Note: Descriptions are shown in the official language in which they were submitted.
-1 RCA 75, 431
CONDUCTOR INKS
This invention relates to thick-film conductor
inks and their use in multilayer electrical circuit
structures on porcelain-coated metal boards.
BACKGROUND_OF T~E INVENTION
The use of specialized ink formulations to form
thick films having various functions on suitable
substrates in the construction of multilayer structures is
well known in the art. Such technology is of increasing
interest in the fabrication of very dense multilayer
integrated clrcuit patterns on various substrates for a
wide variety of applications in the electronics industry.
Significantly improved substrates for the
fabrication of such circuits are disclosed and claimed in
Hang et al., U.S. Patent No. 4,256,796, issued March 17,
1981. The Hang et al. substrates are metal coated with an
improved porc01ain composition comprised of a mixture,
based on its oxide content, of magnesium oxide (MgO~ or
mixtures of magnesium oxide and certain other oxides,
barium oxide (BaO), boron trioxide (B2O3~ and silicon
dioxide (SiO2).
While the porcelain-coated metal substrates of
Hang et al. represent a significant improvement over
previously known substrate materials, they are
disadvantageous only in being incompatible or poorly
compatible with commercially a~ailable thick-film inks.
; This invention is concerned with improved coppe~ conductor
inks compatible with the Hang et al. substrates.
It is generally recognized that it is
advantageous to include bismuth oxide in copper conductor
inks to improve the solderability of films formed
therefrom. Conventionally, such inks contain from about 5
percent up to as much as 10 percent by weight bismuth
oxide. We have found that bismuth oxide in amounts in
excess of about 3 percent by weight of the ink formulation
will frequently cause a reaction at the point of contact
between a conductor film and a resistor. This results in
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a signiEicantly increased resistance at the point of
contact, a distinct disadvantage.
In accordance with this invention, copper
conductor inks are provided which are compatible with the
Hang et al. substrates, and are characterized by good
solderability without the aforementioned point of contact
reaction with resistors.
SUMMARY OF THE INVENTION
The improved conductor inks of this inven-tion
comprise a barium calcium borosilicate glass, copper
powder, bismuth trioxide and a suitable organic vehicle.
DETAILED DESCRIPTION OF T~E INVENTION
In accordance with -this invention, there are
provided improved copper conductor inks of high
reliability useful in the production of complex single or
multilayer thick-film circuits on suitable substrates,
particularly the porcelain-coated metal circuit boards of
Hang et al.
In addition -to being compatible with the
porcelain of the Hang et al. substrates, the improved
copper conductor inks of this invention are compatible
with inks of other functions specifically formulated
therefor. The subject copper conductor inks and other
functional and pro-tec-tive inks formulated for the ~ang et
al. porcelain-coated metal boards, together with the
~boards themselves, represent a significant advance in
multiIayer thick-film integrated circuit structures.
~ The novel copper conductor inks of this
30 ~ invention are comprised of copper powder, a glass frit,
bismuth oxide and a suitable organic vehicle.
The gIass frit of the cond-uctor inks of this
invention is a barium calcium borosilicate glass which is
compatible wi~h the porcelain of the Hang et al. boards.
3~ As a result, thich-film conductors prepared from the
subject in~s have excellent reheat stability and thermal
expansion properties similar to the Hang et al. substrate
boards. In addition, by controlling the amount of bismuth
oxide included in the inks of this invention, conductor
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thick-films formed from the inks of this inven-tion are not
characterized by the aforementioned reaction at point of
contact with resistors, yet possess the solderability
conventionally associated with larger amounts of bismuth
oxide.
The glass frit of the novel inks of this
invention is a barium calcium borosilicate glass
consisting of, on a weight basis:
a) from about 40 to about 55 percent, preferably
about 52 percent, of barium oxide;
b) from about lO to about 15 percent, preferably
about 12 percent, of calcium oxide;
c) from about 14 to about 25 percent, preferably
about 16 percent, of boron trioxide; and
d~ from about 13 to about 23 percent, preferably
about 20 percent, of silicon dioxide. The glass frit
comprises from about 1 to about 15 percent, preferably
from about 2 to about 6 percent by weight, of the total
ink cOmpOsition.
The copper powder utilized in the conductive
inks of this invention is pure copper having a particle
size of about 3.0 to 3.2 micrometers. The copper
comprises from abou-t 70 to about 40 percent, preferably
from about 7~ to about 82 percent by weight, of the
subject ink compositions.
