Electrostatic discharge (ESD) of academic research it is mature to had comparatived, analyse electrostatic event for imitate, forefathers designed model of a lot of electrostatic discharge.

 

Accordingly, mass production manufacturer regards IEC 61000-4-2 is the factual level that ESD tests. The national level of our country (GB/T 17626.2-1998) be equal at I EC 6 1000-4-2. It is the standard that the electrostatic generator that the lab uses presses IEC 6 1000-4-2 namely mostly, cent is osculatory discharge and air discharge. If the model of electrostatic generator pursues 1. Discharge head discharges by the contact and air discharge divides cusp and round head two kinds.

 

 

If the weaveform of the electrostatic discharge of IEC 61000-4-2 pursues 2, can see electrostatic discharge is main electric current is a when an ascendant edge controls in 1nS ascendant edge, should eliminate this ascendant edge to ask ESD protects parts of an apparatus to answer time to want to be less than this time. The energy of electrostatic discharge basically arrives in a few MHz centrally 500MHz, a lot of moment we can consider from spectrum, if filter filter divides the energy of corresponding frequency band,will come true electrostatic defend. Its discharge spectrum is as follows, this graph is myself picture, can qualitative look, cannot mensurable.

 

 

IEC 61000-4-2 set a few test class, at present test of mobile phone CTA is carried out is 3 class, contact discharge 6KV namely, air discharge 8KV. Interior of manufacturer of a lot of mobile phones is carried out taller electrostatic defend grade.

 

 

When integrated circuit (IC) endure electrostatic discharge (ESD) when, the resistor of discharge loop normally very small, cannot restrict discharge electric current. When inserting the cable with electrostatic belt to circuit interface for example, the resistor of discharge loop is almost 0, cause be as high as tens of ampere spark aiguille electric current, flow into corresponding IC pin. Instantaneous big electric current can injure IC badly, local and calorific quantity of heat can melt even silicon chip is in charge of core. ESD still includes in-house metal join to be burned to the injury of IC, passivation layer is destroyed, transistor unit is burned out.

 

The dead lock that ESD still can cause IC (LATCHUP) . The structural unit of this kind of effect and the similar silicon controlled rectifier with CMOS in-house parts of an apparatus is activationed to concern. Tall voltage can activation these structures, form channel of big electric current, it is commonly reach the ground from VCC. The dead lock electric current of serial interface parts of an apparatus can be as high as 1A. Dead lock electric current can maintain all the time, be cut off the power till parts of an apparatus. Arrive nevertheless in those days, IC normally already because of overheat burn down.

 

Circuit class ESD defends method

 

1, shunt-wound discharge parts of an apparatus

 

Commonly used discharge parts of an apparatus has TVS, neat accept diode, pressure quick resistor, gas discharge tube. If pursue

 

 

1.1, neat accept diode (Zener Diodes, also weigh stabilized voltage diode) : The retrorse puncture character that uses neat accept diode can protect ESD sensitive parts of an apparatus. But the electric capacity that neat accept diode has a few PF normally, this to high speed signal (for example 500MHz) , can cause signal distortion. Neat accept diode also has very good absorption to the surge on power source.

 

1.2, twinkling changes voltage arrester TVS(Transient Voltage Suppressor) : TVS is diode of a kind of solid state, use technically at preventing voltage of ESD transient state to destroy sensitive semiconductor device. With the Qi Na of the tradition diode photograph is compared, area of knot of TVS diode P/N is larger, the improvement on this one structure makes TVS has stronger maximum pressure to bear ability, also reduced voltage to end at the same time rate, the security that holds return of voltage of facility low work to protection consequently has better effect.

 

The area of the transient state power of TVS diode and function of transient state electric current and knot becomes direct ratio. The knot of this diode has larger cut area, can handle lightning and the electric current of tall transient state that ESD causes. TVS also can have knot electric capacity, normally 0.3 PF arrive a few PF. TVS has odd polarity and bipolar, when using, want to notice. The TVS that uses on the mobile phone about 0.01$ , the agreement that low look is worth 2-3 divides $ .

 

1.3, multilayer parts of an apparatus of metallic oxide structure (MLV) : The mainland is called commonly pressure quick resistor. MLV also can undertake impact of significant instantaneous high pressure is restrained, this kind of parts of an apparatus is had nonlinear voltage – electric current (impedance is behaved) relation, the 2 ～ that cut-off voltage can amount to first pause voltage 3 times. This kind of character suits to be used at not quite sensitive to voltage circuitry and parts of an apparatus electrostatic or surge protection, be like power source loop, key-press inputs end to wait. The mobile phone is used pressure quick resistor makes an appointment with 0.0015$ , it is the 1/6 of TVS price about, but it is good to defend the effect does not have TVS, and pressure quick resistor has life ageing.

 

2, series connection impedance

 

Can pass series connection resistor commonly or magnetism bead will restrict ESD discharge electric current, achieve antistatic goal. If pursue. Like the tall input of the mobile phone the port of impedance can string together 1K Europe resistor to defend, be like ADC, the GPIO of the input, key-press. Do not fear the resistor of 0402 is met by batter, carrying out a proof is to hit not bad. Here is unspecified fractionize analyse. Do ESD to defend with resistor raise cost scarcely. If use magnetism bead, the price of magnetism bead about 0.002$ , and pressure quick resistor is about the same.

 

 

3, add filter wave network

 

Electrostatic energy spectrum was mentioned in front, if drop main energy with filter filter,also can achieve electrostatic defended purpose.

 

To low frequency signal, if GPIO is inputted, ADC, frequency input can be done with the capacitance of 1k+1000PF electrostatic defend, cost is negligible, function unlike pressure quick resistor is poor, if use 1K+50PF pressure quick resistor (below the compound preventive measure that say) , the effect is better, experience proves such defending that the effect exceeds TVS sometimes.

 

 

To the microwave signal of radio frequency antenna, if use TVS pipe, pressure quick parts of an apparatus of sex waiting for a look will do electrostatic defend, radio frequency signal is met by attenuation, because this asks the electric capacity of TVS is very small, raise the cost of ESD measure so. OK to microwave signal to ground paralell connection the inductance of an a few NH is electrostatic offer channel of a discharge, do not have an influence almost to microwave signal, often use the inductance of 22nH to the mobile phone of 900MHZ and 1800MHz. The energy sponge that can get on spectrum of electrostatic and main energy so is very much.

 

 

4, compound defend

 

A kind of parts of an apparatus calls EMI Filter, he has very good ESD to defend the effect, if pursue. EMI Filter also has those who be based on TVS canal to mix be based on pressure quick of resistor, former effect is good, but very expensive, latter and cheap, general the EMI price of Yu Yamin resistor is in 4 roadbed 0.02$ .

 

 

A resistor below can be used in applying actually + one is pressed quick the means of resistor. He has already low the function that connects filter, have again pressure quick the function of resistor, still have the function of current limliting of resistor series connection. It is a gender valence comparing defends best means, can use 1K resistor to tall block signal + 50PF is pressed quick; To earphone enharmonic frequency output signal can use 100 Europe resistor + pressure quick resistor; To resistor of TP signal series connection cannot too big the linear that affects TP otherwise, can use 10 Europe resistor. Although resistance became little, low connect filter effect to had been done not have, but current limliting effect is very main still.

 

 

5, increase draw return circuit

 

The leakage copper of the ground can increase in sensitive signal accessory, will absorb electrostatic. Truth and lightning rod principle are same. Point discharge is placed to nod on line (spark gap) often also apply in design of mountain fastness mobile phone.