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Comment by bravo22 | Hacker News Reader

A lot of chips are made on mature fab lines because they don't need the performance of 5nm lines or can't justify the mask costs.

No one is investing in mature fab lines because they're not leading edge and they're being run to amortize the initial investmnet made into them years ago. Therefore not much additional capacity for mature lines.

So yes you can see 5nm chips being taped out but the 40-130nm chips are squeezed for capacity. Also this chip is likely not running in the same crazy volumes that ST microcontrollers. It is easier for TSMC to squeeze in a few dozen to a hundred wafers for SiFive on their line.

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> A lot of chips are made on mature fab lines because they don't need the performance of 5nm lines or can't justify the mask costs.

Alternatively: they're car-scale products dealing primarily with high electric currents (10s or 100s of milliamps) and/or higher voltages (5V instead of 1.3V).

Smaller chips use (and therefore output) less current than larger scale chips. But if your goal is to output 10mA to better drive an IGBT or other transistor anyway, then you really prefer 40nm to 130nm ANYWAY, because those larger sizes are just a lot better at moving those large currents around.

Bigger wires mean bigger currents.

High voltage MOSFETs and IGBTs are built on a completely different process. Size is definitely not an issue with them. It is about exotic doping to create the desired characteristics.

They're built using much larger feature sizes but on completely separate lines.

I'm not really in the industry. But I know that high-voltage MOSFETs / IGBTs need substantial amounts of current to turn on / off adequately. Under typical use, there's a dedicated chip called a "Gate Driver" that provides that current, between a microcontroller and the IGBT.

Its not that the IGBT / MOSFETs are built on these microcontrollers. Its that the Gate-Driver can be integrated into a microcontroller (simplifying the circuit design and reducing the number of parts you need to buy).

Under normal circumstances, a microcontroller can probably source/sink 1mA (too little to adequately turn on an IGBT). You amplify the 1mA with a gate-driver chip into 100mA, and then the amplified 100mA is used to turn on/off the IGBT.

By integrating a gate-driver into the microcontroller, you save a part.

Gate drivers are discrete parts and aren't integrated into microcontorllers because they require high voltages (12/24V vs 3.3V) amongst many other reasons.

They also have to be located close to the IGBT and the designers would want it as a separate part because it gives them enormous flexibility. You aren't saving much by adding a gate driver to a micro and I can't think of any micro that has it integrated. There are simple things like motor drivers, etc. that may have a gate driver integrated but that's not a micro and those are also built on large nodes -- much larger than nodes used for microcontrollers.

FWIW: I design advanced node (20-5nm) ASICs for a living, and have designed on older nodes before. I've also worked in power electronics.

Your point is valid, but this is almost certainly a shuttle run, so it won't be even one full wafer.

You're right. Definitely a "hot" wafer for the engineering samples.

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