
The basis of all SBT products is Active Solder Technology,
which modifies conventional solders by addition of active
ingredients to create a chemically reactive material
that forms a bond with surfaces, even ones coated with
a layer of oxide or nitride. Depending upon the product,
joining temperature, and substrate material, the bond
can be based on a chemical reaction with the substrate,
or result from a high level of molecular attraction
between the S-Bond® product and the surface. Please
consult with us (Contact Us)
for further information on your particular materials
and strength requirements. For further information on
our products and their applications see our
Products page.
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Metals
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Ceramics
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MMC’s |
Carbon
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Copper
Aluminum
Silicon
Titanium
Tungsten
Kovar®
Nickel
Gold
Silver
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Silicon Carbide
Al-Nitride
Titanium Carbide
Alumina
Sapphire
Zirconia
Tungsten Carbide
LTCC Materials
Silicon Carbide-Diamond |
Al-Silicon Carbide
Al-Graphite
Nickel-TiC
Metal-Diamond |
Graphite
C-C Composite
Pyrolytic Graphite
Diamond
Foamed Graphite |
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S-Bond® products work with the addition of titanium
and/or rare earth elements to conventional solder
alloy bases. These active elements migrate to any
interface and react with the opposing material surface
to remove oxides and nitrides and transport them into
the bulk of the solder as an inert material. This
process occurs while the material is molten and once
the thin “skin” that forms on the surface
of the molten solder is broken to allow contact between
the bulk solder and the substrate surface. The breaking
of this skin is referred to as “activation”
and is done by application of a low level of mechanical
shearing action at the interface between the S-Bond
material and the substrate. The level of shear required
is small, and can be delivered by brushing or scraping
the surface, sliding the joining surfaces relative
to one another, or application of high frequency vibration
to the parts to be joined.
Once the skin layer has been disrupted, the bulk solder
reacts practically instantaneously and, in the case
of a molecular bond, irreversibly with the substrate
surfaces, creating a tightly held layer of solder
on the substrate. This means that the resulting joint
may be disassembled and reassembled by simply re-heating
above the melting temperature of the SBT product and
then re-joining the parts with some additional activation
to insure reaction with the new solder. The bonded
layer at the substrate surface will not be affected,
so good interfacial bond strength is maintained and
re-activation is not required.
The activation process for S-Bond products is not
ultrasonic soldering, which is where a large amount
of ultrasonic energy is directed against the surface
of the substrate material to break up the oxide surface
layer and allow the molten solder to circumvent and
interpenetrate the layer to reach the base material.
The oxide layer being broken in S-Bond® joining
is very thin, is only on the solder material, requires
very little energy to be disrupted, and does not remain
as part of the bond.
A feature of S-Bond products that is they do not flow
or wick into openings like conventional solders. Unless
pushed, our materials stay where they are placed.
This can be useful in situations where precision joining
is required.
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The specific process to use SBT solder materials depends
on the substrate materials, the joint geometry, and
the production volume. But, in general, the process
flow is to:
Bring the component parts to the proper joining temperature;
Using mechanical shear (usually brushing, scraping,
or ultrasound) uniformly coat the joining surfac es
of the parts;
Using additional solder material to insure a completely
filled joint, bring the surfaces together with additional
shear (usually sliding the parts relative to each
other or ultrasound);
Clamp or hold the parts during cooling to maintain
position and prevent the joint from spreading due
to the surface tension of the solder material.
This general process applies to any metal or ceramic,
with the resulting joint strength varying from 20-55
MPa (3-8,000 psi). Higher joint strengths in carbon
based substrates (e.g. diamond, thermal pyrolytic
graphite, foamed graphite); stainless steel, Kovar,
and other high performance materials are achieved
by replacing the initial coating step with a proprietary
heat treatment process that insures a permanent chemical
bond to the material surface. It may also be possible
to skip the surface precoating steps, depending on
the geometry of the bond area and the substrate materials.
Variations of this generic process are practiced today
in the production of thermal management devices, sensor
housings, and sputter targets. A process for semi-automated
joining using a multi-station carousel has also been
demonstrated. Please Contact Us if you need further
information or help in defining the best process for
your application, or see our Products and Services
page for more information about specific products.
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The following section illustrates typical joint structures
found when using SBT solder products with a variety
of materials.
If you do not see your materials combination, please
Contact Us
Metals
S-Bond alloys can wet and join all metals and all
combinations of metals. There are; however, differences
in the level of metallurgical interactions and in
the strengths of the resultant joints. These figures
illustrate typical joint structures. The first micrograph
is a Cu-SB220 bond, done in air and without flux or
surface treatment.

Below, stainless steel has been bonded to itself
using SB220. A dense adherent joint has been produced
with good wetting at the interfaces. Due to the low
relative joining temperatures there is no discernable
interaction, yet good joint strengths have been measured.
With stainless steel, higher interface strength can
be developed through use of a proprietary surface
bonding treatment that creates a permanently solderable
layer on the stainless steel prior to joining.
A dissimilar metallic joint is demonstrated in the
joint shown in the micrograph below. Aluminum and
stainless steel would normally be very difficult to
bond to, however S-Bond products enable such joint
to be made without flux, preplating, and in air.

