To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The possibility of improving the welfare of fattening rabbits by rearing them in pens instead of cages was investigated. Time budgets, locomotion, ear lesions, breaking strength of the femur and productivity were compared in fattening rabbits kept at the same stocking density (15 rabbits m−2) either in standard cages of 0.4m2 (6 animals) or in pens of 1.6m2 (24 animals). Behavioural observations, performed by video recording at 6 and 9 weeks of age, indicated that the frequency of rabbits walking over one another was higher in cages than in pens at 9 weeks of age. Although the time spent in locomotion did not differ significantly, the number of consecutive hops performed by animals was clearly increased in pens at 6 weeks and tended to be higher at 9 weeks. In pens (without a ceiling), rabbits were observed ‘keeping watch’ with a characteristic fully upright posture; this was not possible for rabbits in cages (with ceilings at 30cm).
Ear lesions were more frequent in caged rabbits than in penned; this might be due to the caged rabbits walking on one another, due to the lack of space to perform locomotory behaviour. Weight, diameter and breaking strength of femur tended to increase in rabbits kept in pens. In penned rabbits, body and carcase weight were significantly reduced (by 2.0% and 3.4% respectively) when compared with caged ones. However, overall, the use of wire-floor pens of 1.6m2, housing 24 animals, was considered to be beneficial to fattening rabbits’ welfare when compared to standard-sized cages holding 6 animals.
A single printed circuit board includes thousands, sometimes even hundreds of thousands, of solder joints. The failure of even a single solder joint is usually enough to compromise the functionality of an electronic device or system. PbSn solder had been the standard ma te rial for these joints until various regulations around the world began to limit Pb use. SnAgCu and related alloys are quickly replacing PbSn, but much still needs to be understood and controlled. None of the paradigms for understanding the mechanical response of PbSn alloys is applicable to lead-free alloys. Much of the surprising behavior of SnAgCu solder arises from the complex and fascinating nature of its solidification behavior. In this ar ticle, the impact of solidification on the microstruc ture and therefore the mechanical properties of these solder joints will be addressed in the context of microelectronics proc essing. The need for better simulations of SnAgCu solder behavior will also be examined. Notably, modelers will have to account for a variety of new parameter dependencies not previously considered.
During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.
Capillary flows of dense, model suspensions and industrial underfill encapsulants are investigated. Flow behavior is characterized by measuring the infiltration rate of an encapsulant or model suspension into a channel formed by parallel surfaces. A capacitance measurement technique is used to track the advancement of the front. Significantly this technique allows the channel surfaces to be formed from opaque materials such as those that found in the principal industrial application of electronics packaging. A scaling law to describe the functional dependence of the front position on channel spacing, surface tension and viscosity is presented.
In flip-chip packaging an underfill mixture is placed into the chip-to-substrate standoff created by the array of solder bumps, using a capillary flow process. The flow behavior is a complex function of the mixture properties, the wetting properties, and the flow geometry. This paper reports on the use of a plane channel capillary flow to characterize underfill materials. The measured flow behavior provides evidence that both the contact angle (θ) and the suspension viscosity (μapp) vary with time under the Influence of changing flow conditions. This nonlinear fluid behavior is modeled for the flow of both model suspensions and commercial underfill materials using an extended Washburn model.
The kinetics of the formation of Cu3Si in Cu/a-Si diffusion couples have been investigated by means of differential scanning calorimetry and x-ray diffraction. Multilayered composites of average stoichiometry Cu3Si were prepared by sputter deposition with individual layer thicknesses varying in different samples between 2 and 100 nm. We observed diffusion limited growth of Cu3 Si upon annealing these diffusion couples below 500 K. Reaction constants were measured for a temperature range of 455 to 495 K for thicknesses of growing Cu3Si between 2.6 and 80 nm. The temperature dependence of the reaction constant, k2, was characterized as k2 = k0 exp(− Ea/kbT) with activation energy, Ea = 1.0 eV/atom and pre-factor, k0 = 1.9×10−3 cm2/s.
Underfill encapsulants, used in direct‐chip‐attachment (DCA) packaging of electronics, consist of an epoxy resin in which a high concentration of solid particles are suspended. As a fluid mixture key features of these encapsulants are their relatively large particle sizes and large particle‐to‐liquid density ratios (ρs/ρ0 ?2.4). Experiments have been conducted to characterize the flow behavior of model mixtures of negatively buoyant, spherical particles suspended in Newtonian liquids. Capillary flow in a parallel surface channel is used to simulate the underfill flow process. The effects of varying the channel spacing, particle size and liquid carrier are reported here. The flow behavior is contrasted with a linear fluid, effective viscosity model. Particle settling appears to be linked to the more complex behavior observed in both our model suspensions and measurements using an actual commercial encapsulant.
