Thickness Of Intermetallic Layer Research Articles

Effects of Trace Amounts of Rare Earth Additions on Microstructure and Properties of Sn-Bi-Based Solder Alloy

The effect of trace amounts of rare earth additions on the microstructure and properties were studied for the Sn-58Bi and Sn-58Bi-Ag solder alloys. At the same time, the intermetallic compounds (IMCs) in the solder alloys and intermetallic layer (IML) thickness at the solder/Cu substrate interface were investigated, both as-reflowed and after high-temperature aging. The results indicate that adding trace amounts of rare earth (RE) elements has little influence on the melting temperature and microhardness of the solders investigated, but adding RE elements improves the wettability and shear strength of the Sn-58Bi and Sn-58Bi-Ag solder alloys. In addition, it was found that the addition of RE elements not only refines the microstructure and size of the IMC particles, but also decreases the IML thickness and shear strength of the Sn-58Bi solder joint after high-temperature aging. Adding trace amounts of RE elements is superior to adding trace amounts of Ag for improving the properties of the Sn-58Bi solder. The reason may be related to the modification of the microstructure of the solder alloys due to the addition of trace amounts of RE elements.

Galvanised steel to aluminium joining by laser and GTAW processes

A new means of assembling galvanised steel to aluminium involving a reaction between solid steel and liquid aluminium was developed, using laser and gas tungsten arc welding (GTAW) processes. A direct aluminium melting strategy was investigated with the laser process, whereas an aluminium-induced melting by steel heating and heat conduction through the steel was carried out with the GTAW process. The interfaces generated during the interaction were mainly composed of a 2–40 μm thick intermetallic reaction layers. The linear strength of the assemblies can be as high as 250 N/mm and 190 N/mm for the assemblies produced respectively by laser and GTAW processes. The corresponding failures were located in the fusion zone of aluminium (laser assemblies), or in the reaction layer (GTAW assemblies).

Effect of rare earth addition on shear strength of SnAgCu lead-free solder joints

In the present study, the effect of adding trace amount of rare earth (RE) on the shear strength of Sn3.8Ag0.7Cu lead-free solder joints has been investigated. The shear strength of the solder joints as-reflowed and after aging at 150 °C for 168 and 336 h was measured at a constant loading rate of 0.3 mm/min and room temperature. The investigation indicates that the shear strength of Sn3.8Ag0.7Cu0.1RE solder joints is lower than that of Sn3.8Ag0.7Cu solder joints. The shear strength of both Sn3.8Ag0.7Cu solder joints and Sn3.8Ag0.7CuRE solder joints was reduced after aging at elevated temperature. However, the shear strength reduction rate of the Sn3.8Ag0.7Cu solder joints was much faster than that of Sn3.8Ag0.7CuRE solder joints. Moreover, the fracture surfaces were examined by scanning electron microscopy (SEM) and the thickness of intermetallic compounds layer (IML) in the solder joints that join Cu substrate was measured. The results indicated that the addition of rare earth elements suppresses the growth of the thickness of intermetallic compounds layer.

Effect of Carbon Nanotubes on the Shear Strength and Electrical Resistivity of a Lead-Free Solder

In this study, the influence of carbon nanotubes (CNTs) on the shear strength and electrical resistivity of 95.8Sn-3.5Ag-0.7Cu lead-free solder was investigated. Composite solders containing various weight percentages of CNTs were synthesized, and electrical resistivity results of the bulk composite solders revealed that the presence of CNTs did not degrade the electrical performance of such solders. Tests conducted on lap-shear solder joint samples showed an improvement in the shear strength of the composite solders. However, at higher amounts of CNT additions (0.04 wt.% and 0.07 wt.%), the strength improvement was only marginal compared to that of the monolithic solder joint. A comparison of yield stress and ultimate stress test results between the solder joint and bulk solder also showed good agreement. Furthermore, the presence of CNTs in the solder matrix had a minimal influence on the thickness of the interfacial intermetallic compound layer formed during soldering.

Phase evolution of an aluminized steel by oxidation treatment

Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe 2Al 5. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe 2Al 5 phase remains at the temperature below 950 °C in 2-h, and the Fe 2Al 5 phase is completely transformed into low iron content Fe–Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe 2Al 5 phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al 2O 3 and the intermetallic Fe 2Al 5, FeAl 2, FeAl and Fe 3Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.

