Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Screen-printable or dispensable active brazing
pastes and process for producing the same
BACKGROUND of the INVENTION
1. Field of the Invention
The invention concerns a screen-printable or dispensable
active brazing paste for brazing a first aluminum oxide
ceramic body to a second aluminum oxide ceramic body, and a
dispensable active brazing paste for brazing an aluminum
oxide ceramic body to a metal body, and processes for
producing them.
The invention further concerns a process for producing an
actively brazed bond between a first aluminum oxide ceramic
body and a second aluminum oxide ceramic body using a first
region of active brazing paste applied to the first alu-
minum oxide ceramic body by screen printing and a second
region of active brazing paste covering the same area as
the first region, applied to the second aluminum oxide body
by screen printing, and a process for actively brazing a
metal body inserted into a hole in an aluminum oxide cer-
amic body using a pad of active brazing paste applied by
dispensing.
2. Description of the Related Art
US Patent 5,095,759 describes an active brazing paste for
brazing a platinum electrode to an aluminum oxide ceramic
body, in which the active brazing paste comprises:
- --------- - -
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- as the active brazing alloy a 99.5%/0.5% mixture of a
98% Au/2% Ni powder and
- a titanium hydride powder, and
- as the organic vehicle, a gel of 1.25% hydroxypropyl-
cellulose and 98.75% 1,2-propanediol,
- such that 90% of the active brazing paste is made up of
the 99.5%/0.5% mixture and 10% is made up of the gel.
Thus, this state of the art shows that active brazing pas-
tes are usually a dispersion of a powder of the metallic
component of the active brazing paste in an organic vehi-
cle. That, in turn, is a polymer in a solvent. The parti-
cles of the powder are as homogeneously distributed as pos-
sible in the vehicle, and thus intimately combined with it.
Various Zr/Ni/Ti alloys suitable for use as an active
brazing material to braze a first aluminum oxide ceramic
body to a second aluminum oxide ceramic body are described
in US Patent 5,334,344. Foils are produced from the alloy
by melt-spinning, and the shapes needed for brazing can be
punched from the foils.
Various Zr/Fe/Ti/Be alloys are described in CA-A 22 11 471.
They are also suitable as active brazing materials for
brazing two aluminum oxide bodies together.
US Patent 5,431,744 describes how hydrogenated powders
which do not lose hydrogen, but remain stable, in air can
be produced.
A screen-printable active brazing paste and a dispensable
active brazing paste are of interest in this invention with
regard to their consistency.
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SUMMARY of the INVENTION
In the context of this invention, "screen-printable" is
understood to mean that the active,brazing paste is com-
pact, viscous and thixotropic so that regions of active
brazing paste of specified dimensions, with specified shape
and thickness, can be applied to the aluminum oxide ceramic
using ordinary silk screen-printing processes, and that
these regions retain their shape after printing. That is,
the active brazing paste must be intrinsically viscous
enough that it does not flow away from the printed regions.
In the context of this invention, "dispensable" is under-
stood to mean that the active brazing paste should be com-
pact, thixotropic, and less viscous than required for
screen printing so that it can, for example, be applied
from a nozzle or the like at a specified location as in-
dividual dots with specified limited dimensions, and that
it should then retain its shape as much as possible, and
thus should as much as possible not flow away. Obviously,
multiple dots can be applied adjacent to each other to
produce lines, etc.
One object of the invention is to disclose screen-printable
or dispensable active brazing pastes which satisfy the
requirements for screen printing or dispensing particularly
well, and which are particularly well suited for brazing a
first aluminum oxide ceramic body to a second aluminum
oxide ceramic body, or one aluminum oxide ceramic body to a
metal body.
Another object is to disclose a process for making an ac-
tively brazed bond between a first aluminum oxide ceramic
body and a second aluminum oxide ceramic body by means of a
first region of active brazing paste applied by screen
printing to the first aluminum oxide ceramic body and a
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second region of active brazing paste applied by screen
printing to the second aluminum oxide ceramic body, with
the coverage of the first region matching the coverage of
the second region, using a Zr/Ni/Ti or a Zr/Fe/Ti/Be alloy,
and a process for actively brazing a metal body inserted
into a hole in an aluminum oxide ceramic body to the alum-
inum oxide ceramic body using a pad of active brazing paste
applied to the aluminum oxide ceramic body and to the metal
body by dispensing.
