Wetting and Interfacial Chemistry of Sn-Zn-Ga Alloys with Cu Substrate

Tomasz Gancarz,Przemyslaw Fima

doi:10.1007/s11665-016-2029-0

Abstract

Wetting of Cu pads by Sn-Zn eutectic-based alloys with 0.1, 0.2, 0.5, and 1.0 wt.% of Ga was studied using the sessile drop method in the presence of ALU33® flux. Wetting tests were performed at 250 °C after 60, 180, 480, 900, 1800, and 3600 s of contact, and at 230, 280, 320 °C for a contact time of 480 s. After cleaning the flux residue from solidified samples, the spreadability of Sn-Zn-Ga on Cu was determined in accordance with ISO 9455-10:2013-03. Selected, solidified solder-pad couples were cross-sectioned and subjected to scanning electron microscopy with energy dispersive spectroscopy and x-ray diffraction study of the interfacial microstructure. Growth of the intermetallic Cu5Zn8 and CuZn4 phase layers was studied at the solder-pad interface. Samples after spreading test at 250 °C for 60 s were subjected to aging for 1, 10, and 30 days at 170 °C.

Highlights

Sn-Zn-based alloys are a group of alloys of particular interest as Pb-free solders in the electronics industry
We investigated the effect of temperature and extended time of contact on the spreading areas of Sn-8.9Zn-xGa alloys (x = 0.1, 0.2, 0.5, 1.0 wt.%) on the Cu substrate, and on the interfacial microstructure of Sn-8.9Zn-xGa/Cu joints
When comparing the results of spreading area, it is important to remember that the spreading areas reported in Ref 10 were determined after 30 s, while the results presented in this paper (Fig. 1b) were determined after 480 s

Summary

Introduction

Sn-Zn-based alloys are a group of alloys of particular interest as Pb-free solders in the electronics industry. Song et al (Ref 5), Hung et al (Ref 6), and recently Gancarz (Ref 7) studied the effect of Ga concentration (up to 1.8, 0.8, and 3.0 wt.%, respectively) on the microstructure of cast alloys. They observed coarsening of Zn-rich precipitates and increasing size of the Sn-phase, as Ga content increased. Zhang et al (Ref 8) were the first to present a ternary Sn-Zn-Ga phase diagram obtained by piecing binary phase diagrams, Zivkovic et al (Ref 9) used the Calphad approach and thermodynamic descriptions of binary systems only, for that purpose They found the calculated pseudo-binary (Sn-Zneut)-Ga diagram to be in agreement with transition temperatures determined with differential thermal analysis (DTA). Selected joints were subjected to isothermal aging at 170 °C and the evolution of the interface was studied

Experimental

Solder-Substrate Interaction

Aging of Joints

Conclusion