In message <[email protected]>, dated Tue, 31 Aug 2010, N.Shani <[email protected]> writes:
>Hello all, not directly EMC affecting, rather (long term) reliability >concern: we received a PCN from one of our semiconductor suppliers that >effective immediately they will change the bond wire from gold to >copper, following industry trend. There was an IEEE bulletin about this a few days ago. > >My immediate reaction was: What? Then, why? Is cost the only issue? >(and this brings me to the perennial issue of Pb-free assemblies and >how long will they last). > >Is anyone on this list aware of this sea change? I recall, from many >moons ago, that gold was deemed superior to anything else for most >semiconductor application. >Aluminum (OK, Aluminium) was reserved for RF devices, but gold ruled >everything else (better conductivity, good plasticity or whatever term >needs to be used, etc). Gold is not better than copper or silver in conductivity. The mechanical and metallurgical differences are more significant. > >Then, we started seeing copper as chip metalization of choice instead >of aluminum (conductivity?) or gold (cost?) - which made sense since it >was encapsulated in silicon dioxide. Now we are going to have copper >wire bonds. These are as low as 0.5 mil (12 um) in diameter... they'll >corrode in no time. We can't assume that no-one has tested the use of copper bond wires. It would be reassuring if the manufacturers released details of the successful tests and the stress levels applied. Provided the encapsulating material has been carefully checked, there is no likelihood of a corrosion problem. Indeed, the use of gold does not eliminate the risk of unforeseen chemistry - some of us remember Purple Plague! -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK If at first you don't succeed, delegate. But I support unbloated email http://www.asciiribbon.org/ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
