Automotive Engineering - October 2022 - 30

KEEPING YOUR SILICON
COOL
THERMAL MANAGEMENT FEATURE
Thermal-interface
material must be
easily dispensed
into targeted
areas, with no post
curing, to speed
the manufacturing
process and offer
visibility to optical
cameras, notes
Parker Chomerics'
senior engineer
Scott Casper.
The board with the material
affixed would undergo a
solder reflow process which
would reach temperatures as
high as 245°C (473°F).
Experiments were run to study the effects of elevated temperatures
on the thermal and mechanical properties of the TIM compound.
TC50 samples were exposed to the 245°C solder reflow process,
and the results concluded that the thermal impedance (TI) and
viscosity did not deviate over the extended time exposure. Finally,
the entire assembly (PCB with the interface material and a cover)
was evaluated in the actual solder reflow profile. It was found that
the material maintained its rheological structure along with its intended
thermal properties and was approved for the program.
Challenge #2: PCB with multiple fill
locations
A premium automotive system manufacturer was
searching for a high-performing TIM for its infotainment
module. The TIM needed to be adaptable to filling
multiple locations on their boards and it needed to
meet a specific temperature threshold.
Specifically, it needed to be capable of filling five locations
on the printed circuit board (PCB), each having
a different footprint and gap height. The manufacturer
needed assistance to determine the best material and
the correct amount of gel to dispense in each location,
as well as equipment to best dispense in the high-volume
application. Compounding the issue, the board
with the material affixed would undergo a solder reflow
process which would reach temperatures as high as
245°C (473°F). The upper operating temperature for
silicone-based gels is 200°C (392°F).
Initially, the customer provided a production PCB
for evaluation, which then was replicated for testing
using an in-house 3D printer. The 3D printed prototype
parts enhanced the five locations for dispensing,
so they could be correctly identified for precise dispense
location.
Using a precision dispensing system installed in the
applications engineering lab, potential materials were
evaluated. Therm-A-Gap TC50 dispensable thermal
putty was ultimately selected for its high thermal conductivity
(5.0 W/m-K) and easy dispensing onto the
3D printed parts for capabilities trials. The prototype
parts were successful in representing the actual PCB.
The customer's engineering team witnessed the tests
and preliminarily approved the material for use.
30 October 2022
Challenge #3: Safety modules for ADAS
As vehicles are relying more on advanced driver-assistance systems
(ADAS), automotive camera and motion sensor companies are expanding
their technologies to meet stringent compliance requirements.
For some ADAS modules, this requires high-performance, robotically
dispensed thermal-interface materials. The TIM must provide
soft compression, ease of dispensing, and a flow rate suited for
high-volume manufacturing. Additionally, the material may need to
be visible to optical cameras.
In this case, the customer initially expressed a preference for thermal
gap pads over dispensables, due to previous negative experiences
with dispensing. However, due to volume production requirements,
it became apparent that pads would not be a feasible option.
In addition, the thermal material needed to be higher in thermal performance
than the pads typically used (> 3 W/m-K).
Through extensive testing, Therm-A-Gap GEL 45 was selected as
the optimal TIM for this application. GEL 45 offers a high flow rate
suited for high-volume manufacturing (55 grams/min) and has a
thermal conductivity of 4.5 W/m-K. The product also is black, so it
can be seen by optical cameras on the assembly line. Finally, the
camera manufacturer ran a battery of tests to ensure the amount of
material dispensed was adequate to the heat and would not damage
the PCB during assembly.
Challenge #4: Non-silicone thermal interface
for ADAS modules
What if an application involves silicone contamination concerns? The
positioning of optic lenses within automotive camera assemblies can
present this issue. Additionally, semiconductor image sensors and
chips within automotive camera assemblies often require enhanced
heat-dissipation efforts.
AUTOMOTIVE ENGINEERING
PARKER CHOMERICS
Automotive Engineering - October 2022

Table of Contents for the Digital Edition of Automotive Engineering - October 2022
