bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Natural Convection in a Cavity With a Cooled Top Wall and Multiple Protruding Heaters
Authors: Desai C. P. , Vafai K. , Keyhani M.
Published: February 2008

Natural convection in rectangular enclosures with multiple protruding heaters mounted on one side wall is of relevance to the cooling of electronic equipment. In some configurations, the top wall behaves as the heat sink while the opposing vertical wall and the bottom wall are insulated. The present work examines the peculiarities introduced in the natural convection process for such configurations. The enclosure considered had five protrusions, cavity width to heater length ratio of 1.2 and cavity height to heater length ratio of 11. It is shown that for such configurations, a stable flow exists only at lower Rayleigh numbers and that above a certain critical Rayleigh number, only quasi-steady solutions exist. At low Rayleigh numbers(Ra* ≤ 1.5 × 107), the flow is stable and characterized by the presence of a primary flow cell and a counter-rotating secondary cell at the top of the enclosure. At higher Rayleigh numbers (Ra* ≥ 3 × 108), however, the isothermal top wall causes a periodic flow pattern to develop within the enclosure. Several interesting characteristics of the flow and temperature fields are presented. Results compared with previous experimental and numerical work are found to be in good agreement.
Plastic Deformation Kinetics of 95.5Sn4Cu0.5Ag Solder Joints
Authors: Guo Z. , Pao Yi-Hsin , Conrad H.
Published: February 2008

The plastic deformation kinetics of 95.5Sn4Cu0.5Ag solder joints were determined in monotonic loading shear over the temperature range of 25°–150°C using three types of tests: (a) constant shear rate, (b) constant shear stress (creep), and (c) differential tests (changes in shear rate or temperature during an otherwise isothermal constant shear rate test). The deformation kinetics were evaluated in terms of the Dorn high temperature plastic deformation equation γ˙p=A(μb/kT)D(b/d)P(τ/μ)n where γ˙p is the shear rate, μ the shear modulus, b the Burgers vector, D the appropriate diffusion coefficient, d the grain size and τ the shear stress. A, p, and n are constants whose values depend on the rate controlling mechanism. It was found that n increased with stress from ~4 at 2 MPa to ~20 at 25 MPa, relatively independent of temperature. The activation ΔH was determined to be 21.1 ± 2 kcal/mole. The constant A, however, decreased with temperature from a value of ~1018 at 25°C to ~1010 at 150°C. The values of n and ΔH suggest that dislocation glide and climb is the rate controlling mechanism and hence that p ≈ 0. It is speculated that the large decrease in A with temperature may be the result of an effect on the microstructure.
Creep Crack Growth Prediction of Solder Joints During Temperature Cycling—An Engineering Approach
Authors: Syed Ahmer R.
Published: February 2008

A model is developed which predicts the creep damage accumulation in solder joints during temperature cycling. The model relates the crack growth rate to the rate of creep energy density dissipated using the C* parameter of nonlinear fracture mechanics for extensive creep damage. For a eutectic tin-lead solder joint, the damage due to both grain boundary sliding and matrix creep is considered. The validity of the model is proved by correlating the predicted fatigue life of solder joints for 84 I/O leadless ceramic chip carriers with the published measured data for a number of test conditions. The published experimental conditions are simulated in a three dimensional, nonlinear, time and temperature dependent finite element analysis. For each test condition, both components of creep energy density, i.e., energy densities because of grain boundary sliding and matrix creep, are determined separately in the finite element analysis. The values are then used to determine the crack growth parameters and predict the crack growth rate in the solder joint using the crack growth model. The predicted results are found to have good correlation with the measured fatigue life for each test condition.
Energy Approach to the Fatigue of 60/40 Solder: Part I—Influence of Temperature and Cycle Frequency
Authors: Solomon H. D. , Tolksdorf E. D.
Published: February 2008

This study correlates previously published fatigue life data with the hysteresis energy, and compares this to the previous correlation’s with the applied plastic strain. It was found that, while the hysteresis energy could be used to describe the fatigue life, corrections must be made to account for the temperature and strain rate dependence of the flow stress. Because of these factors, it is believed that the plastic strain, and not the hysteresis energy, is the true governing factor in determining the fatigue life. Part I (described here) covers only the influence of temperature and cycle frequency for symmetric cycling. Part II, to be published, will deal with hold time and asymmetric cycling.
Plastic Deformation of Solder Joints in Pin Grid Arrays Subjected to Thermal Stress
Authors: Engel Peter A. , Chou Shou-Chien
Published: February 2008

