1.0ScopeThismethodistocomparativelydeterminethe
effectsofprintedconductormaterials,conductorcrosssec-
tionalmeasurements,substratematerials,andprocesseson
thetemperatureD.C.currentcharacteristicsofprintedwiring
boardsonastandardtestsample.
Thetemperaturerisemustbegivenforeachconductormate-
rialsforaparticularvalueofcurrent,foraspecifiedconductor
crosssectionalarea,approximategeometryandsubstrate
material.Theresultsarereportedasaplotoftemperature
risesversuscurrentforeachoftheconductormaterials,cross
sectionalareas,approximategeometry,andasubstrate
material.
2.0ApplicableDocuments
ASTMB193ConductorMaterials,Electrical,Resistivityof
QQ-S-571Solder,TinAlloy,Tin-leadAlloy,andLeadAlloy
3.0TestSpecimensStandardtestspecimen,seeFigure1
TestPattern.Onlyonetestpatternmaybetestedatonetime,
withcurrentpassingthroughonlyoneconductoratonetime.
4.0Apparatus
4.1Potentiometer(0.02%orbetteraccuracy),Leedsand
NorthruptypeK3orequivalent.
4.2Resistors(0.1ohm±0.01ohm)(Caution:Donotuse
lowvoltagebecauseoffluctuation.)
4.3Currentleads,#12AWGstrandedwire.
4.4Potentialleads,#26AWGmagnetwire.
4.5Sn60,Sn62,orSn63solderperFederalSpecification
QQ-S-571.
4.6Temperaturechambercapableofmaintainingrequired
temperaturesinspecification.
4.7Thermometerorothertemperaturemeasuringdevice
suitableformeasuringlaboratoryambienttothenearest0.5°C
[0.9°F].
4.8Apparatusforperformingcrosssections.
4.9Apowersupplywithrangeofatleast0-40volts.
4.10DigitalMultimetercapableoftakingcurrentandvoltage
inspecification.
5.0Test
5.1Preparation
5.1.1Extraneoussurfacecoatingshallberemovedwithout
affectingthedimensionsoftheconductor.Thesampleshall
representthematerialsandprocessesunderinvestigation.
5.1.2Currentleadsshallbesecuredbysolderingtotheter-
minalarea.Pretinningofpartspriortosolderingisadvisable.
5.1.3Potentialleadsshallbesecuredtothetesttabsby
soldering.Pretinningofpartspriortosolderingisadvisable.
5.1.4Theambientairtemperaturemeasuredatapproxi-
mately101.6mm[4″]perpendicularlyfromthecenterofthe
conductorsideoftheboardshallbe25°±5°C[77°±9°F].
Thetemperatureshallberecordedateachmeasurement.
5.2Procedure
5.2.1ThetestsampleshowninFigure1shallbesuspended
bythefourcorners,andcentrallylocatedwithinanenclosure
freeofforcedairmovement.Thesampleshallbesooriented
thattheconductorsarehorizontal.
5.2.2Toachieve3-figuresignificanceintemperaturerise
measurements,allpotentialsshouldbemeasuredaccurately
tofoursignificantfigures.
5.2.3Theresistanceoftheconductoratthereferencetem-
perature(R
t
1
)shouldbedeterminedwithatestcurrentnotto
exceed100milliamperesappliedforasshortatimeaspos-
sible.(Caution:Donotuselowvoltagebecauseoffluctua-
tion.)
5.2.4Passtheconductorcurrentthroughanexternalseries
resistor(R
s
)havingamaximumtemperaturecoefficientof
resistanceof0.00002perdegreeCat25°C.Thefunctionof
TheInstituteforInterconnectingandPackagingElectronicCircuits
2215SandersRoad?Northbrook,IL60062
IPC-TM-650
TESTMETHODSMANUAL
Number
2.5.4.1
Subject
ConductorTemperatureRiseDuetoCurrent
ChangesinConductors
Date
8/97
Revision
A
OriginatingTaskGroup
N/A
MaterialinthisTestMethodsManualwasvoluntarilyestablishedbyTechnicalCommitteesoftheIPC.Thismaterialisadvisoryonly
anditsuseoradaptationisentirelyvoluntary.IPCdisclaimsallliabilityofanykindastotheuse,application,oradaptationofthis
material.Usersarealsowhollyresponsibleforprotectingthemselvesagainstallclaimsorliabilitiesforpatentinfringement.
