bluuebunny/crossref_metadata_2025 huggingface dataset:
Figures of Merit Design Tools for Surface Mount Solder Joint Reliability
Authors: Engelmaier W.
Published: February 2008

In early 1989 the original version of the Reliability Figures of Merit (FM) for the solder attachments of surface mount (SM) assemblies was published. That version of the FM was specifically tailored for telecommunications environments. Misapplications of FMs to use environments, such as military applications and accelerated tests, pointed to a real need for generally applicable FMs. Adequate reliability of SM solder connections can only be assured with a ‘Design for Reliability’ based on solder joint behaviour and the underlying fatigue damage mechanisms. Perceived difficulties with a ‘Design for Reliability’ stem from the very complex and only partially understood nature of the interacting mechanisms underlying thermally induced solder joint fatigue, combined with the highly temperature, time, and stress‐dependent behaviour of some of the materials involved, especially solder. In this paper generic FMs are presented. These are simple design tools, easily applied by users unfamiliar with the underlying complexities of solder fatigue and the reliability assessment results are in Go/No‐go format. The oversimplifications contained in Version 1 of the FMs (originally thought necessary for simple design tools and limiting their applicability) are omitted, making these generic FMs more readily understood.
The Use of Bismuth Alloy Systems for Reflow and Wave Soldering
Authors: Nicholson A. , Bloomfield D.
Published: February 2008

In view of the increasing interest in low temperature and lead‐free solder alloys, a review was made of existing information on the physical properties of bismuth alloys suitable for electronic bonding applications, by reflow and wave soldering. A comparison was made, where possible, with existing tin‐lead alloys already in widespread use, with new information experimentally derived where none was currently available.
SMART group news
Authors: Lea Colin , Willis Bob
Published: February 2008

The UK is a leader in the implementation of surface mount technology, and SMARTEX '91 sponsored by the SMART Group is one of only a few shows organised worldwide which is dedicated solely to this field. Perhaps it was not surprising then that this year's three‐day event proved a great success.
SMT ‐ Components and Capital Investment
Authors: Sage Maurice
Published: February 2008

By the year 2000 electronics will be the largest single industry the world has yet seen, with an output valued at around 1400 billion US dollars. Changes in technologies and markets combined with rapid growth in specialisation and globalisation, is making this an extremely complex industry and SMT is not exempt from these trends.
A Study of the Failure of Soldered SMT Joints during Thermal Cycling
Authors: Huang J.H. , Gao W. , Jian Y.Y. , Jiang Y.H.
Published: February 2008

An installation has been developed for carrying out thermal cycling experiments on soldered SMT joints. Using this thermal cycle installation (which was developed by the authors) and a simulated chip carrier, study has been made of the influence of various factors on the reliability of soldered SMT joints during thermal cycling. These factors include the position of the soldered joint, the temperature range of the thermal cycle, the dwell time, etc.
A Study of the Mechanical Behaviour of SnPb Solders using Viscoelasticity Theory
Authors: Huang J.H. , Jiang Y.H. , Qian Y.Y. , Wang Q.L.
Published: February 2008

This paper presents a viscoelastic model for analysing the mechanical behaviour of SnPb solders which has been developed by combining grain boundary slip with viscoelasticity theory. On the basis of the model, and by using Boltzmann's integral constitutive equation of viscoelasticity, the mechanical behaviour (i.e., the relationships between stress (load) and strain (displacement)) of SnPb solders for one‐dimensional shearing deformation has been investigated and experimentally verified.
Knowledge‐based Adhesive Selection for SMT Assemblies
Authors: Derebail A. , Srihari K. , Westby G.
Published: February 2008

The last decade witnessed the increasing use of Surface Mount Technology (SMT) in the assembly of Printed Circuit Boards (PCBs). This fact coupled with increasing component densities, decreasing component pitch, and the need for reliable PCBs has focused attention on the critical components of the manufacturing process including the adhesive used. Components used in PCBs manufactured using SMT, which are to be wave soldered, must be adhesively attached to the board so that they remain in place during the wave soldering process. Utilisation of non‐conducting adhesives for the attachment of electronic components prior to wave soldering has become common throughout the electronics manufacturing industry. The knowledge based adhesive selection adviser described in this paper assists the user (process engineer) in the selection of adhesives for wave soldering of surface mount components. In addition to guiding the user through the adhesive selection process, it provides dispenser related information. This ‘advice’ is derived from the restrictions imposed by the user (including the user's facility temperature), material property requirements, productivity measures and the adhesive dispensing method. The adhesive selection adviser helps the user understand the relationships that need to be considered during adhesive selection. It is applicable to any existing SMT line that uses adhesives within the commercial PCB manufacturing domain.
Stress Analysis of Component Attachments to Printed Circuit Boards
Authors: Prakash V. , Engel P.A. , Pitarresi J.M. , Albert T. , Westby G.
Published: February 2008

