The Effectiveness of Bismuth Addition to Retard the Intermetallic Compound Formation

The aim of this paper is to study the effectiveness of bismuth addition in the solder alloy to retard the intermetallic compound formation and growth. In this study, three categories of solders such as Sn-4Ag-xCu (x = 0.5, 0.7, 1.0) and Sn-4Ag-0.5Cu-xBi (x = 0.1, 0.2, 0.4) were used. Ni/Au surface finish substrates were dipped into the molten solder at a temperature of 180-190 oC and allowed to cool at room temperature. The intermetallic compound (IMCs) were subjected to the characterization in terms of composition and morphology. The IMC phases were identified by energy dispersive x-ray (EDX), whereas the optical microscope and scanning electron microscopy (SEM) were used to observe microstructure evolution of the solder joint. The results clearly showed that copper concentration dependency was high during the reflow stage. Besides, only Ni3Sn4 and Ni3Sn2 were detected for all copper concentrations. The addition of Bi was found to have no significant effect on the type of IMCs formed, but yet the grain became further refined

The effect of nickel doping on SAC305 lead-free solders and EN(B)EPIG surface finish

Recently, there are many portable electronics product such as i-pad, smart phone and tablet were widely used due to growing needs of busy lives and demanding, more functionalities and compatibility. The growing of these smart technologies made electronic packaging are moving parallel with current technology and expanding rapidly because of global competitive pressure. Thus, flip chip technology is one of the important element need to be considered in order to produce high performance and quality of electronic devices due to shorter electrical connections between the chip and substrate and very high input/output capacity and the smallest possible package size. In flip chip applications, solder bump was used to connect the die to the substrate or circuit board. The addition of doping element in lead-free solder has been discussed have a big influence on the solder joint quality including solder microstructure. It also can enhanced the properties and improve the performance of interfacial reaction at interface and made a reliability of lead-free solder especially on Sn-3.0Ag-0.5Cu was increased. Therefore, this study investigates the effect of nickel doping on Sn-3.0Ag-0.5Cu (SAC305) lead-free solders and electroless nickel (boron)/electroless palladium/immersion gold (EN(B)EPIG) surface finish. In this study, two types of lead-free solders was used which are Sn-3.0Ag-0.5Cu (SAC305) and Sn-3.0Ag-0.5Cu-0.05Ni (SACN30505) with solder size diameter of 500 μm in order to examine the effect of nickel on interfacial reaction during soldering process. Reliability of solder joint has been assessed by performing solid state isothermal aging at 125C for 250, 500, 1000 and 2000 hours. Several characterization techniques will be conducted including image analyzer, optical microscope, field emission scanning electron microscopy and energy dispersive x-ray analysis to characterize the intermetallic formed. After reflow soldering process, it was found that the (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 intermetallic compound (IMC) is formed at interface. (Ni, Cu)3Sn4 dominates in the outside of solder joint while (Cu, Ni)6Sn5 dominates in the centre of joints. Besides that, after soldering and isothermal aging process, SAC305 solder with additions of 0.05% of Ni (SACN30505) made the intermetallics grew slightly faster than in the solder without Ni additions. Hence, analysis by optical microscope revealed that the IMC thickness of the SACN30505 solder produced thicker IMC compared to SAC305 for both situations. This observation is confirmed by the increase in grain size of intermetallics with Ni additions. Moreover, aging time resulted in an increase in thickness and changed the morphology into more spherical, dense and large grain size. In addition, the results also revealed that the thickness of intermetallics formed is proportional to the aging duration

Effect of tin coating thickness on tin whiskers formation and growth

The effect of various thicknesses of tin coating towards tin whiskers formation and growth in 30°C/60%RH environmental condition had been studied. Electroless plating method was used to coat a layer of tin onto copper, Cu substrates. Three different thicknesses were obtained by controlling the plating times of immersion tin. 8 minutes, 12 minutes, and 20 minutes of plating times produced 1.2μm, 1.5μm, and 2.3μm thickness of tin coating respectively. After storage time up to twelve weeks under 30°C/60%RH environmental condition, it was found that the length of tin whiskers in thinnest tin coating (1.2μm) is 48.96pm, followed by 54.24μm in thicker tin coating (1.5μm), and the longest tin whiskers was recorded as 58.58μm in thickest tin coating (2.3μm). Based oil the results, it was clearly shows that the thickness of tin coating affects the growth of whiskers as the thickest tin coating promotes longest whiskers compare to the thinnest tin coating

Boriding and boronitrocarburising effects on hardness,wear and corrosion behavior of AISI 4130 steel

