Archive for the ‘Metallurgy’ Category
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January 4th, 2010
Materials science of wire bonding
Wire bonding remains the most important interconnection technology in semiconductor packaging. It also happens to be the single largest industrial use of gold. Whilst lots has been written about the wire bonding process itself, much less has been written about the materials science of the technology. This latest paper in Microelectronics Reliability by Chris Breach and Frank Wulff takes a look at this area, including how the reliability of the ball bonding process is affected by selection of gold or copper wire. -
December 21st, 2009
New Book – Gold Science and Applications
I’m excited to announce that a new book ‘Gold – Science and Applications’ has now been published.
There have been many excellent books written on certain aspects of the science and technology of gold, most notably the book of the Hanau gold conference, held in 1996 (“Gold. Progress in Chemistry, Biochemistry and Technology”, edited by Hubert Schmidbaur and published in 1999) and there are several new books covering specific sectors of gold science e.g. on catalysis, chemistry and nanotechnology (see here). However, for those seeking a broader reference source on gold and covering all technical sectors, the most appropriate book on gold, Gold Usage by Bill Rapson and Theo Groenewald, was published over 30 years ago in 1978. The world of gold has changed considerably since then. A few years ago Chris Corti and I believed it was time for an updated book that reflects the more recent developments.
With the co-operation of some of the leading experts in their field, we have attempted to produce a book that is a worthy successor to ‘Rapson’ and to provide an authoritive source of information. We have attempted to cover all the main scientific areas as well as the main areas of application. In some cases this has required some very detailed scientific chapters; other fields require less specific detail and have focused more on the practical application. In addition, to help readers place this science and technology in the context of a much wider gold market, a chapter on the supply, demand and pricing of gold is included. Taken together, our aim for the book is to appeal to both those working in academia and industry.
If you are interested, your can read more and purchase it here .
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October 14th, 2009
Powder Metallurgy & Gold
I’ve just received a complimentary e-version of the International Journal of Powder Metallurgy “Precious Metals” Focus Issue. This Journal is published 6 times a year, bringing the latest news in the powder metallurgy and particulate materials industries.In his editorial, Alan Lawley states:
Precious metal powders find wide commercial applications because of their unique characteristics and properties, including thermal/electrical conductivity, corrosion resistance, solderability, and stability at high temperatures, coupled with reliability. Applications include conductive adhesives, dental restorations, catalysts, and sensors to monitor temperature and corrosion, and to detect gases. In comparison with ferrous powder metallurgy (PM), particulate precious metal science and technology receives limited exposure and press in industry news coverage. This “Focus Issue,” coordinated by Pierre Taubenblat and Joe Strauss, traces the history of particulate precious metal technology and gives an overview of market dynamics and current and near-term industrial applications. Comprehensive reviews of precious metal powder production methods and the manufacture of dental restorations are also included.
With so much happening in the application of gold in nanotechnology, catalysis and chemistry, it is good to see the metallurgical applications of gold being highlighted….
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October 12th, 2009
Eureka!
This morning on the way to work I read an interesting letter in the London Times. I’m sure all of you will know the famous anecdote of the Greek philosopher and inventor Archimedes – legend has it on stepping into the bath he noticed the level of the water rise, which led to his sudden understanding that the volume of water displaced must be equal to the volume of the part of his body he had submerged. This meant that the volume of irregular objects could be calculated with precision, a task previously extremely difficult. On realisation of this fact, he is said to have leapt out of the bathtub, shouted ‘Eureka!’ (which translates from Ancient Greek to ‘I have found it’), and in his excitement taken to the streets of Syracuse completely naked.
What people are probably less familiar with is the real reason for his joy. Like any good scientist, Archimedes was excited by the potential applications of his Eureka moment. The King of Syracuse had recently set him a task – basically the King had commissioned a new crown be made for him from solid gold. However, when delivered King Hiero II was suspicious that the goldsmith in question had, in fact, not used pure gold but had instead alloyed the gold with silver, effectively making a ‘cheaper model’. Archimedes had realised that he may be able to tell whether the crown was pure gold or not by how much water it displaced.
