Hi Moss,
there have been nice investigations on wettability performed by my collegues
group Mathias Nowottnick at IZM Berlin. Systematic parameter choice was
temperatures of 5%, 10% and 15% (in degrees Kelvin) above melting for Sn-Bi,
Sn-Pb-Ag, Sn-Ag-Cu, Sn-Ag and Sn-Cu. the results show that in order to
achieve wetting within ca. 1 s (necessary for wave soldering), the
temperature must be somewhat between 5 and 10%. For reference purposes, I
have included the corresponding wetting diagram in a seminar presentation
(in german language) on page 20 of the following document
http://www.weichloeten.de/themenschwerpunkte/online-quellen/14bleifrei-isit-
ta-2proseite.pdf.
This correlates well with the (absolute)minimum of 245°C for SAC and 255°C
for Sn-Cu or Sn-Cu-Ni we found during our trials on commercial double wave
soldering systems. For reflow, as there is longer time for wetting, the
temperatures may be somewhat lower: After all, with vapour phase, we can
solder SAC at 230°C. I will translate this presentation into english, as it
will be given in Madrid (June 7), Lyon (June 23) and Paris (June 25) in the
Rutronik seminar series on leadfree soldering (see www.rutronik.com). Lots
of discussions we had in the past 7 sessions all over Germany and
Switzerland, where astonishingly few electronics manufacturers seem to be
aware that time is closing in at super sound speed with regard to the RoHS
deadline. Tell me if there is interest in the presentation, then I can
publish a link at the end of June for the english language version.
Best regards
Thomas Ahrens, Boostedt
e-mail [log in to unmask]
----- Original Message -----
From: "EMTC Ireland" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, May 25, 2004 7:42 PM
Subject: [LF] Lead Free Wave Solder Alloy Temperatures
Hi all
In reference to Howard H. Manko's book "Solders and Soldering" I'm just
interested in learning from the metallugist fraternity out there his
description of "Tin Pest"
"When cooled to low temperatures, pure tin transforms from a white metallic
material into a grey amorphous powder. In the past this transformation was
called "tin pest", because tin articles for no explainable reason crumbled
into dust." (13.2degC)
The paragraph continues to describe detrimental properties of tin - but can
anyone comment for Sn0.7Cu or any high tin containing alloy if this is of
concern.
Also has anyone Phase Diagrams for the SnCu and SAC alloys that show the
"recommended alloy temperature during wetting" as presented in Manko's book
(Fig 3.8) as opposed to the rule of thumb approx 40degC above liquidus?
All information/references appreciated,
Thanks in advance
Moss
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