What Is an eSIM? The Pros, Cons, and Seeming Inevitability of Embedded SIM ICs

STMicroelectronics announced in June that it is the world's first eSIM manufacturer accredited by the GSMA to personalize eSIMs for mobile and connected IoT devices. What is an eSIM? How could it benefit designers?

Most people these days have some form of mobile device that can be used to make phone calls, send text messages, and even access the internet. In order for any of these devices to access cell networks, they require credentials and information that include authentication keys, identification numbers, country codes, and more.

All of these details are provided when a user signs up to a mobile service company in the form of a SIM (subscriber identity module) card. These cards contain an integrated circuit and are inserted into a mobile device to allow them to access a network to perform tasks such as make phone calls and receive internet access.

 

SIM cards.

 

SIM vs UICC?

Another term you may have heard is UICC or universal integrated circuit card. Before we move on, let's quickly discuss the difference between the two.

UICCs are cards that contain the chips that have largely replaced the use of magnetic strips in items like credit cards. UICCs are sometimes regarded as the successor to SIM cards because they can serve the same purpose as a SIM card, but also do more than simply identify subscribers due to their larger non-volatile memory.

The term UICC is sometimes used synonymously with SIM when talking about mobile devices because a UICC is capable of running a SIM application, providing the hardware on which SIM software operates. This effectively makes a UICC a "SIM card" even if it is capable of more.

Because "SIM card" is the more common term, we'll refer to these devices as "SIM cards" despite that they're more accurately "UICCs that run SIM applications".

 

SIM Card Limitations

SIM cards have been instrumental in allowing our current mobile infrastructure to grow. They are, however, not without their issues. Over the years, manufacturers have reduced the size of SIM cards several times, evolving from SIM to micro SIM to nano SIM. But these size reductions have only reduced the outer plastic packaging that held the contacts and chip. The chip and contacts, themselves, have not reduced in size. In essence, it seems that SIM cards are as small as they can get. In an industry constantly thirsting for smaller device footprints, that's an unwelcome prospect.

Manufacturers could look into redesigning SIM packages to get even smaller cards—but doing so could cause problems for users. Very small SIM cards would allow for smaller devices but, at the same time, they would be very hard for users to install and could be very easily lost. SIM cards are also transferable to different devices which can be advantageous if a mobile device breaks but it can also be problematic as theft of the card can allow an unauthorized user to use the card without any authentication.

So, if they're not going to make SIM cards and their accompanying slots smaller, what are manufacturers doing?

What is an eSIM?

An eSIM is an embedded integrated circuit surface-mounted onto the circuit board of a device. Like the insertable cards that precede them, eSIMs (or eUICCs, if you like) hold all the credentials needed to connect to a mobile network.

eSIM devices have many advantages over traditional SIM cards as they are available in much smaller form factors, provide more security, and provide greater flexibility. They also remove the need for a SIM card slot, allowing designers to more easily protect circuitry inside a device, especially for the purposes of waterproofing.

eSIM devices are being targeted at Equipment OEMs, mobile network operators, and SIM operating system vendors for a range of applications including IoT, mobile devices, and even smart watches. Major device manufacturers, including Google and Apple, have been integrating eSIM technology into their devices over the last year. In October of last year, Google released its Pixel 2 smartphone, touting its eSIM technology as a way to utilize Google's own proprietary cell service, Project Fi. The eSIM is also already in the Apple Watch Series 3, which differentiated itself from its Apple Watch brethren by offering cellular connectivity. (Apple, being Apple, refers to the technology as "Apple SIM".)

