SIMULATION SCHEMATICSIMULATION SCHEMATICSIMULATION SCHEMATICSIMULATION SCHEMATIC AND GRAPHIC AND GRAPHIC AND GRAPHIC AND GRAPHIC REPRESENTATION OF HUREPRESENTATION OF HUREPRESENTATION OF HUREPRESENTATION OF HUMAN BOBY MODEL ESDMAN BOBY MODEL ESDMAN BOBY MODEL ESDMAN BOBY MODEL ESD

Oana Cristina BENIUGĂ Gheorghe Asachi Technical University

of Iaşi

Oana Maria NEACŞU Gheorghe Asachi Technical University

of Iaşi

REZUMAT. REZUMAT. REZUMAT. REZUMAT. În această lucrare este descrisă tÎn această lucrare este descrisă tÎn această lucrare este descrisă tÎn această lucrare este descrisă topologia celui mai întâlnit model pentru simularea descărcării electrostatice. opologia celui mai întâlnit model pentru simularea descărcării electrostatice. opologia celui mai întâlnit model pentru simularea descărcării electrostatice. opologia celui mai întâlnit model pentru simularea descărcării electrostatice. Optimizarea circuitului ce reproduce corpul uman este o abordare în plină evoluţie ce implică analiza deteriorărilor Optimizarea circuitului ce reproduce corpul uman este o abordare în plină evoluţie ce implică analiza deteriorărilor Optimizarea circuitului ce reproduce corpul uman este o abordare în plină evoluţie ce implică analiza deteriorărilor Optimizarea circuitului ce reproduce corpul uman este o abordare în plină evoluţie ce implică analiza deteriorărilor echipamentelor electronice. Articolul propune modelarea evenechipamentelor electronice. Articolul propune modelarea evenechipamentelor electronice. Articolul propune modelarea evenechipamentelor electronice. Articolul propune modelarea evenimentului de descărcare electrostatică generată de modelul imentului de descărcare electrostatică generată de modelul imentului de descărcare electrostatică generată de modelul imentului de descărcare electrostatică generată de modelul corpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentarecorpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentarecorpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentarecorpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentarea a a a schematică a modelului corpului uman ca generator de sarcini electriceschematică a modelului corpului uman ca generator de sarcini electriceschematică a modelului corpului uman ca generator de sarcini electriceschematică a modelului corpului uman ca generator de sarcini electrice nedorite se face utilizând tehnici avansate de nedorite se face utilizând tehnici avansate de nedorite se face utilizând tehnici avansate de nedorite se face utilizând tehnici avansate de instrumentaţie viruală. Simularea în programul SPICE, folosind o arhitectură specifică, permite înţelegerea comportamentului instrumentaţie viruală. Simularea în programul SPICE, folosind o arhitectură specifică, permite înţelegerea comportamentului instrumentaţie viruală. Simularea în programul SPICE, folosind o arhitectură specifică, permite înţelegerea comportamentului instrumentaţie viruală. Simularea în programul SPICE, folosind o arhitectură specifică, permite înţelegerea comportamentului dispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă codispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă codispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă codispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă corpul uman. Testele au condus la concluzia că rpul uman. Testele au condus la concluzia că rpul uman. Testele au condus la concluzia că rpul uman. Testele au condus la concluzia că descărcarea electrostatică provenită de la corpului uman produce nivele ridicate ale curenţilor de descărcare putând cauza descărcarea electrostatică provenită de la corpului uman produce nivele ridicate ale curenţilor de descărcare putând cauza descărcarea electrostatică provenită de la corpului uman produce nivele ridicate ale curenţilor de descărcare putând cauza descărcarea electrostatică provenită de la corpului uman produce nivele ridicate ale curenţilor de