The Plastic Ball Grid Array (PBGA) package and flip-chip technology have been widely used in the microelectronics industry. However, due to the effect of hygroscopic and thermal stresses, the reliability is still of concern during manufacturing and operation, especially for the thermal-mechanical behavior of its corresponding interfaces. Influences of the storage conditions and reflow parameters on the warpage of the PBGA package are investigated in this study first. As the results, the warpage reflected the interaction of the extent of moisture absorption and the change in reflow parameters significantly. Furthermore, a critical relative moisture absorption between 0.25% and 0.30% is found for a considerable warpage response. Next, this study presents an experimental investigation of the adhesion strength of epoxy-based encapsulant material to solder mask coated FR-4 substrate under thermal cycling. Effects of the number of thermal cycles on the interfacial strength are investigated by using button shear test. The relationship between the interfacial strength and thickness of solder mask is also examined. Moreover, to characterize the degradation and fracture behavior, the morphologies of fractured surfaces of the test specimens are analyzed by scanning electron microscopy. The results of this experiment show that the interfacial strength of the epoxy-based encapsulant/solder mask/substrate joint is apparently reduced by thermal fatigue. And, the test specimen with larger solder mask thickness has higher interfacial strength. Finally, the single-lap joint test, nonlinear finite element analysis and Moiré interferometry are employed to obtain strain/stress distributions on the interface of solder mask and substrate. The effects of solder mask thickness and overlap length are then determined, separately. The results of this study can afford important information for characterizing the features of moisture absorption, warpage and interfacial adhesion of PBGA packages. Furthermore, it can be helpful to identify improvements required in reliability of the package design.

The main aim of this paper is to study for the warpage and von Mises stress of PBGA package caused by the variations of mechanical properties of materials in IR-reflow process. At first, taking advantage of the package symmetry only one quarter of the package was modeled by MSC. Marc. The influence of heat transfer was considered by comparing the results of Coupled mechanical-heat transfer analysis and Mechanical analysis. In the second part, the coefficient of thermal expansions and elastic modulus of molding compound and substrate are selected as the four control factors, and the influence of the four control factors to the warpage and von Mises stress were observed. At last, emperical formulas to predicted warpage and von Mises stress values were obtained.

The Salmonella enterica subsp. enterica serovar Typhimurium PhoPQ two-component system is activated within the intracellular phagosome environment, where it promotes remodeling of the outer membrane and resistance to innate immune antimicrobial peptides. Maintenance of the PhoPQ-regulated outer membrane barrier requires PbgA, an inner membrane protein with a transmembrane domain essential for growth, and a periplasmic domain required for PhoPQ-activated increases in outer membrane cardiolipin. Here, we report the crystal structure of cardiolipin-bound PbgA, adopting a novel transmembrane fold that features a cardiolipin binding site in close proximity to a long and deep cleft spanning the lipid bilayer. The end of the cleft extends into the periplasmic domain of the protein, which is structurally coupled to the transmembrane domain via a functionally critical C-terminal helix. In conjunction with a conserved putative catalytic dyad situated at the middle of the cleft, our structural and mutational analyses suggest that PbgA is a multifunction membrane protein that mediates cardiolipin transport, a function essential for growth, and perhaps catalysis of an unknown enzymatic reaction. IMPORTANCE Gram-negative bacteria cause many types of infections and have become increasingly resistant to available antibiotic drugs. The outer membrane serves as an important barrier that protects bacteria against antibiotics and other toxic compounds. This outer membrane barrier function is regulated when bacteria are in host environments, and the protein PbgA contributes significantly to this increased barrier function by transporting cardiolipin to the outer membrane. We determined the crystal structure of PbgA in complex with cardiolipin and propose a model for its function. Knowledge of the mechanisms of outer membrane assembly and integrity can greatly contribute to the development of new and effective antibiotics, and this structural information may be useful in this regard.

This graduation thesis addresses questions to thermal profile measurement of PBGA package during solder reflow process. The first part of thesis deals with problem of reflow process and reliability factors of solder joint connection. Next part analyses operation principles of thermocouples that are commonly used for temperature measurement. The experimental part deals with methods of thermocouples fixation during tests and measurements of dummy PBGA package. There was realized a method of dummy PBGA thermal profiles measurement and sample testing with and without simulated thermal load on PBGA package. The end of thesis concerns on possibilities of thermal profiles evaluation by using PWI method and thermal profile optimization of reflow process.