During the insertion of pin‐in‐hole (PIH) components in a printed circuit board (PCB), adhesively bonded and/or soldered surface mount components (SMCs) already on the board experience mechanical stress. This paper describes the results of a study investigating the forces induced in the adhesive bond and the surface mounts during the insertion of dual inline package (DIP) components. The failure criteria for the glue bonds as well as the gullwing leads were determined from experimental strength tests. The forces in the glue and in the leads were calculated by a combination of analytical and finite element methods. It was found that the adhesive bond as well as the soldered gullwing lead would not fail under the forces induced in the insertion operation.
Calculation of Solder Joint Volume for TAB and MCR Components
Authors: Remmler M.J. , Mödl A. , Hermann F.
Published: February 2008

This paper describes ways of simplifying the equations characterising the equilibrium shape of reflowed solder in the interconnection of TAB (Tape Automated Bonding) and MCR (Moulded Carrier Ring) components with negligible loss in accuracy. A drastic reduction of the numerical effort necessary to calculate the solder volume for fine pitch devices is achieved. The equations are applied to TAB and MCR packages which are hotbar‐soldered to a substrate. The results of these calculations are in good agreement with experimental data.
Laser Trimming SMTs: Automating the Final Electrical Adjustments
Authors: Dobbins W.P.
Published: February 2008

In SMT manufacturing, automation is the key to achieving the highest throughput at the lowest cost. Complex devices of various shapes and sizes often require final electrical adjustments under operating conditions to ensure conformance to electrical specifications. This paper describes the process of laser trimming completed SMT devices and the advantages it has over conventional trimming methods. The material presented is based on laser trimming systems currently used in SMT production applications that will also be described.
The Chemical Design and Optimisation of a Non‐rosin, Water‐soluble Flux Solder Paste
Authors: Frazier J. , Jackson R. , Reich R. , Enno R. , Ables W. , Bosworth L.
Published: February 2008

This paper describes the approach used by the authors to select the flux materials for a simple water‐soluble solder paste flux formulation, what those materials were, and how they interacted to give the correct properties. Consistency of formulation and performance are discussed with emphasis on the need for adequate process parameter control as with any formulation. With this water‐soluble paste formulation various circuit card designs were successfully built possessing 25‐mil pitch, and larger, components. The cards were cleaned in aqueous cleaners and passed IBM standard insulation resistance testing.
SMART group news
Authors: LEA COLIN , O'Mathúna Cian
Published: February 2008

The first results from two collaborative UK programmes assessing the performance of non‐CFC cleaning options for the electronics assembly industry were presented at a one‐day conference on 6 February at the Heathrow Forte Crest Hotel. This was the latest of the long series of meetings on the CFC issue organised by the National Physical Laboratory.
The Relationship of Component Solderability Testing to Board‐level Soldering Performance
Authors: Kwoka M.A. , Mullenix P.D.
Published: February 2008

Visual inspection remains the dominant method of assessing component lead solderability and finished board solder joint quality. In recent years the wetting balance has received much attention as an attractive alternative to the inherently subjective visual inspection method of assessing component termination solderability. Whether direct visual inspection or wetting balance methods are used, the method can be shown to be effective only if the results are in agreement with board‐level soldering performance. This paper addresses the issue of the agreement of visual board‐level solder joint quality with both visual ‘dip and look’ solderability assessment and wetting balance measurement of the components prior to board assembly. A description of visual ‘dip and look’ solderability test assessment and of wetting balance methodology for components is presented, and a compendium of wetting balance tests and indices are documented in the Appendix. The experimental strategy employed is outlined, and details of the experimental technique (including the equipment, materials and component sample preparations) are provided. The experimental results present a comparison of both ‘dip and look’ visual solderability assessment and wetting balance measures with regard to actual board‐level soldering performance. The ability of the various assessment methods to predict board level defects is also explored.
A Study of the Effects of Infra‐red Reflow Profile on Solder Joint Strength and Structure
Authors: Ennis T.J. , Brady N. , Keane B. , Donnelly A.
Published: February 2008

The effects of varying reflow profiles on the tensile pull strength and structure of solder joints of components with tin plated and nickel‐palladium plated leads were studied. It was found that, in the case of tin plated leads, the structure and the tensile pull strength of the resultant solder joints were not significantly affected by varying the reflow conditions from Profile 1 (peak temperature range: 174°C to 195°C, reflow time 24 seconds) and Profile 2 (peak temperature range: 198°C to 218°C, reflow time 30 seconds). On the other hand, the mean pull strength of solder joints of nickel‐palladium plated lead was found to be significantly higher for joints reflowed with profile 2 than that of joints reflowed with Profile 1. Also, for both reflow profiles, the pull strengths of joints of nickel‐palladium plated leads were significantly higher than those of tin plated leads. This higher average pull strength may be due to the dissolution of palladium in the solder and/or the increased density of intermetallic precipitates in the solder fillet, and the increased intermetallic layer thickness at the lead/solder interface.
Stripping and Replacement of Damaged Solderable Coatings
Authors: Harris P.G. , Whitmore M.A. , Fairweather B. , Dunn B.D.
Published: February 2008

