bluuebunny/crossref_metadata_2025 huggingface dataset:
How to Use Automated X‐ray Inspection for Process Monitoring and Control
Authors: Nameth R.
Published: February 2008

The initial excitement over increased solder joint densities, higher manufacturing throughput, and superior electrical performance brought forth by surface mount technology (SMT) has been replaced by frustrations over lower yields and the inherent difficulties of inspecting hidden solder joints. In the plated through hole (PTH) process, rework and inspection tasks were not only relatively easier tasks, but also less costly. The high cost of inspecting and reworking SMT assemblies dictates a rethinking of the assembly process. Increasing first time yields becomes the key to reducing SMT inspection and rework costs. In a high volume facility, a 100% visual inspection process is not feasible because of the high cost of inspection and rework. However, if a company intends to remain competitive, inspection and rework must be reduced without a sacrifice to final product quality. Realising that it is not possible to ‘inspect’ quality into a product, improved yield must result from a controlled process environment. By maintaining a controlled environment, one will be provided with lower inspection costs, lower rework costs, lower scrap and, in the final analysis, improved product quality. At the heart of any process control environment should be a real‐time process control system designed specifically to accommodate SMT process defects. Process monitoring is accomplished by locating and identifying SMT process flaws. These flaws will then be reported to a host system for statistical analysis. These are statistical data used to make timely adjustments to the various stages of the assembly process in a real‐time manner. Being able to monitor the production process objectively in real time, and detect hidden flaws accurately, are the keys to having a successful process inspection system. Automated X‐ray Inspection is gaining acceptance as a viable process monitoring tool, capable of detecting and reporting SMT process flaws, including those hidden flaws not reported with typical visual inspection systems. The purpose of this paper is to show how an Automated X‐ray Inspection system can be integrated into the SMT production process as a cost‐effective method for improving SMT yield.
Surface Mount Technology Trade and Professional Associations
Authors: Lea C.
Published: February 2008

A brief review is presented of the aims and activities of the trade and professional associations that offer a participation in the advancement of surface mount technology. Membership fees and contact addresses are also given.
Vias‐in‐pads for Surface Mounted Components
Authors: DeNure D.G.
Published: February 2008

The demand for higher density circuit packs, limited mounting space, faster switching times and cost‐effective designs has encouraged designers to take another look at placing vias directly in the mounting pads of reflow soldered surface mounted components. The standard reasons for not putting vias in pads (V‐I‐P) such as solder wicking and joint integrity were addressed and found to be surmountable. A study was performed to investigate the effects that a via in the mounting pad(s) has on the solder joint of both discrete components and gull and J‐leaded ICs. The size of the via was varied as well as the location along the centre axis of the pad. It was found that the via diameter is a critical parameter while the via location has no noticeable effect on the solder joint. Different assembly methods were also investigated. Several of the assembled test boards are being subjected to thermal cycling to determine the joint reliability. The results of this study are reported in this document.
How to Make Wave Soldering of SMDs Successful
Authors: Schouten G.
Published: February 2008

To make wave soldering of SMDs a success, one must realise that not only the process involved is important, but also the board design and SMD mounting aspects play an important role as they may differ considerably from the rules established for reflow soldering. To elucidate this difference is the main issue of this article.
Wave Solder Parameter Optimisation Using A Statistical Experimental Design
Authors: Wooldridge J.R.
Published: February 2008

One part of putting a new wave solder machine into service is determining the optimum settings for the machine's operating parameters. Generally this is done on the basis of ‘common’ knowledge or by simply using whatever settings were used on the old machine. In this case, a full factorial statistical experiment was designed and performed to determine the optimum settings for conveyor speed, board topside temperature and solder pot temperature. Using this technique it was possible to determine the size and shape of the optimum processing ‘window’ by constructing contour plots from the data. The experiment was repeated for a different assembly to determine the sensitivity of the parameter settings to board thickness and component density.
Electronics Manufacturing Productivity Facility (EMPF), Ridgecrest, California
Authors: Cullen Lorna
Published: February 2008

With a record of human occupancy for over 10,000 years, the Indian Wells Valley where Ridgecrest is located has long had much to offer casual and experienced desert visitors alike. Ghost‐towns from earlier active gold mining days, fossilised waterfalls, sculptured rock formations, desert tortoises, hiking trails against a High Sierra backdrop feature among the attractions of the area.
Special reports
Authors: Lea Colin , de Kluizenaar E.E. , Rubin W.
Published: February 2008

