John Lohan

A benchmark study of computational fluid dynamics predictive accuracy for component-printed circuit board heat transfer

The application of computational fluid dynamics (CFD) analysis for the thermal design of electronic systems has the potential to enable accurate solutions to be generated and quickly assessed. With the use of validated numerical models, numerical analysis can also be used to provide useful insights into heat transfer processes which could otherwise be difficult to characterize experimentally. However, the capabilities of the CFD tool need to be carefully evaluated so as to provide a degree of confidence in prediction accuracy, thereby minimizing the need to qualify thermal designs. Such an evaluation is presented in this paper, which represents the culmination of a benchmark study by Rodgers et al. [1999]. This overall study assesses the predictive accuracy of a commercial CFD code for both natural and forced convection heat transfer of single- and multicomponent printed circuit boards (PCBs). Benchmark criteria were based on both component junction temperature and component-PCB surface temperature profiles. In the context of the overall study, this paper brings these analyses together to provide a more comprehensive assessment of CFD predictive accuracy for component junction temperature. Additionally the validated numerical models are used to further investigate the sensitivity of component heat transfer to convective environment, both natural and forced, component position relative to the PCBs leading edge, impact of upstream aerodynamic disturbance, and the representation of PCB FR4 thermal conductivity. The significance of the listed variables is quantified by analyzing predicted component energy balances. Qualitative descriptions of the fluid flow fields obtained using a novel paint film evaporation technique are also provided in this study. Both analyses yield new insights of the heat transfer processes involved and sources of numerical error.

Experimental and numerical investigation into the influence of printed circuit board construction on component operating temperature in natural convection

The steady state thermal performance of an isolated SO-8 package is experimentally characterized on five thermal test printed circuit boards (PCBs) and the results compared against corresponding numerical predictions. The study includes the low and high conductivity JEDEC standard, FR4 test PCBs and typical application boards. With each PCB displaying a different internal structure and effective thermal conductivity, this study highlights the sensitivity of component operating temperature to the PCB, provides benchmark data for validating PCB numerical modeling methodologies, and helps one assess the applicability of standard junction-to-ambient thermal resistance (/spl theta//sub JA/) data for design purposes on nonstandard PCBs. Measurements of junction temperature and component-PCB surface temperature distributions were used to identify the most appropriate modeling methodology for both the component and the PCB. Based on these results, a new PCB modeling methodology is proposed that conserves the need for modeling detail without compromising prediction accuracy.

Experimental validation of numerical heat transfer predictions for singleand multi-component printed circuit boards in natural convection environments

Increasing power densities and changing component design have increased the need for accurate prediction of temperature effects that may affect system performance or reliability. To highlight these aspects early in the product development cycle, designers resort to using computational fluid dynamics (CFD) based numerical predictive tools. However, users acknowledge that these predictions require experimental verification which is now readily available during the early design phase. Therefore, a need exists to establish well-defined benchmark test cases to help establish confidence in both modelling methodology and numerical tools. This paper presents such information for three package types (SO16, TSOP48, and PQFP208) which are evaluated on single and multi-component PCBs. Benchmark criteria are based on the prediction of steady state component junction temperature and associated component-PCB surface temperature gradients, which are both compared with experimental measurements. While the detailed numerical models typically predicted junction temperature to within 4/spl deg/C, discrepancies as great as 9/spl deg/C were also recorded. The sensitivity of prediction accuracy was assessed against discretization level and both the thermal conductivity and geometry of package materials. Hence it was considered important that all experimental and numerical modelling details be provided for reference.