Electronic materials, particularly tin‐lead coated component leads, may degrade and acquire a poor solderability as a result of long‐term storage or prolonged periods at elevated temperatures (during burn‐in). This paper presents the results of studies on the surface chemistry and microstructure of such coatings together with a technique for stripping degraded coatings and replacing them with pristine finishes having excellent solderability.
Gold‐Tin Solder Bumps for TAB Inner Lead Bonding with Reduced Bonding Pressure
Authors: Zakel E. , Simon J. , Azdasht G. , Reichl H.
Published: February 2008

Tape automated bonding (TAB) is a suitable technology for assembling ICs with a high number of l/Os. The gang bonding process usually applied requires increasing thermode forces for chips with high lead counts and narrow tolerances regarding thermode parallelism and planarity. Due to the high bonding pressure, TC bonding of Au bumps to Au‐plated tapes becomes critical for these applications. In order to avoid damage to the pad structure an inner lead bonding (ILB) process with reduced pressure is required. A tape metallisation of 0.5–1.0 µm Sn is not sufficient for a significant reduction of thermode pressure. As an alternative, the application of an eutectic Au‐Sn cushion which is deposited on top of the bumps is presented. A modified bumping process was developed for the deposition of the solder bumps. Soldering of the Au‐Sn bumps to a Au‐plated tape was performed successfully by two techniques: thermode gang bonding and laser soldering. Bond parameters and tin layer thickness were optimised. Reliability investigations by thermal ageing were performed. The special metallurgical aspects of the system were investigated with a microprobe.
Methodology for Thermal Characterisation of Surface Mount Devices
Authors: Siegal B.S.
Published: February 2008

Thermal characterisation of surface mount devices (SMDs) has become a growing concern as these components have increased in use—a situation aggravated by the lack of accepted industry standards for making thermal measurements. This paper attempts to provide better understanding of thermal resistance terminology, and to summarise some of the existing problems with current standards and common practices. A defined methodology for obtaining SMD thermal characteristics is proposed, involving measurement by vendors and confirmation by users, and suitable for use in meeting application‐oriented requirements. The importance of providing a clear and complete set of test condition information is also emphasised.
Characterising the Corrosion Properties of Flux Residues
Authors: Turbini L.J. , Schodorf J. , Jachim J. , Lach L. , Mellitz R. , Sledd F.
Published: February 2008

Today's emphasis on alternative flux technology as an approach to eliminate the use of chlorofluorocarbons (CFCs) requires an understanding of the corrosion potential of the new fluxes. In 1989, Dr David Bono proposed that monitoring the effect of different soldering fluxes on the rate of corrosion of a copper wire printed on a circuit board would provide quantitative information on the corrosion potential of a flux. Further analysis of this testby Turbini et al. revealed that the degradation mechanism associated with Bono's test is the growth of conductive anodic filaments along the glass fibres of the epoxy‐glass boards. The original test method has been revised, and the test coupon redesigned with the goal of developing a standard, quantitative test method to characterise soldering fluxes. This paper will describe the equipment, test coupon and electrical circuitry associated with this proposed test method. Procedures chosen to reduce error sources associated with electrical noise will be reported and explained.
SMART group news
Authors: Lea Colin , Willis Bob , Judd Mike , Willis Bob , Beamish John , Moore Karen
Published: February 2008

This conference was the second in the National Physical Laboratory series focusing in turn on each of the non‐CFC options for de‐fluxing soldered electronics assemblies. The first conference was on Controlled Atmosphere Soldering and the third will be on New Solvents.
International association news
Authors: Richards Brian
Published: February 2008

‘The Joining Environment’ Dates: 14–15 October 1992 Venue: Forte Posthouse, Coventry, England This Conference will provide a venue for discussion on advances in joining technology, and papers will cover a wide range of scientific and technical developments, focusing in particular on soldering, brazing and diffusion bonding practices which may involve environmental considerations.
Case Studies in Quality and Reliability Analysis of Fine Pitch Solder Joints
Authors: Barrett J. , Mathúna C.O , Doyle R.
Published: February 2008

