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

Abstract

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 Sn58Bi0.5Ag0.1Cu0.07-Ni0.01Ge (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.

Research Overview on the Electromigration Reliability of SnBi Solder Alloy

“…The coarsening of the microstructure in the solder joint can be attributed to two main factors. In the eutectic solder system of Sn–58Bi, the driving force for Bi coarsening is the reduction of specific interfacial energy at grain boundaries or Sn–Bi interfaces [ 30 ]. At lower current densities, the growth mechanism of the Bi phase is primarily controlled by dislocations.…”

Physical properties of Sn58Bi–xNi lead-free solder and its interfacial reaction with copper substrate

“…Ag, Al, Co, Ga, Ge, In, Ni, Sb, Ti, Zn into a solder is a useful technique to improve the physical properties of the solder. Although these elements could improve certain properties of the solder, they could undesirably alter some properties of the alloy, and different alloying elements react variedly to different solder alloys [10][11][12][13][14][15][16][17][18][19][20][21].…”