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Article
Publication date: 1 February 1994

N.N. Ekere, E.K. Lo and S.H. Mannan

This paper presents a technique for mapping the modelling of manufacturing processes, in which process maps are used to represent information on the models and modelling…

Abstract

This paper presents a technique for mapping the modelling of manufacturing processes, in which process maps are used to represent information on the models and modelling technique (including assumptions used), process and equipment parameters, physical sub‐processes, process variables, and the process performance in terms of quality and/or defects. The mapping approach uses the top‐down methodology, in which any manufacturing process can be represented in a structured, multi‐layered manner, with each layer representing a different level of the modelling spectrum. This structure is designed to provide a clear overview of the process and sub‐processes, and their interactions, while the finer details of the modelling process are still presented at the lower levels of the map. This mapping approach is illustrated with the modelling of the Printing of Solder Paste for the reflow soldering of SMT devices. This case study shows how the mapping process can be used to identify the key research issues, specify the experimental work required, and also identify the analytical modelling techniques which are appropriate for each process (and sub‐process).

Details

Soldering & Surface Mount Technology, vol. 6 no. 2
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 March 1993

S.H. Mannan, N.N. Ekere, E.K. Lo and I. Ismail

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…

Abstract

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.

Details

Soldering & Surface Mount Technology, vol. 5 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 January 1994

N. Geren and N.N. Ekere

Although rework is labour intensive and conflicts with most modern manufacturing/assembly philosophies, realistic defect levels in surface mount technology (SMT) printed…

Abstract

Although rework is labour intensive and conflicts with most modern manufacturing/assembly philosophies, realistic defect levels in surface mount technology (SMT) printed circuit board (PCB) assembly render rework indispensable on the shop floor. Most commercially available rework tools are manual or require very skilled operators for their efficient operation. The challenges of automating SMD rework are significant because the tools, their specifications and rework processes required are not fully understood, and the impact of rework processes on assembly quality and reliability are hotly debated. This paper describes an automated robotic rework cell for SMD and TH boards, and the method used for process characterisation of the solder paste dispensing system. The paper also describes equipment selection, the integration and interfacing of the dispensing equipment to the cell controller and the process characterisation experiments.

Details

Soldering & Surface Mount Technology, vol. 6 no. 1
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 13 April 2010

G. Takyi and N.N. Ekere

The purpose of this paper is to investigate the end point of the plasma cleaning process, in order to save valuable production time and also to prevent the destruction of…

Abstract

Purpose

The purpose of this paper is to investigate the end point of the plasma cleaning process, in order to save valuable production time and also to prevent the destruction of expensive devices through overheating.

Design/methodology/approach

Post plasma cleaning analysis using dynamic contact angle (DCA) analysis and video microscope observations have been conducted on plasma treated Entec coated copper, hot air solder levelled (HASL) and electroless nickel immersion gold (ENIG) surfaces in order to determine the effect of surface finish on plasma process times. Post plasma cleaning and lead-free wave soldering analysis of the three surface finishes have been evaluated.

Findings

The DCA results indicate that the end-point for plasma cleaning of Entec coated copper is achieved within one to three minutes (indicated by a low contact angle hysteresis). Further cleaning after three minutes may lead to surface degradation and poor solder wettability. This is consistent with the results of the video microscope observations which show well soldered component leads and pads with good solder coverage for copper surface finish treated at a short plasma process time (one minute) and poorly soldered component leads and pads for a surface treated at a long process time (ten minutes). Similar work conducted on HASL and ENIG finishes show better results (well soldered component leads and solder pads) for longer plasma process times of five to ten minutes.

Originality/value

This paper indicates that plasma process time determines the wettability and solderability of the treated samples. It shows that the plasma conditions including the process time must be optimised and characterised for every application in order to avoid damage to expensive devices. The findings also give the confidence to implement plasma cleaning of lead-free (99.3Sn/0.7Cu) solder PCBs for fluxless soldering.

Details

Soldering & Surface Mount Technology, vol. 22 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 27 June 2008

R. Durairaj, S. Mallik and N.N. Ekere

The purpose of this paper is to develop a quality control tool based on rheological test methods for solder paste and flux media.

Abstract

Purpose

The purpose of this paper is to develop a quality control tool based on rheological test methods for solder paste and flux media.

Design/methodology/approach

The rheological characterisation of solder pastes and flux media was carried out through the creep‐recovery, thixotropy and viscosity test methods. A rheometer with a parallel plate measuring geometry of 40 mm diameter and a gap height of 1 mm was used to characterise the paste and associated flux media.

Findings

The results from the study showed that the creep‐recovery test can be used to study the deformation and recovery of the pastes, which can be used to understand the slump behaviour in solder pastes. In addition, the results from the thixotropic and viscosity test were unsuccessful in determining the differences in the rheological flow behaviour in the solder pastes and the flux medium samples.

Research limitations/implications

More extensive rheological and printing testing is needed in order to correlate the findings from this study with the printing performance of the pastes.

Practical implications

The rheological test method presented in the paper will provide important information for research and development, quality control and production staff to facilitate the manufacture of solder pastes and flux media.

Originality/value

The paper explains how the rheological test can be used as a quality control tool to identify the suitability of a developmental solder paste and flux media used for the printing process.

