Mark -
when I looked up the densitities of the respective materials, I found (in
g/cm3)
SnPb40 = 8.5
SnAg4Cu0.5 = 7.5
intermetallic compound Cu6Sn5 = 8.3
This tells me that the intermetallics will float on tin-lead, but sink in
lead-free solder. Therefore, when you skim the dross (mostly tin oxide) from
tin-lead, you will remove eventually present intermetallics along with the
oxide, but intermetallics formed in lead-free due to enrichment in copper,
will not necessarily be removed along with the tin oxide. Instead, the
intermetallics may be collecting somewhere in the solder bath, depending on
the melt flow, and may after a time build up and clog the pump channels.
Further, it explains that the copper content builds up more quickly in
lead-free solder pots, because copper is not regularly skimmed with the
dross.
Schön' Gruß
T. Ahrens
Thomas Ahrens, Memellandstr. 8, D-24598 Boostedt
Tel. 04393 97769, e-mail [log in to unmask]
----- Original Message -----
From: "Boyd, Mark" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, March 07, 2005 4:58 PM
Subject: [LF] Lead-Free Dross in Wave Solder systems
> During the IPC conference in 2004, a couple class instructors mentioned
that
> dross formation in some types of lead-free wave solder system could form
> dross that had a density greater than the molten solder - and would
> therefore sink to the bottom of the pot, making dross skimming
unmanageable.
>
> My solder reps assure me that this is not the case in SAC solder, but that
> there may be some intermetallics that would sink.
>
> Has anyone encountered this?
>
> Thanks,
> Mark
>
> M Boyd
> Pelco Engineering
> www.pelco.com
>
>
> --------------------------------------------------------------------------
-----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
-------------------------------------------------------------------------------
|
