hot bar reflow
TRANSCRIPT
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HOT BAR REFLOW
SOLDERINGFUNDAMENTALSA high quality Selective Soldering Technology
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Content
1. HotBarReflowSolderingIntroduction
2. ApplicationRange
3. ProcessDescriptions
>FlextoPCB
>WiretoPCB
4. DesignGuidelines
5. Equipment6. TroubleshootingGuide
page35
page67
page813
page1422
page23
25
page2627
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WhatisHotBarReflowSoldering?
HEAT IS
CONDUCTED
FROM THE
THERMODE
TO THE
PARTS AND
SOLDER
THERMODE HOLDER
THERMODE
PCB
Pulsedheat Thermode (Hot
Bar)
soldering,
is
a
joiningtechnology wheretwopretinnedpartsare
heatedtothemeltingpointofthetin.Thejoining
technologyresultsinapermanentelectro
mechanicaljoint.
Therequiredprocessenergyissuppliedbya
thermode,alsoknowasaHotBar.Thisthermodeis
pressedontheupperparttotransferthethermal
energytobothparts.
Closedloopprocesscontrolisusedtocontrolthe
timetemperatureprofile.
HBRIntroduction
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Howdoesitwork?
LoadPCBin
customizedfixture
Applynoncleanflux
onpads
Loadandposition
Flexon
the
PCB
Startsoldering
process
Thermodemoves
downonthesolderingarea
Uniflowheatsupthe
thermodeto
preheat
temperaturetoactivateflux
Afterapresettime
uniflowramps
up
to
thereflowtemperature
Thereflow
temp
is
keptontemperatureforapresettime
Thermodecoolsdowntothecool
temperature
thermodemovesupfromthesoldering
area
HotBarsolderingprocessiscompleted
HBRIntroduction
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ThebenefitsofHotBarReflowSoldering
Suitableformassproduction
Reliableprocessing,
always
equal
process
conditions
Costeffectiveduetothefactthatnothirdcomponentisneededtoconnectflex/wiretothePCB/substrate(connectororACAcanbeavoided)
Multipleconnectionstobemadesimultaneously.Numberofleadsdependonproduct,pitch,design.
Fasttemperaturerampupandcooldown
Closedlooptemperatureandprocesscontrol.
Veryaccuratepositioningoftheparts
HBR
Introduction
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HotBarReflowSolderingApplications
Flexto
Ceramic Component
to
PCB
FlextoPCB WiretoPCB
Application
Range
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HotBarReflowSolderingApplications
FlextoPCB FlextoPCB
LeadframetoPCBWiretoPCB
Application
Range
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ProcessDescription:
Preparation
InpreparationfortheHotBarReflowsolderingprocess,thefollowingpreparationstepsneed
tobetaken:
1.The
base
substrate
is
located
in
afixture,
and
flux
is
applied
to
the
pads.
2.Theflexispositionedinthepartsfixture,ensuringalignmentofboth
setsofpads.
3.Aprocessstartsignalisgiventothesolderingcontrolunit.
Moreinfoabouttheparts,thefixturesandthefluxingcanbefoundfurtherinthisarticle.The
HotBarReflowSolderingprocessitselfconsists
ofthefollowingprocesssteps:heatingup,reflowandcoolingdown.Theseprocessstepsare
describedinthenextsheets.
ProcessDescriptions
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ProcessDescription:Contacting
TheHotBarorthermodeismountedtoabondingheadby
means
of
a
quick
connect
block.
The
bonding
head
has
an
accurateandstablelinearguidanceforthethermode.
Movementisdonewithapneumaticcylinderoranelectrical
motor.Aninternalspringsystemgenerated anaccurateforce.
Mostreflowjointsofthisnaturerequirefewerthan100Newton
pressure.Forceshouldbe calibratedandsettothecorrectlevel
toachievetherighttransferofthermalenergytothesolder
joint.The
bonding
head
should
have
an
accurate
coplanarity
adjustmenttosettheflatnessofthethermodetotheproduct
accurately.Theseheadsaremodularinconstructionand
thereforeversatileforintegration.
Afterthestartsignalisgiven,thethermodeisgentlylowered
untilit
seats
on
the
product.
The
head
senses
this.
Force
is
build
upuntilthepresetforceisreached.Whentherightforceis
reached,asignalispassedtothepowersupply,whichstarts
heatinguptheHotBar.
ProcessDescriptions
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ProcessDescription:HeatingupBynow,theHotBarholdsdowntheproductwiththepresetforce.TheHotBarisatroomtemperature.The
soldercontrolunit,alsocalledSCUorpowersupplyhasreceivedthesstartsignalforthesoldering
process.
TheSCUsendscurrentthroughtheHotBar.TheHotBarisdesignedsothattheelectricalresistanceishighest
atthebottom(whereittouchestheproduct). Heatisgeneratedbecauseofthecombinationofcurrentand
electricalresistance.Asmallthermocouple isweldedonthefrontofthermocouple.Thisthermocouplefeeds
backtheactualHotBartemperaturetotheSCU.Thismakesacompleteclosedloopregulationforthe
temperaturetimecycle.
