It appears ESD Electrostatic discharge immunity test problems mainly in the following aspects. First phone call interrupted; second is due to electrostatic discharge ESD handset section function failure, but after the end of the electrostatic discharge failure or restart the phone function can be restored. These phenomena can be: abnormal screen, such as screen display white, streaks, show garbled display fuzzy and so on; call quality problems, such as howling or the sound disappears; key function or loss of function of the touch screen; software by mistake alarm, as in the case of the charger plug did not occur frequently at the prompt "connected charging, the charger has been removed." Then the phone automatically shut down or restart the phenomenon. This problem can occur both during the call may also occur during standby. The last reason is due to electrostatic discharge failure or damage to the phone. As part of the device is damaged, some of the phone's features after the restart still can not be recovered, such as a camera function; automatic shutdown situation will not turn again; when the test case is connected to the charger, the charger may also appear failure, damage or explosion and other issues.
 
ESD electrostatic discharge problems specific analysis
 
(1) dropped calls: the main cause of dropped calls is caused by electrostatic discharge on the phone's internal RF circuitry and / or baseband circuits affected, resulting in a decline in communication SNR, signal synchronization problems, resulting in dropped calls. Unreasonable structure design can also lead to dropped calls. Electrostatic discharge test requires the use of a large area of metal material horizontal coupling plate, place only between the phone and the horizontal coupling plate with a thickness of 0.5 mm of insulation pads. Call when the antenna or a large area of the metal parts of the horizontal distance between the coupling plate too close, you may have a mutual coupling, resulting in a mobile phone can actually achieve sensitivity greatly decreased, electrostatic test easier to break, even when not severe electrostatic application interference from mobile phones can not call on hold.
 
(2) automatic shutdown or restart: Reset circuit baseband circuit is disturbed static error cause the phone to shut down or restart.
 
(3) failure or damage to the phone: electrostatic discharge during the high voltage and high current causes thermal insulation breakdown or failure of the device. Electrostatic discharge may also be in the process leading to strong electromagnetic fields affect the device temporarily disabled.
 
(4) software failure: static interference signals are to be treated as a useful signal, causing the operating system error response.
 
Improved ESD ESD issues recommendations
 
(1) consider the issue in ESD design
 
Try to choose high level electrostatic sensitive devices; devices and static power isolation; reduce the loop area (the larger the area, the greater the flow field included, the induced current increases). Specific measures may include: traces as short as possible; power and ground closer the better; there are multiple power and ground group when connected to the grid; long signal lines or power lines must be staggered and ground; signal line closer to the ground, the better; all the components as close as possible; the same characteristics of the device as close as possible; a ground plane design: use complete ground plane on the PCB; PCB ground area the better; do not have a big gap ; PCB grounding line needs to have a good low impedance and isolation; power ground layout in the middle of the plate better than around; placing high frequency bypass capacitor between the power and ground; to protect static-sensitive components.
 
(2) electrostatic problem occurred after corrective recommendations for the electrostatic discharge problems, take the following steps for rectification.
 
a) Try direct discharge and indirect discharge, air and contact discharge, confirm coupling path;
 
b) discharge from different directions, any different observable phenomena to determine all of the discharge point and the discharge path;
 
c) from low to high, at different voltages were tested to determine the phone becomes defective phenomenon in which voltage range;
 
d) more than a few prototype test, analyze commonalities confirm Failure;
 
e) according to the coupling path, the failure phenomenon, the discharge path, sensitive device judged relevant;
 
f) the development of solutions for sensitive devices;
 
g) Finally, we can resolve the problem by experimental verification and correction. Specific corrective measures can be the following: For the chassis slit, key, FPCB usable media issues to deal with isolated manner; for camera, microphone, earpiece and other issues through the dielectric isolation, treatment and other ways to strengthen the ground; a shield shell chip can be strengthened by the shielding effect, shielding shell strengthen grounded way to deal with; the interface circuit, the key chip pin, through the use of protective devices (such as TVS tube, ESD protection devices) to be protected; for software failures, can by adding some logic to properly detect and handle alarms way to improve.