‘Fluxing and Cleaning in Electronics Soldering’ The Grosvenor Hotel, London, 22 February 1989. ‘To clean or not to clean?’ ‘Aqueous or solvent cleaning?’ ‘What is the future for CFCs and other chlorinated solvents?’ The electronics assembly industry is ringing with such questions that make the cleaning of electronic assemblies the key issue for 1989—an issue that urgently requires answers that have the stamp of authority based on fact rather than speculation. This BABS seminar was therefore very timely and attracted a large audience to listen to eight presentations from speakers representing the cleaning equipment manufacturers, flux manufacturers, MoD quality assurance, and users' experience, as well as background on solvents in the environment.
A Call for Action on CFC Usage
Authors: Lea C.
Published: February 2008

220,000 tonnes of the chlorofluorocarbon CFC‐113 are consumed worldwide each year. About half is used for cleaning flux residues from soldered PCB assemblies in the electronic assembly industry.
International association news
Authors: Gordon Tony , Warwick Malcolm
Published: February 2008

The seminar was attended by 19 delegates from wide‐ranging industrial and academic backgrounds and whose needs for automation prompted many diverse and probing questions.
Recent Component Solderability Test Enhancements
Authors: Russell W.R. , Waller B.M. , Barry P.S. , Wolverton W.M.
Published: February 2008

Critical parameters of the MIL‐STD‐202 Method 208 and MIL‐STD‐883 Method 2003 component solderability tests were determined from laboratory experiments. Among the variables examined were steam ager atmosphere, steam ager water quality, component drying, flux quantity, static versus wave pots and visual inspection variability. The test results indicate that one of the most important variables is steam ager atmosphere. This was evaluated by vapour temperature vs metal coupon weight gain. Other critical parameters are the drying process and inspection method. Experimental data for some parameters suggest necessary changes to the relevant Military‐Standard test methods. These changes are proposed based on the experimental work presented, and would improve correlation of solderability test results between suppliers and users.
Moisture Induced Failure in Plastic Surface Mount Packages
Authors: Lea C. , Tilbrook D.
Published: February 2008

There is a reliability concern in the larger plastic surface mounting packages which can exhibit cracks from internal stresses during soldering. A lot of ad hoc information has been given to users of such packages about the origins of the problem and its alleviation. The phenomenon is the result of a combination of moisture absorbed in the plastic and the thermal stresses caused by the different expansions of the metal leadframe and the plastic. The work reported here gives quantitative data regarding the amount of moisture absorption critical to cracking, the range of baking procedures available to reduce this moisture below the critical level, and the acceptable floor life after baking for a wide range of storage temperatures and humidities.
SMT—Wave Soldering, Adhesives and Mixed Technology
Authors: Holder C.D.
Published: February 2008

With the increased functional density requirements of military avionics it is impossible to meet these demands without utilising Surface Mount Technology. The Electronics Manufacturing Technology Group at Boeing Military Airplanes is working to meet SMT design requirements through research and development of processes, materials and equipment for all variations of SMT. Basic processes have been established for both 100% SMT and mixed technology. However, the Group continues to advance its capabilities by evaluating and improving all aspects of SMT manufacturing. A description of the initial thrust into Type III SMT as well as subsequent development is given. This includes a description of the evaluation of Surface Mount Component (SMC) attach adhesives comparing the adhesive used initially with others available by examining the various criteria involved in selecting the appropriate one for a given process. Also, a discussion follows of factors involved in determination of Mil‐spec. passive SMCs which are compatible with wave soldering. Included in the evaluation of passive SMCs is a comparison of the compatibility of the wave solder system in use with the component industry's recommended temperature profiles through an analysis based on in‐house testing to determine the actual component endurance to solder system heating. Throughout this discussion emphasis is placed on a systematic guided approach to examining process development.
Capacitor Cracking due to Thermal Shock in Wave Solder Processing
Authors: Anderton J.M. , Warrens S.G.
Published: February 2008

Increased use of surface mount ceramic capacitors in wave solder applications has resulted in a number of field failures due to migration of microcracks through the capacitor. Cracks are initiated in board assembly by a number of processes including excessive forces of assembly equipment, board warpage and/or deflection, rework temperatures, and wave solder profiles. Thermal shock from wave solder contributes approximately 20–25% of the failures. The majority of capacitor manufacturers recommend no greater than 100°C delta between pre‐heat and wave solder temperature during processing. This can be difficult to achieve when processing a range of board sizes. A delta of 120°C allows for different size boards without using a custom thermal profile for each. This study shows no increased failure rate for X7R 1206 capacitors between the two process deltas of 100°C and 120°C. The suggested delta of 100°C is based on a 15000 psi tensile strength of the dielectric and is conservative. The temperature profile may be extended to include the more versatile 120° delta without compromising the reliability of the component.
Solder Joint Failure Detection: Does Inspection Assure Reliability?
Authors: Keller J.
Published: February 2008

