Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Lead-Free Formulation Selection

#6407

Lead-Free Formulation Selection | 20 July, 2000

Bob: Some people suggest different lead-free solder formulations for wave, reflow, and hand soldering. * What are your thoughts on this? * What are the factors that contribute to using different lead-free solder formulations for wave, reflow, and hand soldering? * What are your recommended lead-free solder formulations for wave, reflow, and hand soldering? Who are the suppliers of these materials? * What are the creep characteristics of these materials compared to common near-eutectic tin-lead solders?

Thanks

reply »

Bob Willis

#6408

Re: Lead-Free Formulation Selection | 20 July, 2000

Personally I would go for one alloy it just makes it all simple to control. I have only used tin/silver and tin/copper so far with good process results.

Reflow is relatively straightforward, I have had more shorts with wave on tin/copper.

To date I have run products from Alpha, Multicore and Indium on the paste side and only Alpha on the wave solder side. These are the materials we have used on all our hands on workshops.

For the material characteristics the best people to contact are the Open University in the UK.

Bob

reply »

C_Herder

#6409

Re: Lead-Free Formulation Selection | 20 July, 2000

What is "Open University"? How do I contact them?

reply »

Bob Willis

#6410

Re: Lead-Free Formulation Selection | 20 July, 2000

Here are the details for the OU

Lead-Free Project Introduction

The Open University Solder Research Group aims to facilitate the implementation of lead-free solders by evaluating their mechanical properties, especially those which are influential to their service performance.

Examination of the corresponding behaviour of model solder joints and comparision with the performance of entire boards provides the underpinning correlation for life prediction and design, and ensures that selection of specific lead -free alloys is soundly based.

Current Position/Results

An extensive assessment of the tensile, creep, fatigue and fatigue-creep behaviour of bulk specimens of Sn-37Pb, Sn-3.5 Ag, Sn-0.5 Cu and Sn-3.5Ag- 0.5Cu has been carried out over a range of temperatures. (down to -40 C in some cases). The effects of temperature and strain rate on monotonic strength are substantial, and may alter the ranking of the alloys.

Fatigue performance may be severely impaired by the presence of a dwell period in the strain cycle although there appears to be a saturation of this effect, in terms of dwell duration. The silver- containing alloy has substantially the best creep resistance.

Tests on simple 'pin-in-ring' joints are beginning and a programme of thermal cycling of complete boards is planned.

Contact Professor W J Plumbridge Materials Engineering Department The Open University Walton Hall Milton Keynes MK7 6AA UK

Tel: 01908 652630 Fax: 01908 653858 Email: W.Plumbridge@open.ac.uk

Full details are available on: http://www-tec.open.ac.uk/materials/srg/srg-hp.html

reply »

SMT Custom Nozzles

Essemtec Fox Compact Automatic Pick and Place