Even as these devices begin integrating eSIMs, however, the switch away from physical SIM cards is complicated by possible hurdles with cellular carriers. According to the Project Fi website, "Project Fi is currently piloting eSIM"—so even the most recent devices equipped with an eSIM still have a slot for a physical SIM, which allows the devices to function with other carriers. Apple offers the ability to work with partner carriers using the eSIM, itself, giving the unprecedented ability to change carriers without needing to bring a device in to have the SIM card physically changed. While the hardware makes it possible to allow devices to hop carriers with ease, the carriers themselves may not be as excited to facilitate this functionality.

eSIM Disadvantages

While eSIM devices could be highly beneficial for mass-produced devices, they are not without their flaws. The first problem that needs to be addressed is the transfer of the credentials into a different device. SIM cards are designed to not be easily copied and not to be remotely accessed. This means that, if a user’s phone breaks and they want to transfer their details to a new phone, they only need to physically transfer the SIM, itself.

If SIM cards are integrated circuits mounted to the PCB in form factors such as QMLF, then this would not be possible. This could mean that eSIM devices cannot transfer their data which may result in users relying on the cloud to store details such as contacts, messages, and other credentials.

 

Tracking could be harder to prevent with eSIM devices. Image courtesy of Surrey County Council News.

 

Another issue with eSIM devices is that, while they offer security and the ability to be reprogrammed, they cannot be physically removed from the device. This may be potentially problematic for those who wish to not be tracked as phone devices with an active SIM card can easily be tracked by the network. So far, it was possible to remove the SIM card from a phone and so prevent it from gaining any access to a network—making it more difficult to track. A hardwired IC effectively removes this option, making it that much more difficult to prevent a device from being trackable.

eSIM Manufacturing and Accreditation

STMicroelectronics announced on June 25th that it has been accredited by the GSMA to manufacture eSIM devices. This means that ST is now able to produce personalized eSIM devices that meet the GSMA specifications for both security and reliability.

The GSMA, previously known as the Groupe Spéciale Mobile Association, is the Global System for Mobile Communications. It is a group of member mobile operators and related mobile companies that represents the collective voices of the mobile industry towards policymakers. This means that they can define and award accreditations and present that organized system to governments or institutions that may legally regulate mobile systems. (They also run the Mobile World Congress event.)

SAS-UP—the "Security Accreditation Scheme for UICC Production"—is an accreditation program for assuring the integrity of UICCs, particularly their security. The GSMA audits manufacturing facilities (or "sites") to determine whether they meet their predetermined accreditation requirements.

According to the GSMA list of SAS-UP Accredited companies, there are 45 separate sites from various companies on the list (including six sites from Gemalto, six from Giesecke & Devrient, and one from NXP Semiconductors) that have attained some form of SAS-UP certification. 42 of these sites have attained either full or provisional "card form factor" personalization accreditation and nine have attained "embedded form factor" personalization accreditation. Some, including ST's site in Caserta, Italy, have attained both.

Only one site, STMicro's site in Rousset, France, currently has "Wafer Level Chip Scale Packaging" accreditation. This means that they're the only company so far accredited to customize eSIMs with connection credentials, personalizing their eSIMs a step further than the other companies on the list before shipping.

 STMicroelectronics eSIM ICs are built around the ST33 secure microcontroller and utilize the ST33 Secure Element platform, which ST They're presently offered in UFDFN, QFN, and WLCSP form factors.

 

Block diagram for the ST33 MCU. Image courtesy of STMicroelectronics.

 

Jean-Christophe Tisseuil, GSMA's Head of SIM and eSIM, echoes the idea that eSIM manufacturing is ramping up so that this technology can become more widespread: "The SAS-UP accreditation of ST's Rousset (France) production site for the personalization of WLCSP SIMs and eSIMs is a significant move in driving widespread adoption of trusted eSIM devices by enabling consumer and IoT device manufacturers to implement eSIM in very small form factors. SAS-UP is a first and essential step towards a secure and trusted eSIM market deployment."

 

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It seems likely that eSIMs are the way the mobile device industry is moving. Like the removable batteries of devices past, removable SIM cards are on their way out. While there are benefits for security and design, there are also drawbacks that proponents of the Right to Repair movement and security advocates are apt to dislike.

What are your views on this trend? Share your thoughts in the comments below.

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