Solder joint failures in military missile systems and commercial communication products were investigated. The study was initiated after it had been determined that visual PWBA solder defect inspection for external surface attributes of solder joints such as brightness, smoothness, evenness, solder quantity and PTH plugs and other attributes (including those of present IPC and DoD‐STD‐2000 criteria) was neither effective nor efficient. It was determined that visual inspection is subjective and varies to a large degree between inspectors.
ACT Two‐day Seminar — Repair, Rework and Modification of Surface Mounted Assemblies
Authors: Cullen Lorna
Published: February 2008

It made a pleasant change to travel a mere 15 miles from base to report on the above two‐day event held at The Hospitality Inn, Irvine. Bypassing Troon en route, and glimpsing the vast marquees and stands erected in preparation for the British Open, there was a sense of relief at escaping the inevitable traffic snarl‐ups predicted for the following week when the international golfing fraternity would invade this normally sleepy, small seaside town.
Multicore Solders (Malaysia), SDN, BHD, Ipoh, Malaysia
Authors: Ellis Brian N.
Published: February 2008

This profile is somewhat more exotic than the usual ones found in this, hopefully, august journal and your reporter would like to dwell on the background more than is usual. If you take your world atlas, you may find Ipoh as an isolated dot in the middle of the Malaysian peninsula, a little to the north‐west of Kuala Lumpur. Viewed thus, why would Multicore Solders choose such an isolated outpost to establish a subsidiary factory? Arriving at the international airport at Kuala Lumpur starts to give one a clue: there are enormous bare scars in the plain. Flying from Kuala Lumpur to Ipoh, these scars multiply. They are the remains of the open‐cast tin mines in the alluvial deposits. Viewed from the air, they are a terrible blot on the landscape. The amazing thing is that they juxtapose oil palm, fruit and rubber plantations and even untouched jungle, but they remain bare and desert for decades. It is evident that no effort has been made to conserve the vegetable soil and replace it after the mining operations are finished, but this may be because the humus layer is so thin that it would be impossible to do so. To the ignorant European that this writer is, I imagined that the jungle was an all‐invading vegetation ready to swallow‐up every square metre of land: not so, it is a very precarious ecosystem where the humus formed by the rotting vegetation is swallowed up by the new growth faster than it can form. The jungle soil is very thin, bare rock being common and such a humus layer may take decades or even centuries to form. Most of the disused tin‐mines are therefore as devoid of life as the starkest desert. It would seem that, after fifty years or so, the first signs of vegetation start to reappear, a very meagre growth which, in time, may develop into scrub or secondary jungle without high trees.
Surface mount technology in the U.S. as viewed by a surface mount council member
Authors: PETERSEN GARY G.
Published: February 2008

As guest editor, I was asked to view Surface Mount Technology (SMT) in the U.S. through the eyes of a member of the Surface Mount Council. As such, my observations are interwoven with the work of the Surface Mount Council.
Contaminant Particles in Electronic Solder Fluxes
Authors: Nasta M.A. , Hill G.R. , Campbell D.
Published: February 2008

The filterable particles found in electronic solder fluxes vary considerably in both concentration and chemistry. Four fluxes from three manufacturers were examined, including both rosin fluxes and mildly activated resin fluxes. Individual particles were examined by optical light microscopy (OLM) and scanning electron microscopy/energy dispersive X‐ray spectroscopy (SEM/EDX). Finally, an automated SEM/EDX system was used to collect and summarise information about the size and chemistry of a hundred or more particles from each flux. The number of particles per microgram of flux was found to vary by two orders of magnitude (0.004 to 0.4 per μg). The particle diameters ranged from 0.2–20 μm with averages of 1–3 μm. A large fraction of the particles (33–75% by number) were organic substances not soluble in the flux. The bulk of the inorganic particles were composed of sulphates, silicates and metal oxides. Thus, some solder fluxes may be introducing several contaminant particles into each solder contact. These contaminants may affect the quality of the solder joint depending on particle size and composition.
Quantitative Solderability Measurement of Electronic Components
Authors: Lea C.
Published: February 2008

The subject of the quantitative measurement of solderability of electronic components is introduced. The wetting balance in various configurations and modes of operation is being used as the focal point to establish a quantitative measurement capability for solderability of conventional leaded components, surface mounting components and printed circuit interconnections. The principles of operation of the wetting balance and the factors that influence the measurement are discussed. This paper is the first of a series that will cover the development of traceable reference standards for wetting balance calibration, the influence of instrumental design on the measurement, the standardisation of the measurement procedures, the choice and evaluation of a solderability index for the dynamic measurement, and the traceability of the measurement to international standards.
Quantitative Solderability Measurement of Electronic Components
Authors: Lea C. , Dench W.A.
Published: February 2008

