Ferrite body containing metallization

A composite comprised of a sintered matrix of spinel ferrite and a non-exposed continuous phase of elemental silver or Ag-Pd alloy ranging to 25 atomic % Pd is produced by co-firing a laminated structure of ferrite powder-containing tapes containing non-exposed metallization-forming material. The composite can be formed into a composite product which contains a continuous silver or Ag-Pd alloy phase with two end portions wherein only the end portions are exposed.

Copending U.S. patent application for "Ferrite Composite Containing Silver 
Metallization", Ser. No. 172,834 filed on Mar. 25, 1988, now U.S. Pat. No. 
4,880,599 in the names or R. J. Charles and A. R. Gaddipati, assigned to 
the assignee hereof and incorporated herein by reference, discloses the 
production of a composite comprised of a sintered matrix of spinel ferrite 
and an electrically conductive phase of elemental silver by co-firing a 
laminated structure of ferrite powder-containing tapes containing a silver 
metallization-forming material having two end portions wherein only the 
end portions are exposed. 
This invention relates to the production of a sintered composite comprised 
of a sintered ceramic ferrite matrix containing a continuous metal phase, 
i.e. metallization, of elemental silver, or of a Ag-Pd alloy which ranges 
in Pd content to 25 atomic %, wherein the metal phase is not exposed to 
the ambient. The composite is useful for producing a composite product 
containing an electrically conductive metallization of silver, or of the 
Ag-Pd alloy, with two end portions wherein only the end portions are 
exposed to the ambient. 
The low melting point (961.degree. C.) and high vapor pressures of silver 
at the temperatures required for the co-firing of silver metallized spinel 
ferrites limit the practical use of silver as a metallization to its 
alloys with other precious metals. In particular, due to requisite melting 
points, metal/ceramic adhesion requirements and cost, the most common 
alloys utilized are those with palladium wherein palladium contents 
generally exceed 30 atomic %. A very large penalty results from the use of 
even 70/30 Ag-Pd since the resistivity of this alloy at 20.degree. .C is 
of the order of 20 times that of silver. 
The present invention enables the formation of a continuous metallization 
of silver in a co-fired ferrite body. 
In another embodiment, the present invention enables the formation of a 
continuous metallization of an alloy of silver and palladium in the 
co-fired ferrite body. The present Ag-Pd alloy ranges in Pd content to 
about 25 atomic % and it is molten or partially molten at the maximum 
firing temperature, i.e. sintering temperature. By partially molten it is 
meant herein that at least about 5% by volume of the Ag-Pd alloy is 
molten. Generally, the Pd content of the alloy ranges from a detectable 
amount, i.e. an amount detectable by microprobe analysis, to about 25 
atomic %, frequently from about 1 atomic % to about 20 atomic %, or from 
about 2 atomic % to about 10 atomic %. An alloy comprised of about 75 
atomic % Ag-25 atomic % Pd has a solidus (fully solid) temperature of 
about 1100.degree. C. and a liquidus (fully molten) temperature of about 
1190.degree. C. As the Pd content of the alloy decreases, its solidus and 
liquidus temperatures decrease. The use of the present Ag-Pd alloy may 
make processing easier. 
Briefly stated, the present process for producing a solid sintered 
composite comprised of a sintered ferrite matrix totally enveloping a 
continuous metallization of elemental silver, or of a Ag-Pd alloy ranging 
in Pd content to 25 atomic %, said ferrite matrix having a resistivity 
greater than 500 ohm-centimeters, comprises: 
(a) providing a ferrite powder; 
(b) admixing said ferrite powder with an organic binding material; 
(c) forming the resulting mixture into tape; 
(d) providing a silver or Ag.TM.Pd alloy metallization-forming material; 
(e) forming a layered structure of at least two of said tapes containing 
said metallization-forming material therewithin in a pattern, said 
metallization-forming material being present in an amount sufficient to 
produce said metallization; 
(f) laminating the layered structure forming a laminated structure wherein 
none of said pattern is exposed; 
(g) firing said laminated structure to thermally decompose its organic 
component at an elevated temperature below about 600.degree. C. leaving no 
significant deleterious residue in the resulting fired structure, said 
firing being carried out in an atmosphere or vacuum which has no 
significant deleterious effect on said composite; 
(h) sintering the resulting fired structure at a temperature ranging from 
about 1000.degree. C. to about 1400.degree. C. in an oxygen-containing 
atmosphere to produce a sintered product having the composition of said 
composite, at least about 5% by volume of said Ag-Pd alloy being molten at 
said sintering temperature, said fired structure having a sufficient open 
volume available to accommodate the silver or Ag-Pd alloy during 
sintering; and 
(i) cooling said sintered product to produce said composite, said sintering 
and cooling being carried out in an atmosphere which has no significant 
deleterious effect on said composite; said ferrite powder having a 
composition which forms said ferrite matrix in said process. 
