Soldering & Surface Mount Technology

ISSN: 0954-0911

Article publication date: 1 December 2001




(2001), "SSTC", Soldering & Surface Mount Technology, Vol. 13 No. 3.



Emerald Group Publishing Limited

Copyright © 2001, MCB UP Limited



Keyword: Conference

The following programme has been announced by NPL for the SSTC Meeting at Kempton Park Conference Centre on 3 October, commencing at 10.00 a.m.:

  • "Halogen-free materials: WEE legislative issues, material availability, process issues and cost" Alun Morgan – Isola

  • "Thermal performance of metal foams as heat sinks" Jerry Lord – NPL

  • "New PCB/component surface finishes, and industry trends" Keith Whitlaw – Shipley

  • "Fine pitch printing performance of solder paste and adhesives" Milos Dusek – NPL

  • "Developments in surface mount technology and the impact on adhesives for the electronics market" Abayomi Olusanya – Loctite

  • "Not so tacky now" Brewin – NPL

  • "Standard SMT process for flip chip assembly on FR-4 substrates" Steve Harris – Solectron

  • "Electrical issues for high frequency materials" Bob Clarke – NPL

Report on the SSTC Spring Conference and Exhibition, 3 May 2001, Kempton Park


This meeting, organised by NPL, the National Physical Laboratory, is part of a series covering important issues that are challenging the industry today. Presentations were made from industry leaders and outlined technology barriers and offered solutions to meet industry's future requirements (see Plate 1). The audience for these popular meetings is technologists, engineers and managers in today's electronic assembly industry.

Plate 1 The NPL SSTC Conference held at Kempton Park 3 May 2001. (Left to right) Martin Wickham - NPL; Dr Chris Hunt - NPL; Mike Bixenman - Kyzen Corporation, USA; Bob Willis - Technical Director, The SMART Group; Dr Paul Tomlins - NPL; Claire Snow - Director, Industry Council for Electrical & Electronic Equipment Recycling; Dr Brian Richards - Chairman, NPL

The status of lead-free soldering in Japan

Bob Willis – Technical Director, SMART Group:

The SMART Group recently organised a DTI sponsored technology mission to assess the status of lead-free soldering in Japan. The mission highlighted a number of important facts relating to the drivers, alloy selection, process details and equipment issues. The presentation gave an overview of the findings of the mission, now included in the published report.

The effect of controlled nitrogen atmospheres and the influence of PCB surface finish on solderability

Chris Hunt – NPL:

NPL in conjunction with BOC has undertaken a study of the effect of controlled nitrogen atmospheres on solderability using lead-free alloys. Results were presented that show the impact of reduced oxygen levels on the solderability of a number of surface finishes. A number of PCB finishes have been evaluated for solderability with a range of lead-free alloys and fluxes. The results emphasize important issues with compatibility with PCB finish and lead-free alloy. A relationship was established for wetting force and pad size that allows a prediction of wetting force for any pad size.

Lead-free electronic assembly and advanced packaging will place more demand on precision cleaning. HFC vapour phase technology offers a viable option

Mike Bixenman: Kyzen Corporation, USA and Abid Merchant: DuPont, USA:

Pb-free flux residue formation will be more difficultto remove due to higher processing temperatures, flux induced interaction with alloys, and formation of insoluble salts. The degree and appearance of residue may be different, which will have a substantial effect on reliability. In addition to Pb-free processing concerns, both assemblies and packaging are moving toward greater component densities, higher electrical and thermal performance, and dense full array footprints to accommodate higher I/O. As a result of these trends, it will be increasingly difficult to achieve true a "no-clean" process. Vapour phase cleaning technology has the properties required to meet these demanding challenges.

Thermal profiling of lead-free assemblies: code of practice to achieve accurate measurement

Martin Wickham – NPL:

NPL has just completed a studio project looking at how to accurately measure thermal profiles during lead-free soldering. Details were given on the work done to generate a code of practice covering a variety of issues, including how to attach thermocouples, where to attach them, and what vehicles to use for both initial profiling and regular profile checking. The code of practice is now available from NPL.

Modelling thermo-mechanical fatigue and the art of reliability prediction

Chris Bailey – Greenwich University:

The response of SnPb and Pb-free solder joints in different thermal cycles is of key interest in any reliability testing. Conventional experimental methods are time-consuming. This paper compared modelling predictions with experimental data, and allowed the model to be verified. The model showed excellent sensitivity to experimental parameters, such as the thermal cycle conditions, component stand-off height, etc. ln the future modelling will greatly lower the evaluation period and will aid industry in reducing the time of testing and hence product introduction to the market. Aspects of the modelling and experimental data were discussed.

Where is the proposed European WEEE and EEE legislation taking the industry?

Claire Snow – Director, Industry Council for Electrical & Electronic Equipment Recycling:

The recent developments in the proposed European legislation, and the (often conflicting) activities of individual member states, present a confusing picture. The likely way ahead was discussed in terms of national and international actions, their legality and timescales.

Intercomparison of lead-free component termination finishes covering process yield, solderability, and tin whiskers

Martin Wickham – NPL:

An NPL studio project with the major chemistry suppliers has compared the alternative lead-free component termination finishes. Results from an intercomparison of Sn, SnAg, SnCu, SnBi, and PdAu finishes were presented, including details of relative process yield, solderability and Sn whisker propensity.

Measuring the adhesion of encapsulants

Paul Tomlins – NPL:

The reliability of bare silicon die is considerably extended by encapsulation in plastic. Hence, the adhesive bond formed between the plastic and the component or substrate is key to the performance of the encapsulation. The type of substrate, surface finish, the cleaning and the encapsulating chemistry affect the strength of this adhesive bond. In this presentation a simple test method was described that can be used to measure reliably the strength of adhesive bond in tension.

For more information please contact: Dr Chris Hunt, The National Physical Laboratory, Teddington TW11 0LW, UK. Tel: +44 (0) 208 943 7027; Fax: +44 (0) 208 614 0428; E-mail:

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