3D Microelectronic Packaging by Yan Li & Deepak Goyal

Author:Yan Li & Deepak Goyal
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Wei et al. [32] studied the EM behavior in Sn-Cu IMCs using edge displacement method as shown in Fig. 9.9. They found Cu6Sn5 is more susceptible to EM than Cu3Sn, which is related to the lower solidus temperature and higher resistivity of Cu6Sn5. They also observed Blech effect in the strips of various length of IMCs. The critical product for Cu6Sn5 IMCs is between 2.5 and 5 A/cm at 225 °C. Just as typical EM fails, voids are formed at cathode side interface where the atomic flux divergence is present. However, the predominant diffusion specie could not be determined in their report because no Cu-rich or Sn-rich areas are found under SEM/EDS examinations after EM testing. The critical product for Cu6Sn5 IMC cannot be directly compared with solder critical products listed in Table 9.1 since big temperature difference. It is expected IMCs should have much higher critical product than Pb-free solders at the same temperature because all the studies indicate that solder joint EM can be dramatically improved once a full IMC joint is formed [30, 31].

Fig. 9.9SEM images shows Cu6Sn5 EM damages at the cathode side of interface where flux divergence is present [32]

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