Dear Erik, James and All,
Some excellent observations and comments.
If I may add on.....
There is no doubt that reflow profiling will become more important as we
transition into the world of lead free. So far I have seen a lot of
interest in the impact of reliability of components after reflowing at
relatively higher temperatures (regardless of how high we go). I have not
seen any discussions of the impact to some of the plastic connectors that
SMA's are typically using. Even though the critical temperature(upper
threshold) that I have heard about may be as low as 250C, even if
reliability of components is confirmed, the window of thermal processing may
be defined by the Liquidus temp (+ 10 to 20C to ensure joint integrity of
high and low mass components) and possibly the limit that any plastic
connector can withstand. Regardless of how the thermal process window will
be defined, we should all be concerned (or at least aware) with minimizing
the difference across the product due to the differences of thermal mass.
As far as a reflow oven is concerned this will mean at least achieving the
highest thermal transfer efficiency, and may mean creative profiling
techniques to include but not limited to increasing liquidus time or
reducing line speed.
At the risk of bad judgement, I would submit this shameless plug for anyone
interested in other reflow issues related to lead free soldering.
http://www.vitronics-soltec.com/_soltec_pagesw46.nsf/Web/02ded034fd00a874412
567690062a282?OpenDocument
Best Regards
Phil
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of <Erik de
Kluizenaar>
Sent: Tuesday, November 16, 1999 11:57 AM
To: [log in to unmask]
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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For technical support contact Gayatri Sardeshpande [log in to unmask] or
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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.leadfree.org ) for additional information.
For technical support contact Gayatri Sardeshpande [log in to unmask] or 847-790-5365.
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