U.S. patent application number 11/824116 was filed with the patent office on 2008-01-31 for method of forming low temperature cofired composite ceramic devices for high frequency applications and compositions used therein.
This patent application is currently assigned to E.l.du Pont de Nemours and Company. Invention is credited to Kenneth Warren Hang, Mark Frederick McCombs, Timothy Mobley, Kumaran Manikantan Nair.
Application Number | 20080023216 11/824116 |
Document ID | / |
Family ID | 37734924 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080023216 |
Kind Code |
A1 |
Hang; Kenneth Warren ; et
al. |
January 31, 2008 |
Method of forming low temperature cofired composite ceramic devices
for high frequency applications and compositions used therein
Abstract
The invention relates to the use of and method of forming Low
Temperature Cofired Ceramic (LTCC) circuits for high frequency
applications. Furthermore, the invention relates to the novel LTCC
thick film compositions and the structure itself.
Inventors: |
Hang; Kenneth Warren;
(Hillsborough, NC) ; Nair; Kumaran Manikantan;
(Head of the Harbor, NY) ; McCombs; Mark Frederick;
(Clayton, NC) ; Mobley; Timothy; (Cary,
NC) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Assignee: |
E.l.du Pont de Nemours and
Company
Wilmington
DE
|
Family ID: |
37734924 |
Appl. No.: |
11/824116 |
Filed: |
June 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11543742 |
Oct 5, 2006 |
|
|
|
11824116 |
Jun 29, 2007 |
|
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60737280 |
Nov 16, 2005 |
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Current U.S.
Class: |
174/250 ; 29/825;
501/32 |
Current CPC
Class: |
C03C 3/19 20130101; C03C
3/253 20130101; Y10T 29/49117 20150115; Y10T 428/24926 20150115;
H05K 1/0306 20130101; H01L 31/00 20130101; C03C 3/068 20130101;
C03C 3/21 20130101 |
Class at
Publication: |
174/250 ;
029/825; 501/032 |
International
Class: |
H05K 1/03 20060101
H05K001/03; C03C 3/078 20060101 C03C003/078 |
Claims
1. A low k thick film dielectric composition comprising, based on
weight percent total inorganic composition: (1) 40-80 percent glass
frit with a log viscosity range of 2-6 Poise; (2) 20-60 percent
ceramic oxide selected from the group consisting essentially of
silica, silicates, and mixtures thereof, wherein said ceramic oxide
has a dielectric constant in the range of 2 to 5 k.
2. The low k thick film dielectric composition of claim 1 further
comprising: up to 5 weight percent inorganic oxides selected from
the group consisting of copper oxide, silicon dioxide, aluminum
oxides and mixed oxides.
3. A method of using a low k thick film in the formation of a low
temperature cofired ceramic structure for high frequency
applications comprising the steps: providing two or more layers of
a low k thick film dielectric tape, having dielectric constant in
the range of 2 to 5 and comprising, based on solids: (a) 40-80
weight percent glass composition; (b) 20-60 weight percent ceramic
oxide; dispersed in a solution of (c) organic polymeric binder;
providing two or more layers of a high k thick film dielectric tape
having a dielectric constant in the range of 5 to 8; collating the
layers of low k and high k thick film dielectric tapes wherein said
dielectric tapes are not separated by a buffer layer; laminating
the layers of low k thick film and high k thick film to form an
assembly; and processing the assembly to form a low temperature
cofired ceramic structure.
4. The method of claim 3 wherein said glass composition consists
essentially of, based on mole percent, 50-6% B.sub.2O.sub.3,
0/5-5.5% P.sub.2O.sub.5, SiO.sub.2 and mixtures thereof, 20-50%
CaO, 2-15% Ln.sub.2O.sub.3 where Ln is selected from the group
consisting of rare earth elements and mixtures thereof; 0-6%
M.sup.I.sub.2O where M.sup.I is selected from the group consisting
of alkali elements; and 0-10% Al.sub.2O.sub.3, with the proviso
that the composition is water millable.
5. A thick film tape comprising the composition of claim 1.
6. A LTCC device comprising one or more tapes of claim 5, wherein
the one or more tapes form a signal processing section.
7. The LTCC device of claim 6, wherein the tape provides X-Y
constraining.
8. The LTCC device of claim 6, wherein the device further comprises
a constraining tape.
9. A method of using a low k thick film tape in the formation of a
low temperature cofired ceramic structure for high frequency
applications comprising the steps: (a) providing two or more layers
of a low k thick film dielectric tape, wherein the tape comprises
the composition of claim 1 dispersed in a solution of organic
polymeric binder; (b) applying a conductor track on the two or more
layers, and applying vias connecting the two or more layers,
forming a functional layer; (c) collating multiple functional
layers; (d) laminating the collated functional layers; and (e)
Processing the assembly to form a low temperature cofired ceramic
structure.
10. The method of claim 9, wherein the LTCC device further
comprises one or more high k thick films.
11. The method of claim 9 wherein, after the lamination of step
(d), the two or more layers of a low k thick film dielectric tape
form a single signal processing section.
12. An LTCC device made by the method of claim 9.
13. A beamformer, filter, antenna, or coupler comprising the LTCC
device of claim 12
14. The beamformer of claim 13, wherein the beamformer is used in
an application selected from the group consisting of: high
frequency sensors, multi-mode radar modules, telecommunications
components, telecommunications modules, and antennas.
15. An electrically functioning circuit comprising one or more
functional layers, wherein a functional layer comprises: (a) two or
more layers of a low k thick film dielectric tape of claim 5; and
(b) a conductor track portion, wherein the conductor track portion
is on the two or more layers of low k thick film dielectric tape,
wherein vias connect the two or more layers.
16. The electrically functioning circuit of claim 15, wherein the
circuit is a microwave module, package, or board.
17. The electrically functioning circuit of claim 15, wherein the
circuit further comprises a surface metallization.
18. The electrically functioning circuit of claim 26, wherein the
two or more tape layers form a signal processing section.
19. The electrically functioning circuit of claim 15, wherein the
tape provides X-Y constraining.
20. The electrically functioning circuit of claim 15, wherein the
circuit further comprises a constraining tape.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the use of and method of forming
Low Temperature Cofired Ceramic (LTCC) circuits for high frequency
applications. Furthermore, the invention relates to the novel LTCC
thick film compositions and the structure itself.
TECHNICAL BACKGROUND OF THE INVENTION
[0002] An interconnect circuit board is a physical realization of
electronic circuits or subsystems made from a number of extremely
small circuit elements that are electrically and mechanically
interconnected. It is frequently desirable to combine these diverse
type electronic components in an arrangement so that they can be
physically isolated and mounted adjacent to one another in a single
compact package and electrically connected to each other and/or to
common connections extending from the package.
