Since my last YubiKey review, Yubico addressed both highligted case design shortfalls: plastic material choice and potential structural weakness around the key ring hole. Yubikey now uses a chemical-resistant thermoplastic that is immune to most household chemicals. I suspect it is nylon-based, but I am no chemist, so don't take my word for it.
The key ring hole has also improved. Antenna conductors still run between the edge of the case and the hole, but Yubico increased PCB width there plus the hole is now generously plated. The hole should be able to withstand prolonged abuse from a key ring. A nice idea was to not cover the hole with plastic, leaving the plating visible. This both improves aesthetics of the case and protects surrounding plastic from direct key ring grinding.
Yubikey 5 also uses much larger, rectangular holes in the board to ensure strong bond between the sides of the case. This improves tamper-resistance and makes it very difficult, if not impossible to use easy access method where you grind the edges of the case off and the case falls apart.
Yubico switched from using two NXP chips (one as a USB controller/primary MCU and one as an authentication controller) to using just a single chip from Infineon. It also allowed Yubico to reduce the number of required discrete SMD components. The Infineon chip is a 16-bit dual-CPU microcontroller with 512Kb of flash and 16Kb of RAM. The chips' CPUs perform cross-verification of each other's calculations, thus protecting the integtity of data, which makes it difficult to tamper with the chip. For example, manipulating power supply to reliably inject logic flaws would theoretically be prevented. Encompassing all functionality in one IC also improves tamper-resistance (no inter-chip communications to tamper with). It should also make the firmware code more manageable and more relable as you only need one vendor-specific toolset/SDK and you don't need to worry about potential communication/timing issues between components.
We suspect that Yubico was able to reduce manufacturing costs by at least 30%. We estimated older keys' manufacturing costs as $6-$8 USD.
Yubikey 5 Neo probably costs around $5-$6 USD to mass-produce. This includes:
Here is Yubikey 5 Neo in all its nakedness. Before you ask, the LED is not invisible, it was lost to the solvent I used to remove the case. To my surprise, the key is still fully operational.