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Comparing Metal-Ceramic
Brazing Methods
The advantages and disadvantages of the various methods for
joining metals to ceramics are outlined

BY C. A. WALKER AND V. C. HODGES

esigners and engineers have many

D options to choose from when con-

sidering how to join metals to non-
metals for structural, electrical, and pack-
A B

aging applications. These options could

include mechanical means of fastening such
as screws, bolts, rivets and other fasteners,
or an elevated-temperature means such as
soldering or brazing. Metal-ceramic braz-
ing, the topic of this article, is particularly
useful for fabricating high-reliability devices
such as those used in high-voltage applica-
tions or requiring hermetically sealed joints.
This article is intended to familiarize the
designer with brazing methods commonly
used to join metals to ceramics, discuss the
advantages and disadvantages of each
method, and show the relative tensile
strengths obtained from samples fabricated
using these methods. Alumina is one of the
most commonly used engineering ceramic Fig. 1 — Commonly used ceramic metallization methods. A — Moly-manganese metal-
materials, offering high hardness and wear lization process; B — thin-film metallization process.
resistance with excellent electrical insula-
tion properties. Alumina ceramic is com-
monly available in purities ranging from 88 Metal-to-ceramic brazing can be Molybdenum-
to 99.9%, with high-temperature glasses accomplished by first applying a metallic
making up the balance of the composition. layer onto the ceramic surface or by braz-
Manganese/Nickel
For most cases discussed, 94% alumina ing directly to the unmodified ceramic Plating Method
ceramic (6% glassy phase) ASTM-F19 ten- (oxide) surface. Several metallization
sile button samples were joined to Fe-29Ni- methods have been proven to work effec- The molybdenum-manganese/nickel
17Co alloy using a gold-or silver-based tively; however, this article is limited to plating method, also known as moly-man-
braze filler metal. The versatile design of the two metallization methods most com- ganese metallization, is performed as fol-
the ASTM-F19 tensile specimen allows a monly used (Refs. 2–4) for joining metals lows: A coating of molybdenum and man-
helium mass-spectrometer leak detection to ceramics: the molybdenum-man- ganese particles mixed with glass addi-
test to be performed prior to tensile testing ganese/nickel plating method and physi- tives and volatile carriers is applied to the
(Ref. 1). cal-vapor deposition or thin-film method. ceramic surface to be brazed — Fig. 1A.

C. A. WALKER (cawalke@sandia.gov) and V. C. HODGES are with Sandia National Laboratories, Albuquerque, N.Mex.

Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Company, for the U.S. Dept. of Energy under contract
DE-AC04-94AL85000.

Based on a paper presented at the International Brazing & Soldering Symposium held during the 2007 FABTECH International & AWS
Welding Show, Nov. 11–14, in Chicago, Ill.

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Fig. 2 — Ceramic-to-metal braze using molybdenum- Fig. 3 — Au/Cu brazed metal-to-ceramic sample made using thin-
manganese/nickel plate metallization. film metallization.

Table 1 — Moly-Manganese/Nickel Plate ASTM-F19 Tensile Button Test Results

Filler Metal Nonmetal Substrate Metal Substrate Brazing Temperature/Time Furnace Atmosphere Average Tensile Strength(a)

65 Cu/35 Au 94% Alumina Fe-29Ni-17Co 1040°C/3 min Dry Hydrogen 14.5 ksi/100 MPa
50 Au/50 Cu 94% Alumina Fe-29Ni-17Co 1000°C/3 min Dry Hydrogen 17 ksi/118 MPa
72 Ag-28 Cu 94% Alumina Fe-29Ni-17Co 810°C/3 min Dry Hydrogen 14.3 ksi/99 MPa
77 Au-13Ag-10 Ge 94% Alumina Fe-29Ni-17Co 495°C/3 min Dry Hydrogen 15.6 ksi/108 MPa
77 Au-13 Ag-10 Ge 94% Alumina Fe-29Ni-17Co 455°C/5 min Dry Hydrogen 16.1 ksi/111 MPa
(2x thk)

(a) Tensile strength averages are ± 2 ksi/14 MPa.

