Abstract
SAC 305 solder bump with 800 μm diameter were produced and soldered to a custom substrate with Cu lines as leads that allow for resistance measurement during current aging. The measured joint resistance values (leads plus solder bump) before aging are 7.7 ± 1.8 mΩ and 11.8 ± 2.8 mΩ at room temperature and 160°C, respectively. In general, the resistance of the solder joint increases instantly by about 1 mΩ, when subjected to a 2.2 A aging current at 160°C. The increase is gradual in the following hours of aging and more drastic as it approaches the final failure. Four stages are identified in the resistance signal curve and compared with observations from cross sections. The stages are IMC growth, crack formation and propagation, intermittent crack healing-forming, and final failure resulting in an open connection at the cathode. Recently a periodical drop and rise behavior was reported for the resistance signal. This behavior is reproduced and attributed to the intermittent crack healing-forming stage. The healing events observed are faster than the sampling time. Possibly, as current is concentrated when bypassing interfacial cracks, local melting occurs partially filling cracks before resolidifying.
| Original language | English |
|---|---|
| Pages (from-to) | 1078-1084 |
| Number of pages | 7 |
| Journal | Electronic Materials Letters |
| Volume | 11 |
| Issue number | 6 |
| DOIs | |
| State | Published - 1 Nov 2015 |
Keywords
- Sn-Ag-Cu solder
- electrical current aging
- electromigration
- four wire method
- in situ monitoring