To use an analogy to describe the economics of node development.
You live on a nice street in a nice house that you currently
rent. There is a better house (it is bigger and more beautiful) on the same street, and it for sale, you want to move into said house and only that house (or the one you currently living in) would do, only a house on this exclusive street.
To move into the nice new house for sale you would have to buy it outright with cash (there is no mortgages in this analogy.) Over the long haul buying the better house across the street will save you money for over the long haul the cheaper variable expenses (no needing to pay rent) is cheaper than the fixed cost of buying the house outright.
If the house that you want to buy is the same price throughout all of time then it makes sense to buy it as soon as possible so you can start receiving the benefits of lower variable cost (no rent) as soon as possible. But what happens if the seller of the nice house will drop the price of the house 30% each year, due to house selling being a tough market and no one has yet bought this nice pretty house. If the house price drops 30% each year, it may be advantageous to wait and buy the house later. Sure you don’t get the benefit of lower variable cost (no rent) but you get the benefit of lower fixed cost instead (cheaper house). If there is no competition for this house it may make sense to wait.
If there is competition for buying this house, other potential buyers, then you may want to buy the house as fast as possible, for once the house is bought there is no turning back and you get the best house on the pretty street.
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Moving to a lower process node for foundries is much the same thing, there is always a better node (a better house on the same street), but you must be able to afford moving into the new node. As long as there is competition in the foundry space it makes sense to move into the better node as fast as possible, but if there is no or little competition in the foundry space then you let science develop a little further so it is cheaper to move into the new node. Business go bankrupt due to lack of cash reserves, either immediately (many business with the 2008 recession) or over the long term (AMD before selling their foundries to global foundries). There is no point in lighting that cash reserves on fire, if there is no return on investment for using that cash.
What will happen to the $/mm² when Intel moves to 450mm wafers?
The variable cost of transistors is cheaper with 450mm wafers. With small dies there is less of a benefit going to 450mm wafers, with big dies their is a huge benefit of going to 450mm wafers.
That said there is a large fixed cost on transitioning to 450mm wafers, intel is going to build 3 new foundries for 450mm, with each foundry costing a couple of billion dollars each for just the building and not the equipment inside the building. Intel is building new foundries instead of repurposing old foundries (which if possible would have been cheaper) for the 450mm requires new buildings for some of the equipment is not reusable.
This is a quick summary of the benefits of moving to 450mm instead of 300mm
Intel breaks ground on first 450mm fab