Silver is a better conductor than gold and in Integrated Circuit package where exposure to air should not be a concern Gold is used. Any particular advantage of using Gold over Silver?
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asked Apr 29, 2017 at 21:27
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1\$\begingroup\$ Conductivity is not the only factor in suitability for wirebonding. If you have institutional access to IEEE Xplore, this paper might be worth a read. \$\endgroup\$– Tom CarpenterCommented Apr 29, 2017 at 21:39
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4\$\begingroup\$ Who said air is the only thing that will react with silver? \$\endgroup\$– Phil FrostCommented Apr 29, 2017 at 21:44
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\$\begingroup\$ @PhilFrost Silver is as much a noble metal as Gold(maybe not as much but close enough). If anything we surely can fabricate packaging(materials) that can keep silver unaffected by elements. \$\endgroup\$– Flood GravemindCommented Apr 29, 2017 at 21:46
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1\$\begingroup\$ Well sure we can, we can fabricate packaging that keeps fluorine from reacting also. But is it worth the effort if it's worth the effort and cost if just making the wires with gold is cheaper? \$\endgroup\$– Phil FrostCommented Apr 29, 2017 at 21:50
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1\$\begingroup\$ Probably needs a discussion of "purple plague" here as well, as JonRB says - a reason not to use gold. \$\endgroup\$– pjc50Commented Apr 29, 2017 at 22:13
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3 Answers
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Apart from oxidisation and tarnishing, silver migration is also a serious concern, to the point that alloys are required to mitigate this.
However alloying silver also means that the advantageous increase in conductivity with respect to gold is somewhat lost. This might be the reason why silver has not taken over gold for wire bonds.
OTOH: nowadays, palladium-plated copper wire bonds look very promising, with their performance very close to gold wire bonds (even better: the copper-aluminium intermetallic products formation is just 1/100th of that of the gold-aluminium system - the co-called "purple plague"), and their cost below silver wire bonds.
Look at this report published by NASA about copper wire bonds. They might even evaluate them for space flight.
answered Apr 29, 2017 at 22:16
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\$\begingroup\$ They should have mentioned palladium coating in the conclusion to their paper, not just in summary and in the body text. \$\endgroup\$ Commented Apr 30, 2017 at 8:34
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1\$\begingroup\$ Agree. However the document linked is more of a state-of-the-art report than an academic/research paper. Maybe the authors meant copper wire bonds in a wide sense (i.e., including palladium-plated ones, which would actually be the only ones that could qualify for space flight), when they mentioned "copper" in their conclusions . \$\endgroup\$ Commented Apr 30, 2017 at 8:58
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\$\begingroup\$ Most probably you are right. It is not scientific paper, but commercial ad for technology. If it is the case, then BOK is wrong to have in its title; its conclusion is shorter than executive summary; it has purely commercial inclination. As scientific paper it should be returned for reworking :) \$\endgroup\$ Commented Apr 30, 2017 at 9:33
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Gold doesn't corrode. Silver will oxidize and tarnish, reducing conductivity and potentially breaking the wire. Gold doesn't react significantly with any common component of air or the plastics used in ICs, even at elevated temperatures, and so it's the material of choice for bond wires.
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2\$\begingroup\$ google "purple plague" \$\endgroup\$– user16222Commented Apr 29, 2017 at 22:12
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\$\begingroup\$ Okay, maybe "gold doesn't corrode" was a bit of a bold statement to make. But gold doesn't corrode as easily as silver. \$\endgroup\$– HearthCommented Apr 29, 2017 at 22:14
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\$\begingroup\$ I'm seeing a lot of notices of switching to copper bond wires. \$\endgroup\$ Commented Apr 29, 2017 at 22:56
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1\$\begingroup\$ @JonRB - Well, technically, Felthry is correct. Purple plague occurs with the formation of gold/aluminum intermetallics. If you can avoid contaminating the gold with aluminum, there's no problem. \$\endgroup\$ Commented Apr 29, 2017 at 23:33
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5\$\begingroup\$ @WhatRoughBeast Purple plague is gold/aluminum intermetallic. "intermetallic" refers to a chemical compound (as opposed to an alloy) made up of two or more metals. Besides, aluminum is the usual metal these bond wires are bonded to, if I remember right! \$\endgroup\$– HearthCommented Apr 29, 2017 at 23:35
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There is a large body of knowledge about bonding with gold wire. Much is known about process and reliability. Gold wire can be stored in air and remains bondable for many months after purchase. It is the most convenient type of wire for setting up a process the first time. Some gold wire types are extremely malleable lending themselves to being bent into almost impossible wire shapes. Some packages with advanced looping are sometimes only possible with gold wire.
