hmmmm I googled around but couldn't find more info on this . . .
Strange, but here
is an OK text (PDF
) on the subject.
[...] so this PCB tech is circa 80's maybe?
Ah well, I couldn't be to sure of that, but I'd guess this particular board to be from somewhere between loosely 1995 to around 2002.
Back in time they were always made on ceramic plates (aluminum oxide) and I don't think anyone would use this technique on regular PCB for anything even remotely critical, as the PCB will flex way more than the (silk screened) terminations of the components will tolerate over time (I have even seen ceramic hybrids shake terminations off) - but the formulas are probably better in that respect nowadays though.
I have a handfull of virgin white ceramic plates intended for hybrids and while they're strong for their thickness, they're very brittle and will chip or even shatter if dropped from 1m to a hard floor
I'm not sure when exactly the hybrids were introduced, but it was before 1980 (I recall the OM-3xx range of HF amplifiers from the 70's as an example). The same techniques used on FR-4 (regular glass fibre PCB, as in the whatever-it-is-circuit) appeared somewhere in the 90's IIRC.
Sometime in the 80's I was chasing the idea of getting a circuit made as a hybrid, but it turned out that I had to get into some real high number of units before they'd even waste time on me.
Perhaps it looks different today and it IS nice to have a complete sub-circuit in a single component (that can be made to very tight tolerances), so with the right market, it may be feasible today, even in smaller series - not that I feel an immediate need though.