Did your phone suddenly lose signal? Why do SIM cards break so easily?

Can a SIM card burn out even when it's left untouched in the phone?

I don't know if you've ever encountered such a situation. The "SIM card", which is the least noticeable part of the whole phone, actually burned out when left untouched in the phone...

Mi Luo from our editorial department was once on a main road in the city center when suddenly his phone couldn't search for a signal.

Later, when he went to the business hall, the staff said that "the card had been used for too long and burned out". They reissued a new card and inserted it, and immediately all the functions returned to normal.

When we searched on Weibo, we found that there were quite a few people who had encountered the same situation as Mi Luo. They all said that the service suddenly stopped while using the phone, and when they went to the business hall, they found that the SIM card had burned out.

Moreover, many iPhone users said that there is a probability of "burning the SIM card" after an OTA update on the phone. One of the complaints was posted by the digital blogger Kang Zong @kang.

So it's quite amazing. Originally, I didn't believe Mi Luo's statement about "burning the SIM card", but with so many examples in front of me, I gradually began to believe it. However, this leads to another question:

The SIM card is just a card. How can it burn out like an electronic device? And what does this have to do with the phone's OTA update? Isn't the system update a software matter? How can it damage the hardware like the SIM card?

You know, although this situation seems absurd, when I checked the working principle of the SIM card, I found that it's actually not impossible.

First of all, in terms of principle, there is no difference between the SIM card and the chips and components on our phone's motherboard. The metal blocks on the back of the SIM card that we usually see are actually its interfaces.

From the complete interface definition, we can see that the SIM card is not just a simple plastic card. It needs to communicate with the phone's motherboard and also relies on the phone for power supply. So if there is any problem with the phone, the SIM card will also be affected.

For example, the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) have stipulated three power supply standards for SIM cards, with the maximum voltages being 1.8V, 3.3V, and 5V respectively. If the phone mistakenly supplies a 3.3V voltage to a 1.8V SIM card, the SIM card will burn out.

So, could a similar situation occur during the OTA upgrade of the phone system? I specifically searched several hardware technology forums and found some relevant analyses of the SIM card hardware design specifications. It turns out that this is indeed possible.

As a complete electronic component, the SIM card needs power supply to work properly. But it's impossible for the SIM card to have its own battery, so it has to rely on the phone for power.

When to power on the SIM card and how much voltage to supply are all controlled by the SIM card interface controller built into the phone's processor chip.

This part of the control seems very low - level, but its interfaces are open to the upper - layer system.

So when the system is updated, if the OTA system package involves the firmware related to the SIM card's power supply and communication, during the hardware initialization stage after rewriting the SIM card communication module, it is indeed possible that the wrong voltage is supplied for a short time, resulting in the SIM card burning out.

However, this situation should be very difficult to occur. After all, mobile phones have evolved for so many years, and it should be difficult to make such a basic mistake.

So when researching, we found another possibility - when the phone is updated via OTA, it tends to heat up easily, which may cause the SIM card to burn out. Especially for those phones where the SIM card slot is close to the main heat - generating parts of the motherboard, the risk is even greater.

Don't laugh. There really have been cases where the SIM card burned out because the phone was too hot, but it was during charging...

After all, we are not the ones who experienced it, so we don't know exactly what happened to the phone. We just want to explain that it's not impossible for the SIM card to burn out. But you don't have to worry too much. The situations mentioned above are all rare cases.

Moreover, when researching, we joined a "SIM card enthusiast group" (a group of players who specifically discuss the cost - effectiveness of mobile phone packages). An experienced old player in the group, "Teacher Shua Zi", told us that iPhones are more likely to encounter the "burned SIM card" situation.

But as long as you take out the SIM card, use an eraser to wipe off the blackened contact points that have been worn, and then re - insert it into the iPhone, it can be recognized again.

The situations they encountered gave us a new way of thinking - indeed, physical SIM cards have "inherent defects". While they are electrically connected to the phone's motherboard, users are allowed to insert and remove them freely.

After a long time, the gold - plated contacts will inevitably oxidize. When the oxidation reaches a certain level, poor contact of individual pins will occur, resulting in communication failure with the phone.

A SIM card with oxidized contacts. Image source: Passerby A - <[Question] Far EasTone's SIM cards are so bad (after updating online customer service)>

Since current base stations need to verify the integrity of the SIM card's identity, if the communication between the phone and the SIM card fails, it naturally can't pass the base station's verification, and thus no signal can be received.

I wonder if there are any of our readers who used to play the Famicom / Little Doctor game consoles. Do you remember that sometimes the game cartridges couldn't be recognized when inserted into the console? The situation with the SIM card now is similar.

Image source: What to Buy -

If you encounter a similar situation, it's not a big deal. Just go to the business hall to re - issue a new SIM card. Once you know the cause of the problem, it can be solved quickly.

To completely solve the problem of no signal after using the SIM card for a few years, we may have to wait for the spread of eSIM technology without a physical card.

Image source: An eSIM Is A Digital SIM Card That Enables You To Use A Cellular Plan

Although the eSIM chip may also malfunction, such as poor contact in the card slot, oxidation of solder joints, solder joint detachment, or water ingress.

But we asked a friend who works in a mobile phone manufacturer. He said that the probability of these problems occurring is much lower than the failure rate of physical SIM card slots.

In general, the SIM card, which seems simple, is actually more difficult to handle than we thought.

We can only hope that the eSIM design, which doesn't require manual insertion and removal, can be popularized earlier. Without external exposure and fewer mechanical structures, the probability of problems can be reduced to a certain extent.

This article is from the WeChat public account "Bad Review X.PIN". Author: Shi Ang, Editors: Mi Luo & Mian Xian. Republished by 36Kr with permission.