The wetting balance is used for the measurement of solderability of electronic components. The wetting force is measured dynamically and the technique gives information about both the degree and the speed of wetting. For practical quality assessment of electronic components, a simple‐to‐use index is required that incorporates the data on both degree and speed of wetting. The index must also have a uniform discrimination between different wetting properties, across the full range encountered in practical soldering. This paper reviews critically the numerous indices suggested in the literature, and supports with quantitative data the choices previously made subjectively in some soldering standards.
Reliability of Soldered Joints: A Description of the State of the Art
Authors: de Kluizenaar E.E.
Published: February 2008

Damage to components during soldering and degradation of soldered joints is determined to a large extent by the mechanical properties and the metallurgy of solder alloys and soldered joints. Knowledge of these properties is required for understanding of the mechanisms of damage and degradation. A compilation of this background knowledge is presented in this first article. It comprises the elastic, strength, creep and fatigue characteristics of tin/lead solders. Further, the metallurgy of tin/lead solders and soldered joints is discussed in terms of solidification structures, formation of intermetallic compounds, ageing of structures and effects of different solderable metallisations and soldering technology.
Wearout Evaluation of Soldered Interconnections for Surface Mounted Leadless and Leaded Components
Authors: Seyyedi J. , Jawaid S.
Published: February 2008

The wearout characteristics were investigated for soldered interconnections of surface mount technology (SMT) chip resistors, chip capacitors and a 44 I/O ceramic leaded chip carrier (CLCC) package. Four double‐sided test vehicles were subjected to accelerated thermal cycling in the — 10°C to + 110°C range; 30°C/min ramp rate; and 1 minute dwell time at each temperature extreme. The test was interrupted at initially 500 cycle and later at 1000 cycle intervals to perform visual inspection of all soldered interconnections, functional performance verification for the test vehicles, and resistance measurement on leaded SMT joints. Metallographic examinations and fractographic studies were also performed after 0, 4500 and 13000 cycles to characterise the micromechanisms of soldered joint strength degradation and failure. The wearout thresholds for soldered joints of chip resistors and capacitors on side 1 were respectively 2500 and 4500 cycles. The greater thermal fatigue resistance of the latter joints was attributed to a lower device‐substrate coefficient of thermal expansion (CTE) mismatch and a more favourable device geometry compared with chip resistors. These passive components on side 2, however, showed a virtually identical soldered joint wearout threshold of 6500 cycles. The constraints imposed by the applied mounting adhesive were primarily responsible for this behaviour. No correlation appeared to exist among various failure criteria used to determine the onset of failure for leaded SMT soldered connections. The concurrent monitoring of electrical resistance and the applied tensile load showed a modest relationship between the load drop and resistance increase, however. The test vehicles continued to pass the functional performance verification, even after 13000 thermal cycles. Nonetheless, the joint wearout thresholds were considered to be 2500, 4500 and 4500 cycles for chip resistor, chip capacitor and CLCC components, respectively. A 50% soldered joint strength drop was considered as the wearout threshold for the CLCC device. Metallographic examination showed limited barrel wall cracking of the vias and no evidence of cracks with the through‐hole soldered joints, even after 13000 thermal cycles.
International association news
Authors: Lea Colin
Published: February 2008

The annual Autumn Conference of the British Association for Brazing and Soldering offers a forum for discussions between scientists and engineers involved with two technologies which, because of their obvious similarities, would be expected to be of mutual benefit and learning. In reality both the science and the practice of brazing and soldering are quite different. I suspect, with some regret, the BABS Management Committee decided that for the first time this division be formally recognised by offering soldering as the subject of the first day and brazing and diffusion bonding the subjects of the second. This report covers the soldering day only, during which seven papers were presented:
Temperature Variations in Soldering and Their Influence on Microstructure and Strength of Solder Joints
Authors: Nylén M. , Norgren S.
Published: February 2008

Since the introduction of surface mounting technology (SMT), interest in solder joints has increased greatly. In this work soldered joints were examined for different kinds of components. Factors which influenced the temperature cycle most strongly were the component size and its placing on the circuit board. These factors led to significant differences in maximum temperature and cooling rate between different solder joints on one and the same circuit board. The microstructure of the solder joints could then be related to their individual cooling rates. The near ternary eutectic Sn‐Pb‐Ag solder presented large variations in microstructure for the interval of cooling rates which was investigated. Strengths of the joints are therefore expected to vary because of the relation between microstructure and strength. Dissolution of elements from metallised coatings can also influence markedly the structures and properties in the solder joints.
Surface Mount Rework—A Review of Techniques and Practice
Authors: Hunn N.
Published: February 2008