In carrying out the present process, a ferrite powder is provided which 
produces the present sintered ferrite matrix having an electrical 
resistivity greater than 500 ohm-centimeters, preferably greater than 
100,000 ohm-centimeters, at a temperature ranging from about 20.degree. C. 
to about 100.degree. C. These powders are available commercially or can be 
prepared by standard ceramic processing, generally by calcining a 
particulate mixture of the constituent oxides which react by solid-state 
diffusion to form the desired ferrite which is then milled to produce the 
desired particle size distribution. By "resistivity" herein, it is meant 
the electrical resistance of the present sintered ferrite in the form of a 
bar one centimeter long and one square centimeter in cross-section. 
The ferrite powder is a magnetic oxide. The term "magnetic" is used herein 
to indicate a material which is magnetized by a magnetic field. The 
ferrite powder is known in the art as a spinel ferrite and it is of cubic 
symmetry. The present ferrite powder has a composition represented by the 
formula MO(Fe.sub.2 O.sub.3).sub.1.+-.x where x has a value ranging from 0 
to about 0.2, preferably ranging from 0 to about 0.1, and where M is a 
divalent metal cation selected from the group consisting of Mg, Mn, Fe, 
Co, Ni, Zn, Cu, and a combination thereof. Representative of useful 
ferrites include nickel zinc ferrite and manganese zinc ferrite. 
If desired, a minor amount of an inorganic oxide additive which promotes 
densification or has a particular effect on magnetic properties of spinel 
ferrites can be included in the starting powder. Such additives are well 
known in the art and include CaO, SiO.sub.2, B.sub.2 O.sub.3, ZrO.sub.2 
and TiO.sub.2 . As used herein, the term "ferrite powder" includes any 
additive which forms part of the matrix of the present composite. The 
particular amount of additive is determinable empirically and frequently, 
it ranges from about 0.01 mol % to about 0.05 mol % of the total amount of 
ferrite powder, i.e. the total amount of matrix-forming powder. 
The matrix-forming powder is a sinterable powder. Its particle size can 
vary. Generally, it has a specific surface area ranging from about 0.2 to 
about 10 meters.sub.2 per gram, and frequently, ranging from about 2 to 
about 4 meters.sup.2 per gram, according to BET surface area measurement. 
The organic binding material used in the present process bonds the 
particles together and enables formation of the required thin tape of 
desired solids content, i.e. content of matrix-forming powder. The organic 
binding material thermally decomposes at an elevated temperature ranging 
to below about 600.degree. C., generally from about 100.degree. C. to to 
about 300.degree. C., to gaseous product of decomposition which vaporizes 
away leaving no residue, or no significant deleterious residue. 
The organic binding material is a thermoplastic material with a composition 
which can vary widely and which is well known in the art or can be 
determined empirically. Besides an organic polymeric binder it can include 
an organic plasticizer therefor to impart flexibility. The amount of 
plasticizer can vary widely depending largely on the particular binder 
used and the flexibility desired, but typically, it ranges up to about 50% 
by weight of the total organic content. Preferably the organic binding 
material is soluble in a volatile solvent. 
Representative of useful organic binders are polyvinyl acetates, 
polyamides, polyvinyl acrylates, polymethacrylates, polyvinyl alcohols, 
polyvinyl butyrals, and polystyrenes. The useful molecular weight of the 
binder is known in the art or can be determined empirically. Ordinarily, 
the organic binder has an average molecular weight at least sufficient to 
make it retain its shape at room temperature and generally such an average 
molecular weight ranges from about 20,000 to about 200,000, frequently 
from about 30,000 to about 100,000. 
Representative of useful plasticizers are dioctyl phthalate, dibutyl 
phthalate, diisodecyl glutarate, polyethylene glycol and glycerol 
trioleate. 
