Danfoss ShowerPower Fact sheet
Application Note
ShowerPower®
cooling concept
This application note gives an introduction to liquid cooling of power modules,
why cooling is needed, how it is done and a description of the Danfoss
ShowerPower® cooling concept. Then follow sections on ShowerPower® thermal
performance data, design guidelines, material choice recommendations and finally
a description on how to perform thermal tests on a ShowerPower® cooler.
siliconpower.danfoss.com
Content
and references
Cooling of power electronics ............................................................................................... 3
Why is cooling needed in power Electronics? 3
Why liquid cooling? 3
Liquid cooling – indirect vs. direct cooling 4
The ShowerPower® concept 4
ShowerPower® thermal performance 6
Simulations 6
Measurements 7
Design considerations 8
Corrosion issues 8
Water tightness 9
Material choices 9
Setting up the test 10
Laboratory equipment needed 10
Connecting the bathtub to the coolant supply 10
Assembly of the power module on the bathtub 11
Connecting the power module 11
References
1. K. Olesen et al., ”ShowerPower® New Cooling Concept”, PCIM Conference Proceedings 2004, Nuremberg.
2. F. Osterwald et al., “Innovative Kühltechnologie für Leistungsmodule”, ‘
Bauelemente der Leistungselektronik und ihre Anwendungen, 10.-11. Oktober 2006, Bad Nauheim.
3. R. Bredtmann et al., “”Power under the hood” Increasing power density of inverters with a novel 3D-approach”,
APE, March 25-26 2009, Paris.
4. K. Olesen et al. “Designing for reliability, liquid cooled power stack for the wind industry”,
EWEC Conference Proceedings 2012.
5. COG “O-ring basics”. http://www.cog.de/en/o-rings-products/o-ring-basics.html
DKSP.PB.301.A3.02
2
Cooling of
Power Electronics
Why is cooling needed in Power Electronics?
Every electronic circuit generates heat
during operation (excluding superconductivity); this is due to conductive and switching losses in active
devices as well as ohmic losses in
conductor tracks. And since every
new generation of power semiconductors becomes smaller than the
predecessor and the market expects
smaller and more compact solutions
the demands to the thermal design
engineer keeps growing. Suffi cient
cooling of Power Eectronics is crucial.
The dominant failure mechanisms in
power semiconductor components
Why liquid cooling?
are related not only to high absolute
temperatures but to changes in
temperature: temperature swings
produce thermo-mechanical induced
stresses and strains in the materialinterfaces of the components (mismatches in coeffi cients of thermal
expansion, CTE) which lead to fatigue
failures.
The most important failure mechanism in power modules is the bond
wire lifto where the aluminum wire
bonds (with a CTE of 24ppm/K) pop
o the silicon chip surface (CTE of Si is
2-3pmm/K) .
Bond wire liftoff after power cycling
Liquid cooling of power electronics
has been around for many years,
primarily due to the ever increasing
power densities and due to the
availability of liquids in certain
applications. Liquid cooling outperforms air cooling by having heat
transfer coeffi cients several orders of
magnitude higher thus enabling
much higher power densities and
more compact solutions.
The acceptance for liquid cooling
varies from business segment to
business segment. The automotive
industry for example has used liquid
cooling for cooling the combustion
engines for more than a hundred
years so the idea of cooling power
electronics in an automotive application is not frightening for the design
engineers. In other segments the idea
of having uids owing through
power electronic assemblies is most
disturbing.
Shower Power® Cooling Concept 3
Liquid cooling – indirect vs. direct cooling
The large amount of liquid cooling
solutions may be divided into two
groups: indirect and direct liquid
cooling.
Indirect cooling means that the
power module is assembled on a
closed cooler, e.g. a cold plate.
Cold plates may be realised e.g. by
gun drilling holes in aluminium plates
or by pressed-in copper tubes in
aluminium extrusions, an example of
which is shown here.
The rst picture shows a P3 module
being assembled onto a cold plate.
When dealing with cold plates it is
necessary to apply a layer of TIM
between the power module and the
cold plate.
Direct liquid cooling on the other
hand means that the coolant is in
direct contact with the surface to be
cooled. Here the cooling effi ciency is
improved by increasing the surface
area of the surface and this is commonly done by various pin n
designs. Below an example of how
the P3 module would look if it was
equipped with a baseplate with pin
n s .
Direct liquid cooling eliminates the
layer of TIM that is traditionally
needed between the backside of the
power module and the cold plate.
Because the TIM layer accounts for
30%-50% of the Rth, junction-coolant,
this TIM-elimination results in an
improved thermal environment for
the power module. Since the dominant failure mechanisms are temperature-driven, this will lead to higher
reliability.
A cold plate for the P3 module.
A baseplate with pin ns for the P3
module may look like this
The ShowerPower® concept
ShowerPower® is a concept for direct
liquid cooling developed by Danfoss.
The main motivation for the concept
was to solve the classical problem
associated with liquid cooling of
power modules namely:
Classical problems
with liquid cooling:
■
Inhomogeneous cooling due to
the calorimetric heating up of the
coolant
■
Thermal interface material (TIM)
related quality issues like pumpout and dry-out e ects
■
High cost
Key freatures are:
■
Ability to homogeneously cool
large at baseplate power modules, and systems of modules,
thereby eliminating temperature
gradients thus improving live and
facilitating paralleling of many
power chips
■
No TIM-related pump-out and
d r y - o u t e e c t s
■
Very low di erential pressure drop
■
Compact, low weight, high degree
of design freedom enabling 3D
designs
■
Low cost: metal-to-plastic conver-
sion into simple plastic parts.
The key element of the concept is the
ShowerPower® turbolator that guides
the coolant along the module
baseplate in cells that are supplied
with coolant in parallel thereby
securing uniform module temperatures. Actually the term turbolator is
misleading: under normal ow
conditions the liquid ow in the ow
channels is laminar; typical Reynolds
numbers range around 500 and the
transition into turbulence occurs at
Reynolds numbers around 2400.
Temperature gradient in standard cooler.
No gradient as in ShowerPower®
DKSP.PB.301.A3.024
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