U.S. patent number 3,833,872 [Application Number 05/262,406] was granted by the patent office on 1974-09-03 for microminiature monolithic ferroceramic transformer.
Invention is credited to Ira R. Marcus, William L. Muckelroy.
United States Patent |
3,833,872 |
Marcus , et al. |
September 3, 1974 |
MICROMINIATURE MONOLITHIC FERROCERAMIC TRANSFORMER
Abstract
A monolithic microminiature transformer element comprising at
least two separate contiguous windings of conductive metal film,
each having an interconnecting magnetically permeable core of
refractory material, immersed in a rectangular block of stratified
refractory material. The element is a contiguous mass of ceramic
material, especially alumina, primary and secondary transformer
windings formed by printing or photoetching loops on a rectangular
piece of ceramic sheet. A method for making this transformer
element wherein paths of conductive material are deposited onto
thin unsintered magnetically permeable ceramic sheet with holes for
interconnection therein to form windings of said transformer and
wherein said holes are aligned and said sheets are laminated such
that upon sintering said metal forms a contiguous conductive path
and provides a primary or secondary winding for said transformer,
and wherein said path is immersed in a contiguous block of
ceramic.
Inventors: |
Marcus; Ira R. (Rockville,
MD), Muckelroy; William L. (Washington, DC) |
Family
ID: |
22997364 |
Appl.
No.: |
05/262,406 |
Filed: |
June 13, 1972 |
Current U.S.
Class: |
336/83; 336/183;
336/232; 336/200 |
Current CPC
Class: |
H01F
41/0246 (20130101); H01F 27/255 (20130101); H01F
41/02 (20130101); H01F 41/046 (20130101); H01F
2027/2809 (20130101) |
Current International
Class: |
H01F
27/255 (20060101); H01F 41/04 (20060101); H01F
41/02 (20060101); H01f 017/04 () |
Field of
Search: |
;336/83,180,200,183,232,221 ;340/174CC,174JA |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kozma; Thomas J.
Attorney, Agent or Firm: Kelly; Edward J. Berl; Herbert
Elbaum; Saul
Claims
What is claimed is:
1. A microminiature transformer comprising:
a. a monolithic block comprised of a plurality of appositioned
strata thermally fused together, each stratum comprised of sintered
refractory ceramic dielectric material;
b. an electrically-insulated magnetically-permeable powder
dispersed in said strata;
c. individual conductive metal primary spirals deposited on some of
the surfaces of said strata, said primary spirals on each said
stratum being coaxially located and enclosed by said block;
d. individual conductive metal secondary spirals deposited on some
of the surfaces of said strata, said secondary spirals on each said
stratum being coaxially located and enclosed by said block;
e. a first hole in each said stratum for housing a means for
interconnecting each primary spiral;
f. a second hole in each said stratum for housing a means for
interconnecting each secondary spiral;
g. said means for interconnecting each primary spiral comprising a
metal film deposited on the inside cylindrical wall of each of said
first hole;
h. said means for interconnecting each secondary spiral comprising
a metal film deposited on the inside cylindrical wall of each of
said second hole.
2. The microminiature monolithic transformer element of claim 1
wherein said primary spirals comprise a primary transformer winding
and wherein said secondary spirals comprise a secondary transformer
winding and wherein said dispersed powder provides a magnetically
permeable flux link for said windings.
3. The microminiature transformer of claim 2 further comprising at
least four deposited metal bonding pads, two of which are located
on one face at said block, two more of which are located on the
opposite face of said block, whereby one parallel and coaxial pair
of said bonding pads form the terminations of the primary winding
and another parallel and coaxial pair of said bonding pads form the
terminations of the secondary winding.
4. The microminiature transformer of claim 3 wherein said powder is
selected from the group consisting of 2-81 permalloy and carbonyl
iron.
5. The microminiature transformer of claim 4 wherein said primary
and said secondary spirals are coaxially oriented.
6. The microminiature transformer of claim 4 wherein said primary
spirals are coaxially arranged about a first axis and wherein said
secondary spirals are coaxially arranged about a second axis, said
second axis being located a distance away from said first axis
greater than the sum of the combined maximum radii of said primary
and said secondary spirals.
7. The microminiature transformer of claim 5 wherein said strata
are of equal thickness.
8. The microminiature transformer of claim 5 wherein said metal
spirals, said metal film, and said metal bonding pads are thermally
matched to said strata.
