Hypothetical question, but somewhat relative to a project I'm working on:
Suppose you have a design where a trace needs to carry 25 amps DC at 24 volts. This trace interfaces two components. One, a high current MOSFET and the other a surface mount fuse. The connection between the two is very short, on the order of 0.25" or so and will be made using 2oz cu. The trace width is smaller then the tab of the FET, but much larger then the pad of the surface mount fuse.
I have done many circuits like this in the past and have made the connetcion to both components a solid, flooded copper connection, usually tapered down to the size of the smaller pad. There have been no issues with soldering either part.
I have been discussing a new design where it has been suggested to use a thermal relief connection to the fuse to aid in soldering. I don't particulary like this approach due to the amount of current involved having to go through the smaller traces of the thermal relief. I suppose it may be possible to size the width of the relief traces such that the sum of their widths comes close to the required trace width, but I don't know if the pad is big enough to support the big relief trace.
I'd be curious to hear others philosophies on using thermal reliefs in high current situations.