Features - Bodo's Power

GUEST EDITORIAL
Materials Development – New
Competencies Required for the
Development of Power Modules
By Dr.-Ing. Frank Osterwald, Senior Director Research & Development, Danfoss Silicon Power
The development
of power
modules and
their components
is a
multi-disciplinary
task.
Power module
developers
have to be
trained in thermal,mechanical,
electrical
and materials engineering. Furthermore,
they must understand requirements coming
from applications, in order to proactively
drive power module development in the right
direction. Typically, “right direction” means to
achieve a targeted quality, reliability and
cost/performance ratio.
The first step in power module development
is to find out what the application requires in
terms of power and in terms of mission profile.
After that, many other requirements
must be taken into account - all of them
influencing the outline, arrangement, and the
material of the ingredients and joints in a
power module in order to obtain the desired
properties.
To get to lower cost, one could try just leaving
out some costly components or parts.
However this is not possible in general – but
an approach like this might work if another
component or part is able to take over the
function of the missing component or part.
Usually, this leads to multifunctional components
or materials.
In the past, for example, for the double function
of good electrical conductivity and thermal
properties, an engineer would have chosen
a suitable material like copper. If more
functions were required, such as corrosion
resistance, a nickel-layer would be added to
ensure that copper surface properties are
properly modified, without significantly
changing good electrical and thermal properties.
Nowadays, there are many examples of
multifunctional materials in power modules,
and more are in development to adapt to
even more functions. Some current multifunction
examples are;
• frame material that fulfil many roles,
• silicone gel that is multi-talented,
• base plates designed to obtain certain
properties in conjunction with soldered
DBC’s, or substrates already including the
functionality of base plates,
• solder that fulfils with good electrical and
thermal properties, while being flexible
enough to withstand thermo-mechanical
stresses,
• mould compounds that protect the power
semiconductors against bad environments
(not just rains and storms) while being
easily processed and without increasing
CTE mismatch,
• AlSiC base plates tailored to perfectly
adapt to the CTE of the substrates that
are soldered to them, while keeping reasonable
thermal conductivity and solderability,
• pressure sinter materials with lowered sintering
temperatures achieved by applying
nano-technologies in the joining materials
leading to better manufacturability and
extended performance of the power modules.
From my point of view, the development of
power modules is currently undergoing a
shift towards more intense material development.
Whenever a discussion targets new
concepts or joining methods for power modules,
we ask the question: “How can this or
that property or behaviour of a certain material
be modified?”
We discuss modification of surface properties
using extra layers, or we look for a
change in the properties or behaviour of the
bulk material itself through adding or removing
ingredients (as little as a few “ppm”), or
to subject the bulk material to heat treatments
or other processes.
Whatever intention we might have as power
module developers will not be achieved without
close cooperation with our materials suppliers.
And since materials development
requires target specifications, our material
suppliers need to be involved in our projects
from the very beginning, as specialized
equipment manufacturers will have to be.
To be able to really achieve a better
cost/performance ratio, together we must
keep a close focus on cost. However, in this
case, the total cost of ownership is to be
considered, rather than just the materials
price per kilo by itself.
In this light it is highly appreciated that more
and more materials specialists decide to
become members of our ECPE family. In the
framework of ECPE research work, materials
suppliers together with other specialists
for engineered materials can help power
module developers hit their targets, not simply
to provide “green” materials. New doped
or alloyed wires, solder or sinter pastes,
adhesives, layer materials and deposition
techniques, as well as completely engineered
base plates, substrates and housing
materials will play a big role in the future, as
we progress to more cost efficient and more
reliable power modules. Thus, materials science
will be the enabler for energy efficiency.
Hopefully, this movement of power electronics
development towards materials science
will make our profession even more attractive
to young talents. We can offer many
challenges for physicists, chemists and
materials scientists, to augment mechanical
and electrical engineering in our research
and development departments. We envision
new multidisciplinary teams for joint development
projects and new breakthroughs that
will continue our record of progress in the
development of power modules.
siliconpower.danfoss.com
16 Bodo´s Power Systems ® August 2009 www.bodospower.com