Normalrisetimeformostthermodes is1.5to2 seconds,
equalingaheating rateofabout200degreesCelsiusa
second.Thenewestgenerationofsoldercontrolunitis
controllingthetemperatureallthewaythroughtheheating
upphase.WhentheREFLOWtemperatureisnearlyreached
thesolder
control
unit
needs
to
slow
down
the
heating
rate
to
preventatemperatureovershoot.Agoodsoldercontrolunit
andHotBarcombinationwillcompensateforalldifferencesin
heatloadsthatcanoccurduringnormalproduction
circumstances.
ProcessDescriptions
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ProcessDescription:Reflow
Duringthereflowperiodthefluxisactivated,theflux
cleansthesurfacesandthesolderisheated untilitstarts
meltingonall
pads.
This
normally
takes
38seconds,
at
HotBartemperaturesaround300C(HotBartouchesthe
leads),400C(HotBartoucheskapton)or500C(ceramics
andMCPCBsoldering).Althoughnormalsolderwillmelt
at180C,idealsoldertemperatureisabove220Ctogeta
goodflowingandwettingbehaviorbutbelow280Cto
preventburningofthesolder.TheHotBarmustbeset
higherduetothethermaltransferlosses.Ideally,timecan
be programmedontheSCUin0.1sec.incrementsand
temperatureinonedegreeincrements.Usetheminimum
timeandtemperaturetoachievethedesiredjointto
minimizethepartsexposuretoheatandchanceof
damage.
ProcessDescriptions
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ProcessDescription:Cooling
Whenthesolderisconnectedonallpads,theenergy
deliverytotheHotBarcanbestopped.TheHotBarwill
startcooling
down.
The
cooling
process
can
be
shortened
by
theuseofforcedaircooling.TheSCUcanswitcharelaythat
controlstheflowofairattheendofthereflowperiodand
coolthejointandHotBarrapidly.Foroptimumprocess
control,coolingisdonetoaspecifictemperature.This
temperatureissetbelowthe soldersolidification
temperature.Therefore,assoonasthesolderbecomes
solid,theprocessisendedandajointisformed.Because
mostconnectionshavearelativelyhighheatsink,the
temperatureinthesolderislowerthanthemeasuredHot
Bartemperature,evenwhenusingforcedaircooling.
Therefore,thereleasetemperaturecanbesetto180Cin
mostcaseswithoutthechanceofreleasingthepartsbefore
solidificationhas
taken
place.
ProcessDescriptions
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ProcessDescription:QualityControlQualitycontrolbefore startingtheprocessisdoneby:
TheMiyachiEurope forcemeasurementkit,whichcontainsaprecisionloadcellwithalarge
contactareatosupporttheThermoplane Thermodeandacontrolpanelincludingareadout
display.
TheMiyachiEurope pressuresensitivepaper,especiallydesignedtooptimizetheplanarityofthe
Thermoplane Thermodeincombinationwiththeproduct.Puttingitinbetweenthermodeand
productsupportwillresultinanaccuratereadoutofplanarity.
KnowingandunderstandingthetemperatureduringallthedifferentHotBarprocessesinsidethe
materialsisessentialforoptimalresults.Theeasytousehandheldtemperaturemetercanbeused
incombination
with
ultra
flat
thermocouples.
The
thermocouple
can
be
sandwiched
between
the
parts,andtheactualprocesstemperaturecanbemeasuredinsidetheconnection.The
thermocoupleisreusable.
Qualitycontrolduringtheentireprocesscycle
ThenewPremiumHotBarMonitoringsystemcombinesMIYACHIEAPROHotBarknowhowwith
MIYACHIPECOtechnicalexpertiseallinoneunit.TheMG3HotBarmeasuresforce,temperature,
timeand
displacement,
allowing
for
continuous
control
throughout
the
entire
process
cycle.
The
compactandflexiblesystemfeatureshighqualityHotBarconnectionsandhighthroughput,all
withinaneasilyadjustableframeconstruction.
Qualitycontrolafterthebondingcycle
UsingtheMG3forHotBar,featuringfullonscreen(SPC)statisticprocesscontrol.
ProcessDescriptions
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FlexDesign:ConnectionType
Design
Guidelines
Openwindowed
flex
design:
Thisdesignhasbothsidesofthepolyimide
materialremovedfromthejointareabuthas
supportfromtheremainingpolyimidematerial
onthesidesandalsoalongtheendofthetraces.
Thisdesigngivessomestrengthtotheassembly
and
is
resilient
to
harsher
handling.Asthetracesareexposed,thethermaltransfer
tothepartsisgoodandexcesssolderhasextra
spacetoflow.Thermodesizingiscriticalasit
mustfitintothewindowandallowspaceforthe
moltensoldertoflow.Thisdesignbehaves
similartotheexposedleaddesign.