The effects of boriding and boronitrocarburising surface treatments on the microstructure and mechanicalproperties of AISI 4130 steel have been investigated. Pack boriding was carried out at 1223 K for 5 h and 8h, while the double treatment of boronitrocarburising consisted of salt bath nitrocarburising at 853 K for 6 hfollowed by pack boriding at the same temperature and times as the boriding treatment. Microstructure examinationof the borided and boronitrocarburised layers was carried out using optical and scanning electronmicroscopy, and phase identification was obtained using X-ray diffraction. Vickers hardness, wear and corrosionweight loss tests were used to evaluate the mechanical properties and corrosion behaviour. The results ofX-ray diffraction analysis revealed the presence of superhard phases such as FeB, Fe2B, CrB, MnB andMnB2, indicating that pack boriding surface treatment conducted at 1223 K for 8 h exhibited the highesthardness, low coefficient of friction and the greatest wear resistance. Boronitrocarburising treatment, on theother hand, caused a reduction in both the depth of iron borides zone and mechanical properties compared tothe boriding surface treatment. These recommended treatments offer to industrialists a particular contributionand interest in the development of these steels, which can be applied in various fields.Keywords: AISI 4130, Boriding, Boronitrocarburising, Microstructure, Mechanical properties

Thermal cyclic test for Sn-4Ag-0.5Cu solders on high P Ni/Au and Ni/Pd/Au surface finishes

In electronic packaging, the reliability of the interconnection changes with the surface finish and the type of solders being used. Thermal cycling is one method of reliability assessment. In thermal cycling experiments, the strain state is simplified by soldering together regular shaped pieces of materials with different coefficients of thermal expansion and exposing the joint to repeated fluctuations of temperature within a certain range. Thus, this study focuses on the intermetallic evolution of Sn-4Ag-0.5Cu on Ni/Au and Ni/Pd/Au surface finishes with thermal cycling up to 1000 cycles with the range of temperature varying from 10 to 80°C. Sandwich samples were prepared by placing solder balls of Sn-4Ag-0.5Cu between two substrates of two different surface finishes: Ni/Au and Ni/Pd/Au. Optical microscope and FESEM (Field emission scanning electron microscope) were used to analyze the samples. From the study, it was observed that the intermetallic changes from (Cu, Ni)6Sn5 to (Ni, Cu)3Sn4 after 1000 thermal cycles for Ni/Au. These changes promote the formation of cracks at the solder joint because of the different mechanical properties between Ni-Sn based intermetallic and Cu-Sn intermetallics. However, for the Ni/Pd/Au surface finishes, no cracks formed after thermal cycling up to 1000 cycles. This shows that the reliability of the solder joint is higher for Ni/Pd/Au surface finishes in this experiment. Based on these results, it can be concluded that the reliability of the Ni/Pd/Au surface finishes with Sn-4Ag-0.5Cu solders is higher within the given condition of this research

Mechanical properties and bio-tribological performance of PVD (Ta/ZrN)n multilayer coatings on UHMWPE in bovine serum lubrication

This work investigated the tribological performance of (Ta/ZrN)n multilayer coatings against ultrahigh molecular weight polyethylene (UHMWPE) material. Three multilayer coatings with different designs were deposited on Ti-6Al-4 V substrate and subjected to wear testing under lubrication of diluted bovine calf serum. The results revealed an improvement in wear resistance of (Ta/ZrN)n multilayer coatings and low coefficient of friction under an applied load of 1 N. High hardness, excellent biotribological properties, and low residual stresses were obtained in the multilayer coating with the thinnest ZrN as the topmost layer of 100 nm. This work demonstrates that Ta/ZrN multilayers can be promising coatings for prosthesis applications

High temperature oxidation of AZ91D magnesium alloy granule during in-situ melting

Oxidation behaviour of AZ91D was investigated by heating the alloygranules in a ceramic mould between 650 and 800 °C, for 30 and 60 min. The granules failed to melt in unprotected environment even when the temperature was increased to 800 °C. Raising the temperature increased the oxides thickness linearly, however, oxidation enhanced beyond 750 °C with severe mould–metal reaction and selective oxidation. Heating duration showed more pronounced effect on oxide formation compared to heating temperature. MgO was found to be the dominant compound in oxidation products. Aluminium participated during severe oxidation or combustion to some extent whilst no zinc oxide was detected

Effect of bismuth on microstructure of unmodified and Sr-modified Al-7Si-0.4Mg alloys

The effects of bismuth and the combination of bismuth and strontium on the eutectic silicon structure in Al-7Si-0.4Mg alloys were investigated under different solidification conditions. The results show that bismuth has a refining effect on the eutectic silicon and its refinement behavior increases with increasing Bi content up to 0.5 (mass fraction). When bismuth is added into the molten alloy modified with strontium, a higher Sr/Bi mass ratio of at least 0.45 is required to attain full modification of the eutectic silicon