Bismuth redistribution induced by intermetallic compound growth in SnBi/Cu microelectronic interconnect

It was found that Bi particles, with a diameter of 100 nm, precipitated along Cu3Sn/Cu interface and Bi crystallites dispersed in Cu3Sn layer in 42Sn58Bi/Cu microelectronic interconnect, when it was aged at 120 °C for 7 days. The mechanism for Bi redistribution like this was discussed. Cu6Sn5 turned into Cu3Sn by Cu diffusion that is dominant in Sn/Cu inter-diffusion during the aging process. Bi precipitation occurred in Cu3Sn due to lower Bi solubility in Cu3Sn than that in Cu6Sn5. The Bi precipitates can traverse the formed Cu3Sn quickly toward the Cu3Sn/Cu interface, attributed to the Kirkendall effect. They stayed and nucleated there to form particles, owing to their unwettability on Cu. The formed Cu3Sn got oversaturated with Bi, when the joint cooled from 120 °C to room temperature. Then Bi crystallites precipitated dispersedly in Cu3Sn layer.

[1]  C. Mcmahon,et al.  Grain boundary segregation and transformations in Bi-doped polycrystalline copper , 1989 .

[2]  I. Sakamoto,et al.  Whisker test methods of JEITA whisker growth mechanism for test methods , 2005, IEEE Transactions on Electronics Packaging Manufacturing.

[3]  P. Vianco,et al.  Intermetallic compound layer formation between copper and hot-dipped 100In, 50In-50Sn, 100Sn, and 63Sn-37Pb coatings , 1994 .

[4]  H. Müllejans,et al.  Bismuth segregation at copper grain boundaries , 1999 .

[5]  Zhi-Quan Liu,et al.  Bi-induced voids at the Cu3Sn/Cu interface in eutectic SnBi/Cu solder joints , 2008 .

[6]  J. W. Morris,et al.  Analysis of low-temperature intermetallic growth in copper-tin diffusion couples , 1992 .

[7]  King-Ning Tu,et al.  Interdiffusion and Reaction in Bimetallic Cu-Sn Thin Films , 1973 .

[8]  R. P. Grant,et al.  Intermetallic compound layer growth by solid state reactions between 58Bi-42Sn solder and copper , 1995 .

[9]  G. Lucey,et al.  The growth of Cu-Sn intermetallics at a pretinned copper-solder interface , 1992 .

[10]  J. Shang,et al.  Segregant-induced cavitation of Sn/Cu reactive interface , 2005 .

[11]  K. Tu.  Cu/Sn interfacial reactions: thin-film case versus bulk case , 1996 .

[12]  King-Ning Tu,et al.  Kinetics of interfacial reaction in bimetallic CuSn thin films , 1982 .

[13]  J. Shang,et al.  Interfacial embrittlement by bismuth segregation in copper/tin–bismuth Pb-free solder interconnect , 2001 .

[14]  Lawrence H. Bennett,et al.  Binary alloy phase diagrams , 1986 .

[15]  Tomi Laurila,et al.  Interfacial reactions between lead-free solders and common base materials , 2005 .

[16]  J. Shang,et al.  Interfacial segregation of bismuth in copper/tin-bismuth solder interconnect , 2001 .

[17]  Michael W. Finnis,et al.  Bismuth embrittlement of copper is an atomic size effect , 2004, Nature.

[18]  K. Tu,et al.  Tin–lead (SnPb) solder reaction in flip chip technology , 2001 .

[19]  M. Abtew,et al.  Lead-free Solders in Microelectronics , 2000 .

[20]  M. Sui,et al.  Novel Crosslinking of High‐order and Multiple Copper Twins in Advanced Microelectronics Packaging , 2004 .