9. The microminiature transformer of claim 6 wherein said strata
are of equal thickness.
10. The microminiature transformer of claim 6 wherein said metal
spirals, said metal film, and said metal bonding pads are thermally
matched to said strata.
11. The microminiature transformer of claim 1 further comprising
melted glass frit dispersed in said conductive metal spirals and
said metal film, whereby said frit provides a ceramic-to-metal
bond.
Description
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured, used, and
licensed by or for the United States Government for governmental
purposes without the payment to the inventor of any royalty
thereon.
BACKGROUND OF THE INVENTION
This invention relates generally to monolithic microminiature
components for use in the assembly classified microcircuitry using
substrates as a basis onto which the various types of components
are mounted. Less generally this invention relates to a monolithic
microminiature transformer element and a method for making the
same. Specifically this invention relates to a microminiature
monolithic transformer element with a magnetically permeable core
comprising a magnetically loaded ceramic material and a process for
making in mass production large quantities of this device at very
economical prices. Moreover, it is related to that class of devices
classified as transformers which possess primary and secondary
windings wound around an inner core having the property of
significantly enhancing the magnetic field. Among the classes of
microelectronic manufacture to which this invention applies are
thick film technology, thin film technology, and hybrid multichip
technology. In any case, the invention is to be used where
reduction in size is required; a large quantity is to be produced;
and cost is an essential factor.
The most closely related device to this particular invention are
spiral inductors which are made by the application of thick and
thin films and by subtractively etching the inductor. A helical
miniature inductor and method related to the invention herein is
discussed in copending application, "Ceramic Inductor and Method
for Making Same," having Ser. No. 230,247. A number of approaches
to making microminiature transformers have evolved. The most
advanced approach and the one most related to this particular
invention is a monolithic transformer comprising fine wire wound
onto iron rods and coated with an epoxy in order to fix the
position of the wire to maintain the characteristics of the device.
Many problems exist with such a structure, one of which is a
possibility of the epoxy breaking down or a particular piece of
wire becoming loose due to the various heat processes necessary to
attach the particular component into electronic circuitry. Such
flaws in this type of device under abnormal physical conditions can
cause severe changes in the circuit characteristics. This is
especially true in military applications where hardware comprising
electronic microminiature circuitry is subjected to large
accelerations and shocks.
There are other designs of monolithic microminiature transformers
essentially the same as the one previously described. The
difference is that these devices are molded into plastic, and
naturally, they are the common structures for transformer elements
which are not microminiature and which are not monlithic in the
sense of this invention in that the various parts of the inductor
are not chemically bonded or thermally fuzed to each other. In
general, in the past transformers in microminiature form-factors
and form-factors easily applicable to hybrid microelectric circuits
have been extremely expensive and in relationship to the cost of
other functional components to be used in the circuits and
therefore offers a cost factor against the use of such
components.
Another inherent disadvantage in the structure of the aforesaid
components is the nature of the conductive terminations formed on
the device for interconnecting it into the particular circuit for
which it is needed. In most cases, such as that of a plastic device
is best only to epoxy such a device to the substrate using a
conductive epoxy material because of the problems involved in
raising the temperature of such a device to that necessary for
soldering into the circuit. The difference in thermal coefficient
between the plastic and the metal terminations at the ends thereof
usually preclude the use of high or even moderate soldering
temperatures for interconnecting such devices into the circuit.
These differences in thermal coefficience are extremely cumbersome
when soldering microminiature devices. In general, in assembling
hybrid circuits it is desirable to reflow solder chip components.
If it is not possible to reflow solder chip components into
circuits, the next feasible alternative is wire bonding for
interconnecting the component into the circuit. Either of these
methods precludes other sensitive semiconductors from having to be
reheated many times. All devices in use today, except
twinspiral-type transformers deposited onto substrates, have
significant thermal mismatches in materials.
In the case of the twin spiral type transformer when one spiral is
coupled to another spiral type winding printed on a substrate such
as alumina or mylar the coupling between the two spirals are not
significantly enhanced because of the lack of a common closed
magnetic circuit. Usually there is free space above the spiral
unless some particular type of coating is applied. One problem with
spiral coaxial transformers are twin-spiral transformers printed
onto to very thin sheets of material is a high probability of
changes in the Q factor by bending of the substrate. Another
problem of the spiral is interconnection. When both terminations of
the spiral are on the same side of the substrate one of the
terminations must be crossed over the respective turns of that
particular spiral to interconnect the spiral to the outside
circuitry. This degrades operation of the device. Even if
terminations are brought out on opposite sides of the substrate the
problem of traversing the respectwve windings is still present.