The introduction of surface mount technology has changed the approach which is needed for successful rework of components. This has been brought about by the requirement of simultaneous reflow of all joints to remove the component from the board. To meet this need, manual soldering methods have been adapted, and subsequently complemented, with dedicated hot bar, hot gas and infra‐red systems. Each of these techniques with their respective applicability is considered, prior to a discussion of the parameters which need to be addressed before embarking on successful rework. All aspects of component, board and the joint itself are considered. The procedure for addressing rework is then laid out, providing a standard methodology to obtain rework joints which maintain the quality of the production joints.
Solder Joint Reliability—Can Solder Creep?
Authors: Hwang J.S. , Vargas R.M.
Published: February 2008

Solder joint long‐term reliability is an ultimate requirement for electronics packaging. Solder joint failure, however, can involve complex mechanisms. One of many basic failure processes in metals/alloys is the creep phenomenon. Creep is defined as a time‐dependent deformation when a material is subjected to a stress for a prolonged period of time. This time‐dependent deformation can theoretically occur at any temperature above absolute zero. However, creep‐dominant failure normally occurs under high temperature in relation to the melting point of the material. Common solders are low temperature alloys with melting point or liquidus/solidus temperature in the range of 120–320°C. Therefore a detectable creep process under low level of mechanical load is expected even at ambient temperature. This paper presents the preliminary data on the comparative creep rate of twenty‐two common solder alloys and attempts to correlate the creep rate to the tensile strength, modulus, melting point and microstructure of alloys. The alloys under study include Sn/Pb, Sn/Pb/Ag, Sn/Ag, Sn/Sb, Sn/Pb/Bi, Sn/Pb/Sb, Sn/Bi, Sn/In, and Pb/In systems. This paper also discusses the proposed mechanisms for solder creep phenomena. It is hoped that the data in this work will provide additional fundamental mechanical properties of various solder alloys, which are much needed to facilitate the design of reliable solder joint structure.
Reliability of Soldered Joints: A Description of the State of the Art
Authors: de Kluizenaar E.E.
Published: February 2008

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In this part, mechanisms of damage and degradation of components and soldered joints during soldering, during transport, and during field life are discussed. Thermal shock damage of components and excessive dissolution of metallisations are the major effects during soldering. During transport, fatigue of leads and fracture may be caused by vibration and mechanical shocks respectively. During field life, degradation is governed primarily by low cycle fatigue of the solder and incidentally also by formation of intermetallic diffusion layers between solder and base metals. This article contains an extended illustration of solder fatigue of joints on a variety of component and board types. Finally, the influence of the variety of soldered constructions in electronic circuits on solder fatigue is discussed.
Special reports
Authors: Lea Colin
Published: February 2008

The key environmental issue of the 1980s has been that of the depletion of the stratospheric ozone. The key environmental issue to be addressed in the 1990s will be that of global warming. These head the list of worldwide ecological problems that arise directly from the activities of man. Each industrial sector has an urgent responsibility to increase awareness of such problems within both management and production and to seek to alleviate its impact upon the environment through development of modified or alternative manufacturing technologies. The electronics assembly sector had the opportunity to consider its future in a more environmentally conscious world at the first conference on Electronics Manufacturing and the Environment. This two‐day event was held at the Bournemouth International Centre. It was organised by Vertical Marketing of Wimborne and sponsored by The Department of Trade and Industry, Du Pont, ICI and Multicore Solders, who must take credit for a well organised and splendidly presented conference. The theme of the conference was one particular implication of environmental awareness, namely the elimination of chlorofluorocarbons (CFCs) as a goal of the electronics manufacturing industry. The conference was aimed at addressing ways in which companies can eliminate the use of CFCs, taking into account the moral and financial implications involved as well as the stringent restrictions in CFC production that are about to be imposed.
Hollis Automation Inc., Nashua, New Hampshire
Authors: Ellis B.N.
Published: February 2008

Nashua is a city of less than 100,000 souls, but it will remain engraved in this chronicler's memory for as long as he lives. Why? Because he finished his visit to Hollis in the Nashua Memorial Hospital Intensive Care Unit! He hastens to state that this was not because he was shocked by what he saw at the Hollis plant! Notwithstanding, the city is essentially a high‐tech, red‐brick one (with a nucleus of beautiful, older, painted wooden buildings of the type for which New England is renowned). It is almost on the Massachusetts border, barely an hour's drive from downtown Boston. Apart from Hollis, some of the big names of the region, on both sides of the state boundary, are Wang and Digital Equipment, and many others. Until recently, the region registered full employment, but the late downturn in the computer industry has caused a certain amount of unemployment, but not necessarily to catastrophic levels, except for those without a job.
International association news
Authors: Chilton A.C.
Published: February 2008

