Search results

In the production of printed circuit assemblies, the demand for higher reliability levels has increased over the years. In order to achieve a high level of soldering quality, it is essential that solderability is built into the system at all stages and various factors must be taken into account. In the first section of this paper some of these factors are discussed. The various solderable coalings that are available are reviewed, some of the problems that can be encountered are illustrated and the effects of impurities in solders discussed. In the second part of the paper, the use of circuit boards having fused tin/lead coatings is discussed from the solderability point of view.

An electronic assembly may consist of a printed circuit and various types of electrical components. Soldering to make the electrical/mechanical connection is a critical process. Both printed circuit and component leads must promote acceptable solder wetting if high reliability is to be obtained. Bulk purchasing of these items can lead to long periods of storage often in poor conditions. This paper describes some of the work which simulates storage conditions by accelerated ageing so that a prediction can be made as to whether solderability will be affected. Due acknowledgement is hereby made to the EIPC for their permission to publish this paper which was presented at a recent EIPC seminar.

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.

Because of recent interest in nickel silver (copper‐zinc‐nickel alloy) in electronic applications, this alloy was chosen for an ageing‐solderability study. An Auger/ESCA study was performed on the surface of samples of nickel silver to determine the chemical nanostructure at various degrees of ageing (0–2 years). During this time a redistribution of the three constituent metals occurred, with migration of copper to the surface. All three metal constituents oxidised at different rates. Additionally, the thickness of the surface carbon layer increased with time. The effect of physical abrading (cleaning by erasing) of the samples on solderability, ageing, and chemical surface was also studied. After erasure, all samples appeared similar to one another and close to the original composition, and the copper oxide layer was completely removed. All the cleaned surfaces, when returned to the atmosphere, experienced air oxidation of copper to copper oxide in less than two days. Angle‐resolved ESCA studies were performed to determine the concentration gradient close to the surface. Nickel was not evenly distributed with depth, but was more concentrated on the surface of the cleaned samples. Solderability studies on nickel silver samples showed no improvement with chemical treatment, attesting to the creation of a resistant passivation layer.

The availability of a wetting balance which can be easily interfaced to a microcomputer has made possible a practical receiving inspection solderability test for component leads that avoids the subjectivity of the present dip‐and‐look test. The wetting balance, in effect, detects the size and shape of the solder meniscus on the lead. Since it is the solder meniscus more than the degree of coverage that is evaluated by inspectors of the completed solder joint, the wetting balance provides a more realistic test of how well the components will perform on the PWA. The software that has been developed for the wetting balance is designed to make it easy for inspection workers to perform the test with a minimum of training. It asks for identification of the part, manufacturer, date code, purchase order number, etc., so that the final results are adequately documented. Use of a computer to present the results means that the wetting force as a function of time can be plotted as a normalised curve (automatically accounting for differences in number and size of leads), and also that the results can be accumulated in a factory computer for statistical quality control. For a given lot of components, there is usually little spread in the observed results. This indicates that a sample size as small as three is sufficient to characterise the lot. With further data accumulation, it should be possible to devise a skip‐lot sampling plan for those manufacturers showing consistently good solderability. Also, the accumulated results of lots from problem manufacturers, coupled with microscopic studies of the causes of poor solderability, can be used as a basis for negotiations. The results are reproducible from one plant to another because they do not require visual interpretation. Judicious application of this method of solderability testing by a component user should allow removal of problem lots (for return or solderability enhancement), and therefore lead to a virtual elimination of solderability‐related defects observed after PWA soldering. Widespread application by component manufacturers (after burn‐in) should lead to a virtual elimination of cases of shipping unsolderable components.

Quality Control and/or Assurance and similar phrases are in common use but can have different meanings, depending on the type of product involved and on economic considerations. It is proposed that, from the soldering point of view, component design and solderability must be as good as possible and must be regularly checked. There must be adequate control over every aspect of the soldering process, and inspection of the completed assembly must be meaningful with realistic accept/reject levels decided upon at the outset. Having established a complete production scheme incorporating quality checking, it is proposed that no alterations should be made without full consultation and collaboration with all the personnel concerned.

The effect of gold (Au) on the reliability of 0.65 mm pitch surface mount solder joints between plastic quad flat packs and Cu‐Ni‐Au FR‐4 printed circuit boards was investigated. Cu‐Ni‐Au is a desirable printed circuit board finish for multi‐chip modules or printed circuit boards that would otherwise require a selective Au finish, for example for edge connectors or wire bondable parts. However, Au is known to embrittle solder when it is present in sufficiently high concentrations, creating a concern that solder joint fatigue life in service will also be adversely affected. This paper reports the results of mechanical shock, mechanical vibration and thermal cycling testing of fine pitch solder joints containing varying amounts of Au. Tests were performed on as‐soldered joints and on joints that had been heat‐treated to evolve the microstructure towards equilibrium. The tests were designed to accelerate in‐service conditions in a typical industrial environment. Under these conditions, the Au concentrations tested did not promote solder joint failures. Microstructural characterisation of the distribution and morphology of the Au‐, Ni‐ and Cu‐Sn intermetallics in the joint before and after accelerated testing was also performed. On the basis of these observations it is recommended that the Au concentration in solder joints between plastic quad flat packs and Cu‐Ni‐Au FR‐4 printed circuit boards not exceed 3.0 wt.%.

This paper focuses on the comparative study on reliability performance of various surface coatings. Only brief descriptions of coating processes, material physical properties, costs, and their applications are given.

This chapter provides an extensive review of literature on the interaction between and interdependence of informal and formal working practices in various workplace settings. The aim of the chapter is to elucidate the organisational, managerial, human relations and social factors that give rise to informal work practices and strategies, on the shop-floor not only at workers and work group levels but also at supervisory and managerial levels. This chapter helps the reader to understand the informal work practice of making a plan (planisa) in a deep-level mining workplace.

The purpose of this paper is to re‐map the neglected phenomenon of organisational misbehaviour (misbehaviour) by reflecting the many approaches taken on this emergent field of study, and articulate a revised research agenda.

Both preceding and recent empirical and theoretical research papers are discussed and possible overlap and convergence of findings are examined. The discussions mainly surround studies from industrial sociology and organisational behaviour, yet studies from industrial relations and gender studies are also considered. From the re‐assessment, a revised map and research agenda for misbehaviour is produced.

More research should be directed towards humour and its uses in contemporary organisations, why managers break the rules, the internet as a tool and framework for defiant activities, informal and hidden employee identities as a framework for self‐organised misbehaviour, functional misbehaviour and informal strategies used by employees to survive work. Further work is required to unify the field and suggestions are made on how this may be achieved.

The paper is based on a re‐assessment of the extant literature and the findings reflect the broadly problematic matter of reconciling incongruous paradigms.

The paper puts forward a revised and updated map of organisational misbehaviour. It also offers insights which managers can use to deal with a broad range of misbehaviour conducted within and outwith the workplace.

The paper provides a new map that goes beyond previous articulations of misbehaviour. The revised research agenda attempts to guide future research on the subject of misbehaviour in a more balanced direction.