Structure and kinetics of Sn whisker growth on Pb-free solder finish

The evolution of internal compressive stress from the intermetallic compound (IMC) Cu6Sn5 growth is commonly acknowledged as the key inducement initiating the nucleation and growth of tin (Sn) whisker. This study investigates the effect of Sn-0.7Cu-0.05Ni on the nucleation and growth of Sn whisker under continuous mechanical stress induced. The Sn-0.7Cu-0.05Ni solder joint has a noticeable effect of suppression by diminishing the susceptibility of nucleation and growth of Sn whisker. By using a synchrotron micro X-ray fluorescence (µ-XRF) spectroscopy, it was found that a small amount of Ni alters the microstructure of Cu6Sn5 to form a (Cu,Ni)6Sn5 intermetallic layer. The morphology structure of the (Cu,Ni)6Sn5 interfacial intermetallic layer and Sn whisker growth were investigated by scanning electron microscope (SEM) in secondary and backscattered electron imaging mode, which showed that there is a strong correlation between the formation of Sn whisker and the composition of solder alloy. The thickness of the (Cu,Ni)6Sn5 IMC interfacial layer was relatively thinner and more refined, with a continuous fine scallop-shaped IMC interfacial layer, and consequently enhanced a greater incubation period for the nucleation and growth of the Sn whisker. These verification outcomes proposes a scientifically foundation to mitigate Sn whisker growth in lead-free solder joint.

Download Full-text

Morphology Analysis of Spontaneous Tin (Sn) Whisker Growth on Lead-Free Solder

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/551/1/012095 ◽

2019 ◽

Vol 551 ◽

pp. 012095 ◽

Cited By ~ 1

Author(s):

Aimi Noorliyana Hashim ◽

Mohd Arif Anuar Mohd Salleh ◽

Noor Zaimah Mohd Mokhtar

Keyword(s):

Whisker Growth ◽

Lead Free ◽

Lead Free Solder ◽

Sn Whisker ◽

Morphology Analysis ◽

Free Solder

Download Full-text

Kinetics of Sn whisker growth from Sn thin-films on Cu substrate

Journal of Materials Science Materials in Electronics ◽

10.1007/s10854-020-04180-2 ◽

2020 ◽

Vol 31 (19) ◽

pp. 16314-16323 ◽

Cited By ~ 1

Author(s):

Balázs Illés ◽

Olivér Krammer ◽

Tamás Hurtony ◽

Karel Dušek ◽

David Bušek ◽

...

Keyword(s):

Thin Films ◽

Growth Rates ◽

Whisker Growth ◽

Layer Structure ◽

Intermetallic Layer ◽

Layer Growth ◽

Sn Whisker ◽

Cu Substrate ◽

Sn Whiskers ◽

Kinetics Of

Abstract The kinetics of Sn whisker growth was investigated on vacuum-evaporated Sn thin-films. Sn film layers were deposited on a Cu substrate with 0.5 and 1 µm thicknesses. The samples were stored in room conditions (22 ± 1 °C/50 ± 5RH%) for 60 days. The Sn whiskers and the Cu–Sn layer structure underneath them were investigated with both scanning electron and ion microscopy. Fast Cu–Sn intermetallic formation resulted in considerable mechanical stress in the Sn layer, which initiated intensive whisker growth right after the layer deposition. The thinner Sn layer produced twice many whiskers compared to the thicker one. The lengths of the filament-type whiskers were similar, but the growth characteristics differed. The thinner Sn layer performed the highest whisker growth rates during the first 7 days, while the thicker Sn layer increased the growth rate only after 7 days. This phenomenon was explained by the cross-correlation of the stress relaxation ability of Sn layers and the amount of Sn atoms for whisker growth. The very high filament whisker growth rates might be caused by the interface flow mechanism, which could be initiated by the intermetallic layer growth itself. Furthermore, a correlation was found between the type of the whiskers and the morphology of the intermetallic layer underneath.

Download Full-text