M. Nasta and H.C. Peebles
A good solder flux must simultaneously perform a number of important functions. It must promote thermal transfer to the area of the solder joint, enhance wetting of the solder on…
Abstract
A good solder flux must simultaneously perform a number of important functions. It must promote thermal transfer to the area of the solder joint, enhance wetting of the solder on the base metal, and prevent oxidation of the metal surfaces at soldering temperatures. However, its primary task is to remove the tarnish layer from the metal joint that is about to be soldered. Despite the fact that the process of soldering electronic devices is a part of a multi‐billion dollar industry, the actual chemical reactions that occur during this cleaning process are not well documented. In the case of organic acid or water‐soluble fluxes, the flux reactions can be modelled by considering the interactions at the metal/metal oxide/electrolyte solution interface. Although such modelling systems have not frequently been applied to the behaviour of solder and fluxes, they are common for a number of other closely related chemical systems which are of practical interest, e.g., passivation layers on metals, electrochemical cells and metal oxide semiconductors. There are two types of reactions that can occur at the oxide/solution interface: acid‐base reactions and oxidation‐reduction reactions. The factors which affect the reaction rates and mechanisms are such variables as the structure of the metal oxide, temperature, pH, concentration of the electrolyte, and the chemical nature of the solute and solvent. By combining information about flux behaviour with available models of surface reactions, it should be possible to develop the theory of the flux reactions and to gain a better understanding of the factors which control the process.
Kamila Piotrowska, Morten Stendahl Jellesen and Rajan Ambat
The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue…
Abstract
Purpose
The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue amount left after subjecting the samples to simulated wave soldering conditions.
Design/methodology/approach
Changes in the chemical structure of the activators were studied using Fourier transform infrared spectroscopy technique and were correlated to the exposure temperatures within the range of wave soldering process. The amount of residue left on the surface was estimated using standardized acid-base titration method as a function of temperature, time of exposure and the substrate material used.
Findings
The study shows that there is a possibility of anhydride-like species formation during the thermal treatment of fluxes containing weak organic acids (WOAs) as activators (succinic and DL-malic). The decomposition patterns of solder flux activators depend on their chemical nature, time of heat exposure and substrate materials. Evaporation of the residue from the surface of different materials (laminate with solder mask, copper surface or glass surface) was found to be more pronounced for succinic-based solutions at highest test temperatures than for adipic acid. Less left residue was found on the laminate surface with solder mask (∼5-20 per cent of initial amount at 350°C) and poorest acid evaporation was noted for glass substrates (∼15-90 per cent).
Practical implications
The findings are attributed to the chemistry of WOAs typically used as solder flux activators. The results show the importance WOA type in relation to its melting/boiling points and the impact on the residual amount of contamination left after soldering process.
Originality/value
The results show that the evaporation of the flux residues takes place only at significantly high temperatures and longer exposure times are needed compared to the temperature range used for the wave soldering process. The extended time of thermal treatment and careful choice of fluxing technology would ensure obtaining more climatically reliable product.
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In a recent edition of the nation's favourite soap, Coronation Street, a small incident occurred which illustrated in a nutshell the problems facing the deviser of an industrial…
Abstract
In a recent edition of the nation's favourite soap, Coronation Street, a small incident occurred which illustrated in a nutshell the problems facing the deviser of an industrial design in seeking to protect that design from being copied. Angie, a student of fashion design at the local polytechnic put on a successful show of her designs. Emboldened by the favourable reception she set out a couple of days later for an appointment with a local dress manufacturer to try and sell her designs. She returned a few hours later in tears and with hopes dashed. She had arrived at the firm only to discover that her designs were already being made up into dresses. The designs had been copied at the show and already sold to or copied by them. The incident was not without its silver lining in that in getting drunk to forget the whole sad affair this lead to a romantic interlude with fellow lodger, Curley Watts! It is the purpose of this article to examine the main strands of protection for industrial designs and to look at a proposed new European Community Design Law which has recently been published by the prestigious Max Planck Institute for Foreign and International Patent, Copyright and Competition Law (Munich, 1991). This proposal is being put to the EC Commission as the basis for an EC Regulation.
Kamila Piotrowska, Feng Li and Rajan Ambat
The purpose of this paper is to investigate the decomposition behavior of binary mixtures of organic activators commonly used in the no-clean wave flux systems upon their exposure…
Abstract
Purpose
The purpose of this paper is to investigate the decomposition behavior of binary mixtures of organic activators commonly used in the no-clean wave flux systems upon their exposure to thermal treatments simulating wave soldering temperatures. The binary blends of activators were studied at varying ratios between the components.
Design/methodology/approach
Differential scanning calorimetry and thermogravimetric analysis were used to study the characteristics of weak organic acid (WOA) mixtures degradation as a function of temperature. The amount of residue left on the surface after the heat treatments was estimated by gravimetric measurements as a function of binary mixture type, temperature and exposure time. Ion chromatography analysis was used for understanding the relative difference between decomposition of activators in binary blends. The aggressivity of the left residue was assessed using the acidity indication gel test, and effect on reliability was investigated by DC leakage current measurement performed under varying humidity and potential bias conditions.
Findings
The results show that the typical range of temperatures experienced by electronics during the wave soldering process is not sufficient for the removal of significant activator amounts. If the residues contain binary mixture of WOAs, the final ratio between the components, the residue level and the corrosive effects depend on the relative decomposition behavior of individual components. Among the WOA investigated under the conventional wave soldering temperature, the evaporation and removal of succinic acid is more dominant compared to adipic and glutaric acids.