Fabrication of Metal/Intermetallic Compound Laminate composites by Thin Foil Hot Press Process

Thin foil hot press process was used to fabricate metal/intermetallic compound laminate composites to induce self-propagating high-temperature (SHS) reaction between different pure metal sheets. In the present study, Ni/Ni-aluminide and Ti/Ti-aluminide laminate composites were fabricated through diffusion bonding, reaction synthesis and post-heat treatment of alternatively stacked pure Ni/Al and Ti/Al foils, respectively. Thick intermetallic layers of NiAl and TiAl3 were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni3Al and TiAl were formed by a solid-state diffusion. Also, Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured from stacked foils of pure Ni, Ti and Al in order of Ni/Al/Ni/.../Ni/Al /Ti/.../Ti/Al/Ti. Nb/Nb-aluminide laminate composite was manufactured with pure Nb and Al multilayered foils, consisting of fine Nb/Nb3Al/Nb2Al/NbAl3 layer structure.

Suppression of intermetallic reaction layer formation by controlling heat flow in dissimilar joining of steel and aluminum alloy

In order to suppress the formation of intermetallic reaction layer during laser welding of steel and aluminum alloy dissimilar materials, effect of backing block (heat sink) was investigated. FEM analysis as well as welding experiments with various backing blocks for controlling heat flow were performed. It was found that thickness of intermetallic reaction layer was reduced by increasing welding speed and by applying a backing block with higher thermal conductivity. FEM analysis also showed that when increasing welding speed or applying a backing block with higher thermal conductivity, molten time of aluminum alloy became shorter and predicted thickness of intermetallic reaction layer became thinner. It could be concluded that the thickness of intermetallic reaction layer could be suppressed by using a backing block (as a heat sink) for controlling heat flow in welding region. The joining strength was strongly dependent on the thickness of intermetallic reaction layer. Therefore the backing block was significantly effective for controlling heat flow and consequently for attaining good joining strength.

レーザ圧接された工業用純アルミニウムと低炭素鋼の接合界面のミクロ観察

Dissimilar metals joints of low carbon steel (SPCC) and pure aluminum (A1050) sheets were produced using the laser pressure welding method by changing the laser power and the roller pressure. The tensile shear strength and peel strength of welded joints were measured. The fractured interfaces of the joints were observed by SEM and analyzed by EDX. Moreover, detailed phases formed in the welded interface were investigated by TEM.In the tensile shear test and peel test, the strengths of the joints yielded under the optimum welding conditions were so high that the fracture occurred in the aluminum base metal. The thicknesses of intermetallic compound layers were about 50 nm to 100 nm. In the TEM observation and electron diffraction pattern results, the amorphous phase and the intermetallic compounds consisting of Fe2Al5 and Fe4Al13 were observed. The welded zone was cooled rapidly due to the heat transfer from the welded zone toward respective base metals and rolls. Therefore, the amorphous phase was formed in the most rapidly cooled part. Moreover, the Fe2Al5 and Fe4Al13 phases were formed in the welded interface.

2kWファイバーレーザを用いた低炭素鋼とアルミニウム合金のレーザロール溶接

Recently, lightening, speed-up and decreasing vibration of the transport vehicles have been discussed for improving of environmental problems. As one of the solution, the material hybrid concept using aluminum alloys and high strength steels has been proposed. Therefore, new welding processes by which these dissimilar materials can be joined in high reliability and productivity are demanded. Laser Roll Welding was developed for joining of dissimilar metals by M. Kutsuna, M. Rathod and A. Tsuboi in 2002. Up to now, a CO2 laser has been used as a heat source. In the present work, Laser Roll Welding of low carbon steel and aluminum alloy using a 2kW fiber laser was investigated to improve the joint properties due to the effective heating characteristics. Effects of the process parameters were studied. Otherwise, the influences of process parameters on the weldability, the formation of intermetallic compound layer and the mechanical properties have been investigated. As a result, various types of intermetallic compound layer were confirmed at the Laser Roll Welded joint interfaces. When intermetallic compound layer thickness was less than 10μm, specimen was failure in the base metal of low carbon steel in the tensile shear test.

Microstructure and mechanical behavior of novel rare earth-containing Pb-Free solders

Sn-rich solders have been shown to have superior mechanical properties when compared to the Pb-Sn system. Much work remains to be done in developing these materials for electronic packaging. In this paper, we report on the microstructure and mechanical properties of La-containing Sn-3.9Ag-0.7Cu alloys. The addition of small amounts of La (up to 0.5 wt.%) to Sn-Ag-Cu refined the microstructure by decreasing the length and spacing of the Sn dendrites and decreased the thickness of the Cu6Sn5 intermetallic layer at the Cu/solder interface. As a result of the change in the microstructure, Sn-Ag-Cu alloys with La additions exhibited a small decrease in ultimate shear strength but significantly higher elongations compared with Sn-Ag-Cu. The influence of LaSn3 intermetallics on microstructural refinement and damage evolution in these novel solders is discussed. Our results have profound implications for improving the mechanical shock resistance of Pb-free solders.