In carrying out the present process, the matrix-forming powder and organic 
binding material are admixed to form a uniform or at least a substantially 
uniform mixture or suspension which is formed into a tape of desired 
thickness and solids content. A number of conventional techniques can be 
used to form the mixture and resulting green tape. Generally, the 
components are milled in an organic liquid or solvent in which the organic 
material is soluble or at least partially soluble to produce a castable 
mixture or suspension. Examples of suitable solvents are methyl ethyl 
ketone, toluene and alcohol. The mixture or suspension is then cast into a 
tape of desired thickness in a conventional manner, usually by doctor 
blading which is a controlled spreading of the mixture or suspension on a 
carrier from which it can be easily released such as Teflon, Mylar or 
silicone coated Mylar or glass. The cast tape is dried to evaporate the 
solvent therefrom to produce the present tape which is then removed from 
the carrier. 
The particular amount of organic binding material used in forming the 
mixture is determinable empirically and depends largely on the amount and 
distribution of solids desired in the resulting tape. Generally, the 
organic binding material ranges from about 25% by volume to about 50% by 
volume of the solids content of the tape. 
The present tape or sheet can be as long and as wide as desired, and 
generally it is of uniform or substantially uniform thickness. Its 
thickness depends largely on its particular application. Generally, the 
tape has a thickness ranging from about 25 microns to about 1000 microns, 
frequently ranging from about 50 microns to about 900 microns, and more 
frequently ranging from about 100 microns to about 800 microns. 
The metallization-forming material can be any material containing or 
comprised of elemental silver or the Ag-Pd alloy which forms the desired 
continuous metallization of elemental silver or the Ag-Pd alloy in the 
present composite. The metallization-forming material comprised of 
elemental silver or Ag-Pd alloy can be in a number of physical forms such 
as particulates, or a solid body such as a strip, wire, sheet or punched 
sheet. 
The metallization-forming material containing elemental silver or the Ag-Pd 
alloy usually is deposited from a suspension, for example, a paste or ink, 
of particles of silver or the present Ag-Pd alloy suspended in organic 
binder. The suspension is deposited, usually by screen printing, on the 
face of a tape and, when dry, produces the desired predetermined pattern 
of metallization-forming material. Such suspensions are known and are 
available commercially, and preferably, they are free of glass frit. 
Generally, the metal particles range in size from about 0.1 micron to 
about 20 microns. Any organic component of the metallization-forming 
material thermally decomposes at a temperature below about 600.degree. C. 
leaving no residue or no significant deleterious residue. 
A layered structure of at least two of the tapes is formed which contains 
the metallization-forming material therewithin in a desired pattern. The 
layered structure can be formed by a number of conventional techniques. 
For example, a pattern of metallization-forming material can be deposited 
on the face of a first tape and a second tape can be deposited on top of 
the pattern to cover it. Preferably, the tapes are substantially 
coextensive with each other, usually forming a sandwich-type structure. 
The configuration of the layered structure should permit the formation of 
the present laminated structure wherein none of the pattern is exposed to 
the ambient. 
In another embodiment, the metallization-forming material is deposited or 
printed in a preselected form on the face of a number of tapes. 
Feedthrough holes may be punched in the tapes as required for layer 
interconnection and provided with metallization-forming material to 
provide a conductive path. The tapes can then be stacked together, 
generally one on top of the other, to produce the present layered 
structure wherein the totally deposited metallization-forming material 
comprises a pattern therewithin. 
In another embodiment, the present layered structure contains a plurality 
of separate individual, i.e. discrete, patterns of metallization-forming 
material therewithin. 
The layered structure is then laminated under a pressure and temperature 
determinable empirically depending largely on the particular composition 
of the organic binding material to form a laminated structure. Lamination 
can be carried out in a conventional manner. Laminating temperature should 
be below the temperature at which there is decomposition, or significant 
decomposition, of organic binding material and generally, an elevated 
temperature below 150.degree. C. is useful and there is no significant 
advantage in using higher temperatures. Typically, the lamination 
temperature ranges from about 35.degree. C. to about 95.degree. C. and the 
pressure ranges from about 500 psi to about 3000 psi. Generally, 
lamination time ranges from about 1/2 to about 5 minutes. Also, generally, 
lamination is carried out in air. 
In the laminated structure, none of the pattern is exposed to the ambient, 
i.e. none of the silver is exposed to the ambient. 
