With the development of smaller and higher density surface mount packages like Quad Flat No-lead (QFN) and Ball Grid Array (BGA), solder joints¡¦ strength of the electronic components has a greater impact on the reliability of an end product. Also, the decrease in size of consumer products such as cellular phones, PDAs and MP3 players, has increased the frequency of accidental drops resulting in solder joint cracks and eventually malfunction of the products. With legislation put in place by government and industrial bodies, electronics companies are driven to eliminate the uses of lead in their products. It thus leads to the concern of reliability of lead-free solders as interconnects. The present work aims at studying the effects of drop impact on the strength of solder joint of lead free solder (Sn4Ag0.5Cu) and BGA substrate metal finish electrolytic Ni and Au. In this study, the effects of internal stresses in BGA Ni layer and Pre-treatment Micro-Etching processing on the strength of Sn/Ag/Cu solder joint are investigated. The drop test and peel off test are adopted in testing the strength according to the standard of JEDEC. The drop test results have shown that the compressive internal stresses in the Ni layer have worse effects on the joint strength than tensile internal stresses can affect. The failure modes are analyzed and can be concluded that all failures occur at the interface of IMC and the surface of Ni layer on BGA substrate. The drop test results have shown also that the strength of the solder joint with the lower concentration of SPS in pre-treatment micro-etching is stronger and all the failures occur at the interface of IMC and the surface of PCB Cu Pad. Comparing with the effect of internal stress in Ni layer, SPS concentration in pre-treatment micro-etching to affect the solder joint strength is more significant.

During their production and normal use, electronic packages experience large temperature excursions, leading to high thermo-mechanical stress gradients that cause fatigue failure of the solder joints. In order to prevent premature failure and prolong the fatigue life of solder joints, there is a pressing need for the characterization of the solder, especially lead-free solder, at the micro-level (joint size). The characterization and modeling of solder behavior at the appropriate scale is a major issue. However, direct measurement techniques are not applicable to characterize the deformation response of solder joints because of their micro scale dimensions. Therefore, a non-contact measurement technique utilizing a Scanning Electron Microscope (SEM) in conjunction with Digital Image Correlation (DIC) has been developed. Validation was achieved by performing a four-point bending test in both an in-house optical system with DIC and inside the SEM. This non-contact measurement technique was then used to extract the stress-strain response of the solder. Mechanical tests were performed on solder joints that were created using the same type of solder balls used in the electronic industry and were representative of normal joint scales. The SEM-DIC technique has been proven to be applicable for the determining the stress-strain response of solder material at the micro-scale.This study resulted in a validated material characterization technique specifically designed for micro-scale material response. One of the main contributions of this study is that the method is a lot simpler and cheaper, yet highly effective, compared to the previous methods. This technique is also readily applicable to the measurement of the stress-strain response of any micro-scale specimen, such as other metals, polymers, etc. Also, the measured displacement field by obtained by DIC can be used as the base for calculating the strain field on the surface of a specimen.

1.Sn/Ag4.0/Cu0.5 solder with better performance by the improved reflow profile. 2.The Sn/Ag2.6/Cu0.6¡BSn/Ag4.0/Cu0.5 with similar reliability test performance.

ABSTRACT In package, it¡¦s easy to have defects in the solder joint, for the request of environment protection, lead-free solder research is one of the most important topics now. In soldering, the adhesion, diffusion barrier, and wettability of the interface between UBM and a lead-free solder, and the caused IMC structure that are important elements to influence long-term reliability tests. The thesis is aimed to investigate the combination of pure tin/Al-NiV-Cu UBM/STD Au substrate under reliability tests. The samples are bare dies in which the combination is pure tin/ Al-NiV-Cu UBM and packages of is pure tin/Al-NiV-Cu UBM/STD Au substrate. The goals are to realize the mechanical properties under multiple reflows and long term HTST tests with different temperatures and the operational life. We also uses SEM to observe the growth of IMC and the failure modes that help us to realize the connection between failure modes and IMC. The results of experiment can be concluded as follows. In a bare die, 260¢Jmultiple reflows test causes delamination between IMC and die, but doesn¡¦t affect the mechanical properties of it, and HTST test lowers the bump shear strength of it. In package, multiple reflows test and HTST test lower the mechanical properties significantly, the result also means that the adhesion between bump and die will drop significantly as tests go on. In HTOL test with the conditions of 150¢J and 320mA, the average stable service time of the package is 892 hours, and the average ultimate service time of the package is 1,053 hours, most probable failure site is in R1 joint.