In an earlier work [1], thermal stresses in soldered pins were calculated under the assumption of an elastically deforming solder barrel. In the present analysis, the nonlinear,temperature dependent stress-strain curve of solder, without creep, is taken into account, yielding an elasto-plastic foundation modulus function. For the thermal mismatch loading, the total temperature range ΔT (e.g., 0–100°C) is divided into a finite number n of temperature stages, and the final responses are superposed from the n contributions each of which done using an isothermal stress calculation. Three solders (Sn-Pb solders 63/37, 70/30, and 10/90), were investigated; the solder barrel thickness and mismatch temperature range were also variable parameters. Comparisons with elastic solder foundation calculation results show that thermal and inelastic solder stress/strain dependence should be included especially in the higher (over 75°C) temperature range.
On Murphy’s Integrated Circuit Yield Integral
Authors: Lau John H.
Published: February 2008

An approximated closed-form integrated circuit (IC) yield formula based on a Gaussian defect density distribution for the compounder in Murphy’s yield integral is presented. Also, a closed-form solution for the average number of faults (AD0) in an IC is obtained for a given IC yield (Y). Furthermore, based on the new IC yield formula a simple equation for determining the number of yielded chips in a wafer is given. Finally, the multichip module yield (Ym) and resultant shipped multichip module yield (Yms) based on the new IC yield formula are provided.
Thermal Deformation Analysis of Various Electronic Packaging Products by Moire´ and Microscopic Moire´ Interferometry
Authors: Han B. , Guo Y.
Published: February 2008

Thermo-mechanical behavior of various levels of electronic packaging products is studied by moire´ and microscopic moire´ interferometry. The global deformations of packages with complex geometries and the local deformations of solder interconnections are determined by displacement measurements of high sensitivity and high spatial resolution. Several packaging studies are reviewed. They include analyses of thin small outline package, leadless chip carrier package, surface mount array package, chip/organic carrier package, deformation near a plated through hole, and determination of an effective CTE. In-situ and quantitative nature of the methods leads to more accurate and realistic understanding of the macro and micro mechanical behavior of packaging assemblies and interconnections, which in turn, facilitates design evaluation and optimization at an early stage of product development.
A Micro-Mechanics Investigation on the Bonding Strength of Heteroepitaxical Film or Strip on a Hard Substrate
Authors: Luo Y. F. , Rajurkar K. P.
Published: February 2008

The bonding strength of deposited metallic thin films or strips on a hard substrate is investigated through micro-strength tests and micro-mechanics analyses. The combination of Ti:W-Au/Cu deposited directly on SiO2/Si substrate was taken as an example in the experiments conducted. Investigations and analyses resulted in a general model concerning the separation mechanism of thin ductile films from a hard brittle substrate. This separation model leads to some systematic methods of improving strip-substrate interconnection strength. Besides strip-substrate adhesion and internal stresses, strip stiffness turns out to be a key factor for the bonding strength of such a system. Hardening processes such as post-deposition heat treatment and work-hardening are proved to be effective in strengthening the bonding strength. These investigations reveal a principle of mechanical compatibility concerning interface micro-deformation. Instead of thin and flexible strips, thick and rigid strips have better compatibility with a hard substrate if the bonded combination is subjected to mechanical loading rather than thermal loading. As far as interface stresses are concerned, a stress distribution strategy is proposed based on the same principle. This original understanding will help to improve common bonding strength problems of various interconnection structures and materials combinations in manufacturing processes.
Environmental Scanning Electron Microscopic Investigation of Failure Mechanisms in Electronic Packages
Authors: Li Mary J. , Pecht Michael
Published: February 2008

Environmental Scanning Electron Microscopy (E-SEM) is a technique which provides the capability to investigate surface morphologies over a variety of controllable environmental conditions. This paper discusses the principal of the E-SEM and presents three experimental investigations of failure mechanisms in electronic packages using E-SEM techniques. The first is a study of thermally induced failures of MMIC devices. The second investigation focuses on mechano-sorptive properties of multilayer thin-film polyimides. The third investigation concentrates on relative humidity and thermal cycling effects on interfacial bonding characteristics of resin/fiber interfaces in printed wiring boards, and microcracks surrounding plated-through-holes.
Application of Statistical Clustering to Screen Printing Process Control
Authors: Skormin V. A. , Herman C. R. , Popyack L. J.
Published: February 2008

Statistical clustering is applied for mathematical description of a surface mount assembly process. The clustering model, intended for process control applications, defines the correspondence between various outcomes of the process and particular regions in the space of process variables. An adaptive version of the clustering model is presented. Prediction, regime selection and control procedures, utilizing the clustering model, are formulated.
Wetting Kinetics of Molten 60Sn40Pb on a Ag-0.33 wt.% Pt Thick Film Conductor
Authors: Campbell J. , Conrad H.
Published: February 2008