The term "refractory material" is used herein to mean a substance
that will not melt, decompose, or materially change under the
processing conditions involved in forming the device herein
described. Refractory material is generally classified into four
broad groups. The group of utility here includes the
polycrystalline materials such as ceramics and includes, for
example porcelains, steatites, aluminas, and ferrites. The present
invention is described with reference to these ceramics and, more
particularly, thin sheets of alumna with ferrites mixed therein.
However, it should be understood that tbe present invention is
equally applicable to the other ceramic materials. The spirals
comprising the secondary and primary windings of the transformer of
this particular invention may be formed from a paste of glass, high
melting point metal such as platinum and gold, and a decomposable
fluid suspending agent, or surfactant, applied to the refractory
oxide by any convenient method, for example, by dipping, brushing,
or spraying. The relative amount of material within the paste may
vary over fairly wide limits. The main consideration is that the
metal content be sufficiently high to insure that the resulting
metal film after processing is continuous. The amount of fluid used
as a suspending agent depends upon the method of application. If
spraying is used, a relatively thin suspension is required. If
brushing or "squeegee" screened processes are employed, thicker
paste suspension should be such as to insure good conductivity of
the deposition.
Magnetic materials usable for this device include 2-81 permalloy
and carbonyl iron insulated powders, and ferroxcube III sintered
powder.
Generally, a mean-particle size range which is suitable is 0.5 to
25 microns for the paste, with the preferred range being between
0.5 and 15 microns. Smaller particles are equally satisfactory. For
the glass flux, a glass which fuzes and bonds to the ceramic at a
temperature below the melting point of the metal and resists
reduction under the usual processing conditions should be used.
Glasses having these properties are readily compounded for mixtures
of silica (SiO.sub.2) and various combinations of the oxides of
sodium (Na.sub.2 O), calcium (CaO), barium (BaO), magnesium (MgO),
aluminum (Al.sub.2 O.sub.3), boron (B.sub.2 O.sub.3), potassium
(K.sub.2 O) and phosphorus (P.sub.2 O.sub.5), among other elements.
Table I is illustrative of some suitable glasses which can be
conveniently compounded from typical oxides specified as to kind
and amount in the table. The table is not intended to be exhaustive
of suitable glasses but indicates a general composition of some
readily fuzable nonreductible glasses. It is noted that this table
encompasses many common types of glasses such as borosilicates,
phosphates and silicates.
TABLE I ______________________________________ Melt Ingredient:
Parts by Weight ______________________________________ Li.sub.2 O
0-15 Na.sub.2 O 0-25 CaO 0-10 BaO 0-20 MgO 0-2 Al.sub.2 O.sub.3
0-35 SiO.sub.2 5-80 B.sub.2 O.sub.3 0-30 K.sub.2 O 0-5 P.sub.2
O.sub.5 0-80 ______________________________________
In the preparation of the glasses, the ingredients are smelted
together in a furnace at a temperature sufficient to melt but not
volatilize the constituent oxides, for example, between
1100.degree. centigrade and 1500.degree. centigrade, until a mass
of uniform quality has been obtained. The melt is fritted by
pouring into cold water, and the resultant frit is ground to the
fineness desired. It is desirable for the glass particles to be
finally divided, for example, on the order of 1/2 micron to 25
microns particle size, so that the paste mixture will, under the
processing conditions, result in a continuous metal layer
adherently bonded to the ceramic.
The glass and metal particles are suspended in a volatile and
decomposable fluid suspending agent or surfactant and applied to
the refractory oxide by any of the methods aforementioned. The
relative amount of metal and glass used may vary over fairly wide
limits. The main consideration is that the metal content be
sufficiently high to insure that the resulting metal film after
processing is continuous. Generally, between five to 50 parts by
weight of metal is used by each part by weight of glass.
