Review on test vehicles for electromigration (EM) study in solder interconnects

The reliability of electronic devices faces the challenges of potential open and short failures due to electromigration (EM) in integrated circuit. This issue is becoming more severe at the background of further miniaturization in solder joint size and higher current carried by solder joint. Various test vehicles have been put forward for EM study. This work summarized the EM test vehicles according to the fabrication complexity and development history, and sorted into four categories: flip chip (FC) interconnect, wire-type interconnect, thin-film interconnect and liquid-phase interconnect. The advantages and disadvantages of these typical test vehicles are carefully compared. Due to the mature process, the test vehicles with FC interconnect can be fabricated with solder joints in uniform size. However, the unique geometric asymmetry induces serious current crowding in the entrance and exit of the joint. The test vehicles with wire-type interconnect are often limited in miniaturizing the dimensions due to the mechanical process in fabricating wires. The thin-film interconnect can adjust the dimensions by controlling the electroplating time, wherever the time to prepare the test vehicle can be much longer. A multi-lines thin-film test vehicle has been proposed to study the effect of EM on the microstructure evolution as well as the lifetime prediction. The liquid phase interconnect with synchrotron radiation facility provides real-time and in-situ observation of EM effect.