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From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Tue, 4 Sep 2007 10:07:20 -0400
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text/plain (438 lines)
Richard,
1) "Tarnish" includes oxidation to an oxide, plus the formation of hydroxides and carbonates, etc., but in all cases the metal itself is oxidizing from a zero oxidation state to a positive state.
2. I don't know about silver, but tin, copper and especially aluminum form tenacious oxides that protect the underlying metals.  However, iron oxides are very flaky and continually fall off allowing oxidation to continue.
3. Don't know. People at CALCE and Battelle that carry our mixed flowing gas testing could tell us.
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, September 04, 2007 9:53 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] Plasma "oxidation"

Thanks, Inge! I found this very interesting.
It raises some questions in my mind. I am not a chemist, so I am posing these questions to you and the Forum.

1. How is silver tarnish different from oxidation? What is the difference in the terms tarnishing and oxidation?

2. I understand that as oxidation occurs, such as copper oxidizing with exposure to air and as iron rusts, some of the base metal is consumed, usually only to the point where the oxidized coating prevents further oxidation. Does silver tarnishing consume the basis metal?

3. Can silver be affected by chemicals in the air, to the point where its uses as described below are affected? I had heard that sulfides and bromides will react with silver. Does this reduce the reliability of silver-plated contacts? 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Friday, August 31, 2007 1:46 PM
To: [log in to unmask]
Subject: [TN] SV: [TN] Plasma "oxidation"

Copied from RF conn manufacturer:

----------------------------------------------------------------------------

Excerpt from PolyPhaser Technical Document PTD1010

Silver oxide is the only oxide (that we know of) that is conductive.  This is one reason why PolyPhaser's N-type coax connectors are all silver with gold center pins.  Copper oxide is not conductive and the proper application of joint compound will prevent oxidation.

End excerpt
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Copied from a Silver Institute, YOU SHOULD SAVE THIS !!:

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Electrical
 

Silver is the best electrical conductor of all metals and is hence used in many electrical applications, particularly in conductors, switches, contacts and fuses. Contacts, a junction between two conductors that can be separated and through which a current can flow, account for the largest proportion of electrical demand.

 

When Samuel F. B. Morse tapped out, "What hath God wrought," on May 24, 1844, the contact points on his telegraph were silver. The high amperage required to push the signal over iron wires from Baltimore to Washington, D.C., demanded a high capacity, non-corroding make/break contact; only silver could do the job.

 

Ordinary household wall switches, which normally carry high electric current for electrical appliances from irons to refrigerators, use silver. Silver is the metal of choice for switch contacts because it does not corrode, which would result in overheating, which could lead to fire. The U.S. electric switch market is on the order of $2.7 billion per year.

 

Today switch manufacturers play it safe by using high-performance silver for ordinary household switch and circuit breaker contacts. Less expensive metal contacts have high resistance which can overheat and cause a fire, says a major supplier of switch contacts. It is this consideration of liability that assures the public of continued preference for silver in switch contacts. With an increasing concern for quality, warranties become more important, and extended warranties mean that industry cannot chance even one failure in a million; that level of performance requires silver.

 

From the very beginning of electricity, silver has been the metal of choice for switch contacts because of its low contact resistance, high thermal conductivity, mechanical wear resistance, chemical stability (it does not corrode), low polymer formation (the build-up of an insulating carbon-polymer film over the contact as a consequence of arcing), and cost-effectiveness (it provides the longest functional life).

 

"Silver's tendency to tarnish does not affect its electrical performance,"
says a report of a 20-year exposure test of thousands of electrical contacts at 4,000 locations in different environments ranging from business offices to severe industrial locations such as petroleum refineries. The tests conducted by the Battelle-Columbus Laboratories, Columbus, OH, show that silver tarnish films are soft and readily wiped off with use; therefore in the field they perform well on tarnish because they are tough and offer high resistance. Films on other metals like copper, even when the corrosion is barely visible, cannot be tolerated.

 

Over 50 categories of electrical components incorporating silver as the contact material are listed by The National Electrical Manufacturers Association, Washington, D.C. These range from silver thick films that are used to make membrane switches which carry 5 volts or less for electronic systems, to large circuit breaker contacts required to interrupt or close the circuits of 75,000-volt power distribution lines.

 

The use of silver for motor control switches is universal. In the home, wall switches, timing devices, thermostats, sump pumps, and virtually all electrical appliances use silver contacts. A typical washing machine requires 16 silver contacts to control its electric motor, pump, and gear clutch. A fully-equipped automobile may have over 40 silver-tipped switches to start the engine, activate power steering, brakes, windows, mirrors, locks, and other electrical accessories.

 

Relays are another important market for silver contacts. Relays are used when low voltage switches (such as membrane switches) are used to activate considerably higher voltage or amperage switches. The increasing use of automated appliances has increased the number of silver contacts manufactured in the US.

