Frank,
Thanks for the info. I do have several comments
First; trying to grow dendrites in a 85/85 environment is difficult at best. Dendrites
require liquid water. the free energy at 85 degrees C is to high. It will not allow a liquid
water film to form. you must be below 40 degrees C to ensure the formation of liquid water.
Second; you can not increase the thickness of immersion silver. It is a chemical process that
replaces one atom of copper with one atom of silver on the surface. Once all the copper has
been replaced the process stops. To get a thicker coating you must electroplate or use an
"electroless" process (if one exists!).
David A. Douthit
Manager
LoCan LLC
Frank Kimmey wrote:
> David,
> Thank you for asking this question. I presently am in the early
> stages of qualifying Immersion Silver and have caused a phenomenon that I
> think may be "Red Plague". After 24 hours in 85/85 environment (we were
> trying to grow dendrites) all PCBs have a reddish brown corrosion
> appearance. One sample was direct from vendor, one sample after 5 thermal
> excursions to reflow temps and another sample after wash with solvent,
> alcohol and 5 thermal excursions. I think this phenomenon is from the
> extremely thin layer created by immersion process causing the Cu/Ag
> intermetallic to actually be the surface of the finish. With this said I
> wonder can Immersion Silver thickness be increased (from 8 to 11 microinches
> [0.2 to 0.3 microns] to maybe 30+ microinch [8+ micron] range)to allow
> non-intermetallic silver to be on surface?
> Hey experts, how about some help?
>
> Thanks in Advance,
> FNK
>
> Frank N Kimmey, C.I.D.+
> Senior PCB Designer
> Powerwave Technologies
> PH. 916-941-3159
> Fax 916-941-3195
>
> -----Original Message-----
> From: David Douthit [mailto:[log in to unmask]]
> Sent: Monday, December 03, 2001 11:58 AM
> To: [log in to unmask]
> Subject: Re: [TN] Red plaque on Silver plated wire?
>
> Does this "Red Plague" effect immersion silver finishes???
>
> David A. Douthit
> Manager
> LoCan LLC
>
> David Fish wrote:
>
> > Expanding on Rainer's points look here:
> > http://www.corrosion-doctors.org/MatSelect/corrsilver.htm
> >
> > Dave Fish
> > ----- Original Message -----
> > From: "Blomberg, Rainer (FL51)" <[log in to unmask]>
> > To: <[log in to unmask]>
> > Sent: Monday, December 03, 2001 6:27 AM
> > Subject: Re: [TN] Red plaque on Silver plated wire?
> >
> > > I have never seen it, but have heard about it during investigation of
> > 'Green
> > > Plague'. The electronics industry term is "Red Plague" not Plaque, and
> is
> > > corrosion associated with the use of silver-plated copper wire. Red
> > Plague,
> > > named for it's color, (as opposed to Green Plague) is the cuprous oxide
> > > (possibly with some black cupric oxide)corrosion product that forms when
> a
> > > galvanic cell is formed between copper and silver. This was first
> studied
> > > in the sixties when it was established that 'red plague' originates at
> > > breaks in the silver plating of copper wire strands in the presence of
> > > moisture and oxygen. Although 'red plague' corrosion of silver plated
> > wire
> > > in service is extremely rare, for high-rel space applications, it is
> > > necessary to control all steps in the handling and processing of the
> wire.
> > > Control seems to be mainly by the wire manufacturer to provide a
> quality,
> > > uniform plated thickness (at least 2 um and preferably 4 um) of silver
> > > without imperfections such as scrapes or porosity. It is important that
> > > manufacturers ensure they do not damage the continuity of the silver
> > > plating. In addition, humidity controls can be implemented
> (dry-nitrogen
> > > backfill or desiccant) for dry packaging to keep wire reels or spools
> > below
> > > 50% RH.
> > >
> > > More information is available and can be found in this book:
> > > Metallurgical Assessment of Spacecraft Parts, Materials and Processes
> > > (Second Edition)
> > > Barrie D. Dunn
> > > Praxis Publishing Ltd.
> > > (See http://www.praxis-publishing.co.uk/space/metal.htm)
> > >
> > > > Rainer G. Blomberg
> > > > Honeywell -Space Systems Clearwater
> > > Staff Production Engineer
> > > > 13350 US Hwy 19 N MS 802-3
> > > > Clearwater, FL 33764-7290
> > > (727) 539-5534 Phone
> > > (727) 790-8738 Pager
> > > (727) 539-4469 Fax
> > > e-mail: [log in to unmask]
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Kasprzak, Bill (sys) USX [mailto:[log in to unmask]]
> > > Sent: Friday, November 30, 2001 3:08 PM
> > > To: [log in to unmask]
> > > Subject: [TN] Red plaque on Silver plated wire?
> > >
> > >
> > > Anybody out there ever hear about having to control red plaque on silver
> > > plated wire?
> > >
> > > This showed up on a spec for a job we're contemplating.
> > >
> > > Any and all ('cept wisecracks) responses appreciated. Thanks.
> > >
> > > Bill Kasprzak
> > > Moog Inc., Electronic Assembly Engineering
> > >
> > >
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