The micrographs above show that SB220 has wetted
and joined Ti to itself, using no flux and no pre-coatings.
The detail, high magnification photograph shows that
a continuous interface has been formed, but as in
the case of stainless steel, the low joining temperature
(250°C) has limited metallurgical interactions.
The bonding strength to both titanium and stainless
steel can be improved by use of our proprietary process
to covalently bond our materials to the metal surface.
The figures below demonstrate the joining of aluminum
in many combinations. On the aluminum side of these
joints, a metallurgical interaction forming Al-Ag
intermetallics has occurred; demonstrating that good
interpenetration between the solder and the base metal
has been achieved.

Ceramics
S-Bond alloys can join a variety of ceramics and has
the capability to join ceramics to metals and other
ceramics and glasses. The joint strengths are generally
lower than metal-to-metal bonds, and the structures
vary with the substrate materials. However, significant
bonding strengths are achieved both and without use
of our surface precoating process. As in any dissimilar
material joint, the joint performance will be influenced
by thermal expansion mismatch derived residual stresses
related to the joint size and geometry. The figures
below show how SB220 has joined 99.6% alumina (Al2O3)
to copper. The highly magnified view shows an Al2O3
interface with S- Bond 220 that has been thermally
exposed at 205°C (sub-solidus) for 10 days.

Aluminum nitride (AlN) has been joined to itself
with SB220, as shown in the photomicrograph to the
left. Note the ceramic is wetted with indication of
interaction at the S-Bond 220/AlN ceramic interface.
An example of zirconia (ZrO2) bonded to stainless
steel is show to the right. The zirconia ceramic is
well wetted and good adherence was achieved.
S-Bond products can also be used to bond carbide materials
including graphite, diamond, and cemented carbides
as illustrated in the two figures below.

Composites
S-Bond® materials will bond to metal, ceramics
and carbide composites individually or if they are
mixed as part of a metal matrix composite (MMC's).
S-Bond® products have a unique ability to bond
to the metal matrix and wet and adhere to the ceramic
particles and/or fibers. Alternative processes involve
precoating or treating the MMC surface followed by
a flux based joining process. The first figure shows
how C:C has been bonded with SB220 to aluminum. The
others figures below indicate joints in Al-MMC structures
using SB220.

S-Bond products are used to join Al:SiC composites,
as seen above. Such Al:SiC composites are leading
candidates for low expansion bases for electronic
substrate heat spreaders, replacing copper and aluminum.
Al:SiC composites are also finding use in precision
machine tools where low CTE and high stiffness are
essential for positioning accuracy. S-Bond 220 joints
between Al:SiC and Kovar® (a low CTE Ni-Fe-Co
alloy).
To the left one can see that another type of Al-MMC
that has been joined. It is an Al:Gr-fiber, metal
matrix composite joined with SB220 resulting in a
dense structure with good adherence.

Electronic Materials
Electronics use a range of metals, ceramics and an
increasing proportion of composite materials, for
function and to thermally manage electronic and opto-electronic
packages. The joint structures depicted in this section
show some joints with typical materials that are used
in electronic packages and in electronics, including
alumina (Al2O3), aluminum nitride (AlN), silicon,
silicon carbide, aluminum, copper and many other metals.

The picture above shows how silicon (Si) has been
wetted and bonded with SB220, which is potentially
useful in direct solder die attach, enabling excellent
potential for silicon device manufacture.
The joint to the left illustrates the structure of
the S-Bond Alloy 220 joined to alumina, used as a
substrate material in chips and other devices.
Aluminum nitride (AlN) is an emerging electronic substrate
material and is emerging as the substrate of choice
in power electronic devices that carry and switch
more current and thus generate more heat. AlN is more
conductive than alumina and thus functions better
to spread and conduct the heat away from the Si devices.
S-Bond has been found to join AlN to itself and to
many metals and composites. The joint structure shown
to the right shows the good interface interaction
a condition for good bonding.
Electronic packages many times involve the joining
of copper to aluminum oxide. The joint structure depicted
to the right demonstrates the S-Bond Alloy 220 can
produce such joints.
Foams
S-Bond alloys are finding increasing application for
joining graphitic and metallic foams. The limited
capillarity and the active nature of S-Bond alloys
enable them to join against porous surfaces. One emerging
use of graphite and metal foams is in thermal management
for electronics due to their high specific surface
area and low weight. Another application for these
foams includes lightweight structures. The figure
to the right and below show examples where graphite
foam has been bonded to Al:SiC composites and graphite
bonded to copper, respectively.area and low weight.
Another application includes lightweight structures.
The figure to the right and below show examples where
graphite foam has been bonded to Al:SiC composites
and graphite bonded to copper, respectively.

Such joints microstructure can be seen in the pictures
below. Note that SB220 has wetted both Al and Graphite
in these two examples and that the alloy is located
at the interface and has encapsulate the foam without
excessive penetration.

The major functional advantage of S-Bond alloys
a re that their metallic joints permit excellent heat
transfer as can be seen in the figure below where
graphite foams and aluminum foams were S-Bond joined
to plate as in the figures above. The test consisted
of heating the plates with a specified power density
then measuring temperatures in the water and the plates.
Note the superior heat transfer capacity of the Gr-Foams
plates

The figure above illustrates another type of foam
joint. The photomicrograph illustrates how stainless
steel foams are bonded to copper. Such joining may
be useful for making fluid or air filters.
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