The application of the coating may be to provide the necessary metallization controlled expansion alloy often used
hand-painted, sprayed, or robotically component materials or metallization when brazing to ceramics. All of the
applied. After air drying, the coating is services. brazed samples shown in Table 1, as well as
fired in a wet hydrogen environment The molybdenum-manganese/nickel those shown in the subsequent tables
(15°–30°C dew point) at 1450°–1600°C plating method also has several disadvan- (Tables 2–4) passed a helium mass-spec-
leaving a “glassy” metallic coating tages. Included in these are the following: trometer leak detection test (leak rate <
300–500 micro-inches (7.6–12.7 microns) 1) Expense. Specialized high-tempera- 2.0–9 atm-cc/s) prior to being tensile test-
thick. The fired coating is subsequently ture furnaces and plating equipment are ed. The crosshead speed used for the ten-
plated with a 0.001–0.003 in. (25.4–76.2 necessary — Fig. 1. sile tests was 3.3–4 in./s (8.38–6 m/s). The
microns) layer of nickel. The nickel plat- 2) Lengthy time requirements. tensile strengths shown in the tables are
ing is sinter-fired at 850°–950°C in a dry Multiple high-temperature furnace oper- averages of samples tested. Variations of
hydrogen (–50°C dew point or less) ations are required as well as the care and ± 2 ksi (14 MPa) from the average tensile
atmosphere leaving a finished metallic maintenance of plating baths. strengths were observed. Formulations of
surface that can be readily brazed using 3) Rework limitations. Excessive nick- brazing filler metals are displayed in wt-%.
standard braze filler metals. el depletion into the braze filler metal can A scanning electron microscope
Some of the advantages of the molyb- lead to poor braze joint performance. (SEM) image of a cross-sectioned brazed
denum-manganese/nickel plating method 4) Geometric constraints. Large sizes metal-ceramic assembly, utilizing moly-
are as follows: and thick cross sections are difficult to manganese metallization and nickel plat-
1) Having been developed in the 1930s process. ing is shown in Fig. 2. The ceramic is 94%
(Ref. 2), moly-manganese metallization is 5) Batch size. Process development for alumina, and the metal member is Fe-
a mature technology with a proven histo- small quantities is often cost prohibitive. 29Ni-17Co. Notice the 25–35-μm-thick
ry of success; Table 1 shows the average strengths reaction zone where the moly-manganese
2) Postmetallization, ceramic materi- typically obtained [14–17 ksi (99–117 metallization diffuses and reacts with the
als can be easily brazed using standard MPa)] when using various gold- and silver- glassy phases of the alumina ceramic. The
braze filler metals; and based brazing filler metals to braze 94% clearly defined nickel plating layer shown
3) Commercial suppliers are available alumina ceramic to Fe-29Ni-17Co alloy, a has been sufficiently wetted by the braz-

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Fig. 4 — Ag/Cu brazed metal-to-ceramic sample made using thin- Fig. 5 — Ti/Au thin-film deposition layer on Ag/Cu brazed metal-
film metallization. ceramic sample.

Table 2 — Thin-Film Metallization ASTM-F19 Tensile Button Test Results

Filler Metal Substrates Thin Films Brazing Temperature/Time Furnace Atmosphere Average Tensile Strength(a)
50 Au/50 Cu 94% Alumina 0.25 μm Ti/ 1000°C/3 min Dry Hydrogen 15.1 ksi/102 MPa
Fe-29Ni-17Co 0.5 μm Au

