Interfacial Microstructure and Mechanical Reliability of Sn-58Bi/ENEPIG Solder Joints

Cheng Chen,Cheng Wang,Hengxu Xue,Hongbo Yin,Dahai Ni,Huhao Sun,Qilin Gu,Xiuli Gao,Kan Bian

doi:10.3390/pr10020295

Abstract

The 42 wt.% Sn–58 wt.% Bi (Sn-58Bi) Ball Grid Array (BGA) solder balls were mounted to electroless nickel-electroless palladium-immersion gold (ENEPIG) pads by employing the reflow process profile. The effects of reflow cycles and aging time on the interfacial microstructure and growth behavior of intermetallic compounds, as well as the mechanical properties, were investigated. Pd-Au-Sn intermetallic compound (IMC) was formed at the Sn-58Bi/ENEPIG interface. With the increase in reflow cycles and aging time, the IMC grew gradually. After five reflow cycles, the shear strength of the Sn-58Bi/ENEPIG solder joints first decreased and then increased. After 500 h of aging duration under −40 °C, the shear strength of the Sn-58Bi/ENEPIG solder joints decreased by about 12.3%. The fracture mode transferred from ductile fracture to ductile and brittle mixed fracture owing to the fact that the fracture location transferred from the solder matrix to the IMC interface with the increase in reflow cycles and aging time.

Highlights

The eutectic Sn-37Pb solder is an important material in the field of electronic packing because of its excellent wettability, electronic conductivity and mechanical properties [1,2].due to the threat of lead to the human body and the environment, lead-free solder has become the development direction in the electronic industry with the restriction of hazardous substances (RoHs) [3,4]
A continuous flake-type intermetallic compound (IMC) layer with a thickness of 1–3 μm was formed at the Sn58Bi/electroless nickel-electroless palladium-immersion gold (ENEPIG) interface
energy-dispersive spectroscopy (EDS) was further carried out to analyze the interfacial reactions between the Sn–58 wt.% Bi (Sn-58Bi) solder ball and ENEPIG finish

Summary

Introduction

The eutectic Sn-37Pb solder is an important material in the field of electronic packing because of its excellent wettability, electronic conductivity and mechanical properties [1,2].due to the threat of lead to the human body and the environment, lead-free solder has become the development direction in the electronic industry with the restriction of hazardous substances (RoHs) [3,4]. The eutectic Sn-37Pb solder is an important material in the field of electronic packing because of its excellent wettability, electronic conductivity and mechanical properties [1,2]. Sn–Ag, Sn–Zn, Sn–Ag–Cu and Sn–Bi alloys are developed in order to reach or approach the properties of the eutectic Sn-37Pb solder [5,6,7,8]. This solder possesses good creep resistance and high tensile strength [9]. It can avoid warpage in printed circuit boards (PCBs) and electronic components due to thermal mismatch during the soldering process [10]

Methods

Results

Conclusion