[Ken Shirriff] likes to take chips apart and this time his target is an NFC chip used in Montreal transit system tickets. As you might expect, the tickets are tiny, cheap, and don’t have any batteries. So how does it work?
The chip itself is tiny at 570 µm × 485 µm. [Ken] compares it to a grain of salt. The ticket has a thin plastic core with a comparatively giant antenna onboard.
Working with such a tiny chip presented additional challenges. A few drops of boiling sulphuric acid freed the die. Then applications of phosphoric acid, Armour etch — nasty stuff, but better than hydroflouric acid — and hydrochloric acid took care of the rest.
With everything exposed, it was time to analyze the different parts. As you’d expect, the NFC tag draws power from the antenna and sends data from a EEPROM. There was some analog circuitry and also some digital gates used to control the output. But there isn’t room for much.
How are these so cheap? You can order an 8-inch wafer with 100,587 chips onboard. The price? Around $9,000 per wafer, so about nine cents per chip. Actually, you may be more because the wafer actually has 103,682 dice but a file included tells you which ones are bad. If you want to bargain shop, a 12-inch wafer is $19,000 but gives you 215,712 dice. What a steal!
Can’t get enough NFC? We understand. There are times you just want to make your own.
I was under the impression that Armor Etch contained precursors that produced hydroflouric acid – it isn’t something that I have ever used, bit I did look into it as a “safe” glass etchant.
9c really isn’t that cheap, how do the Chinese sell those 2c microcontrollers? Government subsidies?
It’s all about scale.
What scale?
– Total number of chips produced?
– Number of chips per wafer?
I agree that 9c is actually a lot for a one-time-use ticket. And that, apparently, is before embedding it, with an antenna, in a bit of paper.
I would think that paper tickets with a QR code can contain a similar amount of information (including a digital signature) and be cheaper to produce.
Dont get hung up on the “quoted” price above. NFC tags on eBay can be bought for ~$0.10/ea in small quantities, so the chips must be available cheaper
Interesting how it pairs with the other.
https://youtu.be/Kk_ehFreeYw
Great article. Good read. Lots of work to disassemble. The photo comparison with a grain of salt hits the mark!