50 Au/50 Cu 94% Alumina 0.25 μm Ti/ 1020°C/10 min Dry Hydrogen 12.9 ksi/89 MPa
Fe-29Ni-17Co 0.5 μm Au

50 Au/50 Cu 94% Alumina 0.25 μm Ti/ 1000°C/3 min Dry Hydrogen 16.1 ksi/111 MPa
Fe-29Ni-17Co 0.02 μm Pd/
0.5 μm Au

50 Au/50 Cu 94% Alumina 0.25 μm Ti/ 1020°C/10 min Dry Hydrogen 11.8 ksi/81 MPa
Fe-29Ni-17Co 0.02 μm Pd/
0.5 μm Au

72 Ag-28 Cu 94% Alumina 0.25 μm Ti 810°C/3 min Dry Hydrogen 13.0 ksi/90 MPa
Fe-29Ni-17Co 0.5 μm Au

63 Ag-27 Cu-10 In 94 % Alumina 0.25 μm Ti/ 755°C/2 min UHP Argon 13.2 ksi/91 MPa
Fe-29Ni-17Co 0.5 μm Pt

63 Ag-27 Cu-10 In 951 LTCC 0.25 μm Ti/ 755°C/2 min UHP Argon 8.2 ksi/57 MPa
Fe-29Ni-17Co 0.5 μm Pt

63 Ag-27 Cu-10 In 951 LTCC 0.5 μm Ti/ 755°C/5 min UHP Argon 6.5 ksi/45 MPa
Fe-29Ni-17Co 0.5 μm Au
63 Ag-27 Cu-10 In 951 LTCC 0.5 μm Ti/ 755°C/5 min UHP Argon 3.8 ksi/26 MPa
Fe-29Ni-17Co 0.5 μm Pd

(a) Tensile strength averages are ± 2 ksi/14 MPa.

ing filler metal to provide high joint to a ceramic substrate so that it may be nium, chromium, niobium, etc. may be
strength and hermeticity. The light and joined using conventional braze filler chosen depending on the application and
dark areas within the brazed joint are the metals. A combination of materials, usu- service temperature. Occasionally, an
silver-rich and copper-rich regions. ally two or three, are deposited onto the intermediate layer or layers are deposited
nonmetallic surface using a physical to prevent unwanted metallurgical reac-
Thin-Film Deposition vapor deposition (PVD) method such as tions between the initial metal layer and
evaporation or sputtering. The first layer the braze filler metal. The top, or outer,
Depicted in Fig. 1B, thin-film deposi- deposited, often titanium, is typically layer is normally a noble metal such as
tion is another commonly used (Refs. 2, 0.05–0.25 μm thick. Other strong oxide- gold, platinum, or palladium that is
3) method to apply a metallization layer forming elements such as hafnium, zirco- 0.25–1.0 μm thick. A noble metal is cho-

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brazing process window (peak tempera-
ture and time ranges) that can be
obtained without the drastic decline in
tensile strength usually witnessed when
using the moly-manganese metallization
method. This is because the thin-film
metallization method, in contrast to
moly-manganese metallization, does not
use nickel plating, which readily dissolves
into the braze filler metal at higher tem-
peratures and longer peak soak times.
Also shown in Table 2 are the tensile
strengths of brazed Fe-29Ni-17Co tensile
Fig. 6 — Direct metal-to-ceramic brazing processes.
buttons to Low-Temperature Co-Fired
Ceramic (LTCC) interlayers. When using
a 63Ag-27Cu-10In braze filler metal, the
sen in order to prevent the underlying few hours total, that simple geometries tensile strengths varied by a factor of two,
layer from oxidizing and subsequently can be prepared for brazing. depending on which thin-film metalliza-
preventing proper braze filler metal wet- The primary disadvantages of thin- tion scheme was chosen (Ref. 5). This
ting and flow. Detailed brazing- film metallization coatings are as follows: strength loss is due to the formation of
related concerns when using thin-film • Specialized equipment is required to brittle intermetallic compounds within
metallization coatings for ceramic assem- apply the coatings. the braze joints or at the braze joint inter-
blies have been published (Ref. 3). • Intricate masking may become neces- faces.
The following are a few of the advan- sary to prevent the deposition of metal Shown in Fig. 3 is an SEM image of a
tages for using thin-film metallization in unwanted locations. cross-sectioned ceramic-metal-ceramic
coatings: • Ceramic geometric constraints, which brazed sample utilizing a thin-film
• They have a proven brazing practice may prohibit the proper positioning of scheme of 2500 Å (0.25 μm) titanium and
history and are forgiving when used the ceramic member or hinder the 5000 Å (0.50 μm) gold. A 50Au-50Cu
with standard filler metals. application of uniform coating thick- brazing filler metal was utilized for the
• Versatility. A wide range of metal nesses, of most thin-film deposition joining operation. The same substrate
choices exist for the engineer or chambers. materials and geometry were joined with
designer that can be deposited to Tensile button strengths obtained a silver-based braze filler metal, 72 Ag-
address special applications or envi- using various thin-film metallization 28Cu, and shown in Fig. 4. In both SEM
ronments. schemes are shown in Table 2. Captured images, the samples exhibit excellent wet-
• Another important advantage is the in Table 2 (compare lines 1 and 2, then ting and flow onto the irregular alumina
speed, which can often be less than a lines 3 and 4) is the increased size of the ceramic surface with little or no base