[0003] Complex electronic circuits generally require that the
circuit be constructed of several layers of conductors separated by
insulating dielectric layers. The conductive layers are
interconnected between levels by electrically conductive pathways,
called vias, through a dielectric layer. Such a multilayer
structure allows a circuit to be more compact.
[0004] Another useful dielectric tape composition is disclosed in
U.S. Pat. No. 6,147,019 to Donohue et al. The Donohue et al.
dielectric tape composition achieves a dielectric constant in the
range of 7-8 and is not suitable as a low k material for electronic
packaging signal processing applications.
[0005] A further useful dielectric tape composition is commercially
available Product No. 951 (commercially available from E.I. du Pont
de Nemours and Company). Once again, this dielectric tape
composition achieves a dielectric constant in the range of 7-8 and
is not suitable as a low k material for electronic packaging signal
processing applications.
[0006] Most prior art LTCC thick film materials do not achieve a
sufficiently low k to allow for use as the low k portion of an
electronic package for signal processing applications. A typical
use of thick film dielectric layers with a dielectric constant (k)
of (prior art noted above details a k of greater than 6) is in
buried passive component applications. In these LTCC buried passive
component applications, dielectric thick films are common. However,
in beamforming, filters, couplers, baluns, and other Radio
Frequency (RF) signal processing applications which prefer lower k
materials than k of 7-8, so the typical materials that are used are
not LTCC materials, rather they are poly-tetra-fluoro-ethylene
(PTFE) materials, such as Teflon.RTM. commercially available from
E.I. du Pont de Nemours and Company.
[0007] These PTFE materials can achieve a dielectric constant (k)
of approximately 3-4. This dielectric constant of 3-4 allows for a
wider line width and creates the ability to maintain 50 ohms and to
achieve lower dielectric loss of the circuit and lower tolerance
effects from the screen patterning the lines. Today, low k PTFE
dielectrics are used in nearly all RF modules above 30 GHz due to
wavelengths in the dielectric media being smaller.
[0008] Antennas and phased arrays are similarly designed utilizing
PTFE materials. Antennas and phased array modules from 1 MHz up to,
and including, mm wavelengths are used in a wide range of
communication and radar applications, such as cellular telephone
base stations, mobile tracking communication system, GPS,
commercial broadcasting linear arrays and planar-rectangular,
planar-circular radar arrays. Additionally, new cellular base
station technology of smart antennas is used to improve overall
communication system capacity and performance.
[0009] Military electronic intercept and related RF intelligence
gathering systems use "beamformers" to precisely locate signal
sources. They are typically broadband to detect emissions in the
range of interest.
[0010] "Beamformers" work by carefully controlling the amplitude
and phase of RF energy conveyed to the radiating elements of an
antenna array. Elements commonly used to make "beamformers" are
quadrature couplers, hybrid junctions, phase shifters and power
dividers.
[0011] When used in conjunction with specialized receivers,
"beamformer" networks can identify the location of an RF energy
source.
When interfaced with suitable transducers, beamformers can be used
in acoustic source location devices related to sonar. Thus,
beamformers are used in many direction finding systems.
[0012] U.S. Pat. No. 5,757,611 to Gurkovich et al. discloses an
electronic package having a buried passive component such as a
capacitor therein, and a method for fabricating the same. The
electronic package includes a passive component portion which
includes a plurality of layers of high k dielectric material, a
signal processing portion which includes a plurality of layers of
low k dielectric material, and at least one buffer layer interposed
between the passive component portion and the signal processing
portion. Gurkovich et al. does not disclose an LTCC structure which
allows for the absence of a buffer layer between the low k and high
k regions. Furthermore, Gurkovich et al. discloses a method of
fabrication which utilizes pressure assisted lamination. Gurkovich
et al. discloses the use of passive component portions in
conjunction with signal processing and does not disclose the
ability for passive component portions and signal processing as
stand-alone features. Additionally, Gurkovic et al. discloses the
use of capture pads along all vertical vias between all layers.
[0013] Additionally, presently available dielectric LTCC tapes
typically have an X-Y shrinkage during processing on the order of
9-13% when formed into a multilayer circuit for high frequency
applications. To minimize the shrinkage, designers utilize
constraining tapes either internally as "non-functional layers"
and/or externally. Internally used constraining tapes have a high
dielectric constant in the order 15-25, which results in an
increase in the dielectric constant of package/device overall.
Externally constraining tapes require removal from the device
because they are non-functional and the circuit surfaces are needed
to add other functional characteristics, such as conductors,
resistors etc. Most constraining tapes are alumina or silica-based
and they do not react with standard thick film dielectric tapes, if
used externally. Thus, allowing for removal.
SUMMARY OF THE INVENTION
[0014] The present invention provides a low k thick film dielectric
composition comprising, based on weight percent total inorganic
composition: (1) 40-80 percent glass frit with a log viscosity
range of 2-6 Poise; (2) 20-60 percent ceramic oxide selected from
the group consisting essentially of silica, silicates, and mixtures
thereof, wherein said ceramic oxide has a dielectric constant in
the range of 2 to 5 k.
[0015] In one embodiment, the low k thick film dielectric
composition above further comprises up to 5 weight percent
inorganic oxides selected from the group consisting of copper
oxide, silicon dioxide, aluminum oxides, mixed oxides and various
other such oxides. Also present may be such products of mixed
oxides such as aluminum silicate.
[0016] In a further embodiment, the present invention provides a
method of using a low k thick film in the formation of a low
temperature cofired ceramic structure for high frequency
applications comprising the steps:
[0017] providing two or more layers of a low k thick film
dielectric tape, having dielectric constant in the range of 2 to 5
and comprising, based on solids: (a) 40-80 weight percent glass
composition; (b) 20-60 weight percent ceramic oxide; dispersed in a
solution of (c) organic polymeric binder;
[0018] providing two or more layers of a high k thick film
dielectric tape having a dielectric constant in the range of 5 to
8;
[0019] collating the layers of low k and high k thick film
dielectric tapes wherein said dielectric tapes are not separated by
a buffer layer;
[0020] laminating the layers of low k thick film and high k thick
film to form an assembly; and
[0021] processing the assembly to form a low temperature cofired
ceramic structure.
[0022] In a further embodiment, the present invention provides the
method above wherein the glass composition consists essentially of,
based on mole percent, 50-56% B.sub.2O.sub.3, 0.5-5.5%
P.sub.2O.sub.5, SiO.sub.2 and mixtures thereof, 20-50% CaO, 2-15%
Ln.sub.2O.sub.3 where Ln is selected from the group consisting of
rare earth elements and mixtures thereof, 0-6% M.sup.I.sub.2O where
M.sup.I is selected from the group consisting of alkali elements;
and 0-10% Al.sub.2O.sub.3, with the proviso that the composition is
water millable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows Insertion Loss comparison as a function of
frequency for various k value materials and how a low k LTCC
demonstrates lower overall loss compared to DuPont existing LTCC
materials (commercially available Product Nos. 951 and 943 from
E.I. du Pont de Nemours and Company) and compared to RO3003 (K=3),
a commercially available PTFE based system.
