Explaining SIM form factors and technologies for IoT

Getting the right connectivity is a vital part of launching a successful IoT solution. Among the available IoT connectivity options, the one that stands out for being simple, scalable and secure is cellular IoT.

For a device to connect to a cellular network it needs a SIM or subscriber identification module. This stores the user’s international mobile subscriber identity (IMSI) number and its related key which provides authentication with the mobile network. There are several SIM card form factors, with the smallest offering substantial reductions in the size of IoT devices.

SIM Technology choices

Once you have decided cellular is the connectivity technology for your project you will then need to pick the right SIM technology. There are two main technology types, the UICC (Universal Integrated Circuit Card) and the Embedded Universal Integrated Circuit Card (eUICC), often referred to as eSIM. Picking either UICC or eUICC for your SIM is in fact one of the most important decisions you will make when it comes to selecting the right technologies for your deployment, however it can be a complicated topic.

SIM Card Form factors (2FF, 3FF, 4FF)

SIMs come in multiple form factors, or sizes, depending on the device type and requirements, and provide a robust and secure way to get your devices connected.

The traditional SIM card is very familiar to anyone who has owned a mobile phone and comes in four form factors - 1FF, 2FF, 3FF and 4FF, which all use the same ISO/IEC 7816 pin arrangement. Although the 1FF option is no longer in use, all other card sizes, from 2FF to 4FF, are still very much in use for cellular connectivity.

2FF is also known as Mini SIM, 3FF as Micro SIM and 4FF as Nano SIM. These SIMs are widely available, relatively easy to operate with, and are well supported by hardware components.

Chip SIM Form-Factor (MFF2)

A popular choice of SIM form factor for IoT applications is the MFF2, also known as Chip SIM. This works in the same way as a regular SIM card but can be soldered directly onto a circuit board. As well as saving board space, the Chip SIM is also ideal for devices located outdoors, as the SIM can be sealed and protected from corrosion.

It’s also a good choice for devices that are constantly moved and in danger of being dropped or knocked, as it is resistant to shock, or for devices that require a longer lifecycle. Because Chip SIMs are permanently installed in the device, they cannot be removed by unauthorized people, giving much greater security.

However, MFF2s have some disadvantages when installed as traditional UICCs, which is why we have recently seen the growth in popularity of eUICC enabled MFF2 SIMs.

And this is where the confusion emerges around the term eSIM. In consumer devices, MFF2s are always eUICC and therefore get called eSIMs.

Yet, eSIM is also used as a synonym for eUICC and any SIM form factor, not just MFF2, can be eUICC enabled, e.g., any SIM form factor can be an eSIM. For MFF2 SIMs, eUICC technology negates the disadvantages of the UICC MFF2.

Installing an MFF2 with UICC means that you can be locked into a single provider for the lifecycle of the device, as you are unable to swap the SIM. By contrast, with eUICC, you can remotely switch operator profiles without ever touching the device, a big benefit when your MFF2 SIM is soldered into your device and that device is deployed in the field.

eUICC - The future of IoT SIM cards

The eUICC eSIM is widely regarded as the future of IoT SIM technology. People often refer to a Chip SIM (MFF2) as an eSIM, but as we have mentioned, this is not always the case. An eSIM offers additional functionality and can come in all modern form factors, such as 2FF, 3FF, 4FF, and also MFF2.

Although it has the same form factors as standard SIMs, deploying as an embedded SIM is where eSIM really shines. The flexibility of being able to remotely provision profiles to an eUICC combined with the size savings and ruggedness provided by embedding the SIM unlocks huge potential for new and improved IoT applications.

eSIM is already widely adopted in newer consumer smart devices and is rapidly gaining popularity for IoT applications as the technology matures. With its many advantages, eSIM is certainly something to consider as you look to develop your next IoT solution or device. If you need any advice or help in picking the right combination of form factor and SIM technology for your project, the team at Pelion can help.