sbrunnoc@hawk.ulowell.edu (Sean Brunnock) (07/13/89)
Hello. I need some outside help to settle a bet. Which is a better conductor gold or silver? Please e-mail to me (and rsilvers@hawk.ulowell.edu if it is not too much trouble) as I am sure the answer is obvious. Sean Brunnock
berryh@udel.EDU (John Berryhill) (07/14/89)
In article <14172@swan.ulowell.edu> sbrunnoc@hawk.ulowell.edu (Sean Brunnock) writes: > > Hello. I need some outside help to settle a bet. > > Which is a better conductor gold or silver? I was surprised to find that (according to my periodic table) the conductivity of Ag is .630 X10^6 (ohm-cm)^(-1) while Au is only .452 X10^6 (ohm-cm)^(-1). The comparison may change with frequency, although the fact that silver is more reflective indicates that it probably wins at high frequency as well. My periodic table, btw, is published by Sargent-Welch Scientific. If you want to check on the figures, stop by ANY chemist's office and ask to see the CRC Handbook of Chemistry and Physics (a jumbled and arcane, but often useful, grab-bag o' data). That does not necessarily mean that silver is a better choice of metal in all conductor applications. The fact that silver tarnishes while gold doesn't should tell you that the surface is probably more likely to develop problems. You wouldn't want to use it as, for example, a card-edge connector, or a battery terminal. Gold is the conductor of choice for most applications that involve exposed surfaces, the fact that it is used for the aforementioned applications is the reason that your mailbox is filling up with messages telling you that gold is the winner, but it ain't so. Surfaces can be a bitch and they'll get you every time.
mmm@cup.portal.com (Mark Robert Thorson) (07/16/89)
As John Berryhill said, gold is used for corrosion resistance on contact surfaces. It's not a very good conductor, as metals go. It's electrical resistance is not important because it's a thin layer. The other important feature of gold is its ductility. Integrated circuits in plastic packages use gold bond wires because the packages flex with temperature. This is one reason IC's in plastic packages are less reliable; the gold bond wire interacts with the aluminum bonding pad on the chip. Gold diffuses into the pad, and aluminum diffuses into the wire. This can create voids in the bond, and it creates a brittle gold-aluminum alloy. Military chips, on the other hand, use ceramic packages. These don't flex, so aluminum bond wires can be used.
cees@maestro.htsa.aha.nl (Cees Keyer) (07/17/89)
In article <20483@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes: >As John Berryhill said, gold is used for corrosion resistance on contact >surfaces. It's not a very good conductor, as metals go. It's electrical >resistance is not important because it's a thin layer. I think that the resistance is important. The reason that it's a thin layer is nonsense because gold is also used in the high frequency technology but in that high freq. region the major part of the resistance is contributed by the "skin effect" so the reason "it's just a thin layer" is nonsense. -- DISCLAIMER: All the opinions expressed are my own. Cees Keyer, Algemene Hogeschool Amsterdam. department of electrical engineering. UUCP: {backbones}!tamtam!cees cees@htsa.aha.nl cees@tamtam.htsa.aha.nl
ornitz@kodak.UUCP (Barry Ornitz) (07/18/89)
In article <996@maestro.htsa.aha.nl> cees@htsa.UUCP (Cees Keyer) writes: >In article <20483@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes: >>As John Berryhill said, gold is used for corrosion resistance on contact >>surfaces. It's not a very good conductor, as metals go. It's electrical >>resistance is not important because it's a thin layer. >I think that the resistance is important. >The reason that it's a thin layer is nonsense because >gold is also used in the high frequency technology >but in that high freq. region the major part of the resistance >is contributed by the "skin effect" so the reason >"it's just a thin layer" is nonsense. The reason gold is used in microwave work is not because of lower surface resistance, but rather because of its chemical inertness. Silver is a much better material to plate microwave cavities with, but silver tarnish is a much poorer conductor than silver. Often an extremely thin layer of gold is plated over silver to provide corrosion protection without seriously degrading the high conductivity of the silver layer. In the chemical industry, connector corrosion on instrumentation is a severe problem. It is even worse in the pulp and paper industry. Heavy gold plating of printed circuit edge connectors is quite necessary. On the custom PC boards we make, we first plate with nickel and follow with gold to avoid problems. Barry ----------------- | ___ ________ | | | / / | | Dr. Barry L. Ornitz UUCP:..rutgers!rochester!kodak!ornitz | | / / | | Eastman Kodak Company | |< < K O D A K| | Eastman Chemicals Division Research Laboratories | | \ \ | | P. O. Box 1972 | |__\ \________| | Kingsport, TN 37662 615/229-4904 | | -----------------
koziarz@halibut.nosc.mil (Walter A. Koziarz) (07/21/89)
Gee, I thought the problem with plastic packages from military standpoint was hermeticity. But, I only share office space with those who write the specs. Agreed on the gold-wire vs aluminum wire portion. Walt K.
