Chris Ammann, Global Technical Marketing Engineer for
The key to optimal thermal management design is understanding that it is as much about how
you design as the technologies you employ. To
ensure component choices and board layout will
support maximum performance, thermal efficiency and relief
must be planned for, designed at the system level, and considered
throughout the design process.
Factors that may impact a device’s thermal requirements include:
• In what environments will the device operate?
• What is the expected system level power consumption?
• Does it need to be sealed from the elements?
• Is the physical form factor fixed?
• How about noise and mechanical reliability, would a fan be
The PCB itself represents one of the best opportunities for
dissipating heat. Design the stack up and select heavier copper
weights to help draw heat out of the components. Be sure to
layout high temp circuits as far away from each other as possible,
and follow design guidelines to maximize heat transfer. Whenever
possible, use copper fills and stitch layers with vias to ground and
For additional relief, heatsinks or fansinks may be installed on
devices such as FPGAs, transceivers, processors, or other devices
that operate at high temperatures. Heat pipes and system level
fans can also be used, but these solutions need to be planned for at
the project level to be most effective.
Sonja T. Brown, Sr. Product Marketing Manager, Piezo
and Protection Devices, EPCOS, a TDK Group Company
Electronic devices heat up most often because electrical currents running through
semiconductors and other components create
thermal losses, some of which can be in the form of
heat dissipation (which can be significant). Thermal management
can be assisted by using PTC thermistors, which provide increased
efficiency of the semiconductor and proper heat dissipation.
PTC thermistors make the most accurate limit temperature
sensors for sensitive electronic components. Due to the non-linear characteristics of PTC thermistors, their resistance is weak
at low or ambient temperatures. Conversely, their resistance
increases as temperature rises. If the current exceeds defined
temperature limits, the thermistor heats up and power dissipation
rises, increasing resistance, limiting the current, and reducing
temperatures. When the component has cooled, the thermistor
returns to its low resistance state.
PTC thermistors are normally mounted near the component
they are protecting to ensure proper thermal contact, resulting
in the fastest response time. They are typically coupled with a
fixed resistor in voltage division circuits to create a temperature-
dependent output voltage. When this is done, the voltage changes
according to the characteristics of the PTC sensor. This allows
the sensor to directly control components such as a switching
transistor or comparator that triggers corresponding functions to
help avoid overheating and associated damages. For example, as
temperature rises, a fan can be triggered or other components can
be switched off.
The exponential resistance change of PTC sensors allows for
the monitoring of multiple hot spots using a single, simple circuit
with sensors in series. PTCs may be connected serially, and ensure
reliable monitoring of individual hot spots as a result.
Ian Wilson, Manager Mechanical Engineering;
Minimizing total assembly volume and keeping electronic devices cool can be a challenge.
First, understand the circuit performance and
establish what components produce high electrical
losses. Discrete component providers, often provide devices in
numerous package styles. While it may be tempting to always
use the smallest envelope, using a different package may reduce a
designer’s operating temperature due to lower thermal resistances.
Similarly, leaded packages can often be mounted in such a
manner that power dissipation is directed into a housing or other
Grouping high-power devices together increases heat flux
density. Therefore, evenly distributing the power within an
assembly reduces thermal gradients and lowers peak surface
temperatures. If a significant percentage of the power loss is
concentrated in one or two devices, consider reducing the losses
by paralleling components. While the overall efficiency will not
change, the power lost in each device will be reduced.
Nevertheless, all is not lost when electrical operation requires
a component be mounted in a thermally sub-optimum location.
Electrical interconnections provide highly conductive paths for
thermal transfer. For example, in glass-copper laminate boards
using heavier copper weights, additional layers and wider traces
can improve performance by reducing the thermal and electrical
resistance. Similarly, when inductance matching or signal timing
is less critical, trace routing can be used to direct heat towards
mounting locations or other cold sources.
Simply put, a balance of thermal considerations and electrical
performance during design and development will reduce
electronic device temperatures. However, when all design tricks
just do not get temperatures low enough, remember Microsemi
is at the forefront of Silicon Carbide which operates at higher