Fig. 7 — SEM backscattered image (BSE) with energy-dispersive Fig. 8 — Energy-dispersive spectroscopy maps showing postbrazed
spectroscopy (EDS) maps showing postbrazed zirconium, oxygen, silver, iron, nickel, and copper concentrations (counterclockwise
and aluminum (counterclockwise from upper left) concentrations from upper left) in an active brazed specimen.
in an active brazed specimen.

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A

B
Fig. 9 — Active brazed molybdenum to 94% alumina ceramic sam-
ple (A and B) and active brazed Fe-29Ni-17Co to 94% alumina ce-
ramic (C and D).

metal erosion. Figure 5 shows higher however, the braze

magnification images of the thin- joint might require a
film/ceramic interface from Fig. 4. Easily redesign to accommo-
seen in these images is the continuous date the preplacement
thin-film metallization layer along the of brazing filler metal
alumina grain boundaries. The dark between the faying
regions seen along the interface and surfaces of the braze-
between the alumina grains are the glassy ment. Capillary flow is
phase of the 94% alumina ceramic. inhibited by the bare
oxide ceramic surface
Active Filler Metal that exhibits limited
Brazing spreading and flow of
the brazing filler Fig. 10 — A — Electron microprobe analysis, and B — SEM
Active filler metal brazing is an area of metal. High-vacuum image of a direct brazed niobium-94% alumina ceramic sample.
high growth within the metal-ceramic or inert atmospheres
brazing community. A primary reason for are required because
this growth is that unlike the moly-man- excessive oxygen in
ganese metallization that is very material the atmosphere can react with the active subsequent standard brazing process. The
dependent, active filler metals display element in the active braze filler metal primary disadvantages are as follows:
good wetting with most ceramic materials and compromise joint strength and 1) Active brazing processes require
(Refs. 6, 7). Active filler metal brazing is integrity (Refs. 9, 10). more stringent atmospheric control;
a metal-ceramic joining method that per- Apart from these limitations, there are 2) Not all braze joint geometries are
mits the use of standard brazing tech- many advantages to using an active filler compatible with active brazing processes;
niques when making metal-to-ceramic metal brazing process for certain brazing 3) Processing equipment capable of
brazements without the need to apply any applications. These include the following: adequate atmospheric control can be a
metallization to the ceramic substrate. As 1) The number of required steps to limiting factor, placing size constraints on
shown in the left-hand portion of Fig. 6, make metal-ceramic brazes are reduced brazed assemblies.
the metal and nonmetal substrates are and greatly simplified; Figures 7 and 8 illustrate the distribu-
cleaned, and the active filler metal pre- 2) There are a variety of commercially tion of elements in an active braze filler
form or paste (Ref. 8) is positioned or available filler metal compositions for use metal following a brazing process. Figure
applied between the faying surfaces of the in a wide range of processing tempera- 7A is a backscattered SEM image show-
brazement. The brazing operation is usu- tures and service conditions; ing a portion of a 94% alumina ceramic
ally performed in an inert or ultrahigh 3) Specialized metallization equip- that has been brazed using a 97Ag-1Cu-
vacuum environment. For certain appli- ment and the associated time-consuming 2Zr active braze filler metal. The sample
cations and component geometries, the metallization processes are eliminated. was brazed at a temperature of 950°C,
transfer from a conventional brazing There are, however, several disadvan- with a peak soak time of 5 min in a 12-
process to an active brazing process is tages of using an active brazing process torr ultrahigh-purity (UHP) argon par-
accomplished quite readily. Many times, over a conventional metallization and tial pressure atmosphere. Figure 7B

