Wetting Behaviors of Sn-Based Solders on Cu and Pd Surfaces

Journal of Materials Science: Materials in Electronics, 2014

In the present work, the effect of reflow time on wetting behaviour, microstructure and shear strength of the eutectic Sn-0.7Cu lead-free solder on Cu substrate were studied. The reflow time was varied from 10 to 10,000 s. The contact angle decreased with the increase in reflow time. The growth of intermetallic compounds (IMCs) increased with the reflow time. The thickness of the Cu 6 Sn 5 IMC layer formed during a reflow time of 10 s was about 3.76 lm and its thickness increased to 3.

Journal of Electronic Materials, 2019

Directional solidification experiments coupled with mathematical modelling, drop shape analyses and evaluation of the reaction layers were performed for three different types of joints produced with the Sn-0.7 wt.%Cu solder alloy. The association of such findings allowed understanding the mechanisms affecting the heat transfer efficiency between this alloy and substrates of interest. Nickel (Ni) and copper (Cu) were tested since they are considered work piece materials of importance in electronic soldering. Moreover, low carbon steel was tested as a matter of comparison. For each tested case, wetting angles, integrity and nature of the interfaces and transient heat transfer coefficients, 'h', were determined. Even though the copper has a thermal conductivity greater than nickel, it is demonstrated that the occurrence of voids at the copper interface during alloy soldering may decrease the heat transfer efficiency, i.e., 'h'. Oppositely, a more stable and less defective reaction layer was formed for the alloy/nickel couple. This is due to the suppression of the undesirable thermal contraction since the hexagonal Cu 6 Sn 5 intermetallics is stable at temperatures below 186°C in the presence of nickel.

Journal of Electronic Materials, 2012

Reactive wetting processes of molten Sn-3.5Ag on Cu substrates at elevated temperatures were investigated by the sessile drop method. Equilibrium contact angles of Sn-3.5Ag on Cu substrates are 36.5°, 32.9°, 25.25°, and 32.1°a t 523 K, 573 K, 623 K, and 673 K, respectively, indicating that the contact angle does not decrease monotonically with increasing temperature. It is also found that the maximal triple-line mobility does not increase linearly with temperature. The complicated temperature effects on the equilibrium contact angles and triple-line mobility are attributable to the fact that Cu substrates dissolve easily in the liquid solder, hindering solder spreading. A description of the equilibrium state helped explain the triple-line region of the Sn-3.5Ag/Cu joint. The calculated results, based on the experimental values of tension balances along each of the three interfaces, show good agreement with the theoretical analysis. The present results are of practical interest for composite lead-free solder preparations and joining of Sn-3.5Ag to Cu substrates.

2007

Three studies on Sn-40Pb, Sn-9Zn and Sn-8Zn-3Bi Pb-free solders were conducted. Spreading of the solders was investigated on 0.13 µm roughness Cu substrate at 250°C. Sn-40Pb has a contact angle of 6°, which is seven times better than Sn-9Zn and Sn-8Zn-3Bi solders. Wetting balance was used to study the wetting time, wetting force and surface tension at different temperatures using two different fluxes. For Sn-8Zn-3Bi solder, MHS (commercial name) flux gives higher wetting force and wetting time compared to HCl flux for increasing temperatures. The surface tension of Sn-40Pb solder decreases with increasing temperature whereas the surface tension of Sn-9Zn and Sn-8Zn-3Bi solders is not influenced by the temperature. However, the addition of 3% Bi reduces the surface tension of the Sn-Zn-Bi system. A study on the spreading of Sn-9Zn solder alloy on Cu with surface roughness between 0.33 and 1.53 µm was also conducted. Surface roughness below 0.62 µm does not contribute to the improvement of wetting but above 0.62 µm, there was an improvement in the contact angle and spreading area.

Engineering Science and Technology, an International Journal, 2018

This work investigates the effect of bismuth (Bi) addition, 1 wt% Bi, on wettability of the Sn-3.0Ag-0.5Cu (SAC305) ternary Pb-free solder alloy. Adding Bi to SAC305 decreased the contact angles (h) of the Sn-2.0Ag-0.5Cu-1.0Bi (SAC-1Bi) quaternary Pb-free solder alloy, which were measured by using of the sessile drop method at various temperatures (250, 280 and 310°C) on Cu substrate in argon (Ar) atmosphere. Microstructures, inter-metallic phases and melting temperatures were analyzed by optical microscope, scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry, and effects of the amount of Bi on microstructure were investigated. The experimental results exhibited that when the addition of Bi was 1 wt%, changing in melting temperature of SAC-1Bi solder was insignificant, but the wetting angles (h) of the solder alloy decreased which were measured by using of the sessile drop method at various temperatures. The lowest h was obtained as 35.6°for SAC-1Bi alloy at 310°C.