Using experimental analysis to evaluate the influence of printed circuit board construction on the thermal performance of four package types in both natural and forced convection

As the functionality of electronic systems increase, so does the complexity of printed circuit board (PCB) design, with greater component packing densities requiring additional internal signal, power and ground layers to facilitate interconnection. The extra copper content introduced increases PCB thermal conductivity and heat spreading capability, which can strongly influence component operating temperature. Therefore, this experimental study sought to quantify the impact of PCB construction on component operating temperature and relate this sensitivity to the package design, PCB effective conductivity and convective environment. This was achieved by measuring the steady state thermal performance of four package types (PSO20: heat slug up, PSO20: heat slug down, LFBGA80 and SBGA352) on up to six different, single-component thermal test PCBs in the standard natural and forced convection environments. Test velocities ranged from 0.5 m/s to 5.0 m/s and all test components contained a thermal test die. Measurements of junction temperature and component-PCB surface temperature distributions are both presented for power dissipation levels within the range 0.5 to 6.0 Watts. The study includes the low and high conductivity JEDEC standard, FR4-based test PCBs and typical application boards. As each PCB had a different internal structure and effective thermal conductivity, this study highlights the sensitivity of component operating temperature to the PCB, provides benchmark data for validating numerical models, and helps one assess the applicability of standard junction-to-air thermal resistance (/spl theta//sub JA/ and /spl theta//sub JMA/), as well as both junction-to-board (/spl Psi//sub JB/) and junction-to-top (/spl Psi//sub JT/) thermal characterisation parameters for design purposes on nonstandard PCBs.

Visualization of forced air flows over a populated printed circuit board and their impact on convective heat transfer

A detailed characterization of the airflow patterns around Printed Circuit Board (PCB)-mounted electronic components has been undertaken using three different, but complementary flow visualization techniques. Uniform airflows of 2 m/s, 4 m/s and 5.5 m/s were directed over Plastic Quad Flat Pack (PQFP) components mounted on a double Euro-Card PCB. The complexity of PCB topology and resulting flow phenomena, was increased in three stages from just one, centrally placed component, to seven components and finally to the most complex case consisting of a symmetrical in-line array of fifteen components. Traditional smoke- and paint-flow visualization techniques, as well as a novel paint-film evaporation technique, were applied to help identify the sensitivity of the flow phenomena and its impact on convective heat transfer, to both air velocity and PCB topology. Combined, these techniques not only helped characteristic features of these flows such as separation/reattachment points, re-circulation zones and horseshoe vortices to be identified, but also showed in a qualitative way, using the evaporation technique, how these flow phenomena impact on PCB/component surface heat transfer. Linking the flow phenomena with the surface heat transfer in this way also provides, in the early design phase, a means of identifying both an appropriate numerical flow modeling strategy for the flow phenomena present, and the locations of high aerodynamic disturbance on the PCB, where temperature prediction accuracy must be viewed with caution.

Effect of both PCB thermal conductivity and nature of forced convection environment on component operating temperature: Experimental measurement and numerical prediction

The steady state thermal performance of two package types is experimentally characterised on up to four different thermal test Printed Circuit Boards (PCBs) operating within two different forced convection environments. Both standard and non-standard test PCBs and test environments were used so that component thermal performance under standard test conditions could be compared with that measured under non-standard conditions that mimics those found in service. The design of the test boards spanned from the low and high conductivity JEDEC standard, FR4 test PCBs to typical eight-layer application boards, whereas forced convection airflows were generated by both a windtunnel, representing the standard test environment, and upstream axial fans that are typically used in applications. All test components contained a built-in thermal test chip, mounted within an SO-8 and SBGA352 package types, and junction temperatures were measured for power dissipation levels of 0.5 and 6 Watts respectively. Windtunnel generated air velocities ranged from 0.5 m/s to 5 m/s, whereas flow rates corresponding to mean velocities of 0.5 m/s to 2 m/s were delivered by a set of four upstream axial fans. While junction-re-ambient thermal resistance (*ja) data for the SO-8 package showed a sensitivity of up to 48% to PCB construction, differences of up to 11% were also recorded between both test environments. The experimental data not only helps identify the sensitivity of component thermal performance to both PCB construction and operating environment, enables one assess the applicability of standard thermal resistance data for design purposes on non-standard PCBs in forced convection fan flows, but also provides benchmark data to assess numerical prediction accuracy in these non-standard but application-type environments.