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Table 3 — Active Filler Metal Brazed ASTM-F19 Tensile Button Test Results

Filler Metal Nonmetal Substrate Metal Substrate Brazing Temperature/Time Furnace Atmosphere Average Tensile Strength(a)

62 Cu-35 Au- 94% Alumina Fe-29Ni-17Co 1006°–1026°C Vacuum/Partial 11–14 ksi/76–97 MPa
2Ti-1Ni 6–8 min pressure Ar

97 Ag-1Cu-2Zr 94% Alumina Fe-29Ni-17Co 990°C/5 min UHV/Dry Hydrogen 15.4 ksi/106 MPa

97 Ag-1Cu-2Zr 94% Alumina Fe-29Ni-17Co 963°C, 3 min Partial pressure Ar 21.3 ksi/147 MPa
above liquidus

63.00 Ag-35.24Cu- 94% Alumina Fe-29Ni-17Co 1040°C/2 min Dry Hydrogen 14.5 ksi/100 MPa
1.75Ti

63.00 Ag-35.25Cu- 94% Alumina Fe-29Ni-17Co 825°–1040°C/2–10 min Partial Pressure Ar 11–14 ksi/76–97 MPa
1.75Ti

63.00 Ag-35.25Cu- 94% Alumina Fe-29Ni-17Co 825°–1040°C/2–10 min Vacuum 11–16 ksi/76–110 MPa
1.75Ti

59.00 Ag-27.25Cu- 94% Alumina Fe-29Ni-17Co 755°C/5 min Vacuum 14.5 ksi/99 MPa
12.5In-1.25 Ti

59.00 Ag- 27.25Cu- DuPont 951 LTCC Fe-29Ni-17Co 755°C/5 min Vacuum 8 ksi/55 MPa
12.5In-1.25 Ti
(a) Tensile strength averages are ± 2 ksi/14 MPa.

shows the migration of the elemental zir- minimal amount of the active element, active braze filler metal. This relatively
conium to the ceramic surface where it titanium, has reacted with the molybde- new (Refs. 17, 18) silver-based filler
reacts with available oxygen and forms num allowing for the majority of the tita- metal uses zirconium as the active ele-
the layer that the primary filler metal ele- nium metal to react with the ceramic sub- ment, but currently has very limited com-
ment, silver, will wet and adhere to. A strate. Figure 9C reveals that a substan- mercial availability.
trace amount of zirconium can also be tial portion of the titanium has reacted
seen in the same image bound to the sur- with the Fe-29Ni-17Co substrate to the Direct-Brazing Method
face of the Fe-29Ni-17Co. Figure 7C point of causing some base metal erosion
shows a small concentration of oxygen to occur and hindering the ability to make The direct-brazing method is the last
that has dissolved into the zirconium-rich a hermetic seal. This scavenging of the method for joining metals to ceramics to
region of the solidified braze filler metal. titanium element can be prevented by be considered. As the name implies, the
Notice in Fig. 7D that a slight amount of coating the Fe-29Ni-17Co member with a direct-brazing method allows metals to be
aluminum from the ceramic material, barrier layer (Refs. 12–14). While some directly brazed to ceramics without the
having been replaced by zirconium, has scavenging of titanium does occur, there need for metallization coatings. Unlike
diffused through the molten braze filler is sufficient titanium in commercially active filler metal brazing, however, the
metal toward the Fe-29Ni-17Co surface. available active brazing filler metals to direct-brazing method utilizes standard
Figure 8 A–D are companion energy dis- make hermetic braze joints to Fe-29Ni- brazing filler metals to accomplish the
persive spectroscopy (EDS) maps that 17Co substrates when careful attention is metal-to-ceramic braze. The direct-braz-
show the silver- and copper-rich phases given to surface preparation, fixturing, ing process is illustrated on the right-
of the resolidified brazing filler metal atmosphere, and the brazing thermal hand side of Fig. 6. Comparisons of the
along with limited dissolved Fe-29Ni- cycle (Refs. 15, 16). two brazing methods portrayed in Fig. 6
17Co base metal. Tensile test results of tensile button illustrate how similar these processes are.
The choice of the base metal substrate samples made with gold- and silver-based Similar to the active brazing process, a
and active filler metal element can have a active braze filler metals are displayed in direct-braze is made by cleaning the
substantial impact on the end product as Table 3. A comparison of the sample ceramic and metal materials, fixturing the
reported by Stephens et al. (Ref. 11), and strengths in Tables 1 and 2 to those in assembly with the braze filler metal pre-
shown in Fig. 9. A and B show a molyb- Table 3 reveals that the results are very placed between the metal and ceramic
denum substrate brazed to a 94% alumi- similar for tensile samples brazed with substrates and then brazing the entire
na ceramic using a gold-based active similar composition filler metal families assembly, usually in an inert or UHV
braze filler metal, 62Cu-35Au-2Ti-1Ni. C and temperatures. Of particular interest brazing atmosphere. During the direct-
and D show the results when the molyb- in Table 3 are the high tensile strengths braze process, specific metal substrates
denum is replaced with Fe-29Ni-17Co. 9B obtained when using the 97Ag-1Cu-2Zr and braze filler metal combinations inter-
and 9C are EDS maps showing the result- active braze filler metal. Samples averag- act to form an adherent metallic oxide
ing titanium concentrations in the brazed ing more than 21 ksi (147 MPa) were layer on the oxide ceramic faying surface.
samples. Figure 9B demonstrates that a obtained using this recently developed The dissolution, migration, and inter-