Rapid feedback on the effect of changes in materials or assembly process parameters on solder joint quality is essential in process optimisation for fine pitch surface mount solder assembly. This is particularly the case where the demands of high volume production do not allow lengthy experimentation to be carried out on the production line. The greater precision and care required in analysis of fine pitch solder joints places a further constraint on the speed at which the analysis can be carried out. The techniques of microstructural analysis, solder joint mechanical strength testing and short duration environmental stress testing must be used to meet a rapid turnaround quality and reliability analysis requirement and to maximise the amount of information obtained from each stage of the analysis. Three case studies are detailed which demonstrate the use of these techniques in a high volume production context to provide rapid feedback on joint quality. The case studies have been selected for presentation not only to demonstrate the analysis techniques but also because they address issues which are of current interest due to the increased usage of fine pitch packages in production and the constraints on the use of solvents for cleaning of circuit boards. The studies are:
The Effect of Adventitious Oxygen on Nitrogen Inerted IR Reflow Soldering with Low Residue Pastes
Authors: Stratton P.F. , Chang E. , Takenaka I. , Onishi H. , Tsujimoto Y.
Published: February 2008

The benefits of Nitraclean I nitrogen inerted reflow soldering are well documented. However, there has been some debate as to the maximum oxygen level that can be tolerated by different types of paste if those benefits are to be realised. It is demonstrated that, for all paste types, solder balls decrease and the spread factor increases with increasing oxygen level, but that it has little effect on either joint strength or microstructure. It is concluded that for RMApastes a maximum oxygen level of 1000 ppm is required and that for low residue pastes the level needs to be reduced to 200 ppm for optimum results.
Voiding Mechanisms in SMT
Authors: Hance W.B. , Lee N.C.
Published: February 2008

The mechanisms for void formation are investigated for applications involving solder paste in surface mount technology. Generally, voids are caused by the outgassing of entrapped flux in the sandwiched solder during reflow. The voiding is dictated mainly by the solderability of metallisation, and increases with decreasing solderability of metallisation, decreasing flux activity, increasing metal load of powder, and increasing coverage area under the lead of the joint. Decrease in the solder powder particle size has only a slightly negative effect on voiding. The data indicate that voiding is also a function of the timing between the coalescing of solder powder and the elimination of immobile metallisation oxide. The sooner the paste coalescence occurs, the worse the voiding will be. Increase in voiding is usually accompanied by an increasing fraction of large voids, suggesting that factors causing voiding will have an even greater impact on the joint reliability than shown by the total‐ void‐volume analysis results. Preliminary data suggest that certain predry treatment and flux solvent with higher boiling point appear to cause increased voiding.
Production Validation of SERA Solderability Test Method
Authors: Tench D.M. , Kendig M.W. , Anderson D.P. , Hillman D.D. , Lucey G.K. , Gher T.J.
Published: February 2008

The sequential electrochemical reduction analysis (SERA) method was evaluated in production and demonstrated to provide a non‐destructive, objective measure of the solderability of production printed wiring boards. Approximately 1000 boards were analysed just before wave soldering and the SERA parameters were correlated with the soldering defect occurrence rates. The data show that PWB solderability is determined primarily by the nature of the surface tin oxide, as reflected in the corresponding SERA plateau voltage, rather than by the oxide thickness. By proper choice of the value of the plateau voltage used as the criterion for solderability, the most advantageous trade‐off between the costs of rejected boards and the rework of defects can be made.
Solder Paste for No Clean Reflow
Authors: Fenner M.
Published: February 2008

This article describes a low‐cost approach to the search for alternatives to CFC cleaners. In this approach the cleaning and soldering cycles are combined under nitrogen. The effects of inerted reflow are reviewed and quantified. A no‐clean solder paste to take advantage of the inert atmosphere is described and compared with conventional formulations. Processing conditions are outlined. Finally, process and capital costs of the new product are compared. The article concludes that the new formulation performs as well as conventional pastes, but leaves fewer residues than a separate cleaning process. Process and capital costs are less than half those of liquid cleaning.
Anisotropic Conducting Adhesives for Electronic Interconnection
Authors: Williams D.J. , Whalley D.C. , Boyle O.A. , Ogunjimi A.O.
Published: February 2008

This paper presents analytical and computational models of adhesive joints constructed from anisotropic conducting materials. Such materials are becoming increasingly important in the construction of fine pitch interconnection, for example the assembly of surface mounted components to printed circuit boards, and are likely to find considerable application in silicon die attach as alternatives to current ‘flip chip’ technologies. The paper presents design models of the mechanical and low frequency electrical behaviour of typical materials and relates these models to manufacturing process parameters.
Facilitating Process and Material Changes in Production Soldering with Nitrogen
Authors: Adams S.M.
Published: February 2008