Comparison of numerical predictions and experimental measurements for the transient thermal behavior of a board-mounted electronic component

Numerical predictive accuracy is investigated for transient component heat transfer using a computational fluid dynamics (CFD) code dedicated to the thermal analysis of electronic equipment. The test cases are based on a single printed circuit board (PCB)-mounted, 160-lead PQFP component, analyzed in still-air, and both 1 and 2.25 m/s forced airflows. Three types of transient operating conditions are considered, namely (i) component dynamic power dissipation in fixed ambient conditions, (ii) passive component operation in dynamic ambient conditions, and (iii) combined component dynamic power dissipation in varying ambient conditions. Benchmark criteria are based on component junction temperature and component-PCB surface temperature, measured using thermal test dies and infrared thermography respectively. Using both nominal component/PCB geometry dimensions and material properties, component junction temperature is found to be accurately predicted for component dynamic power dissipation, in both fixed and varying ambient air temperature conditions.

Climate Variables That Influence the Thermal Performance of Horizontal Collector Ground Source Heat Pumps

The performance characteristics of new heat pumps are usually evaluated under standard test conditions in certified test laboratories prior to their market release. While this data allows potential customers an opportunity to compare different heat pumps under the same conditions it is difficult to assess how variations in operating conditions, particularly around horizontally oriented ground collectors impact on heat pump Coefficient Of Performance (COP). Indeed, harsh winter conditions of continental climates dictate that horizontal collectors are buried sufficiently deep enough to operate in a thermally stable environment, independent of the weather, but this is not as critical in milder maritime climates and shallower collectors that may be influenced by climate are used. This review paper therefore seeks to identify the key climate variables that have been shown to influence the efficiency of horizontal collector heat pump systems. The literature highlights the significant impact of soil moisture content on COP, but the extended relationship between climate, moisture content and COP has not been established. Historical climate data from both a continental and maritime climate is presented and key aspects of their respective weather patterns are compared to assess their capacity to influence soil condition and COP. A series of empirical models linking changes in soil moisture content to fluctuations in soil thermal conductivity, diffusivity and resistance are also presented so that the impact of climate on soil thermal energy content and heat transfer characteristics might be assessed. However, since no one study has experimentally determined the complex relationship between climate, soil heat transfer characteristics and heat pump performance, this paper concludes with an overview of an experimental test facility that allows this relationship to be established for horizontal collector heat pumps in maritime climates.© 2006 ASME

Development of a prototype knowledge discovery portal for energy informatics

This chapter describes the development of a prototype knowledge discovery portal (KDP) for energy informatics. The research domain is Ireland which is increasingly challenged to achieve energy efficiency targets and to implement renewable energy systems (RES). The reason for undertaking this research is to provide a mechanism to disseminate information on energy efficiency and renewable energy technologies to a number of sectors: community, educational, industrial and research. The prototype KDP was developed using design-science methodology. This chapter integrates information both in the horizontal and vertical axes. In the horizontal plane, it provides information to community users, educational bodies and industrial companies. In the vertical plane, it allows deeper access depending on the requirements of the user: from technological overviews to detailed data from the energy system (solar collectors, heat pump and wind turbine). Future work will involve further development of the portal and extending the KDP for energy to other technologies and sectors.

Development and Assessment of Defrosting Strategies for Transport Refrigeration Systems

When commercial transport refrigeration systems operate at temperatures of 0°C frost accumulates on the surface of the evaporator coil. Occasionally, defrost cycles are required to remove frost from the coil to sustain effective operation of the refrigeration system. This paper details results of an experimental investigation undertaken to characterise the performance of an existing defrost strategy that was in turn modified to improve its performance and effectiveness. Results are reported for two significant modifications, the first of which utilises new criteria for terminating the defrost cycle and the second that employs higher compressor speeds during defrost. Results show that the number of defrosts required was reduced by 20 to 40% yielding more stable temperature control and reduced fuel consumption during defrost.Copyright