descărcare putând cauza deteriorări serioase ale echipamentelor electronice.deteriorări serioase ale echipamentelor electronice.deteriorări serioase ale echipamentelor electronice.deteriorări serioase ale echipamentelor electronice. Cuvinte cheieCuvinte cheieCuvinte cheieCuvinte cheie: descărcare electrostatică, instrumentaţie virtuală, modelul corpului uman, simulare SPICE, ABSTRACT. ABSTRACT. ABSTRACT. ABSTRACT. In this workpiece is described the topology of the most common model for electrostatic discharge simulation. The In this workpiece is described the topology of the most common model for electrostatic discharge simulation. The In this workpiece is described the topology of the most common model for electrostatic discharge simulation. The In this workpiece is described the topology of the most common model for electrostatic discharge simulation. The HBM model optimization is a evolutionary approach that invoHBM model optimization is a evolutionary approach that invoHBM model optimization is a evolutionary approach that invoHBM model optimization is a evolutionary approach that involves electronic equipment failure analysis. The present article lves electronic equipment failure analysis. The present article lves electronic equipment failure analysis. The present article lves electronic equipment failure analysis. The present article proposes modeling the HBM ESD event using a realistic model, including all the circuit elements that may be involved in the proposes modeling the HBM ESD event using a realistic model, including all the circuit elements that may be involved in the proposes modeling the HBM ESD event using a realistic model, including all the circuit elements that may be involved in the proposes modeling the HBM ESD event using a realistic model, including all the circuit elements that may be involved in the process. Schematic representation of human body model as electrical process. Schematic representation of human body model as electrical process. Schematic representation of human body model as electrical process. Schematic representation of human body model as electrical charges generator is realized using advanced virtual charges generator is realized using advanced virtual charges generator is realized using advanced virtual charges generator is realized using advanced virtual instrumentation techniques. SPICE simulation, using specific architecture, allows understanding the behavior of devices underinstrumentation techniques. SPICE simulation, using specific architecture, allows understanding the behavior of devices underinstrumentation techniques. SPICE simulation, using specific architecture, allows understanding the behavior of devices underinstrumentation techniques. SPICE simulation, using specific architecture, allows understanding the behavior of devices under test at different external stimulus, in this cause the human body. The test ctest at different external stimulus, in this cause the human body. The test ctest at different external stimulus, in this cause the human body. The test ctest at different external stimulus, in this cause the human body. The test concluded that the electrostatic discharge from the oncluded that the electrostatic discharge from the oncluded that the electrostatic discharge from the oncluded that the electrostatic discharge from the human body produceshuman body produceshuman body produceshuman body produces high levelhigh levelhigh levelhigh levels of discharge currents being able to cause serious damages of electronic equipments.s of discharge currents being able to cause serious damages of electronic equipments.s of discharge currents being able to cause serious damages of electronic equipments.s of discharge currents being able to cause serious damages of electronic equipments. KeywordsKeywordsKeywordsKeywords: electrostatic discharge, virtual instrumentation, human body model, SPICE simulation, 1. ISSUES RELATED TO ELECTROSTATIC DISCHARGES

