Applications for Low
Popular Low Outgassing
Cure for Outgassing
One of the most common issues with respect to adhesives in
High-tech manufacturing industries involves the outgassing
characteristics of adhesives and related encapsulation and sealing
compounds. And that’s understandable because a growing number of
high-tech industries have discovered that their products and
manufacturing processes can be sensitive to outgassed chemical
compounds. As a result, there has been a dramatic upswing in the use of
adhesives, encapsulants and sealants that have been specially
formulated for low outgassing performance.
While it’s true that some standard adhesives do have good outgassing
performance “right out of the tube,” today’s most stringent outgassing
requirements are best met by products formulated to pass an
industry-standard outgassing test known as ASTM E595-07.
The test’s full title is “A Standard Test Method for Total Mass Loss
and Collected Volatile Condensable Materials from Outgassing in a
Vacuum Environment” (see sidebar).
And engineers working on projects for NASA already know all about it.
For years, they have been specifying ASTM E595-compliant adhesives and
other materials for use in space systems.
Now that a growing number of engineers with earthbound applications are
worrying about outgassing too, Figure 1takes a look at what to
expect from low outgassing adhesives, encapsulants and sealants.
Figure 1. Adhesives that have passed the
industry-standard outgassing test (ASTM E595) offer a range of physical
properties tailored to aerospace, optical and electronic applications.
Outgassing from Adhesives
The industry standard test for measuring outgassing in adhesives and
other materials is ASTM E595. Developed by NASA to screen
low-outgassing materials for use in space, the test determines the
volatile content of material samples placed in a heated vacuum chamber.
Samples to be tested are first preconditioned at 50 percent relative
humidity for 24 hours and weighed. They then go into the test chamber
for another 24 hours with the temperature set at 125 C and the vacuum
at a minimum of 5 x 10-5 torr. During that time in the test chamber,
volatiles that outgas from the sample escape through a port in the test
chamber and condense on a cooled (25 C) collector plate.
The sample and condensate on the collector plate are then weighed to
determine the total mass lost (TML) by the sample and the amount of
collected volatile condensable materials (CVCM) on the collector plate.
Materials pass or fail the test based on these TML and CVCM
measurements. If the CVCM exceeds 0.1 percent, the material fails. The
material will also fail if the TML exceeds 1 percent—though the TML may
be offset by water vapor regained (WVR) by the sample in a subsequent
- If CVCM <0.1 percent and TML < 1 percent, the material
- If CVCM <0.1 percent and TML > 1 percent, the material can
pass if the TML-WVR <1 percent.
- If CVCM > 0.1 percent or TML-WVR > 1 percent, the material
While you will occasionally run across proprietary outgassing test
methods, their results should not be considered credible. ASTM E595
currently represents the only widely accepted industry standard for
quantifying the outgassing performance of adhesives. The test does have
its limitations. Among them, this 24-hour test doesn’t predict
long-term outgassing performance. Nor can it determine what specific
outgassing contamination, if any, will occur in real world operating
conditions. Despite these limitations, though, the test is a good way
to evaluate and compare the outgassing potential of adhesives and other
Master Bond has developed UV-curable
adhesives that pass ASTM E595, something these fast-curing
adhesives have traditionally not been able to accomplish.
This development brings the assembly speed of UV-curable adhesives
to outgassing-sensitive applications.
Image 1: Masterbond UV-Curable Adhesives
designed to pass
Applications for Low
The first thing to understand about low
outgassing products is when to use them (see Figure 2. “Typical
Outgassing Applications” for a full list). Other than space systems,
the most common applications for low-outgassing products are those that
involve optical or electrooptical components, which can be clouded or
fogged by outgassed chemical compounds. Outgassing can also affect some
sensitive electrical processes—by interfering with electrical
continuity. Semiconductor manufacturing processes can be very sensitive
to outgassing material systems. And commercial vacuum processes can
also suffer from outgassing issues.
If you suspect outgassing could potentially pose a problem in your
application, specifying adhesives that comply with the ASTM outgassing
standard will make sense as long as one of the compliant grades meets
all of your other technical requirements. And the good news here is
that low outgassing adhesives don’t typically require any sacrifice in
other mechanical or physical properties. What sets low outgassing
products apart from their generic counterparts is that the low
outgassing grades have passed the rigorous ASTM test—often after months
of painstaking formulation work on our part.
The time and expense of all that testing and custom formulation do
not have major cost implications for users of low outgassing products.
The compelling reason to carefully consider whether you truly need a
ASTM E595- compliant grade comes down to freedom of choice, not cost.
Consider that Master Bond has hundreds of adhesives that have not
been tested for low outgassing and over 20 adhesives that have. By
picking an ASTM E595-compliant grade when you do not need one, you may
limit your ability to find the best match between your application
requirements and adhesive properties. For this reason, engineers should
stick with standard products for bonding, sealing, encapsulation and
potting applications that have no known sensitivity to outgassing.
With that caveat in mind, the compliant adhesive products available
today do cover a wide range of capabilities for those times when
nothing else will do (see Figures 1 & 2 and Table 1).