[0024] FIG. 2 represents a cross section view of a microwave module
(Module, Board, Package) utilizing the low k thick film dielectric
tape of the present invention.
DEFINITION OF ITEMS IN THE DRAWINGS
[0025] The numbered items in FIG. 2 are defined as follows: [0026]
(10) Surface Metalization for wirebonding, soldering, brazing, and
other post process applications as well as external RF lines for
interconnect to the Stripline section(s) [0027] (20) 951 LTCC
[0028] (30) Interposer [0029] (40) Signal Vias which connect the
surface devices such is SMT's, IC's, packaged devices and other
signal processing components to the internal microwave circuits on
the internal Low K layers which form the stripline circuits. [0030]
(50) Vias connecting the two stripline grounds in the LowK region
for "via fencing" for microwave designs to improve circuit
performance. [0031] (60) Solid, Gridded, or partial Grounds to form
the grounds for the Stripline Sections [0032] (70) Thru-All
Cavities to access baseplate from surface. Cavities from the top to
place IC's or components or other devices which would benefit from
being recessed planar to the surface of the LTCC. [0033] (80)
Stripline, Buried Microstrip, Covered GCPW, laminated waveguide,
and other methods for guiding propagated RF, microwave, or mmWave
Signals or using for purposes of signal Lines for RF functions
(Beamformer, Filters, antennas, couplers, etc. [0034] (90)
Stripline section Low LTCC [0035] (100)Baseplate for thermal
dissipation and/or mechanical strength which can be soldered,
epoxied, or brazed.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The present invention utilizes both high k thick film
dielectric tape compositions and low k thick film dielectric tape
compositions in the formation of LTCC circuits for use in high
frequency/signal processing applications. In particular, the
present invention provides novel low k tape compositions for use in
the manufacture of LTCC circuits for use in high frequency/signal
processing applications. The present invention provides novel
compositions and methods of using and making these circuits.
[0037] FIG. 1 details the insertion loss comparison as a function
of frequency for various k value materials and how a low k LTCC
thick film dielectric tape of the present invention (Material 3)
demonstrates lower overall loss compared to existing commercially
available LTCC thick film dielectric tape materials, Materials 1
and 2 (Product Nos. 951 and 943, commercially available from E.I.
du Pont de Nemours and Company) and also as compared to Material 4,
polytetrafluoroethylene or in short PTFE material, developed by
E.I. duPont de Nemours Company and trade marketed as "teflon`.
(Product No. RO3003, commercially available not-in-kind
technology/PTFE with a (k=3).
[0038] In a typical case of beamformer circuits, the difference of
using PTFE and LTCC-based material are listed below in Table 1.
TABLE-US-00001 TABLE 1 Comparison of PTFE and Novel LTCC based
Technology for Beamformer Circuit Applications Typical Requirements
PTFE** LTCC Balanced and stable SMT's for resistors either Integral
Thick Film resistors planar on power dividers/couplers on surface
or in cavity internal stripline (20-30% tolerance) and for beam
forming Attach packaged IC's on surface (trimmed to <5%
tolerance) techniques with beamforming By processing at the time on
the same elements layer, the coupler and/or power divider Lots of
routing and are symetrically balanced transitions between IC's and
SMT's are required Active devices on surface Packaged IC's are Bare
IC's can be attached directly to the for additional signal
required, which are then module surface and impedance matching
processing (combining soldered to the top can be done in the LTCC
next to the IC T/R with beamformer) surface or in a cavity.
wirebonds. Connectors/SMT's/Lids can be brazed, soldered,
wirebonded, and/or epoxied all on the same outer layer on any side
of module. Overall low insertion loss K = 3, LT = 0.0013, very
Commercial systems: K = 7.3, LT = 0.0010, between beamforming
stable over frequency and very stable over frequency and elements
well characterized. well characterized. Post process fluids (see
Process parameters like firing and above) could affect the
lamination affect nominal K and LT, but dielectric and have once
understood, is very consistent localized areas of K Developmental
systems: K = 3-4, LT = 0.001-0.003 change. on internal Stripline
structures Highly Mechanical Reliability; Large vias w/ donuts Vias
are filled with metal (Ag or Au (Vertical Transitions to the (more
detailed impedance based) and are sintered at 850.degree. C. outer
surface are required) matching) are required. (chemically and
mechanically bonded Limitations on blind and together). NO design
limitations as buried vias. compared to PTFE vias. Vias are
"mechanically" No donuts or capture pads are required for contacted
from layer to signal vias, but capture pads are layer, reducing the
recommended on ground vias (non critical reliability during thermal
areas) cycle/shock. Localized areas of thermal via arrays can Vias
are hollow, and side be created for higher thermal dissipation.
walls of dielectric are plated w/ Cu. = or >4 layers (= or >2
Large metal ground Dielectric is hermetic and homogeneous.
stripline regions) planes within the PTFE Conductors form a
chemical and body limit the heat mecanical bond with dielectric,
and are an distribution, which create additive pattern (no
etching/plating) on areas of local the internal stripline layers.
delamination. During the etching/plating process, fluids seep into
the delam areas and stay there until post processing, such as
solder reflow for SMT's and degrade reliability X-Y Size <7''
square Difficult to control Flatness will be <2mils/Inch
flatness/camber during lamination, when layer count is >4 layers
and there are large gnd planes for the stripline circuits
**"Microwave Laminate Material Considerations for Multilayer
Military Applications", R. Hornung & J. Frankosky, RF Globalnet
Newsletter, 2006, Arlon Inc.
[0039] Two important components of phased array antennas are phase
shifters and feed networks. With Low K LTCC Phase shifters,
performance can be improved including power handling, losses, and
bandwidth of the phase shifters. Feed networks including series,
parallel, and space can also be implemented. Filters using low k
LTCC can now be improved upon by designing in lower impedance
allowing wider lines, which allows for overall better insertion
loss, return loss, achieving rejection points, bandwidth In the
case of Antenna Arrays path loss 88 db at 60 GHz is pushing the
circuits to its limit. The only way to make up for extra loss at
the higher frequencies is with the use of higher gain antenna
Arrays can be implemented in LTCC, but a major drawback is that
most LTCC systems have a dielectric constant>6, which lowers the
gain and bandwidth of the antenna. A lower k-based LTCC (k=3 or 4)
with lower dielectric loss material has the antenna array allowing
for higher gain and improved bandwidth and other improved metrics.
In summary, use of low k dielectric thick film materials either by
themselves or in combination with other LTCC systems designs can be
improved in the case of Phase Shifters, Feed Networks, Frequency
Scanning Arrays, Wideband Arrays, Radar Phased Arrays, Beam
formers, Filters, Couplers, Baluns, Power Dividers, Quadrature
Couplers, Hybrid Junctions and others. Through the use of LTCC
technology and the newly available low k dielectric thick film
materials, layers of low k thick film dielectric materials may be
placed in specified z locations in the electronic package stackup
which allows for more degrees of freedom for the designer for RF,
microwave, and mmwave signal processing.
