Guangdong is back to Nantian again! Faced with such a humid south, MOSFETs can't help but ask: Where does the static electricity come from on me?
The climate in the north is relatively dry, and the humidity in the south is less likely to generate static electricity (see figure below).
However, that doesn't mean MOSFETs won't be static! So, where does this static electricity come from?
Electrostatic discharge: It is the number one problem in the design and manufacturing of most devices and ICs.
Electrostatic discharge (ESD) is generally artificially generated, and static electricity will accumulate in the human body, instruments or equipment during production, assembly, testing, storage and handling, but the components themselves will also accumulate static electricity.
There are usually four ways to generate static electricity: human body discharge (HBM), machine discharge (mm), component charging (CDM), and electric field sensing (FIM), and the two main test modes are usually human body discharge (HBM) and machine discharge.
HBM: The industry's ESD standard for HBM (MIL-STD-883C Method 3015.)7. The equivalent human capacitance is 100pf, and the equivalent human body resistance is 15kohm)
mm: The static electricity generated by the machine movement is released by the pin when it touches the chip, ESD standardeia/jesd22-a115-a), the equivalent machine resistance is 0 (metal, and the discharge time is short, between ms or us), and the capacitance is 100pf].
Since the equivalent resistance is 0, the current is very high, and in addition, there is a lot of coupling between the wires in the machine itself, which can interfere and change.
CDM: The device is electrostatically charged and discharges when it comes into contact with a grounded conductor.
Under the same electrostatic voltage level, the degree of device damage: mm cdm hbm, common hbm, mm in product specifications, and the standard for electronic devices is hbm contact 2kv.
After receiving the above statement, do you know why MOS tubes should be anti-static?
As we know, the MOS tube is an ESD-sensitive device, which has a high input impedance and a small capacitance between G-S, which is susceptible to external electromagnetic field or electrostatic induction.
There are two modes of electrostatic breakdown for MOSFETs:
Voltage type: the thin oxide layer of the G pole breaks down to form a pinhole, which shortens the G-S pole and G-D;
Power type: The metallized thin film aluminum strip is fused, resulting in an open circuit at the G and S poles.
The vast majority of MOSFETs are rarely exposed to ESD-prone environments, but in some applications, MOSFETs will add an ESD protector between the GSs to improve their ESD protection capabilities.
However, most MOSFETs nowadays are not so easy to break down, especially high-power VMOS, which are generally diode protected and have large gate capacitance to induce high voltage. Some CMOS devices have added IO port protection, but you should not directly touch the pins of the CMOS device with your hands, which will lead to poor solderability.
Electrostatic discharge
The formation is a short-term large current, and the time constant of the discharge pulse is generally much smaller than the time constant of the device heat dissipation.
When an electrostatic discharge current flows through the PN junction, it generates a large instantaneous power density and forms a localized overheating that even exceeds the temperature of the material itself (silicon's melting point of 1410), which will cause the PN junction to short and fail the device.
The lower the power density, the less susceptible the device is to damage.
Compared with other devices, the ESD sensitivity of MOS transistors is a little higher. However, ESD is random, and even if ESD is generated, it may not necessarily break down the MOS tube.
Solution
When storing and transporting, it is best to pack in metal containers or conductive materials to avoid chemical fiber items;
During assembly and commissioning, tools, instruments and workbenches should be well grounded, and operators should avoid wearing nylon and chemical fiber clothing to cause static interference;
The MOS transistor is voltage-driven, and the suspended G is highly susceptible to external interference to make the MOS on, and the external interference signal charges the G-S junction capacitor. G suspension is very dangerous and can easily cause a pipe burst. Let the G pole connect a pull-down resistor to the ground, and the external interference signal will not be straight-through, generally this gate resistance can be 10-20K.
The role of this gate resistor has also been mentioned before:
A bias voltage is supplied to the MOS.
It plays the role of a bleeder resistor.
That's all for this issue, thanks**
Microbi vbsemi