• Applied Science and Convergence Technology
• /
• v.23 no.6
• /
• pp.345-350
• /
• 2014

The surface oxidation mechanism of lead-free solder alloys has been investigated with multiple reflow using X-ray photoelectron spectroscopy. It was found that the solder surface of Sn-Ag-Cu-In solder alloy is surrounded by a thin $InO_x$ layer after reflow process; this coating protects the metallic surface from thermal oxidation. Based on this result, we have performed a wetting balance test at various temperatures. The Sn-Ag-Cu-In solder alloy shows characteristics of both thermal oxidation and wetting balance better than those of Sn-Ag-Cu solder alloy. Therefore, Sn-Ag-Cu-In solder alloy is a good candidate to solve the two problems of easy oxidation and low wettability, which are the most critical problems of Pb-free solders.

• The Journal of Engineering Geology
• /
• v.20 no.3
• /
• pp.281-295
• /
• 2010

A new, automated apparatus is proposed for calculating the Soil-Water Characteristic Curve (SWCC), representing a simple and easily applied testing device for continuous measurements of the volumetric water content and suction of unsaturated soils. The use of this apparatus helps to avoid the errors that arise when performing experiments. Consequently, the apparatus provides greater accuracy in calculating the SWCC of unsaturated soils. The apparatus is composed of a pressure panel, flow cell, water reservoir, air bubble trap, balance, sample-preparation accessories, and measurement system, among other components. The air pressure can attain 300 kPa, and a general test can be completed in a short time. The apparatus can simply control the drying process and wetting process. The changes in volumetric water content that occur during the drying and wetting processes are shown directly in the SWRC program, in real time. As a case study, we performed an SWCC test of Joomunjin sand (75% relative density) to measure matric suction and volumetric water content during both the drying and wetting processes. The test revealed hysteresis behavior, whereby the water content on the wetting curve is always lower than that on the drying curve for a specific matric suction, during the wetting and drying processes. Based on the test results, SWCCs were estimated using the Brooks and Corey, van Genuchten, and Fredlund and Xing models. The van Genuchten model performed best for the given soil conditions, as it yielded the highest coefficient of determination.

• Proceedings of the KWS Conference
• /
• 2006.10a
• /
• pp.199-201
• /
• 2006

The wetting balance test was carried out to compare the wettability of Sn-Xwt%Cu($0{\sim}3$wt%) solders. And, IMCs which were formed at interface between solders and substrates were investigated by using XRD(x-ray diffractometer), SEM(scanning electron microscope) and EDS(energy dispersive spectroscope). The value of ${\gamma}_[fl}$ and(${\gamma}_{fs}-{\gamma}_{ls}$) had a tendency to increase with increasing wetting temperature. The activation energy that was calculated between the bare Cu substrate and flux was increased in the following order Sn-0.7wt%Cu(68.42 kJ/mol);Sn-3.0wt%Cu(72.66 kJ/mol);100wt%Sn solder(94.53 kJ/mol).

• Journal of the Microelectronics and Packaging Society
• /
• v.7 no.4
• /
• pp.7-15
• /
• 2000

The purpose of this work is to evaluate the solderahility and characteristics of solder joints. Bridge defect of solder joint was examined in natural atmosphere and $N_2$ condition. Consequently, wettability was excellent for each of Sn-Pb plated Cu specimen, Sn plated Cu specimen, and Cu polished in $N_2$ condition. The wetting time in $N_2$ condition was shorter than that of natural atmosphere condition, showing the decreasing values of about 0.2~0.45 seconds. The max. wetting force under the $N_2$ condition was more increasing that of natural atmosphere condition, showing the increasing values of about 1.8~2.8 N. With the result of wetting balance test, the wetting time ($t_2$) and wetting farce according to increasing amount of $N_2$ from 10 1/min to 30 1/min, the wetting time ($t_2$) was reduced about 0.25 second and wetting force was increased about 2.3 N. In non-cleaning flux, when $N_2$ gas is applied, it is compensated to decrease of wettability. In the case of using the $N_2$ gas, the wettability was improved. The reason for improving wettability is due to preventing the formation of dross. The generation rate of bridge in $N_2$ condition decreased than that of natural atmosphere, and when the specimen had a fine pitch, the rate of bridge defects was considerably decreased in $N_2$ condition, showing the decreasing rate of 25~75%.