Like any legend from millennia past, many people have questioned its authenticity. I like to think it’s true though…
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July 10th, 2009
Au-based die attach materials
The issues relating to the use of gold-based alloys as die attach materials in the electronic packaging industry is highlighted by Anwar Mohammed from Infineon Technologies in Solid State Technology. He writes:
“To keep up with demanding power requirements, some savvy companies rely on eutectic attach materials such as AuSn and AuSi for die attaching to obtain superior thermal performance. The die attach temperatures are much higher relatively: ~320°C for AuSn, and ~420°C for the AuSi; but the thermal conductivity is significantly better with AuSn performing at ~70W/mK and AuSi performing at >150W/mK. The disadvantage of this approach is that it is a very tricky and sensitive process with a narrow processing window that needs to be monitored carefully.”
The reason I found this interesting (other than because it explains why Au-based materials are useful in die attach applications) is that there are direct similarities with gold-based catalysts. Like the eutectics described above, these catalysts have significant performance benefits in many reactions (selectivity, activity), but applications have been limited due to processing concerns. The problems in ‘processing’ can be related to either making the catalysts or operating them under practical conditions, where the process window may be limited. Thankfully things are now progressing well. Gold catalysts can be successfully manufactured and purchased from the likes of 3M, Strem Chemicals, AuTEK and Nanostellar (automotive) and there are applications where they are able to operate under a suitable range of processing conditions.
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July 8th, 2009
Next issue of Gold Bulletin now available!!
Hi everyoneIt’s here at last, Issue 42(2) of Gold Bulletin.
We have an issue bursting with lots of gold news and science and a superb Guest Editorial from Prof James (Jim) Johnstone from Victoria University of Wellington New Zealand.
We have all the lastest information about Gold 2009 ; the Keynote presentations , the opening Plenary presentations and all the info on the main conference sessions
We have seven wonderful scientific papers from a range of disciplines including Metallurgy, Catalysis, Analytical and also Nanotechnolgy. Also a book review of Mark Grimwade’s Introduction to Precious Metals – Metallurgy for Jewellers and Silversmiths.
Also our regular features of Highlights from Recent Literature and a summary of Calendar Events comming up in the near future.
Hope you enjoy it. Let me know what you think. I always like to hear your views.
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May 8th, 2009
Hydrogen purification membranes
In the heart of the old gold mining region called Golden in Colorado, they are working on what could potentially be an important new industrial application for gold. …..Today I had a project review meeting at the Colorado School of Mines where a research group led by Prof Doug Way is further improving the alloys used in hydrogen purification using palladium membranes. This is an important technology for the emerging hydrogen economy and fuel cell power systems.
Doug Way’s team has demonstrated that the use of palladium-gold alloys in this application has clear advantages, especially with respect to reducing poisoning of the membrane with sulphur and carbon monoxide. He and his team have made great strides since his early findings and their latest results are summarised in a new publication ‘F. Roa, P.M. Thoen, S.K. Gade, J.D. Way, S. DeVoss, G.O. Alptekin, Palladium-copper and palladium-gold alloy composite membranes for hydrogen separations, in Inorganic membranes for energy and environmental applications, A.C. Bose, Editor. 2009, Springer: New York p. 221-239.’ See here.
The Wade research group will also be presenting their work on these membranes at GOLD 2009.