The fluid suspending medium serves to disperse the paste mixture in
the desired pattern on the substrate and to hold the pace in this
pattern until processing commences. During processing the
suspending medium should volatize leaving no residue. The
suspending medium should not react with the metallic or glass
components of the coating composition before or during firing. To
insure proper dispersion and bonding of the paste, many of the
common suspending media contained two components. The first
component acts as a dispersing medium for the paste and as a
solvent for the second component which insures proper bonding of
the pace to the "green ceramic" or refractory oxide until
processing commences. Examples of suitable dispersion media which
are solvents for the below listed binders are benzene; the esters
of fatty acids; alcohols of low molecular weight such as ethyl,
butyl, and amyl; acetates including "cellosolve acetate" (ethylene,
glycol, monoethyl, ether, acetate), diethylene glycol monoethyl
ether acetate; ketones such as acetone and methyl-ethyl-ketone; and
higher ethers such as glycol diethyl ether. Suitable binders are,
for example, the vinyl or substituted vinyl polymers.
In general, any ceramic which is resistant to the usual processing
conditions may be used as a refractory ceramic substrate. The
following table is illustrative of various ceramic compositions
that have been successfully used. The compositions are expressed in
parts by weight.
TABLE II ______________________________________ Porcelain Steatite
Alumina Composition A B C D E F G
______________________________________ Feldspar 35 50 30 25 Ball
Clay 15 10 8 10 Kaolin 30 30 37 40 15 Talc 60 Dolomite 2 BaCO.sub.3
17.5 MgCO.sub.3 1 7.5 SiO.sub.2 20 10 25 22 9-10 2 CaO 1 1 MgO 3-4
1 Na.sub.2 O 1-5 1/2 Al.sub.2 O.sub.3 (1) 95.5
______________________________________ .sup.1 Remainder
In order to form a ceramic slurry with good flow properties, the
aforementioned thermoplastic organics are used as flow promoting
binders for the refractory oxide. The prime step is to coat the
fine alumina particles with these thermoplastics. This step is
facilitated by intense mixing at high temperatures in the range
from 100.degree. centigrade to 400.degree. centigrade. Water
emulsions of the organic plastic agents facilitate the initial
mixing of the organic with the ceramic particulates, and the
initial contact can be made by using an aqueous or nonaqueous
slurry and solution. Removal of the volatile constituients provides
an intimate mixture of the organic and the "green ceramic."
In a typical process, firing of the laminate is done in a furnace
in which both atmosphere and temperature can be controlled. The
firing is done in a reducing atmosphere. This firing step is
carried out under conditions sufficient to volatilize the fluid
suspending media, and to commence formation of a refractory
ceramic-to-glass-to-metal bond. The temperature and firing time are
interdependent. The fluid suspending vehicle used and the
temperature required commences formation of the refractory
ceramic-to-glass-to-metal bond. This temperature is dependent upon
the temperature required to sinter the ceramic and to cause wetting
of the refractory ceramic and at least part of the metal by the
glass in the paste system. Such wetting and sintering temperatures
are dependent upon the glass flux used. Temperatures ranging from,
for example, 1400.degree. centrigrade to 1600.degree. centrigrade
have been successfully used.
The maximum temperature is limited by the melting point of the
metal while the minimum temperature is again dependent upon the
wetting and the sintering temperature of the glass flux employed
and the temperature required to sinter the ceramic wetted by the
glass comprising the paste.
The invention described herein overcomes many of the disadvantages
of the foregoing constructions. It is therefore the object of this
invention to provide a new and novel process for manufacturing
monolithic microminiature transformer elements with a magnetically
permeable core.
It is yet another object of this invention to provide a new and
novel microminiature transformer element with a magnetically
permeable core which is monolithic and comprises materials having
coherent thermal coefficients.
It is yet an additional object of this invention to provide a new
an novel device and process for manufacturing said device which is
economical and easily adaptable to high volume manufacturing used
in the thick film industry.
It is yet an additional object of this invention to provide a
monolithic trnasformer having conductive primary and secondary
windings comprising combinations of spiral helical conductive paths
emmersed in a magnetically permeable ceramic material with bonding
paths thereon suitable for attachment of metal tabs or for wire
microbonding the components to the appropriate electronic
circuitry.
It is another object of this invention to provide a microminiature
monolithic transformer element which has a form factor compatible
with that of other components used in hybrid microelectronics.
It is still an additional object of this invention to provide a
microminiature monolithic transformer element with a structure made
of ceramic and cermet materials.
It is yet another additional object of this invention to provide a
transformer having a surface of refractory ceramic material.
It is yet an additional object of this invention to provide a
microminiature monolithic transformer with a new and novel core
comprising a magnetically permeable alumina ceramic.
It is yet an additional object of this invention to provide a
combination helical spiral path winding for a transformer, said
path being imbedded in a magnetically permeable alumina ceramic
having a rectangular solid form factor.