• Proceedings of the International Microelectronics And Packaging Society Conference
• /
• 2002.05a
• /
• pp.104-108
• /
• 2002

This paper was investigated the lead free solder characteristics by P mass percentage chang e. Tension test, wetting balance test, spread test, and analysis of intermetallic compound after isothermal aging of Sn-2.5Ag-0.7Cu-0.005P, Sn-2.5Ag-0.7Cu-0.01P, Sn-2.5Ag-0.7Cu-0.02P, Sn-0.7Cu-0.005P were performed for estimation. By adding P on the solder alloys, it was showe d improvement of tensile strength, reduction of intermetallic compound growth and reduction of oxidization of fusible solder under wave soldering processes. After comparing solder alloy containing P with tin lead eutectic solder alloy, p containing solder alloys showed much better solderability than eutectic solder alloys.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.791-797
• /
• 2002

This paper introduces the partial melting process for solder application and characterization of its feasibility using Sn-Ag, and Sn-Cu solder alloys. ill order to show that the liquid phase in the semi-liquid state maintains the similar wettability as single-phase liquid, the wetting balance tests are conducted with varying temperatures and compositions. Also, as a new soldering technology, the microstructural and mechanical test were investigated. The results from this research indicate that the partial melting can yield satisfactory sider joints as long as the liquid phase acquires sufficient chemical activity. At a condition where the partial melting is effective, a direct correlation between the wettability and the surface tension is found to exist.

• Journal of the Microelectronics and Packaging Society
• /
• v.8 no.3
• /
• pp.43-47
• /
• 2001

Sn-3Ag-8Bi-5In was developed for the intermediate melting point solder. Although In-contained solder is expensive, its melting point is lower than these of Sn-Ag-Cu alloys. Sn-3Ag-8Bi-5In solder used for this research has a melting range of 188~$204^{\circ}C$. On this study wetting characteristics of Sn-3Ag-8Bi-5In were evaluated in order to investigate its availability as a Pb-free solder. Wettabilities of Sn-37Pb and Sn-3.5Ag solders were also studied to compare these of the Sn-3Ag-8Bi-5In. Experimental results showed that the zero-cross-time and wetting time at $240^{\circ}C$ for the Sn-3Ag-8Bi-5In were 1.1 and 2.2 second respectively. These values are a little better than these of Sn-37Pb and Sn-3.5Ag solders. The equilibrium wetting farce of the Sn-3Ag-8Bi-5In was 5.8 mN at $240^{\circ}C$, and it was tuned out to be a little higher than that of Sn-3.5Ag and lower than that of Sn-37Pb.

• Journal of the Microelectronics and Packaging Society
• /
• v.7 no.2
• /
• pp.63-68
• /
• 2000

This paper introduces the partial melting process for solder application and characterization of its possibility using off-eutectic Pb-Sn alloy. In order to show that the liquid phase in the semi-liquid state maintains the wettability as the single-phase liquid, the wetting balance test are conducted with varying temperatures and compositions. The results are then compared with the surface tension of liquid, both measured and calculated, to examine the correlation. The results from this investigation indicate that the partial melting can yield satisfactory solder joints as long as the liquid phase acquires sufficient chemical activity. At a condition where the partial melting is effective, a direct correlation between the wettability and the surface tension is found to exist. All alloys are found to show a reasonable wettability in semi-liquid state.

• Journal of the Microelectronics and Packaging Society
• /
• v.25 no.4
• /
• pp.123-128
• /
• 2018

Effect of activators in flux on the printability and wettability of a solder paste was evaluated in this study. The activators in this study were dicarboxylic acids, which were oxalic acid (n = 0), malonic acid (n = 1), succinic acid (n = 2), glutaric acid (n = 3), adipic acid (n = 4), and pimelic acid (n = 5). When the solder pastes were observed with a SMT scope, solder with glutaric acid showed clean and shiny surface when it was melted. Slump ratio of the solder pastes was low when the carbon numbers of the dicarboxylic acid were 1-3. Spreadability was high when the carbon number was over 2. Zero cross time of wetting balance test was under 1 sec when the carbon number was over 3. When activator was oxalic acid or malonic acid, zero cross time was over 1 sec and maximum wetting force was low. Fluxes with the oxalic acid and malonic acid showed decomposition at the temperature close to melting point. Among the dicarboxylic acids, glutaric acid provided excellent slump, spreadability, and wettability.

• Journal of Welding and Joining
• /
• v.30 no.5
• /
• pp.64-69
• /
• 2012

Sn-Bi eutectic alloy has been widely used as one of the key solder materials for step soldering at low temperature. The Sn-58Bi solder paste containing chloride flux was adopted to compare with that using the chloride-free flux. The paste was applied on the electroless nickel-immersion gold (ENIG) surface finish by stencil printing, and the reflow process was then performed at $170^{\circ}C$ for 10 min. After reflow, the solder joints were aged at $125^{\circ}C$ for 100, 200, 300, 500 and 1000 h in an oven. The interfacial microstructures were obtained by using scanning electron microscopy (SEM), and the composition of intermetallic compounds (IMCs) was analyzed using energy dispersive spectrometer (EDS). Two different IMC layers, consisting of $Ni_3Sn_4$ and relatively very thin Sn-Bi-Ni-Au were formed at the solder/surface finish interface, and their thickness increased with increasing aging time. The wettability of solder joints was investigated by wetting balance test. The mechanical property of each aging solder joint was evaluated by the ball shear test in accordance with JEDEC standard (JESD22-B117A). The results show that the highest shear force was measured when the aging time was 100 h, and the fracture mode changed from ductile fracture to brittle fracture with increasing aging time. On the other hand, the chloride flux in the solder paste did not affect the shear force and fracture mode of the solder joints.