The metallization-forming material should be present in the laminated 
structure, i.e. the unsintered structure, in an amount at least sufficient 
to produce a continuous metallization in the sintered composite. The 
amount of metallization-forming material can vary with the particular 
amount for a given pattern depending largely on the desired thickness of 
the metallization in the sintered composite or composite product. Such 
amounts are determinable empirically. 
Generally, the laminated structure is plastic, pliable or moldable and it 
can be arranged or shaped by a number of conventional techniques into a 
desired simple, hollow and/or complex form which is retained after 
sintering. For example, the laminated structure can be wound around into a 
coil in a single plane, or into a spiral form in a plurality of planes. 
The laminated structure is fired to produce the present composite. At a 
temperature of less than about 600.degree. C., thermal decomposition of 
organic material is completed producing a fired porous structure. Thermal 
decomposition can be carried out in any atmosphere, generally at about or 
below atmospheric pressure, which has no significant deleterious effect on 
the sample such as, for example, air. If desired, thermal decomposition 
may be carried out in a partial vacuum to aid in removal of gases. 
The fired structure should have an open volume available to accommodate the 
metal, i.e. silver or Ag-Pd alloy, during sintering of the ferrite matrix. 
densifies, i.e. it shrinks in volume, and the silver is totally molten 
whereas the Ag-Pd alloy is partially or totally molten. Since the metal is 
located within the structure, it cannot evaporate to any significant 
extent. Since the metal cannot shrink, it must have an open volume to 
squeeze into during sintering. The open accommodating volume should be 
sufficient to prevent bloating of the sintered composite and is 
determinable empirically. Generally, the open volume which should be made 
available to the metal prior to sintering of the ferrite matrix ranges 
from about 30% to about 60% by volume of the total volume of silver or 
Ag-Pd alloy. Preferably, the open volume is about 50% in excess of the 
total volume of metal. Also, preferably, no significant amount of the 
accommodating open volume remains in the sintered composite. 
Sufficient open volume can be made available to the metal before sintering 
occurs by a number of techniques. It can be produced in the layered or 
laminated structures or in the fired structure. The open accommodating 
volume is directly connected with the metal prior to sintering but it may 
be located only at a portion of the pattern, or along a boundary thereof, 
or it can be dispersed through the pattern. For example, when the 
metallization-forming material is totally solid, such as a wire with two 
end portions, the accommodating volume can be comprised of a depression in 
the supporting tape open to each end portion. 
Preferably, the accommodating volume is produced in the fired structure by 
depositing the pattern on the tape from a suspension of particles of 
elemental silver or of the Ag-Pd alloy, such as by screen printing. 
Typically, the metal particles occupy only about 50% by volume of the 
dried screen printed material with the remainder being organic material. 
The organic material thermally decomposes before sintering occurs and such 
decomposition automatically produces an open volume in the fired structure 
of about 50% in excess of the total volume of metal which frequently is 
the required open volume. 
The pattern of metallization-forming material in the unsintered laminated 
structure can vary and depends largely on the pattern of the metallization 
desired in the sintered composite. Generally, the pattern is distributed, 
frequently significantly uniformly, in the unsintered laminated structure. 
In one embodiment, the pattern in the unsintered laminated structure has 
two end portions, and in another embodiment, it is in the form of a 
circle. However, the pattern in the unsintered laminated structure should 
form a metallization in the sintered composite which permits it to be 
useful for producing the present composite product. 
The fired structure is sintered at a temperature ranging from about 
1000.degree. C. to about 1400.degree. C., frequently from about 
1100.degree. C. to about 1300.degree. C., depending largely on its 
composition and the particular composite desired. A temperature below 
about 1000.degree. C. generally is not operable to produce the present 
composite. A temperature higher than about 1400.degree. C. provides no 
advantage and may not produce the present composite. 
Sintering is carried out in an oxygen-containing atmosphere the composition 
of which depends largely on the composition of the matrix-forming powder 
as well as on the matrix composition desired. Also, upon completion of 
sintering, the sintered product may be cooled in the same atmosphere used 
for sintering, or in some other atmosphere such as, for example, an 
atmosphere which may be needed to maintain certain matrix compositions. 