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Table 4 — Direct Brazed ASTM-F19 Tensile Button Test Results

Filler Metal Nonmetal Substrate Metal Substrate Brazing Temperature/Time Furnace Atmosphere Average Tensile Strength

92 Au-8Pd 94% Alumina Niobium 1270°C/4 min Vacuum 12.8 ksi ± 1.8 ksi/
88 MPa ± 12 MPa

62 Cu-35Au-3Ni 94% Alumina Niobium 1058°C/3 min Vacuum 8.8 ksi ± 1.0 ksi/
61 MPa ± 7 MPa

50 Au-50Cu 94% Alumina Niobium 1000°C/3 min Vacuum 8.8 ksi ± 1.0 ksi/
61 MPa ± 7 MPa

action of the base metal with the filler 2) Good atmospheric control, while The designer, engineer, or user can
metal and ceramic surface are shown in not as stringent as that required when choose from a traditional metallization
Fig. 10 (Ref. 19). Electron microprobe active brazing, is also necessary when method such as moly-manganese/nickel
analysis (EMPA) of a niobium-94% alu- using the direct-brazing method. plating or from a variety of thin-film coat-
mina ceramic sample brazed with 62Cu- 3) The strengths obtained using the ings applied using PVD methods, which
35Au-3Ni (BAu-3) braze filler metal direct-braze method are slightly inferior are specifically tailored to meet the needs
shows how the niobium base metal is to those obtained using the other dis- of the application. Active braze filler met-
enriched at the alumina ceramic surface, cussed metal-ceramic brazing methods, as als can be used as a replacement system
where it forms a relatively stable oxide. To seen when comparing the strength data in for most metal-to- ceramic brazed assem-
perform a successful direct-braze, candi- blies with no loss of mechanical proper-
date metal substrates must contain an ties. Whether choosing to use metallized
element or elements able to form ther- ceramics or the direct-braze process, con-
mally stable oxides and have sufficient
Active braze filler ventional braze filler metals can be used
solubility within the chosen liquid braze for the brazing operation. The direct-
filler metal. As shown in Table 4, the
metals can be used braze process has been demonstrated
direct-braze method was used to produce as a replacement with a limited set of conventional filler
tensile button assemblies having average metals to have adequate bond strength
tensile strengths ranging from 9 to 13 ksi
(61–88 MPa). For these assemblies, niobi-
system for most when used in conjunction with niobium
metal substrates. Premetallized sub-
um base metal provided the active ele- metal-to-ceramic strates may be used without joint geome-
ment required to react with the alumina try restrictions; however, active and
ceramic. brazed assemblies direct-brazing techniques work best with
There is a host of benefits for the butt or lap-style braze joint geometries
designer or engineer to use the direct- with no loss of where the brazing filler metal may be pre-
brazing method. Some of these advan- placed between the faying surfaces.◆
tages are mechanical
1) Ease of use and lower expense,
compared to other metal-ceramic brazing properties. Acknowledgments
methods;
2) No metallization equipment or The authors wish to express their
associated processes and process devel- Table 4 to that shown in Tables 1–3. thanks and appreciation to Mike Hosking
opment is required; Transmission electron microscopy (TEM) and Paul Vianco for guidance and project
3) A variety of conventional braze analysis results on niobium-94% alumina support; Don Susan for his review of the
filler metals can be utilized covering a ceramic direct brazed samples (Ref. 20) manuscript; and Tom Crenshaw, Alice
wide range of temperatures; showed the niobium bonded with the Kilgo, and Bonnie McKenzie for their
4) The direct-brazing method has glass-phase only. Though not yet evaluat- mechanical testing capabilities, metallo-
been successfully used to hermetically ed, it is anticipated that a metal with the graphic sample preparation, and image
join metal-ceramic components used in ability to form more thermally stable analysis skills.
high-reliability long-term applications. oxides than those of niobium will be
There are several disadvantages to required to adequately join high-purity
using the direct-braze method. Among alumina ceramics using the direct braze References
these are method.
1) Not all joint designs are viable. In conclusion, high-strength, hermeti- 1. AWS C3.2M/3.2:2008, Standard
Similar to active brazing in this regard, the cally sealed metal-ceramic assemblies can Method for Evaluating the Strength of
braze filler metal must be preplaced be successfully brazed using a variety of Brazed Joints. 2008. Miami, Fla.:
between the faying surfaces because the methods, some requiring metallization of American Welding Society. pp. 17–23.
filler metal is unable to be drawn by capil- the ceramic member and others allowing 2. Brazing Handbook, 5th Edition.
lary forces along the bare ceramic surface. the direct brazing of metals to ceramics. 2007. Miami, Fla.: American Welding

