A manufacturer of industrial appliances had a new power conditioning
and control system with very limited heatsink space available. The new
system had three high power IGBT’s in close proximity with a small
thermal window due to a 50°C max ambient temperature condition. To
compound the complexity of the project, there was a transient condition
to the system that would double the power for 1 minute every 10
minutes. Aavid, Thermal division of Boyd Corporation, had assisted
many other projects with similar form factors although not with this level
of power.
The cabinet that housed the heatsink had two fans for forced convection
but the airflow was shared with another heatsink to cool an SCR.
Although the heatsinks were fully ducted to force all of the available air
through them, the top of the system was obstructed by baffling the
restricted 65% of the airflow. The new heatsink design would need to
mind the difficult balance of airflow vs pressure drop through the entire
cabinet.
Similar applications in the past had been addressed by Aavid with
extruded solutions but with this high power the fin density of an
extrusion was not going to cut it. A bonded fin approach with higher fin
density was adopted to increase the surface area for heat transfer. The
next performance enhancement was to spread the power throughout as
much of the base as possible to lower the temperature of the localized
hot spots. Using multiple heat pipes under each IGBT, the effective
footprint of each device was increased. This made it easier for heat to
get into the fins that were not directly over the IGBT’s.
The heat pipes embedded in the base helped to meet the thermal
requirements for the 9 minute steady state but the performance was
still lacking for the double power 1 minutes transient state. To give the
heatsink a performance bump, heat pipes were run from the top of the
base and then in through the middle of the fins. By transporting heat to
the middle of the fins, the fin tips furthest from the base became more
effective.
Following extensive thermal CFD design work, prototypes were built and
tested with passing results. This design is now in successful mass
production.
The end result was a very efficient heatsink that took up no more
volume than a typical extruded or plain bonded fin heatsink.