 

Electric motor control switches use the largest amount of silver for each contact. The range of applications is enormous, covering: washing machines, dryers, automobile accessories, vacuum cleaners, electric drills, elevators, escalators, machine tools, and so on up to railway locomotives and marine diesel engines. Silver contacts start motors, set them to run forward or reverse, or at partial or full power. The silver contacts carry electrical power ranging from a fraction of an ampere, for small appliances, to 600-ampere loads required for oil-well drilling motors; their performance is required to be flawless.

 

Nearly half of the 20 million troy ounces of silver consumed in the USA yearly for contacts and conductors is used for motor controls.

 

The circuit breaker is the second major user of silver for contacts. For circuit breakers, silver combines the highest heat conductivity and the highest electrical conductivity of all metals, with almost unlimited performance. Circuit breakers are used to interrupt loads ranging from 10 amperes (small household lines) to 4000 amperes (high-tension power lines).

 

The circuit breaker is the most demanding use of silver contacts because the temperature of the arc generated by the interruption of high electrical power often exceeds the melting point of silver. As a consequence, silver is alloyed or infiltrated into other metals such as Tungsten to provide long-term performance.

 

Batteries | Bearings | Brazing and Soldering | Catalysts | Coins | Electrical | Electronics | Electroplating | Photography | Medical Applications | Jewelry and Silverware | Mirrors and Coatings | Solar Energy
| Water Purification

 

Electronics
 

In electronics, silver is also widely used. Uses include silk-screened circuit paths, membrane switches, electrically heated automobile windows, and conductive adhesives.

 

Every time a home owner turns on a microwave oven, dishwasher, clothes washer, or television set, the action activates a switch with silver contacts that completes the required electrical circuit.

 

The majority of the keyboards of desk-top and lap-top computers use silver membrane switches. These are found behind the buttons of control panels for cable television, telephones, microwave ovens, learning toys like touch and tell or speak and spell, and the keyboards of typewriters and computers. The low-current capacity of the membrane switch matches the low electrical current used for digital electronics. In an office environment, membrane switches are normally rated for a life of 20 million cycles. Typically, the membrane switch is made of a conductive ink of silver flakes in a polyester binder with carbon. This thick film is then silk-screened in an electrical circuit pattern onto each of two Mylar sheets. The two surface patterns of silver face each other close enough so that gentle touch by a finger will make the electrical contact. A latching transistor circuit is simultaneously activated to keep the circuit closed after the membrane is released.

 

Today's electrical appliances, such as microwave ovens, are controlled by membrane switch panels, where the contacts are silver. Membrane switch panels are found in automobiles and under the keys of personal computers.
Due to their reliability and wide use, the silver-contact membrane switch market in the U.S. is a multi-million dollar industry.

 

The use of silvered windshields in General Motor's all purpose vehicles reflects away some 70% of the solar energy that would otherwise enter the car, reducing the load on air conditioners in summer.

 

A universal safety feature of every automobile produced in America, and most throughout the world, is the silver-ceramic lines fired into the rear window. The heat generated by these conductive paths is sufficient to clear the rear window of frost and ice.

 

Printed circuit boards (PCBs) use silver in two ways: in solders for surface mounted components (see Brazing and Soldering) and for connecting paths of electronic circuitry.

 

Epoxy resin/silver formulations provide very low viscosity (important in filling holes connecting components) and higher silver content than is possible with other resins. Furthermore, silver-filled resins provide higher conductivity than copper systems, allowing smaller volume conductors and as well do not allow silver to migrate under any condition, which is not true of many other resin systems.

 

Du Pont's laboratory studies have shown silver-epoxy thick films to provide a conductive network of extended reliability, higher conductivity, improved solderability, and more rapid assembly over other metal formulations. And silver particulate fillers provide superior long-term performance in polymer thick films. Copper, for example, is often unstable and deteriorates with age.

 

The critical importance of printed circuitry boards in the electronics industry is shown by the value of monolithic integrated circuits. Printed circuit boards are essential to the electronics that control the operation of aircraft, automobile engines, electrical appliances, security systems, telecommunication networks, mobile telephones, television receivers, etc.

 

Giant magnetoresistance is a newly discovered magnetic property of multiple layered silver/nickel-iron alloy films, each about a millionth of an inch thick. These films are being exploited by computer hard drive manufacturers.
The films are potential candidates for the next generation of read-out heads for personal computer storage systems.

 

Not only do these new silver alloys exhibit extremely high changes in electrical resistance in response to infinitesimally small magnetic signals (hence the term giant magnetoresistance) but importantly the films maintain their physical dimensions unchanged despite the rapidly changing magnetic fields.

