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Confar rmity
PlateMonitor
Usinga Charged
Dissipative
to TestStaticandHandTools
Materials
and MaciejA. Noras
by Christopher
J. Lemke
chargcdplatc n.ronitor(CPM) is an instrumont
commonlyusedfor evaluationof air ionizer
performance.Thc basicconstructionof the CPM tcst
systcmis shown in Figurc l, as taken from thc Illectrostatic
Association(ESDA) standard"ANSylrSD
Dischargc
2
S T M 3 .I 0 0 0I o n i z a t i o n["1 1 .
That slandardinvolvcs threc scparatctcstsof the ionizcr: iort
balancctcst,positivcdischargctcst anclncgativcdischargc
test.Irorall thc tests,a l5 by 15 cm motalplatewith a flxccl
of20 pF is used(l"igurcl). The
plate-to-carth
capacitancc
conductingplateis usuallyconncctcdto a monitoringclcvicc
(CIPM),which rneasurcs
thc clectricpotcntialo1the platcin
rcferenccto the rcfcrenocgroundof thc Cl'M. Ilither an
or an
voltmctcqor a I'rcldmcter,
noncontacting
clcctrostatic,
can be uscdas a CPM. For thc ion balancclcst
elcctrometcr
the voltagc is a rcsult of the net chargeo1 the
measurcmcnt,
airborneions impinging on thc platc. Ihcsc ions are creatctl
by an ionizcr.Ideally,for a perf'ectlybalancedionizcq thc
voltagccqnalszero. Positivcand negativedischargctcsts
involve prc-chargingthe platc 1oa spccilicdvoltagevalue
usinga hrghvoltagepowcrsupply.
of matcrials;and 2) dctcnniningElectrostatic
charactcristics
Discharge(ESD) complianccof handtools.
of Materials
Charge
Dissipation
Characleristics
Testing
ngAppIications
MateriaI Tesli
'l'he
is irnportant,
tor staticclissipation
testingof r-natcrials
to assurcthatthe
especiallyin ESD scnsitivcenvirontnct.tts,
do in firctmcct
matcrialschoscnlbr usc in suchapplications
thc nccdto avoid or prcventIISD evcnts.Suchtcstingis
utilizcdby rlanulacturingpcrsottncland rcscarchstalf to hclp
guiclcand clircctthcir cffirrtsrcgardingmaterinlcvalttatiotrs
and dccisions.
TeslMelhods
l"rclmycars of rcsearch,it hasbeendctermineclthat surfacc
rcprcsent
do not col'nplctcly
and bulk resistivityoharactcristics
problcrns
to
rcsulting
a rnatcrial'sability to avoidor succumb
frorn staticelcctricitycharging[2]. Thc tcchniclucof chargc
clccaymcasurcmenthas bcen introcluccdas iit.tadclitional
'fhis
tcchniqucprovidcsa mcans
methoclto evaluatetnaterials.
to clctcrminchow quicklythe electricchargcscandccay
Next, thc plate is disconncctcdfi'ornthc power supplyanci
neutralizcdby the impinging airborncions.Thc tirne needecl
of the plate is a measurcof an ionizercapability
for clischargc
o f p ro d u c i n ga n dd c l i v c irn g i t l n s .
The designof thc CPM tcst systemallows fbr its usc tn
bcyondionizcrcvaluation.In this article,wc will
applications
describetwo suchapplications:1) testingchargedissipation
Dischargetrmsl
and MaciejA. Norasare withTREK,lnc.,
Christopher
). Lemke
by e-mailat ChristoperLemke@trekinc.com,
and can be reached
platem0nil0r
system
Figure
1: Construction
ol lhecharged
or Mactej.N oras@trekinc.com.
40
C o n f o r m i t g ' D e c e m b e r2 o o 6
r mi t y . c om
www.confo
i
-
r
rcaIil r{1
throughthe bulk and along thc surfaceof a rnatcrial,down to
earthground.Variousr.ncthods
exist for chargedccay
rneasurements,
as publishcdin appropriatcstaridards
and
literature.1'hecliargcdplatc monitor is usedin scveralof
thoseniethods,as discusscd
below.
samplerestsclna supportntaclcof dielectricmaterial.For
testingthe chargecleoaycharacteljsticsofrnatcrials,a
groundedrnctallrlateis typically usedfor support,instcaclof
the diclcctricn-ratcrial
sLlonort.
Method
Based
onANSI/ESD
STM4.2-1998
[1]and
tEc61340-2-1
t3l
TestAssembly
'Ihc
SampleProcessing
Tlris techniqucusesa specialfixlurc sliownin Figrrre2. Thc
tcstapparatus
includesa special6 in. (15.24crn)dianteter
concluctivcdisk, a disk raising/lowcringn.rcchanism,
and zr
samplcsupporttableclcctricallyisolatccl
fiom thc ground,all
cncloscdin a housingasscrnbly.