To solve these objects, a first variant of the invention
consists in a screen-printable active brazing paste for
brazing a first aluminum oxide ceramic body to a second
one, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and,
- as an organic vehicle
-- poly(butylmethyl methacrylate) or poly(n-decylmeth-
acrylate) as the polymer and
-- the camphor ketal of 2,2,4-trimethylpentane-l,3-diol
and/or 5-nonylmethyl ether as the solvent for the
polymer.
To solve the aforementioned objects, a second variant of
the invention consists in a dispensable active brazing
paste for brazing a first aluminum oxide ceramic body to a
second aluminum oxide ceramic body, or an aluminum oxide
ceramic body to a metal body, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and
- as an organic vehicle a mixture of
-- poly(butylmethyl methacrylate) dissolved in the camphor
ketal of 2,2,4-trimethylpentane-l,3-diol as a first
solvent, as a first component of the mixture and
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-- poly(butylmethacrylate) dissolved in 5-nonyl methyl
ether, as a second solvent, as a second component of
the mixture.
5 To solve the aforementioned objects, a third variant of the
invention consists in a process for producing a screen-
printable active brazing paste, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and,
- as an organic vehicle
-- poly(butylmethyl methacrylate) or poly(n-decylmeth-
acrylate) as the polymer and
-- the camphor ketal of 2,2,4-trimethylpentane-l,3-diol
and/or 5-nonylmethyl ether as the solvent for the
polymer,
in which process, after dissolving the polymer in the
solvent
- in a first step, in air or in a protective gas
atmosphere, a specified amount of the powder is mixed
with just enough vehicle that all the particles of the
powder are wetted, and,
- in a second step, in air, the particles of the powder are
completely dispersed mechanically in the vehicle.
To solve the aforementioned objects, a fourth variant of
the invention consists in a process for producing a dis-
pensable active brazing paste, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and
- as an organic vehicle a mixture of
-- poly(butylmethyl methacrylate) dissolved in the camphor
ketal of 2,2,4-trimethylpentane-l,3-diol as a first
solvent, as a first component of the mixture and
-- poly(butylmethacrylate) dissolved in 5-nonyl methyl
ether, as a second solvent, as a second component of
the mixture,
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in which process, after production of the two components of
the mixture, and their mixture,
- in a first step, a specified quantity of powder is mixed,
in air or in a protective gas atmosphere, with just
enough vehicle that all the particles of the powder are
wetted by the vehicle, and
- in a second step, in air, the particles of the powder are
completely dispersed mechanically in the vehicle.
To solve the aforementioned objects, a fifth variant of the
invention consists in a process for producing an active
brazed bond between a first aluminum oxide ceramic body and
a second aluminum oxide ceramic body using a first region
of active brazing paste applied to the first aluminum oxide
ceramic body by screen printing or dispensing and a second
region of the active brazing paste congruent with the first
region and applied to the second aluminum oxide ceramic
body by screen printing or dispensing, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and,
- as an organic vehicle
-- poly(butylmethyl methacrylate) or poly(n-decylmeth-
acrylate) as the polymer and
-- the camphor ketal of 2,2,4-trimethylpentane-l,3-diol
and/or 5-nonylmethyl ether as the solvent for the
polymer,
in which process
- the first region is applied to the first aluminum oxide
ceramic body and the second region is applied to the
second aluminum oxide ceramic body
- then both regions are dried in air at about 100 C
- then the two regions with the two aluminum oxide ceramic
bodies
-- are placed in contact with each other,
-- are then heated in a reactor held at high vacuum at
temperatures increasing by a rate of about 3 K/min up
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to about 125 C and held at that temperature until the
solvent has evaporated,
-- then the bodies are heated in the same reactor at
temperatures increasing by a rate of about 1.5 K/min up
to about 400 C and are heated at that temperature
until the polymer has completely decomposed, and
-- then they are brazed in the same reactor at high vacuum
at about 900 C.
