Effect of reaction time on mechanical strength of the interface formed between the Sn-Zn(-Bi) solder and the Au/Ni/Cu bond pad |
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Authors: | Ahmed Sharif Y C Chan |
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Affiliation: | (1) Department of Electronic Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong |
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Abstract: | In this work, the shear strengths and the interfacial reactions of Sn-9Zn, Sn-8Zn-1Bi, and Sn-8Zn-3Bi (wt.%) solders with
Au/Ni/Cu ball grid array (BGA) pad metallization were systematically investigated after extended reflows. Zn-containing Pb-free
solder alloys were kept in molten condition (240°C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging
from 1 min. to 60 min. to render the ultimate interfacial reaction and to observe the consecutive shear strength. After the
shear test, fracture surfaces were investigated by scanning electron microscopy equipped with an energy dispersive x-ray spectrometer.
Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The solder ball shear
load for all the solders during extended reflow increased with the increase of reflow time up to a certain stage and then
decreased. It was found that the formation of thick Ni-Zn intermetallic compound (IMC) layers at the solder interface of the
Au/electrolytic Ni/Cu bond pad with Sn-Zn(-Bi) alloys deteriorated the mechanical strength of the joints. It was also noticed
that the Ni-Zn IMC layer was larger in the Sn-Zn solder system than that in the other two Bi-containing solder systems. |
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Keywords: | Sn-Zn-based lead-free alloys extended reflow ball grid array (BGA) solder joints shearing load |
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