Electromigration testing of wire bonds

Wire bonding is the dominant first-level interconnection technology for packaging of microelectronics. This paper presents the results of testing silver and gold wire bonds for electromigration with substrate temperatures from 100 degrees Celsius to over 200 degrees Celsius. Wire resistances were measured during testing, and, following testing, the wires were imaged by optical and scanning electron microscopy. Silver wires withstood 4 × 10⁵ amperes per square centimeter for 180 hours at a peak temperature of 190 degrees Celsius without detectable damage. For the same current density, gold wires showed surface cracking and a small increase in the resistance of one wire after 330 hours of testing at a peak temperature of 350 degrees Celsius. For a current density of 2.5 × 10⁵ amperes per square centimeter and peak temperatures above 600 degrees Celsius, silver wires showed severe distortion from electromigration along grain boundaries, followed by open circuit failures after between 35 and 50 hours of testing.