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Emerald Group Publishing Limited
Copyright © 2002, MCB UP Limited
...Brevity is the sister of talent (Friedland, 1964)
Keywords: Internet, Hybrid circuit, Lead frames
The most usual quotation regarding brevity is, of course, Hamlet's, "brevity is the soul of wit". However, I thought my soul should be witty by blowing my trumpet about my talent! The crux of the matter is that this Internet Commentary will, perforce, be brief, because I have a problem with my right hand which makes it very difficult to type or to use my mouse. I therefore ask my readers to forgive me for giving you just a few lines on each of a multiplicity of sites, hoping I will be back to normal by the time I type the manuscript for the next issue.
In the hopes of finding the state-of-the-art about lead-free interconnections, I typed hybrid circuit leadframes OR "lead frames" solderability into Google and came back with a mere 20-odd responses. Let's have a look at what they offer us.
This page is a glossary of terms beginning with the letter S. I assume that we got here through the key word solderability and probably the other key words are also in this page. However, the site is not entirely without relevance, because the company concerned does indeed make modules with lead frames. Navigation round the site is not very easy, but I could find no references in 20 minutes of assiduous search to lead-free assembly. Nevertheless, some photographs did show modules with what appeared to be gold-plated lead frames which would, of course, be lead-free, even if the module contents were soldered with a lead-containing solder.
This is a PDF file of a technical paper relating to the lead-free implementation of power electronics modules. The first part of the paper summarises the regulatory position of using lead-containing solders in different countries of the world. The second part is more technically oriented but the only mention of lead frames is to ensure that the solderable finish will not contain lead. An interesting paper!
This is simply a very long list of the product categories which the organisers hope will be exhibited at the forthcoming UK Nepcon exhibition in Birmingham.
This page is a bit of a mystery! It describes a large number of vocational courses available in the field of microelectronics, organised by a community college, apparently in Arizona. Thus far, nothing is exceptional. What is exceptional is that there is no way to navigate within this website! So, you can learn all about what the courses contain but nothing else, whatsoever, about the college!
Least said, soonest mended. This site describes a book, which I wrote!
This is another book from the same stable as the last one, A Scientific Guide to Surface Mount Technology by Colin Lea. This bible is, of course, very well known.
I thought at first that this site would be quite interesting, but was greatly disappointed when I found that it did not work, at least when I tried it out. Theoretically, it would allow you to put in an application, such as hybrid circuit lead frames, the characteristics that you desired and it would come up with the answer of the best alloys for your particular requirements. Unfortunately, it responded with a "Page not accessible".
This is a magazine article entitled, "Solder Trends in Microelectronics", by Dr Malcolm Warwick. Although it only vaguely touches on lead frames, this article is more like the kind of thing that we are susceptible to look for, because it deals comprehensively with the problems of lead-free electronics.
This page is a list of abstracts published by the National Physical Laboratory and offered for sale at a reasonable price. Several of these are very pertinent to our search because they treat both the problem of the lead frames themselves and lead- free finishes on them. Be warned, though, that the NPL site is on a fairly slow server and it may take you some time to download this page at busy times.
One of the problems that has been noted with the use of lead-free finishes on lead frames is the formation of tin whiskers where the finish is an electroplated pure tin. This is a comprehensive paper describing the problem in good technical detail. However, be aware that it is several megabytes long, including the figures, and may take a long time to download.
I don't think that anyone would dispute the importance of JEDEC when it comes to lead frames. This long document is a résumé of the work done and is being done by a number of committees. Some of these deal directly with the problems of the lead-free soldering and finishes and is therefore very relevant to the search. Downloading may take some time, because it is a 32 page document.
This is another paper dealing essentially with leadless chip scale packages. As such, it is not really relevant to this article, lead frames being mentioned once, en passant. There is no mention of leadfree finishes, either. Not withstanding, the paper makes good reading.
This is a funny one! It consists of a short course on interconnection technology, of American origin. Notwithstanding, the site is Turkish and I suspect that it may have been plagiarised. For those wanting an introduction to the subject, it may be adequate but details are lacking.
Nobody needs any introduction to IMAPS. This is their 2001 technology road map and I find it astonishing that there are so few references to either lead frames or lead-free finishes within this important document.
This site is a kind of mini-bookshop dedicated to surface mount technology. The page in question is an index to specific subjects. Both lead frames and lead-free are mentioned in this index, but, unfortunately, with no links, at least at the time of writing. However, the range of books offered does not compare with that of some other sources.
This is another hefty PDF document, issued by the US military, describing alternatives to the use of cadmium as a protective finish. It is not really relevant to this critique but, if you happen to still be using cadmium, other than in solders, then it could be useful.
This is a MIL Spec, revised in 1996, taken up by the CERN in Geneva, describing test methods for microelectronic modules. As such, it is relevant to this article, although it is weak on lead-free finishes. The scope is best described by the following quotation (and if you think that my sentences are long...!): This standard establishes uniform methods, controls, and procedures for testing microelectronic devices suitable for use within Military and Aerospace electronic systems including basic environmental tests to determine resistance to deleterious effects of natural elements and conditions surrounding military and space operations; mechanical and electrical tests; workmanship and training procedures; and such other controls and constraints as have been deemed necessary to ensure a uniform level of quality and reliability suitable to the intended applications of those devices...
This is certainly a heterogeneous collection of websites of varying degrees of utility. Of course, I can never be sure whether a site which I consider as useful would be to others or one that I consider as useless may be exactly what someone is looking for. Another problem that I have is to know how much detail you really want in a website criticism. I would like you to tell me!
Brian EllisCyprusb_ellis@protonique.comFriedland, L. S. (Ed.) (1964) "Letter to Alexander Chekhov, 11 April 1889", Anton Chekhov: Letters on the Short Story