Hi James! The folks at the DOE Ames Laboratory at Iowa State University in
Ames Iowa USA have been and are currently working on the impact of
specific elemental additions on the solidification behavior of Pbfree
solder alloys. Dr. Iver Anderson has been heavily involved in the
investigations. Some of the completed work has been published in the
Journal of Electronic Materials, TMS, and the ASM monthly publications.
Dave
James Vincent
<james.vincent@BO
OKHAM.COM> To
Sent by: Leadfree [log in to unmask]
<[log in to unmask] cc
>
Subject
Re: [LF] 96.5% Tin / 3.5% Silver
08/03/2005 07:57 vs. SAC305
AM
Please respond to
"(Leadfree
Electronics
Assembly Forum)"
<[log in to unmask]
>; Please respond
to
James Vincent
<james.vincent@BO
OKHAM.COM>
All
Always good to see IDEALS get a mention - although it's also rather
worrying to think that the project completed its experimental phase
nearly 6 years ago.
One consideration regarding alloy choice we had at that time was in
external visual appearance. Even the eutectic SAC387 alloy behaves as a
tin-rich alloy in solder joints, so the solidification is heavily
dominated by tin dendrites, in alignment with what Keith Sweatman said
in his post earlier in this strand. This means that the surface can
appear to be dull as light is scattered rather than reflected and also
that there can be surface 'cracking' caused by the withdrawal of the
inter-dendritic liquid that is the last to solidify. At the time this
was seen as an issue because of the impact it would have on visual
inspection standards (and on people's perception of Pb-free joints). We
noted that an immersion silver board finish improved (brightened) the
visual appearance, presumably because the additional 0.3% of so silver
this contributed to the joint was moving the composition nearer the
effective eutectic.
I understand that the silver content to yield 'eutectic' solidification
in a solder joint in Sn-Ag is over 5%, which illustrates the scale of
the effect.
So two questions arise for comment:
1) Is the visual appearance of joints a function of silver content?
And does this now matter even if it is?
2) Is anyone aware of work along the lines Keith suggests of modifying
the effective eutectic composition under solder joint solidification
conditions?
Regards to all
James
James H Vincent
Lead Engineer, Reliability Engineering
Bookham, Caswell
+44 (0)1327 356318
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]
Sent: 03 August 2005 10:30
To: [log in to unmask]
Subject: Re: [LF] 96.5% Tin / 3.5% Silver vs. SAC305
The report is useful and good news for the industry as a whole in that
it says that there is no practical difference in SMT assembly between
SAC305 which seems to be gaining the favourite spot in Japan and US due
mainly to lower Ag content, and the SAC387 which appears to be possibly
more favoured in UK and Europe due perhaps to original selection of the
IDEALS project. Its clear however with issues over various Pb-free
solder patents etc that the solder companies do have a vested interest
in having the industry use mostly one standard alloy and would obviously
prefer their customer to choose the one which suits their business
better.
I'm intrigued that this thread says that the NEMI report into Pb-F wave
soldering is not testing the SAC387 alloy only the SAC305 against the
patented SnCu+X variants. Does anyone know why this is? We decided to go
with SAC for all our processes and chose SAC387 for wave and selective
because it is somewhat closer to the SAC eutectic than SAC305, going
with the same selection basis that we use SnPb 63/37 instead of the
cheaper 60/40, and that the plastic range would be less affected by
copper pick-up than SAC305.
-----------------------------------------
This message (including any attachments) may contain confidential
information intended for a specific individual and purpose. If you are
not the intended recipient, delete this message. If you are not the
intended recipient, disclosing, copying, distributing, or taking any
action based on this message is strictly prohibited.
------------------------------------------------------------------------
-------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/(start) delivery of Leadree for vacation breaks
send: SET Leadfree NOMAIL/(MAIL)
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 847-615-7100
ext.2815
------------------------------------------------------------------------
-------
=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
-------------------------------------------------------------------------------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/(start) delivery of Leadree for vacation breaks send:
SET Leadfree NOMAIL/(MAIL)
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
847-615-7100 ext.2815
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------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/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
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 847-615-7100 ext.2815
-------------------------------------------------------------------------------
|
