Thermal Management: A growing concern
The demand for compact, multi-functional, high performance electronics has led to a dramatic increase in the power density of devices. In particular, the thermal dissipation per area of chip and per volume of system enclosure has increased dramatically in the last decade. To make matters worse, system-level requirements for small devices often include low skin temperatures and minimal or no vent openings, as well as restrictions to throttling (that is, turning down the clock frequency to reduce thermal dissipation) since that can adversely affect performance. At the Integrated Circuit (IC) level, the continued reduction of lithographic scales means that size scales of 45-30 nm are now common. But each reduction in these scales is also associated with exponentially higher leakage power, making thermal dissipation that much more difficult. Finally, operating temperatures must be kept low to assure good product reliability. The combination of these factors can create a perfect storm, if not managed properly using thermal management techniques.
In general, most electronics fit into a particular sector that has associated cooling methods. For example, many cell phones have minimal to no vent openings, therefore conduction heat transfer is the primary method of heat dissipation to the exterior. On the other hand, in CPU’s, there is a larger system volume, vents and possible air flow, so that it is common to transport heat out of the device using convection heat transfer driven by multiple fans. In this case, heat spreaders and heat sinks help dissipate and transfer heat to the air, and in some cases heat pipes are used that utilize phase change (evaporation and condensation of a substance) to efficiently transport heat away from sources.
Important aspects of system-level thermal management include quantifying the thermal operating budget and accurately characterizing component-level thermal performance. This can be done through a combination of analyses and numerical simulations, as well as actual laboratory measurements. Finally, a system-level solution with adequate conduction and convection paths to dissipate and transport heat from component sources to the exterior environment must be put in place. Future blogs will discuss using simulations to determine feasibility and optimization, highlight the need for performing test measurements and describe the purpose of validation (comparison) between analysis and measurements.
One technique that we incorporate to achieve optimal system level thermal management is metrology characterization and refinement. The reason is that although our numerical models provide key insights and predictions, they are most effective when based on validated input parameters, and once the required model fidelity has been determined. In challenging thermal applications it can also be helpful to validate thermal models with experimental measurements, in order to reduce guard bands and thereby provide more thermal margin.
Over the past year, AltaSim has helped plan and execute thermal validation testing, including protocols and procedures to check and improve client measurement systems. One of the best ways to do this is by performing Measurement System Analysis (MSA), also known as Measurement Capability Analysis (MCA), where the uncertainty of the metrology is determined and compared to the spec window, to assure that adequate measurement resolution is available. Once the MSA is complete, measurements of the component, board, air and case temperatures all help to validate the models. If thermal resistances of components are not known, then JEDEC standard measurement characterizations can be employed (theta_jc and theta_jb, see JESD51-12)
Bringing AltaSim’s considerable experience in computational analysis, modeling and experimental validation to bear on thermal management of electronics has been a rewarding process. We look forward to aiding more clients in this area. Please feel free to contact us or just stay tuned for future thermal blogs if you would like to find out more.