Re: Sort of inbetween
Even for a new design, a less dense process might not make financial sense. Microcontrollers often use older processes because pads and analogue circuits do not scale as well as logic or memory and because minimum cost rather than price-performance is a common design goal (high voltage support and on-chip support for persistent memory are also factors). Production volume also has an impact since newer processes have larger non-recurring expenses (e.g., more expensive mask sets).
Older process equipment can be fully depreciated, so selling capacity near incremental cost makes sense (but there is also pressure to upgrade a fab if all the new equipment fits space, power, etc. requirements, which is not a given as new processes tend to add steps). However, if one gets 90% more chips per wafer on 20nm than 28nm — very good design scaling — and gain some power and/or performance that adds value (or perhaps improve cost/power/performance by integration), that one major node older process will have to be a lot less expensive unless NRE is a major factor.