This February meeting began in somewhat dramatic fashion—not with the actor's usual injunction to ’break a leg‘ but with the Chairman's announcement that Stuart Briggs, the fourth of the seven presenters, had broken an ankle. It subsequently transpired that he had evidently ’only‘ torn the ligaments, but his presence at the seminar was sorely missed and I know all will wish him a speedy recovery.
Quantitative Solderability Measurement of Electronic Components
Authors: Lea C.
Published: February 2008

The wetting balance is being used as the focal point to establish a quantitative measurement capability for solderability of electronic components of all configurations. This paper considers the factors influencing solderability measurement that arise directly from the thermal design and construction materials of the wetting balance instrument. The work is illustrated by the differences between the three commercial wetting balances currently manufactured within the European Community.
Reliability of Soldered Joints: A Description of the State of the Art
Authors: de Kluizenaar E.E.
Published: February 2008

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In Part 2, mechanisms of damage and degradation of components and soldered joints during soldering, transport and field life have been discussed, the most important mechanism being low cycle fatigue of the solder metal. In this third part, the determination of the fatigue life expectancy of soldered joints is discussed. Accelerated testing of fatigue is needed, as the possibilities of calculations are strongly limited. A temperature cycle test under specified conditions is proposed as a standard. A model is worked out for the determination of the acceleration factor of this test. A compilation of a number of solder fatigue test results, generated in the author's company, is presented.
A Thermoanalytical Study of the Components and Formulation of a Rosin Based Flux
Authors: Sherman K. , MacKay C.A.
Published: February 2008

Thermoanalytical spectra of the components of a typical rosin based flux and the interactions of the components with each other, the substrate and the solder are presented. The study includes heating rates up to those experienced in typical soldering operations.
Cycle Life Prediction for SMT Solder Joints on TCE‐Mismatched Substrates
Authors: Riemer D.E.
Published: February 2008

A method for the prediction of solder joint cycle life in surface‐mount assemblies is presented, based on the conversion of plastic solder shear strain into cycle life by means of an equation derived by Engelmaier. The paper introduces a different analytical procedure for the determination of solder joint shear strain. Shear strain is normally calculated from temperature and TCE differentials between package and interconnect board without consideration of elastic deformations. The suggested method derives average plastic shear strain of the solder joint at maximum temperature excursion from finite‐element analysis of a simple model consisting of an interconnect board, a solder joint and a package. All materials in the model have linear (elastic) properties, except solder which has non‐linear (elastic/plastic) characteristics. The solder stress/strain curve is described to the finite‐element programme with temperature‐dependent bilinear approximations. The solder joint is modelled as a single finite element so that only one value is computed for the plastic shear strain in the solder joint. This value represents the average shear strain which is converted into solder joint cycle life. The cycle life predictions with the finite‐element method are confirmed by cycling results obtained on actual hardware. The described method can serve as a design tool in the optimisation of surface‐mount assemblies. The procedure can help to define accelerated temperature cycling conditions.
Fine Pitch Solder Creams
Authors: Chilton A.C. , Gaugler K.W.
Published: February 2008

There is continuous pressure in the electronics industry towards miniaturisation. This has led to the development of fine pitch soldered devices, and this paper considers the concept of solder creams which use a restrictive flux system as suitable for this work, rather than those that employ finer powder. It is shown that the latter type of solder cream must use metal powders with a higher oxide content which will require the cream to contain a more active flux.
SMART group news
Authors: Lea Colin , Mathuna C. O
Published: February 2008

A large group of SMART Group members visited the Henley premises of Electrovert on 9 May. After the welcome and introduction where Mike Judd emphasised Electrovert's commitment to SMT, a number of papers were presented by the Electrovert team during the morning session.
International association news
Authors: Chilton A.C. , Franckel Mark
Published: February 2008

The meeting, held on 17 May 1990, was opened promptly by the Chairman Andrew Nicholson, who welcomed everyone to the Seminar and introduced Tony Harman, who gave a very good review of the present situation of cleaning electronics assemblies before turning to future developments. In his paper ‘An Assessment of CFC Replacements—Proposed UK Collaborative Programme’, Tony developed the ideas which had led the UK Government to support this work. He did, however, point out that the funding was only now becoming available and this had delayed the start of the programme. Nevertheless, the itinerary of the cleaning trials had been decided and the practical work would commence shortly. In general terms, the programme will cost £¾m and will use between 600 and 700 test boards. As this programme is funded by Central Government, the results will be widely disseminated, especially to Small and Medium Enterprises.
Industry news
Authors: Goldie W. , Lea Colin , Ellis B.N.
Published: February 2008

