Cooling rates for solder reflow processes
Do a search on "vapour phase versus infra red reflow" and you should find loads of references,  this was a matter of some debate at the time that IR was being introduced to replace VPR as the dominant technology. Superior grain structure was held to be a key benefit and thus the search should reveal the info you want as it was rationally investigated. I think the definitive paper was by IVF Sweden or Helsinki University, maybe both.
 
The conclusions at the time were that yes you could get a difference in grain structure from differences in cooling rate from one method to the other (as claimed) but it didn't matter because as already posted they equalised out to the same in use with no difference in service life reliability.

Best regards

Mike Fenner
Applications Engineer, European Operations
Indium Corporation
 T: + 44 1908 580 400
M: + 44 7810 526 317
 F: + 44 1908 580 411
 E: [log in to unmask]
W: www.indium.com
Leadfree: http://Pb-Free.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ochenas, Tom
Sent: Friday, August 24, 2001 5:52 PM
To: [log in to unmask]
Subject: [TN] Cooling rates for solder reflow processes


Hi Technetters,

My first post (although I do work with the estimable Glenn Pelkey so perhaps my question will garner a response or two) to Technet:

There is debate within my group about the recommended cooling rate (to optimize grain structure and fatigue resistance of the solder joints) for eutectic solder (incidentally we are using a convection type reflow oven)... One camp holds that a fast cooling rate (~ 3C/sec) should be maintained to a temp. of liquidus MINUS 50C to optimize grain structure. The other camp contends that what happens below the liquidus temp. is of little consequence to the grain structure. If anyone can resolve this argument with a materials science based explanation I would be extremely grateful...

Best Regards,
Tom Ochenas
Maxtek Components Corporation
[log in to unmask]