EquipmentreferencedisfortheconvenienceoftheuseranddoesnotimplyendorsementbytheIPC.
Page1of3
thisresistoristoprovideareferenceformeasuringthecur-
rent.Itsvalueshouldbeofthesameorderofmagnitudeas
thatoftheconductorundertesttominimizescalechangesin
measurements.
5.2.5Measurementsatspecificcurrentsaretobemade
afterthermalstabilization.Theelapsedtimebetweenthese
twomeasurementsshouldbeassmallaspossible.
5.2.6Measurethevoltagedropsacrosstheexternalseries
resistorandthetestsectionofthecurrentcarryingconductor
(R).
5.3Evaluation
5.3.1Thevalueofthetemperaturecoefficientofresistance
(α)shallhavebeendeterminedandidentified.Temperature
coefficientsforvariouselectricalconductormaterialsaregiven
inAmericanSocietyforTestingMaterials-B193-65.
5.3.2Whenthetemperaturecoefficientofresistanceofthe
conductorisunknown,itmaybedeterminedbymeasuring
theresistanceoftheconductoratdifferentoventempera-
tures,andcalculatedbytheformula:
α
t
1
=
R
t
2
–R
t
1
R
t
1
(t
2
–t
1
)
andadjustedtothedesiredambienttemperatureby:
α
t
=
1
1
α
t
1
+(t–t
1
)
5.3.3Determinethecrosssectionalareaoftheconductor
undertestbyuseoftheformulaforvolumeresistivity.
p
v
=
A
L
R
wherep
v
=volumeresistivityinohm-circularmil/ft
A=crosssectionalareaincircularmils
L=gagelength,usedtodetermineRinfeet
R=measuredresistanceinohms(R
t
1
,see
calculations)
A=
p
v
L
R
wherep
v
=11,529ohmcirmil/ft@25°Cfor1/2oz.of
copper
=10.827ohmcirmil/ft@25°Cfor1oz.andover
L=0.5ft.(Fig.1-testpattern)
A=Areincirmils.
Ax0.7854=Areainsquaremils
5.4CalculationsThetemperatureriseofaconductoris
determinedbymeasuringthechangeinresistanceofthetest
lengthofconductorandusingtherelationship.
R
t
=R
t
1
[1+α
t
1
(t–t
1
)]
R
t
=Resistanceofconductoratthedesiredcurrent.
R
t
=Resistanceofconductoratreferencetemperature(t
1
).
α
t
1
=Temperaturecoefficientofresistanceofconductorat
referencetemperature(t
1
).
t
1
=Referencetemperature;thatambienttemperatureat
whichR
t1
wasmeasured.
Thefollowingrelationshipcanbederivedfromtheforegoing
usingvoltagedrops:
?
t
=
1
α
t
1
[
R
t
R
t
1
–1
]
R
t
=
E
R
t
R
S
E
S
t
?
t
=
1
α
t
1
[
R
R
1
E
S
t
R
S
R
t
1
–1
]
=
1
α
t
1
[
E
R
t
E
S
t
E
S
t
1
E
R
t
1
–1
]
E
R
t
=Voltagedropacrosstestconductoratthedesiredcur-
rent.
E
R
t
1
=Voltagedropacrosstestconductoratthereference
current.
E
S
t
=Voltagedropacrosstheexternalseriesresistoratthe
desiredcurrent.
E
S
t
1
=Voltagedropacrosstheexternalseriesresistoratthe
referencecurrent.
R
s
=Resistanceofexternalseriesresistor.
R
t
1
=Resistanceoftestconductoratthereferencetempera-
ture.Determinedbymeasuringvoltagedropwithless
than100mAcurrentpassingthroughconductorand
determinedfrom
R
t
1
=
E
R
t
1
l
1
wherei
1
=
E
S
t
1
R
S
IPC-TM-650
Number
2.5.4.1
Subject
ConductorTemperatureRiseDuetoCurrentChangesin
Conductors
Date
8/97
Revision
A
Page2of3
IPC-2541-1
Figure1TestPattern
IPC-2541-2
Figure2TestCircuit
IPC-TM-650
Number
2.5.4.1
Subject
ConductorTemperatureRiseDuetoCurrentChangesin
Conductors
Date
8/97
Revision
A
Page3of3
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