After 50 years in the electronics industry, Bert Child, Manager of Alpha Metals Ireland, is preparing to hang up his soldering irons and will retire later this year.
ESCA Analysis of Ageing of Metallic Surfaces: Solderability of Nickel Silver
Authors: Marshall J.L. , Miiller D.E.
Published: February 2008

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.
Substitution of CFC‐113 in Developing Nations
Authors: Ellis B.N.
Published: February 2008

Developed nations have problems converting from chlorofluorocarbon solvents to non‐polluting cleaning methods. This problem is amplified in developing nations which could have economic difficulties in implementing the provisions of the Montreal Protocol. This paper sheds some light on some of the problems involved and how they can be overcome.
Impurities in Solder—Their Impact on Solderability and Corrosion
Authors: Becker G.
Published: February 2008

German silver was tinned at three temperatures with solder containing 17 different impurities at up to five different concentration levels. The tinning process was carried out in a wetting balance. After this, the samples were subjected to corrosion and tested in a wetting balance again. It was established that bismuth at high concentration levels has a corrosion resistant effect which gives superior solderability. Silver, aluminium, bismuth, cadmium and copper, in amounts accepted by specifications, make the tinned surface unsolderable after corrosion. Statistical evaluation of a large number of tests — 1755 tests with 21,060 evaluated points — gave valuable information on how a wetting balance curve should be evaluated and which criteria should be established for good soldering.
Quantitative Solderability Measurement of Electronic Components
Authors: Lea C.
Published: February 2008

The three European Community manufacturers of commercially available wetting balances for measuring the solderability of electronic components have participated in an intercomparison assessment of surfaces of standard solderability that have the potential for calibrating the balance instruments. The development of the standard surfaces, as well as the small adjustments needed to improve the uniformity of design of the different instruments, and the standardisation of the procedures for their use, have been described in the preceding papers in this series. This paper gives details of the experimental procedures used for the intercomparison and the significance of the comparative data from each balance type.
Characterising the Corrosion Properties of Flux Residues
Authors: Turbini L.J. , Freeman G.B. , Smith M.H. , Finney J.D. , Boswell R.D. , Lane J.F.
Published: February 2008

A new corrosion test for assessing flux residues is applied to marginally cleaned water soluble fluxed test boards and low solids/no clean fluxed test boards. This test method developed by Bono has been modified to accelerate the corrosion process. The corrosion mechanism observed in this study is conductive anodic filament (CAF), a corrosion mechanism proposed in 1979 by Lando et al. It is postulated that this degradation mechanism is due to the high bias voltage (190 V) coupled with the high humidity (85%) and high temperature (85°C) conditions used in this test. Important parameters in the test method are discussed and recommended refinements are given.
SMART group news
Authors: Wood Tony
Published: February 2008

This design‐based seminar was aimed at broadening the horizons of designers and engineers. The greatest area of cost reduction in any electronics project is in making the right choices at the conception and design phases. This seminar was one step in this direction: a piece of 1·6 mm FR‐4 is not always the best substrate to use.
International association news
Authors: Shackleford R.A.
Published: February 2008

The programme will cover various aspects of high technology joining processes ranging from soldering and brazing to diffusion and adhesive bonding. The papers presented will cover the latest developments in production techniques, methods of enhancing quality, joint inspection, new or improved materials, design/properties of joints and long‐term reliability.
Outer Lead Bonding (Flat‐pack Soldering)—A Precision Soldering Process Demanding High Standards
Authors: Lindner K. , Reinders T.
Published: February 2008

Outer lead bonding and flat pack soldering are techniques which are becoming more and more important. Due to the fact that pitches decrease and chip sizes increase, the soldering process is critical if one does not closely monitor all parameters. This article describes some of the most important parameters of the precision reflow soldering process for TABs and flatpacks.
Reliability Prediction Tools for SMD Solder Joints
Authors: Whalley D.C.
Published: February 2008

There is continued concern over the ability of SMD solder joints to survive in the harsh operating environments endured, for example, by automotive and aerospace products. This paper will review the techniques available for analysing solder joint fatigue behaviour and then describe a software tool designed to allow estimation and comparison of the thermal fatigue life of solder joints exposed to a complex operating profile. The modelling technique takes account of the large changes with temperature of the solder alloys stress/strain‐rate behaviour and also the complex geometry of the component/solder/PCB assembly, whilst avoiding the very high cost of non‐linear finite element analysis. This is achieved by first performing a linear stress analysis of the assembly in order to determine its compliance, and then using this compliance estimate in the solution of a non‐linear differential equation describing the relationship between temperature, stress and strain‐rate in the joint. The technique has been implemented as a software package known as ECLIPS—Electronic Connection Life Prediction System. This software package will run on a workstation or PC and has been shown to give results very close to those from non‐linear finite element analysis, but at approximately 1/20th of the cost.
Evidence that Visual Inspection Criteria for Soldered Joints are no Indication of Reliability
Authors: Lea C.
Published: February 2008

