SIMULATION SCHEMATIC AND GRAPHIC
REPRESENTATION OF HU MAN BOBY MODEL ESD
Oana Cristina BENIUG Ă
Gheorghe Asachi Technical University of Ia ş i
Oana Maria NEAC Ş U
Gheorghe Asachi Technical University of Ia ş i
În această lucrare este descrisă t opologia celui mai întâlnit model pentru simularea descărcării electrostatice. corpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentare a dispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă co rpul uman. Testele au condus la concluzia că
ABSTRACT. 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 invo lves electronic equipment failure analysis. The present article test at different external stimulus, in this cause the human body. The test c oncluded that the electrostatic discharge from the high level s of discharge currents being able to cause serious damages of electronic equipments.
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.
_____________________________________________________________________________________________
Buletinul AGIR nr. 4/2011 ● octombrie-decembrie 171

the test equipment can produce very high voltage or current that can result into irreversible failure or even integral destroy of the device.
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
HBM ESD
Generator
100pF/1.5 k Ω switch
Device under test
R
500 Ω
Current transducers
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.
_____________________________________________________________________________________________
172 Buletinul AGIR nr. 4/2011 ● octombrie-decembrie

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
Fingers holding key
Entire hand holding key
Forearm
Full arm
Torso
Whole body
Diameter
(cm)
2
7.5
9
9
30
30
Lenght
(cm)
6
12.5
30
60
60
120
C
(pF)
L
(µH)
2 0.02
5 0.02
10 0.1
20 0.27
20 0.13
60 0.43
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.
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.
_____________________________________________________________________________________________
Buletinul AGIR nr. 4/2011 ● octombrie-decembrie 173

V1
0
R1
25
L1
150nH
0
C1
40pF
Legs
L2
0
150nH
C2
30pF
R2
25
0
L3
50nH
C3
30pF
Torso
R3
15
0
L4
40nH
C4
5pF
R4
50
Arm
0
C5
4pF
L5
50nH
R5
50
0
R6
30
L6
15nH
C6
5pF
Hand
R7
250
C7
10pF
0
L7
15nH
Hand – metal object
L8
R8
0
1
U1
3nH 80
2
C9
C8
3pF
1.5pF
Hand – metal impedance
0
I
Value = 500
Load
Fig. 3
. HBM ESD schematic circuit with V
HBM
= 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-inductancecapacitance) 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. 5
. Discharge current waveform for HBM ESD, V
HBM
=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. 4
. EN 61340-3-1-2: 2007 - Current waveform for HBM ESD Fig. 6
. Discharge current waveform for HBM ESD, V
HBM
=25kV
_____________________________________________________________________________________________
174 Buletinul AGIR nr. 4/2011 ● octombrie-decembrie

Interior shielded wall
Voltage source
R = 50 k Ω
S
1
Ceramic rack 10 mm
Exterior shielded wall
Connector
BNC
S
2
S
3
To Coulomb model
6517A
,
Rubber ground carpet
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
The present approach enables better evaluation of certain capacitance.
This capacitance can be measured through a indirect method. In figure 6 is presented a the electrical discharges from the human body. In this paper was investigated the discharge current 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 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 with a precisely know capacitor, the measurements being realized using coulomb function of a through each circuit component.
The realistic system was test for two different programmable electrometer.
For charging the human capacitor it was used a charge voltages, at 8 k Ω and 25 k Ω , the resulting discharge currents being able to cause damages or build-in programmable source, applying d.c. voltage to the human operator, maintaining the switches S
1 and S
3 open and the S
2 closed. The electrostatic 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 charge was estimated using the formula (1), where
U
K is the well known voltage from the build-in source. voltage (current) vary with their geometry.
The human body capacitance determined through
C
H
=
Q
(1) calculations is around 300 pF, and is different from the standard value of 100 pF, which takes into
U
K consideration only the capacitance by a completely isolated sphere, neglecting the potential capacity of
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. 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.
_____________________________________________________________________________________________
Buletinul AGIR nr. 4/2011 ● octombrie-decembrie 175

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.
[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. S ă lceanu, Oana Neac ş u, E. Lunc ă
, 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
_____________________________________________________________________________________________
176 Buletinul AGIR nr. 4/2011 ● octombrie-decembrie