Electrostatic discharges (ESD) are a serious

reliability issue in electronic environment design and

manufacturing.

Nowadays, ESD are mainly addressed in standard

electrical engineering and the increases in

performance and design leads to very small electronic

components. In this situation, the thinner regions

cannot withstand the variable voltages and discharge

currents produced by ESD phenomena.

The sources of ESD produce large amounts of

charge and the combination between sensitive ESD

devices and no protection to charge accumulation

increases the incidence of damages and failures.

As the electronic technology advances are needed

extra precautions and discharge current and fields’

limitation. Those limitations involves circuit

protection by improving the self protection of

integrate circuits or by adding elements for charge or

voltage rerouting.

The voltage produced during discharge describes

the charge’s forcing conditions and the current

produced is described by the speed the charge moves.

The ESD event is a two body system, as one

charged body comes into contact with an uncharged

body and so appears a charge imbalance.

The produced current pulse is characterized by

two body’s capacitance, the initial voltage

differences and the impedance between them during

the phenomenon. In order to prevent, limit or

estimate the electrostatic discharge, in time were

created and standardized different types of event’s

equivalent system.

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171

HBM ESD Generator 100pF/1.5

kΩ

Device under

test

Current

transducers

R

500 Ω switch

2. GRAPHIC REPRESENTATION OF HUMAN BODY MODEL

In the electronic and information &

communication technology are standardized three

basic models implicated in the ESD event. The

models are based on the localization of charge

storage and grouped as:

a. Human Body Model (HBM);

b. Machine Model (MM);

c. Charged Device Model (CDM).

Under certain conditions the electrical charged

human body can transfer his charge to electronic

devices by simply handling, operating or assembling

them.

As the basic immunity test method for personnel

electrostatic discharge is IEC 61000-4-2, for the

simulation of electrostatic effects – HBM, MM, CDM

are adopted the standards EN 61340-3-1, 3-2, 3-

3:2007.

The standards covers HBM, MM, CDM ESD

waveforms for use in general test methods and for

applications to materials or objects, electronic

components and other items for ESD withstand test

or performance evaluation purposes.

The HBM is the most popular ESD model and

models the ESD event coming from a person that

enters into direct contact with an electronic

component or circuit (device under test), represented

in figure 1:

Fig. 1. Human body – DUT electric discharge

The schematic representation of HBM described

in EN 61340 -3-1:2007 is illustrated in figure 2:

This figure shows the real case HBM ESD event,

the static charges being initially stocked in the human

body and then transferred to the device under test by

finger contact or through a metal tool in contact with

the human hand. The accumulation of charges into

the test equipment can produce very high voltage or

current that can result into irreversible failure or even

integral destroy of the device.

Fig. 2. HBM ESD waveform generator

The current transducers measure the current

resulted from the discharge either through a shorting

wire, either through a 500 Ω low inductance resistor,

with a tolerance of ± 1% appropriately rated to the

voltages that will be used for waveform qualification.

The ESD event main failure reasons are related to

the discharge current that affects the devices under

test functionality. The discharge current is

characterized by the rise time, the peak to peak value,

the current at 30 ns and at 60 ns. The current

transducer introduces a parasitic inductance into the

ESD discharge path, which results in slower current

rise times.

In a ESD event the human body can generate very

high voltage levels as 5,000 volts by simply walking

across a linoleum floor, 15,000 volts by a carpeted

floor, while a human body wearing nylon clothes can

supply 21,000 volts. Walking across a carpet with

leather shoes and low-humidity can raise the human

body capacitance charge up to 25,000 volts.

The actual amount of energy in a given ESD event

depends on the types of materials involved (wool

fabrics generate less than nylon), the humidity (low

humidity offers less resistance to the discharge), the

amount of physical energy (friction) involved, and

how quickly the energy is released. For example, a

human body that carries a static charge of 30,000

volts stores an electrical energy about 0,045 joules.

In order to model the ESD process are used

equations describing the physical process that

simulates the response to external stimulus. The

mathematical simulation allows understanding the

behavior at different stimulus.

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3. HUMAN BODY MODEL SIMULATION APPROACH

There are a number of factors that influence the

human body model waveform creating a discrepancy

between the reality and the standard specifications of

this ESD model:

- the non uniform ESD environment conditions;

- the circumstances of electrostatic discharge that

can occur and can not be predicted;

- the different configurations of human body

(different charges and circuit parameters);

- lack of unstandardized procedure or method for

capturing the ESD event. Commonly, there are

various software solutions that can approximate the

ESD spark and the current produced.

HBM ESD simulation process takes into account

certain considerations. First, the ESD simulation on

electrical circuit level must forecast all the entrance

data that allows reproducing the real event. Then, the

electrical components must be provided with

protection design so that those can be unaffected by

the electrostatic discharge.

The actual ESD standards must deliver

opportunities for testing the immunity of electronic

components under the action of direct or indirect

discharge from human body.

Table 1. Approximate values for different sections of human

body

The simulation will generate a lot of data that

must be graphical estimated and interpreted by

specific software and which will help in predicting

the levels of break-down, according to the discharge

current amplitude.

According to the IEEE standard C62.47-1992, the

table 1 presents the electrical parameters of human

body, calculated based on spherical or cylindrical

approximations of the human body segments

involved in an electrostatic discharge.