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March 31st, 2009
GOLD 2009 – update
The decisions of the various technical committees and organising committee,with respect to oral and poster presentations at GOLD 2009,will be communicated to authors this week. The very high quality of submitted abstracts means we are promised an excellent event.The various plenary and keynote talks should also be a highlight. The following are confirmed invited speakers:
Plenaries:Richard Puddephatt, University of Western Ontario, ‘Molecular engineering in gold chemistry: From molecules to polymers and network materials’
Paul Mulvaney, University of Melbourne, ‘Single gold nanocrystal spectroscopy – Steps towards active plasmonics’
Pietro Cavalotti, Politechnico Milano, ‘The art and future of gold electroplating’
Wayne Goodman, Texas A & M University, ‘Catalysis by Au and Au Alloys: From Single Crystals to Nanoparticles’
Masatake Haruta, Tokyo Metropolitan University ‘A New Frontier in Heterogeneous Catalysis: Gold Clusters’
Dean Toste, UC Berkeley ‘Homogenous Catalysis with Gold: Development, Applications and Enantioselective Catalysis’
Graham Hutchings, Cardiff University ‘Nanocrystalline gold catalysts for selective chemical synthesis’
Keynotes:Luigi Messori, University of Florence (Gold cytotoxicity)
Mohammad Omary, University of North Texas (Gold luminescence)
Konrad Seppelt, University of Berlin ‘Gold Fluorides and their role in Metal-Xenon Compounds’
Boonrat Lohwangwatana, Chulalongkorn University ‘Design and Synthesis of Gold Metallic Glass and its Applications’
Tobias Müller, W. C. Heraeus GmbH ‘Gold wire bonding in microelectronics – an overview’
Brahim Lounis, Université Bordeaux ‘Optical detection of individual Gold Nanoparticles’
Ulrich Heiz, Technische Universität München ‘Catalysis of Gold: Each atom counts!’Didier Astruc, Université Bordeaux, ‘Interplay between Gold Nanoparticles and Dendrimers’
Vincent Rotello, University of Massachusetts, ‘Gold Nanoparticles as Diagnostics and Therapeutics’
Mikael Käll, Chalmers University of Technology, ‘SPR goes nano : using gold nanostructures for efficient refractive index sensing’
Avelino Corma, Universidad Politécnica de Valencia ‘Gold (III)-Metal organic frameworks for bridging the gap between homogeneous and heterogeneous gold catalysts’ -
March 17th, 2009
New gold bonding wire product
As those working in the microelectronics industry will know, wire bonding technology is the most widespread and reliable interconnection technique. Whilst aluminum, copper and their alloys can all be used as wire materials, high purity gold bonding wire remains the material of choice, having been widely used in semiconductor devices since the assembly of semiconductor packages began approximately 40 years ago. Gold is used because of its ductility, low electrical resistance and resistance to oxidation.
Last week W. C. Heraeus announced the launch of Rel-k, a new 99.5% pure gold wire. Rel-k is available in production quantities and is being shown for the first time in public this week at Heraeus’s booth at Semicon China
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March 3rd, 2009
Size Matters for the Strength of Gold
What is the mechanical strength of pure gold?
Well, it appears to depend on size when one reaches the micro-scale, according to Professor William Nix of Stanford University. He gave the Von Hippel Award talk at the MRS Fall Meeting in Boston in November 2007 (transcript in MRS Bulletin, February 2009 vol 34 (2), 82-91) on “Exploiting New Opportunities in Materials Research by Remembering and Applying Old Lessons”. He reports on how the strength of single crystal gold substantially increases at the sub-micron scale. Surprised? I was!
Material Scientists all know that there is a grain size dependency on the strength and ductility of metals and alloys according to the Hall-Petch equation, but this does not apply in the case of single crystal test specimens. Nix reports on the work of Julia Greer and co-workers (J R Greer et al, Acta Mater. 53, 1821, 2005) on simple uniaxial compression testing of small sub-micron pillars, 400nm diameter and 1960 nm high, of single crystal gold, oriented in the <001> direction, which are made by focused-ion beam machining. These tests show very high levels of flow stress – over 500 MPa compared to around 30MPa for bulk gold. Reducing the pillar diameter to 290 nm increases the flow stress to around 750 MPa. Truly amazing values in my opinion.
The reason for the jerky stress-strain curves and high flow stress values seen in these experiments were explained in terms of old literature reports from the 1950s/60s (i.e. ‘learning from old lessons’) on how dislocations multiply, i.e. from other dislocations. Nix comments that if the pillar diameter is smaller than the characteristic dislocation length for multiplication, we can expect moving dislocations to exit the crystal more frequently than they multiply. Nix argues that in such situations, the crystals harden by a ‘dislocation starvation’ mechanism; here, plastic deformation is controlled by dislocation nucleation, which requires very high stresses. He also states that this mechanistic theory is hotly debated and disputed by others. Nonetheless, the high strength values are not in dispute!
It is interesting to speculate how one might make use of this phenomenon in real engineering materials. Anyone got any bright ideas for nano-engineered gold?
Richard Holliday
Trevor Keel
Tricia Harris
Chris Corti
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