Electrically conductive PSAs.
As electronic devices become increasingly smaller and more
complex, reducing the size of component space becomes more important.
Electrically conductive pressure-sensitive adhesives (PSAs) enable smaller
electronic designs through thin, effective bonds because they not only bond
components together, but also provide the added functionality of providing pathways
for electrical currents. By eliminating the need for other conductive elements,
electrically conductive PSAs present options for simplifying electronic device
design and manufacture. Electrically conductive PSAs are suited for
applications such as electrical interconnections for low-current circuits;
splicing conductive materials; bonding electromagnetic interference gaskets;
ground plane assembly; and static control for printed circuit boards and
The days of “glue” simply bonding electrical components have passed. Today’s
adhesive systems have evolved into sophisticated polymer formulations capable
of delivering reliable bonds with added functionality. For example,
electrically conductive PSAs are highly tailored polymer formulations loaded
with materials to create conductive properties in the adhesive. The adhesive is
then coated onto a carrier/substrate that may also contribute to the tape’s
conductive properties in single- or double-faced constructions. PSAs may also
take the form of a self-wound transfer adhesive.
When uniformly dispersed, conductive particles create
pathways within the adhesive matrix to make contact from one surface to
another. The conductive fillers may comprise a number of materials, such as
nickel, silver, carbon, or a combination of these. The adhesive matrix may be
formulated from silicone, acrylic or rubber polymers to ensure maximum
flexibility and compatibility with metal, film, and potentially
Adhesives Research Inc., a leader in the development of electrically conductive
adhesive technology, has been designing, developing and manufacturing
leading-edge, electrically conductive adhesive products for over 20 years. The
company's electrically conductive PSAs are based on a patented homogeneous
carbon-based adhesive technology that delivers exceptionally stable bonds to
electrical contact points, even under extreme stress. The bonds are
particularly reliable because the conductive particles within the adhesive form
strong carbon chains for good point-to-point conductivity. The chains are
flexible, allowing for movement with the adhesive as it expands or contracts
against bonded substrates during temperature changes. This flexibility results
in uninterrupted electrical contact for reliable electrical interconnections.
Depending upon the application, a number of adhesive or film formulations can
be created in combination with the carbon particles to achieve the desired
outcome, including carbon-filled adhesive matrix; carbon- and metal-filled
adhesive matrix; carbon and silver compound adhesive; adhesive-embedded
composites for X-Y vs. Z conductivity control; and conductive films and
The carrier or substrate can also play an important role in the conductive
performance of the adhesive system, or it can address specific design
challenges, like the metal foil or fabric substrates used in EMI shielding
gaskets and seals. A number of specialized substrate materials are available, ranging
from plastic films to galvanized foils and metallized fabrics. Today, design
engineers have more material choices for conductive substrates than ever,
including metal-coated polyesters, metal-plated mesh fiber and carbon mesh.
Performance is Key
In recent years, advancements in conductive PSAs have
enabled formulators to tailor the adhesive’s physical properties for
resistivity, conductivity and a number of environmental stresses, including
shock and moisture resistance. For example, the Adhesives Research conductive
technology can achieve Z-axis resistances from a few milli-ohms to a few ohms,
and can be produced in thicknesses of 25-100 microns. This technology is also
proven for use in fine pitch connections where X-Y isolation is critical, and
it provides reliable connections down to 300 x 300 microns.
As applications for electronic devices broaden, the adhesives in these are also
required to withstand a wider range of harsh environmental conditions,
including significant humidity and temperature fluctuations. Adhesives
Research’s technology demonstrates stable bonding performance through
temperature cycling (-20-85°C) and up to 95% relative humidity. The adhesive
system can also be tailored to provide a degree of removability, which is
important for parts requiring re-work during the manufacturing process.
Design engineers should consider the process and handling benefits of PSAs when
selecting an adhesive for their product designs. PSAs form instant bonds, and
provide reliable electrical contact without mechanical pressure or cure times.
Because these adhesive systems are manufactured in a continuous web format,
rolls can be manufactured into wide roll formats, or slit to specified widths,
lengths or sheets, and further converted into die-cut components. The
manufactured PSA rolls are easy to handle and process, with no messy cleanup
Applying the Technology
conductive PSAs are sought out for a number of applications, including
electrical interconnection and assembly, EMI/RFI shielding and grounding, and
static dissipation and control in a range of electronic, medical, and
pharmaceutical applications. Examples of Adhesives Research’s electrically
conductive technology are listed in the Table.
Electrically Conductive Bus Bars for Photovoltaic Modules
An area where interest for conductive adhesives is growing
is thin-film photovoltaic modules (PV) for solar-energy applications. In
thin-film PV modules, the electrical current generated in the module’s semiconductor
is extracted by contacts on the front and rear of the cell. Widely spaced thin
metal strips, often referred to as fingers, transport the electrical current
generated within the cells to a larger metal bus bar strip. The purpose of the
bus bar is to efficiently gather the electrical current from the individual
fingers and transport the current from the solar module to a nearby junction
90038 is a 2.4-mil, highly conductive PSA tape
featuring a 1-ounce, tin-plated copper foil backing that demonstrates excellent
conductivity and corrosion resistance for bus bar applications. Rated UL 510,
this tape features Adhesive Research’s patented homogenous conductive adhesive
technology that forms exceptionally stable, conductive bonds to electrical
contact points even under extreme environmental stress. The adhesive-coated
foil tape construction offers a clean, easy-to-use format for efficient
application, unlike copper ribbons and conductive adhesives or epoxies that
require a two-step bonding process.
Adhesives Research also offers a range of PSA products to compliment ARclad
90038 for a number of PV module applications, including electrical
interconnections, wire management, bonding and assembly, and encapsulation.
conductive adhesives provide bonding performance and conductivity - two
desirable features as electronics become smaller and more complex. Standard
electrically conductive adhesive products are available, but Adhesives Research
finds that most design projects begin with a base technology that is then
customized for each application. Some aspects of the adhesive system that can
be tailored by application include: adhesive performance properties and
formulations; finished thicknesses (25-150 microns); and substrate and release
liner material selections. The conductive properties of the adhesive itself can
be tailored to range from 1 milli-ohm to 10,000 milli-ohms depending upon the
needs of the application. Development work continues to push the technology
envelope for conductive adhesives, including the combination of these with
conductive films, coatings and inks for added conductive capabilities.
About the Author
Hariharan is the Electronics Business Manager for Adhesives Research Inc.
Hariharan has a Ph.D. in chemical engineering from Purdue
University, a degree in chemical
engineering from the Indian Institute of Technology, and an MBA from the University of Maryland.
For more information about Adhesives Research Inc., phone (800)
(717) 235-7979, or visit www.adhesivesresearch.com.