To Study the High Temperature Effects on Ball Bonds Using Low K Material in Wire Bond Devices

Wire bonding is widely used as one of the main interconnect alternatives. This technique applies significant mechanical stresses on the bond pads along with heat and ultrasonic energy to form a bond. An interconnection of copper plus low k material has been a focus of the semiconductor industry with the goal of reducing interconnection delays. The material is below the wire bond pads and complicates the mechanical stability of the device during wire bonding. The low k materials that are suggested are very sensitive to these mechanical stresses. This generates a significant reliability concern for the underlying metal structures. In addition, the integrity of the bond formed may be negatively impacted from a reliability perspective because of the softer material properties of the dielectric. This research explores the ball bond integrity for die with SiO₂ and low k dielectric underlying material respectively, using 0.8 mil thick (20 microns) gold wire. Accelerated tests, such as high temperature storage at 150°C and 175°C, were conducted to assess the reliability of these bonds. The results of this investigation reveal that the ball bond’s strength degrades after high temperature tests due to the occurrence of Kirkendall voids between the gold wire and the aluminum bond pad. The degradation recorded was more severe for regular die than its low k counterpart.