I agree fully with the tight process window. The PWB industry has not had
to face true tight process windows in the past outside of specialty jobs.
Carey
-----Original Message-----
From: <Erik de Kluizenaar> <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, November 16, 1999 10:14 AM
Subject: Re: [LF] high temp Pb-free
Dear James, dear all,
Yes, with a very tight process you may be able to limit the reflow peak
temperature to, say, 245 degrees C.
However, most processes are not tight. There are two major aspects which
often widen up the reflow process: variations in thermal mass of components
and type of solderable finish (fusible - Sn and SnPb; non-fusible - Ni/Pd,
Ag, Ni/Au, AgPd, AgPt, etc.).
Thermal capacity of components varies strongly and solderable finishes can
be non-fusible (particularly in the lead-free future, when the fusible SnPb
finishes will no longer exist). Both aspects will raise the minimum reflow
peak temperature.
The maximum temperature difference between, thermally speaking, heavy and
light components is about 20 degrees with the modern hot gas convection
ovens.
Non-fusible finishes require a superheat of 20 degrees or more in order to
dissolve and disperse the finish into the solder.
If you sum up and look at the the consequences, this implies that 260
Celcius is a reasonable value for the reflow peak temperature of the
thermally light components and, in extreme cases, this value may even be
exceeded. Consequently, today's practice
of tuning the oven profile to the thermal design of the boards to be
soldered will be even more necessary with lead-free reflow soldering.
Best regards,
Erik
----------------------------------------------------------------------------
----
Erik E. de Kluizenaar
Philips CFT - Electronic Packaging & Joining (EP&J)
Building SAQ-p
p/o box 218
5600 MD Eindhoven - The Netherlands
Tel/Fax: (+31 40 27) 36679/36815
E:mail [log in to unmask]
http://pww.cft.philips.com/cfteurope/processtech/elpajo/index.htm
----------------------------------------------------------------------------
----
Leadfree <[log in to unmask]> on 99/11/16 05:33:49 PM
Please respond to james.h.vincent <[log in to unmask]> @ SMTP
To: Leadfree <[log in to unmask]> @ SMTP
cc:
Subject: Re: [LF] high temp Pb-free
Classification: Restricted
Dear All
I have seen several references recently to 260°C as being the reflow
temperature for lead-free solder.
This is just a reminder that the IDEALS project found that satisfactory
joints
(inspectable and reliable) were made using SnAg3.8Cu0.7 solder at a peak
reflow
temperature on the joint of 225°C.
Obviously the temperature experienced by individual components depends on
the
board and the process, but in my opinion the more likely temperature range
of
concern for packages is to a max of 240°C (and even 230°C in a very tight
process) - still plenty hot enough, but not 260°C.
Regards
James
+++++++++
From: James H Vincent
Marconi Materials Technology
Caswell, Towcester NN12 8EQ, UK
Tel: +44 1327 356321 (direct), G-Net: +942 6321
+44 1327 350581 (switchboard)
Fax: +44 1327 356775
E-mail: [log in to unmask]
WWW: http://www.gmmt.co.uk
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IPCWorks -October 25-28 featuring an International Summit on Lead-Free Electronic
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For technical support contact Gayatri Sardeshpande [log in to unmask] or 847-790-5365.
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