Hi All,
The problem with lead-free (SAC) wave soldering is that cooling the pot
does not work as it does with a SnPb process. SAC alloys are much less
dense than Sn/Pb. Because the density of the CuSn intermetallic is
greater than that of SAC, the copper sinks to the bottom of the pot
(instead of floating on the top) when the pot is cooled.
We suggest keeping the Cu level below 1.5%.
We wrote a paper on this issue that can be found at
http://www.aimsolder.com/technical_articles.cfm#21
Regards,
David Suraski
AIM
+1-401-463-5605 ext. 5210
www.aimsolder.com
-----Original Message-----
From: Colin McVean [mailto:[log in to unmask]]
Sent: Thursday, August 19, 2004 8:09 AM
To: [log in to unmask]
Subject: Re: [TN] Allowable copper contamination for SAC 305?
Either run two types of bar, or perform regular dragout of copper rich
dross, by running the pot cool for a period of time, and skimming the
top out. It's how we treat our HASL process.
Regards,
Colin McVean
Circuit Manufacture Ltd
Unit 9-12
Rowleys Green Lane
Longford
Coventry
CV6 6AG
Tel: 02476 666168
Fax: 02476 637089
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Chapman
Sent: 19 August 2004 12:57
To: [log in to unmask]
Subject: Re: [TN] Allowable copper contamination for SAC 305?
We just returned from a seminar by Cookson which said 1% would be
contamination point. Additional solder bars without copper would need to
be added to bring the balance in line. I imagine now we would need to
have SAC bars and SA bars to keep balance, either way close monitoring
of pot composition seems to be inevitable.
Dave C.
-----Original Message-----
From: Richard Kraszewski [mailto:[log in to unmask]]
Sent: Wednesday, August 18, 2004 4:08 PM
To: [log in to unmask]
Subject: [TN] Allowable copper contamination for SAC 305?
If one was to use a SAC305 alloy in a wave or selective soldering
application, how much copper contamination do you think would be
allowable before the melting range would become unacceptable. From what
I can see from the phase diagram, it appear one might be OK until you
reached ~ 0.8-0.9% copper?
Your thoughts would be appreciated.
Rich K / KEDS
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