The use of nitrogen‐based soldering environments, rather than ambient air, has been widely promoted for both reflow and machine soldering. Earlier claims of process improvements derived mainly from the enhancement of process windows related to improved solderability. The improvements seem to be accepted in the industry but may not be very significant except when accompanying other changes in production soldering facilitated by the use of inert environments. Appropriate process changes include the use of finer pitch devices and more densely populated boards and changes in cleaning technology or the use of no‐clean processes. Material changes include the increased use of new technology for both pastes and fluxes (generally no‐clean), increased use of high temperature solder alloys and the possible need to use lead‐free alloys for environmental reasons. This paper discusses the relationship between atmosphere effects on soldering processes, and process and material changes which favour soldering in atmospheres other than air. It presents some recent data on improvements to soldering resulting from the use of nitrogen environments.
Solder Mask Strategies for Surface Mount Assembly
Authors: Paczkowski M.A. , Reddy S.T.
Published: February 2008

Over the past few years there has been increasing utilisation of higher density surface mounting on printed wiring boards. As components and pads decrease in size, the topography of the solder mask relative to the conductors becomes an important solderability issue. There exists convincing evidence that thinner, more conformal solder mask geometries improve soldering yields of both stencilled and wave soldered surface mount components. In order to provide the solder mask coverage required for improved assembly performance, the authors critically compared several commercially available solder mask coating technologies. The coating methods were appraised according to both assembly and printed wiring board manufacturing criteria. Within this programme, seven liquid photoimageable solder masks were also evaluated. The materials were rated according to their final cured properties (electrical, mechanical, chemical performance), their manufacturability in the printed wiring board manufacturing process (maximum throughput, major defects, etc.) and their performance in assembly operations (soldering yields, propensity to ‘solder ball’ formation, white residues, scratches, etc.). The information obtained was used to choose a solder mask strategy which would not only improve assembly efficiency but also increase PWB manufacturing yields and flexibility.
Industrial Qualification of a No‐clean Solder Cream
Authors: Mantrant‐Le Bot A.
Published: February 2008

No‐clean is an attractive alternative for eliminating CFC consumption. For high complexity and reliability boards, a very low residue solder cream, free of halides, should be chosen. Only three of the pre‐selected solder creams passed both the chemical analyses and the preliminary tests, conducted to check compatibility with Bull's current processes. Then, a specific test board with 28 interdigitated QFPs was designed for reliability and ongoing tests. After several weeks in production, Ecorel AP44 solder cream, manufactured by Promosol, was qualified.
SM Placement Technology
Authors: Pawlischek H.
Published: February 2008

This paper, which will be published in two parts in consecutive issues of Soldering & Surface Mount Technology, reproduces a chapter of the recently published book ‘Handbook of Printed Circuit Technology: New Processes, New Technologies’, edited by G. Herrmann and K. Egerer and published by Electrochemical Publications Ltd, Port Erin, Isle of Man.
Predicting Scooping and Skipping in Solder Paste Printing for Reflow Soldering of SMT Devices
Authors: Mannan S.H. , Ekere N.N. , Lo E.K. , Ismail I.
Published: February 2008

This paper examines the rôle that the squeegee plays in the solder paste printing process. Although the printing of solder paste is only one stage of many in the surface mount assembly process, it is crucial to deposit the correct amounts of solder paste cleanly onto the substrate. The amount of solder paste deposited affects the reliability and strength of the reflowed solder joint. Surface mount component lead pitches are continually being reduced due to the requirements of packing more and more components into a given space on the PCB, and this necessitates a proper understanding of the printing process and in particular of the squeegee which plays an important part in determining paste heights and the occurrence of defects. The paper outlines a model which predicts scooping and skipping in the stencil printing of solder pastes used in the reflow soldering of surface mounted devices. The model is based on the forces acting on the squeegee blade, which determines the paste flow pattern ahead of the squeegee, and on the stencil aperture geometry. The paper also examines the interactions between the paste properties and squeegee material properties. These interactions produce printing defects such as scooping, skipping and wet bridging. Results of an experimental comparison of different types of squeegee blade used in the stencil printing of solder pastes for reflow soldering in SMT, as well as the experimental results for squeegee deformation into stencil apertures, were used for validating the model. The empirically enhanced model which results takes into account the force on the squeegee due to solder paste flow and some of the non‐Newtonian properties of the solder paste. The main utility of the proposed model is the control of solder paste printing quality.
Thickness Testing of Electroplated and Related Coatings
Authors: Ray G.P.
Published: February 2008

After obtaining his membership of the Institution of Metallurgists (now Institute of Materials), Dr Ray attended City of London Polytechnic, gaining an MSc degree in corrosion science and engineering and a PhD in fatigue properties of steel. He was awarded the Johnson Matthey Silver Medal in 1978 for a research paper, based on his MSc Thesis, in potential sources of corrosion in transistor packages. He is a Fellow of the Institute of Materials, Institute of Corrosion and Institute of Metal Finishing.
International association news
Authors: Shackleford R.A.
Published: February 2008

