Whisker Growth Behavior Research Articles

Effect of Isothermal Annealing on Sn Whisker Growth Behavior of Sn0.7Cu0.05Ni Solder Joint

This paper presents an assessment of the effect of isothermal annealing of Sn whisker growth behavior on the surface of Sn0.7Cu0.05Ni solder joints using the hot-dip soldering technique. Sn0.7Cu and Sn0.7Cu0.05Ni solder joints with a similar solder coating thickness was aged up to 600 h in room temperature and annealed under 50 °C and 105 °C conditions. Through the observations, the significant outcome was the suppressing effect of Sn0.7Cu0.05Ni on Sn whisker growth in terms of density and length reduction. The fast atomic diffusion of isothermal annealing consequently reduced the stress gradient of Sn whisker growth on the Sn0.7Cu0.05Ni solder joint. It was also established that the smaller (Cu,Ni)6Sn5 grain size and stability characteristic of hexagonal η-Cu6Sn5 considerably contribute to the residual stress diminished in the (Cu,Ni)6Sn5 IMC interfacial layer and are able to suppress the growth of Sn whiskers on the Sn0.7Cu0.05Ni solder joint. The findings of this study provide environmental acceptance with the aim of suppressing Sn whisker growth and upsurging the reliability of the Sn0.7Cu0.05Ni solder joint at the electronic-device-operation temperature.

Growth kinetics of tin whiskers in Ti2SnC phase

The extrusion of Sn whiskers from Ti2SnC phase, a layered ternary carbide ceramic MAX phase, has ultrafast whisker growth behaviors and good experimental repeatability. This makes MAX phase an ideal research platform for the investigation of metallic whiskers. This work aims at revealing the growth kinetics of Sn whiskers from Ti2SnC substrate, which still does not exist. By conducting a quantitative analysis on the whisker growth behavior, three stages of the growth of Sn whiskers on the Ti2SnC substrate are identified: nucleation, germination and saturation. Moreover, the function of volume change versus cultivation time is well fitted using the Avrami equation, implying that the growth of Sn whiskers from Ti2SnC substrate follows a general crystallization pattern.

The influence of non-uniform copper oxide layer on tin whisker growth and tin whisker growth behavior in SnAg microbumps with small diameter

Abstract A non-uniform copper oxide layer with several hundred nanometers thick was observed covering the surface of 10 μm-diameter Cu/SnAg microbump. Tin whiskers were also found to form on the weak spots of this copper oxide layer, where were localized stress relief centers. The HRTEM results reveal the existence of twin grain boundary between tin whisker and neighboring grain. Numerous dislocations at the twin boundary provide paths for the tin atoms to slip into tin whisker. It is the first time that the existence of copper oxide layer and the relationship between copper oxide layer and tin whiskers growth was studied and revealed in micron-level bumps. This present study has significant meaning for 3D electronic packaging as small size microbumps become increasingly prevalent and in which, surface diffusion becomes more important.

Effect of Nd on whiskers growth behavior of SnAgCu solders in electronic packaging

The effects of rare earth Nd on the whisker growth were investigated, it is found that the presence of Nd causes the risk of whisker growth due to the oxidation of RE-rich NdSn3 intermetallic compounds. The relationships between average diameters of NdSn3, Nd contents, storage time, storage temperature and the whisker were tested, the oxidation mechanisms were selected to expound the whisker growth behavior. The compressive stress induced by volume expansion during oxidation procedure was suggested as the driving force for the growth of whisker in SnAgCu-xNd lead-free solders.

Growth behaviors of tin whisker in RE‐doped Sn‐Zn‐Ga solder

PurposeThe purpose of this paper is to investigate the growth behavior and mechanism of Sn whisker induced by RE addition in Sn‐Zn‐Ga‐Pr solder at ambient condition.Design/methodology/approachBy means of aging treatment, FIB and SEM microstructure analysis, the whisker growth behavior was investigated.FindingsIt was found that the morphologies of tin whisker are changed during air exposure. After 60 days aging, the average length of the longest whiskers could reach up to 70 μm, some whiskers even can grow to a length of 100 μm. It was discussed that the oxidation of Pr‐Sn intermetallics provides driving force for whisker growth.Originality/valueTin whisker growth is a complex reliability issue for lead‐free solder. The current research can be helpful in re‐understanding the issue of tin whisker growth as well as an enriched understanding on the effects of REs on lead‐free solders.

Sn whisker growth on Sn plating with or without surface treatment during the room temperature exposure

The establishment of lead-free plating technology and countermeasures for whisker formation are some of the critical issues remaining to be solved for lead-free electronics packaging. This study examined a method for mitigating Sn whisker formation by depositing a thin metal layer, such as Au, Pd and Ni, on pure Sn plating. Au, Pd and Ni layers with thicknesses ranging from 50nm to 200nm were deposited on matte Sn plating using a flash-coating process. The Sn whisker growth behavior of pure Sn plating and metal layer/Sn plating samples at room ambient over a period of 10,000h was observed. The metal layer/Sn plating was considerably more stable against Sn whisker formation in room ambient environment than the pure Sn plating.