To solve the aforementioned objects, a sixth variant of the
invention consists in a process for actively brazing a
metal body inserted into a hole in an aluminum oxide cer-
amic body using pads of an active brazing paste applied by
dispensing to the aluminum oxide ceramic body and to the
metal body, comprising:
- as the active brazing material a hydrogenated powder of a
Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and
- as an organic vehicle a mixture of
-- poly(butylmethyl methacrylate) dissolved in the camphor
ketal of 2,2,4-trimethylpentane-l,3-diol as a first
solvent, as a first component of the mixture and
-- poly(butylmethacrylate) dissolved in 5-nonyl methyl
ether, as a second solvent, as a second component of
the mixture,
in which process,
- the active brazing paste applied is heated in a reactor
with temperatures increasing by a rate of about 1.5 K/min
up to about 400 C and heated at that temperature until
the solvent has evaporated and the polymer has completely
decomposed, and
- then the aluminum oxide ceramic body and the metal body
are brazed under high vacuum in the same reactor at about
900 C.
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In a first preferred embodiment of the first variant of the
invention using poly(butylmethyl methacrylate) or poly(n-
decyl methacrylate) as the polymer and the camphor ketal of
2,2,4-trimethylpentane-l,3-diol as the solvent, the active
brazing paste comprises 70% to 90% by weight active brazing
powder and 30% to 10% by weight vehicle, which itself com-
prises 5% to 10% polymer and 95% to 90% solvent.
In a further preferred embodiment of this first embodiment,
the active brazing paste comprises 82.4% by weight active
brazing powder and 17.6% by weight vehicle, which itself
comprises 7.5% by weight polymer and 92.5% by weight sol-
vent.
In a second preferred embodiment of the first variant of
the invention with poly(butylmethyl methacrylate) as the
polymer and 5-nonyl methyl ether as the solvent, the active
brazing paste comprises 65% to 90% by weight active brazing
powder and 35% to 10% by weight vehicle, which itself
comprises 20% to 30% polymer and 80% to 70% solvent.
In a further preferred embodiment of this second embodim-
ent, the active brazing paste comprises 75% by weight act-
ive brazing powder and 25% by weight vehicle, which itself
comprises 25% by weight polymer and 75% by weight solvent.
In a preferred embodiment of the second variant of the in-
vention, the active brazing paste comprises 70% to 90% by
weight of active brazing powder and 30% to 10% by weight
vehicle, which itself comprises 12% to 25% by weight poly-
mer and 88% to 75% solvent, and in which the ratio of the
first solvent to the second solvent is about 1:2.
In a further preferred embodiment of the second variant of
the invention the active brazing paste comprises 80.8% to
83.9% by weight active brazing powder and 16.1% to 19.2% by
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weight vehicle, which itself comprises 19.75% to 19.80% by
weight polymer and 80.25% to 80.20% by weight solvents.
The invention has the following advantages:
- The screen-printable active brazing pastes have the
rheologic properties required for screen printing; that
is, they have the necessary intrinsic viscosity and the
necessary ability to wet the ceramic body and/or the
metal body.
- The screen-printable and dispensable active brazing
pastes are sufficiently stable to sedimentation. That is,
the particles in the finished active brazing paste settle
extremely slowly if at all.
- There is no chemical reaction in the active brazing
pastes between the vehicle and the surface of the
particles at ambient temperature, i.e. about 20 C.
- When the vehicle decomposes thermally, no carbon-
containing residues which could deactivate the active
brazing compound during brazing remain on the surfaces of
the powder particles.
- The active brazing pastes accordingly adhere very well to
the ceramic and metal bodys, and even after brazing the
adhesion, mechanical strength, and density of the brazed
bonds are so outstanding that they do not tear off in the
bending test. The breakage occurs only within the ceram-
ic, and the soldered bonds remain vacuum-tight for a long
time.
- The solvents evaporate in vacuum without residue, even
below 200 C.
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- The vehicle of the screen-printable or dispensable active
brazing pastes can be removed before brazing without
leaving a residue and without causing difficulty,
especially in a high vacuum (on the order of 10-9 bar
5 = 10-4 Pa) at no more than 400 C, so that there are no
residues on the bodies which are yet to be brazed.
