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Notes: The effects of hydrostatic pressure on the solid-phase epitaxial growth (SPEG) rate v of intrinsic Ge(100) and undoped and doped Si(100) into their respective self-implanted amorphous phases are reported. Samples were annealed in a high-temperature, high-pressure diamond anvil cell. Cryogenically loaded fluid Ar, used as the pressure transmission medium, ensured a clean and hydrostatic environment. v was determined by in situ time-resolved visible (for Si) or infrared (for Ge) interferometry. v increased exponentially with pressure, characterized by a negative activation volume of −0.46Ω in Ge, where Ω is the atomic volume, and −0.28Ω in Si. The activation volume in Si is independent of both dopant concentration and dopant type. Structural relaxation of the amorphous phases has no significant effect on v. These and other results are inconsistent with all bulk point-defect mechanisms, but consistent with all interface point-defect mechanisms, proposed to date.A kinetic analysis of the Spaepen–Turnbull interfacial dangling bond mechanism is presented, assuming thermal generation of dangling bonds at ledges along the interface, independent migration of the dangling bonds along the ledges to reconstruct the network from the amorphous to the crystalline structure, and unimolecular annihilation kinetics at dangling bond "traps.'' The model yields v = 2 sin(θ)vsnr exp[(ΔSf + ΔSm)/k] exp− [(ΔHf + ΔHm)/kT], where ΔSf and ΔHf are the standard entropy and enthalpy of formation of a pair of dangling bonds, ΔSm and ΔHm are the entropy and enthalpy of motion of a dangling bond at the interface, vs is the speed of sound, θ is the misorientation from {111}, and nr is the net number of hops made by a dangling bond before it is annihilated. It accounts semiquantitatively for the measured prefactor, orientation dependence, activation energy, and activation volume of v, and the pressure of a "free-energy catastrophe'' beyond which the exponential pressure enhancement of SPEG cannot continue uninterrupted due to a vanishing barrier to dangling bond migration. The enhancement of v by doping can be accounted for by an increased number of charged dangling bonds, with no change in the number of neutrals, at the interface. Quantitative models for the doping dependence of v are critically reviewed. At low concentrations the data can be accounted for by either the fractional ionization or the generalized Fermi-level-shifting models; methods to further test these models are enumerated. Ion irradiation may affect v by altering the populatio

Notes: In this paper, some strategies taken to improve the reliability of solder joints on power devices in single device and multi-chip packages are presented. A strategy for improving solder joint reliability by adjusting solder joint geometry, underfilling and utilization of flexible substrates is discussed with emphasis on triple-stacked solder joints that resemble the shape of an hourglass. The hourglass shape relocates the highest inelastic strain away from the weaker interface with the chip to the bulk region of the joint, while the underfill provides a load transfer from the joints. Thermal cycling data show significant improvements in reliability when these techniques are used. The design, testing and finite-element analyses of an interconnection structure, termed the Dimple-Array Interconnect, for improving the solder joint reliability is also presented.

Notes: The reliability of solder joints in flip chip assemblies with both compliant (flex) and rigid(PCB) substrates was studied by accelerated temperature cycling tests and finite element modeling(FEM). In-process electrical resistance measurements and nondestructive evaluations were conductedto monitor solder joint failure behavior, hence the fatigue failure life. Meanwhile, the predictedfatigue failure life of solder joints was obtained by Darveaux’s crack initiation and growth models. Itcan be concluded that the solder joints in flip chip on flex assembly (FCOF) have longer fatigue lifethan those in flip chip on rigid board assembly (FCOB); the maximum von Mises stress/strain and themaximum shear stress/strain of FCOB solder joints are much higher than those of FCOF solder joints;the thermal strain and stress in solder joints is reduced by flex buckling or bending and flex substratecould dissipate energy that otherwise would be absorbed by solder joint. Therefore, the substrateflexibility has a great effect on solder joint reliability and the reliability improvement was attributed toflex buckling or bending during temperature cycling

Notes: Today, reflow soldering is a commonly used technique to establish large-area joints inpower electronics modules. These joints are needed to attach large-area (〉1 cm2) powersemiconductor chips to the substrate, e.g., a direct-bond copper substrate, and the multichip modulesubstrate to a copper base plate for heat spreading. Thermal performance, specifically thermalconductivity and thermomechanical reliability, of these large-area joints are critical to the electricalperformance and lifetime of the power modules. Soft solder alloys, including the lead-tin eutecticand lead-free alternatives, have low thermal conductivities and are highly susceptible to fatiguefailure. As demands mount for higher power density, higher junction temperature, and longerlifetime out of the power modules, reliance on solder-based joining is becoming a barrier for furtheradvancement in power electronics systems. Recently, we successfully demonstrated lowtemperaturesintering of nanoscale silver paste as a lead-free solution for achieving highperformance,high-reliability, and high-temperature interconnection of small devices (〈0.09 cm2).In this paper, we report the results of our study to extend the low-temperature sintering technique tolarge-area joints. The study involved redesigning the organic and inorganic components of thenanoscale silver paste, analyzing the burnout kinetics of the various organic species sandwichedbetween large-area plates, and developing desirable temperature-time profile to improve sinteringand bonding strength of the joints