The effects of time (10-6000 s) and temperature (194°-265°C) on the wetting of a Ag-0.33 wt percent Pt thick film (10 μm) conductor substrate by molten 60Sn40Pb were investigated using the sessile drop method. The wetting occurred in three stages. In Stage I the solid alloy piece melted and spread rapidly to form a spherical cap. The spreading slowed down appreciably in Stage II but increased again in Stage III, the time exponent in Stage III being of the order of 0.1–0.25, which was 2–3 times that in Stage II. In general, the contact angle θ and the time exponent decreased with temperature. The activation energy for the effect of temperature on the contact angle in Stages II and III and on the transition time tc between these stages was approximately 7 kcal/mole. This value was concluded to represent the diffusion of Sn atoms over the halo surface as a precursor to the formation of the intermetallic compound Ag3Sn at the molten solder/substrate interface.
A Rubbery Cure Shrinkage Model for Analyzing Encapsulated Assemblies
Authors: Chambers R. S. , Lagasse R. R. , Guess T. R. , Plazek D. J. , Bero C.
Published: February 2008

Electrical component assemblies are encapsulated to provide delicate parts with voltage isolation and protection against damage. The stresses generated by cure shrinkage, although typically smaller than the thermal residual stresses produced by cooling, can cause delamination or fractures in an encapsulant. Mechanical failures can be reduced by optimizing the encapsulation process or altering the component geometry. This paper documents the performance of rubbery constitutive equations in analyzing the stresses and strains generated by isothermal curing. A rubbery cure shrinkage model was installed in a finite element program and material inputs were obtained by measuring the rubbery shear modulus and volumetric shrinkage of a gelled epoxy during isothermal curing at several temperatures. A test was performed to measure the structural response produced by curing, and the data were compared to finite element predictions. The rubbery model performs well when the glass transition temperature of the curing epoxy does not exceed the cure temperature.
Boundary Layer Fracture in Composite Solder Joints
Authors: Clough Roger B. , Shapiro Alexander J. , Bayba Andrew J. , Lucey George K.
Published: February 2008

Composite solder connections, modeled as miniature single-lap shear layers between copper plates, were fabricated and pulled to fracture. The solder layers (3.1 × 3.1 × 0.50 mm) were eutectic lead-tin/particulate Cu6Sn5 composites. Under load, shear fractures extended along paths about 10 µm inside of the interfaces from opposite edges. These boundary layer fractures were characterized and a fracture model was developed. A corresponding test method for measuring JII and δII, the crack extension energy and crack tip shear displacement for Mode II crack growth, is given, and the results are discussed. Composite strengthening is shown to significantly improve the ductility and the creep life, properties associated with improved reliability and creepfatigue life.
Integrated Infrared Failure Analysis of Printed Circuit Boards
Authors: Miles J. J. , Zelak C. R. , Kliman J. M. , Sunderland J. E.
Published: February 2008

A method is presented to test automatically for latent faults, those which elude detection during conventional electronic testing, on printed circuit boards. Testing is intended for implementation in a volume manufacturing environment and involves the application of infrared imaging tools. Successful incorporation of infrared testing into existing test processes requires that: a procedure for handling variable radiation heat transfer properties across a printed circuit board be developed; a thermally-controlled test enclosure be provided; PASS/FAIL criteria be established. These tasks are addressed, testing procedures are described, and favorable results are presented. The feasibility of an infrared test process is demonstrated.
Computations for a Three-by-Three Array of Protrusions Cooled by Liquid Immersion: Effect of Substrate Thermal Conductivity
Authors: Mukutmoni D. , Joshi Y. K. , Kelleher M. D.
Published: February 2008

A computational study of natural convection in an enclosure as applied to applications in cooling of electronic components is reported. The investigation is for a configuration consisting of a three by three array of heated protrusions placed on a vertical substrate. The vertical sidewalls are all insulated, and the top and bottom walls serve as isothermal heat sinks. A thin layer at the back of each protrusion is the heat source, where heat is generated uniformly and volumetrically. The coolant is the flourinert liquid FC75. The code was first validated with experimental results reported earlier on the same configuration. The effect of the substrate conductivity, κs on the heat transfer and fluid flow was then studied for power levels of 0.1 and 0.7 Watts per protrusion. The computations indicate that the effect of increasing κs is dramatic. The protrusion temperatures which were found to be nominally steady, were substantially reduced. The percentage of generated power that is directly conducted to the substrate increased with an increase in κs. The fluid velocity field, which was unsteady, was not significantly affected by changes in κs.
Effect of Wall Conduction on Natural Convection in an Enclosure With a Centered Heat Source
Authors: Huang Yi-Hsiang , Aggarwal Suresh K.
Published: February 2008

