Electric Current Induced Brittle Failure of Eutectic Lead and Lead-free Solder Joints with Electroless Ni-P Metallizatio
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0968-V05-06
Electric Current Induced Brittle Failure of Eutectic Lead and Lead-Free Solder Joints with Electroless Ni-P Metallization Aditya Kumar1,2, Zhong Chen1, C. C. Wong1, S. G. Mhaisalkar1, and Vaidhyanathan Kripesh2 1 School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore 2 Institute of Microelectronics, 11 Science Park Road, Singapore, 117685, Singapore
ABSTRACT The mechanical properties of thermally-aged and electric current-stressed eutectic lead (Sn-37Pb) and lead-free (Sn-3.5Ag) solder joints with electroless Ni-P metallization were investigated using tensile testing. Multi-layered test samples, electroless Ni-P/solder/electroless Ni-P, having two electroless Ni-P/solder interfaces were prepared. Tensile testing results showed that for both types of solder, high density electric current causes the brittle failure of solder joint. The eutectic lead solder joint was found to be more prone to current induced brittle failure compared to the lead-free solder joint. In the eutectic lead solder joint, brittle failure always occurred at the cathode side electroless Ni-P/Sn-37Pb interface (where electrons flowed from NiP to solder), whereas no such polarity effect was observed in the case of lead-free solder joint. INTRODUCTION High I/O density requirements in electronic packaging are shrinking the size of interconnects, leading to increased current density. High current density (~104 A/cm2) causes the electrical failure of solder interconnects due to electromigration [1]. Even at moderate current density (~103 A/cm2), electromigration influences the interfacial compound (IFC) formation in solder joints [2]. In addition, there are a few examples in which electric current has been reported to influence intermetallic formation, precipitation, and recrystallization in different materials [3]. In this study, the effect of electric current has been investigated on the mechanical properties of electroless Ni-P/Sn-3.5Ag and electroless Ni-P/Sn-37Pb solder joints. EXPERIMENT For the investigation, multi-layered test samples, electroless Ni-P/solder/electroless Ni-P, having two electroless Ni-P/solder interfaces were prepared. The electroless Ni-P/Sn-3.5Ag test samples were prepared by plating consecutively electroless Ni-P (~9.9 µm) and immersion Au (~50 nm) on a surface-cleaned Cu plate of size of 70 mm × 25 mm × 6 mm, then cutting the Ni-P coated Cu plate into two plates of sizes of 40 mm × 25 mm × 6 mm and 30 mm × 25 mm × 6 mm, then joining them using Sn-3.5Ag solder wires with the help of reflow process (at 250°C for 60 sec), and finally cutting the joined plates into a number of small test sample as shown in figure. 1. A detailed preparation method of electroless Ni-P/Sn-3.5Ag test sample has been described in our previous work [4]. For electroless Ni-P/Sn-37Pb test sample, preparation
method was the same, but Sn-37Pb solder was used instead of Sn-3.5Ag and the thickness of electroless Ni-P metallization deposited on Cu plate was around 7 µm
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