Electromigration Behaviors and Effects of Addition Elements on the Formation of a Bi-rich Layer in Sn58Bi-Based Solders

• Published in: Journal of electronic materials 2014-11, Vol.43 (11), p.4179-4185
• Main Authors: Zhao, Xu, Saka, Masumi, Muraoka, Mikio, Yamashita, Mitsuo, Hokazono, Hiroaki
• Format: Article
• Language: English
• Subjects: Applied sciences; Boundary layer; Brazing. Soldering; Characterization and Evaluation of Materials; Chemical elements; Chemistry and Materials Science; Condensed matter: structure, mechanical and thermal properties; Diffusion in solids; Electromigration; Electronics and Microelectronics; Exact sciences and technology; High temperature; Instrumentation; Joining, thermal cutting: metallurgical aspects; Materials Science; Metals. Metallurgy; Optical and Electronic Materials; Physics; Soldering; Solid State Physics; Transport properties of condensed matter (nonelectronic)
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-014-3400-2

This study investigates the electromigration (EM) behaviors and effects of the addition elements on the formation of a Bi-rich layer in Sn58Bi-based solders including Sn58Bi (SB), Sn58Bi0.5Ag (SBA) and Sn58Bi0.5Ag0.1Cu0.07Ni0.01Ge (SBACNG) solders. The EM tests were conducted at a relatively high temperature of 373 K and at a current density of 30 kA/cm 2 . Although the dominant diffusing atom was Bi, hillocks were formed from Sn more easily than from Bi. The electrical resistance increased in the solder during the current stressing, and the dominant factor was attributed to the formation of a Bi-rich layer. SBACNG solder showed the highest resistance to the formation of a Bi-rich layer, followed by SBA, and then SB solder. The possible addition elements enhancing the resistance of SBACNG solder are Ag, Ni and Ge. The effects of the addition elements are summarized as follows: (1) Ag distributes in the Sn phase as Ag 3 Sn intermetallic compounds (IMCs) that enhance the mechanical strength of Sn; (2) Ni distribution in Bi as Ni-Bi IMCs stabilizes Bi and suppresses its migration; and (3) Ge may distribute in Bi, stabilizing Bi, or Ge exists at the phase boundaries as a precipitate that inhibits Bi migration.