Papers by Javier Goicochea
IMAPS other content, 2011
Journal of heat transfer, Apr 6, 2006
IMAPS symposia and conferences, 2012
Thermal underfills are crucial to support integration density scaling of future integrated circui... more Thermal underfills are crucial to support integration density scaling of future integrated circuit packages. Therefore, a sequential process using hierarchical selfassembly of micro-and nanoparticles is proposed to achieve percolating thermal underfills with enhanced particle contacts. The three main process steps hereby are assembly of filler particles by centrifugation, formation of nanoparticle necks by capillary bridging, and the backfilling of the porous structure with an unfilled capillary adhesive. Numerical simulations predicting trajectories and distributions of micron-sized particles dispensed into a rotating disk are presented. The trajectories exhibit a strong dependence on the particle size; thus in the case of polydisperse filler particles nonuniform particle beds may result. An efficient centrifugal disk design with spiral-like guiding structures is experimentally validated. Defect-free, percolating particle beds in confined space with fill fractions of 46 vol-% to 66 vol-%, i.e., close to the theoretical limit, are also presented. The self-assembly of nanoparticles, forming enhanced thermal contacts between the percolating filler particles, is discussed. Two consecutive evaporation patterns during the capillary bridging process were identified: 1) dendritic network growth and 2) collapse of capillary bridges. The concave neck topology could only be achieved at temperatures below the boiling point. An optimal evaporation temperature of 60°C with respect to in-plane uniformity and neck shape was identified. Existing thermal gradients normal to the cavity surface resulted in strongly asymmetric neck formation in the cavity. Hence, uniform heating in an oven is the preferred method to initiate evaporation. Two types of bimodal dielectric necks are demonstrated. Polystyrene acts as the adhesive between thermally conductive alumina particles to form mechanically stable dielectric necks after an annealing step at 140°C. Interstitial and core-shell necks are presented. Finally, a benchmark study was performed to compare the effective thermal conductivity of the percolating thermal underfill with and without necks with state-of-the-art capillary underfills. A close to fivefold improvement could be obtained for diamond filler particles with silver necks (3.8 W/m-K).
2010 14th International Heat Transfer Conference, Volume 3, 2010
ABSTRACT Two mechanisms that increase heat dissipation at solid-liquid interfaces are investigate... more ABSTRACT Two mechanisms that increase heat dissipation at solid-liquid interfaces are investigated from the atomistic point of view using nonequilibrium molecular dynamics (NEMD) simulation. The mechanisms include surface functionalization, where −OH terminated headgroups and self-assembled monolayers (SAMs) with different chain lengths are used to recondition and modify the hydrophilicity of silica surface, and vibrational matching between crystalline silica and liquid water, where three-dimensional quartz nanopillars are grown at the interface in the direction of the heat flux with different lengths to rectify the vibrational frequencies of quartz surface atoms. The heat dissipation is measured in terms of the interfacial thermal conductance at the solid-liquid interface, whereas the thermal conductance is obtained by imposing a one-dimensional heat flux across the simulation domain. The heat dissipation is enhanced by a factor of 2 to 3 for both fully hydroxylated and pillar modified surfaces. The SAMs enhance the overall thermal conductance between silica and water further (20% higher thermal conductance compared to the fully hydroxylated silica surface). Moreover, the modification of the vibrational states at the silica surface provides a tunable path to enhance the heat dissipation, which can also be easily applied to other fluids.
