Electrically conductive adhesives enabling low temperature electronics

Tuesday 5 April 2016
Electrically conductive adhesives enabling low temperature
electronics
IDTechEx
Cambridge, UK

Electrically conductive adhesives enabling low temperature
electronics

By Rachel Gordon, Technology Analyst, IDTechEx

Materials are needed to replace the estimated 50,000 metric tons
of tin-lead solder currently used each year, but there are no
“drop-in” replacements for eutectic tin-lead solder. $1.2 billion of
electrically conductive adhesives (ECAs) are already selling each year, and
they are becoming increasingly common to replace solders in a variety of
functions, applications and industries. The new IDTechEx Research report Electrically Conductive Adhesives 2016-2026 covers
the three main categories of conductive adhesives available as safe and
environmentally-sound solder alternatives.

ECAs consist of a polymeric resin (such as an epoxy, or a
silicone) that provides physical and mechanical properties such as adhesion,
mechanical strength and impact strength, and a metal filler (such as
silver, gold or nickel) that conducts electricity. In order to reduce the
volume of filler used, increase the electrical conductivity, and decrease the
finest possible pitch width, there is research into using nanoparticle fillers
including silver nanowires, silver nanoparticles, nickel nanoparticles and
carbon nanotubes.

Figure 1: Diagram showing some of the most important parameters
to consider when choosing an electrically conductive adhesive. Source: IDTechEx
Research report Electrically Conductive Adhesives 2016-2026 (www.IDTechEx.com/adhesives).

Obviously in all these materials, the electrical conductivity is
of primary importance. However, the thermal conductivity must also be high
enough so that components do not overheat. The thermal conductivity of ICP is
approximately 20 W/m.K, compared to 60 W/m.Kfor lead solders. Adhesion to the
mating surfaces must be good enough that there will not be adhesive failure,
and the tensile strength must be high enough to avoid cohesive failure, even
under bending and flexing conditions. The viscosity must be low enough for
easy dispensing, but high enough after curing to avoid pump out and dry out. In
some applications, the operating temperature will be important and, whereas
solders can operate up to 270ºC, ECAs are limited to around 200ºC. It must be
non-toxic, because there is no point replacing lead with another equally toxic
material.

Lead solder melts at 215ºC, whereas isotropic conductive paste
can be cured as low as 110ºC. This opens up possibilities for using plastic
substrates to allow a new generation of flexible electronics. In order to use
PET substrates, without the risk of buckling or warping during curing, the cure
temperature needs to be brought below 80ºC.

Key applications

·  
Photovoltaic modules –
ECAs have suffered from poor stability when applied to copper and tin metals,
but improved ECAs for PV applications have been available since 2010. Lower
temperature interconnections can allow thinner wafers, and reduce warpage and
breakage of solar cells.

·  
LCD and OLED displays –
ACFs have found a particular niche market in packaging flat panel displays. In
general, bending or physical deformation of ECAs can degrade the electrical
conductivity. Therefore, novel flexible electrically conductive materials which
respond well to repeated bending or high elongations will be required
for future flexible display technologies.

·  
Touch panels – The damage
to the substrates can be reduced by lowering the bonding temperature during
assembly. The penetration of touch panels in the cell phone market is
forecasted to reach more than 40% in the near future.

·  
LEDs – It is quick and
cheap to mount LEDs using conductive adhesives and the thermal penalty is
tolerable if the adhesive layer is kept thin. 

·  
RFID chips – Conductive
adhesives are used for mounting temperature-sensitive chips on smart cards,
because of low curing temperatures.

Figure 2: Chart showing the ACF market share in 2015 by
application. Source: IDTechEx Research report Electrically Conductive Adhesives 2016-2026 (www.IDTechEx.com/adhesives).

Currently, 74% of Anisotropic Conductive Film (ACF) is used in
the manufacture of LCD or OLED displays. Displays are becoming more widely used
in consumer electronics, aerospace, defence, automotive, and infrastructure
sectors. UV-thermal cure mechanisms must be developed to lower cure temperature
to allow plastic substrates for flexible displays. However, according to
IDTechEx Research’s report Electrically Conductive Adhesives 2016-2026, this
market is still set to diversify with the market for ACF in non-display
applications reaching over $1 billion by 2026, due to the reliable properties,
thinness and ease of processing. Metallic coatings on polymeric particles will
allow lower cost fillers.

Electrically Conductive Adhesives 2016-2026 offers
worldwide coverage of electrically conductive adhesives, most of which are
manufactured in Asia-Pacific but start-ups and innovation exists in Europe and
North America. The report is based on extensive research and includes twelve
primary interviews with the market leading manufacturers. It includes forecasts
by revenue, split by technology and function, until 2026.