Details

Soldering & Surface Mount Technology, vol. 20 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 August 2001

R. Durairaj, T.A. Nguty and N.N. Ekere

The paste printing process accounts for the majority of assembly defects, and most defects originate from poor understanding of the effect of printing process parameters…

Abstract

The paste printing process accounts for the majority of assembly defects, and most defects originate from poor understanding of the effect of printing process parameters on the printing performance. As the current product miniaturisation trend continues, area array type package solutions are now being designed into products. The assembly of these devices requires the printing of very small solder paste deposits. The printing of solder pastes through small stencil apertures typically results in stencil clogging and incomplete transfer of paste to the PCB pads. At the very narrow aperture sizes required for flip‐chip applications, the paste rheology becomes crucial for consistent paste withdrawal. This is because, for smaller paste volumes, surface tension effects become dominant over viscous flow. Proper understanding of the effect of the key material, equipment and process parameters, and their interactions, is crucial for achieving high print yields. During the aperture filling and emptying sub‐process, the solder paste experiences forces/stresses as it interacts with the stencil aperture walls and the pad surfaces, which directly impact the paste flow within the apertures. As the substrate and stencil separate, the frictional/adhesive force on the stencil walls competes directly with the adhesives/pull force on the PCB pads, often resulting in incomplete paste transfer or skipping/clogged apertures. In this paper, we investigate the effect of stencil design on the printing process and in particular the effect on paste transfer efficiency.

Details

Soldering & Surface Mount Technology, vol. 13 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 March 1994

C.Y. Chan, A.H. Redford and N.N. Ekere

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…

Abstract

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.

Details

Soldering & Surface Mount Technology, vol. 6 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 January 1993

E.K. Lo, N.N. Ekere, S.H. Mannan and I. Ismail

The use of fine‐pitch SMD devices has increased the need for accurate and consistent solder paste deposits for reflow soldering. Continued miniaturisation in PCB and SMD…

Abstract

The use of fine‐pitch SMD devices has increased the need for accurate and consistent solder paste deposits for reflow soldering. Continued miniaturisation in PCB and SMD lead sizes is presenting the user, paste supplier and print equipment manufacturer with paste printing challenges. Most of these challenges are user‐driven, and are generally met by enhancing associated print equipment and solder paste materials. Recent developments in fine‐particle pastes, water‐soluble and no‐clean pastes are among the improvements in materials. Vision‐assisted stencil aperture and PCB pad alignment, the use of metal squeegees and new stencil fabrication methods are among the latest developments on the equipment side. Printing tests have shown that there is a physical limit for the solder paste printing process, which is defined partly by the nature of the stencil fabrication process, the physical forces and the stencil's ability to meter a precise volume of paste. The challenge as SMD lead sizes decrease is to improve the printing process to match component lead sizes. There is a fear that we are now operating at the very limits of the solder paste printing process. To meet future component developments, there is a need to develop alternative printing processes for solder reflow.

Details

Soldering & Surface Mount Technology, vol. 5 no. 1
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 11 April 2008

S. Mallik, N.N. Ekere, R. Durairaj and A.E. Marks

The purpose of this paper is to investigate the rheological behaviour of three different lead‐free solder pastes used for surface mount applications in the electronic industry.

Abstract

Purpose

The purpose of this paper is to investigate the rheological behaviour of three different lead‐free solder pastes used for surface mount applications in the electronic industry.

Design/methodology/approach

This study concerns the rheological measurements of solder paste samples and is made up of three parts. The first part deals with the measurement of rhelogical properties with three different measuring geometries, the second part looks into the effect of frequencies on oscillatory stress sweep measurements and the final part reports on the characterisation and comparison of three different types of Pb‐free solder pastes.

Findings

Among the three geometries, the serrated parallel plate was found effective in minimising the wall‐slip effect. From the oscillatory stress‐sweep data with different frequencies; it was observed that the linear visco‐elastic region is independent of frequency for all the solder paste samples. To understand the shear thinning behaviour of solder paste, the well known Cross and Carreau models were fitted to the viscosity data. Moreover, creep‐recovery and dynamic frequency‐sweep tests were also carried out without destroying the sample's structure and have yielded useful information on the pastes behaviour.

Research limitations/implications

More extensive research is needed to fully characterise the wall‐slip behaviour during the rheological measurements of solder pastes.

Practical implications

The rheological test results presented in this paper will be of important value for research and development, quality control and facilitation of the manufacturing of solder pastes and flux mediums.

Originality/value

This paper shows how wall‐slip effects can be effectively avoided during rheological measurements of solder pastes. The paper also outlines how different rheological test methods can be used to characterise solder paste behaviours.

Details

Soldering & Surface Mount Technology, vol. 20 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 December 2005

S.R. Hillman, S.H. Mannan, R. Durairaj, A. Seman, N.N. Ekere, M. Dusek and C. Hunt

To investigate how jamming of particles in a solder paste varies as a function of the gap through which the particles flow, and to correlate this with skipping defects…

Abstract

Purpose

To investigate how jamming of particles in a solder paste varies as a function of the gap through which the particles flow, and to correlate this with skipping defects during the printing process.

Design/methodology/approach

Solder pastes with particle sizes of types 2, 3, 4 and 5 were sheared between the parallel plates of a rheometer. Jamming events that cause the solder particles to be forced against each other were detected by monitoring the electrical current flowing between the plates under a bias of 1.0 V or less. Solder paste printing trials were conducted with the same pastes, and solder paste skipping monitored.

Findings

Jamming was detected when the ratio of plate gap to largest particle diameter is reduced to a value between 3.8 and 5.0. Decreasing the gap further results in increased jamming. A strong correlation between levels of skipping and jamming was found.

Research limitations/implications

More extensive printing trials are required before rheometric jamming detection can be used to predict printing performance.

Practical implications

The common rule of thumb used in solder paste printing that the aperture width should be no smaller than 4‐5 particle diameters is justified.

Originality/value

This paper presents a new technique for detecting jamming events which are too brief to be detected using normal rheometric techniques, but which have long been thought to be responsible for stochastic skipping defects during printing. Evidence supporting the link between jamming and this type of defect is presented.

Details

Soldering & Surface Mount Technology, vol. 17 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of 120