Springer eBooks, May 19, 2006
Understanding and predicting thermal transport at extremely short time and length scales is essen... more Understanding and predicting thermal transport at extremely short time and length scales is essential to further advance a variety of emerging technologies. The trend towards miniaturization of electronic devices has lead to device features in the sub-micron and nanometer range. In fact, transistors with gate lengths on the order of 65 nm are already in production, and silicon-on-insulator (SOI) transistors are predicted to reach a gate length of 45 nm by the year 2005 [1]. The thermal conductivity of silicon at these scales is smaller than that of bulk silicon due to the scattering of the energy carriers with the boundaries of the device [2, 3]. Heat dissipation becomes an important issue, since overheating can negatively affect the reliability of the transistor. In addition to applications in microelectronics, micro/nanostructures such as quantum wells, nanowires, nanotubes and superlattices (periodic arrays of thin films), are appearing in optoelectronic devices [4], semiconducting lasers [5] and thermoelectric applications [6]. The thermal properties of nanowires [7-9], superlattices [10-12] and nanotubes [13] have recently attracted attention because of their special characteristics [8, 9, 14-16]. Carbon nanotubes, for example, have the potential for very high thermal conductivity [13, 17], while the thermal properties of superlattices can be controlled by adjusting the thickness and composition of its components. Theoretical modeling can be an important tool to further the understanding of thermal transport. Different approaches are needed to study the thermal properties of devices whose components span length scales from the nanoscale to the macroscopic [18]. Phonons, which are quantized lattice vibrations [19, 20], are the predominant energy carriers in dielectrics and undoped semiconductors. Fourier diffusion yields erroneous predictions under the following two conditions: (a) when the mean free path of the energy carriers ( ) becomes comparable to or larger than the characteristic length scale of the device/system under consideration (L); and/or (b) when the time scale of the processes under consideration becomes comparable to or smaller than the relaxation time of the energy carriers [15, 21, 22]. Under these conditions, if the wave nature of the energy carriers can be neglected [23], the semi-classical Boltzmann transport equation (BTE) can be employed to solve for the distribution function of the energy carriers. Molecular dynamics (MD) involves solving the atomistic equations of motion, from which phonon and thermal properties can be obtained. Being an entirely classical method, molecular dynamics is strictly applicable to solids only at temperatures above Debye’s temperature (for silicon, D ~ 625K [19]), where the system behaves classically. Several corrections have been proposed in the literature to partly account for quantum effects in molecular dynamics simulations of thermal transport when these effects become relevant, such as when the temperature of the system is smaller than its Debye temperature, as reviewed in [24]. However, when the temperature and dimensions of the system are such that the characteristic
Engineering with Computers, 2003
Abstract Typically, the optimization of oil production systems is conducted as a non-systematic e... more Abstract Typically, the optimization of oil production systems is conducted as a non-systematic effort in the form of trial and error processes for determining the com-bination of variables that leads to an optimal behavior of the system under consideration. An optimal or near opti- ...
Revista Tecnica De La Facultad De Ingenieria Universidad Del Zulia, 2001
This paper establishes the conditions under which discharge and loss coefficients can be predicte... more This paper establishes the conditions under which discharge and loss coefficients can be predicted, and the conditions which permit the use abrupt expansion as a measurement of flow. The prediction is done by a computer simulation based on Patankar´s finite volume method, which resolves the continuity and quantity of movement equations for turbulent flow. The comparison of the results obtained with those available from other works, show that it is feasible to use abrupt expansion as a flow-meter and supports the effectiveness of the program utilized.
In this work, a methodology for the formulation of densely packed percolating thermal underfills ... more In this work, a methodology for the formulation of densely packed percolating thermal underfills is presented. The methodology involves centrifugal acceleration of particles, which are placed in chip cavities of 60 micrometer in height due to the action of the applied centrifugal force. Each cavity mimics the gap between a chip and a laminate or between dies in 3D packages.
Journal of Heat Transfer, Oct 1, 2010
A hierarchical model of heat transfer for the thermal analysis of electronic devices is presented... more A hierarchical model of heat transfer for the thermal analysis of electronic devices is presented. The integration of participating scales (from nanoscale to macroscales) is achieved by (i) estimating the input parameters and thermal properties to solve the Boltzmann transport equation (BTE) for phonons using molecular dynamics (MD), including phonon relaxation times, dispersion relations, group velocities, and specific heat, (ii) applying quantum corrections to the MD results to make them suitable for the solution of BTE, and (iii) numerically solving the BTE in space and time subject to different boundary and initial conditions. We apply our hierarchical model to estimate the silicon out-of-plane thermal conductivity and the thermal response of an silicon on insulator (SOI) device subject to Joule heating. We have found that relative phonon contribution to the overall conductivity changes as the dimension of the domain is reduced as a result of phonon confinement. The observed reduction in the thermal conductivity is produced by the progressive transition of modes in the diffusive regime (as in the bulk) to transitional and ballistic regimes as the film thickness is decreased. In addition, we have found that relaxation time expressions for optical phonons are important to describe the transient response of SOI devices and that the characteristic transport regimes, determined with Holland and Klemens phonon models, differ significantly.
2010 16th International Workshop on Thermal Investigations of Ics and Systems, 2010
In this work, we use the effective medium approximation (EMA) to numerically assess the thermal p... more In this work, we use the effective medium approximation (EMA) to numerically assess the thermal performance of thermal interface materials (TIMs). The performance is measured in terms of the effective thermal conductivity of the composite material subject to changes in the filler dimensions, volume fraction, aspect ratio, filler-matrix interface resistance and thermal conductivity of carbon nanotubes (CNTs) and spherical metallic
Journal of Microelectronics and Electronic Packaging, 2012
Thermal underfills are crucial to support integration density scaling of future integrated circui... more Thermal underfills are crucial to support integration density scaling of future integrated circuit packages. Therefore, a sequential process using hierarchical self-assembly of microparticles and nanoparticles is proposed to achieve percolating thermal underfills with enhanced particle contacts. The three main process steps are assembly of filler particles by centrifugation, formation of nanoparticle necks by capillary bridging, and backfilling of the porous structure with an unfilled capillary adhesive. Numerical simulations predicting trajectories and distributions of micron-sized particles dispensed into a rotating disk are presented. The trajectories exhibit a strong dependence on particle size; thus, in the case of polydisperse filler particles, nonuniform particle beds may result. An efficient centrifugal disk design with spiral-like guiding structures is experimentally validated. Defect-free, percolating particle beds in confined space with fill fractions of 46 vol.% to 66 vo...
