Eric,
Have you not seen this good source: the corrosion doctors? Lots to read about metal corrosion:
http://www.google.com/custom?q=lead+corrosion+rates&hl=sv&lr=&ie=UTF-8&oe=UTF-8&cof=AWFID:f726934c33ffd3b9%3BL:http://www.corrosion-doctors.org/CorrDocs/images/logoL.gif%3BT:Corrosion_Doctors_Web_site%3BAH:center%3BS:http://corrosion-doctors.org%3B&domains=corrosion-doctors.org&sitesearch=corrosion-doctors.org&start=20&sa=N
On your q: don't know if Pf-free is better or worse than Sn/Pb, assume we've not done so many tests yet to give a satifactory answer. As Tin is a superb coating for marine equipments, I think the high Sn %age in leadfree solders ought to be a positive factor. We have kilograms of reports telling about diff between the two categories, but they all have something in common: very little about corrosion.
Ingemar
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-----Original Message-----
From: Eric CHRISTISON [mailto:[log in to unmask]]
Sent: den 5 maj 2004 11:00
To: 'TechNet E-Mail Forum.'; Ingemar Hernefjord (KC/EMW)
Subject: RE: [TN] Corrosion resistance of Ni/Au plating
Ingemar/David,
Certainly one customer uses salt spray because the alternative corrosion
tests require much more specialised equipment. I presume that their
specification is based on the experience of having several hundred million
phones in use in the field and a pass gives them a degree of confidence that
nothing horrible will go wrong in the field. After all corrosion failures
are some of the most expensive types of failures you can have. You're
unlikely see anything happen for several months by which time a phone
manufacturer will have shipped several million units to their customers...
Thanks for the guidance - certainly gives pause for thought.
One other thing - no one has answered my last question which I asked out of
curiosity.
Are lead free solders generally more or less corrosion resistant that Sn/Pb?
Regards,
Eric Christison Msc
Mechanical Engineer
Consumer & Micro Group - Imaging Division
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF
UK
Tel: +44 (0) 131 336 6165
Fax: +44 (0) 131 336 6001
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: Wednesday, May 05, 2004 8:03 AM
To: [log in to unmask]
Subject: Re: [TN] Corrosion resistance of Ni/Au plating
From our point of view (mobile making too) salt spray test seems a very
harsh test to perform on such a board. You have gold, copper, tin, lead,
nickel, iron and lot more in that soup. Add temperature and chlorine and
you'll have a fermentation bucket, like making own wine. Only way to get an
inert board in your case would be to wax the whole thing. I'm little curious
(Sony-E reading this?), why salt spray on a commercial pocket thing? We have
salt spray chambers, but they are most oftenly used for comparison of e.g.
chromated parts from various suppliers. Ingemar
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you believe this message has been sent to you in error, please notify the
sender by replying to this transmission and delete the message without
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Eric CHRISTISON
Sent: den 4 maj 2004 18:45
To: [log in to unmask]
Subject: Re: [TN] Corrosion resistance of Ni/Au plating
It's a mobile phone application.
Salt mist is often used as a way of obtaining a measure of the general
corrosion resistance of an assembly. However I'm sure you could spend your
coffee break thinking up salty environments anywhere in the world that a
mobile phone could experience....
Eric Christison Msc
Mechanical Engineer
Consumer & Micro Group - Imaging Division
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF
UK
Tel: +44 (0) 131 336 6165
Fax: +44 (0) 131 336 6001
-----Original Message-----
From: David Douthit [mailto:[log in to unmask]]
Sent: Tuesday, May 04, 2004 5:56 PM
To: TechNet E-Mail Forum.; Eric CHRISTISON
Subject: Re: [TN] Corrosion resistance of Ni/Au plating
Eric,
Just exactly how does this "salt fog" test correspond to your possible end
use environments?
David A. Douthit
Manager
LoCan LLC
Eric CHRISTISON wrote:
>Ok, thanks for the info.
>
>No clear cut answers but I guess PCB finish doesn't make that much
>difference.
>
>Can anyone tell me if lead free solders perform better in corrosive
>environments?
>
>Thanks,
>
>Eric Christison Msc
>Mechanical Engineer
>Consumer & Micro Group - Imaging Division
>STMicroelectronics
>33 Pinkhill
>Edinburgh
>EH12 7BF
>UK
>
>Tel: +44 (0) 131 336 6165
>Fax: +44 (0) 131 336 6001
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
>Sent: Tuesday, May 04, 2004 3:48 PM
>To: [log in to unmask]
>Subject: Re: [TN] Corrosion resistance of Ni/Au plating
>
>
>Hi folks! Some additional data - we (e.g. the industry technoweinees)
>are much too quick to jump to the conclusion that we have a galvanic
>compatibility problem when using either immersion gold or immersion
>silver pwb finishes. Rockwell Collins published a paper at the 2003 IPC
>Fall meeting which demonstrated that the galvanic impact was secondary
>to a standard corrosion reaction in a salt fog test - i.e. our tin/lead
>test samples which were in a galvanically happy couple situation
>underwent healthy corrosion. The galvanic compatibility tables are very
>important and should not be ignored but they also can be misleading
>depending on the environment/configuration. Collins has a follow up
>immersion silver, immersion gold, immersion tin, and tin/lead galvanic
>corrosion study in progress and will report the results sometime in
>early 2005.
>
>Dave
>
>
>
> Vladimir Igoshev
> <[log in to unmask] To: [log in to unmask]
> > cc:
> Sent by: TechNet Subject: Re: [TN] Corrosion
>resistance of Ni/Au plating
> <[log in to unmask]>
>
>
> 05/04/2004 09:19
> AM
> Please respond to
> "TechNet E-Mail
> Forum."; Please
> respond to
> Vladimir Igoshev
>
>
>
>
>
>
>
>Rudy,
>
>It's not supposed to be any Au layer left after re-flow. It desolves in
>solder.
>
>Vladimir
>Sent from my Blackberry Wireless
>Vladimir Igoshev, 519-888-7465 ext.5283
>
>
>-----Original Message-----
>From: Rudy Sedlak <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Sent: Tue May 04 10:05:27 2004
>Subject: Re: [TN] Corrosion resistance of Ni/Au plating
>
>Central to this issue is the question of whether the Gold was
>completely covered by the Tin/Lead solder.
>
>I suspect it was not, and if it was not, this would set up a galvanic
>cell, which would accelerate the attack on the Tin Lead dramatically.
>
>Rudy Sedlak
>RD Chemical Company
>
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