Practical implications
The findings are attributed to the chemistry of WOAs typically used as flux activators for wave soldering purposes. The results show the importance of controlling the WOA content and ratio between activating components in a flux formulation in relation to its tendencies for evaporation during soldering and the impact of its residues on electronics reliability.
Originality/value
The results show that the significant levels of flux residues can only be removed at significantly higher temperatures and longer exposure times compared to the conventional temperature range used for the wave soldering process. The potential corrosion issues related to insufficient flux residues removal will be determined by the residue amount, its composition and ratio between organic components. The proper time of thermal treatment and careful choice of fluxing formulation could ensure more climatically reliable product.
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Alexander Hanss and Gordon Elger
For soldering, flux is essential because it enables the wetting of the molten solder. Fluxless soldering, i.e. residue-free soldering with the aid of gaseous activators, has been…
Abstract
Purpose
For soldering, flux is essential because it enables the wetting of the molten solder. Fluxless soldering, i.e. residue-free soldering with the aid of gaseous activators, has been known for many years, but is only well established in the field of opto- and microwave electronics where the solder is applied as preform. In high-volume SMD applications where solder paste is printed, this technology is rarely used until now. The reducing effect of a gaseous activator like formic acid vapor on certain solder alloys is known in practice. However, the corresponding reactions which occur under soldering conditions in nitrogen atmosphere have so far not been systematically investigated for different solder alloys. This study aims to analyze the different chemical reaction channels which occur on the surface of different solders, i.e. catalytical dissociation of formic acid on the pure or oxidized metal surface and the formation and evaporation of metal formates. Based on this analysis, a residue-free solder process under formic acid is developed for solder paste applications.
Design/methodology/approach
In this paper, different solder alloys (SnAgCu, SnPb, BiSn, In) were analyzed with thermal gravimetric analysis (TGA) under formic acid flow. Details on mass change depending on the soldering temperature are presented. Activation temperatures are estimated and correlated to the soldering processes. Based on the analysis, fluxless solder pastes and suitable soldering processes are developed and presented. Major paste properties such as printability are compared to a commercial flux solder paste. High-power flip chip LEDs which can be assembled directly on a printed circuit board are used to demonstrate the fluxless soldering. Likewise, the soldering results of standard paste and fluxless paste systems after a reflow process are evaluated and compared.
Findings
The experimental results show that TGA is an efficient way to gain deeper understanding of the redox processes which occur under formic acid activation, i.e. the formation of metal formates and their evaporation and dissociation. It is possible to solder residue-free not only with preforms but also with a fluxless solder paste. The resulting solder joints have the same quality as those for standard solder paste in terms of voids detected by X-ray and mechanical shear strength.
Originality/value
In the fluxless soldering process, the reduction of oxide layers, and therefore the wetting of the solder spheres, is enabled by gaseous formic acid. After the soldering process, no cleaning process is necessary because no corrosive residues are left on the circuit boards and components. Therefore, soldering using solder paste without aggressive chemical ingredients has a high market potential. Expensive preforms could be replaced by paste dispensing or paste printing.
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Some twenty years ago, however, the realisation came that the economy of the animal body calls for the activities of substances with functions apparently akin, in many respects at…
Abstract
Some twenty years ago, however, the realisation came that the economy of the animal body calls for the activities of substances with functions apparently akin, in many respects at least, to those of the hormones, which the body itself is nevertheless unable to produce, and therefore must receive them in its food. The indispensable functions of these, like those of the hormones, are adequately fulfilled by extraordinarily small amounts of each one. These food constituents yield therefore no appreciable supply of energy, nor do they serve in any ordinary sense as structural materials. Their presence like that of the hormones is necessary rather for the normal progress of active events. They have dynamic functions. I am alluding, of course, to the vitamins.
Imad B. Baalbaki and Naresh K. Malhotra
By standardizing the marketing effort over similar worldwidesegments and differentiating it across dissimilar worldwide segments,the international marketing manager is able to…
Abstract
By standardizing the marketing effort over similar worldwide segments and differentiating it across dissimilar worldwide segments, the international marketing manager is able to reap the advantages of both standardization and customization. The choice of the variables by which to segment the global market is crucial. Traditionally, purely environmental bases (geographic, political, economic, and cultural) were used as bases for international market segmentation. Proposes that international marketers group relevant markets based on both environmental as well as marketing management bases. The marketing management bases are classified as: (1) product‐related; (2) promotion‐related; (3) price‐related; and (4) distribution‐related. Derives number of propositions with direct implications for international marketing strategy and segmentation with respect to these bases. Highlights the managerial implications of the variables encompassed by these bases. Proposes the empirical investigation of the derived propositions as a research agenda for the future.
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Lucretia D. Peebles and Toby Hopstone
Surprisingly, urban principals seldom learn transformative leadership in their administrator preparation programs, thus missing out on its value in redefining the moral and…
Abstract
Surprisingly, urban principals seldom learn transformative leadership in their administrator preparation programs, thus missing out on its value in redefining the moral and ethical imperatives to improve with effective leadership and teaching, poor and minority students’ academic learning outcomes and performance on NCLB-mandated high-stakes accountability tests for professional learning communities. This chapter historicizes contexts and analyzes kaleidoscopic reflections of newly practicing urban school principals to illuminate chaos that often forces them into survival-mode managing rather than leading transformatively with structural reforms, and to make them aware of “equity traps” resistant to leadership intent upon radically transforming schools into productive and socially just learning communities.