- The spreading behavior of the active brazing pastes, that
is, their ability to flow at the brazing temperature, is
10 outstanding.
DETAILED DESCRIPTION of PREFERRED ELKBODIMEN'PS
The invention, and further advantages, are now explained in
more detail using preferred embodiments of the active braz-
ing pastes and the process variations of the invention.
The following applies for all examples: A hydrogenated
powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy with a
grain size not greater than 40 m is used. The particular
compositions of these alloys emphasized in the previous
discussion of the state of the art are preferred. The
vehicle is made up of a polymer and a solvent for the
polymer. The polymer is either poly(butylmethyl
methacrylate) or poly(n-decyl methacrylate). The solvent is
either the camphor ketal of 2,2,4-trimethylpentane-1,3-diol
or 5-nonyl methyl ether, and vehicles containing both sol-
vents may be used.
Example 1
A screen-printable active brazing paste using the camphor
ketal of 2,2,4-trimethylpentane-1,3-diol as the solvent
comprises 70% to 90% by weight, and in particular, 82.4% by
weight powder, and 30% to 10% by weight, in particular
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17.6% by weight vehicle. The vehicle comprises 5% to 10% by
weight, in particular, 7.5% by weight, polymer and 95% to
90% by weight, in particular, 92.5% by weight, solvent.
Example 2
A screen-printable active brazing paste with 5-nonyl methyl
ether as the solvent comprises 65% to 90% by weight, in
particular, 75% by weight, active brazing powder and 35% to
10% by weight, in particular, 25% by weight, vehicle. The
vehicle comprises 20% to 30% by weight, in particular, 25%
by weight, polymer and 80% to 70% by weight, particularly
75% by weight, solvent.
A first aluminum oxide ceramic body can be brazed to a
second aluminum oxide ceramic body with the active brazing
pastes of Example 1 or 2. The aluminum oxide can be of the
usual purity (96%). lt can, but need not, be highly pure
(99.9%).
Capacitive or resistive pressure sensors are a principal
area of application of aluminum oxide ceramic bodies with
must be brazed. For example, a capacitive pressure sensor
comprises a disk-shaped substrate and a thin disk-shaped
membrane. The two parts are brazed together at their edges.
The facing areas of the substrate and membrane have metal
surfaces, of tantalum, for instance.
The amount of active brazing compound required is set by
screen-printing or dispensing (see Example 3 for more
details). This quantity is determined so that it also acts
as a spacer ring between the substrate and membrane during
brazing, forming a chamber between the substrate and mem-
brane.
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Away from the brazed joint, then, the membrane is separated
from the substrate, and the two metal surfaces form an
electrical capacitor. Furthermore, the membrane moves when
pressure acts on it. That alters the distance between the
two metal surfaces, so that the capacitor changes its capa-
citance.
For such a capacitive pressure sensor to be used as an
absolute pressure sensor, for instance, the brazed bond
must be tight to high vacuum for a long time.
Example 3
A dispensable active brazing paste contains poly(butyl-
methyl methacrylate) as a first mixture component dissolved
in the camphor ketal of 2,2,4-trimethylpentane-l,3-diol as
a first solvent, and poly(butylmethyl methacrylate) as a
second mixture component dissolved in 5-nonyl methyl ether
as a second solvent.
This active brazing paste comprises 70% to 90% by weight,
in particular 80.8% to 83.9% by weight, active brazing
powder and 30% to 10% by weight, in particular 16.1% to
19.2% by weight, vehicle. The vehicle comprises 12% to 25%
by weight, in particular, 19.75% to 19.80% by weight,
polymer, and 88% to 75% by weight, in particular, 80.25% to
80.20% by weight solvents, with the ratio of the first
solvent to the second solvent being about 1:2.
With the active brazing paste according to Example 3, a
first aluminum oxide ceramic body can be brazed to a second
aluminum oxide ceramic body, or an aluminum oxide ceramic
body can be brazed to a metal body.
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One major area of application of the brazing initially
mentioned is, again, the ceramicceramic brazing of
capacitive pressure sensors. In this case, as noted just
above, a ring of active brazing paste made of many adjacent
dots in contact with each other is applied to the edge of
the membrane and to the edge of the substrate.
