one of the untold reasons is the endless price pressure on parts and the dropping of orders at zero notice.
buyer negotiates hard to get cut-throat pricing from manufacturer
buyer loses his customer , or decreased product sales , jiffy market situation.
buyer panics , cancels running order.
the problem is that, in the semiconductor world , by the time the cancellation goes in, you have oodles of material in the line. a wafer takes 4 to 5 weeks from entering the fab to coming out ! so the manufacturer needs ot decide : do i ditch 4 weeks of material , or do i keep fabbing it hoping it will sell. or, do i ditch and shove something else in the line ( knowing that too will take 4 weeks to come out and be potentially cancelled by then )
so the semiconductor makers are pissed off ! the usual struggle for 'slots' to produce anything is now flipped to the struggle what to push in the line that will sell 4 weeks from now !. operating cost of a waferfab is hundreds f millions of dollars ( whether doing something or sitting idle. those machines cannot sit idle. if they have nothing to do the chemistry drifts so you need to keep running the cleanroom , gasses , chemicals personnel . To give you an example : a plasma etcher needs to run continuously. if it stops for 4 hours it needs a reactor clean that shots down the machine for 4 hours. the reaction byproducts start flaking off the reactor wall unless you keep 'coating' with new exhaust. so they actually take blank wafers, spend money sputtering aluminum on them , and send them through the machine to be etched. and then sputter again and etch again. after 1500 wafers the machine needs a reactor clean. that is barely 30 hours of work for a fast etcher. so every 30 hours of operation you have 4 hours of down time. don't operate it and after four hours you hit the downtime. due to these short intervals you want to keep cycling production wafers and not dummies.
what to do ? shove products in the line that are guaranteed to sell. sod the crap that is yes/no/yes/no/maybe/maybe next week/we don't know/our market collapsed/we're not sure.
and thus you end up where we are now : all the 'uncertain' parts are on hold and the fabs are full with 'certain' parts ( high-flyers / large or prepaid contracts)
yes there is a semiconductor shortage, but the fabs are full and bursting at the seams to get stuff made !
There is another thing at play right now : the running process nodes need a specific type of silicon wafer. ( diameter, doping ) . The nodes that are shut down use a different type. So the bare wafer makers have actually shut down those lines. there simply isn't any bare silicon for those products! running the smelters costs a lot of money. the rising cost of energy in europe (quadrupled) and the energy restriction in china (china is capping what you can use in a given year) has caused several wafer makers to simply shut down !
https://www.emarketer.com/content/european-silicon-output-expected-shrink-electricity-prices-quadruplehttps://www.theregister.com/2022/01/22/eu_silicon_metals/https://www.bloomberg.com/news/articles/2021-10-01/silicon-s-300-surge-throws-another-price-shock-at-the-world- the demand for wafers is larger than ever and outstrips the production capacity of wafers
- the production capacity of bare wafers is hampered by energy prices/ availability
- the fabs need to cover their butt
add all this up and you get : if you can get wafers (shortage) you want to make something that will sell (guaranteed sales). and you end up where we are now.
there's more pain coming down the pipe...