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Bare copper wire bond in ultra fine pitch application pose high challenge during reliability stress especially reliability test that involved high temperature and humidity stress such as Highly Accelerated Temperature/Humidity Stress Test (HAST). Electrical open failure is the common problem encountered after HAST test due to IMC separation that induced during corrosion process with the presence of moisture and halogen ion [1,2]. At the same time, bare copper by itself, an easily oxidized material compare to gold and palladium coated copper wire, has become another challenge during manufacturing process as post bond related stoppages such as short tail or missing ball problem become manufacturability issue and affect production output [3]. Therefore, great characterization efforts are required to focus on wire, capillary and manufacturing control to define optimum operating window for bare copper wire bond on ultra fine pitch process in terms of reliability and manufacturability. |
