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Showing papers in "Journal of Electronic Packaging in 2005"





Journal ArticleDOI
TL;DR: In this article, the capacity of moisture absorption by a typical polymer material was analyzed and some important parameters, which will be used frequently in subsequent sections, as follows: In order to understand better the capacity, the authors introduced some important parameter parameters, such as the CTE and Young's modulus, as well as other properties of polymer materials.
Abstract: Polymer materials have wide applications in microelectronic packaging. Some polymer materials are used in bulk form, such as encapsulant molding compound and carrier or printed circuit boards FR4 and BT . Some polymer materials are used as adhesives, such as die-attach, underfill, or other structural and thermal adhesives. Polymers are also used in thin or thick film as an isolation layer, such as a solder mask on a printed circuit board or passivation layer in the wafer level. Despite the diversities of the chemistry and compositions, the polymer materials applied in microelectronics can be either thermoset or thermoplastic materials 1 . Both types of materials have a glass transition temperature around which the material properties, such as the CTE and Young’s modulus, are very sensitive to temperature. Another common feature of polymer materials is the high porosity, which makes the material susceptible to moisture absorption. In order to understand better the capacity of the moisture absorption by a typical polymer material, let us introduce some important parameters, which will be used frequently in subsequent sections, as follows:

69 citations



Journal ArticleDOI
TL;DR: In this paper, the thermal-mechanical durability of the Pb-free Sn3.8Ag0.7Cu solders is investigated by a systematic approach combining comprehensive thermal cycling tests and finite element modeling.
Abstract: As the ban of the Pb use in electronics products is approaching due to the waste electrical and electronic equipment (WEEE) and restriction of hazardous substances (ROHS) directives, electronics companies start to deliver the products using the Pb-free solders. There are extensive databases of mechanical properties, durability properties (for both mechanical and thermal cycling), and micromechanical characteristics for Sn-Pb solders. But similar databases are not readily yet available for Pb-free solders to predict its mechanical behavior under environmental stresses. In this study, the thermo-mechanical durability of the Pb-free Sn3.8Ag0.7Cu solder is investigated by a systematic approach combining comprehensive thermal cycling tests and finite element modeling. A circuit card assembly (CCA) test vehicle was designed to analyze several design and assembly process variables when subjected to environmental extremes. The effects of mixed solder systems, device types, and underfill are addressed in the thermal cycling tests. The thermal cycle profile consisted of temperature extremes from −55to+125° Celsius with a 15min dwell at hot, a 10min dwell at cold, and a 5–10° Celsius per minute ramp. Thermal cycling results show that Sn3.8Ag0.7Cu marginally outperforms SnPb for four different components under the studied test condition. In addition, the extensive detailed three-dimensional viscoplastic finite element stress and damage analysis is conducted for five different thermal cycling tests of both Sn3.8Ag0.7Cu and Sn37Pb solders. Power law thermo-mechanical durability models of both Sn3.8Ag0.7Cu and Sn37Pb are obtained from thermal cycling test data and stress and damage analysis. The results of this study provide an important basis of understanding the thermo-mechanical durability behavior of Pb-free electronics under thermal cycling loading and environmental stresses.

58 citations


Journal ArticleDOI
TL;DR: In this article, the results of an investigation of the thermal performance of a graphite foam thermosyphon evaporator were presented, and a simple model based on heat transfer from the outer surface was proposed.
Abstract: This paper presents the results of an investigation of the thermal performance of a graphite foam thermosyphon evaporator and discusses the foam’s potential for use in the thermal management of electronics. The graphitized carbon foam used in this study is an open-cell porous material that consists of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper. While the bulk graphite foam has a thermal conductivity similar to aluminum, it has one-fifth the density, making it an excellent thermal management material. Furthermore, using the graphite foam as the evaporator in a thermosyphon enables the transfer of large amounts of energy with relatively low temperature difference and without the need for external pumping. Performance of the system with FC-72 and FC-87 was examined, and the effects of liquid fill level, condenser temperature, and foam height, width, and density were studied. Performance with FC-72 and FC-87 was found to be similar, while the liquid fill level, condenser temperature, geometry, and density of the graphite foam were found to significantly affect the thermal performance. The boiling was found to be surface tension dominated, and a simple model based on heat transfer from the outer surface is proposed. As much as 149W were dissipated from a 1cm2 heated area.