vaso@mips.COM (Vaso Bovan) (07/22/89)
In article <1378@nosc.NOSC.MIL> koziarz@halibut.nosc.mil.UUCP (Walter A. Koziarz) writes: >Gee, I thought the problem with plastic packages from military standpoint >was hermeticity. But, I only share office space with those who write the >specs. Agreed on the gold-wire vs aluminum wire portion. > >Walt K. Does the military still consider that ceramic/cerdip packages also have better thermal characteristics, in general. Even with copper lead frames, a problem with plastic packages is that the plastic is (relatively) a heat insulator, so that little heat gets out the top of the package. Most heat must flow through the leads. Thus, fan cooling is less effective with plastic packages. With this in mind, many companies have a rule of thumb which says that junction temperatures determine whether plastic or ceramic/cerdip is used. My rule of thumb is 125C worst case junction temperature, well below the glass transition temperature. Is this a reasonable rule of thumb in ROME's opinion ?
aj-mberg@dasys1.UUCP (Micha Berger) (07/24/89)
There are really two questions here (since silver tarnishes): Which is more conductive: 1- gold or silver? 2- gold or silver oxide? Even if silver is more conductive, it wouldn't help much unless silver oxide is too. -- Micha Berger "Always should [the child of] Adam have awe of G-d in secret and in public, admit the truth, and speak truth in his heart."
DAVIS@ohstpy.mps.ohio-state.edu (JOHN E. DAVIS) (07/26/89)
Which is a better conductor: Gold or Silver?
At room temperature silver is a better conductor but at low
temperatures gold conducts better. So as many have replied it
depends upon one's application.
--John E. Davis
OSU Physicsmyers@hpfcdj.HP.COM (Bob Myers) (08/01/89)
>Does the military still consider that ceramic/cerdip packages also have better >thermal characteristics, in general. Even with copper lead frames, a problem >with plastic packages is that the plastic is (relatively) a heat insulator, >so that little heat gets out the top of the package. Most heat must flow >through the leads. Thus, fan cooling is less effective with plastic packages. I don't know about the military, but my experience in testing the beasts is that a ceramic package is certainly better as far as thermal characteristics go; ceramic has also been considered "more hermetic" than plastic, although more recent (last five years or so) plastioc packages have been very good. The best package, IMHO, is still the ceramic "sidebraze" (leads brazed on to pads on the side of the ceramic package proper) with a metal lid. Unfortunately, it's also the most expensive. One other little item to keep in mind is that a CERDIP package (ceramic "sandwich" with a frit seal and a leadframe as found in plastic packages) is NOT as good as the older ceramic sidebraze style. Thermally, it's OK, but I've found the frit seal to be fragile - and once it's cracked, it's worse than plastic for letting moisture and assorted gunk inside. Automatic insertion equipment can do a real number on these packages if you don't watch it carefully. (Most AI machines squeeze the leads - which are normally "sprung out" a bit, as with a plastic package - together slightly when positioning the part for insertion. This can stress and break the seal on a cerdip part.) Bob Myers | "Writing is not necessarily something to be ashamed of - myers%hpfcla@hplabs. | but do it in private, and wash your hands afterwards." hp.com | - Lazarus Long/Robert A. Heinlein
vaso@mips.COM (Vaso Bovan) (08/16/89)
In article <1986@kodak.UUCP> ornitz@kodak.UUCP (Barry Ornitz) writes: >Often an extremely thin layer of gold >is plated over silver to provide corrosion protection without seriously >degrading the high conductivity of the silver layer. In the chemical industry, >connector corrosion on instrumentation is a severe problem. It is even worse >in the pulp and paper industry. Heavy gold plating of printed circuit edge >connectors is quite necessary. On the custom PC boards we make, we first >plate with nickel and follow with gold to avoid problems. > Barry On the subject of gold plating, I have two questions: 1) How important, in gold plating of edge connectors etc, is it to have soft gold on one surface and hard gold on the other ? 2) How do the palladium alloy plating compare with gold plating ?
logo@gorn.santa-cruz.ca.us (David Kiviat) (09/06/89)
Hi! This discussion reminds me of a question I have had for many years since I worked in a final test department of a large chipmaker. The company decided they wanted to replace gold as the substrate (or was it the preform- I forget-it's been a long time) with silver. They put a lot of research into it and seemed to pull it off. The only problem I remember was that we had to centrifuge all those chips and a fairly high percentage of them went kabloey in the process. At the time we were told that despite the higher losses the cost savings made the change worthwhile. My question is did this catch on in the industry or is using silver instead of gold to hold the die in place now a rare thing?
strong@tc.fluke.COM (Norm Strong) (09/08/89)
In article <673@gorn.santa-cruz.ca.us> logo@gorn.santa-cruz.ca.us (David Kiviat) writes: } }Hi! This discussion reminds me of a question I have had for many years }since I worked in a final test department of a large chipmaker. The company }decided they wanted to replace gold as the substrate (or was it the preform- }I forget-it's been a long time) with silver. They put a lot of research into }it and seemed to pull it off. The only problem I remember was that we had }to centrifuge all those chips and a fairly high percentage of them went }kabloey in the process. At the time we were told that despite the higher }losses the cost savings made the change worthwhile. } }My question is did this catch on in the industry or is using silver instead of }gold to hold the die in place now a rare thing? The usual die attach these days is conductive epoxy. This works well unless you intend to run lots of substrate current. -- Norm (strong@tc.fluke.com)