The constant pursuit to reduce silicon area, and accordingly silicon cost, continues to drive the bond pad size and pitch down to smaller dimensions as time moves forward. The reduction in bond pad pitch will require a progressive step reduction in wire diameter due to the smaller bonded ball size that is required for the smaller bond pad openings. As the silicon area is reduced, and wire diameters get smaller, the wires are typically getting longer and ever more susceptible to the molding stresses in ball grid array (BGA) packages, especially when multiple BGA's are molded simultaneously using a single cavity on a single substrate. This molding configuration while providing the most cost-effective substrate utilization causes higher wire, sweep, thus increasing the opportunity of adjacent wires shorting to one another and causing device failure.To facilitate a smaller wire diameter in an existing package many things must be analyzed and experiments must be designed. The wire type and diameter, mold compound's formulation, molding process parameters, and wire bond layout design must be carefully considered to account for the increase in wire sweep expected with a smaller diameter wire.The methodology and experimentation used to address the packaging and assembly requirements of a smaller diameter wire will be discussed. The experiments demonstrate that wire type, wire looping profile, mold transfer speed, and mold compound filler size and distribution prove to be significant in reducing wire sweep.

Driven for further silicon reduction, wireless applications utilize Copper interconnection and increase metal layer count from three to five layers. More aggressive ESD structures placed under the bond pads offer a significant opportunity for additional die area and cost reduction. Capping Copper bond pads with Aluminum was selected as the primacy approach for probing and wire bonding Copper devices. There exists an integral relationship between probe damage on the bond pads and the subsequent wire-bondability. As the pad geometry gets smaller, the ratio of the area of probe damage to the bond pad size will get proportionally larger, thereby reducing the available Aluminum necessary to form reliable Gold-Aluminum intermetallic coverage. This paper will describe probe and assembly processes developed for a fine pitch three-metal layer Copper interconnect device with ESD structures placed under bond pads. The relationship between probe conditions and wire-bondability were examined. Ball shear, wire rip and corresponding failure modes were evaluated at various readpoints of thermal aging studies to evaluate the integrity of ball bonds onto the metal stack. Reliability assessment was also performed. Based on the investigations studying the relationship among the pad structures, probe and wire bond quality, recommendations were derived to ensure high quality, stable and reliable bonds for fine pitch wire bonding on multi-layer Copper interconnect devices.

Driven for further silicon reduction, wireless applications utilize copper interconnection and increase metal layer count from three to five layers. More aggressive ESD structures placed under the bond pads offer a significant opportunity for additional die area and cost reduction. Capping copper bond pads with aluminum was selected as the primary approach for probing and wire bonding of copper devices. There is an integral relationship between probe damage on the bond pads and subsequent wire-bondability. As the pad geometry decreases, the ratio of the area of probe damage to the bond pad size becomes proportionally larger, thereby reducing the available aluminum necessary to form reliable gold-aluminum intermetallic coverage. This paper describes probe and assembly processes developed for a fine pitch three-metal layer copper interconnect device with ESD structures placed under the bond pads. The relationship between probe conditions and wire-bondability were examined. Ball shear, wire rip and corresponding failure modes were evaluated at various read points of thermal aging studies to evaluate the integrity of ball bonds to the metal stack. Reliability assessment was also performed. Based on the investigations studying the relationship between the pad structures, probe and wire bond quality, recommendations were derived to ensure high quality, stable and reliable bonds for fine pitch wire bonding on multi-layer copper interconnect devices

Digital visualization of complex boundary layer transition along the concave side of a curved plate under a periodic unsteady flow condition and zero longitudinal pressure gradient is presented in this report. The concave side simulates the pressure surface of a turbine blade with zero degree of reaction. Experimental investigations were carried out on an unsteady flow research facility using a rotating cascade of rods positioned upstream of the curved plate with a zero longitudinal pressure gradient. A specially designed traversing system and hot-wire probe enabled detailed boundary layer measurements that were analyzed by the ensemble-averaging technique. The results presented in the temporal-spatial domain allow clear visualization of the transition phenomenon and further development of the boundary layer, specifically the ensemble-averaged velocity and turbulence intensity. Furthermore, they contribute to better understanding the transition phenomenon, which is essential for development of a comprehensive boundary layer transition model.

Boundary layer transition and development on a turbomachinery blade is subjected to highly periodic unsteady turbulent flow, pressure gradient in longitudinal as well as lateral direction, and surface curvature. To study the effects of periodic unsteady wakes on the concave surface of a turbine blade, a curved plate was utilized. On the concave surface of this plate, detailed experimental investigations were carried out under zero and negative pressure gradient. The measurements were performed on an unsteady flow research facility using a rotating cascade of rods positioned upstream of the curved plate. Boundary layer measurements using a hot-wire probe were analyzed by the ensemble-averaging technique. The results presented in the temporal-spatial domain display the transition and further development of the boundary layer, specifically the ensemble-averaged velocity and turbulence intensity. As the results show, the turbulent patches generated by the wakes have different leading and trailing edge velocities and merge with the boundary layer resulting in a strong deformation and generation of a high turbulence intensity core. After the turbulent patch has totally penetrated into the boundary layer, pronounced becalmed regions were formed behind the turbulent patch and were extended far beyond the point they would occur in the corresponding undisturbed steady boundary layer.