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Plastic ball grid array packages were aged for up to 2000 hours. Various solder ball pad metallurgies were studied and solder ball shear tests were conducted at a range of ageing times. The solder ball shear strength was found to decrease after an initial hardening stage. The deterioration of solder ball shear strength was found to be mainly caused by the formation of intermetallic compound layers, together with microstructural coarsening and diffusion related porosity at the interface. For the ball pad metallurgy, two distinct intermetallic compound layer structures were observed to have formed after ageing. Once two continuous intermetallic compound layers formed fracture tended to occur at their interface. For the ball pad metallurgies which do not form two continuous intermetallic compound layers, the shear strength still decreased, due to the coarsening of the microstructure, intermetallic particle formation and diffusion related porosity at the surface of the Ni₃Sn₄.

The purpose of this study is to demonstrate that isothermal intermetallic growth data for gold ball bonds can be non-parabolic with explanations of why deviation from parabolic kinetics may occur.

Intermetallic thickness measurements were made at the centre of cross-sectioned ball bonds that were isothermally annealed at 175°C. Intermetallic growth kinetics were modelled with a power law expression(x(t) − x₀)² = α₁t^α₂. The parameters of the power law model were obtained by transformation of the response and explanatory variables followed by data fitting using simple linear regression (SLR).

Ball bonds made with 4 N (99.99%Au) and 3 N (99.9%Au) gold wires exhibited two consecutive time regimes of intermetallic growth denoted Regime I and Regime II. Regime I was characterised by reactive diffusion between the gold wire and the aluminium alloy bond pad, during which Al was completely consumed in the formation of Au–Al intermetallics with non-parabolic kinetics. In Regime II, the absence of a free supply of Al to sustain intermetallic growth led to the conclusion that thickening of intermetallics was caused by phase transformation of Au₈Al₃ to Au₄Al. Ball bonds made with 2 N (99%Au) wire also exhibited non-parabolic kinetics in Regime I and negligible intermetallic thickening in Regime II.

The analysis of intermetallic growth is limited to total intermetallic growth at a single temperature (175°C).

The value of this study lies in showing that the assumption that only parabolic intermetallic growth is observed in isothermally aged gold ball bonds is incorrect. Furthermore there is no need to assume parabolic growth kinetics because with an appropriate data transformation, followed by fitting the data to a power law model using SLR and with the use of statistical diagnostics, both the suitability of the kinetic model and the nature of the growth kinetics (parabolic or non-parabolic) can be determined.

The dissolution processes and subsequent intermetallic reactions between high tin solder bump alloys and Cu‐ or Ni‐based UBM‐metallisations were investigated both theoretically and experimentally. The results showed that when the Cu UBM layer is used together with eutectic or higher Sn‐based solder alloys the dissolution of Cu and the rate of the Cu₆Sn₅ formation is too high for reliable interconnections. On the contrary, Ni provides feasible solution for UBM/high tin solder applications. Although there is strong chemical interaction between nickel and high Sn solder bump alloys, the dissolution and subsequent Ni₃Sn₄ layer growth rates are very low. Thus, a thin Ni layer can sustain interactions with high Sn liquid as well as solid solders during high temperature use. On the basis of the results obtained flip chip bonding with Ni‐based UBM structures provides a viable interconnection solution for reliable fine‐pitch applications.

This paper aims to present the results of a 32-year-old laboratory study of whisker growth from tin electrodeposits that was originally undertaken to gain an increased understanding of the phenomenon of tin whisker growth.

Whisker growth was evaluated using electroplated C-rings (both stressed and un-stressed) that were stored throughout in a desiccator at room temperature. Analysis has recently been undertaken to evaluate whisker growth and intermetallic growth after 32 years of storage. Scanning electron microscopy analysis has been performed to investigate whisker length and, using polished cross-sections, the morphology, thickness and type of intermetallic formation.

Normal tin-plated deposits on brass and steel with a copper barrier layer nucleated whiskers within five months, and in each case, these grew to lengths between 1 and 4.5 mm. For normal tin electroplated onto brass, a one- or two-month nucleation period was needed before whiskers developed. They reached a maximum length of about 1.5 mm after six months, and little or no further growth occurred during the subsequent 32 years. Very few whiskers grew on the tin-plated steel samples and no intermetallic formation was observed. None of the fused tin plating samples nucleated whiskers during the 32-year period.

Knowledge about vintage whiskers is important to take steps to increase the resiliency of space missions. Similarly, such knowledge is important to engineers engaged in products reaching their nominal end-of-life, but where, for reasons of economy, these products cannot be replaced.

This study represents a unique insight into whisker growth and intermetallic formation over an extremely long time period.

The purpose of this study is to investigate the addition of 0.05 Wt.% carbon nanotube (CNT) into the Sn-1.0Ag-0.5Cu (SAC) solder on the intermetallic (IMC) growth. Lead-based solders play an important role in a variety of applications in electronic industries. Due to the toxicity of the lead in the solder, lead-free solders were proposed to replace the lead-based solders. Sn-Ag-Cu solder family is one of the lead-free solders, which are proposed and considered as a potential replacement. Unfortunately, the Sn-Ag-Cu solder faces some reliability problems because of the formation of the thick intermetallic compounds. So the retardation of intermetallic growth is prime important.

The solder joint was aged under liquid state aging with soldering time from 1 to 60 min.

Two types of intermetallics, which are Cu₆Sn₅ and Cu₃Sn were observed under a scanning electron microscope. The morphology of Cu₆Sn₅ intermetallic transformed from scallop to planar type as the soldering time increases. The addition of carbon nanotube into the SAC solder has retarded the Cu₆Sn₅ intermetallic growth rate by increasing its activation energy from 97.86 to 101.45 kJ/mol. Furthermore, the activation energy for the Cu₃Sn growth has increased from 102.10 to 104.23 kJ/mol.