Piezoelectric materials find applications in number of devices requiring inter-conversion of mechanical and electrical energy.  These devices include different types of sensors, actuators and energy harvesting devices. A number of lead-based perovskite compositions (PZT, PMN-PT, PZN-PT etc.) have dominated the field in last few decades owing to their giant piezoresponse and convenient application relevant tunability. With increasing environmental concerns, in the last one decade, focus has been shifted towards developing a better understanding of lead-free piezoelectric compositions in order to achieve an improved application relevant performance.  Sodium potassium niobate (KxNa1-xNbO3, abbreviated as KNN) is one of the most interesting candidates in the class of lead-free piezoelectrics. Absence of any poisonous element makes it unique among all the other lead-free candidates having presence of bismuth. Curie temperature of 400"C, even higher than that of PZT is another advantage from the point of view of device applications. Present work focuses on the development of fundamental understanding of the crystallographic nature, domain structure and domain dynamics of KNN. Since compositions close to x = 0.5 are of primary interest because of their superior piezoelectric activity among other compositions (0 < x < 1), crystallographic and domain structure studies are focused on this region of the phase diagram. KNN random ceramic, textured ceramic and single crystals were synthesized, which in complement to each other help in understanding the behavior of KNN. K0.5Na0.5NbO3 single crystals grown by the flux method were characterized for their ferroelectric and piezoelectric behavior and dynamical scaling analysis was performed to reveal the origin of their moderate piezoelectric performance. Optical birefringence technique used to reveal the macro level crystallographic nature of x = 0.4, 0.5 and 0.6 crystals suggested them to have monoclinic Mc, monoclinic MA/B and orthorhombic structures respectively. Contrary to that, pair distribution function analysis performed on same composition crystals implies them to belonging to monoclinic Mc structure at local scale. Linear birefringence and piezoresponse force microscopy (PFM) were used to reveal the domain structure at macro and micros scales respectively. A noble sintering technique was developed to achieve > 99% density for KNN ceramics. These high density ceramics were characterized for their dielectric, ferroelectric and piezoelectric properties. A significant improvement in different piezoelectric coefficients of these ceramics validates the advantages of this sintering technique. Also lower defect levels in these high density ceramics lead to the superior ferroelectric fatigue behavior as well. To understand the role of seed crystals in switching behavior of textured ceramic, highly textured KNN ceramics (Lotgering factor ~ 88 %) were synthesized using TGG method. A sintering technique similar to one employed for random ceramics, was used to sinter textured KNN ceramics as well. Piezoresponse force microscopy (PFM) study suggested these textured ceramics to have about 6¼m domains as compared to 2¼m domain size for random ceramics.  Local switching behavior studied using switching spectroscopy (SS-PFM) revealed about two and half time improvement of local piezoresponse as compared to random counterpart. / Ph. D.

Glass-ceramic composites and nanocrystalline glass-ceramics containing barium titanate (BT) or potassium sodium niobate (KNN) ferroelectric phases have been studied, with particular regard to their use as dielectric energy storage materials. Barium borosilicate glass (BBS) was used as a sintering aid for BT and KNN, producing glass-ceramic composites. The temperatures required to achieve densification were reduced from 1400 to 1200 °C for BCZT (Ca, Zr-doped BT) and 1170 to 1050 °C for KBN (Bi, Na, K, Zr-doped KNN) by the use of glass additives. An unexpected observation, found in both BCZT and KBN systems, was the heterogeneous dissolution of dopant elements into the glass, inducing additional anomalies in the relative permittivity-temperature relationships. For BCZT, the orthorhombic-tetragonal phase transformation temperature shifted upwards to ≈ 50 °C, which was attributed to modification of the Ca/Zr ratio by preferential dissolution of Ca into the glass phase. Similarly, for KBN the dopant elements appeared to be leached into the liquid phase during sintering, resulting in relative permittivity-temperature characteristics similar to those of pure KNN. A modified BBS glass having various KNN contents was prepared by the conventional melt-quenching method and then heat-treated to induce crystallisation, producing nanocrystalline glass-ceramics. It is shown that crystallisation of an intermediate barium niobate phase initiates at temperatures in the region of 650 °C; this is subsequently converted into perovskite KNN together with a second phase of Ba3Nb5O15 at temperatures from 700 to 800 °C. The final crystallite size was in the region of 30±7 nm. The highest dielectric energy storage density of 0.134(4) J cm-3 was obtained for a glass-modified BT ceramic at an electric field level of 5 kV mm-1. However, the energy storage efficiency of the BT-based ceramics was relatively poor and they displayed a general tendency for saturation, indicating potentially poor performance at higher field levels. On the other hand, the KNN-based ceramics exhibited slightly lower energy storage density values, up to 0.108(1) J cm-3, but with much improved linearity and energy storage efficiency. Therefore, the latter is considered to be more suitable as energy storage dielectrics. The BBS-KNN glass-ceramics yielded relatively low energy storage density, 0.035(2) J cm-3, but the dielectric linearity and storage efficiency were similar to or better than those of the KNN ceramics, indicating good potential for use as energy storage dielectrics at very high electric field levels as a result of their nanocrystalline microstructures.

