The only info with real specs I found on this topic is an old Motorola/ON App note, AN-1040D, it does discuss these anodized transistor insulators towards the end of the article. you can find it from ON semi here:
https://www.onsemi.com/pub/Collateral/AN1040-D.PDF
I would not be so keen to use these older anodized insulators in actual life, I see zero advantage compared to more
modern techniques, and I doubt the voltage breakdown is as good as even poor film, pads or mica.
all the best,
walter? (walter2 -at- sphere.bc.ca
sphere research corp.