[0040] As used herein, the terms "thick film" and "thick film
paste" refer to dispersions of finely divided solids in an organic
medium, which are of paste consistency or tape castable slurry and
have a rheology suitable for screen printing and spray, dip, ink
jet or roll-coating. As used herein, the term "thick film" means a
suspension of powders in screen printing vehicles or tape castable
slurry, which upon processing forms a film with a thickness of
several microns or greater. The powders typically comprise
functional phases, glass and other additives for adhesion to the
substrate, etc. The vehicles typically comprise organic resins,
solvents and additives for rheological reasons. The organic media
for such pastes are ordinarily comprised of liquid binder polymer
and various rheological agents dissolved in a solvent, all of which
are completely pyrolyzable during the firing process. Such pastes
can be either resistive or conductive and, in some instances, may
even be dielectric in nature. The thick film compositions of the
present invention contain an inorganic binder as the functional
solids are required to be sintered during firing. A more detailed
discussion of suitable organic media materials can be found in U.S.
Pat. No. 4,536,535 to Usala, herein incorporated by reference. In
some embodiments, fired dielectric thick film layers are on the
order of 3-300 microns for a single print or tape layer, and all
ranges contained therein. In further embodiments, the thickness of
the fired dielectric thick film layer is in the range of 3-5
microns, 5-10 microns, 10-15 microns, 30-250 microns.
I. High k Dielectric Tape Composition(s)
[0041] The present invention utilizes commercially available
dielectric thick film tape compositions as a constraining tape,
either externally or internally. These commercially available high
k dielectric thick film tapes comprise crystallizable glass-based
systems such as borate-, borosilicate, or boro-phospho-silicate
glass networks, as used in commercially available tape Nos. 951,
943 or tapes described in U.S. patent application Ser. No.
11/543,742, herein incorporated by reference (commercially
available from E.I. du Pont de Nemours and Company). These
commercially available high k tapes are particularly useful in the
present invention. As used herein, "high k" tapes are in the range
of 6 to 8 k. The dielectric tapes noted immediately above are not
standard constraining tapes. Standard constraining tapes, and will
react with the functional tape layers and cannot be removed from
the LTCC device, without damaging the circuits.
[0042] The high k tapes useful in the present invention are
typically very reactive and would likely react with standard
constraining tapes noted above, if used internally or externally;
and therefore, high frequency properties such as dielectric loss
and dielectric constant may degrade. Therefore, standard
constraining tapes are not useful for use in conjunction with these
borate-based, low loss dielectric tapes used in high frequency
applications.
[0043] The present inventors have developed low k dielectric thick
film compositions and methods for their use which provide (1) low
dielectric loss tape for high frequency application with lower
dielectric constant than the presently available k 6-8 (2) a lower
shrinkage value than that presently available shrinkage value of
7-12% without using a constraining tape and (3) in some
embodiments, a low k tape which provides the added property of
constraining the high k dielectric tape (Commercially available
Product Nos. 943, 951 and commercially available tape disclosed in
U.S. patent application Ser. No. 11/543,742), and finally (4) the
low k dielectric tape reacts with the high k dielectric tape and
upon firing results in a continuous structure without delamination
and which allows the circuit designers to incorporate several
k-value tapes at appropriate locations in the z-direction of the
circuits to control the functional property of the circuits at the
appropriate locations. In some embodiments, upon firing the low k
and high k tapes, a homogeneous structure (i.e., a structure in
which the individual tape layers are indistinguishable)
results.
[0044] The present inventors have developed a novel low k and low
dielectric loss tape. Furthermore the low k tape described in this
invention is compatible with the commercially available dielectric
thick film tapes and could be used in specific layers of the LTCC
structure. The novel low k tape has lower shrinkage than any
commercially available functional LTCC tapes with an additional
property of constraining presently available other functional green
tapes (for example the high k dielectric tapes disclosed above), if
used in conjunction.
[0045] Typically, a LTCC tape is formed by casting a slurry of
inorganic solids, organic solids and a fugitive solvent on a
removable polymeric film. The slurry consists of glass powder(s)
and ceramic oxide filler materials and an organic based
resin-solvent system (medium) formulated and processed to a fluid
containing dispersed, suspended solids. The tape is made by coating
the surface of a removable polymeric film with the slurry, so as to
form a uniform thickness and width of coating.
[0046] In one embodiment, LTCC tape materials available for use as
a dielectric tape layer in high frequency LTCC applications are
disclosed in U.S. patent application Ser. No. 11/543,742, the
parent application of the present invention to which the present
invention claims priority. Furthermore, some embodiments of the
dielectric thick film tape composition of U.S. patent application
Ser. No. 11/543,742 are useful in the present invention as the high
k thick film tape layer. This dielectric tape is designed to
eliminate potentially toxic constituents and exhibits a uniform and
relatively low dielectric constant in the range of 6-8.
Additionally, the dielectric tape has a low dielectric loss
performance over a broad range of frequency up to 90 GHz or
sometimes higher depending on the metal loading.
II. Low k Thick Film Dielectric Tape Composition(s)
[0047] The low k tape has a very low shrinkage compared to
commercially available "LTCC circuit functional tapes" and in
addition, it constrains other commercially available tapes if used
in the z-direction of the LTCC structure and does not require
removal after processing. The low k tape exhibits processing and
materials compatibility with conductors and passive electronic
materials when used to build high density, LTCC circuits. The low k
tape system or "low k tape-based composite system" with other
commercially available low loss tapes provides low dielectric loss
over frequencies up to 90 GHz or higher, more circuit design
freedom than PTFE structures, superior X-Y constraining effect and
good bonding between the low k tape and high k tape without
delamination of layers under the standard processing conditions of
LTCC system described in the invention. No buffer layer is required
between the thick film dielectric tape layers of the present
invention.
[0048] Overall, the present invention provides a self constrained
LTCC system which allows higher integration of RF, Microwave,
and/or mm wave signal processing capability into one module,
package, or board. There is no LTCC or multilayer ceramic system
that exists which allows use of multiple high and low k dielectric
layers to be used together in one composite module, package, or
board (i.e., structure) which is self constrained in the X-Y
direction and which also has low k and low loss. This invention
will use combinations of layers consisting of various high k and
low k values, thicknesses, and loss values into one LTCC
structure.
[0049] Commercially available dielectric green tapes useful for
LTCC devices have a lowest dielectric constant of approximately
6-7. Circuit designers are looking for a k value that is much lower
than the commercially available dielectric thick film LTCC tapes.
The low K dielectrics are used in nearly all RF modules above 30
GHz. Being able to place layers of K lower than 6-8 in certain z
locations in the stack-up allows more degrees of freedom for the
circuit designer.
