Effect of Graphene Layers on Phenomena Occurringat Interface of Sn-Zn-Cu Solder and Cu Substrate

Janusz Pstruś,Piotr Ozga,Katarzyna Berent,Tomasz Gancarz

doi:10.1007/s11664-017-5529-2

Abstract

Cu and graphene-coated Cu substrates spread with Sn-Zn eutectic-based alloy containing 0.5 wt.%, 1 wt.%, or 1.5 wt.% Cu have been studied at 250°C. Soldering experiments were performed for wetting time of 3 min, 8 min, 15 min, 30 min, and 60 min in (1) presence of flux without argon protective atmosphere and (2) fluxless in argon atmosphere. Solidified solder–pad couples were cross-sectioned and examined using scanning electron microscopy with energy-dispersive spectroscopy to study their interfacial microstructure. To assess the effect of graphene coating on solder, Cu pads were covered by graphene using chemical vapor deposition. The results revealed that the liquid solder did not wet the graphene-coated copper in the absence of flux. Wetting took place only with use of flux, because it destroyed the graphene layer and enabled contact of the liquid solder with the copper. Experiments were designed to demonstrate the effect of Cu addition and graphene coating on the kinetics of the formation and growth of Cu5Zn8 and CuZn4 phases identified by x-ray diffraction analysis, Raman spectroscopy, and energy-dispersive spectroscopy. A decrease of about 60% in the thickness of the intermetallic layer was observed when applying the graphene interlayer in presence of flux. Addition of copper to the Sn-Zn alloy improved the wettability as the copper content was increased.

Highlights

The search for alloys which can eliminate Sn-Pb solders from conventional use is ongoing
In the most recent published work describing wetting of copper and copper covered by graphene with Sn-Ag-Cu (SAC) solder,[25] the authors describe the role of the graphene coating as a diffusion barrier, suggesting that the graphene layer should reduce copper diffusion from the substrate and thereby inhibit growth of the intermetallic layer
The results show that, at the beginning of the spreading test (3 min), the thickness of intermetallic compounds (IMCs) on the Cu substrate coated with the graphene layer is around 55% lower compared with that on the Cu substrate

Summary

INTRODUCTION

The search for alloys which can eliminate Sn-Pb solders from conventional use is ongoing. In the most recent published work describing wetting of copper and copper covered by graphene with Sn-Ag-Cu (SAC) solder,[25] the authors describe the role of the graphene coating as a diffusion barrier, suggesting that the graphene layer should reduce copper diffusion from the substrate and thereby inhibit growth of the intermetallic layer. It would be of interest to determine the mechanism of wetting of materials with graphene coatings with liquid metals and its effect on the growth kinetics of IMCs. Description of the formation of intermetallic phases and the kinetics of their growth, as well as the influence of various alloying additions and technological conditions, are separate issues. This process slows down the growth of the IMC layer

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSIONS