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Intermetallic-layer formation and growth in Pb-free solder joints, during solder reflow or subsequent aging, has a significant effect on the thermal and mechanical behavior of solder joints. In this study, the influence of initial intermetallic morphology on growth rate, and kinetics were examined in a Sn-3.5Ag solder reflowed on Cu. The initial morphology of the intermetallic was tailered by cooling in water, air, or furnace conditions. Solder aging was conducted at 100°C, 140°C, and 175°C and aged for 0-1,000 h. Cooling rate, aging temperature, and aging time played an important role on microstructure evolution and growth kinetics of Cu 6 Sn 5 (η) and Cu 3 Sn (ε) intermetallic layers. Prior to aging, faster cooling rates resulted in a relatively planar Cu 6 Sn 5 layer, while a nodular Cu 6 Sn 5 morphology was present for slower cooling. Intermetallic-growth rate measurements after aging at various times, indicated a mixed growth mechanism of grain-boundary and bulk diffusion. These mechanisms are discussed in terms of the initial intermetallic thickness and morphology controlled by cooling rate, diffusion kinetics, and the competition between Cu 6 Sn 5 and Cu 3 Sn growth.

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One method used to examine the relationship between behavioral strategies and anatomical adaptation is to study the results of mechanical stress associated with a given behavior and compare this with skeletal adaptations to other behaviors. This comparative approach is appropriate for highlighting combinations of features that are specializations to specific types of behavior. The purpose of this paper is to compare femoral mechanics in Galago senegalensis with previously collected data for macaques and humans as a basis for discussing structural adaptations in the primate hindlimb to leaping. The stiffness and load carrying capabilities of the femoral diaphyses of 27 G. senegalensis were analyzed using the SCADS computer program. The data suggest that the galago femur is well adapted to sustain large sagittal plane compressive loads rather than large bending loads. The straightness of the femoral shaft and large midshaft area moments of inertia prevent buckling from these large compressive loads. Calculations indicate that the ratio of critical buckling load to body weight in galago is 31 times that in macaques and 55 times that in humans. The femur of this saltatory primate is morphologically adapted to resist buckling when subjected to large compressive loads, while those of macaques and humans are better adapted to resist bending moments caused by ground reaction forces acting on the extended limb. The differences between galago on the one hand and macaques and humans on the other suggest that relatively smaller moments about the hip and relatively larger moments about the knee accompany more quadrupedal and bipedal walking, while habitual leaping is associated with relatively larger moments about the hip. These data reinforce the apparent similarity of the mechanical effects of quadrupedal and bipedal locomotion on the femur and dissimilarity with femoral mechanics in habitually saltatory primates.