[0050] Antennas are now similar to those designed in PTFE due to
the use of lower K dielectrics on the external layers of the
module. Using lower K allows wider RF lines to maintain a
resistance of 50 ohms. This has a two-fold impact on the designs:
(1) wider lines have higher yields because the line width tolerance
has a smaller effect than does a narrower line and (2) wider lines
give better performance (i.e. attenuation is lower) than narrower
lines.
[0051] All green tapes shrink during the LTCC processing. The
shrinkage is a function of many parameters: including particle size
and particle size distribution of inorganic oxide present in the
tape; ratio of organic to inorganic materials; kinetics of
"Un-zipping" and depolymerization of polymers and "burn-out" of
carbonaceous species; kinetics of glass-softening; interaction of
glass components to inorganic filler materials present in the tape,
if any; nucleation and growth of crystals, if the glass is
crystallizable. Even though shrinkage is a three dimensional
phenomenon, the most important aspect for LTCC circuit designers is
X-Y shrinkage. Preferred crystal growth has less impact on the
design. However elongated crystal growth could produce surface
roughness, unwanted property variations. Zero X-Y shrinkage and/or
control of shrinkage to a lowest possible level is a desirable.
Ceramicists have developed materials and tapes to control and
constrain the LTCC tapes. These constrain tapes are based on least
sinterable ceramic materials such as alumina and silica at the LTCC
processing temperature. Other requirements for these constraining
tapes is that it should be easily removable from the surfaces of
the LTCC circuits after the sintering of the circuits; i.e., least
reactive to the functional tape layers. Some constraining tapes are
used internally by inserting in the Z-direction of composite layers
of the functional tapes and they will become part of the circuit
and will not be removed unlike tapes used to constrain externally.
All the available internally constraining such tapes have high
dielectric constants compared to the dielectric constant needed for
high frequency applications. The LTCC tapes used in high frequency
applications and described in the earlier section is borate or
boro-silicate, or boro-phospho-silicate glass based system which
will crystallize at the LTCC processing conditions, leaving behind
a low viscosity "remanent glass". The externally constraining tapes
react with the "remanent glass" so it is difficult to remove after
processing without damaging the circuits, and/or leaving behind
residues. Presence of such residues on the surface makes it
impossible to add functional units on the surface. So an ideal
solution is to develop a LTCC tape with a lower shrinkage value
closer to zero or lowest acceptable shrinkage for design
requirements without using a constraining tape.
[0052] The applications described in 1 of this section, also need
the new tape that should be compatible with other commercially
available low loss tapes to mix and match several different tapes
with different dielectric properties that circuit designers' need.
Furthermore the new tape should have a property to constrain other
high shrinkage tapes commercially available, if used in conjunction
with high frequency circuits. For example, U.S. patent application
943 Green tape described in U.S. Pat. No. 6,147,019 and EL-0518 has
a shrinkage of 9.5% when used in LTCC devices. Without
constraining, it is difficult to incorporate tapes with different
shrinkages into a composite for the complex electronic functions
listed earlier.
[0053] Constraining the tape internally and/or externally and
reducing the shrinkage of the composite to a minimum are the
essential needs for the future device requirements. Standard
constraining tapes cannot be used in conjunction with these tape
chemistries because they react together and cannot be removed after
processing, thus degrading dielectric properties: increased K,
dielectric loss, and circuit surface damage if constraining tape is
removed mechanically.
[0054] The present invention is directed to a borate,
boro-silicate, or a boro-phospho-silicate crystallizable
glass-based tape with ceramic oxide filler components to control
the crystallization of the glass, control the viscosity of the
"remanent" glass, and lower the dielectric constant of the fired
composite. Furthermore, the new tape may be compatible with other,
commercially available low dielectric loss tapes so that they can
integrated together for several property functions.
[0055] Furthermore the new tape may be incorporated into any LTCC
composite system with compatable chemistry if the circuit designer
so desires to incorporate specific layers of lower K and low loss
dielectric properties in the circuits. Such incorporation may
introduce alternations in the functional property of other tape
layers in the system.
[0056] The materials are characterized by their freedom from toxic
metal oxides such as oxides of lead cadmium. The materials are
designed to process at about 850-875 oC useful in current tape
dielectric materials. The processing conditions can be adjusted for
a particular LTCC circuit. The tape is designed to cofire with
conductors, buried capacitors and other passive electrical
components applied by screen printing or tape casting or other
similar processing conditions.
A. Ceramic Oxide(s)
[0057] The compositions described, that have small SiO.sub.2
additions, have shown significant improvement in the compatibility
with Ag based conductor lines. The tendency to interact in
proximity to Ag conductor lines is suppressed in the tape
compositions tested that were made from glasses that give high
viscosity "remanent glass". The dielectric loss properties reported
unexpectedly shows that the addition of small amount of SiO.sub.2
in the composition do not alter significantly the dielectric
characteristics of the tape dielectric. The low addition levels of
SiO.sub.2 addition to glass shown in this case was not reported in
Donohue et al. U.S. Pat. No. 6,147,019. The addition of SiO.sub.2
was indicated as not beneficial to dielectric loss.
[0058] In the present invention, significantly higher amount of
silica is added as second crystalline phase filler to borate or
boro-silicate or boro-phospho-silicate glasses to reduce the
dielectric constant and green tape shrinkage to satisfy the low k
needs of LTCC designers.
[0059] Therefore, the present invention provides a low k thick film
dielectric tape composition comprising, based on wt % total
inorganic composition: (1) 40-80%, preferably 45-55% borate-based
or, boro-silicate, or boro-phospho-silicate-based glass composition
such as glass chemistry described in U.S. Pat. No. 6,147,019;
EL-0518; DUPONT glass used in Green Tape 951, or similar
crystallizable glasses with a log viscosity range at the peak
firing temperature 2-6 Poise (2) 20-60%, preferably 30-50% ceramic
oxide or mixed oxide fillers such as silica, silicates compatible
to glass chemistry (3) 0-5% other inorganic oxides and compounds
such as copper oxide and others with similar chemistries.
B. Glass Frit
[0060] In the formulation of tape compositions, the amount of glass
relative to the amount of ceramic material is important. A filler
range of 20-60% by weight is considered desirable in that the
sufficient densification is achieved. If the filler concentration
exceeds 60% by wt., the fired structure is not sufficiently
densified and is too porous. Within the desirable glass to filler
ratio, it will be apparent that, during firing, the filler phase
will become saturated with liquid glass. The glass-filler ratio
variation is also depends on the viscosity of the glass at the
softening point, viscosity of the "remanent glass", and the nature
of the filler to the so-called glass "net-work formers"
[0061] For the purpose of obtaining higher densification of the
composition upon firing, it is important that the inorganic solids
have small particle sizes. In particular, substantially all of the
particles should not exceed 15 um and preferably not exceed 10 um.