Yet another additional object of this invention is to provide a new
and novel microminiature monolithic transformer element whose
electrical paths are formed by metalization paths of thick film and
thin films.
Still an additional object of this invention is to provide a new
and novel method for making a microminiature monolithic transformer
in which the electrical conductive paths are formed onto unfired
alumina ceramic tape by a subtractive etching technique.
Still yet an additional object of this invention is to provide a
new and novel design of metalization which provides a helical
spiral path that provides transformation of voltage and current
functions within a compact area.
These and other objects of the present invention will become more
fully apparent with reference to the following specifications and
numerous drawings which relate to several variations of a preferred
embodiment of the invention described herein.
SUMMARY OF THE INVENTION
A monolithic microminiature transformer comprising a combination
helical spiral conductive path for the primary and secondary
windings, of deposited metal film immersed in a rectangular block
of magnetic refractory material. The transformer is either made
with a coparallel windings or intermeshed windings. The
terminations of the transformer are metallized paths located
thereon. A method for making this transformer wherein spirals of
conductive metal are deposited onto a thin unsintered magnetically
permeable unsintered ceramic sheet with holes therein for
interconnection and wherein said holes are aligned and said sheets
are laminated such that upon centering said metal forms a spiral
helical combination path of contiguous conductive material immersed
in a contiguous block of ceramic.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific nature of the invention as well as other objects,
aspects, uses, and advantages thereof will clearly appear from the
following description and from the accompanying drawings, in which:
FIG. 1 (a) is an illustration of the process of manufacturing
magnetically permeable ceramic tape.
FIG. 1 (b) is a flow chart of the method for manufacturing
magnetically permeable ceramic tape.
FIG. 2 (a) is an illustration of the pattern deposition processed
by which conductive paths are formed on the ceramic tape.
FIG. 2 (b) is a flow chart of the pattern deposition process.
FIG. 3 is a flow chart of the manufacturing process by substractive
etching.
FIG. 4 (a) is a top view of the layers of a biaxial embodiment of
the microminiature monolithic transformer.
FIG. 4 (b) is a bottom view of the layers of a biaxial
microminiature monolithic transformer.
FIG. 5 (a) is an illustration of two adjacent layers of ceramic
tape with conductive patterns thereon for lamination.
FIG. 5 (b) is an illustration of two adjacent layers laminated with
the interconnection of the conductive metallization from one layer
to the next.
FIG. 6 is a graphic illustration of a coaxial microminiature
monolithic transformer showing the spatial configuration of the
various spirals.
FIG. 7 (a) is a top view of the various layers of a coaxial
microminiature monolithic transformer.
FIG. 7 (b) is a bottom view of the layers of a particular
embodiment of a coaxial microminiature monolithic transformer.
These and other objects of the present invention will become more
fully apparent with reference to the following specifications and
the drawings which relate to several variations of a preferred
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The manufacturing process of the present invention will be easily
understood in broad aspects by reference to FIG. 1 (a) wherein
there is illustrated the basic steps in the manufacture of the
magnetically permeable ceramic tape. The construction principle of
the multilayer ceramic transformer chip begins with the mixing of a
slurry 14 of alumina powder and various binders that can be cast
into thin layers 10 on a flat surface 11. However, before casting,
a magnetically permeable powder 12 is added to the slurry of
ceramic material 14. A doctor-blade 29 is normally used to achieve
the required thinness and uniformity. Organic binders in the slurry
give enough strength and flexibility to the tape 10 after drawing
for removal and handling. Strips 19 are cut out of this tape and
backed with insulating paper 17 and then holes are punched with the
tool 16 and the resulting strips are rolled onto rolls 18.
Stripping or cutting of strips is done with tool 15. In order that
this particular portion of the process may be easily understood it
is presented in flow-chart form. In FIG. 1 (b) step 20 consists of
adding a portion of magnetic powder to the ceramic slurry 14. The
proportion of the magnetic material added to the ceramic material
may vary between 5 and 30 percent of the volume of ceramic
material. The next step of the process 21 is to spread this slurry
material by doctor blade to the desired thickness. After step 21 is
accomplished the ceramic sheet material is dried, step 22, by
convection or infrared or other heat transfer means. Once the
ceramic sheet material is dry it acquires a plastic and rubber-like
characteristic and becomes very flexible, yet not brittle. In step
23, this tape-like, rubber-like material is cut into long strips
19. In order to prevent the slurry tapes from sticking together due
to temperature changes during rolling, a paper of plastic backing
is appositioned, step 24, to the tape and the tape is then, in step
25, punched with holes at the required locations. The long strips
of tape are next rolled onto reels, step 26. This completes the
process for formation of the tape.
