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.