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Article
Publication date: 1 August 2004

W.J. Plumbridge

The decision to move to lead‐free solders has been made, but processing and performance challenges remain. This paper considers the transition in terms of performance, with…

1609

Abstract

The decision to move to lead‐free solders has been made, but processing and performance challenges remain. This paper considers the transition in terms of performance, with particular emphasis on long term, high reliability applications. Comparison of key mechanical properties indicates generally beneficial outcomes of the transition to lead‐free alloys, although there is a lack of understanding surrounding “anomalous” observations, such as the effects of the bismuth. The lower melting point of Sn‐Zn‐Bi alloys, together with their comparable mechanical properties, provide further impetus to address their shortcomings during processing. Some lead‐free alloys, such as Sn‐0.5Cu, are susceptible to tin‐pest formation following prolonged exposure below 13°C, and this possibility remains for the more concentrated Sn‐3.8Ag‐0.7Cu alloy.

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Soldering & Surface Mount Technology, vol. 16 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 December 1999

W.J. Plumbridge

While the implementation of lead‐free solder technology has been the focus of much recent research, the challenge of joint structural integrity should not be overlooked. The paper…

352

Abstract

While the implementation of lead‐free solder technology has been the focus of much recent research, the challenge of joint structural integrity should not be overlooked. The paper summarises the significant variability in the mechanical properties of solders, both in terms of the prevailing testing conditions and between the alloys themselves. Using conventional routes to life prediction for an elementary creep situation, it demonstrates the critical importance of understanding the failure processes and utilising materials data that are appropriate.

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Soldering & Surface Mount Technology, vol. 11 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 January 2006

W.J. Plumbridge

To draw attention to the need to consider design and performance, as well as production, in the implementation of lead‐free solders.

321

Abstract

Purpose

To draw attention to the need to consider design and performance, as well as production, in the implementation of lead‐free solders.

Design/methodology/approach

The potential failure modes of solder joints and their underlying causes are reviewed. A hypothetical design exercise is employed to demonstrate key requirements for reliable design.

Findings

The substantial variation in influential mechanical properties over the ranges of stress, temperature and strain rate is likely to be encountered in service. In addition to these three parameters, there is the need to consider time‐temperature profiles in the service cycle and the prior thermal history of the joint materials.

Originality/value

The demonstration that reliable design and life prediction can only be achieved by employing appropriate properties in appropriate constitutive expressions.

Details

Soldering & Surface Mount Technology, vol. 18 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 9 February 2010

W.J. Plumbridge

The purpose of this paper is to describe the effects of mechanical testing and thermal treatment prior to storage at either −18 or −40°C, for periods in excess of ten years on the…

319

Abstract

Purpose

The purpose of this paper is to describe the effects of mechanical testing and thermal treatment prior to storage at either −18 or −40°C, for periods in excess of ten years on the Sn‐37Pb alloy.

Design/methodology/approach

For over a decade, The Solder Research Group at The Open University has studied tin pest development in several of the new lead‐free solders. Bulk samples, employed for mechanical testing, are laid down at −18 and −40°C, and inspected periodically.

Findings

In a previous examination in 2006, there was no evidence of tin pest formation in this alloy. On re‐examination of the same specimens in 2008, about one in ten of the samples stored at −18°C, both “as cast” and “tested”, exhibited warts of tin pest. Storage at −40°C increased this ratio to about one in three following treatment.

Originality/value

The paper's findings demonstrate that, even with high concentrations of lead present, eventually tin pest will form. So, for interconnections used in long‐term applications, whether lead‐free or lead‐bearing solders are employed, performance and structural integrity considerations should not ignore tin pest.

Details

Soldering & Surface Mount Technology, vol. 22 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 April 2003

W.J. Plumbridge

With the continued miniaturisation of electronics equipment, a more detailed examination of the mechanical behaviour of solders is required to ensure reliability in performance…

882

Abstract

With the continued miniaturisation of electronics equipment, a more detailed examination of the mechanical behaviour of solders is required to ensure reliability in performance. The paper reviews various aspects of the interpretation of the creep response of lead‐containing and lead‐free alloys. It demonstrates the necessity of acquiring stress‐rupture data over as long a period as possible to avoid non‐conservative extrapolation. For example, at 75°C, the transition in slope of the applied stress vs time to rupture plot occurs after about 1,000 h for Sn‐37Pb, although for the lead‐free alloys examined no such transition is observed within this timescale. Sometimes, deformation may be a more appropriate failure criterion than rupture, and it is shown that for Sn‐37Pb this may result in substantially shorter failure times than utilising a rupture criterion. The quality of life estimation methods then depends upon the extent of this stage when the creep rate is a minimum. The Y factor (tm : tr) where tm is the time spent in steady state or within 10 per cent of the minimum creep rate, for all the solders examined at 75°C generally falls into the 20‐30 per cent range. Estimations of creep life may substantially under predict because of this.

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Soldering & Surface Mount Technology, vol. 15 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 13 February 2007

W.J. Plumbridge

To review the literatures, and to consider the latest results regarding the formation of tin pest in lead‐free solders and interconnections.

904

Abstract

Purpose

To review the literatures, and to consider the latest results regarding the formation of tin pest in lead‐free solders and interconnections.

