Influence of Interfacial Intermetallic Growth on the Mechanical Properties of Sn-37Pb Solder Joints under Extreme Temperature Thermal Shock

Chunjin Hang,Ruyu Tian,Yanhong Tian,Liyou Zhao

doi:10.3390/app8112056

Abstract

Solder joints in thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments during deep space exploration. In this study, extreme temperature thermal shock test from −196 °C to 150 °C was performed on quad flat package (QFP) assembled with Sn-37Pb solder joints to investigate the evolution and growth behavior of interfacial intermetallic compounds (IMCs) and their effect on the pull strength and fracture behavior of Sn-37Pb solder joints under extreme temperature environment. Both the scallop-type (Cu, Ni)6Sn5 IMCs at the Cu lead side and the needle-type (Ni, Cu)3Sn4 IMCs at the Ni-P layer side changed to plane-type IMCs during extreme temperature thermal shock. A thin layer of Cu3Sn IMCs was formed between the Cu lead and (Cu, Ni)6Sn5 IMC layer after 150 cycles. The growth of the interfacial IMCs at the lead side and the Ni-P layer side was dominated by bulk diffusion and grain-boundary diffusion, respectively. The pull strength was reduced about 31.54% after 300 cycles. With increasing thermal shock cycles, the fracture mechanism changed from ductile fracture to mixed ductile–brittle fracture, which can be attributed to the thickening of the interfacial IMCs, and the stress concentration near the interface caused by interfacial IMC growth.

Highlights

IntroductionThe formation and growth of intermetallic compounds (IMCs) at interface between the solder and the substrate are inevitable during soldering and processing [4,5]
During space exploration, thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments with large temperature variations, such as under the condition of Moon (−180 ◦ C to 150 ◦ C), Mars (−140 ◦ C to 20 ◦ C) and Giant Planets (−140 ◦ C to 380 ◦ C) [1].Solder joints provide mechanical support and electrical connection in microelectronic assemblies, the performance and quality of solder joints are vital to the overall functioning of microelectronic assemblies [2,3].The formation and growth of intermetallic compounds (IMCs) at interface between the solder and the substrate are inevitable during soldering and processing [4,5]
In our previous study [9], we found that the fast growth of interfacial IMCs in Sn-3Ag-0.5Cu solder joints was responsible for the early formation of cracks at the

Summary

Introduction

The formation and growth of intermetallic compounds (IMCs) at interface between the solder and the substrate are inevitable during soldering and processing [4,5]. The evolution and growth of interfacial IMCs significantly affect the mechanical properties and reliability of solder joints due to the intrinsically brittle nature of IMCs [6,7,8]. In our previous study [9], we found that the fast growth of interfacial IMCs in Sn-3Ag-0.5Cu solder joints was responsible for the early formation of cracks at the. Sn-3Ag-0.5Cu solder/IMC layer interface under extreme temperature thermal shock from −196 ◦ C to 150 ◦ C, and the growth of interfacial IMCs and crack formation at the IMC layer/solder interface led to the reduction in pull strength of Sn-3Ag-0.5Cu solder joints.

Methods

Results

Conclusion