Due to the introduction of Restriction of Hazardous Substances (RoHS) directive Pb containing solders have been banned from the electronics industry and a reliable replacement for the Sn-Pb solder is being sought for by industry around the globe. Medical and Defense industries are currently exempt from the directive and use Sn-Pb solder in their manufacturing process. The switch to lead-free has led component manufacturers to use different lead-free solders, thus causing mixed solder joints of lead-free components with Sn-Pb paste. In this study, mixed assembly microstructures and mechanical properties were examined. Furthermore, six novel lead-free solders were prepared using SAC105 solder doped with elements: Ti, Ni, Mn, La, Ce and Y. The solidification microstructures, fracture behavior and wetting properties of these solders were evaluated to find a suitable replacement for SAC105 solder.

Due to the introduction of Restriction of Hazardous Substances (RoHS) directive Pb containing solders have been banned from the electronics industry and a reliable replacement for the Sn-Pb solder is being sought for by industry around the globe. Medical and Defense industries are currently exempt from the directive and use Sn-Pb solder in their manufacturing process. The switch to lead-free has led component manufacturers to use different lead-free solders, thus causing mixed solder joints of lead-free components with Sn-Pb paste. In this study, mixed assembly microstructures and mechanical properties were examined. Furthermore, six novel lead-free solders were prepared using SAC105 solder doped with elements: Ti, Ni, Mn, La, Ce and Y. The solidification microstructures, fracture behavior and wetting properties of these solders were evaluated to find a suitable replacement for SAC105 solder.

Georgia Techs Packaging Research Centers vision of System on Package (SOP) requires that the ball grid array (BGA) package be eliminated and the integrated circuit (IC) directly assembled on the printed wiring board (PWB). Flip-Chip on board (FCOB) emerges as a viable solution which meets the industry requirements of (i) increased I/O, (ii) increased functionality and (iii) improved performance at lower costs. Nevertheless flip-chip on board (FCOB) reliability continues to be an important concern in electronic packaging industry. Moreover transition to Pb-free solder for interconnects and continuously shrinking geometries result in new modeling challenges. In addition, the integrity of the intermetallics (IMCs) at the interfaces of the solder/PWB and solder/die is one of the determinant factors in the reliability and continuity of electrical signals in flip-chip interconnects. Pb-free solder studies for the flip-chip assembly studies are limited and simplified so far, not fully incorporating the effect of intermetallics in the reliability. New modeling challenges involve many details, from geometry to material properties. A brittle IMC will lead to a fracture at the interface. Also IMC thickness can cause the variation in stresses in the underlying layers, causing delamination. Moreover IMC morphology can also depend on the metal finishes on the PWB. In this work, a combined numerical and experimental program has been developed to address the challenges mentioned above. The flip-chip on board assembly is modeled in 3-D for reliability studies, taking into consideration material non linearities and a 104 order of geometric variation to capture the die size in mm to sub-micron intermetallic thickness. The study intends to determine the stresses induced at the critical interfaces under thermo-mechanical loading incorporating the intermetallic material properties. Various failure modes of these assemblies were studied. Experiments were carried out for comparative reliability studies of Pb-free solder with eutectic Pb-based solder. Intermetallic formation and growth are characterized during thermal aging and its effect on reliability is determined. Parameters affecting intermetallic like under-bump Metallurgy (UBM) thicknesses are varied and its effect evaluated. Moreover experiments with three new substrate pad finishes on PWB are carried out to evaluate them as an alternative to Electroless nickel immersion gold (ENIG) for new Pb-free solder. The final aim of this study is to reach a better understanding of the reliability issues in FCOB.

Thermal fatigue failure, due to the fracture of solder bumps which was cased by the coefficient of thermal expansion mismatch deformation, is frequently encountered in flip-chip package. Therefore, this thesis attempts to study the effects of geometric parameters variation on lead-free flip-chip package under temperature cycling test. First, we used the finite element method to simulate the thermal loading response of lead-free flip-chip. The accumulated equivalent creep strain and accumulated creep strain energy density of the lead-free solder bumps were calculated, and were used to predict the thermal fatigue life of lead-free flip-chip package. The Taguchi method is applied to obtain the optimal design parameters in order to enhance reliability of the lead-free flip-chip under temperature cycling loading. The analysis of variance (ANOVA) is also used for estimating the influence of the factors quantitatively. The obtained results can be adopted as references for the lead-free flip-chip package design.