Well, if that is the case, Apple. could start buying risk wafers of their customized N3 process and have enough good A17 SoCs for at least the iPhone Pro models - they've done this before (essentially funding the ramp to HVM). If yields improve enough - that process could be used in M3 SoCs. The geometric and electrostatic gains for that node are good enough.
I'm not singling you out in any way, your post is just the most recent one to mention the potential use of risk starts. When it comes to their official communications, TSMC tries very hard to reference certain milestones in a consistent manner, because they tend to have a material impact on financial results. A few of the commonly mentioned milestones include:
- design solution development
- customer design start
- customer product tape-out
- risk production
- volume production
Volume production in TSMC parlance is critical because it indicates the beginning of revenue recognition for that manufacturing process. TSMC does not recognize revenue for a node until after reaching volume production (i.e. they have fully qualified customer designs, good wafer outs that they can get paid for, and are beginning the volume ramp in earnest). This milestone is similar in some ways to PRQ for an Intel chip design.
Ultimately, Apple doesn't pay TSMC for wafer starts, they pay them for wafer outs. TSMC is obligated to report that revenue, which in turn pushes the node past the volume production milestone. Due to the way TSMC defines risk and volume production, it is impossible for TSMC to meet Apple's iPhone SoC requirements using risk starts alone. Furthermore, all of this is carefully coordinated and planned years in advance. That's why TSMC was able to tell investors three years ago that N3 would reach volume manufacturing in H2'22, but not to expect revenue from N3 until 2023 due to the long cycle times.
For their size and complexity, Apple's A-series chips are some of the highest volume SoCs manufactured. Even with the A16 only being in the iPhone 14 Pro and 14 Pro Max, Apple still required tens of millions of finished chips well in advance of the September launch. Apple is TSMC's largest customer, potentially representing around 25% of their total revenue. iPhone is Apple's largest product category, potentially representing around 50% of their total revenue. From a financial perspective, it's no exaggeration to say that the SoC for a given year's halo iPhone is the most important bit of silicon that TSMC produces.
edit: grammah