The sintering and cooling atmospheres should have no significant 
deleterious effect on the present composite. Generally, the sintering and 
cooling atmospheres are at about atmospheric or ambient pressure, and 
generally the sintered product is cooled to about room temperature, i.e. 
from about 20.degree. C. to 30.degree. C. The sintering and cooling 
atmospheres for the production of spinel ferrite bodies are well known in 
the art. 
As an example, when all of the cations of the matrix-forming powder are in 
their highest valence, and such valence state is to be retained in the 
sintered matrix, sintering is carried out in an oxidizing 
oxygen-containing atmosphere. In such instance, oxygen generally is 
present in an amount greater than about 50% by volume of the atmosphere 
and the remaining atmosphere frequently is a gas selected from the group 
consisting of nitrogen, a noble gas such as argon, and a combination 
thereof. Usually, the sintering atmosphere is comprised of air or oxygen. 
Also, in such instance, the sintered product generally is cooled in an 
oxidizing oxygen-containing atmosphere, usually the same atmosphere used 
for sintering, or some other atmosphere in which the sintered product is 
inert or substantially inert to produce the desired composite. 
However, as another example, if the matrix-forming ferrite powder contains 
Fe.sup.2+ cation, or if the Fe.sup.3+ is to be reduced to produce a 
certain small amount of Fe.sup.2+ cation to produce certain magnetic 
properties, sintering is carried out in a reducing oxygen-containing 
atmosphere wherein the oxygen content is controlled to produce and/or 
maintain the Fe.sup.2+ cation in the desired amount. Also, in this 
instance, upon completion of sintering, at least during part of the 
cooling cycle, the oxygen content of the atmosphere is controlled, usually 
decreased, to maintain the desired amount of Fe.sup.2+ cation. Generally, 
the reducing oxygen-containing atmosphere is comprised of oxygen and 
nitrogen or an inert gas such as argon wherein the effective amount of 
oxygen generally ranges up to about 10% by volume of the atmosphere. 
Generally, sintering can be controlled in a conventional manner, i.e. by 
shortening sintering time and/or lowering sintering temperature, to 
produce a sintered matrix having a desired density or porosity or having a 
desired grain size. Sintering time may vary widely and generally ranges 
from about 5 minutes to about 5 hours. Usually, the longer the sintering 
time or the higher the sintering temperature, the more dense is the matrix 
and the larger is the grain size. 
In one embodiment of the present invention, where silver or Ag-Pd wire 
having a diameter of less than about 5 mils is used to form the 
metallization, or part of the metallization, in the sintered composite, 
open volume generally need not be provided to accommodate the molten metal 
during sintering. In such instance, plastic deformation of the matrix 
during sintering may accommodate ferrite shrinkage without cracking the 
sample. In this embodiment, the wire can vary in length as desired but 
generally its length is greater than about 10 mils. 
The present sintered matrix has a porosity ranging from about 0%, or about 
theoretical density, to about 40% by volume of the sintered matrix. The 
particular porosity depends largely on the particular magnetic properties 
desired. For several applications, the porosity of the sintered matrix 
ranges from about 5% to about 30%, or from about 10% to about 25%, and 
frequently it is about 15%, by volume of the total volume of the matrix. 
Generally, the lower the porosity of the matrix, the higher is its 
magnetic permeability. In the present composite, porosity is distributed 
therein, preferably significantly or substantially uniformly. Generally, 
the pores in the sintered matrix range in size from about 1 micron to 
about 100 microns, frequently from about 10 microns to about 70 microns. 
The pores may be closed and/or interconnecting. 
Generally, the average grain size of the present sintered matrix ranges 
from about 5 microns to about 100 microns, frequently from about 10 
microns to about 80 microns, or from about 20 microns to about 60 microns, 
or from about 30 microns to about 50 microns. Generally, with increasing 
grain size, the magnetic permeability of the composite increases. On the 
other hand, generally with decreasing grain size, the lower are the 
electrical losses. 
The present sintered composite is comprised of a polycrystalline matrix of 
ferrite totally enveloping a continuous metallization of elemental silver 
or of a Ag-Pd alloy ranging to 25 atomic % Pd. The sintered ferrite matrix 
is in direct contact with the metallization. In one embodiment, the 
present composite contains a plurality of continuous metallizations of 
silver alone, or of the Ag-Pd alloy, which are electrically isolated from 
each other. Frequently, each metallization has two end portions. The 
presence of the metallization in the composite can be determined by x-ray. 