56 citations


Journal ArticleDOI
Woon-Seong Kwon1, Myung-Jin Yim1, Kyung-Wook Paik1, Suk-Jin Ham2, Soon-Bok Lee1 
TL;DR: In this article, Choi et al. proposed a MEMS lab at the Korea Advanced Institute of Science and Technology (KAIST) in Daejon 305-701, South Korea.
Abstract: a Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejon 305-701, South Korea b MEMS Lab., Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, South Korea c CARE-Electronic Packaging Laboratory, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, South Korea

52 citations


Journal ArticleDOI
TL;DR: In this article, the failure modes of flip chip solder joints under high electrical current density are studied experimentally and three different failure modes are reported: electromigration and thermomigration, where void nucleation and growth contribute to the ultimate failure.
Abstract: The failure modes of flip chip solder joints under high electrical current density are studied experimentally. Three different failure modes are reported. Only one of the failure modes is caused by the combined effect of electromigration and thermomigration, where void nucleation and growth contribute to the ultimate failure of the module. The Ni under bump metallization–solder joint interface is found to be the favorite site for void nucleation and growth. The effect of pre-existing voids on the failure mechanism of a solder joint is also investigated

50 citations




Journal ArticleDOI
TL;DR: In this article, a viscoplasticity model unified with a thermodynamics-based damage concept is presented to model the thermal viscastic behavior and fatigue life of solder joints in microelectronics packaging.
Abstract: Sn-Pb eutectic solder alloy is extensively used in microelectronics packaging interconnects. Due to the high homologous temperature, eutectic Sn-Pb solder exhibits creepfatigue interaction and significant time-, temperature-, stress-, and rate-dependent material characteristics. The microstructure is often unstable, having significant effects on the flow behavior of solder joints at high homologous temperatures. Such complex behavior makes constitutive modeling an extremely difficult task. A viscoplasticity model unified with a thermodynamics-based damage concept is presented. The proposed model takes into account isotropic and kinematic hardening, and grain size coarsening evolution. The model is verified against various test data, and shows strong application potential for modeling thermal viscoplastic behavior and fatigue life of solder joints in microelectronics packaging. DOI: 10.1115/1.1939822

Journal ArticleDOI
TL;DR: In this article, the authors present some fundamental aspects of interfacial fracture mechanics and describes some of the numerical techniques available for calculating the strain energy release rate and mode mixity at the tips of cracks at interfaces in plastic-encapsulated IC packages.
Abstract: Ever since the discovery of the “popcorn” failure of plastic-encapsulated integrated-circuit (IC) packages in the 1980s, much effort has been devoted to understanding the failure mechanism and modeling it. It has been established that such failures are due to the combined effects of thermal stresses and hygrostresses that arise during solder reflow of plastic IC packages. In recent years interfacial fracture mechanics has been applied successfully to the analysis of delamination or crack propagation along interfaces in plastic IC packages. This paper presents some fundamental aspects of interfacial fracture mechanics and describes some of the numerical techniques available for calculating the strain energy release rate and mode mixity at the tips of cracks at interfaces in plastic-encapsulated IC packages. A method of calculating the combined effects of thermal stress and hygrostress on the energy release rate is also described. Some case studies are presented that illustrate how the techniques are applied to predicting delaminaton in IC packages. Some experimental verification of predictive methodology is also presented.



Journal ArticleDOI
TL;DR: In this article, a two-phase micro-channel heat sink design is presented, where the heat sink parameters are grouped into geometrical parameters, operating parameters, and thermal/fluid parameters.
Abstract: This study provides a comprehensive methodology for optimizing the design of a twophase micro-channel heat sink. The heat sink parameters are grouped into geometrical parameters, operating parameters, and thermal/fluid parameters. The objective of the proposed methodology is to optimize micro-channel dimensions in pursuit of acceptable values for the thermal/fluid parameters corresponding to a given heat flux, coolant, and overall dimensions of the heat generating device to which the heat sink is attached. The proposed optimization methodology yields an acceptable design region encompassing all possible micro-channel dimensions corresponding to a prescribed coolant flow rate or pressure drop. The designer is left with the decision to select optimum channel dimensions that yield acceptable values of important thermal/fluid parameters that are easily predicted by the optimization procedure. DOI: 10.1115/1.2056571

Journal ArticleDOI
TL;DR: In this article, a general procedure to perform submodeling analyses for path-dependent thermomechanical problems without a priori assumptions on the structural response is presented, which is conducive to the numerical assessment of fatigue lives of electronic packages.
Abstract: In a finite element analysis, when localized behavior of a large model is of particular concern, generally one would refine the mesh until it captures the local solution adequately. Submodeling is an alternative way for solving this kind of problem. It provides a relatively accurate solution at a modest computational cost. For a valid submodeling analysis, the boundaries of the submodel should be sufficiently far away from local features so that St. Venant’s principle holds. Moreover, special treatments are required for solving problems that involve path-dependent characteristics. This paper presents a general procedure to perform submodeling analyses for path-dependent thermomechanical problems without a priori assumptions on the structural response. The procedure was benchmarked using a bimaterial strip and demonstrated through analyses on a bump chip carrier package assembly. The procedure is conducive to the numerical assessment of fatigue lives of electronic packages.