This study presents a numerical investigation of the effects of wall conduction on laminar natural convection heat transfer in a two-dimensional rectangular enclosure. The heat transfer is driven by a constant-temperature heat source in the center of the enclosure. The time dependent governing equations in the primitive form are solved numerically by the use of a finite-volume method. The numerical algorithm is first validated by comparing our predictions with those of Kim and Viskanta for a square cavity surrounded by four conducting walls. A parametric study is then conducted to examine the effects of wall conduction on the natural convection heat transfer. The parameters include the Rayleigh number, wall thickness, wall thermal conductivity ratio and diffusivity ratio. In addition, the effects of varying thermal boundary conditions on the outside walls are reported. Results indicate that the qualitative features of natural convection heat transfer in the laminar range are not significantly altered by the inclusion of wall conduction. However, the quantitative results may be significantly modified by the wall conductance. In general, the wall conduction reduces the rate of heat dissipation from the enclosure. The average Nusselt number decreases as the wall thickness ratio is increased and/or the wall thermal conductivity is reduced. Results also indicate that it may be possible to define an effective Rayleigh number that includes the effects of wall thickness and conductivity.
Simulation of Heat Transfer in a Reflow Soldering Oven With Air and Nitrogen Injection
Authors: Son Y. S. , Bergman T. L. , Hyun M. T.
Published: February 2008

Reflow soldering with nitrogen injection is simulated. Soldering is performed in a process oven that is equipped with porous panel heaters through which air or nitrogen is introduced to the reflow environment. The injected gas is introduced selectively through top or bottom infrared heaters in order to dampen temperature fluctuations which can be established by thermal buoyancy forces in the oven gas. The heat transfer processes are simulated using an existing, general numerical model that accounts for multimode effects, and is capable of predicting large and small scale thermal and species concentration phenomena. With selective injection, it is shown that high frequency convective heating and/or cooling of the card assembly can be eliminated, and oxygen concentrations in the reflow section can be controlled to low levels.
Review of Heat Transfer Technologies in Electronic Equipment
Authors: Yeh L. T.
Published: February 2008

Thermal control has become a critical factor in the design of electronic equipment because of the recent trends in the electronic industry towards increased miniaturization of components and device heat dissipation. A great demand on the system performance and reliability also intensifies the needs for a better thermal management. The further evidence of importance of thermal consideration to an electronic system is due to the survey by the U.S. Air Force indicating that more than fifty percent of all electronics failures are caused by the undesirable temperature control. This paper reviews recent technologies in thermal control and management of electronic equipment.
The Mechanics of the Edge Delamination Test
Authors: Mirman Boris
Published: February 2008

A new test to measure the adhesion of thin polymeric coatings (the so-called “edge delamination test”) has been recently proposed by Shaffer et al. (1993), where the authors translate the test measurements into the values of the debond energy by finite element modeling. The present paper suggests another interpretation of the mechanics of the edge delamination test and translates the measurements of this test into conventional values of the adhesion strength—the ultimate peeling stress, using a simple closed-form solution.
Statistical Model for the Inherent Tilt of Flip-Chips
Authors: Goldmann Lewis S.
Published: February 2008

The tilt of flip-chips is becoming increasingly important in optical and high-power electronic applications. This paper outlines the principal sources of tilt, and presents a mathematical algorithm for the statistical variation in inherent tilt, the component related to variability of solder pad dimensions. With the assistance of a Monte Carlo simulation, closed form equations are developed for several common families of symmetric pad footprints. Possible extension of the analytical tools to other important cases is discussed.
Comparison of the Cooling Performance of Staggered and In-Line Arrays of Electronic Packages
Authors: Wirtz R. A. , Colban D. M.
Published: February 2008

The cooling performance of in-line and staggered regular arrays of simulated electronic packages is compared for both sparse and dense packaging configurations. At equal flow rates, staggered arrays exhibit higher element heat transfer coefficients and friction factors than in-line arrays. Furthermore, an increase in the packaging density of the elements results in a moderate reduction in the friction factor with negligible change in the heat transfer coefficient. However, when performance is expressed in terms of heat transfer rate per unit packaging system volume, dense arrays are found to out perform sparse arrays at equal flow rate, applied pressure gradient or pumping power. Furthermore, no significant difference in performance is observed between staggered and in-line configurations when they are compared on the basis of either equal coolant flow pressure drop or pumping power.
A Model for Deformation of Solder Bumps From Ramp Loading
Authors: Goldmann Lewis S.
Published: February 2008

A simple model is presented to predict the mechanical squashing or stretching of an axisymmetric solder joint when subjected to a ramp loading. This is a situation which can frequently arise, accidentally or by design, in the processing of flip chip solder bumps, or in surface mounted Ball Grid Array modules. Excessive squashing can have ramifications for subsequent processing or for joint reliability. The proposed method, while involving an extremely simple algorithm, has been found to agree well with experimental data, and is very general in its applicability.
Controlling the Dimensions of Laser Chemical Vapor Deposited Metallurgy
Authors: Economikos L. , Kotecki D. E. , Surprenant R.
Published: February 2008

The application of pyrolytic laser chemical vapor deposition (LCVD) to repair defects on multichip modules with a high circuit density requires tight control of the dimensions of the deposited metal. It is shown that by creating micro-channels into the substrate on both sides along the laser scan path, shorting to adjacent lines is eliminated and better control of deposited metal is achieved. A finite element model shows how the presence of the micro-channels reduces the temperature in the deposited material in the direction perpendicular to the laser scan, causing the deposition process to self-limit in this direction.
Shock and Vibration of Solder Bumped Flip Chip on Organic Coated Copper Boards
Authors: Lau John , Schneider Eric , Baker Tom
Published: February 2008

