PCB News - ESD protection knowledge of smart phone PCB design

We also often have some experience in our lives. Some electronic products were fine when they were first bought back, and after a while, they suddenly broke down inexplicably. These problems are mostly caused by static electricity breaking down and burning the functional chips in your electronic products, causing the functional chips to fail. Therefore, how to protect electronic products from being destroyed by static electricity has always been an important issue for designers. This problem has become more serious in recent years, because in the past ten years, electronic products have been scaled down from the 0.5 micron process to the current 45 nanometer process, reducing the chip component size by more than a hundred times. The thickness of the gate electrode of the transistor has also been continuously reduced, so that the semiconductor component's ability to protect against static electricity continues to decline, and the product is easily damaged by sudden static electricity and fails. Every time we touch electronic products intentionally or unintentionally, it is easy to cause damage to these electronic products by the electrostatic discharge carried on our body. Unfortunately, static electricity is a natural phenomenon produced by friction. There is no simple way to prevent it from being generated. Therefore, we can only make necessary protective designs for electronic systems.

After being attacked by static electricity, electronic systems with inadequate protection often crash, crash, or part of the system functions abnormally. Some will fail briefly and then return to normal. These are phenomena that may be caused by static electricity, while electronic systems with complete protection can It is completely unaffected by static electricity. The electrostatic events that can occur in the environment range from 3KV to 35KV. Therefore, the electrostatic test specification of the electronic system needs to be determined according to the PCB design status of its own product and the environment in which it is used. Taking a smart phone as an example, the test specification should be 12KV Take off. Because the covering material of the mobile phone itself can usually withstand the electrostatic energy below 12KV from entering the electronic system of the mobile phone, but there are often electrostatic events exceeding 12KV in the environment, so only the test specification is pulled above 12KV to confirm the design of the mobile phone in the use environment It can be used safely without being disturbed by static electricity. There are many ways to protect against static electricity, among which the easiest and most economical is to add protective parts, such as TVS chips, where necessary. The TVS chip has a fast response speed, and the clamping voltage is so low that it is close to the normal working voltage of the electronic system, which can provide good protection. Especially now that the core chips of mobile phones or computers have a working voltage of 1V-1.8V, only TVS chips can provide the necessary protection.

Take smartphones as an example, static attacks often occur in the following places:

Touch screen: Every time a hand touches the touch screen, it is an electrostatic attack. Or when talking on the phone, the cheek is easily touched by the touch screen, which is also a static attack.

Earphone terminal: When the earphone is plugged in or unplugged, it is an electrostatic attack.

Mobile phone charging terminal: every time the mobile phone charging line is connected, it is an electrostatic attack.

USB terminal: When USB is plugged in or unplugged, it is an electrostatic attack. Especially when using USB ON THE GO, there is a chance of surge attack.

Antenna: The mobile phone antenna itself is more susceptible to external charges.

Sim/Flash card: When the mobile phone Sim/Flash card is plugged in and unplugged, it is also an opportunity for electrostatic attack.

Keyboard: Mobile phone keyboards are also vulnerable to static electricity.

Because the space of a smart phone is very small, almost every module block will be attacked by static electricity, as shown in Figure 1. The places where ESD Protector is added in the picture are all vulnerable to static electricity.

The above is an introduction to the knowledge of ESD protection in smart phone PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology