Electro- and thermomigration-induced IMC formation in SnAg3.0Cu0.5 solder joints on nickel gold pads

• AC stress tests on SnAgCu bumps on Ni/Au contact pads.
• Electromigration driven Ni3Sn4 formation process in Cu containing lead free solders.
• Material parameters for the quantification of the Ni3Sn4 and (CuNi)6Sn5 formation.
• Long- and short-term temperature storage investigations of the (CuNi)6Sn5 formation.
• Current crowding effects on the (CuNi)6Sn5 formation during electromigration test.

The progress in three dimensional packaging leads to smaller solder joints. A growing part of their volume consists of IMCs (intermetallic compounds). The IMCs are formed through migration processes during the soldering. These phenomena continue during use of the component. As a consequence micro bumps (ø < 30 μm) completely consist of intermetallic compounds. Intermetallic compounds also enable electromigration induced void formation at the contacts surfaces of flip chip solder joints. It is essential for the fabrication of micro bumps and for the investigation of failure mechanisms in flip chip solder joints to characterize the migration-induced IMC formation. This study is based on the combination of electromigration, thermomigration and temperature storage tests on SnAg3.0Cu0.5 solder joints with NiAu pads. For the investigation of migration processes due to temperature gradients (thermomigration), alternating current tests for solder joints were developed. Finally, more accurate material parameters for the description of the migration-induced intermetallic compound formation are extracted, namely the activation energy (EA), the diffusion constant (D0), the effective charge of the moving ions (Z*) and the heat of transport (Q*).