Subject to these maximum size limitations, it is preferred that at
least 50% of the particles, both glass and ceramic filler, be
greater than 1 um and less than 6 um.
[0062] One embodiment of the glass composition used in this
invention is a boro-phospho-silicate glass network consisting
essentially of, based on mole percent, 50-56% B.sub.2O.sub.3,
0.5-5.5% P.sub.2O.sub.5, SiO.sub.2 and mixtures thereof, 20-50%
CaO, 2-15% Ln.sub.2O.sub.3 where Ln is selected from the group
consisting of rare earth elements and mixtures thereof, 0-6%
M.sup.I.sub.2O where M.sup.I is selected from the group consisting
of alkali elements; and 0-10% Al.sub.2O.sub.3, with the proviso
that the composition is water millable. Another glass used in this
invention has been described in Donahue and others in Hang et al.
The inorganic filler used in this invention is silica powder has
the surface area of 0.5-15.0 m2/gm preferably 7.0-13.0 m2/gm. Other
mixed ceramic oxides and/or mixtures of ceramic oxides compatible
to the wetting characteristics of the crystallizable glasses that
have a log viscosity range 2-6 Poise at the maximum firing
temperature of 850 oC.
C. Organic Medium
[0063] The organic medium in which the glass and ceramic inorganic
solids are dispersed is comprised of an organic polymeric binder
which is dissolved in a volatile organic solvent and, optionally,
other dissolved materials such as plasticizers, release agents,
dispersing agents, stripping agents, antifoaming agents,
stabilizing agents and wetting agents.
[0064] To obtain better binding efficiency, it is preferred to use
at least 5% wt. polymer binder for 90% wt. solids (which includes
glass and ceramic filler), based on total composition. However, it
is more preferred to use no more than 30% wt. polymer binder and
other low volatility modifiers such as plasticizer and a minimum of
70% inorganic solids. Within these limits, it is desirable to use
the least possible amount of binder and other low volatility
organic modifiers, in order to reduce the amount of organics which
must be removed by pyrolysis, and to obtain better particle packing
which facilitates full densification upon firing.
[0065] In the past, various polymeric materials have been employed
as the binder for green tapes, e.g., poly(vinyl butyral),
poly(vinyl acetate), poly(vinyl alcohol), cellulosic polymers such
as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose,
methylhydroxyethyl cellulose, atactic polypropylene, polyethylene,
silicon polymers such as poly(methyl siloxane), poly(methylphenyl
siloxane), polystyrene, butadiene/styrene copolymer, polystyrene,
poly(vinyl pyrollidone), polyamides, high molecular weight
polyethers, copolymers of ethylene oxide and propylene oxide,
polyacrylamides, and various acrylic polymers such as sodium
polyacrylate, poly(lower alkyl acrylates), poly(lower alkyl
methacrylates) and various copolymers and multipolymers of lower
alkyl acrylates and methacrylates. Copolymers of ethyl methacrylate
and methyl acrylate and terpolymers of ethyl acrylate, methyl
methacrylate and methacrylic acid have been previously used as
binders for slip casting materials.
[0066] U.S. Pat. No. 4,536,535 to Usala, issued Aug. 20, 1985, has
disclosed an organic binder which is a mixture of compatible
multipolymers of 0-100% wt. C.sub.1-8 alkyl methacrylate, 100-0%
wt. C.sub.1-8 alkyl acrylate and 0-5% wt. ethylenically unsaturated
carboxylic acid of amine. Because the above polymers can be used in
minimum quantity with a maximum quantity of dielectric solids, they
are preferably selected to produce the dielectric compositions of
this invention. For this reason, the disclosure of the
above-referred Usala application is incorporated by reference
herein.
[0067] Frequently, the polymeric binder will also contain a small
amount, relative to the binder polymer, of a plasticizer that
serves to lower the glass transition temperature (Tg) of the binder
polymer. The choice of plasticizers, of course, is determined
primarily by the polymer that needs to be modified. Among the
plasticizers which have been used in various binder systems are
diethyl phthalate, dibutyl phthalate, dioctyl phthalate, butyl
benzyl phthalate, alkyl phosphates, polyalkylene glycols, glycerol,
poly(ethylene oxides), hydroxyethylated alkyl phenol,
dialkyldithiophosphonate and poly(isobutylene). Of these, butyl
benzyl phthalate is most frequently used in acrylic polymer systems
because it can be used effectively in relatively small
concentrations.
[0068] The solvent component of the casting solution is chosen so
as to obtain complete dissolution of the polymer and sufficiently
high volatility to enable the solvent to be evaporated from the
dispersion by the application of relatively low levels of heat at
atmospheric pressure. In addition, the solvent must boil well below
the boiling point or the decomposition temperature of any other
additives contained in the organic medium. Thus, solvents having
atmospheric boiling points below 150.degree. C. are used most
frequently. Such solvents include acetone, xylene, methanol,
ethanol, isopropanol, methyl ethyl ketone, ethyl acetate,
1,1,1-trichloroethane, tetrachloroethylene, amyl acetate,
2,2,4-triethyl pentanediol-1,3-monoisobutyrate, toluene, methylene
chloride and fluorocarbons. Individual solvents mentioned above may
not completely dissolve the binder polymers. Yet, when blended with
other solvent(s), they function satisfactorily. This is well within
the skill of those in the art. A particularly preferred solvent is
ethyl acetate since it avoids the use of environmentally hazardous
chlorocarbons.
[0069] In addition to the solvent and polymer, a plasticizer is
used to prevent tape cracking and provide wider latitude of
as-coated tape handling ability such as blanking, printing, and
lamination. A preferred plasticizer is BENZOFLEX.RTM. 400
manufactured by Rohm and Haas Co., which is a polypropylene glycol
dibenzoate.
Application
[0070] A green tape is formed by casting a thin layer of a slurry
dispersion of the glass, ceramic filler, polymeric binder and
solvent(s) as described above onto a flexible substrate, heating
the cast layer to remove the volatile solvent. This forms a
solvent-free tape layer. The tape is then blanked into sheets or
collected in a roll form. The green tape is typically used as a
dielectric or insulating material for multilayer electronic
circuits. A sheet of green tape is blanked with registration holes
in each corner to a size somewhat larger than the actual dimensions
of the circuit. To connect various layers of the multilayer
circuit, via holes are formed in the green tape. This is typically
done by mechanical punching. However, a sharply focused laser or
other method(s) can be used to volatilize and form via holes in the
green tape. Typical via hole sizes range from 0.004'' to 0.25''.
The interconnections between layers are formed by filling the via
holes with a thick film conductive ink. This ink is usually applied
by standard screen printing techniques. Each layer of circuitry is
completed by screen printing conductor tracks. Also, resistor inks
or high dielectric constant inks can be printed on selected
layer(s) to form resistive or capacitive circuit elements.
