Automotive Engineering - June 2021 - 24

HOW EVs AND THEIR ELECTRONICS
STICK
TOGETHER
New
adhesives play
an increasingly
vital role in vehicle
structures, battery
packs, and in protecting
sensitive electronic
components from extreme
thermal cycling and contaminants.
by Venkat Nandivada and Rohit Ramnath
T
hermal management and vehicle weight reduction
are among the challenges facing electric
vehicles (EV) and automated driving systems,
as engineers focus on improving vehicle range,
performance, and safety. Adhesives, sealants, and
coatings are playing a vital role in these developments.
Their lightweight, functional properties are key to the
industry's increased use of mixed-material structures,
including battery packs. They also serve as electronic
encapsulants to protect sensitive electronic components
from extreme thermal cycling and contaminants.
Compared with traditional metal fasteners, structural
adhesives offer improved inventory management,
an overall reduction in design weight and a more reliable
joint. Compared with rivets or welds, they can
disperse the load over a larger area, thereby reducing
the localized stress on a fastener and also improve
joint reliability. Dispersing the stresses over a larger
area may also allow for caliper reduction of the components
with a resulting weight savings.
Epoxy adhesives, two-part or one-part cure, are
the workhorse of the automotive industry. Many advances
in the packaging and delivery systems of the
24 June 2021
Certain grades of epoxy can withstand
rigorous thermal cycling and shock.
Good flow properties and lower exotherm can be
desirable for potting and encapsulation applications.
adhesive further improve manufacturing efficiency and reduce
waste. Developments such as dual-cure, UV + Heat curing allow for
higher manufacturing speeds and throughput.
Selecting the right adhesive
Whether used in a structural capacity or to reinforce and protect
electronic assemblies, adhesives must possess the correct mechanical
properties. Depending on the nature of the joint, modulus or
stiffness will determine the joint stability and whether the adhesive
will readily deform to absorb stress or stay rigid and maintain high
dimensional stability. In certain assemblies, lower modulus may also
allow an adhesive to mitigate and relieve stresses that accumulate
due to differences in thermal expansion, or to dampen vibration and
shock. Conversely, a higher modulus is important in flip-chip microelectronic
assemblies where the adhesive is used as an underfill. If
the modulus is too low, the underfill will inadequately protect the
solder joint. And a modulus that is too high may overly redistribute
stresses to the silicon chip and result in die cracking.
Depending on the nature of the joint and the applied stresses, the
adhesive's shear, tensile and compressive strengths are critical in joint
design as well as the bonding strengths to the employed substrates.
Given proper surface prep, a good adhesive bonds well to a variety of
AUTOMOTIVE ENGINEERING
MASTER BOND

Automotive Engineering - June 2021

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