Effect of Current Densities on the Electromigration Failure Mechanisms of Flip-Chip Sn-Ag Solder Bump

摘要

The effect of current densities on the electromigration (EM) failure mechanism of flip chip Cu/Ni/Sn-Ag/Cu solder bumps was investigated under stressing conditions at current densities ranging from 5.0 similar to 6.9 x 10(3) A/cm(2) at 150 degrees C. The EM failure times at 5.0 x 10(3) A/cm(2) were around 11 times longer than at 6.9 x 10(3) A/cm(2). A systematic failure analysis considering stressing time showed that a current density of 5.0 x 10(3) A/cm(2) induced pancake void propagation near the Cu6Sn5 intermetallic compound/solder interface at the cathode, while a current density of 6.9 x 10(3) A/cm(2) produced severe Joule heating due to high current crowding near the solder/Cu6Sn5 interface. This was due to electrons entering the location at the cathode, which led to local melting of the solder and fast Cu consumption. It was determined that the EM failure mechanisms of flip chip Sn-Ag solder strongly depend not only on the Ni barrier effect but also on current density, which drives the dominant failure mechanisms of pancake voiding and local Joule-heating melting.