Furthermore, specially formulated high dielectric constant green
tapes similar to those used in the multilayer capacitor industry
can be incorporated as part of the multilayer circuitry.
[0071] After each layer of the circuit is completed, the individual
layers are collated and laminated. A confined uniaxial or isostatic
pressing die is used to insure precise alignment between layers.
The laminate assemblies are trimmed with a hot stage cutter. Firing
is typically carried out in a standard thick film conveyor belt
furnace or in a box furnace with a programmed heating cycle. This
method will, also, allow top and/or bottom conductors to be
co-fired as part of the constrained sintered structure without the
need for using a conventional release tape as the top and bottom
layer, and the removal, and cleaning of the release tape after
firing.
[0072] The dielectric properties of the fired tape (or film) of the
present invention depend on the quantity and/or quality of total
crystals and glasses present and other factors. The low temperature
co-fired ceramic (LTCC) device dielectric properties also depend on
the conductor used. The interaction of conductor with the
dielectric tape may, in some embodiments, alter the chemistry of
the dielectric portion of the device. By adjusting the heating
profile and/or changing the quality and/or quantity of the filler
in the tape and/or chemistry of the conductor, one skilled in the
art could accomplish varying dielectric constant and/or dielectric
loss values.
[0073] As used herein, the term "firing" means heating the assembly
in an oxidizing atmosphere such as air to a temperature, and for a
time sufficient to volatilize (burn-out) all of the organic
material in the layers of the assemblage to sinter any glass, metal
or dielectric material in the layers and thus density the entire
assembly.
[0074] It will be recognized by those skilled in the art that in
each of the laminating steps the layers must be accurate in
registration so that the vias are properly connected to the
appropriate conductive path of the adjacent functional layer.
[0075] The term "functional layer" refers to the printed green
tape, which has conductive, resistive or capacitive functionality.
Thus, as indicated above, a typical green tape layer may have
printed thereon one or more resistor circuits and/or capacitors as
well as conductive circuits.
[0076] It should also be recognized that in multilayer laminates
having greater than 10 layers typically require that the firing
cycle may exceed 20 hours to provide adequate time for organic
thermal decomposition.
[0077] The use of the composition(s) of the present invention may
be used in the formation of electronic articles including
multilayer circuits, in general, and to form microwave and other
high frequency circuit components including but not limited to:
high frequency sensors, multi-mode radar modules,
telecommunications components and modules, and antennas. The system
described in the present invention allows higher integration of
microwave functions into one module, package, or board. Other Major
Significance is that no other LTCC or multilayer ceramic system
that exists which allows use of multiple dielectric layers to be
used together in one composite module, package, or board. This
invention will use combinations of layers consisting of various K
values, thicknesses, loss values into one composite structure.
Multilayer Circuit Formation
[0078] The present invention further provides a method of forming a
multilayer circuit comprising the steps:
[0079] wherein, said circuit achieves a x,y-shrinkage in the range
of 0-5% and wherein said low k constraining tape layer has a k
value in the range of 2-5, and wherein said tapes allow more
degrees of freedom for high-frequency LTCC circuit designers to mix
and match several tapes with the tapes described in this invention
for specific circuit requirements
[0080] FIG. 2 details one embodiment of the present invention-based
circuit of a microwave module. The following items are detailed in
FIG. 2: [0081] 10 Surface Metalization for wirebonding, soldering,
brazing, and other post process applications as well as external RF
lines for interconnect to the Stripline section(s) [0082] 20 High k
thick film tape [0083] 30 Interposer [0084] 40 Signal Vias which
connect the surface devices such is SMT's, IC's, packaged devices
and other signal processing components to the internal microwave
circuits on the internal Low K layers which form the stripline
circuits. [0085] 50 Vias connecting the two stripline grounds in
the LowK region for "via fencing" for microwave designs to improve
circuit performance. [0086] 60. Solid, Gridded, or partial Grounds
to form the grounds for the Stripline Sections [0087] 70 Thru-All
Cavities to access baseplate from surface. Cavities from the top to
place IC's or components or other devices which would benefit from
being recessed planar to the surface of the LTCC. [0088] 80
Stripline, Buried Microstrip, Covered GCPW, laminated waveguide,
and other methods for guiding propagated RF, microwave, or mmWave
Signals or using for purposes of signal Lines for RF functions
(Beamformer, Filters, antennas, couplers, etc. [0089] 90 Stripline
Section of low k LTCC [0090] 100 Baseplate for thermal dissipation
and/or mechanical strength which can be soldered, epoxied, or
brazed.
[0091] These multilayer circuits require that the circuit be
constructed of several layers of conductors separated by insulating
dielectric layers. The insulating dielectric layer may be made up
of one or more layers of the tape of the present invention. The
conductive layers are interconnected between levels by electrically
conductive pathways through a dielectric layer. Upon firing, the
multilayer structure, made-up of dielectric and conductive layers,
a composite is formed which allows for a functioning circuit (i.e.
an electrically functional composite structure is formed). The
composite as defined herein is a structural material composed of
distinct parts resulting from the firing of the multilayer
structure which results in an electrically functioning circuit.
[0092] Another circuit design by mix and match with other
commercially available tapes and tape of this invention is shown
below
EXAMPLES
[0093] Tape compositions used in the examples were prepared by ball
milling the fine inorganic powders and binders in a volatile
solvent or mixtures thereof. To optimize the lamination, the
ability to pattern circuits, the tape burnout properties and the
fired microstructure development, the following volume %
formulation of slip was found to provide advantages. The
formulation of typical slip compositions is also shown in weight
percentage, as a practical reference. The inorganic phase is
assumed to have a specific density of 3.5 g/cc for glass and 2.2
g/cc for silica and the organic vehicle is assumed to have a
specific density of 1.1 g/cc. The weight % composition changes
accordingly when using other glasses and oxides other than silica
as the specific density may be different than those assumed in this
example. TABLE-US-00002 TABLE 2 Slip Composition wt % Inorganic
Phase 73.8 Organic Phase 26.2
[0094] The above weight % slip composition may vary dependent on
the desirable quantity of the organic solvent and/or solvent blend
to obtain an effective slip milling and coating performance. More
specifically, the composition for the slip must include sufficient
solvent to lower the viscosity to less than 10,000 centipoise;
typical viscosity ranges are 1,000 to 4,000 centipoise. An example
of a slip composition is provided in Table 2. Depending on the
chosen slip viscosity, higher viscosity slip prolongs the
dispersion stability for a longer period of time (normally several
weeks). A stable dispersion of tape constituents is usually
preserved in the as-coated tape.
[0095] If needed, a preferred inorganic pigment at weight % of 0.1
to 1.0 may be added to the above slip composition before the
milling process. TABLE-US-00003 TABLE 3 The inorganic chemical
composition of the tape formulation. Tape # 1 2 3 Glass Powder 57%
50% 45% Silica 43% 50% 45%
Glass powder used in this composition is a phospho-boro-silicate
glass described in commonly assigned patent application Ser. No.
