Showing papers in "Journal of Electronic Packaging in 2017"

Moisture Ingress, Behavior, and Prediction Inside Semiconductor Packaging: A Review

Abstract: Reliability issues associated with moisture have become increasingly important as advanced electronic devices are nowhere more evident than in portable electronic products. The transition to the Pb-free solders, which require higher reflow temperature, makes the problem further exacerbated. Moisture absorbed into semiconductor packages can initiate many failure mechanisms, in particular interfacial delamination, degradation of adhesion strength, etc. The absorbed moisture can also result in catastrophic crack propagation during reflow process, the well-known phenomenon called popcorning. High vapor pressure inside pre-existing voids at material interfaces is known to be a dominant driving force of this phenomenon. This paper reviews various existing mechanisms of water accumulation inside voids. The procedures to obtain the critical hygroscopic properties are described. Advanced numerical modeling schemes to analyze the moisture diffusion phenomenon are followed with selected examples. [DOI: 10.1115/1.4035598]

Thermal Performance and Efficiency of a Mineral Oil Immersed Server Over Varied Environmental Operating Conditions

Abstract: Complete immersion of servers in dielectric mineral oil has recently become a promising technique for minimizing cooling energy consumption in data centers. However, a lack of sufficient published data and long-term documentation of oil immersion cooling performance make most data center operators hesitant to apply these approaches to their mission critical facilities. In this study, a single server was fully submerged horizontally in mineral oil. Experiments were conducted to observe the effects of varying the volumetric flow rate and oil inlet temperature on thermal performance and power consumption of the server. Specifically, temperature measurements of the central processing units (CPUs), motherboard (MB) components, and bulk fluid were recorded at steady-state conditions. These results provide an initial bounding envelope of environmental conditions suitable for an oil immersion data center. Comparing with results from baseline tests performed with traditional air cooling, the technology shows a 34.4% reduction in the thermal resistance of the system. Overall, the cooling loop was able to achieve partial power usage effectiveness (pPUECooling) values as low as 1.03. This server level study provides a preview of possible facility energy savings by utilizing high temperature, low flow rate oil for cooling. A discussion on additional opportunities for optimization of information technology (IT) hardware and implementation of oil cooling is also included. [DOI: 10.1115/1.4037526]

Bio-Based Epoxy Resins Derived From Eugenol With Low Dielectric Constant

Abstract: In this paper, a series of bio-based epoxy resins containing organic silicone were prepared from eugenol through a mild synthetic route. Then, 4,4'-diaminophenyl methane (DDM) was applied to cure these epoxy resins, and bisphenol A epoxy resin (DGEBA) was used as a control. The chemical structures of the synthesized resins were characterized by nuclear magnetic resonance (H-1-NMR). Properties of the cured epoxy resins were investigated by dielectric test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Compared with DGEBA, the bio-based epoxy resin containing cyclic organic silicon structure exhibited a dramatically lower dielectric constant at both low and high frequencies (3.46, 1 kHz, room temperature). Moreover, the silicone-modified bio-based epoxy resins demonstrated no weight loss below 325 degrees C and higher residues at 800 degrees C than that of DGEBA.

Modeling and Analysis for Thermal Management in Gallium Nitride HEMTs Using Microfluidic Cooling

Abstract: In this paper, thermal management in GaN (gallium nitride) based microelectronic devices is addressed using microfluidic cooling Numerical modeling is done using finite element analysis (FEA), and the results for temperature distribution are presented for a system comprising multiple cooling channels underneath GaN high-electron mobility transistors (HEMTs) The thermal stack modeled is compatible for heterogeneous integration with conventional silicon-based CMOS devices Parametric studies for cooling performance are done over a range of geometric and flow factors to determine the optimal cooling configuration within the specified constraints A power dissipation of 2-4W/mm is modeled along each HEMT finger in the proposed configuration The cooling arrangements modeled here hold promising potential for implementation in high-performance radio-frequency (RF) systems for power amplifiers, transmission lines, and other applications in defense and military

Measurement of Air Flow Rate Through Perforated Floor Tiles in a Raised Floor Data Center

Abstract: In a raised floor data center, cold air from a pressurized subfloor plenum reaches the data center room space through perforated floor tiles. Presently, commercial tool “Flow Hood” is used to measure the tile air flow rate. Here, we will discuss the operating principle and the shortcomings of the commercial tool and introduce two other tile air flow rate measurement tools. The first tool has an array of thermal anemometers (named as “Anemometric Tool”), and the second tool uses the principle of temperature rise across a known heat load to measure the tile air flow rate (named as “Calorimetric Tool”). The performance of the tools is discussed for different types of tiles for a wide range of tile air flow rates. It is found that the proposed tools result in lower uncertainty and work better for high porosity tiles, as compared to the commercial tool. [DOI: 10.1115/1.4035596]

