The chip shortage that started in 2021 caught most embedded teams off guard. We had clients whose production lines stopped because a 40-cent microcontroller went from eight weeks lead time to 52 weeks, at 10× the price. The lesson wasn't "order more safety stock" — it was "design in parts that can be replaced."
The second-source question
Before you commit to an MCU, ask: if this part disappears tomorrow, what drops in?
For some families the answer is easy. The STM32F4 and STM32L4 families have binary-compatible siblings from multiple vendors. You can often swap in a GD32 or an APM32 with a recompile and a resistor change — no board re-spin required.
For others — particularly some Arm Cortex-M0+ and proprietary-ISA parts — there is no second source. If you pick one of these, you own that supply chain risk.
Pin-compatible families
The strongest protection is a pin-compatible upgrade path within a single vendor's lineup. STMicroelectronics does this well: the STM32G0, G4 and L4 families share enough pinout overlap that you can often step up to a part with more flash or a faster core with only a footprint change and no schematic revision.
On Aurora we originally used an STM32L433. When a 240 kB binary outgrew its 256 kB flash, we swapped to an STM32L476 — same LQFP48 package, same pinout, rebuilt the firmware the same afternoon.
The cost argument
The "cheapest part" calculation usually omits the cost of a board re-spin when the part is discontinued. A board re-spin for a four-layer PCB runs to about €8k in engineering time and €3k in prototype tooling. If a €0.30 saving per unit drives you into a dead-end part and you ship 10,000 units, you're trading €3k for €8k+ of risk.
Our default position: pick a part from a family with an active roadmap, at least one second source, and a vendor with a track record of long-term supply commitments (10+ years is a meaningful signal). Pay the extra €0.50 per unit. It is almost always the right call.
A practical checklist
Before committing to an MCU:
- Is there a pin-compatible upgrade path in the same family with 2× the flash?
- Does the vendor publish a product lifetime commitment (longevity program)?
- Is there at least one second-source or pin-compatible alternative from another vendor?
- Is the part available from two or more distributors today with > 10k units in stock?
If you can't answer yes to all four, the part needs a stronger justification.