The reliability of solder bumped flip chips on organic coated copper (OCC) printed circuit board (PCB) has been studied by shock and vibration tests and a mathematical analysis. Two different chip sizes (7 mm and 14 mm on a side) have been studied, and the larger chips have many internal solder bumps. For the in-plane and out-of-plane and out-of-plane shock tests, the chips were assembled with and without underfill encapsulants. However, for the out-of-plane vibration tests all the chips were underfilled with epoxy.
Fatigue Crack Initiation in Solder Joints
Authors: Zhang Z. , Yao Daping , Shang J. K.
Published: February 2008

A backface strain technique is introduced to examine fatigue crack initiation in solder lap joints. The technique detects the fatigue crack initiation by monitoring the backface strain at the end of the overlap. Variation of the backface strain with the development of a crack was simulated by finite element method. The simulation indicated that the backface strain at the end of the overlap reached a peak value when a fatigue crack initiated. Experimental verification was carried out in 63Sn-37Pb solder joints. The backface strain was recorded as a function of stress cycle to demonstrate the applicability of this technique. Experimental results showed that fatigue crack initiation took about half of the fatigue lifetime of the solder joints.
Solder Joint Reliability Prediction by the Integrated Matrix Creep Method
Authors: Iannuzzelli R. J. , Pitarresi J. M. , Prakash V.
Published: February 2008

The integrated matrix creep method for predicting the fatigue life of solder joints is presented. The application of the matrix creep life prediction method to a variety of solder joint/load combinations with a comparison to measured reliability data is presented as a validation of this technique. For a leadless chip carrier, the strain distribution in the solder is studied both through modeling and laser Moire interferometry. Finally, using this methodology as a design tool, the fatigue life simulation of a gull wing leaded package is presented in which various design parameters are modified and their effect on the fatigue life determined.
A Nonlinear Multi-Domain Stress Analysis Method for Surface-Mount Solder Joints
Authors: Ling S. , Dasgupta A.
Published: February 2008

Solder joint fatigue failures are a potential reliability hazard in surface-mount electronic packages under cyclic thermal loading environment. Proper design and reliability assessment are thus crucial to ensure the fatigue endurance of the electronic packages. Accurate modeling of the stress and strain fields within the solder joint under cyclic thermal loading condition is of extreme importance since ultimately, a reasonable fatigue life estimation depends not only on a appropriate fatigue model, but more fundamentally, on accurately predicted stress and strain fields. Modeling stress and strain fields in solder joint in surface-mount electronic packages have never been an easy task since solder undergoes elastic, plastic and time dependent creep during each loading and unloading cycle. Some of the existing closed-form stress analysis models tend to oversimplify this complicated viscoplastic stress state, thus failing to give a reasonable prediction of the solder joint fatigue endurance. Extensive finite element analyses require prohibitive investment in terms of the analysis time and analyst expertise, especially when full scale elastic, plastic and creep analyses are performed. A generalized multi-domain approach proposed earlier by the authors is further developed in this paper to obtain the stress and strain fields in J-leaded surface-mount solder joint undergoing elastic-plastic deformation, under cyclic thermal environment (Ling et al., 1995). The Rayleigh-Ritz energy method based on a multi-field displacement assumption is used. In a previous paper (Ling et al., 1995), the results for analysis within elastic region had been demonstrated and were proved to be in agreement with finite element analysis. In this paper we further develop the methodology into plastic deformation region. Hysteresis loops for both the global and the local CTE mismatch problem can finally be generated. Results for two-dimensional elastic-plastic analysis are presented in the current paper. Creep deformation can be further modeled with this scheme by using time-stepping incremental techniques, and will be presented in a future paper. The final goal of this research is to predict the stress, strain and energy density distributions in the solder joint with reasonable accuracy. The fatigue assessment of the solder joint can then be performed by combining results from this stress analysis model with an appropriate damage model, for example, the energy-partitioning fatigue model (Dasgupta et al., 1992).
A Procedure for Automated Shape and Life Prediction in Flip-Chip and BGA Solder Joints
Authors: Subbarayan G.
Published: February 2008

In this paper, a three-dimensional shape prediction model and a finite element solution procedure for flip-chip and BGA solder joints are developed. The developed system is capable of calculating the solder joint geometry and the fatigue life automatically without any intervention from the user. The automation achieved will enable fast reliability estimation and improved accuracy, since the two-dimensional finite element mesh used for solder shape prediction is used to generate the three-dimensional finite element mesh for stress analysis. The implementation of the procedure is verified using the solution for a flip-chip joint from literature, and the capability of the code is demonstrated on a hypothetical three-dimensional solder joint with square pads that are rotated with respect to each other, and offset from each other. The system developed in the study represents the first instance of an integrated, automated finite element procedure for both shape and fatigue life prediction in general three-dimensional solder joints. The automation achieved in the system enables fast reliability estimation in a design environment, and the optimal design of flip-chip and BGA solder joint configurations for maximum life.
Simulation and Interpretation of Wetting Balance Tests Using the Surface Evolver
Authors: Whalley D. C. , Conway P. P.
Published: February 2008