Effect of adding 0.3 wt% Ni into the Sn–0.7 wt% Cu solder : Part II. Growth of intermetallic layer with Cu during wetting and aging

The growth behavior of intermetallic layer with or without adding 0.3 wt% Ni into the Sn–0.7Cu solder was studied during the wetting reaction on Cu-substrate and thereafter in solid-state aging condition. The Cu-solder reaction couple was prepared at 255, 275 and 295 °C for 10 s. The samples reacted at 255 °C were then isothermally aged for 2–14 days at 150 °C. The reaction species formed for the Sn–0.7Cu/Cu and Sn–0.7Cu–0.3Ni/Cu soldering systems were Cu 6Sn 5 and (CuNi) 6Sn 5, respectively. The thickness of the intermetallic compounds formed at the solder/Cu interfaces and also in the bulk of both solders increased with the increase of reaction temperature. It was found that Ni-containing Sn–0.7Cu solder exhibited lower growth of intermetallic layer during wetting and in the early stage of aging and eventually exceeded the intermetallic layer thickness of Sn–0.7Cu/Cu soldering system after 6 days of aging. As the aging time proceeds, a non-uniform intermetallic layer growth tendency was observed for the case of Sn–0.7Cu–0.3Ni solder. The growth behavior of intermetallic layer during aging for both solders followed the diffusion-controlled mechanism. The intermetallic layer growth rate constants for Sn–0.7Cu and Sn–0.7Cu–0.3Ni solders were calculated as 1.41 × 10 −17 and 1.89 × 10 −17 m 2/s, respectively which indicated that adding 0.3 wt% Ni with Sn–0.7Cu solder contributed to the higher growth of intermetallic layer during aging.

Rare-earth additions to lead-free electronic solders

The research in lead(Pb)-free solder alloy has been a popular topic in recent years, and has led to commercially available Pb-free alloys. Further research in certain properties to improve aspects such as manufacturability and long term reliability in many Pb-free alloys are currently undertaken. It was found by researchers that popular Pb-free solders such as Sn-Ag, Sn-Cu, Sn-Zn and Sn-Ag-Cu had improved their properties by doping with trace amounts of rare earth (RE) elements. The improvements include better wettability, creep strength and tensile strength. In particular, the increase in creep rupture time in Sn-Ag-Cu-RE was 7 times, when the RE elements were primarily Ce and La. Apart from these studies, other studies have also shown that the addition of RE elements to existing Pb-free could make it solderable to substrates such as semiconductors and optical materials. This paper summarizes the effect of RE elements on the microstructure, mechanical properties and wetting behavior of certain Pb-free solder alloys. It also demonstrates that the addition of RE elements would improve the reliability of the interconnections in electronic packaging. For example, when Pb-free-RE alloys were used as solder balls in a ball grid array (BGA) package, the intermetallic compound layer thickness and the amount of interfacial reaction were reduced.

Interfacial microstructure and mechanical properties of aluminium–zinc-coated steel joints made by a modified metal inert gas welding–brazing process

The microstructure and properties of aluminium–zinc coated steel lap joints made by a modified metal inert gas CMT welding–brazing process was investigated. It was found that the nature and the thickness of the high-hardness intermetallic compound layer which formed at the interface between the steel and the weld metal during the welding process varied with the heat inputs. From the results of tensile tests, the welding process is shown to be capable of providing sound aluminium–zinc coated steel joints.

Investigations of Interfacial Reaction and Shear Strength between Pb-Free Flip Chip Solder and Electroplated Cu UBM

In the present work, we investigated the interfacial reactions and shear properties between Sn-3.0Ag-0.5Cu flip chip solder bump and Cu UBM after multiple reflows. The quantitative analyses of the intermetallic compound layer thickness as a function of the number of reflows were performed. After six reflows, the reaction product could be distinguished by two intermetallic compounds: Cu3Sn adjacent to the substrate and Cu6Sn5 which was the dominant phase. The thickness of total intermetallic compound layers increased with the number of reflows. The shear strength value did not significantly change as a function of the number of reflows. Nearly all of the test specimens showed ductile failure mode, and this could be well explained with the results of FEM analyses.

An investigation of effects of Sb on the intermetallic formation in Sn-3.5Ag-0.7Cu solder joints

