Why we need to print a PCB module on ceramic?
For an old telephone system. There were multiple lines,
some digital, some analogue, and in the output stage these
modules were standing on the main PCB and soldered to it.
There were a couple of other sub-PCBs on this thing,
but only those were of this ceramic type.
Why are those printed on ceramic?
This is a snapshot in the evolution of surface mount technology. In the middle of 1980s, people were desperate to increase circuit densities. Existing technology was chip and wire hybrid, where IC die were mounted and wire bonded to thick-film hybrid substrates.
My answer is that the superior thermal and mechanical characteristics of ceramic versus the other typical materials were the reasons for using it for this application.
This is an inexpensive method of construction if you are making tens of thousands of units.