 

Elsewhere, the combination of giant magnetoresistance with zero changes in dimension in magnetostriction during recording head operations means that there is no unwanted shift in the optimal sensing function of the read head held over the spinning magnetic field of a personal computer's hard drive.
By avoiding dimensional changes during head operations, unwanted magnetic fields generated by the recording head are eliminated. This results in improved fidelity in the playback of data, music, and video recordings, and larger storage capacity. Also eliminated is the expansion/contraction of the head that would limit its useful life.

----------------------------------------------------------------------------

So, I'm convinced.

/Inge




-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För David D. Hillman
Skickat: den 31 augusti 2007 18:55
Till: [log in to unmask]
Ämne: Re: [TN] Plasma "oxidation"

Hi Eric! There must be a number mix-up somewhere in the ether! All of my references state that silver oxide is as conductive as parent silver. The funny thing is that none of my references list the resistance of either silver oxide, silver sulfide or silver chloride so I can't produce a conductivity or resistivity value to compare to the values you found (I have all of the values for the metals but not the surface species). 

Hey TechNet - anyone have a reference source for a value comparison?

Dave



Eric CHRISTISON <[log in to unmask]> Sent by: TechNet <[log in to unmask]>
08/31/2007 09:55 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Eric CHRISTISON <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] Plasma "oxidation"






Dave,

Can I just pick you up on your assertion that Silver oxide is as 
conductive as Silver. As I'm very bored this afternoon I did a quick web 
search and came across the following:

"First let's begin with some resistivities for the materials being 
discussed. Resistivity is the opposite of conductivity so the smaller 
the number, the less intrinsic resistance (greater conductivity) it 
possesses.

Copper: 1.7 X 10^-8 ohm-m
Silver: 1.6 X 10^-8 ohms-m
Gold: 2.4 X 10^-8 ohms-m
Silver Sulfide: 1.5 to 2.0 X 10^-3 ohm-m
Silver Oxide: 1 x 10^+9 ohms-m    "

So this guy thinks silver oxide is 17 orders of magnitude less 
conductive than silver. Did he just mix up a plus sign with a minus sign?

Regards,




Hernefjord Ingemar wrote:
> Furthermore, it seems as oxidation MUST occur before silver migrates,
> i.e. silver ions have to be created. And as such
> humidity>corrosion>oxidation is a perfect way. So, instead of
> inhibitation of silver migration, we have enhanced migration. Please,
> don't laugh, someone can begin to ask what kind of processing engineers
> we have..he-he
> /Inge 
>
> -----Original Message-----
> From: Hernefjord Ingemar 
> Sent: den 31 augusti 2007 14:55
> To: 'TechNet E-Mail Forum'; [log in to unmask]
> Subject: RE: [TN] Plasma "oxidation"
>
> Hi Dave!
> In fact, that is what I wanted to hear! Ditto Bev.
> If my decision is anchored in the rockwell&rim cliffs, that's enough.
> Thanks both. Alea acta est...
> /Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: den 31 augusti 2007 14:08
> To: [log in to unmask]
> Subject: Re: [TN] Plasma "oxidation"
>
> Hi Inge! Apparently, the lack of material science knowledge can go a
> long way. Just because a metal oxidizes, doesn't necessarily mean it
> can't play a role in electrochemical migration. And silver oxide is as
> conductive as silver metal (silver is one of those metals with some
> pretty wild properties). Sorry, I don't buy the "plasma oxidation"
> process validity.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Hernefjord Ingemar <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 08/31/2007 03:52 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to Hernefjord
> Ingemar <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] Plasma "oxidation"
>
>
>
>
>
>
> 
> Yup. Strange title. I've been asked about a strange process, which one
> was introduced without my knowledge, and I'm going to throw it out. But
> I thought of consulting TN before. This is the case:
>
> LTCC substrates are silver epoxy dispensed for chip mounting. In order
> to avoid risk for silver migration, a guy invented plasma "oxidation",
> i.e. he use a plasma cleaner, runs Argon with 6% Oxygen for a couple of
> minutes on mounted substrates. The silver epoxy dots become blackish
> because of oxidation, and oxidized epoxy is meant to minimize risk for
> silver migration. The oxide is of course just nanometer thick. The guy
> worked at a wafer manufacturing plant and had experience of cleaning
> procedures.
>
> I mean that this process is nonsense. If humidity gets in and condense
> on the substrate, and if the electric field is high enough, and if there
> are salts or contaminations, there is still enough silver to start
> migration. Oxidation of the silver dot's surface is meaningless. Anyone
> heard of such a strange process? Plasma operation on mounted LTCC
> substrates is foreign to me, I want it out.
>
> TrikeMan?
>
> Inge
>
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-- 
Eric Christison Msc
Mechanical Engineer
Home Personal, Communication Sector
Imaging Division

STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom

Tel:             +44 (0)131 336 6165
Fax:             + 44 (0)131 336 6001

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