This study investigates the microstructural evolution and kinetics of intermetallic (IMC) formation in Sn-3.5Ag-0.7Cu lead-free solder joints with different percentages of Sb element, namely, Sn-3.5Ag-0.7Cu-xSb (x=0, 0.2, 0.5, 0.8, 1.0, 1.5, and 2.0). To investigate the elemental interdiffusion and growth kinetics of IMC formation, isothermal aging test is performed at temperatures of 100/spl deg/C, 150/spl deg/C, and 190/spl deg/C, respectively. Scanning electron microscope (SEM) is used to measure the thickness of intermetallic layer and observe the microstructural evolution of solder joint. The IMC phases are identified by EDX and XRD. Results show that some of the antimony powders are dissolved in the /spl beta/-Sn matrix (Sn-rich phase), some of them participate in the formation of Ag/sub 3/(Sn,Sb) and the rest dissolves in the Cu/sub 6/Sn/sub 5/ IMC layer. There is a significant drop in IMC thickness when Sb is added to 0.8 wt%. Over this amount the thickness of the IMC increases slightly again. The activation energy and growth rate of the IMC formation are determined. Results reveal that adding antimony in Sn-3.5Ag-0.7Cu solder system can increase the activation energy, and thus reduce the atomic diffusion rate, so as to inhibit the excessive growth of the IMC. The solder joint containing 0.8 wt% antimony has the highest activation energy. SEM images reveal that the number of small particles precipitating in the solder matrix increases with the increase in Sb composition. Based on the observation of the microstructural evolution of the solder joints, a grain boundary pinning mechanism for inhibition of the IMC growth due to Sb addition is proposed.

Effect of adding 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder alloy on the intermetallic formations with Cu-substrate during soldering and isothermal aging

Intermetallic compound (IMC) formations of Sn–2.8Ag–0.5Cu solder with additional 1 wt% Bi were studied for Cu-substrate during soldering at 255 °C and isothermal aging at 150 °C. It was found that addition of 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder inhibits the excessive formation of intermetallic compounds during the soldering reaction and thereafter in aging condition. Though the intermetallic compound layer was Cu 6Sn 5, after 14 days of aging a thin Cu 3Sn layer was also observed for both solders. A significant increase of intermetallic layer thickness was observed for both solders where the increasing tendency was lower for Bi-containing solder. After various days of aging, Sn–2.8Ag–0.5Cu–1.0Bi solder gives comparatively planar intermetallic layer at the solder–substrate interface than that of the Sn–2.8Ag–0.5Cu solder. The formation of intermetallic compounds during aging for both solders follows the diffusion control mechanism and the diffusion of Cu is more pronounced for Sn–2.8Ag–0.5Cu solder. Intermetallic growth rate constants for Sn–2.8Ag–0.5Cu and Sn–2.8Ag–0.5Cu–1.0Bi solders were calculated as 2.21 × 10 −17 and 1.91 × 10 −17 m 2/s, respectively, which had significant effect on the growth behavior of intermetallic compounds during aging.

Solid state intermetallic compound layer growth between Sn-8Zn-3Bi solder and bare copper substrate

The growth kinetics of the intermetallic compound layer formed between Sn-8Zn-3Bi solder and a bare Cu substrate by solid-state isothermal aging were examined at temperatures between 343 and 423 K for periods ranging from 0 to 100 days. A quantitative analysis was performed of the intermetallic compound layer thickness as a function of the aging time and aging temperature. For the identification of the intermetallic compounds, both Energy Dispersive X-ray and X-Ray Diffraction were employed.

Growth Kinetics of Intermetallic Compound and Interfacial Reactions in Pb-Free Flip Chip Solder Bump during Solid State Isothermal Aging

In the present work, the growth kinetics of intermetallic compound layer formed in Sn-3.5Ag flip chip solder joints by solid-state isothermal aging was examined at temperatures between 80 and 150 °C for 0 to 60 days. The bumping for the flip chip devices was performed using an electroless under bump metallization. The quantitative analyses were performed on the intermetallic compound layer thickness as a function of aging time and aging temperature. The layer growth of the Ni3Sn4 intermetallic compound followed a parabolic law within a given temperature range. As a whole, because the value of the time exponent (n) is approximately equal to 0.5, the layer growth of the intermetallic compound was mainly controlled by diffusion mechanism in the temperature range studied. The apparent activation energy of the Ni3Sn4 intermetallic was 49.63 kJ/mol.

In-Situ Fabrication and Fracture Characteristics of Structural Gradient Ni/Ni-Aluminide//Ti/Ti-Aluminide Layered Materials

Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and TiAl3 were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni3Al and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the interruption of crack growth in metal layers. The Ni3Al and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of TiAl3 layer was found to be a intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance.

Dissimilar material laser welding between magnesium alloy AZ31B and aluminum alloy A5052-O

Joining technology of lightweight dissimilar metals between magnesium and aluminum alloys is essential for realizing hybrid structure cars and other engineering applications. In the present study, the normal center-line welding of lap joint was carried out by laser welding. It was found that the intermetallic layer formed near interface between two metals significantly degraded the joining strength. FEM heat transfer analysis was carried out to find out an available method to control penetration depth and width of molten metal, which contributes to control thickness of intermetallic compound layer. Based on the results of FEM analysis, the edge-line welding of lap joint was carried out, which could easily control the thickness of intermetallic layer and successfully obtained high joining strength.