We don't have room in print for all your letter and blog pingbacks, but do here. There was interest in Google's Street View, and Lord Erroll...
STREET VIEW I was surprised by your comment (Our house, in the middle of Google's street, April 10) that 'under UK law, permission must be obtained before broadcasting images of private citizens'. A moment's thought suggests this cannot be so, or all broadcasters and newspaper websites are breaking the law every time they show a busy street, a football crowd, or a concert audience. In fact I believe I read somewhere (on a photographers' website) that this is a 'common misperception'. Could you confirm the true situation please? Hazel McGee, Guildford
>> The Guardian rehashes the old privacy concerns in the article. It also claims that Street View costs between $125 and $700 per mile of video footage - which I think is probably an overestimation. virtualtourism.blogspot.com
ON A ROLL WITH ERROLL Lord Erroll rightly highlights failures in tackling internet crime (One Lord Leaping, 10th April). His committee's call for a central cybercrime unit to handle low-level internet fraud is understandable but misplaced: There aren't central units for dealing with fraud committed door-to-door, by mail order or on a market stall .Instead each police officer is trained to deal with these commonplace crimes locally. The internet has given fraud and theft a new medium to exploit, the mechanics of which are little understood by many police officers, businesses and much of the public at large. A few hours of careful training for all police officers combined with the right tools and timely industry assistance would be far more effective than creating a new centralised bureaucracy. Daryl Kayes, Leeds
>> He's in the Lords, not in the Government. The only person in the Government with first hand experience of database systems (though in the sense of having sold them to government in his business career, rather than having dealt with the geeky concerns of technical analysis and getting things to work) is Liam Byrne MP, who is an utter party loyalist and a true believer in Transformational Government. forum.no2id.net
ELEMENTARY? Kate Bevan in Technophile (10th April) might also have mentioned that the Amazon website says you need an Intel-based Mac to run Photoshop Elements, but the Adobe website says it is fine to run the software on an iMac G5. Another example of why more in-box documentation is needed. Warren Newman, London
TINIER... If the whole point of Tinyurl is to reduce long web addresses to more manageable proportions why isn't the resulting prefix something like www.tu.com/. And now that we've all got the hang of it why not reduce www. to a single w. From there we could wander the rich pastures of .uk instead of uniquely in this wide world having to suffer the .co prefix. Rob Carthy, Bromley
MORE TIN Congratulations on the very interesting article on tin whiskers last week. You may be interested to hear of another phenomenon associated with the introduction of lead-free solders in electronics. This known as Tin Pest. Tin is a strange element: It is allotropic, changing its internal atomic arrangement according to the temperature. Above 13°C, it is known as β, or white, tin while at lower temperatures it exists as α, or grey, tin. Unfortunately, the transition temperature is quite likely to be encountered in service. This is more than mere scientific curiosity because the white version possesses acceptable mechanical properties whereas prolonged exposure at lower temperatures results in a brittle, fragile, material (grey tin) – quite incapable of providing the strength necessary for a joint. Because the new lead-free solders are quite dilute – consisting of more than 95% tin – an obvious question is 'Will these alloys be susceptible to tin pest formation and lead to subsequent interconnection failure?' The consequences of a control system failure could range from mere inconvenience to loss of life and prodigious costs (hundreds of millions of pounds in aerospace applications, for example). Considerable research into the allotropy of tin was carried out some 80 years ago. Tin pest was found to occur by a process of nucleation and growth, and was extremely slow – often requiring years to complete. Since the transition to grey tin involved a 27% increase in volume, its formation was restricted to the surface where there was less resistance from the surrounding material. Some alloy additions favoured the transition while others inhibited it, and it was never observed for periods up to ten years. Recently, tin pest has been reported in bulk samples of lead-free solder alloys (tin-copper, tin- silver and tin-silver-copper) following a few years exposure at -18°C, the usual freezer temperature. To date, it has not been observed on actual joints, and this may be due to the limited free surface available or the physical constraint provided by the components on the board, as compared with bulk samples. In addition, lead-free interconnections have been in service for a relatively short time. The figure shows various stages of tin pest development in a tin-0.5 copper alloy. Surface eruptions, or warts, gradually spread and eventually total disintegration of the massive sample is observed. This is due to the brittle nature of the grey tin and the large volume expansion that accompanies its formation. A critical feature of the experimental findings, both for pure tin many years ago and for the new lead-free solder alloys, is their inconsistency. Nominally identical specimens with the same thermal history commonly respond quite differently: one may display extensive tin pest while the other appears quite unaffected. This highlights the fact that we do not really understand the process and adds further confusion for the designers of electronic equipment. Although the effects of different alloy additions are known, it could well be that the presence, or absence, of certain impurities in tin are critically important. Development of the new lead-free solder alloys focused upon their properties and processing attributes. However, no consideration was given to the problems that may surround tin pest formation in service. Some leading practitioners have already dismissed this possibility, but the evidence is uncertain, and burying heads in sand does not constitute good engineering practice. Although we do not yet know whether it is necessary to shut the stable door, we should make more effort to understand and control tin pest formation. Only time will tell whether it represents a real problem in electronics – by then it could be too late! Professor Bill Plumbridge, Faculty of Technology, The Open University
