April 18
10
E
mbedded
C
omputing
Development of a cooling
system for a COM carrier system
By Stefan Djuranec,
Pentair Technical Solutions
During the development process
of the Pentair Schroff COM carrier
system, thermal simulations were
used to optimize passive cooling
through the cooling element. The
result is a modular system that can be
modified to meet various customer
requirements through selection from
a series of available cooling elements.
Increasing electronics density and higher
power
dissipation
require
continuous
improvement of heat dissipation solutions for
electronic components and systems. This is
why the cooling design for the Schroff COM
carrier from Pentair was integrated into the
development process and monitored in paral-
lel from the start of development. Using state-
of-the-art simulation methods, a wide range of
solutions can be validated before actual devel-
opment starts. The result is a modular set of
components that makes it possible to support
a wide range of customer requirements while
still presenting the right solutions quickly.
In the past, an iterative development process
in the test lab using prototypes achieved satis-
factory cooling results. However, this method
is no longer practical due to the high cost and
development time (time to market). The spe-
cific problem is that prototypes and samples
are usually not available until very late in the
development process. There is always a risk of
design changes in later project phases, which
may cause delays and higher costs.
Computational development methods, on the
other hand, have made tremendous advances
in recent decades with respect to accuracy and
user-friendliness. Thanks to the computing
capacity of state-of-the-art hardware, these
methods have become an efficient tool. This
method does require that developers make a
few simplifications and design assumptions,
requiring in turn that the simulations be val-
idated using measurements and trials of the
physical cooling devices. Using simulations,
the number of trials and versions can be sig-
nificantly reduced. This is why a combined
method was used for developing the cooling
concept of the Schroff COM carrier. The sys-
tem was designed with the aid of thermal sim-
ulations and a series of measurements were
then carried out on the real parts to validate
simulation results.
The goal is for the Schroff COM carrier to
support COM express modules up 45W using
only thermal conduction and convection air
flow. In this design, the exposed surface of a
heat sink must not have a temperature over
50°C in order to prevent burn injuries. In
addition, demand is growing for easy module
replacement, which requires an easy-to-open
case with simple cooling device removal. For
this reason, an adapter plate is used (figure
1). This plate is permanently connected to the
heat spreader of the COM module, sealing
the case against the ingress of dirt, water and
electromagnetic waves. In addition, the plate
establishes the thermal connection between
the heat spreader and the cooling element.
Thermal gap fillers compensate for tolerances
and unevenness.
The cooling elements are specially designed
for the carrier system at the beginning of the
process with the help of simulations. In order
to efficiently achieve a wide range of variants
for the test series, additional cooling elements
from standard profiles are procured from sup-
pliers. Because the positions of the primary
heat sources vary on different COM mod-
ules, dummy modules with load resistors and
heat spreaders with easily adjustable thermal
loads are created for the measurements. The
components in the thermal conduction path
(modules, heat spreaders, adapter plates and
cooling elements) are equipped with tempera-
ture sensors at all four corners and on both
sides. The sensors are sunk into grooves made
in the surface and glued in with thermal adhe-
sives to ensure that they do not interfere with
heat transfer. The trials are carried out in a
climate chamber with the option of adjusting
the ambient temperature. In addition, poten-
tial disturbance variables are evaluated and
minimized at the beginning of the test series.
Each individual measurement is carried out
for as long as it takes to achieve a steady state.
At the beginning of the measurements, it was
shown that the thermal inertia of the cooling
element is very high and that the measure-
ments must be prolonged over several hours
before the cooling element reaches a steady
state. This is due in particular to the high
Figure 1. The COM carrier
system: 1) removable cooling
element; 2) adapter plate; 3)
removable front and top covers
for easy access to the electronics.
