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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 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.

The role of intermetallics in soldered joints is ambivalent. They are an essential part of joints to common basis materials and at low levels they have a strengthening effect on solder alloys. At higher levels, however, it is well known that they can cause joint embrittlement. In this paper three aspects of their role have been studied: the microstructure of intermetallic containing solder alloys, the effects of soldering parameters on the quantity of intermetallic formed and, finally, the rates of growth of intermetallic compounds in the solid state. The results suggest that alloys which are pre‐doped with copper tend to form slightly more interfacial intermetallic during soldering than those which are not. In the solid state the rates of growth appear to be a function of the melting point of the alloy, with the higher melting point lead‐free alloys exhibiting lower rates than lower melting point alloys such as 63Sn37Pb (183∞C) or 42Sn58Bi (138∞C).

Tin and solder coatings interact with substrates commonly used in the electronics industry to produce layers of intermetallic compounds at temperatures above and below the melting point of the coatings. Observations on the rates of compound growth at room temperature for durations of up to 12 years are reported and related to the published results for shorter times at higher temperatures. Recent results concerning the effect of intermatallic compound growth on the solderability of coatings and on the strength of soldered joints are presented. In both cases it is apparent that retarding the rate of compound growth could be useful and the use of barrier layers for this purpose is considered.

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 paper is to present the results from work on a project aimed at evaluating six different copper alloy substrates coated with pure tin for tin whisker growth. The influence of intermetallic growth between the copper alloy substrate and the tin‐plating on the growth of tin whiskers has been investigated.

The experiment consisted of six substrates of different alloys of copper, plated with bright tin including copper beryllium, cartridge brass, phosphor bronze, Cu‐Ni‐Si “7025” and Cu‐Ni‐Sn “spinodal”. The samples were mechanically stressed and then subjected to temperature humidity storage conditions for 1,000 h. These samples were then evaluated for tin whisker growth and intermetallic layer thickness.

Of the six samples five showed tin whisker growth. For these samples the intermetallic layer thickness has little effect on tin whisker growth. Sample with Cu‐Ni‐Sn “spinodal” alloy substrate showed very low whisker density and comparatively lower maximum whisker length than the other tested substrate material.

More samples per condition should be evaluated to bolster the conclusions. For the sample without tin whisker growth, holes on the surface of the plating were observed. The holes in the plating provide an opportunity for stress relaxation after the plating process. Since stress in the plating layer is low, tin whiskers are not formed on the sample surface.

The paper details the tin whisker growth on six tin plated copper substrate samples. The intermetallic layer thickness for each copper alloy substrate is calculated. The relationship between the intermetallic layer thickness and tin whisker growth for the six substrates are discussed.

To investigate effects of the thermal history on intermetallic thickness and morphology and on the resulting shear strength of the ball attachment for a variety of BGA components.

In this study, a variety of BGA components with balls made of Pb‐free Sn‐Ag‐Cu (SAC) 305, Sn‐Pb eutectic and high‐temperature 90Pb‐10Sn alloys, were subjected to different thermal histories, including up to ten reflow cycles, and aged at 125°C from 24 to 336 h. The intermetallic thickness and morphology after these thermal events were then examined under optical and scanning electronic microscopes. Ball shearing tests were conducted to investigate effects of the thermal history and intermetallic thickness and morphology on shearing strength of these solder balls.

The results show that effects directly from intermetallic layers may or may not be detectable; and the shear strength of solder balls is largely dependent on the solder alloy and its microstructure. Shear strength increases are observed after multiple reflow cycles and ageing at elevated temperature for the two Pb‐bearing alloys, while the SAC305 lead‐free alloy shows slight reductions in both strength and ductility after thermal exposure.

Presented results can be used for estimation of reliability for electronic assemblies subjected to multiple rework and repair operations, which expose sensitive components, such as BGAs, to elevated temperatures.

It is believed that a sound understanding of the effects of intermetallic morphology and thickness on reliability of BGA solder balls can lead to more intelligent choice of soldering processes, as well as to rework/repair process optimisation and to establishing their operational limits.

High‐density packaging devices have unique characteristics which make their assembly, test and repair very difficult. The only realistic method of rework is to replace the defective component with a new or re‐balled component. Although a wide range of rework techniques is available, degradation in assembly reliability may accompany the process. The formation of brittle secondary intermetallic compounds following CSP rework can adversely affect the mechanical properties of the joint, particularly when they make up a significant proportion of its thickness. Reports on the effects of different CSP rework techniques on intermetallic layer formation. Two PCB pad‐cleaning methods and three flux/paste deposition methods are investigated. The reworked joints are analysed using optical microscopy to determine the extent of intermetallic growth. Their quality is also assessed using shear strength testing prior to, and after, thermal ageing at 1008C to accelerate the growth of intermetallic compounds and evolution of the solder grain structure.

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.

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.