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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