Date: 20 October 1993 Venue: The Regency Hotel, Shirley, Solihull, West Midlands Introduction This conference will provide a forum for discussions on recent advances in high technology joining process such as soldering, brazing, diffusion and adhesive bonding. Papers cover a wide range of scientific and technical developments and latest advances in production techniques, particularly those which may involve environmental considerations, and highlight the technological advances being made in the move towards the 21st century.
Industry news
Authors: Dunn B.D.
Published: February 2008

As part of a global expansion programme, Alpha Metals have announced two senior personnel changes which will strengthen their sales operations both in the UK and in the USA.
Process Yield and Reliability of 0.65 mm Pitch Technology in Surface Mounting
Authors: Liu J.
Published: February 2008

This paper describes the influence of soldering parameters on solder joint quality and reliability of 0.65 mm pitch QFP technology. Soldering process parameters such as soldering temperature, conveyor speed and board size have systematically been varied using factorial experimental analysis. Solder joint quality has been characterised in terms of solder ball formation, open joints and porosity behaviour. Equipment used includes microfocus X‐ray non‐destructive testing apparatus, optical and scanning electron microscope. The reliability of solder joints has been investigated by temperature cycling from −55 to + 125°C for 1000 cycles. The time per cycle was approximately 1 hour. The results from the present work show that pad layout on the printed circuit board (PCB) and the quality of pretinning during PCB production have a considerable influence on the solder joint yield. No failures have been observed during temperature cycling. This indicates that 0.65 mm (25 mil) pitch QFP components have very high reliability in respect of temperature cycling and are extremely compliant for absorbing the thermal stress developed during temperature cycling.
Quality Optimisation of Fine Pitch Surface Mount Solder Joints using Taguchi Experimental Design Techniques
Authors: Yamada T. , Barrett J. , Doyle R. , Boetti A.
Published: February 2008

The use of Taguchi experimental design techniques to examine the effects of package type, solder paste type and solder reflow technique on the quality of fine pitch surface mount IC package solder joints is described. In particular, the effect of the use of ceramic or plastic packages, copper or Alloy 42 leadframes, silver loaded or non‐silver loaded solder paste and infra‐red, laser or hot‐bar reflow on solder joint metallurgical structure, electrical resistance and mechanical strength is evaluated. In addition to these solder joint parameters, an associated visual inspection was used to find the best process parameters to minimise solder balling, bridging etc. and a correlation between paste contacts at placement and solder bridges after reflow was also conducted. The experiment used an L9 array to find the optimum parameters from three factors, each at three levels. An extension to the basic Taguchi array was included in the form of an outer (noise) factor to include the effect of climatic stress on the solder joints under investigation. Response tables separate out the contribution of each factor level to the mechanical strength and electrical resistance of the assemblies. By comparing the response tables before and after climatic testing it is possible to estimate the effect of each factor level on the long‐term quality of the solder joints. It is shown how Taguchi experimental design techniques can be used to minimise the number of experiments required to predict optimum solder assembly process parameters. The accuracy of the prediction is shown by the results of a confirmation run which yielded mechanical strengths very close to those predicted, both before and after highly accelerated stress testing of the solder assemblies.
Important Issues in Reflow Soldering
Authors: de Klein F.J.
Published: February 2008

For reflow soldering in today's changing component and soldering technology, requirements with respect to profiling seem to be difficult to determine and even harder to meet. State‐of‐the‐art reflow trackers can be of help here, but, without some knowledge of the fundamentals in profiling, it will be easy to misunderstand measurements. The use of nitrogen as a protective gas for reflow soldering can be advantageous for fine pitch technology, bare copper boards and low residue solder pastes. However, because reflow solder defects are related to more than just the use of nitrogen, one may find different benefits for the use of nitrogen, depending on how the investigations are carried out. Wetting under nitrogen is certainly better and more reproducible, while the near absence of oxygen is beneficial to oxidation‐related problems. For high numbers of solder joints per board, it is not easy to achieve an acceptable first pass yield. Only with low, controlled defect levels found within a robust reproducible process is it possible to achieve this. Using forced convection together with nitrogen for reflow soldering is becoming the preferred method.
Life Prediction of SMT Solder Joints under Thermal Cycling
Authors: Huang J.H. , Pei J.Y. , Qian Y.Y. , Jiang Y.H.
Published: February 2008

In this paper, a formula for life prediction of SMT solder joints under thermal cycling has been established on a damage model. The major failure mechanisms such as fatigue, creep and atmospheric oxidation have been considered in the formula. The experimental verification shows that the life formula established in this paper coincides with the experimental results.
SMART news
Authors: Fenner Michael , Hodson Norman
Published: February 2008

