as well as permanently clamped structures. The performance characteristics remained essentially unchanged after the endurance test.

Example 2 An inductor of the same size and properties as in Example 1 was prepared using the same adhesive compound but with one difference. That is, after performing an initial application of adhesive at room temperature, the clamped assembly is placed in an oven,
Removed within 5 minutes after achieving a temperature of 150 ° C. The test results did not change.

[Brief description of drawings]

FIG. 1 is a schematic representation of the surface to be mated, with reference to which a general process description is provided.

FIG. 2 is a schematic illustration of an unassembled inductor with a magnetic E-core structure.

FIG. 3 shows the same assembled E-core inductor.

[Explanation of symbols]

 Body 10 mating surface 12, 13 meniscus surface 15

 ─────────────────────────────────────────────────── —————————————————————————————————————————————————————————————————————————————————————————— ———————————————————————————————————————————————————————————————————————————————— of times of such hand-holding methods, are you instructed to do so? Riet 520 (72) Inventor Applevalloy United States 75087 Rockwell, Texas, Amesbury Avenue 1602

Claims (12)

[Claims] 1. A method of manufacturing a device whose operation depends on a magnetic path, which requires completion of the magnetic path by adhesive bonding of the mating surfaces of the magnetic elements that contribute to the magnetic path when the manufacturing method is bonded, Adhesive bonding is accomplished by wetting at least a portion of these surfaces with a substantially uncured thermosetting adhesive, followed by curing, such that the wetting is prior to approximating a mating relationship. A manufacturing method characterized by a capillary flow of the uncured adhesive between these fixed surfaces. 2. The device comprises an electrically conductive coil, the coil being substantially within a magnetic core for providing inductive coupling in operation, the mating surface being the surface of a core part. The manufacturing method according to claim 1, which is characterized in that. 3. The method of claim 2 wherein the coil is made by a wire wound on a hollow member and the path consists essentially of at least one loop partially contained within the member. Method. 4. The method according to claim 3, wherein the core part is made of an essentially soft magnetic material. 5. The method of claim 4, wherein the core part consists essentially of a ferrite material. 6. The method of claim 5 wherein the pre-fixed surface-to-surface spacing is a small dimension with a maximum of 10 mils. 7. The method of claim 6, wherein the mating surface is pre-fixed into physical contact such that the small dimension is numerically zero. 8. The method of claim 7, wherein the pre-fixed mating surface is contacted with a clamp during capillary flow. 9. The uncured adhesive is held at an elevated temperature for a period of time, during which time capillary flow is promoted with a reduced viscosity of the adhesive.
Manufacturing method. 10. The method of claim 9, wherein the uncured adhesive is heated after introduction and before any significant capillary flow occurs. 11. At least one of said core parts has at least three legs, said hollow member enclosing a seam formed between the central legs of said parts, and a seam formed between outer legs being joined. 7. The manufacturing method according to claim 6, wherein: 12. A product manufactured by any of the methods of claims 1-11.