The increase in the activation energy indicates that the growth of the intermetallics was slower. This implies that the addition of carbon nanotube increases the reliability of the solder joint and are suitable for microelectronics applications.

It is an accepted fact that copper‐tin intermetallic formation is necessary to produce a solder wetted copper surface. It is also a fact that this same beneficial intermetallic formation could result in subsequent problems, such as brittle solder joints, tin depletion of solder and intermetallic cracking, if its formation is uncontrolled and excessive. Since its formation is a function of temperature, time, and the availability of reactants, these parameters must be controlled to some degree in order to minimise the chances of problem occurrence.

The wetting performance and intermetallic formation of a Sn/Ag/Cu alloy on printed circuit board (PCB) surfaces and on component terminations were studied in this work. Two different PCB surface finishes, immersion gold over electroless nickel (Ni/Au) and an organic solderability preservative (OSP), were studied. Chip components with Sn/Pb coating and a gull‐wing type component with 100% Sn coating were used in these experiments. Different reflow profiles were tested, and the dependence of the wetting performance, intermetallic layer thickness and the microstructure of the solder joints on the reflow profile were investigated.It was found that reflow process conditions did not significantly influence the spreading or intermetallic formation on either of the surfaces. Neither the wetting onto the component nor the general microstructure of the solder joints varied significantly with the reflow profile. When a Sn/Pb ‐coated component was used, the content and size of Pb‐rich phases in the solder joint increased with a longer time above liquidus or a higher reflow peak temperature.

Substitution of lead‐free solders in electronic assemblies requires changes in the conventional Sn:Pb finishes on substrates and component leads to prevent contamination of the candidate solder. Options for solderability preservative coatings on the printed wiring board include organic (azole or rosin/resin based) films and tin‐based plated metallic coatings. This paper compares the solderability performance of electroless tin coatings versus organic azole films after exposure to a series of humidity and thermal cycling conditions. It is shown that the solderability of immersion tin is directly related to the tin oxide growth on the surface and is not affected by the formation of Sn‐Cu intermetallic phases as long as the intermetallic phase is protected by a surface Sn layer. For a nominal tin thickness of 60 ?inches, the typical thermal excursions associated with assembly were not sufficient to cause the intermetallic phase to consume the entire tin layer. Exposure to elevated temperatures, in the presence of humidity, promoted heavy tin oxide formation which led to solderability loss. In contrast, thin azole films were shown to be more robust to humidity exposure; however, upon heating in the presence of oxygen, they decomposed and led to severe solderability degradation. Evaluations of lead‐free solder pastes for surface mount assembly applications indicated that immersion tin significantly improved the spreading of Sn:Ag and Sn:Bi alloys compared with azole surface finishes.

The purpose of this research is to show the characteristics of a Cu–Ti dissimilar interface produced by a wire arc-based additive manufacturing process. The purpose of this research was to determine the viability of the Cu–Ti interface for the fabrication of functionally graded structures (FGS) using the wire arc additive manufacturing (WAAM) process.

This paper used the WAAM process with variable current vis-à-vis heat input to demonstrate multiple Ti-6Al-4V (Ti64) and C11000 dissimilar fabrications. The hardness and microstructure of the dissimilar interfaces were investigated thoroughly. The formation of Cu–Ti intermetallic at the Ti64/Cu fusion interface is been revealed by scanning electron microscopy and energy dispersive X-ray analysis, while X-ray diffraction was used to identify various Cu–Ti intermetallic phases. The effect of microstructure on interfacial sensitivity and hardness are also investigated.

The formation of CuTi intermetallic and the β-phase transformation in Ti-6Al-4V are found to be heat input dependent. The Cu diffusion length increases as the heat input for Ti64 deposition increases, resulting in a greater Cu–Ti intermetallic thickness. The Cu–Ti interface properties improve when the heat input is less than approximately 250 J/mm or the deposition current is less than 90 A. The microhardness ranges from 55 to 650 HV from the Cu-side to the interface and from 650 to 350 HV from the interface to the Ti-side. Higher current increases interface hardness, which increases brittleness and makes the interface more prone to interfacial cracking.

Nonlinear components are needed for a variety of extreme engineering applications, which can be met by FGS with varying microstructure, composition and properties. FGS produced using the WAAM process is a novel concept that requires further investigation. Despite numerous studies on Ti-clad Cu, information on Cu–Ti interface characteristics is lacking. Furthermore, the suitability of the WAAM process for the development of Cu–Ti FGS is unknown. As a result, the goal of this research article is to fill these gaps by providing preliminary information on the feasibility of developing Cu–Ti FGS via the WAAM process.

An overview has been presented on the topic of alternative surface finishes for package I/Os and circuit board features. Aspects of processability and solder joint reliability were described for the following coatings: baseline hot‐dipped, plated, and plated‐and‐fused 100Sn and Sn‐Pb coatings; Ni/Au; Pd, Ni/Pd, and Ni/Pd/Au finishes; and the recently marketed immersion Ag coatings. The Ni/Au coatings appear to provide the all‐around best options in terms of solderability protection and wire bondability. Nickel/Pd finishes offer a slightly reduced level of performance in these areas which is most likely due to variable Pd surface conditions. It is necessary to minimize dissolved Au or Pd contents in the solder material to prevent solder joint embrittlement. Ancillary aspects that include thickness measurement techniques; the importance of finish compatibility with conformal coatings and conductive adhesives; and the need for alternative finishes for the processing of non‐Pb bearing solders are discussed.