Well I am surprised ass silver is a popular finish, it works well for
tin/lead and lead free but is dependent on the suppliers control of his
finish like any other. If one company does an evaluation and the results are
poor then they may reject it.
The key issue is the process and its control and the customer evaluating
finishes correctly with his supplier. I have had good quality silver finish
just the same as I have had poor quality from the UK and China. I have run
some silver boards in a no clean process with lead free that were 18month
old with no issue, not recommended. Recent trials with two selective
soldering suppliers with lead-free were also very good with 8 month old
boards.
In the case of tin I have not run any tin boards with long delay. I have
experienced problems with current production, again its the quality of the
process during PCB and the final washing stages.
Hope this helps
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA
Tel: 01245 351502
Fax: 01245 496123
Mobile: 07860 775858
Email: [log in to unmask]
Web: www.leadfreesoldering.com
Web: www.bobwillis.co.uk
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Reuven ROKAH
Sent: 16 November 2003 11:13
To: [log in to unmask]
Subject: [LF] Silver finish out Immersion Tin in???
Hi All,
During my visit in Europe PCB shop and in prudoctronica, I was informed
that Silver finish was rejected as an alternative by one of the big
international telecom companies and also there is a whiskers free process
in Immersion Tin process.
Does anyone have backup to the above information?
Best Regards
ROKAH Reuven
MA/NY DDave
<[log in to unmask] To: [log in to unmask]
M> cc:
Sent by: Subject: Re: [LF] Potential
Problems with Mold Compound
Leadfree
<[log in to unmask]
G>
21/09/2003 17:16
Please respond
to "(Leadfree
Electronics
Assembly
Forum)"; Please
respond to MA/NY
DDave
Hi Brian, Werner, TI-Doug, and IPC LF Listservers,
Well I was hoping that by today someone would give a link so that I would
know for the Maxim article first listed in this series if I had a leg to
stand on, or if Brian was correct that the Ag migration problem was inside
the package.
When I read the article I looked at some of the names involved with the
package in question and I initially felt it couldn't be an internal package
problem.
So anyway two articles and I am gone till later.
http://www.ul.com/pwb/
- A UL article kind of supporting me that my position may have value.
After I sent my other scenario I realized I forgot to add higher Ag
concentration in the solder, high voltage etc.
http://www.circuitree.com/ct/cda/articleinformation/coverstory/bnpcoverstory
item/0,2135,86472,00.html
- a Circuitree "Tin Man" article on Surface finishes that tends
to agree with Brian
<=== copied from the above Circuitree article
"One more high-profile issue with respect to electrical reliability:
electrochemical migration. Questions of electrochemical migration were
raised with the recent revival of silver as a PCB surface finish. By now,
many are familiar with the stories decades ago of dendrite formation on
thick, electrolytic silver used in high voltage switching apparatus.
Acutely aware of this experience, the industry has exhaustively tested the
new immersion silver finishes. Hundreds of studies conducted by the
chemical suppliers, fabricators, assemblers, OEMs, and independent labs
have tested the heck out of the new finishes. Telcordia's GR-78-CORE and
IPC's TM-6502.6.14.1 detail the procedures. Even with such a reference list
of migration studies, some engineers remain reluctant to specify silver.
The added burden of a UL test specific to high-voltage devices may have
slowed silver's penetration of the surface finish market. UL recently
provided some relief with documentation changes."
<=== copied from the above Circuitree article
YiEngr, MA/NY DDave
----------------------------------------------------------------------------
---Leadfee
Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop delivery of Leadree for vacation breaks send: SET
Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
----------------------------------------------------------------------------
---
----------------------------------------------------------------------------
---Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop delivery of Leadree for vacation breaks send: SET
Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
----------------------------------------------------------------------------
---
-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-------------------------------------------------------------------------------
|
