This was a Fire Retardant Plastic Box which was made for the SSR I/O Stackable Modules. DC Control for an AC Load. Usually it is to control another Big Three phase contactor;
Pneumatic or Steam Valve, Solenoids-Motors. When Mounted at the end of the PCB it offers over 2kV Isolation from the Digital Circuits. The Output 230V signals NO-NC, can control Light Loads like the Coil of a Big 230V Relay also called contactor.
It could be Mounted on a PCB by soldering or a Plugin Base. It is better to have Crimped connections or Terminals. A very good quality spring Loaded Socket may also work but it has to be rated for many operations. Things like Nickle Alloy Plated, Beryllium Copper were the Materials Jargon. A contact resistance in the Terminals, a mismatch of alloys, electrochemical reactions, Corrosive Fumes, Brine or High Humidity can build a Loose connection into a Dangerous Sparking Contact.
Not only the Functionality of the SSR will be affected in a Sparking Contact, but a Risk of a Fire Developing. When Inflammable Materials or Volatile Liquids are Present Nearby, the risk is even greater.
This is the safe enclosure for the Encapsulated Mini RTD PT100 Transmitter and was first made for the Electronic Relay with no moving parts, The Solid State Relays - SSR.
Potted, Encapsulated in epoxy, hermetically sealed. It has a Nickel Plated Aluminum Plate insert molded. For removing heat from BTA41600. The plastic is a fire retardant high temperature grade.
The epoxy is ciba araldite, fine alumina is filler. A transparent terminal cover for safety. The BTA41600 from Thomson-CSF Semiconductor (STMicro) was Excellent for this application. The Metal tab of the device was Insulated from the Silicon inside the device. This device along with MOC3041 (motorola) made a great pair for IO control. Both devices may have had isolation in excess of 2000 V DC, if i remember right.
In case you have other Thyristors that do need insulation use Mica for Robust Applications, Silpads for moderate heat, PolySulfone Isolators for low heat. Alumina Blocks for High Heat and Excellent Isolation. The best being thin Alumina Slabs.
You can see in the PCBs below the distance between the input and output tracks is more than 5mm. The opto is itself a few kilovolts of isolation and we should take care of the creepage distance on the PCB and surface.
This thing is Hermetically Sealed using a Alumina Powder filled Epoxy. This combination gives good thermal conductivity and Excellent Insulation.