Experiments and Modeling of the Hydraulic Resistance of In-Line Square Pin Fin Heat Sinks With Top By-Pass Flow

Extensive experiments were performed aimed at obtaining physical insight into the behavior of in-line pin fin heat sinks with pins of square cross-section. Detailed pressure measurements were made inside an array of square pins in order to isolate the inlet, developing, fully developed, and exit static pressure distributions as a function of row number. With this as background data, overall pressure drop was measured for a self-consistent set of aluminum heat sinks in side inlet side exit flow, with top clearance only. Pin heights of 12.5 mm, 17.5 mm, and 22.5 mm, pin pitch of 3.4 mm to 6.33 mm, and pin thickness of 1.5 mm, 2 mm and 2.5mm were evaluated. Base dimensions were kept fixed at 25 × 25 mm. In total, 20 aluminum heat sinks were evaluated. A “two-branch by-pass model” was developed, by allowing inviscid acceleration of the flow in the bypass section, and using pressure loss coefficients obtained under no bypass conditions in the heat sink section. The experimental data compared well to the proposed hydraulic models. Measurements in the array of pins showed that full development of the flow occurs after nine rows, thus indicating that none of the heat sinks tested could be characterized as fully-developed.

Raised Floor Computer Data Center: Effect on Rack Inlet Temperatures When Adjacent Racks Are Removed

This paper focuses on the effect on inlet rack air temperatures when adjacent racks are removed. Only the above floor (raised floor) flow and temperature distributions were analyzed for various air flowrates exhausting from the perforated tiles and the rack. A Computational Fluid Dynamic (CFD) model was generated for the room with electronic equipment installed on a raised floor with particular focus on the effects on rack inlet temperatures of these high powered racks. The baseline case was with forty racks of data processing (DP) equipment arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. To see the effect of missing racks adjacent to high powered racks various configurations were analyzed. The numerical modeling was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.

Flip Chip Thermal Test Vehicle Design: Requirements, Evaluations, and Validations

This paper reviews the design of a flip chip thermal test vehicle. Design requirements for different applications such as thermal characterization, assembly process optimization, and product burn-in simulation are outlined. The design processes of different thermal test chip structures including the temperature sensor and passive heaters are described in detail. In addition, the design of fireball heater, a novel test chip structure used for evaluating the effectiveness of heat spreading of advanced thermal solutions, is also illustrated. The design considerations and processes of the package substrate and printed circuit board with special emphasis on the physical routing of the thermal test chip structures are described. These design processes are supported with thermal data from various finite-element analyses (FEA) carried out to evaluate the capability and limitations of thermal test vehicle design. Design optimization as the outcome of these analyses is also elaborated. Lastly, the validation and calibration procedures of the thermal test vehicle are presented in this paper.

Thermal Performance Measurement for Confined Heat Sinks by Using a Modified Transient Liquid Crystal Technique

A series of experimental investigations with a new modified transient liquid crystal method on the studies related to the fluid flow and heat transfer characteristics in a channel installed with a heat sink have been successfully performed. The parametric studies on the local and average effective heat transfer characteristics for confined heat sinks have been explored. The influencing parameters and conditions include air preheating temperature at channel inlet, flow velocity and heat sink types. Besides, a concept of the amount of enhanced heat transfer (AEHT) is introduced and defined as the ratio of j/f. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink. The j/f ratios are 0.0603 and 0.0124 for fully-confined and unconfined heat sinks, respectively.

Deformation and Damage in Solder During Fast Cyclic Loading

Experimental and numerical studies on fast cyclic loading of eutectic tin-lead solder and relevant micromechanical issues are presented. High-frequency twin-lap shear tests on solder joints show cracking inside the solder but often connecting the intruded tips of the intermetallic. Finite element modeling was carried out to study the effect of intermetallic morphology. Without the influence of local phase coarsening, the intrusion of intermetallic into the solder alloy is seen to trigger strain localization which promotes failure. The effect of local phase coarsening was also studied numerically, taking into account the individual phase arrangement. A coarser phase structure always shows a faster accumulation of local plastic strain, leading to early failure. Such results, in agreement with typical thermomechanical fatigue features, cannot be obtained from the traditional argument of strength vs. microstructural size. Modeling of the entire lap-shear specimen was also conducted for the purpose of quantifying the deformation behavior. The exact geometry of solder is found to play a dominant role in affecting the shear response.

