The developed bonding process utilizes AuSn solder and provides liquid-proof sealing and multiple reliable electrical connections between the bonded wafers. The bond can withstand 300ºC and features a thin bond line (2-3 µm), high bond strength, excellent bond gap control, and low stress due to small amount of bonding material. A Nb/Au seed layer was shown to be an optimal adhesion and barrier film.
Many attempts have been made to understand the problem of transverse cracking in continuous casting process. Much of this research has involved the study of hot ductility using 'conventional' isothermal hot ductility testing. In these tests, the specimens were isothermally tensile tested to fracture, at temperatures achieved by cooling from a solutionizing temperature, close to the solidus, or above the liquidus. These studies showed that hot ductility at the test temperature is highly depended on the thermal path followed by the specimens. The thermal histories experienced by strands during continuous casting were found to be quite complex and invariably involve rapid cooling and heating cycles. This may therefore lead to high thermal gradients, which, in turn, can generate strains in the surface of the solidifying strand. This then may alter the microstructural evolution of the strand surface and the corresponding hot ductility, a possibility that has not been addressed in any previous studies. Thus, the purpose of this study was to consider the effect of the thermomechanical history on the hot ductility of steel.After in-situ melting and solidification, Nb-Ti microalloyed tensile specimens were subjected to a thermal history typical of a continuously cast billet. Different degrees of deformation were imposed on the specimens at selected stages of this thermal history, before tensile testing to fracture point at the time and temperature corresponding to the unbending stage of the billet casting. It was found that the hot ductility varied from 1 to 98 %, depending on the stage in the thermal history at which deformation was executed. The microstructural evolution during the thermomechanical profile was followed to study the effect of thermomechanical history on the hot ductility.
Pressure non-uniformity in a wafer to wafer bond chamber was characterized using pressure sensitive paper. The effect of poor pressure uniformity is discussed, and the nonuniformity was corrected for use in a eutectic Au/Sn based wafer-to-wafer bond. Several types of under solder metallization were also investigated, with Nb/Au seed metal providing the best overall result with good solder compression, liquid proof seal, and minimal solder spill-out. Thirdly, solder compression versus pressure applied was studied to achieve an excellent gap control (2-3 µm) between the bonded substrates.
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