Revista Técnica de la Facultad de Ingeniería Universidad del Zulia
This paper establish s the conrlitions und er wh ich disch arge and loss coefficients can be p re... more This paper establish s the conrlitions und er wh ich disch arge and loss coefficients can be p redicted. and the conditlons which p errnit the use abrupt expansion as a measurement of flow. The p rediCtion Is don e by a computer simulation based on Patankar's finite volume method, which resolves the continuity and quanUty ofmovement equaUons for turbu lent flow. The comparlson of the r sults obtained with those available from otherworks. show that it is feasible lo u se a brupt expansion as a fl ow-meter and supports the effectivenes s of the program utilized .
Journal of Electronic Packaging, 2014
This work presents enhanced composite joints that support both electrical and thermal transport i... more This work presents enhanced composite joints that support both electrical and thermal transport in electronic packages. The joints are sequentially formed by applying a nanoparticle suspension, evaporating a solvent, self-assembling of nanoparticles by capillary bridging, and the formation of so called “necks” between micrometer-sized features. This sequence is used to either form low temperature electrical joints under copper pillars or enhanced percolating thermal underfills (ePTU) with areal contacts between filler particles of the composite. The report discusses processing aspects of the capillary bridges evolution and of uniform neck formation, it discusses strategies to achieve mechanically stable necks, and it compares the performance of the achieved joints against state-of-the-art solutions. The capillary bridge evolution during liquid evaporation was investigated in copper pillar arrays and random particle beds. The vapor–liquid interface first penetrates locations of low p...
Proceedings of SPE Asia Pacific Oil and Gas Conference and Exhibition, 2002
The resolution and accuracy provided by the existing technology for downhole (pressure and temper... more The resolution and accuracy provided by the existing technology for downhole (pressure and temperature) and rate measurements are unprecedented. However, while the potential benefits have been outlined, the models and processes required to reap these benefits (in particular the quantifiable ones) have not been sufficiently documented. In addition, considering the increasing number of reported work in this area, it is necessary to provided a framework for the analysis and discussion of existing and upcoming applications. This paper presents a: i) summary and classification of downhole and flow rate measurements applications, ii) a discussion of their benefits for reservoir description and production optimization, and iii) the models and processes required to obtain those benefits. The above-referenced applications are classified in three main areas: reservoir characterization, reservoir/well flow modeling, and process monitoring. The discussion of each application includes: benefits, previously reported work, required measurements and other relevant data, and a general description of the necessary models and processes. The paper is expected to be useful assessing the possible impact of investments (business cases) in permanent downhole and flow rate measurements, designing plans for the development or acquisition of applications, and establishing the knowledge requirements in the context of training programs.
2012 13th International Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, 2012
ABSTRACT Electronic packaging increasingly aims at copper pillars as an interconnect concept, bec... more ABSTRACT Electronic packaging increasingly aims at copper pillars as an interconnect concept, because of their benefits for fine pitches, high aspect ratios, high electromigration stability and excellent thermal conductivity. The thermal expansion and high stiffness of the pillars remains a design challenge when building-up more copper volume close to the silicon die. Specific pillar geometries and structured underfills have been suggested but included only few parameter variations. To gain profound insight into the thermo-mechanical aspects of copper pillars we present a parametric finite element approach and an according multivariate analysis of the design space. We chose a 3D slice model to represent a copper pillar matrix and varied height, width and thickness at a constant pitch to consider different aspect ratios and cross sections, and vary the material's CTE and Young's modulus. The general assumption of aiming higher columns without underfill as the most compliant design when controlling for BEoL layer thickness must be rejected. If exploiting the multivariate design space wholly, processing steps may be eliminated, such as structuring an underfill layer. Tailoring the CTE may be used to lower the stress level for a desired aspect ratio, and the ratio of Cu volume to total pillar layer volume should be considered. To accommodate the display of multivariate stress results we propose an appropriate small multiple visualization.
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Papers by Javier Goicochea