The present invention enables the direct production of a sintered composite 
of desired shape and size. The sintered composite is free of bloating. 
The present sintered composite is useful for producing a composite product 
which is comprised of the ferrite matrix enveloping a continuous, i.e. 
electrically conductive, metallization of silver or the present Ag-Pd 
alloy with two end portions, wherein only both end portions are exposed to 
the ambient and are at least sufficient for electrical contact to be made 
such as, for example, by soldering a lead thereon. 
A number of conventional techniques can be used to produce the composite 
product. In one embodiment, where the sintered composite contains a 
metallization with two end portions, a portion of the matrix can be 
removed, for example by polishing it off, to expose the end portions. In 
another embodiment, the sintered composite is sliced or cut, for example 
by means of a diamond saw, to produce one or more of the present composite 
products. In yet another embodiment, where the sintered composite contains 
a plurality of electrically isolated continuous metallizations, it can be 
sliced to produce one or more composite products with a plurality of 
electrically isolated continuous metallizations wherein each metallization 
has two end portions which are exposed to the ambient. 
The continuity of the metallization in the composite product can be 
determined by a number of conventional techniques such as, for example, by 
contacting its exposed end portions with leads to determine electrical 
conductivity. 
The thickness of the electrically conductive metallization in the sintered 
composite or composite product can vary depending largely on its 
application. Generally, it ranges from about 2 to about 800 microns, 
frequently from about 20 to about 150 microns. 
The present sintered ferrite matrix is a soft magnetic material of cubic 
symmetry. Its composition is the same as that given herein for the 
matrix-forming material. It can be magnetized but loses its magnetization 
when the source of magnetization is removed. For example, when a voltage 
is applied across both exposed end portions of the metallization in the 
present composite product, current is passed therethrough producing a 
magnetic field which magnetizes the ferrite matrix thereby storing 
electrical energy therein. When the voltage is removed, the ferrite matrix 
will demagnetize giving back the electrical energy as a reverse electrical 
current in the metallization. 
The present composite product has a number of uses. It is useful as an 
electrical component in an electrical circuit. It is particularly useful 
as an electrical inductor such as, for example, a tuning coil or a filter 
coil. 
When the present composite product contains two or more separate 
metallizations, i.e. conductors or windings, each of which is accessed by 
two exposed end portions, such a composite product is useful as an 
electrical transformer. 
The invention is further illustrated by the following examples wherein the 
procedure was as follows unless otherwise stated: 
An air furnace with molybdenum disilicide heaters was used. 
The firing, sintering and cooling was carried out in air at about 
atmospheric pressure. 
The ferrite powder was a sinterable powder. 
The organic binding material used to form the tape was comprised of 
commercially available organic binder comprised of polyvinylbutyral 
(average molecular weight of about 32,000) and commercially available 
liquid plasticizer comprised of polyunsaturated hydroxylated low-molecular 
weight organic polymers. Specifically, the organic binding material was 
comprised of 4.13 grams of polyvinylbutyral and 1.48 grams of liquid 
plasticizer per 100 grams of ferrite powder. 
The screen printing ink was a commercially available ink comprised of a 
suspension of silver particles in a solution of organic binder. About 50% 
by volume of the dried screen printed material was comprised of silver 
particles with the remainder being organic material. 
In the laminated structure, none of the silver was exposed to the ambient. 
Standard techniques were used to characterize the composite for density, 
microstructure and electrical properties.

EXAMPLE 1 
A calcined ferrite powder having a composition comprised of 14.12 mol % 
NiO, 24.45 mol % ZnO, 1.15 mol % MnO and 60.28 mol % Fe.sub.2 O.sub.3 was 
used. It had a specific surface area of about 1 m.sup.2/ g. 
Ferrite tapes were prepared by the tape casting technique. 5.61 grams of 
the organic binding material were dissolved at ambient temperature in 50 
grams of a mixture of 33 grams of toluene and 17 grams of methyl alcohol. 
The resulting solution was admixed with 100 grams of ferrite powder in a 
ball mill for about 4 hours at room temperature. The resulting slurry was 
tape cast on a Mylar sheet using a doctor blade, then dried in air at room 
temperature and atmospheric pressure to remove the solvent, and the 
resulting tape was stripped from the Mylar sheet. 