The next phase necessary in the production of these monolithic
microminiature transformers with magnetically permeable ceramic
cores is a formation of conductive paths by pattern deposition as
shown in FIG. 2 (a). The reels of ceramic tape 27 are fed through a
printer 30 which screens conductive pattern necessary to form the
spiral windings of the transformer onto the tape 19. The tape 19 is
then fed through a drying oven or apparatus 31 which removes the
highly volatile components from the metallization silk screened
onto the substrate 19. After the metallization is dried the paper
is separated from the ceramic tape 19 and rolled onto reels 50 for
reuse. The ceramic tape 19 is then fed into a compressor and
laminator apparatus 35 along with reels of tape from other lines
similar to the one we have just described as illustrated in 34.
Sections of these sheets are aligned and stacked and the stacked
structure 36 is compressed and laminated by compression apparatus
35 and the resulting compressed structure is cut from the tape
sources and trimmed with cutting apparatus 37. These large
compressed sheets of ceramic tape with metallization thereon
contain many transformers. These laminated structures 38 are then
carried by belt 41 to a sintering oven 39 which cures the ceramic
block of transformers 38 at temperatures up to 1600.degree.
centrigrade transforming the laminated structure 38 into a
monolithic mass of conductive, ceramic, and magnetically permeable
powder immersed and surrounded by the various granules and
molecules of alumina ceramic. Once this essential step is completed
it is necessary to use a diamond cutter 40. The above steps are
illustrated in flow chart form in FIG. 2 (b). Note that the step 58
of FIG. 2 (b) indicates that metal terminations are attached to the
individual transformers. Step 58 is a final increment in the
production of these transformers. Usually metal tabs are attached
to the various exit bonding terminations. In particular, FIG. 3
shows the various steps necessary in order to form the proper
pattern and to get the proper interconnections between the various
layers to compose an interconnected spiral transformer. If we were
to take a transformer cut from the laminae 38 which, for instance
is comprised of 5 layers of ceramic tape 19 the structure would
look as indicated and illustrated in FIGS. 4 (a) and 4 (b), FIG. 4
(a ) illustrating the top view and FIG. 4 (b) illustrating a bottom
view of the printed matter on the layers 19. Taking one of the dice
of laminae 38 and on stacking it such that the top layer 113, the
next layer 114 and so on to the bottom layer 117 are illustrated in
FIG. 4 (a) and FIG. 4 (b). First looking at the top of a particular
layer as illustrated in FIG. 4 (a) and then looking at the bottom
of a particular layer as illustrated in FIG. 4 (b) we obtain a view
of the interconnections and corresponding parts between various
layers of the transformer 110. One layer 113 of the transformer in
FIG. 4 (a) is shown metallization pad 111 with hole 127 therein.
This hole 127 is formed therein by tool 16 and similarly for holes
128, 129, 130, 131, 136, 141, 138, 142 and 140 as illustrated in
FIGS. 4 (a) and 4 (b). Conductive metallization 111 is connected to
the other side of layer 113 via hole 127 which connects 111 to
spiral 121 and specifically to metallization pad 133. Metallization
pad 133 is connected to spiral 123 and metallization pad 134
through metallized holes 129 and 131. Metallized pad 134 of FIG. 4
(b) is connected via hole 141 and 142 to terminating bonding pad
125. The conductive path from pad 111 to pad 125 through layer
members 113, 114, 115, 116 and 117 comprises the secondary winding
for this particular embodiment of a biaxial microminiature
monolithic transformer element 110. The conduction path from pad
112 to pad 126 through layers 113, 114, 115, 116 and 117 in which
spirals 122, 119, 124 and 120 are interconnected comprises the
primary winding for the microminiature monolithic transformer
110.
Turning further to FIGS. 5 (a) and 5 (b) the intricacy of
interconnecting a metallization pad 151 on the surface of one layer
150 to a metallization pad 154 on the surface of another layer 155
is described. FIG. 5 (a) shows two layers 150 and 155 of ceramic
tape with metallizations 151 and 154 thereon and metallized
through-hole 152 therein before lamination and interconnection.