The wettability of PCB pads and component terminations, and the variation of wetta-bility with time, are important factors in the successful formation of a solder joint. However, reliable techniques for determining these properties, under conditions representative of the soldering process, do not as yet exist. The development of wetting balance tests has provided a technique for the qualitative comparison of surface wettability, but the test has poor repeatability and it is difficult to relate the test results to the actual surface properties. The small size of the terminations in surface mount technology (S.M.T.) prevents successful use of the conventional solder bath based wetting balance test. The globule wetting balance goes some way towards removing this limitation and is now often used as a means of comparing the solderability of S.M.T. devices, but is even worse in terms of repeatability and interpretation. This paper presents results from an evaluation of conventional and globule wetting balance tests using both computational modelling and experimental techniques. The results from the experimental tests show that reasonable consistency in the measured force can be obtained, but that the insensitivity of this force to the wetting angle of the component, particularly in the globule block test, precludes their ability to accurately establish the wetting angle. It is therefore concluded that this test is unsuitable for providing direct quantitative measurements of the wetting angle of the surface of interest. The computational models, through allowing an analysis of the sensitivity of the test to the uncontrolled test variables also provide an explanation for the significant scatter obtained in wetting balance test results. It is also seen, from comparison with test results, that models which incorporate commonly quoted text book values for the solder surface tension do not adequately predict the forces empirically observed. A technique is therefore also described whereby the solder surface tension under the actual test conditions may be deduced using the results from a scanning mode wetting balance test, thereby greatly improving the capability of the models to predict the surface tension forces, although significant errors in the predicted meniscus shape remain.
Parametric Finite Element Method for Predicting Shapes of Three-Dimensional Solder Joints
Authors: Nigro N. J. , Zhou F. J. , Heinrich S. M. , Elkouh A. F. , Fournelle R. A. , Lee P. S.
Published: February 2008

This paper discusses the application of the parametric finite element method for predicting shapes of three-dimensional solder joints. With this method, the surface of the joint is meshed (discretized) with finite elements. The spatial variables (x, y, z) are expanded over each element in terms of products of interpolation (blending) functions expressed in parametric form and element nodal coordinates. The element nodal coordinates which are not constrained by the boundary conditions are determined by minimizing the potential energy function which governs the joint formation problem. This method has been employed successfully in the past to predict the shapes of two dimensional fillet and axisymmetric joints. In this paper, the method is extended to three dimensional problems involving sessile drops formed on a rectangular pad and solder columns formed between two horizontal planes and subject to a vertical force.
Reliability Simulations for Solder Joints Using Stochastic Finite Element and Artificial Neural Network Models
Authors: Subbarayan G. , Li Y. , Mahajan R. L.
Published: February 2008

The field reliability of solder joints depends on the manufacturing process tolerance of design parameters and on the capability of manufacturing processes to achieve the tolerance. This process capability is usually expressed through measures such as “six-sigma.” In this paper, a systematic procedure to estimate the reliability of solder joints due to manufacturing process induced variations on the design is presented. The reliability is calculated using the stochastic finite element method and is most naturally expressed in terms of a mean life and a standard deviation in life. An integrated finite element solution procedure for predicting solder joint profile (during reflow) and life is also presented in the paper. A physico-neural approach in which the finite element models are used to build an artificial neural network model is next developed to combine the accuracy of the finite element models with the computational efficiency of neural networks. This physico-neural approach is shown to reduce the computational time required per design evaluation by four orders of magnitude without significant loss of accuracy. The developed procedures are applied to the 72 I/O OMPAC BGA package from Motorola, Inc. It is shown that a ±10 percent process tolerance on solder joint height, volume and pad sizes with a “six-sigma” process capability on these variables will result in solder joint with over ±20 percent variations in life about the mean life at ±6σ level. It is also shown that variations in life of BGA solder joints are most sensitive to variations in solder joint height. Variations in PWB pad size, solder volume, and substrate pad size are relatively less important, but in the order listed.
Verification of Numerical Models Used in Microelectronics Packaging Design by Interferometric Displacement Measurement Methods
Authors: Han B. , Guo Y. , Lim C. K. , Caletka D.
Published: February 2008