The conductor inks of this invention contain
from about 0.5 to about 3.0 percent, preferably from about
1 to about 2 percent by weight, of bismuth oxide. It is
critical that the bismuth oxide content does not exceed
about 3 percent by weight of the total ink composition.
It i~s also necessary that the subjec-t inks contain no lead
; oxide since its presence will cause the same termination
reactions, even where the bismuth oxide content is well
below the 3 weight percent maximum. The bismuth oxide and
the glass frit are preferably present in the subjec-t inks
in a weight ratio of from about 1:1 to abou-t 1:3. The
bismuth oxide may be added to the subject inks as a powder
or may be present in the-glass frit itself.
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I -4- RCA 75,431
The oryanic vehicles are blnders such as, for
example, cellulose derivatives, particularly ethyl
cellulose, synthetic resins such as polyacrylates or
methacrylates, polyesters, polyolefins and the like. In
general, conventional vehicles utilized in inks of the
type described herein may be used in the subject inks.
Preferred commercially available vehicles include, for
e~ample, pure liquid polybutenes available as Amoco H-25
Amoco H-50~and Amoco I.-100 from Amoco Chemicals
Corporation, poly n-butylmethacrylate available from E. I.
duPont de Nemours and Co., and the like.
The above resins may be utilized individually or
in any combination of -two or more. A suitable viscosity
modifier can be added to the resin material if desired.
These modifiers can be sol~ents such as those
conventionally used in similar ink compositions, e.g. pine
oil, terpineol, butyl carbitol acetate, an ester alcohol
available from Texas Eastman Company under the trademark
Texanol and the like, or solid materials such as, for
example, a castor oil derivative available from N.L.
Industries under the trademark Thixatrol.
The vehicle of the subject inks may also contain
; up to about 25 percent by weight, preferably from about 10
to about 20 percent by weight, based on the vehicle, of a
suitable wetting agent of the type conventionally used in
copper conductor inks to aid in coating the particles of
~copper powder with the organic vehicle. As is the case
with all components of the organic vehicle,the wetting
0 agent must fire cleanly in nitrogen, i.e., without leaving
a carbonaceous residue.~ A preferred wet-ting agent is a
dispersion of a complex multifunctional, aliphatic
hydrocarbon in an aliphatic hydrocarbon oil available
under the trademark Hypothiolate 100 from Central
Compounding Company, Chicago, Illinois. The organic
vehicle comprises from about ~to about 25 percent by
weight, preferably from about 12 to about 15 percent by
weight,~of the subject inks.
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The improved copper conductor inks of this
invention are applied to the substrate, e.g., conventional
alumina boards or the improved porcelain-coated metal
boards of Hang et al. by conventional means, i.e. screen
printing, brushing, spraying and the like, with screen
printing being preferred. The coating of ink is then
dried in air at 100 - 125C for about 15 minutes. The
resulting film is then fired in nitrogen at peak
10 -temperatures of from 850 to 950C. for from 4 to 10
minutes.
Films formed from the novel conductor inks of
this invention have been demonstrated to be comparable
with conventional copper conductor inks in all properties
including solderability and to be clearly superior in
compatibility with the ~ang et al. por~elain-coated metal
substrate boards. Films formed from the novel copper
conductor inks of this invention demonstrate compatibility
bo-th with films formed from conventional thick-film tin
oxide or indium oxide resistor inks and resistor inks
formulated to be compatible with the Hang et al.
porcelain-coated metal boards. The films likewise
demonstrate good conductivity, solderability, solder leach
resistance, wire bondability and resistance to long term
exposure to high humidity.
The following Examples further illustrate this
inven-tion, it being understood that the invention is in no
way intended to be limited to the details described
therein. In the Examples, all parts and percentages are
on a weight basis and all temperatures are in degrees
Celsius unless otherwise stated.
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EXAMPLE 1
Copper conductor :inks were prepared from the
following formulations:
Percent by Weight
Ingredient A B C D E
Copper Powder81.0881.08 81.08 79.37 81.08
Glass Frit* 3.24 2.16 1.08 2.11 ---
Bi23 1.08 2.16 3.24 4.23 2.16
Commercial** -- --- --- --- 2.16
Pb/B/Si Glass
Vehicle*** 14.60 14.60 14.60 14.29 14.60
* The glass frit had the following composition:
BaO 51.32 percent; CaO 12.51 percent; B2O3 19.42
percent; and sio2 16.75 percent.
