Victor, Reflow soldering has to meet several considerations that relate to:

1. Solder Paste composition, solder balling, removal of volatiles etc. 
2. Components sensitivity to moisture, popcorn affect, other damage.
3. PCB stresses affecting panel warping.
4. Formation of intermetallics ie dissolution of different metals on pads and
leads.

In IR reflow soldering, it is possible to rapid heat the assembly, but care
should be taken to avoid damaging components. The assemblies need to be pre
-dried prior to reflow. Overheating may also char the flux, thereby making it
difficult to remove during cleaning process.

The paste volatiles, when driven off too fast have a tendency to 'explode'
causing splatter of solder droplets. That is the reason that all 'In-line'
reflow systems have preheat zones to drive off the volatiles and allow the
chemical reaction necessary prior to solder reflow.

Slumping charateristics of the paste is also affected by rapid heating and
need to be evaluated. The components can move during relow causing defective
solder joints.

The chemical reaction of flux to clean the metal pad and lead to be joined is
very critical for a reliable solder joint. Depending upon the oxidation of
the surfaces to be joined, a certain time is required for this oxide removal
that may not occur in a very short cycle.

The mechanics of the solder joint formation is described in many standard
texts. The reflow of solder paste is especially interesting since the paste
is a collections of many small particles of solder that melt individually
first and then coalesce into a molten mass prior to the solder fillet
formation. The conditions which disturb this thermo mechanical equilibrium
will produce poor quality solder joints.  

Component damage is important especially for moisture sensitive types. Again
the pre-heat zone allows slow drying of the moisture without damaging the
component. 



I hope this information is useful to you in your research. Good luck.

Pratap Singh
RAMP Labs
512-255-6820