Chip Heat Research Articles

SIMULTANEOUS HEAT and MASS TRANSFER DURING the DEEP FAT FRYING of TORTILLA CHIPS

The heating and water loss of a single tortilla chip during deep fat frying was investigated experimentally and the data were analyzed by writing two heat and mass transfer balances. the equations were solved using explicit finite difference technique. Oil uptake as a function of frying time was described by a first order exponential equation. the empirical and theoretical heat and mass transfer agreed well.The effect of oil temperature on the moisture loss and oil uptake as a function of frying time was analyzed. Moisture loss rate increased as temperature increased. the effects of temperature on oil uptake were not significant during the first 15 s of frying, however, the final oil content was higher for the tortilla chip fried at 190C than at 150C for 60 s.

Behaviour of polarized ammonia in an intense electron beam

Polarized target experiments with intense particle beams suffer from the depolarization effects due to radiation damage and beam heating. The local depolarization of the target material 14NH 3 at the electron beam spot has been investigated by hitting it with 1.2 GeV electrons. This beam has been delivered from the electron stretcher accelerator ELSA of the Bonn University. The polarized target consists of a 4 T superconducting magnet with a Helmholtz configuration and a 4He evaporation cryostat which operates at a temperature around 1 K. The heating of the target chips by the electron beam has been measured up to an intensity of 70 nA using a specific set-up of the nuclear magnetic resonance apparatus for the polarization measurements.

Behavior of delaminated plastic IC packages subjected to encapsulation cooling, moisture absorption, and wave soldering

Plastic IC packaging subjected to moisture is vulnerable to delamination and cracking during the solder reflow process. Modeling the response of the delaminated plastic package is an essential step to fundamentally understand failure mechanisms and mechanics involved in the cooling, moisture absorption, and solder reflow process. A nonlinear finite element model was developed for predicting the deformation, stress, and fracture behavior of delaminated plastic packages induced by mechanical and hygro-thermal loads. The model consists of a sequentially coupled hygro-thermo-mechanical analysis considering moisture absorption, evaporation and interface contact and fracture analysis. A Lagrange Multiplier method was utilized to model the delamination interface condition. A general contact model was adopted which can handle complex contact conditions, such as arbitrary slippage and discontinuous curvature. A thermal contact was utilized to model the contact along delamination surfaces. Mixed mode fracture modes were elaborated. The model was verified by comparing existing analytical results with the predictions in the case of pulsed heating of the IC chip. Packaging responses and failure mechanisms due to encapsulation cooling, moisture absorption and evaporation, wave soldering, and interfacial moisture pressure loading are investigated, with consideration of temperature-dependent material properties change around the glass transition temperature for both die attach and molding compound. Packaging deformation and stress, crack tip driving force, doming of the delamination, and delamination growth stability as a function of time are discussed. >

Applications of advanced composites for satellite packaging for improved electronic component thermal management

Improved thermal management (TM) of electronics using advanced materials provides the potential to improve spacecraft electronics reliability with a resultant increase in the functional life of the spacecraft and cost savings to the user. Electronic packaging in this study includes the total heat transfer path in the spacecraft from the chip heat source to the heat rejection system, since it must be an integrated system. The cost effectiveness of all spacecraft material is increased when it is designed to fulfil multiple satellite functions including carrying structural loads, providing environmental protection for internal components, conducting electric current to minimize electrical charge buildup, providing electromagnetic shielding, as well as TM. The development of lighter weight multi-functional TM materials must flow from the satellite functional requirements down to the material design level, if possible. The composite materials must be designed to satisfy the maximum number of requirements. One essential property for satellite electronic TM applications is high specific thermal conductivity. The composite materials being considered consist of a combination of fibers, whiskers, and/or particles in a matrix. The two classes of composites that will be the primary focus of this paper are organic (or resin) matrix composites and metal matrix composites. This paper will address satellite systems/components that would significantly benefit from improved thermal management. It will identify candidate advanced materials, and present component design alternatives associated with the new materials and their potential performance improvement. It will summarize some of the key composite material property information associated with the materials used in the candidate applications and conclude with an assessment of the impact of the TM materials on the performance of a candidate component.

