A
die photo of RCA CA3018 from Zeptobars shows two unconnected transistors. Anyone knows what’s the story behind them? The chip is a pair of transistors and a darlington pair on one die:
RCA CA3018 datasheet.
At first I was thinking about producing more transistors per chip to accomodate for manufacturing errors and use only good ones. But the metal layer offers no flexibility.
CA3018 die shot from another source shows exactly the same layout too.
A different metal layer could be used for another model, with the transistors themselves reused. But 11 out of 12 pins in the
TO-101 package are used, leaving no space for more connections. Was that for an alternative chip, but with a completely different configuration? CA3036 would require only 4 transistors (2 per each darlington pair).
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After writing that post I found CA3026, which contains two independent differential pairs, each consisting of three NPN transistor. The part has the same absolute maximum ratings, the same package, is designed to operate in the same frequency range and was produced in the same period. Could be a candidate for silicon reuse.