Ceramic tape 150 is positioned and aligned on top of ceramic tape
155. Appositioned onto ceramic tape 150 is a metallization
connection path 151. This metallization connection path 151 is
connected to metallization connections path 154 through hole 152.
It is noted that hole 152 is metallized throughout. FIG. 5 (b)
shows two ceramic tape layers appositioned to each other and
appropriately compressed. What is shown is ceramic tape 150 on top
and juxtaposed to the ceramic tape 155. Metallized hole 152 is
compressed into metallized connection pad 154 forming a continuous
conductive path from 151 to pad 154 with the metallization in hole
152 serving as the connecting means.
In FIG. 6 a diagrammatic cross section of a microminiature
monolithic transformer having coaxial primary and secondary spiral
windings is illustrated. In this embodiment the transformer is
comprised of layers 76, 77, 78, 79, 80, 81 and 82. These layers
aforementioned have holes therein to provide a conductive path
through the monolithic block interconnecting the leads of the
primary and secondary windings. In particular, the primary winding
comprises complimentary spirals 86, 87, 90 and 91. The secondary
winding comprises complimentary spirals 88 and 89. Leads 72 and 73
provide exit terminations for the primary winding and leads 74 and
75 provide exit terminations for the secondary winding. Tracing the
primary winding from end termination 72 conductive material passes
through hole 83 to conductive spiral 86 through hole 85 to
conductive spiral 87 through hole 100 and holes 99 and 98 to
conductive spiral 90 and then through hole 102 to complimentary
conductive spiral 91 and finally through hole 97 to exit
termination 73. Note that spiral winding 86 may be appositioned
either to layer 76 or layer 77. Similarly for conductive spiral
winding 87 which may also be attached to layer 77 or alternately to
layer 78. This also holds for conductive spiral windings 88, 89, 90
and 91 because of the unique way in which the various layers are
interconnected due to lamination. Secondary winding for the
monolithic transformer comprises end termination 74 which passes
through hole 84 and holes 92 and 93 to complimentary spiral 88 and
then through holes 101 to complimentary spiral 89, then to holes 94
and 95 and 96 to termination 75.
In FIGS. 7 (a) and 7 (b) are illustrated a top view and a bottom
view, respectively, of the coaxial construction of the monolithic
transformer as illustrated diagrammatically in FIG. 6. Tracing the
conductive path of the primary winding of the microminiature
monolithic transformer illustrated in FIGS. 7 (a) and (b ) we start
from conductive pad 191 of transformer 200 which is connected to
square spiral 195 through hole 171. Note that spiral 195 terminates
in conductive hole 172. And, metallized hole 170 is connected to
metallized pad 171 terminating spiral 195. Conductive hole 172
interconnects spiral 195 to complimentary spiral 196, spiral 196
terminating in conductive pad 173. Conductive pad 173 interconnects
to conductive hole 174, conductive hole 175 and through conductive
hole 176 to conductive pad 177 interconnected to spiral 197 and
terminating in conductive hole 178 which is interconnected to
complimentary spiral 198 which terminates in conductive pad 179.
Conductive pad 179 is interconnected to terminating pad 193 via
conductive hole 180. The above denotes the path of the primary
winding for the transformer 200 illustrated in FIG. 7 (a) and 7
(b). It is useful to note that kovar strip tabs may be welded to
pads 191 and 192 and extended in the same direction. Similar kovar
tabs extending in the opposite direction of those attached to pads
191 and 192 may be attached to pads 193 and 194 either by welding,
soldering or other metal to metal joining means. Now to trace the
secondary winding of the transformer 200 in FIGS. 7 (a) and 7 (b)
we begin with conductive path 192. Conductive pad 192 is connected
to spiral 199 via holes 181 and layer 201, hole 182 and layer 202
through hole 183 and layer 203 through the conductive spiral 199 to
the conductive interconnecting pad 184. Interconnecting pad 184 is
connected to spiral 208 via interconnecting hole 185. Spiral 208
interconnects interconnection hole 185 to conductive
interconnecting pad 186 which in turn is connected to the
terminating pad 194 on layer 207 via holes 187, 188 and 189.
It is to be understood that barium titanate (BaTiO.sub.3) may also
be used in the slurry to enhance the properties of the refractory
ceramic material.
The inventor wishes it to be understood furthermore that he does
not desire to be limited to the exact details of construction shown
and described herein for obvious modifications will occur to a
person skilled in this art.
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