Journal
JOURNAL OF ELECTRONIC MATERIALS
Volume 47, Issue 1, Pages 35-48Publisher
SPRINGER
DOI: 10.1007/s11664-017-5685-4
Keywords
Electromigration; copper-tin intermetallic formation; lead-free solder diffusion; stress effects; intermetallic aging; current density of metal films
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Funding
- Taiwanese Ministry of Science and Technology [MOST 104-2221-E-005-009-MY2]
- country's Ministry of Education under the ATU plan
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This study investigated the effects of electric current and external stress on electromigration of intermetallic compounds (IMC) between solder and copper substrate. Different samples were tested under three different sets of conditions: (1) thermal aging only, (2) thermal aging with electric current ,where resistivity changes were measured using four-point probe measurements, (3) thermal aging with electric current and external stress provided using a four-point bending apparatus. The micro-structural changes in the samples were observed. The results were closely examined; particularly the coupling effect of electric current and external stress to elucidate the electromigration mechanism, as well as the formation of IMC in the samples. For thermal-aging-only samples, the IMC growth mechanism was controlled by grain boundary diffusion. Meanwhile, for thermal aging and applied electric current samples, the IMC growth mechanism was dominated by volume diffusion and interface reaction. Lastly, the IMC growth mechanism in the electric current and external stress group was dominated by grain boundary diffusion with grain growth. The results reveal that the external stress/strain and electric current play a significant role in the electromigration of copper-tin IMC. The samples exposed to tensile stress have reduced electromigration, while those subjected under compressive stress have enhanced electromigration.
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