MFF2 is the machine-to-machine SIM form factor defined by ETSI TS 102 671. Physically it is a 6×5×0.9 mm DFN8 with eight PCB-soldered contacts, automotive grade (−40 to +105 °C typical, some variants to +125 °C) and 10+ years of expected life. If your device is a buried meter, a car, or a vibrating machine, this is the form factor.
Footprint and placement
- Follow the chip vendor's recommended footprint; not every MFF2 sticks to the ETSI reference. Some parts have extra pads for mechanical mounting.
- Keep the MFF2 at least 5 mm from the cellular modem. VCC_SIM, RST, CLK and I/O traces are sensitive to TX PA coupling; keep them short (ideally < 10 cm) but away from the antenna and PA path.
- Place decoupling caps on VCC_SIM as close to the pin as possible (100 nF + 1 µF). Without them some MFF2 parts lose authentication keys on power cycle.
- If manual rework is on the table, add two fiducials within 3 mm of the part; placement repeatability improves a lot.
Reflow profile
MFF2 follows the JEDEC J-STD-020 profile. Check the vendor datasheet:
- Typical peak: 245–260 °C for 20–40 s maximum.
- Max two reflow passes (on double-sided panels, put MFF2 on the second pass, or use adhesive on the first).
- Respect the MSL (Moisture Sensitivity Level) — usually MSL 3 — and bake out if the part has been exposed to ambient for more than 168 h.
More than 60% of soldered-SIM failures we see in postmortem trace back to a misadjusted reflow profile or damp parts, not to the SIM itself. Ask the contract manufacturer for the actual panel reflow curve and compare it to the recommended one.
ESD and protection
- VCC_SIM and I/O lines need low-capacitance TVS diodes (< 3 pF) if the MFF2 is accessible through an external connector — especially on fleet devices opened for programming.
- Some modems include protection already; read the modem hardware design guide before adding extras.
Production testing
- Add an IMSI self-test to the device bring-up: read IMSI via AT+CIMI and validate against the expected range before passing the PCB. Catches bad solder joints, wrong orientation or an inverted ORIENTATION pin.
- Measure VCC_SIM current during boot. A sustained anomalous peak points to a short or a corrupt applet.
- Do an actual network registration in the EOL test, not just an IMSI read. A SIM can read IMSI and still fail AKA challenge because of a bad Ki.
eSIM in MFF2
Almost everything above applies equally to eUICC in MFF2 (eSIM M2M). The difference is that you can order the card with your preferred bootstrap profile and keep the option to move to another carrier via RSP later. If you are designing fresh, do not spec a non-eUICC MFF2: the eUICC premium is marginal and will save you a redesign later.