Bond offers ASTM E595 products for structural bonding, potting,
encapsulation and sealing. Also available are E595-certified
electrically and thermally conductive products as well as medical and
cryogenic adhesives. Recently, Master Bond introduced a UV-curable
adhesive, one of the first in the industry to pass the standard ASTM
- Disk drive assemblies
- Voice coil motors
- MEMs devices
- High-vacuum applications
- Solar arrays and panels
- Fiber optic assemblies
- Optical telescopes
- Space systems
- Optics used in aircraft and space applications
- Lens mounts and prisms
- Wavelength-division multiplexing (WDM) applications
- Medical filter applications
- High-power voltage supplies
- Optoelectronic assemblies
- Piezo devices
- Clean room applications
- Satellite assemblies
- Electronics underfill applications
- Laser applications
- Mirrors (including mirrors for telescopes)
- Bonding voice coil to
- suspension arm
- Broadband and highfrequency RF power applications
- Avalanche photodiodes (APDs)
Figure 2: Typical Applications for Low-Outgassing
When looking for low-outgassing products, keep in mind that not
all adhesives start on a level playing field when it comes to passing
ASTM E595. Some adhesives, such as two-part epoxies, can be specially
formulated to achieve outgassing levels well below what ASTM E595
Other types of adhesive chemistries have traditionally not been able
to pass ASTM 3595. UV-curable adhesives once fell into this category,
which kept these fast-curing adhesives out of some otherwise suitable
Only recently have Master Bond’s chemists been able to “crack the
code” of UV-curables that do pass the test.
The adhesives that outgas most severely are those that cure through
the action of solvents or moisture. These would include a variety of
pressure-sensitive and contact adhesives as well as cyanoacrylates.
These types of adhesives are not be the best choice in applications
that have a known sensitivity to outgassing.
It’s worth noting that even within a given family of adhesives, the
outgassing potential of the individual adhesive grades can vary
substantially. This variance results from the optimization of each
grade’s physical and mechanical properties through modifications to the
underlying adhesive chemistry. To take one common example, the more
flexible grades within the epoxy family tend to be
more prone to outgassing—possibly because they have a lower
crosslink density than their more rigid counterparts.
At the end of the day, adhesives are best looked at as individuals
rather than families when evaluating outgassing performance. And the
only way to know for certain whether a specific adhesive meets the low
outgassing criteria spelled out in ASTM E595 is to test it.
Bond offers a wide variety of certified low-outgassing
adhesives. Some of the most popular grades are described here:
Table 1: Masterbond Low Outgassing
Adhesives Properties and Applications
|Low viscosity, cryogenically
serviceable epoxy with excellent physical properties for bonding or
potting. Withstands cryogenic shocks. Superior electrical insulation
properties. Optically clear.
|Thermally conductive, two-component epoxy with
paste consistency. Cryogenically serviceable. High temperature
resistant for bonding and sealing. Cures at room temperature. Service
temperature range 4K to 400°F.
|Thermally conductive, lower
viscosity, easy to use epoxy system that cures flexible. Resistant to
vibration, impact and shock. For potting and bonding. Cryogenically
|Superior physical properties, excellent optical
outstanding chemical resistance profile. Low viscosity enables easy
Service temperature range 4K to 300°F.
|One part, no-mix system
requiring oven curing at 250° to 300°F with extraordinary
physical properties. High peel and tensile shear strength.
Resistant to vibration, thermal shock and impact.
|One component UV curable adhesive/sealant.
Exceptionally fast curing. Excellent clarity and light transmission
properties. Service temperature range -60°F to 300°F. Easy application.
|Highly flexibilized thermally
conductive two-component epoxy system. High shear and peel strength.
Superior electrical insulation and heat dissipation properties. Cures
at room temperature. Ideal for bonding dissimilar substrates. Resistant
to thermal cycling.
|High purity silver conductive epoxy
adhesive/sealant. Service temperature range from 4K to 400°F. One part,
no mix system. Resists vibration, shock and thermal cycling. 100%
reactive. High peel and shear strength properties.
|Resists up to 400°F. High
thermal conductivity and excellent electrical insulation properties.
Cryogenically serviceable. One-component, no-mix system. Resists
exposure to many chemicals and thermal cycling. Cures at elevated
temperatures. Low ionics.
Cure for Outgassing
When selecting adhesives for low-outgassing applications, engineers
often don’t pay much attention to cure schedules. That’s understandable
since so many modern adhesive formulations do indeed cure well at room
temperature, developing better than adequate mechanical and physical
properties for their intended use. Yet the addition of a heat cycle
will optimize a host of desirable physical properties—low outgassing
among them. With adhesives, in other words, it’s often the case that a
room temperature cure is good, but a heat cure is better.
In low-outgassing applications, heat can even be
essential. Heat tends to improve the crosslink density, which in turn
limits outgassing. Master bond have seen cases where individual
adhesives did not pass ASTM E595 when cured at room temperature but
passed after a heat cycle. For that reason, Master bond recommend the
addition of a heat cycle for applications where outgassing performance
is critical. A typical cure schedule would be room temperature
overnight, followed by 2–5 hours at 60-80 °C.
This article has been created from material supplied by Master
About Master Bond
Bond is a leading adhesive manufacturer offering high quality
adhesives, sealants, coatings, and potting compounds. Master
Bond’s product line consists of epoxy adhesives, polyurethane,
silicone, cyanoacrylate and latex adhesives.Master
adhesives offer design flexibility and provide excellent bonding
performance with a vast array of 3,000 custom designed adhesive
formulations. Adhesive properties differ in viscosity, cure speed,
chemical and temperature resistance, strength, electrical and thermal
Specific adhesive systems are designed to meet USP Class
VI certification for medical use or NASA requirements for low
outgassing.Master Bond products are successfully
implemented in medical, optical, aerospace, electronic, and other
Source: Master Bond
For more information on this source please visit Master Bond.