WELDING JOURNAL 49
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BRAZING & SOLDERING TODAY

Society. pp. 462–464, 579–580. J., Vianco, P. V., and Walker, C. A. 2000. International Brazing and Soldering
3. Humpston, G., and Jacobson, D. M. Microstructural and mechanical charac- Symposium, Chicago, Ill.
1993. Principles of Soldering and Brazing. terization of actively brazed alumina ten- 12. Stephens, J. J., Vianco, P. V.,
Metals Park, Ohio: ASM International. sile specimens. Welding Journal 79(8): Hlava, P. F., and Walker, C. A. 2000.
pp. 140–143. 222-s to 230-s. Microstructure and performance of
4. Schwartz, M. M. Ceramic Joining. 8. Walker, C. A., Neugebauer, G. L., Kovar® alumina joints made with silver-
1990. Metals Park, Ohio: ASM Susan, D. F., and Hodges, V. C. 2007. copper base active metal braze alloys.
International. pp. 89–93. Brazing optimization of mechanically Advanced Brazing and Soldering
5. Walker, C. A., Uribe, F., Monroe, S. applied active braze filler metal paste. Technologies, eds. P. T. Vianco and M.
L., Stephens, J. J., Goeke, R. S., and 2007. Proceedings of the LOT 2007, 8th Singh. Metals Park, Ohio: ASM
Hodges, V. C. 2006. High-temperature International Conference, Brazing, High International. pp. 240–251.
joining of low-temperature co-fired Temperature Brazing and Diffusion 13. Vianco, P. V., Stephens, J. J.,
ceramics. Proceedings of the 3rd Bonding. Aachen, Germany. Hlava, P. F., and Walker, C. A. 2003.
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6. Mizuhara, H. 2000. Ceramic-to- 10. Jacobson, D. M., and Humpston, Hlava, P. F., and Walker, C. A. 2003. A
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Zr active braze filler metal for
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18. Stephens, J. J., and Neilsen, M. K.
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19. Stephens, J. J. 2001. Metal/ceramic
brazing for hermetic components. AWE
presentation. Aldermasten, UK.
20. Headley, T. 2004. TEM characteri-
zation of two Nicoro/Nb/AL500 brazes.
Unpublished internal work, Sandia
National Laboratories, Albuquerque,
N.Mex.

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