The inductances and capacitances of different

sections of human body are dependent on their

geometry, while their resistance is dependent on

various nongeometric factors.

For different types of electrostatic discharge, like

body/finger or hand/metal, the bulk resistance of

body sections is in series with skin resistance, the last

one being believed that is influenced not only by

humidity but also by skin secretions chemistry.

Because the effective resistance can not be

accurately estimated, the best way to determine this

parameter is to computer model using advanced

virtual instrumentation techniques and then to make

comparison with real ESD event. In the scientific

literature are data that the body/metal electrostatic

discharge total resistance is in the range 300 ÷ 1500

Ω and the total capacity is around 100 pF.

Typically, the human body model failure modes

consists in visible thermal damages or integrate

circuit error, as voltage flow which discharges a lot

amount of current into the electronic component in a

short time period of several hundred nanoseconds.

4. SPICE APPLICATION EXEMPLE

The basis for the most circuit’s simulation and

modeling today is the program SPICE (Simulation

Program with Integrated Circuit Emphasis) and

allows connecting linear and nonlinear circuit

elements in order to simulate their time or frequency

behavior. In the realistic human body model

simulation, the resistors will keep their resistance the

same, independent of current flowing through them

or the voltages across them. The temperature is

modeled only to define the ambient temperature at

the start of the simulation. A real resistor will have

non linear characteristics under high bias conditions,

so the results do not model the physical circuit

accurately if the current through the resistor causes

non linear behavior.

A potential way to make the analysis of

electrostatic discharge from the human body more

accurate is parametric modeling using SPICE

software, because this program is well suited to

model the electrical circuits.

Diameter (cm)

Lenght (cm)

C (pF)

L (µH)

Fingers holding

key

2 6 2 0.02

Entire hand

holding key

7.5 12.5 5 0.02

Forearm 9 30 10 0.1

Full arm 9 60 20 0.27

Torso 30 60 20 0.13

Whole body 30 120 60 0.43

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173

Fig. 3. HBM ESD schematic circuit with VHBM= 25,000 Volts In figure 3 is presented the schematic

representation of human body equivalent circuit,

modeled in SPICE. There were configured and

approximated the RLC (resistance-inductance-

capacitance) elements that define the different

sections of the human body, holding a metal object.

The tests were performed with a very high voltage

charge of 25,000 volts. The source simulates a

transient pulse generator, as the real ESD event

happens. The output load take into account has a

value of 500 Ω. Moreover, the analysis allows

estimating the current and voltage flow through each

circuit element, from source until the output marker.

In figure 5 is illustrated the graphical

representation of the discharge current in time

distribution. As it can be seen, comparing the

simulated waveform of the human body discharge

from this figure with the waveform presented in the

EN 61340-3-1:2007 standard (figure 4), can be

noticed the time representation of discharge current

waveforms similitude.

Fig. 4. EN 61340-3-1-2: 2007 - Current waveform for HBM ESD

Fig. 5. Discharge current waveform for HBM ESD, VHBM=8kV

The peak value of discharge current I (R9), at the

output of human body circuit, before the output load

of 500 Ω is approximately 0.75 A in the nanaseconds

range.

Fig. 6. Discharge current waveform for HBM ESD, VHBM=25kV

Legs Torso Arm

R1

25

L1

150nH

L2

150nH

C1

40pF

0 00 00

V1

C2

30pF

R2

25

C3

30pF

L3

50nH

R3

15

C4

5pF

L4

40nH

L5

50nH

R4

50

R5

50

C5

4pF

R6

30

C6

5pF

0

L6

15nH

U1

0

1 2

L7

15nH

0

C7

10pF

R7

250

0

C8

3pF

L8

3nH

R8

80

Value = 500C9

1.5pF

I

0

Hand Hand – metal

object

Hand – metal

impedance

Load

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Buletinul AGIR nr. 4/2011 octombrie-decembrie

Fig.7. Experimental configuration for HBM indirect measurement

If the charge voltage is 25 kV the resulted

discharge current peak value is about 12 A.