** Exact formulation not available. Estima-ted
lead oxide content 60 percent.
*** On a weight basis: 62.96 percent of a 6
percent solution of ethyl cellulose in the ester
alcohol Texanol available from Texas Eastman
Company; 18.52 percent Hypothiolate 100 wetting
agent available from Cen-tral Compounding
~ ~25 Company, Chicago, Ill. (dispersion of hydroxyl
; ~ ~ containing, multifunctional aliphatic hydrocarbon
in aliphatic hydrocarbon oil) and 18.52 percent
of an 11.2 percent dispersion of the castor oil
derivative Thixatrol, available from N.L.
30~ Industrles, in Texanol.
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The~powder ingredients were combined with the
organic vehicle, initiaIly mixed by hand and then on a 3
rol~l~ mil~l;with shearing to~obtain a smooth paste suitable
35 ~for screen printing. Additional vehlcle was added to
replace loss during mixing and~-to assure proper rheology.
Conductor terminations~were printed with the thus formed
inks on~a porcelain coated steel board of the type
disclosed by Hang et al.~ using a stainless steel screen
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(200 mesh, 1 mil emulsion). The terminations were dried
in air at 125 for 15 minutes and then fired in ni-trogen
ill a bel-t furnace at peak temperature of 850 ~ 10 for
8-12 minutes. Indium oxide resistor inks were then
printed, dried in a similar manner and fired in nitrogen
at 900 ~ 5 for 4-7 minutes at peak temperature. The
resistor widths varied from 50 to 100 mils. The resistor
inks utilized were prepared from the following
formulations:
Percent by Weight
Ingredient _ _
Indium Oxide 46.51 34.09
Glass I 27.91 ---
Glass II --- 38.64
Magnesium Oxide --- 4.55
Ethyl Cellulose, 6 percent, 25.58 22.72
Solution in Texanol
The glass frits utilized in the above resistor
ink formulations had the following composition.
:
Percent by Weight
~SE__ient ~ I II
`Barium Oxide 50.32 51.59
Calcium Oxide 12.28 12.58
Boron Trioxide 19.05 15.62
Silicon Dioxide ~16.43 20.21
Cobalt Oxide 1.92 ---
Average Particle Size 3.4 ~m 4.3 - 4.5 ~m
The sheet resistance of each of the five copper
conductor ~ilms was determined for each of the two
resl~stors. The results are reported in Table I.
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1 -8~RCA 75,431
TABLE I
Conductor Sheet Resistance KQ/o
Formulation I II
S A 9.8202.3
11.3297.3
C 16.3516.7
D 19.5882.3
E 28.9460.0
The data for formulations C and D demonstrate
that, when the bismuth oxide content of the inks exceeds 3
percent, the sheet resistance begins to rise sharply.
Formulation E shows that, even if the bismuth oxide
content of the copper ink is less than 3 weight percent,
the presence of lead oxide in the glass causes an
undesirable terminal point reaction.
EXAMPLE 2
A copper ink was prepared according to the
procedure of Example 1 from the formulation designated
"B". In this example, however, the bismuth oxide powder
was added to the oxides melted to make the glass frit as
opposed to being added to the~ink as a separate
ingredient. Terminations were printed and fired on a
conventional alumina board and two porcelain-coated steel
boards of the type disclosed by Hang et al. The
porcelains of the Hang et al.~,~ type boards had~the
following composition~
30~ Weight Percent in Porcelain
Ingredient~ A ~ B~
` Magnesium~Oxide ~ ~40.98~ ~ 27.96
Barium Oxlde ~ l8.82 37.34
Boron Triox~ide 24.41 16.96
;35~ Silicon~Diox~ide~ ~ ~ 15.79~ 17.74
Two~commercial stannic oxide containing resistor
inks~available~ from TRW,~Inc.,~Philadelphia, Pa. were
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printed and fired on the subs-trates in the manner of
Example 1. The sheet resistivities are reported in Table
II.
TABLE II
Sheet Resistance KQ/o
Resistor Ink Alumina Porcelain A Porcelain B
TS104 30.8 51.9 341
TS105 119.8 142.9 1157
The high resistance readings for porcelain B are
the result of the migration of iron into the porcelain
which in turn reduces the stannic oxide in the commercial
inks. The change in resistivity is due to the substrate
and not the copper inks. The data in Table II further
: demonstrates the compatibility of the copper conductor
inks of this invention with various substrates as well as
with films formed from commercial resistor inks.
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