11/543,742. Silica in the composition #1 and #2 has a PSD
.about.1.5 (D50) and silica in composition #3 is finer with surface
area .about.8-12 m2/gm. Property Measurements: Dielectric
Properties
[0096] The measurement of dielectric constant, E.sub.r and
dielectric loss (tangent delta) has been performed for selected
samples of tape made from the tapes indicated in Table 2. These
measurements were performed using a (non-metallized) split cavity
method in a range of frequency from 3.3 GHz to 16 GHz. A reference
to the measurement method is given in "Full-Wave Analysis of a
Split-Cylinder Resonator for Nondestructive Permittivity
Measurements" by Michael Janezic published in IEEE Transactions on
Microwave Theory and Techniques, Vol 47, No. 10, October 1999. Data
for two frequencies are provided in Table 2. The data, (E.sub.r and
loss), for all measured samples shows a very slight increase with
frequency. TABLE-US-00004 TABLE 4 Dielectric Properties of LTCC
Based on Inorganic Materials Described in Table 1 along with
properties of some standard LTCC tapes. Frequency of Tape ID#
measurement K Loss Tangent 1 10.73 GHz 3.01 0.004 2 10.44 GHz 3.94
0.003 3 LTCC (EL#518) 7.34 0.001 943-A5 (low loss LTCC) 7.66 0.001
851-AT (standard LTCC) 7.53 0.004
The dielectric constant reduced to approximately 50% however and
dielectric loss is increased slightly for the LTCC tape in the
current invention.
[0097] The dielectric properties of the fired film of this
invention, which is a "devitrified glass-ceramic-glass composite",
depend on the quantity and/or quality of total crystals and glasses
present in the composite. The LTCC dielectric properties also
depend on the conductor film which is a "metal-devitrified
glass-ceramic composite".
[0098] It was stated earlier, one of major contributions of this
invention should give freedom for circuit designers to incorporate
different layers of LTCC tapes for different function in a
composite format.
Tape Shrinkage and Refire Stability
[0099] The shrinkage values have been measured then calculated
using the "Hypotenuse" method, known to those skilled in the art.
All parts were fired at 850.degree. C. following a standard green
tape firing profile. Several composite test format have been made
to demonstrate the shrinkage of the tape of this invention and its
ability to constrain other commercially available tapes if
incorporated within the composite.
[0100] Details of a some typical eight layer composite structures
are given below. A refers to 951 and B refers to 943 are commercial
tapes of DUPONT COMPANY, Wilmington, Del. E refers to the tape
described in EL#518 and C refers to tape of this invention. Table 4
is a representation of some typical test pattern builds and Table 5
is the shrinkage of 8 layer composites after firing in a typical
green belt furnace profile. All results show up to approximately
80% more constraining than the shrinkage of some of the
commercially available LTCC tape. The shrinkage of the LTCC tape of
this invention has a shrinkage of .about.1%. TABLE-US-00005 TABLE 5
Some Typical 8 layer Composite LTCC Structures based on Different
Constraining Format:* Test Build #1 #2 #3 #4 #5 #6 Tape Layer #1 A
A C A A B Tape Layer #2 C C E E C C Tape Layer #3 B E E C C C Tape
Layer #4 B E E E C C Tape Layer #5 B E E E C C Tape Layer #6 B E E
C C C Tape Layer #7 C C E E C C Tape Layer #8 A A C A A B #1, #2
& #4 are internally constraining Composite Format and #3 is
externally constraining composite format. #5 & #6 are typical
circuit systems using the tape of this invention in composite
format. "C" is the Tape of this invention. "A", "B" and "E" are
commercially available tape or tapes described in U.S. Pat. App.
No. 11/543742 Microstructures taken using Scanning Electron
microscope of the fired film of all the composites show (1) no
delamination between the layers (2) good microstructures in terms
of grain and grain boundaries and (3) no significant increase in
the level of porosity
[0101] TABLE-US-00006 TABLE 6 X-Y Shrinkage the LTCC Tape of This
Inventionn (TTI) Some Other LTCC Composites Incorporating with TTI.
Eight Layer X-Y Shrinkage Tape Specification Composite Structure
(%) -951 + TTI 951 (6) + TTI (2)** 4.32 -943 + TTI(#2) 943 (6) +
TTI (2)** 2.42 -993 + TTI(#3) 943 (6) + TTI (2)** 0.98 -944 (1) +
TTI(#2) 944 (6) + TTI (2)** 3.15 -944 (2) + TTI(#2) 944 (6) + TTI
(2)** 3.20 -951 Alone 12.75 -943 Alone 9.84 -944 (1)* Alone 10.92
-944 (2)* Alone 9.50 *944 (1) and 944 (2) are based on two
different tape chemistries convered in U S Patent application
11/543742 (Attorney Docket # EL-0518USNA). Finer silica-based based
tape of this invention (#3) gave lower shrinkage when used in the
composite structure described here compare to tape contains coarser
silica (#1 & #2) **Two layers of "tape of this invention" (TTI)
are inserted anywhere in a symmertical manner as ahown in the table
within the 8 layers of commecially available green tapes, 951, 943,
& 944. TTI layers are "circuit functional layers" of the
overall circuit and need not to be removed. TTI layers could be
connected with other tape layers through via-fill conductors, and
circuit conductor lines in the conventional manner.
Microstructure of the Fired Composites The microstructral analysis
on Scanning Electron Micrographs of several combinations of low K
tape and other LTCC tapes composites has shown (1) complete
interfacial microstructral compatibility (2) good densification of
the low k tapes and (3) no significant microstructural defects of
any kind.
[0102] Dielectric constant of two different tape formulations in a
buried composite form is measured. Results show the effect of
conductor binders on the K values. TABLE-US-00007 TABLE 7 A TTI
Buried Composite With Different Conductors and Other LTCC Tape 943
Tape Conductor Low K Tape of This invention Conductor 943 943 943
943 Low K Tape of This invention 943 Tape
[0103] K values of the low K tape as measured within the buried
form for three different conductors are given below. Used vias to
measure the cap values. Results show the conductor binder effect on
the dielectric constant K values are calculated from the measured
capacitor value at frequency 1 KHz and calculated thickness values
using tape shrinkage data from table 6. TABLE-US-00008 TABLE 8
Variation of K values as Measured in Buried Form With Different
Conductors for the Composite format in Table 7 Tape ID Glass/Filler
(%) Conductor Capacitance (pF) K Tape 1 57/43 Gold 117 2.7 Tape 1
57/43 Silver - 1 125 2.8 Tape 1 57/43 Silver - 2 154 3.4 Tape 2
50/50 Gold 152 2.7 Tape 2 50/50 Silver - 1 236 4.2 Tape 2 50/50
Silver - 1 256 4.6
* * * * *