Hi John,
Here is what two Consortium members said about immersion Ag (I am
posting this to the larger LF group, figuring that others may be
interested in their comments):
---------------------------------
Immersion silver is very similar to immersion tin - it has additives in it
that result in an effectively tarnish-free surface that can be soldered to
and appears not to have the electromigration problems associated with silver
in electronics. It performed about as well as immersion tin in the last
paper.
Silver and tin and silver and copper do behave differently than the other
finishes (of course) with different intermetallics and behavior but it is
also a viable alternative.
Cheers,
Dick Anderson, PhD
M/A-COM Tycoelectronics
Lowell, MA
---------------------------------
I know from Schneider experiences it has the following negatives: few
vendors offer it, it has shelf life issues as a board finish, and it
should not be used in an industrial environment which has sulfur or
chlorides in use.
Mark
_______________________________
Schneider Electric
Products & Technology Division
American Global Products
One High St.
North Andover, Ma. 01845
Tel: 978-975-9172
eFax: 978-725-3038
---------------------------------
Regards,
Todd MacFadden
TURI - Toxics Use Reduction Institute
UMass Lowell
John Burke wrote:
>What happened to immersion Ag??
>
>John
>
>-----Original Message-----
>From: Leadfree [mailto:[log in to unmask]]On Behalf Of Todd MacFadden
>Sent: Wednesday, July 21, 2004 2:05 PM
>To: [log in to unmask]
>Subject: Re: [LF] LeadFree and Land Patterns
>
>
>Hi Doug,
>
>The Massachusetts Lead Free Consortium has tested five LF surface
>finishes: solder mask over bare copper with hot air solder leveling
>(SMOBC/HASL) (pure tin), matte tin, immersion silver (Ag), organic
>solder preservative (OSP), and electroless nickel immersion gold (ENIG).
>As you've probably guessed, there is no drop in substitute, and thus the
>choice involves weighing various trade-offs. A short summary of tradeoffs:
>
>- We found significantly more visual defects with lead free SMOBC/HASL
>than the other finishes we tested.
>- ENIG gives good coplanarity and solderability, but is more costly, can
>cause black pad and is not appropriate for press fit.
>- Immersion Sn is cost-effective, has relatively good solderability, but
>opens up the whiskering issue and can grow intermetallics with Cu during
>storage.
>- OSP is cost effective, but is susceptible to various processing
>defects and constraints.
>
>Weighing these and other trade-offs, and based on our test results, our
>belief is that ENIG and immersion Sn will be the most widely adopted LF
>board finishes.
>
>You can find some of our results in papers and presentations at:
>http://www.turi.org/content/content/view/full/460
>
>Regards,
>Todd
>
>
>
>Doug Barnhard wrote:
>
>
>
>>Could I get some direction on some of the board surface finishes the
>>designers have gone to in order to get away from the HASL process which
>>contains lead. Also any explanation of problems or issues with whatever
>>you are using would be helpful.
>>
>>
>>
>>Thanks
>>
>>Doug
>>
>>
>>
>>
>
>*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_
>Todd MacFadden
>Project Manager
>Toxics Use Reduction Institute
>University of Massachusetts Lowell
>One University Ave
>Lowell, MA 01854
>
>978.934.3391
>978.934.3050 (fax)
>
>[log in to unmask]
>www.turi.org
>
>Because not everyone can live upstream.
>,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_,.-:*'
>
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--
*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_
Todd MacFadden
Project Manager
Toxics Use Reduction Institute
University of Massachusetts Lowell
One University Ave
Lowell, MA 01854
978.934.3391
978.934.3050 (fax)
[log in to unmask]
www.turi.org
Because not everyone can live upstream.
,.-:*'``'*:-.,_,.-:*'``'*:-.,_,.-:*'``'*:*:-.,_,.-:*'*:-.,_,.-:*'
-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
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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
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