If so, roughly what year electronic could be user by hobbyists?
Would it be better to abandon the existing transistors and etch the gaps or could the old be integrated?
Would it be a green process or would the process be too wasteful for any potential gains from re-using old electronics?
I did a course in photolithography, including a lab session where I literally made an unpackaged ASIC by hand, using technology that was current in the mid 90s. Etching silicon and doing photolithography is completely out of the reach for a hobbyist, even from scratch, even with 30 year old technology. Reusing a random chip and adding to it is simply impossible.
Essentially, you are looking at the following problems with simply creating a new chip:
- Need access to a large clean room
- Need a furnace that can heat up your silicon wafers to silly temperatures in order to do doping via sputtering.
- Need chemical handling equipment, including safety gear required for handling hydrofluoric acid.
- Need a photolithography device with your designs.
- Need to cut, test, and package chips after they are created.
And the additional problems with using an existing chip:
- Need to decapitate the existing chip and remove it from the package.
- Need to work with a single already sliced chip instead of a wafer.
- A completed chip will have metal vias that cover a large portion of the silicon, you would need to perform your chemical etching without harming these or any silicon that has been used.
- Generally, Asics don’t have wasted space, but simply larger components. There would be no footprint available for your design, even if your hobbyist tooling was smaller than the one used for the components, which is probably wouldn’t be.
Hypothetically, it might be possible, but there aren’t practical gains to be had from it. Easier to fabricate a new chip.
The optimal design is unlikely to be a straightforward modification of an older chip.
Even if it were, modification would add more variables, where we’re constrained by yields today.
And our processes today aren’t designed for it.
No, it would not be possible, the etching process would destroy extant features on any silicon. There are multiple steps to it and some will destroy the work of the steps that come after, so putting a finished chip through would remove the existing features.
Generally fabrication is done on a circular 300mm wafer, printing a grid of identical chips on it that are then cut out. It would be highly inefficient to do each chip one at a time, doing one small chip or 50 chips at once on one wafer takes the same amount of time and effort.
And the bare silicon left after the first few steps isn’t really worth much. You can go buy a blank high end 300mm wafer for like 81 bucks online. The material value of the silicon is nothing compared to the value of the machine time.
Modifying an existing chip is pretty much impossible. Chips contain structures on multiple layers, but you can only really work on the topmost layer directly. There also usually aren’t really unused gaps, components are placed as tightly packed as possible because if you can make the chip smaller then you can get more chips out of each wafer (because manufacturing costs depends mostly on the amount of wafers and amount of layers on each wafer, not on the amount of chips per wafer).
I guess in theory you could grind the old circuitry off the chip to then build up new circuits on the old chip, but that’d be much more challenging than starting from a new wafer and also not really offer up any benefits.
