You will not find data sheets.
Names: sub modules, ceramic monolith sub modules, etc.
They are little printed circuits boards, or ceramic boards, with many surface mount parts soldered on. Resistors are often printed on (painted on) and not real resistors. These were (are) used on a 1 or 2 layer large board often with through hole parts. The sub modules mostly use surface mount and may have many layers. Often used at a time when many factories could not do surface mount and could not afford multilayer boards. But the new micros came only in surface mount. Often used in power applications where the power parts are through hole only and the brains are surface mount only. They are some times dipped in the black paint you see in the picture.
They are used as a cross over between ways of making electronics. Or a way of mixing different ways in the same product.