Managing ΔT during reflow is an important part of a well-controlled soldering process. We've learned about reflow process control with Durafuse® LT, and how it can be a little bit different from a typical solder paste before. In some assemblies, it can help provide a wider process window during reflow that will still deliver reliable solder joints.
On large boards with a mix of small and very large components, not everything heats up evenly. Many components and boards aren't supposed to be exposed to temperatures above 255 or 260℃. Typically this isn't an issue since a standard SAC305 profile will have a maximum temperature of only about 245℃. However, if the board is VERY uneven it is important to make sure the coldest solder joint on the board has a reliable solder joint, while the hottest point on the board doesn't damage the component.
One of the great things we've learned about Durafuse® LT is how to control the lowest temperature point on the board during reflow for reliability - and everything above that temperature is fine! We also know that at peak temperatures at or above 210℃, the reflow profile shape for Durafuse® LT looks very similar to a SAC305 or SnPb type profile. In fact, Durafuse® LT is 100% compatible with a standard SAC305 profile.
What does that mean for controlling ΔT? It means if a board has 30℃ of ΔT (this is HUGE!) you can still have a reliable Durafuse® LT solder joint at every place on the board - whether it was at 215℃ or 250℃.