Shlomo Novotny

New attempt of forced-air cooling for high heat-flux applications

The electronic industry requires increased forced-air cooling limits in order to adequately cool high-end server CPU and also the power electronic IGBT. Improving the air-cooled heat sink thermal performance is one of the critical areas for increasing the overall air-cooling limit. One of the challenging aspects for improving the heat sink performance is utilizing relatively large air-cooled fin surface areas when heat is being transferred from a relatively small heat source (CPU) with high heat flux. Similar to heat pipe technology, the pulsating (or oscillating) heat pipe utilizes two-phase flow to transfer heat from the CPU. However, unlike heat pipe technology, the pulsating heat pipe does not contain wicking structure. This study shows that the pulsating heat pipe (Heatlane technology) enables the high-end server CPU power to be efficiently spread to the heat sink fin structure. Measured results show that the Heatlane heat sink will yield sink-to-air thermal impedances that are less than the measured impedance for conventional (all-metal) heat sink design.

Simulation of PWB warpage during fabrication and due to reflow

As the electronic packaging industry moves towards the manufacturing of high density, multi layer PWBs, a key challenge, is the warpage of a PWB during fabrication, solder masking and reflow soldering process. Residual stresses caused by the coefficient of thermal expansion (CTE) mismatch between different board materials combined with thermo mechanical effects introduce the warpage. The excessive warpage not only adversely creates various manufacturing difficulties but also significantly causes serious reliability problems during normal operation. This paper investigates the warpage of large multi layered, high-density boards, and the effect of the layup on the warpage. Finite element analysis was used to model the thermally induced warpage of a 24 layer 492 mm/spl times/208 mm/spl times/4.88 mm PWB, due to reflow soldering. Wide ranges of, peak temperatures and cooling rates during reflow soldering were used to study the warpage of boards of varying thickness. The whole range of material properties of copper and FR4, which have been published, are used in this analysis. The warpage results, which were obtained at the end of the simulation, is presented. This analysis aid in identifying the impact of PWB layup on warpage and make recommendations to minimize warpage.

Rear Door Heat Exchanger Cooling Performance in Telecommunication Data Centers

The increase in the data center server heat density waves a scope for developing improved cooling technologies without raising the power consumption. It is commonly observed that 40% of the total data center energy is consumed by its cooling equipments. For higher server density cabinets, typical air cooling techniques leads to a substantial increase in the power consumption. Rear door heat exchanger, an open looped cooling technique is one of the solutions for such scenarios. In this paper, emphasis is laid on the analytical determination of the optimum heat load after calculating the effectiveness of heat exchanger at given operating conditions of the data center and heat exchanger. Later, thermal analysis is performed and the working of heat exchanger is compared for different data center heat loads. Based on the results, a ‘rule of thumb’ is verified that rear door heat exchanger could be 100% efficient in cooling the cabinets of heat loads up to 27kW. Thus, for rack heat loads less than 27KW, CRAC units can be non-operational resulting in energy savings. Furthermore, effect of RDHx in different configuration is studied and compared.Copyright

Heatlane Technology for High Heat Flux Chip Cooling

This paper proposes a new solution for high heat flux chip cooling. The authors attempted to apply Heatlane technology for a heat sink of high-end server chip cooling. This unique technology, which is also called oscillating or pulsating heat pipe, showed very high thermal performance, and the experimental results were compared with conventional copper base heat sink in this paper. The experimental and analysis results showed that the Heatlane technology transferred heat very effectively and highly improved the fin efficiency. And the Heatlane heat sink also showed very small gravity effect and high reliability under vibrating conditions. Those experimental results were also shown in this paper. From this study, the authors has convinced that the Heatlane technology for a heat sink can be a strong candidate to solve a thermal issue of high heat flux chip cooling, especially for high-end server applications.Copyright

A Methodology for an Integrated (Electrical/Mechanical) Design of PWBA

This paper describes a general methodology an electrical circuit design data is mapped into an intermediate analyzable representation which supports the information requirement of several thermo-mechanical analyses including product optimization/idealization. This paper describes other issues encountered such as how to integrate product data that spans more than one tool, how to modify and add analysis data that is necessary during analysis, and how to use data stored in the analysis module from different programming environments. The advantage the process offers is also described by considering a PWBA design such as layout and layup in electrical design system.Copyright

A system design approach to liquid-cooled microprocessors

This paper describes a compact fluid-cooled computer system, comprised of micro-channel heat exchangers, a fan, and a small pump, to remove heat from a microprocessor. Computational fluid dynamic analysis was used to determine the optimal micro-channel fin array design. Normal flow heat exchanger (NFHX) and parallel flow heat exchanger (PFHX) designs were evaluated. Due to packaging constraints, a micro-channel radiator was used. Integral to the radiator design was the selection of a reliable 30 SCFM blower. Fluid flow and pressure requirements were on the order of 0.5 LPM and 4 PSID respectively. The cooling system developed provided a heatsink to air thermal resistance of 0.155/spl deg/C/W. An understanding was developed of the effect of airflow, liquid-flow, and heatload on the system performance leading to work which would achieve a heatsink to air thermal resistance of 0.100/spl deg/C/W and lower.

The Impact of Board Layout and Layup on PWB Warpage During Fabrication and Due to Reflow Solder Process: A Review of Literature

PWBA warpage is further compounded by the high densification of the PWBA, where heat dissipation occurs over a very small area during in-service operation. Automated component placement or insertion is difficult and sometimes impossible to achieve on a warped board. PWB assembly warpage will results in many problems including non co-planarity, chip/component surface crack, delamination, poor connectivity, floating, creep, failure and so on. Also PWBAs are sometimes subjected to mechanical loading as well as thermal loading during their lifetime, which will cause PWB deflection and stress/strain in the PWB assemblies. These mechanical loading will increase stress/strain level inside PWB and may have an effect on interconnect, PWB, or package reliability. In order to evaluate the reliability of PWBA, an optimal modeling is necessary. This paper reviews the literature with an understanding of layout and layup impact on PWB warpage for minimizing warpage of PWB architecture. This compilation of literature would help to enhance the quality and reliability of products by minimizing failures of device and component from PWB excessive warpage and to reduce production cost because of minimizing repair needs on the production line.Copyright