Verified/predictive modeling has become an integral part of electronic packaging product development in order to reduce costs and cycle time. In this paper, interferometric displacement measurement methods are utilized to verify the validity of numerical models for microelectronics packaging design. Three optical methods with submicron sensitivities are employed: moire´ interferometry, microscopic moire´ interferometry and Twyman/Green interferometry. The first two provide contour maps of in-plane displacement fields, and the third maps out-of-plane displacement fields. Their high sensitivity and high spatial resolution make them ideally suited for verification of numerical models. By combining numerical modeling and experimental verification until the results merge, numerical models become more accurate and dependable. Then, the models can be applied extensively to optimize the package designs with confidence that the models provide effective information on material and geometry sensitivity.
Prediction of Fatigue Failure of 60Sn-40Pb Solder Using Constitutive Model for Cyclic Viscoplasticity
Authors: Ishikawa Hiromasa , Sasaki Katsuhiko , Ohguchi Ken-ichi
Published: February 2008

This paper treats the prediction of fatigue life of 60Sn-40Pb solder alloy using the plastic strain work density per unit time calculated from the proposed constitutive model for cyclic viscoplasticity. At first, in order to verify the applicability of the proposed constitutive model to the deformation of 60Sn-40Pb solder alloy, a series of basic experiments, such as creep tests and cyclic tension-compression loading tests are performed at 303K, 323K, 343K. Then, the proposed constitutive model is used to predict fatigue failure of the solder alloy. As a result, it is clarified that the proposed constitutive model is applicable to explain the viscous deformation of the solder alloy, and that its fatigue failure can be predicted using the plastic strain work density per unit time.
Dynamic Aspects of Wetting Balance Tests
Authors: Moon K. W. , Boettinger W. J. , Williams M. E. , Josell D. , Murray B. T. , Carter W. C. , Handwerker C. A.
Published: February 2008

The relationships between the force measured during wetting balance tests and the observed changes of contact angle and meniscus shape are studied. Experiments using silicone oil at 25, 50, and 100°C on glass plates as well as Pb-Sn eutectic solder on Au-coated glass plates are reported. Discrepancies between the measured force and height and those expected for a static meniscus are detailed. Equilibrium meniscus shapes are computed for wide plates using the elastica solution and for narrow plates using the public-domain software package, “Surface Evolver.” For room temperature experiments with oil, the measured force discrepancy disappears when the meniscus rise is complete. Thus, the force discrepancy may be due to shear stress exerted on the sample by fluid rising up the sample. For static menisci with heated liquids, force and meniscus height discrepancies do not disappear when the meniscus rise is complete. These discrepancies can be explained by Marangoni flow due to temperature gradients in the fluid for the oil experiments but not for the solder experiments.
Experimental Investigation of the Formation of Surface Mount Solder Joints
Authors: Conway P. P. , Kalantary M. R. , Williams D. J.
Published: February 2008

As part of a major project to develop a computer-based model to support the product and process design activity for reflow soldered assemblies, it has been found necessary to carry out fundamental investigations of the processes occurring as solder pastes approach and pass the reflow temperature. This paper presents the results and our interpretation of the observed physical phenomena arising from recent high-speed video microscopy studies of the reflow of bulk deposits of solder paste and also of the formation of solder joints during infrared reflow soldering. These studies have provided insights into the physical phenomenology of reflowing solder paste, the interpretation of wetting curves and the mechanisms behind the formation of manufacturing driven defects.
Vibration Induced Fatigue Life Estimation of Corner Leads of Peripheral Leaded Components
Authors: Sidharth  , Barker D. B.
Published: February 2008

The rapid advancement of integrated circuits and associated electronic technologies have placed increasing demands on electronic packaging and its material structures in terms of the reliability requirements. In addition to the thermally induced stresses, electronic packages often experience dynamic external loads during shipping, handling, and/or operation. This is especially important for automotive, military, and commercial avionics operating environments. These dynamic loads give rise to large dynamic stresses in the leads causing fatigue failures. For peripheral leaded packages the corner leads are the most highly stressed leads. This paper addresses the determination of the out-of-plane displacement of the corner leads of peripheral leaded components when the local peripheral leaded component/board assembly is subjected to bending moments in two directions. The solution is achieved by using a combination of Finite Element Analysis (FEA), Design of Experiments (DOE), and analytical techniques. The out-of-plane displacement can then be applied as a boundary condition on a local lead model to determine the stresses which in turn can be used to estimate the fatigue life.
Calculation of Forced-Air Cooling of Electronic Modules With a Two-Fluid Model of Turbulence
Authors: Ilegbusi O. J.
Published: February 2008

The flow and heat transfer characteristics in a forced-air cooled electronic device are calculated with a two-fluid model of turbulence. The fluids are defined as turbulent and nonturbulent, and precludes the need for low-Reynolds number model in the near-wall regions. Transport equations are solved for the zone-averaged variables of each fluid. Empirical relations, established in prior work, are used to express interchange of mass, momentum, and energy at the interface. Gradient-diffusion flux is considered an intrafluid source of turbulence. Several cases are considered showing effects of Reynolds number and heat-dissipation density on the flow and thermal fields. A critical comparison is made between the results based on the application of this model and the conventional k-ε model. Such results include velocity vectors and temperature distribution. In addition, the two-fluid model predicts spatial distribution of the intermittency factor, which provides a measure of the extent of turbulence and mixing in the electronic system.
An Ultra-High Power Two-Phase Jet-Impingement Avionic Clamshell Module
Authors: Johns Murray E. , Mudawar Issam
Published: February 2008

