Sorry, I worked for that company around 2001-2003. But I can describe it to you.
Our design was two stacked boards (FR4 and IMS), one on top of each other. The lower one was the IMS which was securely attached to a large heat sink.
The top one was the FR4 where all of the control circuit was installed.
Connection between the two was for the small signals (gate drive, thermistor sense, etc) via an off-the-shelf header. But the connection for the power signals was made with these custom copper posts.
As I mentioned earlier these were custom made. A shop purchased solid annealed copper wire, cut them into lengths. Then with a small pneumatic press and a die, one side was stamped flat and that was the side which would sit and solder on the IMS board.
For final assembly, the two boards were connected together and the post's round side was then hand-soldered to the FR3 board with a large soldering iron.
Four corner standoffs provided additional mechanical rigidity to the assembly.