The human body from figure 1, isolated from

ground is actually an insulated conductor that has a

certain capacitance.

This capacitance can be measured through a

indirect method. In figure 6 is presented a

configuration method for estimating the human body

capacitance using an electrometer. The operator is

placed inside a Faraday cage (which has the role to

remove the disturbing fields), on a ceramic rack, on a

rubber carpet.

As it is well described in another previous work

the indirect method is based on charging with voltage

the human capacitor whose value is unknown and

then determine his value by placing him in parallel

with a precisely know capacitor, the measurements

being realized using coulomb function of a

programmable electrometer.

For charging the human capacitor it was used a

build-in programmable source, applying d.c. voltage

to the human operator, maintaining the switches S1

and S3 open and the S2 closed. The electrostatic

charge was estimated using the formula (1), where

UK is the well known voltage from the build-in

source.

K

HU

QC = (1)

In a previous paper it was determined that the

human capacity is about 300 pF (potential capacity

and isolated sphere capacity), different from the

standard 100 pF capacitor, illustrated in figure 1.

5. CONCLUSION

The present approach enables better evaluation of

the electrical discharges from the human body. In this

paper was investigated the discharge current

generated by the electrostatic human body model,

because the electronic components from the

electronic technology are very sensitive to this

parameter.

For human body model simulation was used a

virtual instrumentation program that allowed

configure and graphic visualizing the discharge

current waveform. Moreover, it could be estimated

and graphic represented the currents and voltages

through each circuit component.

The realistic system was test for two different

charge voltages, at 8 kΩ and 25 kΩ, the resulting

discharge currents being able to cause damages or

break-downs to the electronic components which they

came in contact.

Comparing to other human body model tested

circuits, can be concluded that the peak to peak

voltage (current) vary with their geometry.

The human body capacitance determined through

calculations is around 300 pF, and is different from

the standard value of 100 pF, which takes into

consideration only the capacitance by a completely

isolated sphere, neglecting the potential capacity of

human body. The high transient current in an ESD

event can lead to real reliability problems and the

tests using HBM simulation can successfully recreate

a real event.

R = 50 kΩ

Ceramic rack 10

mm

Rubber

carpet

ground

Connector

BNC

S1 To Coulomb

model 6517A,

S2

S3

Voltage source

Exterior shielded

wall

Interior shielded

wall

Buletinul AGIR nr. 4/2011 octombrie-decembrie_____________________________________________________________________________________________

175

ACKNOWLEDGEMENT

This paper was supported by the project

PERFORM-ERA "Postdoctoral Performance for

Integration in the European Research Area" (ID-

57649), financed by the European Social Fund and

the Romanian Government.

REFERENCES

[1] E. Franell, S. Drueen, H. Gossner, and D. Schmitt-Landsiedel, ESD full chip simulation: HBM and CDM

requirements and simulation approach Advances in Radio

Science, Volume 6, 2008, pp.245-251

[2] Ming-Douker, Jeng-Jie Peng, Hsin-chin Jaing, ESD Test

Methods on Integrated Circuits: an Overview, IEEE 2001

ICECS, pg. 1011 - 1014 vol.2

[3] A. Sălceanu, Oana Neacşu, E. Luncă, V.David, Indirect

Measurements on the Capacity in the Electrostatic HB Model,

2007, 15-th IMEKO TC 4 International Symposium on

Novelties in Electrical Measurements and Instrumentation, Vol.

I, pag. 38-41, ISBN 978-973-667-261-3

[4] M.A. Kelly, G.E. Servais and T.V. Pfaffenbach, An

Investigation of Human Body Electrostatic Discharge, ISTFA

’93: The 19th International Symposium for Testing & Failure

Analysis, Los Angeles, California, USA/15–19 November 1993

[5] EN 61340-3-1:2007 Electrostatics — Part 3-1: Methods for

simulation of electrostatic effects — Human body model (HBM)

electrostatic discharge test waveforms

[6] IEEE Std C62.47-1992 - Guide on Electrostatic Discharge

(ESD): Characterization of the ESD Environment

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