Every electronics manufacturing company wants to know how effective its process is compared with industry leaders; to date this has not been possible. From an initial concept by Bob Willis, Chairman of the SMART Group, a data collection package has been jointly developed in conjunction with the Surface Mount Club.
International association news
Authors: Harris Paul
Published: February 2008

There can have been few periods in the history of the electronics soldering industry when the introduction of new technologies was so widespread and prevalent. Many of these changes have the objective of improving the efficiency of the process, and examples of this might be nitrogen soldering and the new developments in reflow soldering. Other changes, however, are being forced upon the industry by the impact of environmental legislation, and examples in this case include the ban on the use of CFCs and the growing pressure to replace lead‐containing solders with non‐toxic alternatives. The content of the soldering session reflected these concerns, with papers on nitrogen soldering, developments in reflow soldering and environmental issues.
Know‐How?
Authors: GOOLD EILEEN
Published: February 2008

Engineers working in an electronics assembly environment require an ability to evolve new solutions to problems and new products. How is this ‘know‐how’ acquired?
Solder Replacement
Authors: Hvims H.L.
Published: February 2008

Environmental issues have an ever‐increasing influence on the selection of material and processes in electronic manufacturing. This paper discusses the use of conductive adhesives as a replacement for solder on SMT printed circuit boards. As a result of a world‐wide market survey, a number of conductive adhesives have been selected. One of the two key issues of this paper has been to uncover the market for adhesive types and their composition. The other key issue has been the technical investigation of the influence of component termination and printed circuit surface types on adhesive bonding stability. Four different types of adhesives on two different metal surfaces are compared with conventional solder technology. Each adhesive has been applied to the PCBs by either screen printing or dispensing according to the manufacturer's recommendation, followed by curing. All PCBs went through thermal and humidity cycling followed by electrical measurements of resistance. Finally, all variants have been adhesion tested. All adhesive variants have been microsectioned for metallurgical and microstructure examination. Energy dispersive analysis of X‐ray (EDAX) of the metal particles in the adhesive has been carried out and documented. Rework of conductive joints is briefly commented on. Finally, aspects of occupational health are discussed concerning work with adhesive types. Work with epoxy based adhesives has been brouaht into special focus.
Historical Failure Distribution and Significant Factors Affecting Surface Mount Solder Joint Fatigue Life
Authors: Nicewarner E.
Published: February 2008

Solder joint failure history has generally been assumed to follow a straight line when plotted as a lognormal or 2‐parameter Weibull distribution. Test results presented here show that a deviation from straight‐line behaviour occurs at low percentage failure probabilities. This indicates that solder joint failure history is more correctly characterised as a 3‐parameter Weibull distribution with a failure‐free period of life for true wearout failures. The solder joint failure distribution characteristic is also affected by applied strain. Lower strain, in addition to increasing median life, also improves the distribution such that the number of cycles‐to‐first‐failure is increased compared with the median cycles‐to‐failure. The ratio of cycles‐to‐first‐failure/median cycles‐to‐failure and apparent Weibull slope increases as strain decreases in a predictable manner. The effects of part elevation, part size, solder joint volume and shape, conformal coating, temperature differential, and alternative board materials are also presented with test data showing the effect of variation of these parameters.
Characterising Soldering Fluxes
Authors: Turbini L.J. , Cauffield D.
Published: February 2008

For a number of years electronic manufacturers of printed circuit assemblies have used rosin‐based soldering fluxes. Post‐solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are considering alternative cleaners for rosin flux or new flux choices which can be cleaned with water or left uncleaned. Many of the flux formulations are relatively new and their long‐term effect on the performance of products manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, there is no direct relationship between the total ionic level and the corrosivity of the soldering flux. Surface insulation resistance testing is used in the industry, but the results are misunderstood by many. This is due to the fact that SIR data represent a complex dependency on a number of factors including (1) the test conditions (temperature, humidity, bias), (2) the area of interactions (often referred to as the number of squares), (3) the separation between lines on the interdigitated comb pattern, (4) the presence or absence of bias voltage during the test and (5) the nature of the substrate. All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally reported by Dr David Bono, is being modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French UTE, will result in a new international standard. This paper reports the latest data on this important test development.
The Influence of Flux Residues on the Quality of Electronic Assemblies
Authors: Schmitt‐Thomas Kh.G. , Schmidt C.
Published: February 2008

Ionic contaminations, especially flux residues due to manufacturing, cause various faults and failures of printed circuits during service. The contamination (µg‐eq NaCI), surface insulation resistance (SIR), electromigration and corrosion caused by flux residues of six different fluxes (categories: F‐SW26, F‐SW32 and F‐SW34 according to DIN 8511) have been investigated. The main effort was applied to the investigation of electromigration, which is understood as the formation of short circuits by metallic bridges between two conductors of different voltage.
Development of a Novel No‐clean Low Residue Solder Paste for Fine Pitch Applications
Authors: Beikmohamadi A.
Published: February 2008