MATERIALS TRANSACTIONS, 2010

In this study, trace amounts (0.5-2 mass%) of indium (In) are added to the binary Sn-9Zn alloy to examine the effect of such addition on wetting properties of Sn-9Zn-In soldering. Results show that addition of In to Sn-9Zn alloy leads to decrease in eutectic temperature; and the greater the amount of In added, the larger the decrease is. On the other hand, the maximum wetting force, an indicator of wettability and solderability, increases with increasing mass% of In added. In addition, the higher the eutectic temperature, the better the wettability of solder is. Increasing In content in the solder also enhances the dissolution of Cu. Moreover, the higher the In content, the faster the dissolution rate is. At wetting temperatures of 220 C and 240 C, the wetting time achieved is shorter than 3 s, which can meet practical needs for industrial applications. In sum, the addition of 0.5 mass% of In is optimal in that it can achieve good wettability while maintaining low dissolution rate, which would also enhance solderability.

Journal of Electronic Materials, 2006

Soldering with the lead-free tin-base alloys requires substantially higher temperatures (;235-250°C) than those (213-223°C) required for the current tin-lead solders, and the rates for intermetallic compound (IMC) growth and substrate dissolution are known to be significantly greater for these alloys. In this study, the IMC growth kinetics for Sn-3.7Ag, Sn-0.7Cu, and Sn-3.8Ag-0.7Cu solders on Cu substrates and for Sn-3.8Ag-0.7Cu solder with three different substrates (Cu, Ni, and Fe-42Ni) are investigated. For all three solders on Cu, a thick scalloped layer of h phase (Cu 6 Sn 5) and a thin layer of e phase (Cu 3 Sn) were observed to form, with the growth of the layers being fastest for the Sn-3.8Ag-0.7Cu alloy and slowest for the Sn-3.7Ag alloy. For the Sn-3.8Ag-0.7Cu solder on Ni, only a relatively uniform thick layer of h phase (Cu,Ni) 6 Sn 5 growing faster than that on the Cu substrate was found to form. IMC growth in both cases appears to be controlled by grain-boundary diffusion through the IMC layer. For the Fe-42Ni substrate with the Sn-3.8Ag-0.7Cu, only a very thin layer of (Fe,Ni)Sn 2 was observed to develop.

Journal of Materials Engineering and Performance, 2012

Wetting angles of Sn-8.8Zn and Sn-8.8Zn-xIn alloys (x = 0.5, 1.0, 1.5 wt%) were studied with the sessile drop method. Wetting tests were carried out for 900 s in the presence of ORM0 flux at 493, 523, and 573 K on copper and at 523 K on nickel substrates, respectively. It was found that the addition of In to Sn-8.8Zn alloy improves its wetting on both substrates by reducing the value of apparent wetting angle. Also, with increasing temperature a decrease of wetting angle on copper is observed in the case of 0 and 1.5 wt% of In alloys. Solidified solder-substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis. Interlayers were found at the interface of solders with copper and nickel, and their compositions are close to Cu 5 Zn 8 and Ni 5 Zn 21 intermetallics, respectively. However, in the case of Sn-8.8Zn-1.5/Ni couple small scallops are observed instead of continuous interlayer.

Journal of Alloys and Compounds, 2009

The effects of Cu addition into Sn-9Zn solder reacting with an Au substrate at 160 • C for 24 h were investigated in this study. The intermetallic compound (IMC) evolution sequences at the Sn-9Zn + xCu/Au interface and in the solders were (i) the (Au 3 Zn 7 + AuZn 2 + AuZn) and Au 3 Zn 7 phases at the Sn-Zn/Au couple; (ii) the (Au 3 Zn 7 + AuZn), (Au, Cu) 3 Zn 7 phases, as x was 1 wt%; (iii) the AuSn and Cu 5 Zn 8 phases, as x was 4 wt%; (iv) ((Cu, Au)Sn + AuSn) and CuZn phases, as x was 7 wt% and (v) ((Cu, Au)Sn + AuSn) and CuZn phases at the Sn-9Zn + 10 wt%Cu/Au couple. When x is less than 3 wt%, the free Zn atoms in the liquid solder can easily react with the Au substrate to form Au-Zn IMC at the interface. The amount of active Zn atoms in the liquid solder decreases when 3-6 wt%Cu is added into the Sn-Zn solder. Thus, most of the Zn atoms react with Cu to form a Cu-Zn short-range-ordered structure IMC in the solder. Sn atoms then become the dominant diffusion specimens and react with the Au substrate to form the binary Au-Sn IMC at the solder/Au interface. When 6-10 wt%Cu is added into Sn-9Zn solders, the solder/Au interface converts completely into the Sn-Cu/Au system. Crown

2003

Increasing concerns regarding environmental contamination is driving the soldering research community to develop lead-free solder alloys. Previous studies have shown that Sn-based alloys such as Sn-3.5Ag, Sn-0.7Cu, Sn-9Zn, and Sn-3.2Ag-0.8Cu have promising mechanical properties, and can be considered as serious candidates to replace the Sn-Pb alloy. However, for joint life and reliability predictions, information about the interaction between these alloys and the most used substrates is needed. In that sense, the formation and growth of intermetallic compounds at the interface between the Cu-plated substrates and Sn-3.5Ag, Sn-0.7Cu, Sn-3.2Ag-0.8Cu, and Sn-9Zn have been studied. Coupons of joints prepared with each solder alloy on a Cu-plated circuit board were subjected to thermal aging test for 20, 100, 200, 500 hours at 70, 100 and 150 degrees Celsius. Each sample was analyzed using metallographic techniques, light microscopy, SEM and EDS. The results indicate that the formation o...