Showing papers by "Paul S. Ho published in 1990"

Effect of Geometry on the Fracture of Metal-Polymer Interfaces

Abstract: The fracture behavior of the Au(Cr)/PMDA-ODA interface was investigated using a stretch deformation method. The study has been focused on thc effects of metal dimension on the delamination behavior, the fracture morphology, and energy dissipation rate of the interface. The delamination behavior shows complex geometrical dependence, with changes observed in the magnitude of strain at failure as well as the progression of the fracture process. The fracture morphology and energy dissipation rate also show apparent dependence on the metal dimensions. The crack growth, as examined by the rate of energy dissipation, seems to consist of thrce stages: crack initiation, crack growth and post growth. Only the growth region exhibits a constant dissipation rate and the fracture energy determined in this stage is in good agreement with that obtained from energy balance. These results can be attributed to the change in the mechanical coupling between the metal and the polymer layers, which was evaluated using a finite element analysis with plastic deformation taken into aiccount.

Measurement of the Triaxial Stress State of Confined Line Structures During Thermal Cycling

Abstract: A method based on the bending beam technique has been developed to measure the mechanical stresses of fine lines confined by a dielectric layer. This method has been employed to determine the thermal stress of AI(2at%Cu) lines passivated by a quartz overlayer between room temperature and 400oC. The effect of quartz confinement was analyzed by matching the thermal strains at the metal/quartz interfaces and imposing a mechanical equilibrium condition on the structure. The analysis enables us to deduce the triaxial stress components of metal and quartz from measurements of the substrate bending parallel and perpendicular to the length direction of the lines. Results of the measurementshow a substantial stress enhancement as a result of the confinement, with the stress level significantly higher than that of a passivatecd blanket film. The magnitude of the stress depends on the line geometry, the layer deposition conditions and the extent of plastic deformation during thermal cycling. Results of this measurement are consistent with those determined using X-ray techniques.

Phase Formation in Cr/Co/Au and Cr/Co/Au/Pb(Sn) Multilayered Structures

Abstract: Thin-film reaction with solder and its influence on stress have been investigated in Cr/Co/Au and Cr/Co/Au/Pb(Sn) structures. Results from X-ray analysis and RBS measurements reveal that without the Pb(Sn) layer the dominant reaction occurs by interdiffusion of Co and Cr followed by the reaction of Cr and Au. In contrast, the addition of the Pb(Sn) layer leads to a rapid dissolution of Au into Pb, which is followed by subsequent reaction of Co and Sn. In this reaction the intermetallic phases CoSn and CoSn2 are formed. These material reactions are correlated with measurements of the mechanical stresses of the multilayer structure during annealing which were carried out using a bending beam method. The overall reaction scheme of the multilayer structure and the individual reaction kinetics are discussed.

Stress development, intermetallic phase formation, and reaction kinetics in Co-Cr and Co-Ti thin films

Abstract: The stress generated during thermal cycling of electron‐beam‐evaporated Cr‐Co and Ti‐Co films on quartz substrates was measured by means of the cantilever bending‐beam technique between 20 and 550 °C. The thickness ratio was selected to correspond to an atom ratio of [Co]/[Cr] and [Co]/[Ti]>3. In the unreacted films, the residual stress after cycling is tensile and comparable with that in pure Co. In Co‐Cr films there is only a slight increase in stress after complete reaction, whereas a marked increase in tensile stress is observed in Co‐Ti films. Phase formation and reaction kinetics were investigated by Rutherford backscattering and x‐ray diffraction. The dominant phases in Co‐Cr are solid solutions of Cr in Co and Co in Cr with the same structure as the original films. In Co‐Ti the main reaction product is the intermetallic compound Co3Ti with the Cu3Au structure. The formation of Co3Ti, which is accompanied by volume shrinkage, is diffusion controlled. The high activation energy of 2.4±0.2 eV suggest...