Thermodynamic Efficiency of Porous Glass Electroosmotic Pumps

This paper presents an analytical and experimental study of electroosmotic (EO) pumps designed to be integrated with two-phase microchannel heat exchangers with load capacities of order 100 W and greater. We have fabricated sintered glass EO pumps that provide maximum flow rates and pressure capacities 33 ml/min and 1.3 atm, respectively, at 100 V applied potentials. We have developed an analytical model to solve for electroosmotic flow rate, total pump current, and thermodynamic efficiency as a function of pump pressure load for these porous-structure EO pumps. The model uses a symmetric electrolyte approximation valid for the high zeta potential regime and numerically solves the Poisson-Boltzmann equation for charge distribution in the idealized pore geometry. The model also incorporates an approximate ionic-strength-dependent zeta potential formulation. The effects of pressure and flow rate on thermodynamic efficiency are also analyzed theoretically and compared to our measurements.

A Numerical Analysis on the System Impedance in a Fan Cooling System

To seek the fan operating point on a cooling system with fans, it is very important to determine the system impedance curve and it has been usually examined with the fan tester based on ASHRAE standard and AMCA standard. This leads to a large investment in time and cost, because it could not be executed until the system is made actually. Therefore it is necessary to predict the system impedance curve through numerical analysis so that we could reduce the measurement time and effort. This paper presents how the system impedance curve (pressure drop curve) is computed by CFD in substitute for experiment. In reverse order to the experimental principle of the fan tester, pressure difference was adopted first as inlet and outlet boundary conditions of the system and then flow rate was calculated. After determining the system impedance curve, it was compared with experimental results. Also the computational domain of the system was investigated to minimize computational time.

Multiphysics Design and Analysis Simulations for Power Electronic Device Wirebonds

Multiscale multiphysics simulations were performed to analyze wirebonds for power electronic devices. Modern power-electronic devices can be subjected to extreme electrical and thermal conditions. Fully coupled electro-thermo-mechanical simulations were performed utilizing CFDRC’s CFD-ACE+ multiphysics simulation software and scripting capabilities. Use of such integrated multiscale multiphysics simulation and design tools in the design process can cut cost, shorten product development cycle time, and result in optimal designs. The parametrically designed multiscale multiphysics simulations performed allowed for a streamlined parametric analysis of the electrical, thermal, and mechanical effects on the wirebond geometry, bonding sites and power electronic device geometry. Multiscale analysis allowed for full device thermo-mechanical analysis as well as detailed analysis of wirebond structures. The multiscale simulations were parametrically scripted allowing for parametric simulations of the device and wirebond geometry as well as all other simulation variables. Analysis of heat dissipation from heat generated in the power-electronic device and through Joule heating were analyzed. The multiphysics analysis allowed for investigation of the location and magnitude of stress concentrations in the wirebond and device. These stress concentrations are not only investigated for the deformed wirebond itself, but additionally at the wirebond bonding sites and contacts. Changes in the wirebond geometry and bonding geometry, easily changed through the parametrically designed simulation scripts, allows for investigation of various wirebond geometries and operating conditions.

A Novel Electronics Cooling System Using Water Heat Pipes Under Freezing Conditions

A novel electronics cooling system that uses water heat pipes under an ambient temperature range from −30°C to 40°C has been developed. The system consists of several water heat pipes, air-cooled fins, and a metal block. The heat pipes are separated into two groups according to the thermal resistance of their fins. One set of heat pipes, which have fins with higher thermal resistance, operates under an ambient temperature range from −30°C to 40°C. The other set, which have lower resistance, operates from 0°C to 40°C. A prediction model based on the frozen-startup limitation of a single heat pipe was first devised and experimentally verified. Then, a prediction model for the whole-system was formulated according to the former model. The whole-system model was used to design a prototype cooling system, and it was confirmed that the prototype has a suitable cooling performance for an environmentally friendly electronics cooling system.

High-Density Through-Wafer Electrical Interconnects in Pyrex Substrate Integrated With Micromirror Array

A method for the construction of high density (2.4 mm−2) vertical leads through a pyrex substrate is presented. The pyrex substrate behaves as a TCE (Thermal Coefficient of Expansion) matched interposer that permits anodic bonding of silicon micromirrors on one side and flip-chip bumping of multiplexing electronic chips on its opposite side. Electrical leads consist of 250±25 μm-diameter holes formed by AJM machining and coated with evaporated Au yielding via resistances of 0.5–0.7 Ω. The via holes are sealed with a new spin-cast polyimide tenting process that enables the subsequent patterning of multiple levels of metal using conventional lithographic techniques.