Each tape was about 6 inches wide, 30 inches long and had a substantially 
uniform thickness of about 20 mils. Ferrite powder was distributed in each 
tape substantially uniformly and comprised about 52% by volume of the 
tape. 
Each tape was cut to lengths of about 1.5 inches and width of about 1.5 
inch to form blanks. 
With a screen mask, a pattern was screen printed on a face of a single 
layer blank to form a pattern which was a partially closed circle with two 
extending, parallel legs (a Greek letter Omega shape). The outside 
diameter of the partial circle was 0.900 in., the trace width was 
uniformly 0.100 in., the legs extended from the circle perimeter by about 
0.25 in. The screen printing was dried in air at room temperature and when 
dried was about 1 mil thick. 
An unprinted blank was placed on top of the printed blank covering the 
pattern and forming essentially a sandwich structure. This structure was 
laminated in air in a laminating press at about 93.degree. C. under a 
pressure of about 800 psi for about 1/2 minute. No portion of the pattern 
extended to any surface of the resulting laminated structure. 
The laminated structure was placed in an open alumina boat and fired in 
air. As the temperature was raised, the organic component thermally 
decomposed and vaporized away below 600.degree. C. The sample was sintered 
at a temperature of about 1280.degree. C. for 30 minutes and then 
furnace-cooled to room temperature. 
The resulting composite was comprised of a polycrystalline ferrite matrix 
which totally enveloped a phase of elemental silver. 
From other work it was known that the ferrite matrix had a composition 
which was the same as, or did not differ significantly from, that of the 
starting ferrite powder, and that it was of cubic symmetry. 
A rotating diamond saw was used to cut off a portion of the ferrite matrix 
which was then polished in a standard manner to expose the two leg 
portions of the silver phase thereby producing the present composite 
product. Electrical resistance measurements between the leg sections was 
less than 0.1 ohm. Since the resistivity of the ferrite matrix was greater 
than 1 megohm-cm, the electrical measurements of the silver phase, i.e. 
trace, showed that the silver conduction path was continuous. A structure 
of this type would be useful as an electrical inductor. 
For examination purposes, a portion of the matrix was cut and polished away 
across the circle portion of the omega-shaped silver phase. Examination of 
the resultant product, as well as an x-ray of the sintered composite 
before it was cut, showed that the silver metallization was fully retained 
within the sintered matrix and uniformly shrank in trace width and shape 
to accommodate about a 19% linear shrinkage of both the silver ink deposit 
and the ferrite. The sintered ferrite matrix showed a grain size of about 
10 microns and a porosity of about 10 volume %. The final silver trace was 
almost it's initial thickness (about 1 mil). 
EXAMPLE 2 
Two printed blanks and an unprinted blank were produced as disclosed in 
Example 1. The blanks were assembled into a three layer structure with the 
blanks substantially coextensive with each other and the two printed 
patterns separated and within the structure. The layered structure was 
laminated as disclosed in Example 1. 
In the laminated structure, none of the patterns were exposed to the 
ambient. 
The laminated structure was fired in the same manner as disclosed in 
Example 1 and furnace-cooled to room temperature. 
The resulting composite was comprised of a polycrystalline ferrite matrix 
which totally enveloped each of two electrically isolated continuous 
phases of elemental silver. The sintered composite showed by x-ray two 
separate, continuous silver phases. 
The sintered composite showed a linear shrinkage of about 19%. 
Standard structural analysis of the sintered composite showed that the 
silver phase, i.e. windings, were continuous and electrically isolated 
from one another, each with a thickness of about 1 mil. The ferrite matrix 
showed the same structural characteristics as the matrix produced in 
Example 1. 
A structure of this kind, i.e. the sintered composite product which could 
be produced by removing portions of the matrix to expose the two end 
portions of each silver phase, would be useful as an electrical 
transformer. 
EXAMPLE 3 
Several unprinted ferrite tapes, i.e. blanks, were produced as disclosed in 
Example 1. 
A sandwich structure of three blank layers, i.e. the layers were 
coextensive with each other, was laminated as disclosed in Example 1. 
Several of such three layer laminated structures were produced. 
Solid strips of elemental silver about 5/8inch long and 0.125 inch by 0.003 
inch cross-section were used. 