We find differential scanning calorimetry to be suitable for the characterization of the energetics and kinetics of interdiflusion in solder/metal diffusion couples. Differential scanning calorimetry studies of interdiffusion in Cu/Cu6Sn5 diffusion couples have shown that the driving force for interdiffusion is similar for thin film composites and for bulk diffusion couples. The heat of formation of Cu3Sn from Cu6Sn5 and Cu thin films was found to be ΔHr = −4.3 + 0.3 kJ/mol. Portions of our differential scanning calorimetry scans are identified with diffusion limited growth of Cu3Sn. From these calorimetry data we have estimated D(cm2 / s) = Do exp(−E / kbT), where kb is Boltzmann's constant, D0 = 3.2 × 10–2 cm2/s, and E=0.87 eV/atom.
Using differential scanning calorimetry, supplemented by measurements from scanning electron microscopy images, we have investigated solid state reactions in Pd/Sn multilayer composites to form PdSn4 and PdSn3. Planar diffusion couples of Pd and Sn were prepared by means of mechanical co-deformation in a rolling mill. A phase formation sequence was determined using differential scanning calorimetry and x-ray diffraction. Growth of the PdSru phase was studied from room temperature to the melting point of Sn. For temperatures between 430 and 460K diffusion limited growth of PdSn4 was observed. From heat flow data over this limited temperature range, the form of the reaction constant was found to be k2 −k0 exp(−Ea / kbT), where k0= 0.16 cm2/s and Εn= 0.8 eV/atom. Also determined was a heat of formation, ΔHf = −27±1 kJ/mol for PdSn4 from Pd and Sn.
The mechanisms of metallic glass formation and competing crystallization processes in mechanically-deformed Ni-Zr multilayered composites have been investigated by means of differential scanning calorimetry and x-ray diffraction. Our investigation of the heat of formation of amorphous NixZr1−x alloys shows a large negative heat of mixing (on the order of 30 kJ/mole) for compositions near Zr55Ni45 with a compositional dependence qualitatively similar to that predicted by mean field theory. We find that the products of solid state reactions in composites of Ni and Zr can be better understood in terms of the equilibrium phase diagram and the thermal stability of liquid quenched metallic glasses. We have determined the composition of the growing amorphous phase at the Zr interface in these Ni-Zr diffusion couples to be 55 ± 4% Zr. We investigated the kinetics of solid state reactions competing with the solid state amorphization reaction and found the value of the activation energy of the initial crystallization and growth of the growing amorphous phase to be 2.0 ± 0.1 eV, establishing an upper limit on the thermal stability of the growing amorphous phase.
Differential scanning calorimetry and x-ray diffraction analysis were utilized to monitor solid state reactions in mechanically deformed Ni/Ti multilayered composites. Solid state reactions at temperatures less than = 650 K result in the formation of a highly disordered phase which is apparently amorphous.The subsequent nucleation and growth at higher temperatures of intermetallic compounds from the amorphous phase is examined. The relatively small thickness of amorphous material (less than 100 Å) which can be grown by solid state reaction in our Ni/Ti samples, combined with the indication that a disordered interface such as that produced by mechanical deformation facilitates these reactions in the Ni-Ti system, may provide some explanation for the relatively high degree of success experienced in the production of amorphous Ni- Ti by means of ball milling. Comparisons are made to results obtained in the Ni-Zr system.
Amorphous Zr–Rh and Zr–Pd hydrides are prepared both by hydriding metallic glasses and by hydriding metastable, polycrystalline fcc alloys. The thermal stabilities of the amorphous hydrides produced by these two distinct methods are examined by means of differential scanning calorimetry and are found to be similar. The enthalpy difference between the fcc phase and the amorphous phase of Zr81Rh19 is determined to be 0.6 kcal/mol. The thermal stability of Zr–Rh hydrides as a function of hydrogen concentration is investigated.
Differential scanning calorimetry and X-ray diffraction have been utilized to monitor the solid state amorphization reaction in crystalline Ni/Zr multilayers. Enthalpy of mixing of amorphous NiZr alloys has been measured. Kinetics of amorphous phase formation and thermal stability have been discussed in some detail.
Email your librarian or administrator to recommend adding this to your organisation's collection.