[Show abstract][Hide abstract] ABSTRACT: In recent years, interfacial fracture becomes one of the most important problems in the assessment of reliability of electronics packaging. Especially, underfill resin is used with solder joints in flip chip packaging for preventing the thermal fatigue fracture in solder joints. In general, the interfacial strength has been evaluated on the basis of interfacial fracture mechanics concept. However, as the size of devices decrease, it is difficult to evaluate the interfacial strength quantitatively. Most of researches in the interfacial fracture were conducted on the basis of the assumption of the perfectly bonding condition though the interface has the micro-scale structure and the bonding is often imperfect. In this study, the mechanical model of the interfacial structure of resin in electronic components was proposed. Bimaterial model with the imperfect bonding condition was examined by using a finite element analysis (FEA). Stress field in the vicinity of interface depends on the interfacial structure with the imperfect bonding. In the front of interfacial crack tip, the behavior of process zone is affected by interfacial structure. However, the instability of fracture for macroscopic crack which means the fracture toughness is governed by the stress intensity factor based on the fracture mechanics concept.
[Show abstract][Hide abstract] ABSTRACT: The recent development of electric and electronic devices has been remarkable. The miniaturization of electronic devices and high integration are progressing by advances in mounting technology. As a result, the reliability of fatigue life has been prioritized as an important concern, since the thermal expansion difference between a package and printed circuit board causes thermal fatigue. In addition, because the development time of the product is being intensified, shortening the development time and reducing the cost are important concerns. It is demanded a good quality product which has short development time. However, it is difficult to guarantee quality during the design phase, because it is hard to know which design factors will prolong the fatigue life. The authors have investigated the influence of various design factors on the reliability of soldered joints in BGA model by using response surface method. However, it became clear that this sensitivity analysis was not enough for reliability design because of the effect of design factor correlation. So, it is necessary that the correlations between design factors of BGA package should be clarified. In order to investigate correlations between design factors, the authors have proposed a new approach to emboss efficiently the each design factor by applying cluster analysis. By using this technique, the correlation structure of the all design factor was clarified. Based upon the analytical results, design engineers can rate each factor's effect on reliability and assess the reliability of their basic design plan at the concept design stage
Thermal and Thermomechanical Phenomena in Electronics Systems, 2006. ITHERM '06. The Tenth Intersociety Conference on; 01/2006
[Show abstract][Hide abstract] ABSTRACT: Clarifies the dynamic behavior of BGA or CSP packaging subjected to an impact loading, and establishes a simple analytical method of impact reliability assessment for solder joints. In order to take dynamic material properties into account, a high deformation speed tension test and a vibration test were carried out to obtain the strain rate dependence of yield stress and Young's modulus of solder materials and PCB. A 3-D analytical model of PCB mounted with a BGA chip was used to simulate the impact behavior of BGA packaging, and explicit-based FEM code LS-DYNA was used to carry out the dynamic analysis. It was found that the impact reliability of solder joints is greatly affected by the falling posture. However, it was found that fine meshing of solder joints causes a rapid augmentation of calculation cost. In this study, the authors proposed a new method of transient response analysis by utilizing implicit-based FEM code NASTRAN to drop the calculation cost of impact study. It was shown that the present method can accurately simulate the dynamic behavior of BGA packaging including the time histories of the deformations and stresses, and it can drop the CPU time to about one tenth of that of LS-DYNA analysis.
Thermal and Thermomechanical Phenomena in Electronic Systems, 2002. ITHERM 2002. The Eighth Intersociety Conference on; 02/2002
[Show abstract][Hide abstract] ABSTRACT: In this paper, the authors discuss the first step in theapproach to the fundamental mechanism of small-scale local wear/fracturenear the contact surface between a viscoelastic body and a rigidtraveling roller. A rectangular viscoelastic strip made of epoxy resinwas loaded by a cylindrical hard roller moving along the upper straightedge. A convenient photoviscoelastic method using computer immageprocessing was applied to investigate the time-dependent stress andstrain around a contact region under a typical type of non-proportionalloading conditions. On the other hand, the finite element method (FEM)was used to analyze the viscoelastic stress and strain under the severalconditions. The results obtained from the two methods qualitativelycompared the time variation for the photoviscoelastic fringe patternsand the contour bands of stress/strain distribution patterns. Moreover,the time variation for principal stress differences, principal straindifferences and the directions of principal stress/strain undernon-proportional conditions, were evaluated, at which time the materialshowed remarkable viscoelastic and rubber-like properties.