simulation schematic simulation schematic and graphic

SIMULATION SCHEMATIC AND GRAPHIC
REPRESENTATION OF HUMAN
HUMAN BOBY MODEL ESD
Oana Cristina BENIUGĂ
Gheorghe Asachi Technical University
of Iaşi
Oana Maria NEACŞU
Gheorghe Asachi Technical University
of Iaşi
REZUMAT. În această lucrare este descrisă topologia
topologia celui mai întâlnit model pentru simularea descărcării electrostatice.
Optimizarea circuitului ce reproduce corpul uman este o abordare în plină evoluţie ce implică analiza deteriorărilor
echipamentelor electronice. Articolul propune modelarea evenimentului
evenimentului de descărcare electrostatică generată de modelul
corpului uman utilizând un model realistic ce include toate elementele de circuit ce pot fi implicate în proces. Reprezentarea
Reprezentarea
schematică a modelului corpului uman ca generator de sarcini electrice nedorite se face utilizând tehnici avansate de
instrumentaţie viruală. Simularea în programul SPICE, folosind o arhitectură specifică, permite înţelegerea comportamentului
dispozitivelor supuse testării sub acţiunea diverşilor stimuli externi, în speţă corpul
corpul uman. Testele au condus la concluzia că
descărcarea electrostatică provenită de la corpului uman produce nivele ridicate ale curenţilor de descărcare putând cauza
deteriorări serioase ale echipamentelor electronice.
Cuvinte cheie:
cheie descărcare electrostatică, instrumentaţie virtuală, modelul corpului uman, simulare SPICE,
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 involves
invo 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
process. Schematic representation of human body model as electrical charges generator is realized using advanced virtual
instrumentation 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 concluded
c oncluded that the electrostatic discharge from the
human body produces high levels
levels of discharge currents being able to cause serious damages of electronic equipments.
Keywords:
Keywords 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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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, 33:2007.
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.
HBM ESD
Generator
100pF/1.5
kΩ
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.
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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
Fingers holding
key
Entire hand
holding key
Forearm
Full arm
Torso
Whole body
Diameter
(cm)
2
Lenght
(cm)
6
C
(pF)
2
L
(µH)
0.02
7.5
12.5
5
0.02
9
9
30
30
30
60
60
120
10
20
20
60
0.1
0.27
0.13
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.
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.
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L2
L3
R2
150nH
Arm
Torso
Legs
L4
R3
25
50nH
L5
L7
R4
15
40nH
Hand – metal
object
Hand
L8
R5
50
50nH
R8
50
15nH
R1
25
80
3nH
0
1
U1
2
R6
30
R7
V1
L1
150nH
L6
15nH
250
C2
30pF
C3
30pF
C4
5pF
C5
4pF
C6
5pF
Value = 500
1.5pF
Load
Hand – metal
impedance
C7
C1
40pF
I
C9
C8
3pF
10pF
0
0
0
0
0
0
0
0
0
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-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. 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
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Interior shielded
wall
Exterior shielded
wall
Connector
BNC
Voltage source
S2
S1
To Coulomb
model 6517A,
R = 50 kΩ
S3
Ceramic rack 10
mm
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
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.
CH =
Q
UK
(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.
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ACKNOWLEDGEMENT
This paper was supported by the project
PERFORM-ERA "Postdoctoral Performance for
Integration in the European Research Area" (ID57649), financed by the European Social Fund and
the Romanian Government.
REFERENCES
[1] E. Franell, S. Drueen, H. Gossner, and D. SchmittLandsiedel, 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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