Metal-ceramic active brazing is also used for these capa-
citive pressure sensors. lt is necessary to make electrical
contacts with the metal areas acting as capacitor plates,
as noted above. That is accomplished for the metal surface
of the membrane through the fact that it extends into the
brazed joint and contact is made there, as it is accessible
from the outside.
On the other hand, the metal surface of the substrate is
contacted by inserting a metal pin, which may, for instan-
ce, also be of tantalum, from the outside through a hole
provided in the substrate. The metal pin extends through
this hole to the metal surface, and the metal pin must be
brazed into the hole.
Another major area of application of metal-ceramic active
brazing, mentioned above, is found in electromagnetic flow
meters with ceramic measuring tubes, see US Patent
5,095,759, mentioned at the beginning. Here, at least two
metal pins acting as electrodes must be brazed in place.
They extend to the inner surface of the measuring tube, and
pick off a voltage induced by an electrically conductive
liquid flowing through the measuring tube, induced acc. to
Faraday's law of induction by a magnetic field.
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Example 4
A screen-printable active brazing paste is produced as
follows: First, the polymer is dissolved in the solvent.
That is done by stirring, and specifically by mechanical
stirring for large quantities.
Then, in a first step, a specified amount of powder is
mixed with just enough vehicle so that all the particles of
the powder are wetted by the vehicle. That is, the "oil
value" is set. That is done in air or in a protective gas
atmosphere; under argon, for instance.
Finally, in a second step, the particles of the powder are
completely dispersed mechanically in the vehicle in air. An
ordinary three-roll machine can be used for that.
Example 5
A dispensable active brazing paste is produced as follows:
First, the two components of the mixture are produced. That
is, the poly(butylmethyl methacrylate) is dissolved in the
camphor ketal of2,2,4-trimethylpentane-l,3-diol and in
5-nonyl methyl ether. That is done by stirring, and
particularly by mechanical stirring for large quantities.
Then the mixture components are mixed in the required
proportions, such as mentioned in Example 3 above.
Then, in a first step, a specified amount of powder is
mixed with just enough vehicle so that all the particles of
the powder are wetted by the vehicle. That is, the oil
value is set again. That is done in air or in a protective
gas atmosphere; under argon, for instance.
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Finally, in a second step, the particles of the powder are
completely dispersed mechanically in the vehicle in air. An
ordinary three-roll machine can be used for that.
Example 6
Two aluminum oxide ceramic bodies are brazed together as
follows: A first region of active brazing paste is applied
to the first aluminum oxide ceramic body by screen-printing
or dispensing. A second region of active brazing paste con-
gruent with the first region is applied in the same manner
to the second aluminum oxide ceramic body.
Then both regions are dried in air at 100 C, and are
placed together with the two aluminum oxide ceramic bodies
together, and the aluminum oxide ceramic bodies are heated
in a reactor held at high vacuum with temperatures rising
at a rate of 3 K/min up to 125 C and held at that temper-
ature until the solvent has evaporated.
Then the aluminum oxide ceramic bodies are heated in the
same reactor, with temperature rising at a rate of
1.5 K/min up to 400 C and held at that temperature until
the binder has been destroyed, so that the powder is free
of the vehicle, which can also be called the binder, until
the polymer has completely decomposed and vaporized. Final-
ly, the aluminum oxide ceramic bodies are brazed in the
same reactor at 900 C under high vacuum.
Example 7
An aluminum oxide ceramic body and a metal body inserted
into a hole in the aluminum oxide ceramic body are brazed
as follows: Dots of the active brazing paste are dispensed
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in the shape of a pad on the aluminum oxide ceramic body
and on the metal body.
If, in this process, the metal body is aligned with the
outer surface of the aluminum oxide ceramic body, the pad
can cover the end of the metal body up to the ceramic. If
the metal body extends beyond the outer surface, then the
pad is laid down in a ring shape around the metal body.
Then the active brazing paste which has been applied is
heated in a reactor with temperatures rising at a rate of
1.5 K/min up to 400 C and held at that temperature until
the solvent has evaporated and the polymer has decomposed
completely.
Finally the aluminum oxide ceramic body and the metal body
are brazed in the reactor under high vacuum at 900 C.
