Q: What are the best methods to optimize thermal management in electronic devices?
By Chris Ammann, Global Technical Marketing Engineer for Power, Avnet
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 allowed?
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 power planes.
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.
Demand for devices that are smaller, more portable, and powerful will continue to compound the thermal management challenges designers face. Trying to shoehorn in thermal solutions, late in the design cycle, adds unnecessary complexity. Instead, make sure thermal management is a line item in the design spec and give the attention it deserves up front.
By 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.
Thanks to their characteristic resistance curve, PTC thermistors are ideal for thermal management. They not only help control temperature, but improve efficiency, reliability, and life span of the electronic devices in which they are used.
By Ian Wilson, Manager Mechanical Engineering; Microsemi Corporation
Minimizing total assembly volume and keeping electronic devices cool can be a challenge. As a discrete device and system solutions provider for aerospace and defense, communications, data center and industrial markets, Microsemi has honed its expertise in keeping semiconductor and FPGA devices cool. While they seem simple, these straightforward philosophies can greatly improve system reliability.
First, understand the circuit performance and establish what components produce high electrical losses. Microsemi, and other 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 mechanical structure.
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 temperatures.