Exemplary data are given that demonstrate unequivocally the inapplicability of commonly used visual inspection criteria for judging the long‐term service reliability of soldered joints. The data are obtained from a controlled model system. Plated‐through hole (PTH), wave soldered joints are used in this work, having a controlled degree of voiding, blowholing and solder blowout, covering the full range of normal visual assessment, from perfect to very bad, for this particular type of visible fault. The joint performance is assessed in terms of its joint pull strength, thermal shock, mechanical high frequency fatigue, low cycle thermal fatigue and propensity as a corrosion initiation site. No evidence was found that the visible outgassing faults degraded the solder joint performance. Indeed, in all the fatigue tests, the visually unacceptable solder joints performed significantly better. Furthermore, in a related research project, manual reworking of joints has been found to be demonstrably detrimental to solder joint reliability.
After CFCs
Authors: Lea C.
Published: February 2008

The demise of the CFC‐113/alcohol azeotropic solvent for de‐fluxing circuit assemblies after soldering has led, in recent years, to the electronics assembly industry being offered other cleaning technologies, some new and some new to this industry. In terms of uptake, one of the most successful will be semi‐aqueous cleaning involving the use of an organic solvent of low volatility to dissolve the contamination followed by an aqueous rinsing process. Two families of solvent have evolved based on natural products (terpenes) and synthetic hydrocarbon chemicals. This paper reviews the possible semi‐aqueous processes and the development of the solvents that has taken place. The cleaning performance is considered as well as the potential for effluent control and fully closed‐loop systems.
SMART group news
Authors: Willis Bob , Jackson Glyn , Lea Colin , Mathuna C.O , Healy Padraig
Published: February 2008

Electronics exhibitions are the same the world over, very tiring affairs. If your stand is busy, time flies; if not, the strain is more noticeable.
International association news
Authors: Whitmore M.A.
Published: February 2008

This, the first BABS meeting to be held at the Institute of Metals was well supported with over 60 delegates in attendance. The seminar Chairman, Dr Hector Steen of Multicore Solders Ltd, is to be congratulated on putting together such an excellent programme which I am certain helped ensure the success of the event. I hope that all future BABS seminars will be as well supported.
Empirical Modelling of Surface Mount Solder Joints from 132 Pin Quad Flat Pack Components
Authors: Brady N. , Ennis T.J.
Published: February 2008

Tensile pull strength tests were used to study the strength of solder joints of 25 mil gull wing leads on 132 pin quad flat pack components. The authors generated quadratic and linear models which can be used to predict the pull strength of a solder joint given its geometry. The shape parameters studied were stand‐off height between the lead and substrate, height of heel fillet, radius of curvature of heel fillet, length of heel fillet, height of solder at toe region, and thickness of solder on the lead. The most significant parameters in determining the tensile pull strength of the solder joint are the height and length of the heel fillet. A study was performed to quantify the effect of lead finish on the accuracy of these models. The lead finish was found to have a significant effect on the solder joint strength. The effect of lateral misregistration on the tensile pull strength of solder joints was also investigated. No correlation between the extent of lateral misregistration and joint pull strength has been found.
A Comparison of Laser Types for Reflow Soldering
Authors: Dunkerton S.B.
Published: February 2008

The increasing complexity of microelectronic devices and the advent of surface mount technology has led to interest in alternatives to mass reflow soldering techniques. One method with advantages for rapid automation and minimal heat input, is laser soldering. Various laser methods are available for application to reflow soldering, the prime options being continuous wave CO2, continuous wave Nd/YAG and pulsed Nd/YAG. This paper presents the results of work to compare and contrast the three techniques. The paper concentrates on the soldering of leadframes and SMD (gull wing and J‐lead) to plated Al2O3 substrates, but also mentions soldering to FR4 PCBs.
Analysis of the Ball‐forming Process in Copper Ball Bonding
Authors: Hongyuan F. , Yiyu Q. , Yihong J.
Published: February 2008

Pulse control, SEM analysis and metallographic examination have been used to record and study the process by which a ball is formed at the tip of an ultra‐fine copper wire. The process by which the copper ball is formed, and the laws governing this process, are presented.