Journal ArticleDOI
TL;DR: In this paper, the isothermal mechanical durability of three NEMI recommended Pb-free solders, 95.5Sn-3.9Ag-0.6Cu, 96.5sn-3,5Ag, and 99.3sn-0,7Cu, is tested on the TMM setup under two test conditions: room temperature and relatively high strain rate, and high temperature and low strain rate.
Abstract: This study is motivated by the urgent need in the electronics industry for mechanical properties and durability of Pb-free solders because the use of Pb will be banned in the EU by July 1, 2006. The isothermal mechanical durability of three NEMI recommended Pb-free solders, 95.5Sn-3.9Ag-0.6Cu, 96.5Sn-3.5Ag, and 99.3Sn-0.7Cu, is tested on the thermo-mechanical-microscale (TMM) setup under two test conditions: room temperature and relatively high strain rate, and high temperature and low strain rate. The test data are presented in a power law relationship between three selected damage metrics (total strain range, inelastic strain range, and cyclic work density) to 50% load drop. The obtained mechanical durability models of three Pb-free solders are compared with those of the eutectic 63Sn-37Pb solder at the two selected test conditions and at the same homologous temperature of 0.75. The results of this study can be used for virtual qualification of Pb-free electronics during design and development of electronics under mechanical loading.


Journal ArticleDOI
Tae-Sang Park1, Soon-Bok Lee2
TL;DR: In this paper, a low-cycle fatigue test for ball grid array (BGA) solder joints is proposed to give a proper and accurate estimation of the fatigue life of BGA solder joints.
Abstract: To give a proper and accurate estimation of the fatigue life of ball grid array (BGA) solder joints, a mechanical fatigue test method under mixed-mode loading is proposed. Experiments were conducted with 63Sn/37Pb and Sn/3.5Ag/0.75Cu solder joints in room temperature. The mechanical low cycle fatigue tests were performed under several loading angles. The loading angle is controlled by several grips which have specific surface angle to the loading direction. Constant displacement controlled tests are performed using a micro-mechanical test apparatus. It was found that the normal deformation significantly affects the fatigue life of the solder joint. Throughout the whole test conditions at room temperature, Sn/3.5Ag/0.75Cu solder alloy had longer fatigue life than 63Sn/37Pb alloy. Failure patterns of the fatigue tests were observed and discussed. A morrow energy model was examined and found to be a proper low cycle fatigue model for solder joints under mixed mode loading condition. DOI: 10.1115/1.1871192




Journal ArticleDOI
TL;DR: In this paper, a new method based on the strain rate ratio was developed, which predicted the creep-fatigue life within a factor of 4 scatter band, and the method was applied to the experimental data.
Abstract: This paper studies creep-fatigue life prediction under shear loading by making extensive torsion creep-fatigue experiments using four kinds of strain waves. The linear damage rule, strain range partitioning method, frequency modified fatigue life, and ductility exhaustion model were applied to the experimental data, but no methods accurately predicted the creep-fatigue life. A new method based on the strain rate ratio, which predicted the creep-fatigue life within a factor of 4 scatter band, was developed.


Journal ArticleDOI
TL;DR: In this article, an area-selective adhesive wafer bonding using photosen BCB from Dow Co. was reported, where the strength of the fabricated bonds was characterized using wedge-opening and tensile methods.
Abstract: This paper reports on an area-selective adhesive wafer bonding, using photosen BCB from Dow Co. The strength of the fabricated bonds is characterized using wedge-opening and tensile methods. The measured fracture toughness is 53.5 63.9J/m with tensile strength up to 71 MPa. The potential application of BCB bonding is dem strated on a concept of wafer-level chip-scale package for RF applications and micro array for microfluidic applications.@DOI: 10.1115/1.1846059 #

Journal ArticleDOI
TL;DR: In this article, the authors present a more direct and convenient approach to consider wire density effect by including wires in the mesh model for three-dimensional (3D) mold-filling analysis.
Abstract: More wires in a package and smaller wire gaps are the trend in the integrated circuit (IC) packaging industry. The effect of wire density is becoming increasingly apparent, especially on the flow pattern of the epoxy molding compound during the molding process and, hence, on the amount of wire sweep. In most mold flow simulations, the wire density effect is ignored. In order to consider the wire density effect on the predicted amount of wire sweep in the analysis, several indirect approaches were used by researchers before. But those approaches were not general enough to be applied to all cases. This paper presents a more direct and convenient approach to consider wire density effect by including wires in the mesh model for three-dimensional (3D) mold-filling analysis. A thin small outline package (TSOP) with 53 wires is used as the demonstration example, and all the wires are modeled in the 3D mesh. By comparison with experimental results, it is shown that this approach can accurately describe the wire density effect. When the wires are included in the mesh model, the predicted wire sweep results are better than those without considering the wire density effect.