Andy - We find the same thing with the lead-free alloys that are high
tin-based.  As long as the reflow temperature is above the melting point of
pure tin 232°C, soldering takes place acceptably. It figures, the trend
seems to be to go to tin-copper, tin-silver, tin-silver-copper, and all of
these are really intermetallic floating around in the tin matrix.

Some people have problems even with reflow at 235°C because of component
concerns.  With wave soldering, components on the board topside don't get
hot enough to worry about.  THEN, the potential reliability concern pops up
if people see cracked components or lifted circuit board pads.

-----Original Message-----
From: Andy Mackie [mailto:[log in to unmask]]
Sent: Thursday, July 29, 1999 9:58 AM
To: [log in to unmask]
Subject: [LF] Cat among pigeons...


I'm amazed that there is still this concern about the requirement for
high-temperature stability of components. One of the conclusions from the
IDEALS
consortium was that it was possible to do reflow with a spike minimum of
225-230°C. Even with a wave set to 260°C, the top side temperature shouldn't
reach over 230°C, so what am I missing here?

We've just done some reflow work with 95.5Sn/Cu0.5/Ag4 that shows that you
get
the same wetting/spreading area on copper if you have a 230°C spike with 30
secs
over 217°C or a 250°C spike with 60 secs over the m.p. The extra buys you
nothing.

I must buy a new beef-locator, 'cos I can't find any...

Andy

################################################################
Leadfree E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask]
with following text in the body:
To subscribe:   SUBSCRIBE Leadfree <your full name>
To unsubscribe:   SIGNOFF Leadfree
################################################################
IPCWorks -October 25-28 featuring an International Summit on Lead-Free
Electronic
Assemblies.
Please visit IPC's Center for Lead-Free Electronics Assembly
(http://www.ipc.org/html/leadfree.htm ) for additional information.
For technical support contact Gayatri Sardeshpande [log in to unmask] or
847-790-5365.
################################################################

################################################################
Leadfree E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask]
with following text in the body:
To subscribe:   SUBSCRIBE Leadfree <your full name>
To unsubscribe:   SIGNOFF Leadfree
################################################################
IPCWorks -October 25-28 featuring an International Summit on Lead-Free Electronic
Assemblies.
Please visit IPC's Center for Lead-Free Electronics Assembly
(http://www.ipc.org/html/leadfree.htm ) for additional information.
For technical support contact Gayatri Sardeshpande [log in to unmask] or 847-790-5365.
################################################################