System cooling design for the water-cooled IBM Enterprise System/9000 processors

The high operating speed and corresponding high chip heat fluxes in the IBM Enterprise System/9000™ water-cooled mainframe processors are made possible by improvements in component- and system-level cooling. The heart of the closed-loop water-cooling system is a coolant distribution frame (CDF) common to all water-cooled processors. The CDF provides a controlled water temperature of 21.7°C to the central electronic complex (CEC) at water flow rates up to 245 liters per minute (lpm) and rejects heat loads of up to 63 kW for the largest processor. The water flow provides cooling to multichip thermal conduction modules (TCMs), to power supplies, and to air-to-water heat exchangers that provide preconditioned air to channel and memory cards. As many as 121 chips are mounted on a TCM glass-ceramic substrate, with chip powers reaching 27 W or a heat flux of 64 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A separate cold plate was developed to cool these modules. The power supplies with high heat densities are primarily cooled by water which flows through a unique separable cold plate designed for ease of serviceability of the power supply. Although water cooling is utilized for components with high heat fluxes, air cooling is employed for elements of the system with lower power densities. For cards cooled by forced air, careful trade-off studies among acoustical power, chip reliability, and high availability were required. The acoustic noise emissions of all the fans and blowers were determined, and a system model was constructed to measure the noise radiated from each frame in the system. The data were used to design top covers and other components to ensure that the system could meet its thermal/acoustical requirements. A closed-loop frame in which all the heat was rejected to water was developed to meet these requirements.

Electronic packaging in the 1990s-a perspective from America

The advanced packaging technologies that can be expected in the 1990s in high-performance systems are discussed in terms of chip connection, power distribution, heat removal, and thick- and thin-film wiring and package interconnections. The following topics are discussed in detail: (1) chip-level connection providing the required connections between the chip and the package; (2) power distribution to the chip and heat removal from the chip; (3) first-level packages providing all the necessary wiring, interconnections, and power distribution; (4) first-to-second level interconnections; and (5) second-level packages providing all the necessary wiring, connections, power distribution, and power supply connection. >

Fine structure of heat flow path in semiconductor devices: A measurement and identification method

A new method has been developed in order to identify the thermal environment of a semiconductor device chip. The identification algorithm operates on the thermal transient response of the device recorded during a one-shot pulse measurement. A deconvolution operation performed in the logarithmic time domain gives the “time-constant spectrum” of the chip-case-ambient thermal structure. A further transformation leads to the “structure-function” that is the cross-sectional area of the heat conducting materials vs thermal resistance (related to the heat source). The structure function has a good and quantitatively evaluable correspondence to the physical chip environment and heat conducting structure. Separating the different regions of the heat-flow path (corresponding to the chip, bond, header, case) as well as the detection of eventual heat-transport irregularities (mounting errors) is possible.

Semiconductor-laser thermal time constant

Thermal time constants of semiconductor lasers (‘‘test lasers’’) are measured by transient heating of test laser chips by use of another laser (‘‘pump laser’’). Pump laser emission impinging on the test laser p contact generates local heating. Thus, current-independent thermal responses are studied. Thermal time constants of 5.6 and 7.2 μs are measured and tend to confirm heat diffusion as the mechanism governing transient laser thermal behavior for times in the several microsecond range.

Impinging water jet cooling of VLSI circuits

This communication describes a new method of cooling of planar Very Large Scale Integrated (VLSI) circuits which allows one to obtain chip heat fluxes in excess of 500 W/cm 2 with acceptable temperature rises. It is shown that by scaling impinging fluid jet heat transfer technology to small geometrical dimensions, and by using water as the coolant, a high-performance cooling system can be designed. The convective heat transfer coefficients obtained in this method are significantly greater than that obtained in the convectional liquid cooling technology used for microelectronic devices, including the immersion cooling. The method lends itself to control of non-uniformities in the temperature field which could result from uneven heat dissipations in the integrated circuit elements. Experimental verification of predictions of the present analysis is planned.

Growth and characterization of Al-substituted iron garnets for submicron diameter bubble films

Al-substituted rare-earth iron garnet films have been grown that support submicron diameter bubbles. In developing small diameter bubble films, reduction of the saturation induction of a film, 4πMS, is very important because power consumption in drive coils and chip heating increase drastically with higher magnetization. Aluminum ions have been found to be one of the most suitable substitution ions for this purpose. Moreover, owing to the small ionic radius of Al ions, it is easy to meet the lattice matching requirement between films and GGG substrates without lattice adjusting ions such as lutetium. Submicron diameter bubble films are easily grown by the conventional LPE technique in the garnet system (YSmGd) 3 (FeAl) 5 O 12. They show good bubble properties, well suited to practical use.