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TECHNOLOGY TRENDS

Improving semiconductor packaging with

advanced silicones

By Jayden Cho, Roderick Chen [Dow]

D esigners who are familiar wires and interconnects; and epoxy, activated and heat-cured with a thickness

between 25µm and 2000µm at room
polyimide or phenolic for printed circuit
with epoxies for chip-level
packaging have new options
heat sinks. Because each of these materials
that is sandwiched between two release
for wafer-level packaging and boards (PCBs), which also contain metal temperature. Products consist of a thin film
even panel-level packaging. As 8-inch and expands and contracts at a different rate, liners that are either clear or black in color.
12-inch wafers become increasingly thinner stresses are imparted that can cause Functional fillers can impart thermal
to support new product designs, the challenge fracture. Conversely, advanced silicones are or electrical conductivity. When heat is
of applying epoxies in thicknesses under stress-relieving and can help mitigate wafer applied, SHF becomes flowable at 90°C
10µm requires forward-thinking solutions. warpage caused by CTE mismatches. and above. After curing, SHF resists the
Advanced silicones can provide very thin, Chip designers also need to consider the high temperatures associated with today’s
very uniform coatings for encapsulation effects of thermal shock, a mechanical load electronics and provides exceptional stress
along with effective stress management for caused by a rapid change in temperature, relaxation. This advanced silicone is
reduced wafer warpage. Whether alone, or in especially in packages that undergo rapid designed to simplify package processing
combination with epoxies to produce novel heating and cooling, such as for electric and can encapsulate large substrates, even
hybrid materials, advanced silicones are vehicle (EV) power electronics and those with uneven surfaces, to a uniform
driving packaging innovation. 5G communications systems. With 5G thickness. For cost-effective processing,
Epoxies are widely used for chip devices, resistance to high temperatures SHF supports compression molding and
encapsulation because they combine strong is required because there are more heat- vacuum lamination.
and reliable bonds with low shrinkage and generating components packed into very The melt viscosity of silicone hotmelt
excellent moisture and chemical resistance. small spaces, such as in smartwatches, or film is a function of temperature. At lower
Epoxy die attach film (DAF) can be difficult both small and slim spaces, such as in ultra- temperatures, SHFs have a higher melt
to apply in thicknesses less than 10µm, thin smartphones. Flexible displays can be viscosity for less flowability and greater
however, and these organic materials are large, and these devices may be subject to control of bond line thickness (BLT). At
relatively hard with a high modulus—a repeated folding and bending along with higher temperatures, SHFs have lower
measure of resistance to elastic deformation the high temperatures associated with 5G melt viscosity and are more flowable;
when stress is applied. Because they are components. Compared to epoxies, silicones however, they offer reduced control
less elastic than silicones, epoxies are more can resist those high levels of heat while of BLT. Flowability, like SHF’s gap-
prone to cracking when an electronic device withstanding a wide range of temperatures filling capabilities, is not just a function
encounters physical shock, such as when and stresses from CTE mismatches. of temperature, however. During the
a smartphone is dropped. The vibrations compression molding or vacuum lamination
that industrial and automotive electronics Silicone hotmelt solutions processes, pressure and time are also
encounter also produce stresses, but the Traditionally, epoxies have offered factors. Vacuum lamination is simpler for
use of thinner wafers in various types chip designers advantages in terms of encapsulating large areas, but compression
of electronics pose special concerns. If adhesion, hardness and processability. molding is used to encapsulate chips with
stresses on the front and back of a wafer are With silicone hotmelt solutions, however, flexible, core-less substrates that could
imbalanced, warpage can break the dies. semiconductor manufacturers can achieve easily warp.
Wafer warping can be caused by the excellent adhesion to a variety of substrates Silicone hotmelt films are fabricated as
formation of intrinsic stresses during thin- while leveraging silicone’s fundamental B-stage films, partially-cured products.
film deposition, but mismatches in the advantages in thermal stability and These advanced silicone products can
coefficients of thermal expansion (CTE) durability. Compared to liquid silicone, support both fan-out wafer-level packaging
can also cause unwanted dimensional these solid silicone products are easier to (FOWLP) and fan-out panel-level packaging
changes. The CTE, a material property handle and cure more quickly for faster (FOPLP)—advanced packaging techniques
that indicates the extent to which a material processing times and reduced energy that are designed to meet growing demand
expands with heat, differs by material type costs. Today, chip designers can choose for heterogeneous integration in products
– and today’s electronic devices use many from advanced silicone hotmelts in films, such as 5G smartphones, data centers, high-
different types of materials. Examples cartridges and tablets. Cured silicone DAF performance computing (HPC), artificial
include plastic, ceramic or glass for the and novel silicone hybrids are also used. intelligence (AI), and Internet of Things
package; gold or copper for the bonding Silicone hotmelt film (SHF) is UV- (IoT) applications.

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