Whisker Growth Behavior of Sn and Sn Alloy Lead-Free Finishes

Sn whisker growth behavior, over periods of time up to 10,080 h at room temperature, was examined for Sn and Sn-Cu, Sn-Ag, Sn-Bi, and Sn-Pb coatings electroplated on copper in 2 μm and 5 μm thicknesses to understand the effects of the alloying elements on whisker formation. Sn-Ag and Sn-Bi coatings were found to significantly suppress Sn whisker formation compared with the pure Sn coatings, whereas whisker growth was enhanced by Sn-Cu coatings. In addition, annealed Sn and Sn-Pb coatings were found to suppress Sn whisker formation, as is well known. Compared with the 2-μm-thick coatings, the 5-μm-thick coatings had high whisker resistance, except for the Sn-Cu coating. Whisker growth was correlated with coating crystal texture and its stability during storage, crystal grain microstructure, and the formation of intermetallic compounds at Sn grain boundaries and substrate–coating interfaces.

Ｓｎめっきのウィスカ成長に及ぼす恒温恒湿試験による腐食雰囲気の影響

This study investigated the effects of a corrosive atmosphere on whisker growth of a Sn film and a Sn/Cu film that were electrodeposited onto a 42 alloy substrate.No whiskers were generated on the Sn single layer. However, numerous whiskers with length exceeding 100 μm were generated on the Sn/Cu double layer during 7000 hr in an ambient atmosphere. The whisker generation and growth of both the Sn single layer and the Sn/Cu double layer changed remarkably during 7000 hr under a corrosive atmosphere. This whisker growth behavior that occurred in the corrosive atmosphere was attributed to both the change of the Cu6Sn5 compound based on the mutual diffusion and the state transition of oxide film, depending on corrosion of the Sn film at the surface side.

Effects of reflow atmosphere and flux on Sn whisker growth of Sn–Ag–Cu solders

We evaluated the Sn whisker growth behavior of Sn–Ag–Cu solder fillets on lead frames of quad flat packages (QFPs) upon OSP printed circuit boards that were exposed to 85 °C/85% relative humidity (RH) exposure. Three different concentrations of halogen flux for activated Sn-3.0wt%Ag–0.5wt%Cu were used to solder in air and in an inert N2 reflow atmosphere. The lead frames of the QFPs consisted of Sn plated Cu and Fe-42wt%Ni (alloy 42). Sn whiskers were observed on the surface of the QFP solder fillet joints that were reflowed with halogen containing flux in an air atmosphere. A substantial amount of Sn oxides were formed in those solder fillets while whisker growth and the amount of Sn oxides increased with the halogen content. Sn oxide formation apparently enhanced whisker formation. The combination of air reflow atmosphere and high halogen flux was the worst combination for solder fillet oxidation resulting in Sn whisker formation regardless of the electrode’s lead frame composition of Cu or alloy 42. In contrast, an inert N2 reflow atmosphere obviously prevented Sn whisker formation on Sn–Ag–Cu solder fillets under all conditions used in this work.

Tin whisker growth on bulk Sn–Pb eutectic doping with Nd

Tin whisker growth is a serious reliability concern for electronics using high-density packaging. Whisker growth behavior of tin lead eutectic solders doped with different neodymium concentration (5–0.1wt.%) was studied in present work. Results indicate that the Nd in the all of the Sn–Pb–Nd alloys mainly exists in NdSn 3 intermetallic compound, and that the distribution of the NdSn 3 phase is very non-uniform in the alloy with low Nd concentration. Tin whiskers growth was observed on all samples doped with Nd. All of these whiskers were seen to originate from the NdSn 3 phase, it appears that the Pb does not suppress whisker growth in these alloy because it does not influence the formation of the tin–rare earth intermetallic compound. These results suggest that the addition of rare earth elements into tin alloy systems renders whisker formation nearly inevitable. Therefore, any suggestion to dope tin-based solders with rare earth elements for application in high-density electronic packaging should be carefully reconsidered.

Investigation of Sn-Cu intermetallic compounds by AFM: new aspects of the role of intermetallic compounds in whisker formation

It has been observed that different tin whisker growth properties can result from the same tin deposit on two copper leadframe materials, C19400 and C70250. It was also found that modification of the surface condition of identical substrates, through pretreatment prior to Sn-plating, affects whisker growth behavior. Here, we report an atomic force microscopy (AFM) investigation of intermetallic compounds (IMC) formed on samples with significantly different whisker growth tendencies. AFM data analysis in conjunction with the IMC growth rate, determined using the weight gain method, provides quantitative data of the IMC characteristics. It was found that the whisker propensity is not directly related to the uneven growth front of IMC as detected by AFM. Whisker growth tendency, with respect to whisker density and length, decreases when the unevenness of the IMC layer exceeds a certain level. The results of this work show evidence that the whisker propensity is associated with the copper substrate texture as well as the substrate surface topography.