Peltier effect on CoSn3 growth in Sn/Co/Sn couples with different substrate lengths

• The Peltier effect is significant in Sn/Co/Sn couples under current stressing.
• With increasing Co length, the temperature difference at both interfaces is greater.
• Simulated results are in good agreement with the experimental observations.
• The Peltier effect in the Sn/Ni/Sn and Sn/Cu/Sn couples was also examined.

Interfacial reactions in Sn/Co/Sn couples with different lengths of Co substrate (100 μm–2000 μm) were examined under current stressing of 5000 A/cm2. Uniform CoSn3 layers were formed at both interfaces. Notably, the CoSn3 layer at the Sn/Co cathode side was thinner than that of the Co/Sn anode side. Moreover, with the increase of substrate length, the thickness difference increased. This strong asymmetric CoSn3 growth was attributed to the Peltier effect, rather than electromigration. For the Sn/Co(2000 μm)/Sn case, the temperature difference was as high as ∼14 °C, resulting in that the growth rates significantly differed at both interfaces. Additionally, the simulation model was developed to calculate the temperature difference. The agreement of calculated and experimental values appears to be very well. Furthermore, the Peltier effect on the couples of Sn with Cu and Ni substrates was also studied. Thin Co layers (5 μm) were deposited on the Cu or Ni substrate as temperature indicator. The Peltier effect was negligible in the Sn/Cu system, while the temperature difference in the Sn/Ni system was considerable, about 60% of the Sn/Co system.