Flow Boiling Heat Transfer and Pressure Drops of R1234ze(E) in a Silicon Micro-pin Fin Evaporator

Abstract: The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study, an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm(2) containing 66 rows of cylindrical in-line micro-pin fins with diameter, height, and pitch of, respectively, 50 mu m, 100 mu m, and 91.7 mu m. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m(2) s to 1750 kg/m(2) s and heat fluxes ranging from 20 W/cm(2) to 44 W/cm(2). The effects of saturation temperature on the heat transfer are investigated by testing three different outlet saturation temperatures: 25 degrees C, 30 degrees C, and 35 degrees C. In order to assess the thermal-hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high-speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m(2) K, whilst in two-phase flow it goes up to 30 kW/m(2) K.

Solid-State Microjoining Mechanisms of Wire Bonding and Flip Chip Bonding

Abstract: Low-temperature microjoining, such as wire (or ribbon) bonding, tape automated bonding (TAB), and flip chip bonding (FCB), is necessary for electronics packaging. Each type of microjoining takes on various aspects but has common bonding mechanisms regarding friction slip, plastic deformation, and friction heating. In the present paper, solid-state microjoining mechanisms in Au wire (ball) bonding, FCB, Al wire bonding (WB), and Al ribbon bonding are discussed to systematically understand the common bonding mechanisms. Ultrasonic vibration enhances friction slip and plastic deformation, making it possible to rapidly obtain dry interconnects. Metallic adhesion at the central area of the bonding interface is mainly produced by the friction slip. On the other hand, the folding of the lateral side surfaces of the Au bump, Au ball, and Al wire is very important for increasing the bonded area. The central and peripheral adhesions are achieved by a slip-and-fold mechanism. The solid-state microjoining mechanisms of WB and FCB are discussed based on experimental results. [DOI: 10.1115/1.4038143]

Experimental and Numerical Investigation of Interdie Thermal Resistance in Three-Dimensional Integrated Circuits

Abstract: Three-dimensional integrated circuits (3D ICs) attract much interest due to several advantages over traditional microelectronics design, such as electrical performance improvement and reducing interconnect delay. While the power density of 3D ICs increases because of vertical integration, the available substrate area for heat removal does not change. Thermal modeling of 3D ICs is important for improving thermal and electrical performance. Experimental investigation on the thermal measurement of 3D ICs and determination of key physical parameters in 3D ICs thermal design are curtail. One such important parameter in thermal analysis is the interdie thermal resistance between adjacent die bonded together. This paper describes an experimental method to measure the value of interdie thermal resistance between two adjacent dies in a 3D IC. The effect of heating one die on the temperature of the other die in a two-die stack is measured over a short time period using high-speed data acquisition to negate the effect of boundary conditions. Numerical simulation is performed and based on a comparison between experimental data and the numerical model, the interdie thermal resistance between the two dies is determined. A theoretical model is also developed to estimate the value of the interdie thermal resistance. Results from this paper are expected to assist in thermal design and management of 3D ICs. [DOI: 10.1115/1.4036404]

Transient Data Processing of Flow Boiling Local Heat Transfer in a Multi-Microchannel Evaporator Under a Heat Flux Disturbance

Abstract: Multi-microchannel evaporators are often used to cool down electronic devices subjected to continuous heat load variations. However, so far, rare studies have addressed the transient flow boiling local heat transfer data occurring in such applications. The present paper introduces and compares two different data reduction methods for transient flow boiling data in a multi-microchannel evaporator. A transient test of heat disturbance from 20 to 30W cm(-2) was conducted in a multi-microchannel evaporator using R236fa as the test fluid. The test section was 1 x 1 cm(2) in size and had 67 channels, each having a cross-sectional area of 100 x 100 mu m(2). The micro-evaporator backside temperature was obtained with a fine-resolution infrared (IR) camera. The first data reduction method ( referred to three-dimensional (3D)-TDMA) consists in solving a transient 3D inverse heat conduction problem by using a tridiagonal matrix algorithm ( TDMA), a Newton-Raphson iteration, and a local energy balance method. The second method ( referred to two-dimensional (2D)controlled) considers only 2D conduction in the substrate of the micro-evaporator and solves at each time step the well-posed 2D conduction problem using a semi-implicit solver. It is shown that the first method is more accurate, while the second one reduces significantly the computational time but led to an approximated solution. This is mainly due to the 2D assumption used in the second method without considering heat conduction in the widthwise direction of the micro-evaporator.