A silver strip was placed on top of the three layer laminated structure, 
i.e. on a face thereof, and two additional ferrite blank layers were 
placed on top of the silver to form a five layer sandwich structure which 
was laminated as disclosed in Example 1. None of the silver in the 
laminated structure was exposed to the ambient. Three such five layer 
laminated structures were produced and are shown as Runs 1-in Table I. 
A slot was machined into a face of the remaining three layer laminated 
structures. A silver strip was placed in each slot. Each slot was 0.003 
inch deep by 5/8inch long. The slots varied in width to accommodate excess 
volumes in the slots unoccupied by the silver strips in amounts equal to 
15, 20, 25, 30, 50 and 60% of the initial volume of the individual solid 
silver strip. Two additional blank layers were placed on top of each 
silver strip to form a five layer sandwich structure which was laminated 
as disclosed in Example 1. None of the silver in the laminated structures 
was exposed to the ambient. 
Each of the laminated structures was fired in the same manner as disclosed 
in Example 1 and furnace-cooled to room temperature. The results are shown 
in Table I. 
TABLE I 
__________________________________________________________________________ 
Excess Silver 
Silver 
Sintered 
Sample Slot 
Shrinkage 
Conductor 
Conductor 
composite 
Run 
No. Vol. % 
% linear 
thickness 
form integrity 
__________________________________________________________________________ 
1 Q1MT 
8A 0 19 3 mil discont. 
catastroph- 
8B 0 19 " " ically 
3 
8C 0 19 " " cracked 
4 Q1MT 
9A 15 18 " continuous 
small 
5 
9B 20 " " " internal 
6 
9C 25 " " " cracks 
7 
9D 30 " " " sound 
8 Q1MT 
13A 
50 19 " continuous 
sound 
9 
13B 
60 " " " " 
__________________________________________________________________________ 
Runs 7-9 illustrate the present invention. In the sintered composites of 
Runs 7-9, none of the silver phase was exposed to the ambient and the 
ferrite matrices showed a grain size, shrinkage and porosity which were 
substantially the same as that disclosed for the ferrite matrix in Example 
1. The sintered composites of Runs 7-9 were free of bloating. 
The results in Table I show that by incorporating an appropriate excess 
internal volume around the metallization which is sufficient to account 
for the volume shrinkage of the ferrite during co-firing, integral 
structures of ferrite with continuous pure silver conductors may be 
obtained without providing access of the metallizations to a free surface 
for liquid metal pressure equalization and without developing internal 
pressures which crack the body. Table I shows that such excess volume 
ranges from about 30% to about 60% of the elemental silver within the 
unsintered structure. 
If portions of the ferrite matrix were removed from the sintered composites 
produced in Runs 7-9 to expose only both end portions of each silver 
phase, the resulting composite products would be useful as electrical 
inductors. 
EXAMPLE 4 
Several unprinted ferrite tapes, i.e. blanks, were produced as disclosed in 
Example 1. 
A sandwich structure of three blank layers, i.e. the layers were 
coextensive with each other, was laminated as disclosed in Example 1. 
Solid wires of elemental silver half-inch long and 25 mil in diameter were 
used. 
A pocket was machined into a face of the laminated structure. A silver wire 
was placed across the pocket. Two additional blank layers were placed on 
top of the silver wire to form a five layer sandwich structure which was 
laminated as disclosed in Example 1. None of the silver in the laminated 
structure was exposed to the ambient. The pocket was geometrically 
centered within the resulting laminated structure and was machined to 
accept the wire with a pocket volume of about 50% in excess of the wire 
volume. 
A second five layer laminated structure was prepared in the same manner 
except that the pocket was machined to accept the wire with a pocket 
volume of about 60% in excess of the wire volume. 
The five layer laminated structures were fired at about 1280.degree. C. for 
30 minutes in an open boat in air and then cooled to room temperature. 
In the resulting sintered composites, none of the silver was exposed to the 
ambient. 
The resulting sintered composites were free of cracks and warpage and 
showed by x-ray that the wires remained continuous and also assumed the 
general shape of the original machined pockets reduced by a linear 
shrinkage of about 20%. The wire embedded in the pocket of 50% excess 
volume showed a smoother conformation to the original pocket shape 
indicating that the preferred excess volume for the silver to accommodate 
ferrite shrinkage is about 50%. 
If portions of the ferrite matrix were removed from the sintered composites 
to expose only both end portions of each silver phase, the resulting 
composite products would be useful as electrical inductors.