Thermosonic ball bonding behavior and reliability study of Ag alloy wire

Recently Silver (Ag) wire has drawn attention to the packaging industry because of the bonding quality and long term reliability concerns with the Cu and Pd coated wire. Ag wire has low cost, high thermal and electrical conductivity as compared to Au while their mechanical properties such as hardness, elongation and breaking load are similar to Au. In the present study, free air ball (FAB) formation, bonding behavior and reliability of Ag alloy wire (Ag-Au-Pd) bonding was studied. The careful control of electronic flame off (EFO) current, time and gas flow rate leads to spherical FAB ball formation without defects. The Ag alloy wire delivers good and stable bonding capability using nitrogen as ambient gas. Both the bonded ball and stich bonding show good bond integrity. The reliability is determined by the high temperature storage life test (HTSL) test. Intermetallic compound (IMC) growth behavior during reliability test is characterized by the scanning electron microscopy (SEM) and energy dispersive spectrometer analyses (EDS). Two types of IMCs Ag2Al and Ag3Al were observed. The Ag alloy wire show floor life time of minimum 10 weeks based on bonded ball shape, workability and bondability test.