The disk assemblyshould
havea maximumcapacitance
of 1,5pF',as mcasurecl
at the
distanccof 1.875cm (0.075in.) abovctlrc grounclcd
concluctivc
planc,and wcigh 227g ( f /- -5g). Thc disk is
clcctricallyconnccledto {.hcchargcdplateo1'thcCPM.
'fhis
tcstapparatus
was initiallydcsigncdlbr tcstingIrSD
pt'otective
surfaceswhich havca groundtcrnrinalalrcady
incorporatcd
into thc suriacestructure(i.c. matswhich havca
spccialconncctotrnountcdclnthcm);in suchcascsthc tcst
o{rfic{ A.^[ E{icn
tcst rnaterialsantplesshouldbe environmcntally
conditionedbel'olctcsting(4tl hours in 23 +l- 2 "C,
1 2 1 l - 3 % R I I a n d2 3 r l - 2 ' C , 5 0 r / - 3 % R l I , r c s p c c t i v e l y ) .
Thcn,thc san.rple
is placcdon thc groundccl
mctalplatc
(supporttablc)anclthc conductivedisk (suspended
ovcr the
specimen)is connccted
to the chargccl
platcof thc CPM and
I kV of voltagcis appliedto thc clisk,by thc CIPM.'l-hcdisk
(elcctrodc)is thenlowcreclonto thc surfaccof'thc tcsr
n.ratcrial
samplcl'or-5s, and thcn raised.l'hc rcmrining
voltageon thc chargcdplateindicateshow wcll thc tcst
matcrialwas ablcto disclrargc
thc cliskin the 5 sccondpcriod
Resulls
'l'his
mcthodhasscvcraldrawbacks.
First,it is ciifficultto
assurepropcrcontactbctwccn thc tcst sarnltlcanclthc ground.
'Ihc
samcproblcnioxistsin the disk-sarnplc
contact,whcre
alr gapscaltcourproutisc
rcsults(Figule3). Scconclly,
thc
rflDcril sq-oorDs
\.
m( u6u6/
tilIftts
t/to{ArGL
[""
It$ rPpr8^il6
HCUgfic
coilRq.P||(r
ll5r srral g,ePofinal
Figure
2:ANSI/ESD
charge
testapparalus
dissipation
[1].
42
C o n f o r m i t gD
' e c e m b e2r0 0 6
www. c o n fo rm ity. co m
FcaLr:r'*
thoughnot a star.rdard,
can bc
usedfor evaluationand
compzrrison
of dissipativc
propertiesof varioustest
sarnpleuraterials.
r---4
- r= - / /
weightelectrode
high'
voltage
relay
material
sample
Summary
thoscmr:ntionedabove)that
chzrracleristical
ly retain
and/oraccumulatca charge,
prescnta clcfiniteESD thrcat.
Testing
Justification
'lcsting
of hancltoolsutilizcd
Threc diflcrcnt rrrcthodstbr
in variousBSD-scnsitivc
testinga material'sclischargc
Ittnnu
l - a c { u r i rpr lgo c c s s ciss
charactoristics
wcrc prcsclttcd.
s u g g c s t cbdy I r S D At r n d
All of thcm usc a chargcd
induslry I1SDprograrn
platentonitor fclr thc
rniuragers
as an cffcctive
plate,
charged
20
dischargcmeasurertrcnts.
It is
safegr.rard
to rcclucethe
pF, 1 kV
inrportantto rcr.ncmbcrthat
chancco1-anIISD incidcnt
cornparisonof cliff'crent
and to insurccornpliancc
Figure
5 : S u g g e s t et eds ts e t u pw i t hw e i g het l e c l r o daen da h i g h
matcrialsusingany of thc
vollage
relay
with an ESI) rnanagcrncnt
aforementionecl
tochniqucs
program.Ilx:rrnination
of
can be donconly whcn thc sarnplcsof matcrialsarc of'thc
suchhandtoolsshoulclbe pcrformecl,
whclherinitializinga
samesizcand shapc.Alscl,rcsultsobtaincdfrornonc method
ncw []SD conh'olprogriimor refining an cxistingltrograln.
cannotbc ciircctlycontparcdwilh rcsultsreccivccl1l'orr
anothcrmcthod.
Irr additionkl the costsavingsgcncratcdby
controlling/rcclucing
DSDclamagc,
aclclitional
savingscurr
Determining
ESD
Compliance
0l Hand
T00ls
acclucin conncclionwitlr tlrcpurchascof ncw tools(for
initialcontpliancc)
or rcltlaccmcnt
tools(undcran cxisling
Pcriodicmonitoringof ilcms rrscclin an lrlcctrostatic
progranr).
clischarge
Protcctccl
Arca (tlPA) is rcquircclfor cffbctivc USD
managelncnt.
