This post is in response to a suggested topic on this blog. The following answer was provided by Brian J. Toleno, Ph.D., Director Technical Service at Henkel:
When profiling a flip-chip to an organic substrate you typically want the delta T across the component to be as low as possible in order to minimize stresses and warpage. Of course, like any good profile, making sure that the solder bumps and solder paste reach liquidus, stay above the liquidus temperature for the recommended time, and have a controlled cool down as possible are key. In addition, if the flip chip device is going to be underfilled, then it is important that when using a no-clean flux solder paste that the solder paste is fully activated in order to minimize any possible flux/underfill interactions. So making sure you measure the temperature at the flip-chip bump/solder paste/solder pad area is important. You also want to make sure you measure the temperature at the centre and the corners (making sure they track close together). While there typically is not as great of a chance of a large delta T, like there would be in a BGA or CSP device – when one does occur it can be more catastrophic.