Boiling jet impingement heat transfer from a simulated electronic chip to Fluorinert FC-72 within a clamshell avionic module was investigated for dependence upon inlet fluid temperature, nozzle diameter, nozzle to chip spacing, jet velocity, and chip length. The clamshell module was designed and fabricated to accommodate both single and multiple chip boards and to demonstrate the feasibility of an ultra-high power (on the order of several kilowatts) module. Critical heat flux (CHF) was found to be directly dependent upon subcooling and jet velocity, but relatively unaffected by the nozzle to chip spacing variations examined. The effect of varying the chip size was evaluated and found to produce higher CHF values as chip size was decreased. A correlation accounting for both geometric and subcooling effects was adapted to predict the CHF database with a mean absolute error of 9.6 percent. The module is shown to be capable of dissipating a heat load of 12,000 W at a module flow rate of 8.01 × 10−4 m3/s (12.7 gpm), thus eclipsing the current technology available in avionic cooling.
An Experimental Investigation of the Effects of Cycling Frequency and Temperature on the Fatigue Life of 60 Tin/40 Lead Solder
Authors: Leece Gregory D. , Miskioglu Ibrahim , Nelson David A.
Published: February 2008

The effects of cycling frequency and temperature on the fatigue life of solder has been analyzed. Mechanical fatigue life experiments were conducted under load control while varying the temperature and cycling frequency. Using the experimental data, a fatigue model was formulated based on the Basquin and the Coffin-Manson relations, introducing the effects of temperature and frequency. The model parameters were obtained by a statistical method incorporating multiple linear regression. Using the model, estimated values of cycles to failure at each of the testing temperatures and frequency were calculated. Using the estimated values, an evaluation of each of the models was conducted, resulting in strong correlations between the model’s estimation and the experimental data.
Pool Boiling Heat Transfer With an Array of Flush-Mounted, Square Heaters on a Vertical Surface
Authors: You S. M. , Simon T. W. , Bar-Cohen A.
Published: February 2008

Results from pool boiling heat transfer experiments with flush-mounted, square heat sources on a vertical surface cooled with electronic cooling fluid, FC-72, are presented. The fluid contains moderate levels of a dissolved, noncondensable gas. Each heat source, 25mm2 in area, has an aluminum oxide surface covering a sputtered thin film of platinum. It is intended that these heaters and their juxtaposition simulate the distribution of heating on semiconductor chip arrays. The results show that, in pool boiling, the incipience event is highly variable, while the remainder of the boiling curve is repeatable. The effect of heating an element on the initiation of boiling of nearby elements is documented. Boiling from a heater below the test heater is shown to eliminate the excursion in temperature at incipience. This is attributed to the transport of noncondensable gas component which is contained in the rising bubbles to the embryonic bubbles which reside within the test heater surface. Such transport allows a concomitant rise of the gas partial pressure within the embryonic bubbles.
Micro Heat Exchangers Consisting of Pin Arrays
Authors: Yin Xiaoqing , Bau H. H.
Published: February 2008

The performance of micro heat exchangers fabricated on silicon wafers and consisting ofpin arrays and straight channels is evaluated theoretically using three-dimensional numerical simulations. The coolant is liquid nitrogen and the objective is to maintain the wafer’s temperature below 90K so as to facilitate the use of high temperature superconductor interconnects in multichip modules. Both developing and periodic flows are considered. Comparisons of the performance of various geometric configurations are presented It is demonstrated that by proper selection of the heat of the heat exchanger’s geometry, the thermal resistance can be minimized.
Thermal Analysis and Optimization of Substrates With Directionally Enhanced Conductivities
Authors: Sikka K. K. , Fisher T. S. , Torrance K. E.
Published: February 2008

An approximate analytical solution for the thermal resistance of the axisymmetric chip-on-substrate problem is presented for a substrate with a direction dependent (orthotropic) thermal conductivity. The substrate may be convectively cooled on either, or both, of its planar surfaces. The solution reveals substrate geometries with low maximum substrate temperatures. These optimal substrate sizes are mapped for Biot numbers typical of microelectronic applications. The effects of varying the radial and axial substrate conductivities are investigated. In general, radial conductivity enhancement is beneficial for bottom-side and both-side convective cooling of thin substrates, and for top-side cooling of all substrates. For thin substrates, radial conductivity enhancement provides comparable thermal performance to an equivalent isotropic conductivity enhancement. For electronic packaging applications thin substrates are desirable and radial conductivity enhancement is more beneficial than axial conductivity enhancement.