A good cxanrplcot'ESD monitoringwithin an
IIPA contrcllled
workspaceis thc pcriodiccvaluationof
protcctivcccluiptncnt
suchas staticdissipativcrrats/lkloring,
ganronts,pcrsonalgrouncling
dcviccssuchas wrist or hccl
straps,and ionizationsystcnts.
HandToolMaterials
An oftcn-ovcrlookccl
categorylbr ESD rnonitoringis hand
tools.Iland toolsuseclduringthc asscmbly,
tcst,calibration
and rcpair of clcctroniccquipn.rcnt
prescnta challcngcin an
ongoingESD control program.lland tools madc 1ior.n
materialsthat arc not staticdissipativegcneratetwo concems
whcn atternptingto n.raintainan EPA controllcclworkspacc
11,3,7,81.
First,toolscontainingmatcrialssuchas polyurethanc,
polystyrcnc,polypropylencand PVC have a tcndencyto
chargcby triboclcctrification.'kiboelectrification
is thc
gcncrationof an electricchargewhen two or rlore dillbrcnt
matcrialscontactone anotherand then arc subjectto
movementor suddenscparation.Dcpcndingon the matcrials
and the rateof motion,high lcvelsof
chargehazardousto ESD-sensitivc
dcvicescanbc gencrated[5,6].
Another conccntregardingsuchtools is
chargerctcntion.Af1cr a triboelectric
eventhas occurred,a material'sability to
distributeand dissipatethe chargeis an
equallyimporlantcharactcristic.Tools
cmploying insulatingmaterials(like
44
C o n f o r m i t gD
' e c e m b e2r0 0 6
l'cstingol'cxistingtools,rvhcninitialingalt DSI) arrclil,can
clinrinatcnon-contpliant
rnatcrials
ll'clntcurlcntancl/orlulurc
consiclcration;
srrchtcstingmay alsoccr-tilyaltel'nltivc
matcrialslor uscr.l,ithin
an llPA controllodworkspacc.In
aclclition,
undcran existingIiSD program,itcrnsmay bc
tcstcdand trackecl,
allowingfbr a tinrctablcof uscfullifc,
hclpingto optimizctool cxpcnditures.
Suchtcstingmay also provc el'f-cctivc
with rcgardto industryspecilicor custom-madc
tools,cspcciallyiI'tcstingindicatcs
that suchcuslomor rcdesigncdtools arc not neccssary.
Boleof Surlactants
An cffcctivcrnethoilo1'testing
handtoolsfor ESD
complianceis perfonnedusingthe CPM. This proccdureis an
acccptedstanclard
endorscdby the Intcrnalional
Elcctrotechnical
Commission(IEC) [3]. A similarmcthocllbr
thc testingof work surfacesis outlincdin an ESD Association
pr"rblication
[1]; thoughnot directlyrclaredto handtool
tcstingthc mcthodoutlinessimilaruseof a CPM
Figure6: Teslingof a handloolwilh a CPM
Two aspectsshouldbc considered;a)
the hand tool shouldbe testedfirst in its
stateof use,meaningit shouldnot bc
cleancdprior to testing,and b) the tool
shouldthcn be cleancdwith a 70 to
100%isopropylalcoholsolutionar.rd
retestcd.
By followingthis two-steptcsr
ploblemsattributabieto the
sequence,
build up of oils from the hand are
w w w .c o n f o r m i t v . c om
Addendum from TREK, INC.
Operator should verify correct operation / performance of selected
charged plate monitor prior to conducting any material or tool testing.
To verify correct operation refer to manufacturer's documentation and
recommendations.
Basic checks may include but are not limited to:
Capacitance verification of plate.
Plate voltage measurement should indicate potential on charged plate
is < 1100V
Verification that charged plate discharge current is less than 1.0 mA.
Method of discharge current verification:
Charge the plate to 1000V of either positive or negative polarity.
Measure the plate voltage with either a non-contacting electrostatic
voltmeter (ESVM) or an electrostatic field meter.
Next connect the low side of a DMM set as an ammeter to ground.
The ammeter shall have capability to measure in the 2.0mA range
with resolution within the uA range.
Set the DMM to the Min/Max function.
Connect the high side of the DMM to the charged plate to discharge
the plate through the ammeter.
Verify that the peak current does not exceed 1mA. A value higher
than 1mA peak indicates that a peak current higher than 1.0 mA has
passed through the device.
IEEE, IEC and other organizations state that the human perception
level of a DC current is 1.0 mA. Levels below 1.0 mA therefore
should not be noticeable to human touch.