Just a quick correction... "low-pitch" should be "high-pitch" (i.e., with large lead-to-lead and wirebond spacing, aka low density :-). Thanks.
On Tue, Aug 31, 2010 at 8:48 PM, Oscar Fallah <[email protected]> wrote: Hi Naftali, The main driver for Au-Cu conversion is cost. This has been happening for some time (at least for the last three-four years), and I have seen many PCNs >from tier-1 semiconductor suppliers for such conversions. Most of the conversions I have seen affected low-pitch parts such as transistors and diodes. This is well understood that Cu bonds are stronger, and do not suffer from the same intermetallic compound growth issue that is associated with Au/Al bond interface. The main reliability culprits are wire oxidation and bond-pad cratering. In both cases, supplier must have completed the relevant reliability tests to demonstrate Cu wire bond reliability equivalency with Au counter part. Also, supplier must demonstrate and document all assembly equipment and process changes that they have made to accommodate the special storage, assembly operation, and handling required for Cu wire bonding. For example, floor life of Cu wire spool is limited to 48 hrs once installed on the wirebonder, and there is need for employing a masking gas (such as nitrogen) during wire bonding operation. All of the above information should have been provided along with the PCN, and/or be at the least readily available upon request if your supplier has done all of their homework. Thanks, Oscar On Tue, Aug 31, 2010 at 9:54 AM, John Woodgate <[email protected]> wrote: In message <[email protected]>, dated Tue, 31 Aug 2010, N.Shani <nshani.ca <http://nshani.ca/> @gmail.com <http://gmail.com/> > 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 <http://www.jmwa.demon.co.uk/> and www.isce.org.uk <http://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]> - 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]>