An experiment was conducted to examine the effect of post‐reflow no‐clean solder paste residue on near‐end and far‐end signal crosstalk due to changes in dielectric constant and leakage resistance in the circuit environment. Additionally, the effect of different frequency levels on post‐reflow residue was examined. Data from these studies are presented in this paper.
Soldered Joint Reliability for Interstitial Pin Grid Array Packages
Authors: Seyyedi J.
Published: February 2008

The reliability of solder joints and plated‐through‐hole (PTH) copper structure was investigated for 503 I/O interstitial pin grid array packages with two different pin diameters. Each package type was wave soldered to printed wiring boards having two different surface finishes and PTH sizes, by using the 63Sn–37Pb alloy. Accelerated thermal cycling with continuous monitoring was used in conjunction with metallographic analysis to determine reliability and to elucidate the failure threshold. The microstructural features and failure modes were found to be similar among the solder joints despite the physical differences. The measured solder joint fatigue lifetimes varied from 2450 to 3700 thermal cycles, depending on pin and PTH combinations. The reliability of PTH copper exceeded 4000 thermal cycles regardless of the PTH size. The solder joint fatigue results were used to predict the reliability under operating conditions.
Effects of Voids and Their Interactions on SMT Solder Joint Reliability
Authors: Liu S. , Mei Y.H.
Published: February 2008

Several finite element models were proposed to investigate the effects of voids and their interactions on SMT solder joint reliability in thermal mismatch loading. Both linear elastic analysis and non‐linear and time‐dependent finite element analysis were performed on models with different sizes and locations of voids in solder joints. The focus was on the interactions of the two voids. Various distances between voids are considered. Constitutive equations accounting for both plasticity and creep for one solder material were assumed and implemented in a finite element program. The following observations have been obtained: (i) the stress and strain in a solder joint of two voids are different from those of a one void joint; (ii) the stress and strain reach a maximum for a particular void size and location either along the interface of the solder joint or at the edges of voids; (iii) the initiation of interfacial debonding may be induced by the interaction of the voids; (iv) creep due to thermal cycling has a significant effect on solder joint reliability.
Hot‐bar Soldering of TAB Components with 0.150 mm OLB Pitch
Authors: Mödl A.
Published: February 2008

Tape automated bonding (TAB) is a powerful technique for connecting fine‐pitch integrated components to the corresponding substrates. This paper describes the specific example of hot‐bar soldering TAB components with an outer lead bonding (OLB) pitch of 0.150 mm to FR‐4 printed wiring boards. The prerequisites to be taken into account, the outer lead bonding process parameters, the hot‐bar soldering results and recommendations are presented.
Cell Controller Software Modelling for PCBA Rework Cell
Authors: Chan C.Y. , Redford A.H. , Ekere N.N.
Published: February 2008

Rework is an integral part of printed circuit board assembly (PCBA) manufacturing. However, the state‐of‐the‐art for PCBA rework still relies on operator activity and is therefore semi‐automatic. As a result, the quality of rework depends very much on the skill of the operator. When developing an automatic PCBA rework cell, the cell controller is an essential part which organises and controls the overall rework operation. This paper describes the software modelling of the cell controller for the PCBA rework cell which has been implemented for reworking through‐hole and surface mounted components. The software model is based on hybrid representations and rule‐based control.
The Genesis of a Programmable Controller
Authors: Finck A.
Published: February 2008

Over the past twenty years the programmable controller has been developed from a relatively simple hard‐ wired device used for controlling sequential operations to being almost a ‘computer’ in its own right capable of handling many distributed processing tasks on the factory floor in real time. This short feature takes a brief look into how Siemens is using CIM to produce programmable controllers more efficiently. Siemens has such a state‐of‐the‐art CIM‐based production line in Amberg, Germany, which is notable for the short time it took to be ‘up‐and‐running’. But why is the company increasing production in a recession? The answer is because of Far East markets, where the aggregated demand for programmable controllers is estimated to grow at some 15% per annum. Consequently, the company has changed its production techniques to gain ‘an edge’ in these burgeoning markets and in doing so has adopted heretofore Japanese attitudes to ongoing product quality.
SMART group news
Authors: Doyle Rory
Published: February 2008

The SMART Group has been investigating joining methods for ball grid arrays (BGAs). Originally a development of IBM, and expected to be a dominant packaging technology, the BGA is best visualised as a legless PGA. It has the same advantages—high lead count, wide pitch, small area—but does not need holes. The problem of the BGA is that the interconnects are not visible. This places a high demand on process control and material selection — it really is a case of ‘right first time’. The investigation concentrated on this aspect.