Design/methodology/approach

Previous work, over almost a century, on tin pest formation in tin and its alloy has been critically analysed. Samples of the new generation of lead‐free solders, which have experienced long term storage at −18 and −40°C, have been examined.

Findings

Tin pest has been observed in bulk samples of tin −0.5 (wt%) copper solder after exposure at −18°C although not at −40°C. Other lead‐free alloys (Sn‐3.5Ag, Sn‐3.8Cu‐0.7Cu and Sn‐Zn‐Bi) have been immune to date. Large‐scale model joints exhibit tin pest but actual joints may be resistant due to the limited free solder surface available and the constraint of intermetallic compounds and components.

Research limitations/implications

The possibility of tin pest formation in joints remains. It seems that impurities are essential protection against it, but for long term applications there is no certainty that tin pest and joint deterioration will never occur.

Originality/value

The paper considers the various factors that may affect tin pest formation and demonstrates its existence in one of the more popular new lead‐free alloys.

Details

Circuit World, vol. 33 no. 1
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 1 April 2000

W.J. Plumbridge

Impressions gained from two visits to Japan, discussing with representatives of industry and academe the current status regarding the implementation of lead‐free technology, are…

255

Abstract

Impressions gained from two visits to Japan, discussing with representatives of industry and academe the current status regarding the implementation of lead‐free technology, are presented. Driven by the commercial rewards of lead‐free goods, Japan appears to have more clearly articulated targets for the removal of lead, in advance of the expected timescales in EU legislation. Various strategies for combating problems associated with the higher melting point of lead‐free solder alloys have been investigated. Design and development generally involve a broader approach than in Europe, involving stress analysis, materials properties and life prediction to underpin empirical data obtained by thermal cycling of boards. Despite the existence of several committees to facilitate the introduction of lead‐free solders, a lack of cohesion is sometimes apparent, particularly regarding heat treatment of materials prior to testing. It is proposed that a challenge as demanding as this would benefit from greater collaboration internationally.

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Soldering & Surface Mount Technology, vol. 12 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 April 1996

W.J. Plumbridge

An overview of the mechanical behaviour of commonsolder types is presented, with particular emphasis placed upon those properties relevant to theperformance of soldered joints in…

417

Abstract

An overview of the mechanical behaviour of common solder types is presented, with particular emphasis placed upon those properties relevant to the performance of soldered joints in service. The requirements for more sophisticated and complex information are highlighted in order to assist design for the increasingly arduous demands associated with miniaturisation.

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Soldering & Surface Mount Technology, vol. 8 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 27 May 2014

Agata Skwarek, Jan Kulawik, Andrzej Czerwinski, Mariusz Pluska and Krzysztof Witek

The purpose of this study is to develop a testing method for tin pest in tin – copper (SnCu) alloys. Tin pest is the allotropic transformation of white β-tin (body-centered…

1005

Abstract

Purpose

The purpose of this study is to develop a testing method for tin pest in tin – copper (SnCu) alloys. Tin pest is the allotropic transformation of white β-tin (body-centered tetragonal structure) into gray α-tin (diamond cubic structure) at temperatures < 13.2°C.

Design/methodology/approach

Bulk samples of Sn99Cu1 weight per cent (purity, 99.9 weight per cent) were cast in the form of roller-shaped ingots with a diameter of 1.0 cm and a height of 0.7 cm. The samples were then divided into four groups. The first group included samples artificially inoculated with α-tin powder. The second group was inoculated in the same way as the samples from the first group but additionally subjected to mechanical pressing. The third group of ingots was only subjected to mechanical pressing. The fourth group of samples consisted of as-received roller-shaped ingots.All samples were divided into two groups and kept either at −18°C or at −30°C for the low-temperature storage test. For tin pest identification, a visual inspection was made, using a Hirox digital microscope over 156 days at intervals not longer than 14 days. The plot of the transformation rate, presented as the average increase in the area of α-tin warts in time, was also determined. To demonstrate the differences between regions of β- and α-tin, scanning ion microscopy observations using the focused ion beam technique was performed.

Findings

The first symptoms of tin pest were observed for the inoculated, mechanically pressed samples stored at −18°C, as well as those at −30°C, after less than 14 days. In the first stage of transformation, the rate was higher at −30°C for some time but, after about 75 days of storage at sub-zero temperatures, the rate at −30°C became lower compared to the rate at −18°C. Inoculation via the application of substances which are structurally similar to α-tin was efficient for the proposed new approach of rapid testing only when applied with simultaneous mechanical pressing. Infection from pressed-in seeds, leading to conventional seeded growth, was more rapid than infection in contact with seeds (without mechanical pressing), where the transition mechanism was induced by the epitaxial growth of metastable ice.

Originality/value

The new rapid method for the diagnostic testing of the susceptibility of different SnCu alloys to tin pest in a period much shorter than 14 days (within single days for storage at −30°C) is proposed and described. The test procedure described in this paper produced results several times quicker than conventional procedures, which may take years. In effect, the behavior of tin alloys in the face of tin pest may be predicted much more easily and much earlier. The same procedure can be applied to other SnCu alloys used in electronics (and in other areas), if the test samples are prepared in a similar manner.

Details

Soldering & Surface Mount Technology, vol. 26 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 December 2002

140

Abstract

Details

Soldering & Surface Mount Technology, vol. 14 no. 3
Type: Research Article
ISSN: 0954-0911

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