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FlexDesign:ConnectionType
Singlesidedflexdesign:
Thisdesign
has
the
polyimide
removed
on
onesideonly.HeatisconductedfromtheHot
Barthroughthesolidpolyimidesurfacetothe
exposedtracesunderneath.Thepolyimide
conductsheatthroughtheinsulationtothe
exposedtracesandpadsonthePCB.The
polyimidethicknessinthejointareaislimited
toabout50microns,enablingconduction.Ifthepolyimidehastobeheated past400
425C,burningofpolyimideandHotBar
contaminationcanresult.Thisdesignisless
tolerantofexcesssolderonthePCBpads
becauselittleroomexistsforexcesstoflow.
Thesingle
sided
flex
is
most
suitable
for
small
pitches.Pitchesassmallas200micron,
arrangedinoneortworows,arepossible.
Design
Guidelines
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FlexDesign:ConnectionTypeExposedleadflexdesign:
Thisdesignhasbothsidesofthepolyimide
(kapton)materialremoved,leavingthetraces
freeof
insulation.
The
Hot
Bar
contacts
the
tracesdirectlyandconductsheattotheparts.If
thePCBpadsandHotBarfootprintaresized
correctly,thisdesignwillbemosttolerantto
excesssolderonthepads,assoldermayflow
intoopenareas.Duringtheprocess,solderwill
also
wet
to
the
top
of
the
trace.
Caution
must
be
exercisedinparthandlingasthetracesmaybe
easilybentordamaged.Becauseofthedirect
HotBartoleadcontact,thisdesign willhavelow
HotBartemperaturesandshortprocesstimes.
TheHotBarwillpollutewithfluxresidues,and
willrequirecleaning.Akaptonfeedermodule
(seethe
section
on
equipment)
will
solve
these
objections.
Design
Guidelines
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FlexandPCBdesign:ConnectionTypePolyimide flex types
Design
Guidelines
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PCB
track
design
recommendations: PCBtrackwidth:>150%ofwirediameter
PCBtracklength:>3mm
Minimumpitch(centrecentretrack):0.8mm
Minimumspacingbetweentracks:0.4mm
Wirerecommendations
Wirestrippedlengthminimum:PCBtracklength
Pretinningofparts
EstimatedpretinningheightonthePCBtracks:5080micron(eachreflowofsolderpaste)
Eachindividualwireinthecablemustbepretinnedtoenableasolidwirepriortothesolderprocess
WireandPCBdesign:ConnectionTypeForWirePCBsolderinguptothermodelengthof40mm
Design
Guidelines
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Designguidelines
TrackandgapofPCBshouldbeboth
50%
of
the
pitch
Trackoftheflexshouldbe80%ofthetrackofthePCB
this
allows
excessive
solder
to
flow
Flextracksshouldbeapprox.0,2mmshorterthanPCBtracks Visualinspectionpossible
Easyalignment
check
Allowexcessivesoldertoflow
Design
Guidelines
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Designguidelines
Thicknessofpolyimideinsolder
areashould
be
as
thin
as
possible
Recommendeddiameterfor
locatingpinsshouldbeatleast1,5
mm
Locatingpinsshouldhavea
minimumdistanceof1,5mm
fromtheoutsidetracks
Design
Guidelines
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Groundplanesand
throughholes
should
be
isolatedfromthetracks
withthermalneckswitha
lengthof2mmanda
widthassmallaspossible
Groundplanesinlayers
belowthesolderingarea
shouldbeminimizedin
sizeand
mass
Designguidelines
Design
Guidelines
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SoldermustbepretinnedonPCBpriortoHotBarprocess
Startpointforscreenprintingisa150micronsthickstencilwithamaskopeningthatresultsina40%padcoverage.
(Afterreflow
oven
approx 40
%
of
thesolderpasteremains)
Forsmallpitchapplicationsitisrecommendedtopretintheparts
byelectro
plating
as
being
the
mostaccuratetechnology.
FlexandPCBdesigns:pretinning
Design
Guidelines
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MIYACHIEAPRO
Reflow
Soldering
DesktopSystems
HotBarReflowSolderingEquipment
TheMiyachiEAPRODesktopSystemsarealineof(semi)automaticsystemsdevelopedforHotbarSoldering,HeatSeal
Bondingand
ACF
Laminating.
The
Desktop
Series
deliver
the
same
high
bonding
quality
as
the
larger
and
more
automated
systems.Forallproductionenvironmentswherelaborcostsareconservative,itoffersanidealpriceperformance
(throughput)ratio.ThesystemflexibilitymakesitalsoperfectlysuitableforR&Denvironmentsand
integrationinlargersystems.
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MIYACHIEAPRO
Reflow
Soldering
StandaloneSystems
HotBarReflowSolderingEquipment
MiyachiEurope
has
aproventrackrecordof
systemscompleted
successfullyasfullyor
semiautomatedunits.
MiyachiEurope
combinesknowledge
fromourinhousedesign
departmentwiththe
expertiseinourinhouse
applicationandresearch
labswhenscreeningthe
feasibilityofyour
application.
Enjoymaximum
process
stabilityandexcellent
reproducibilitywithour
reliableandproven
ReflowSoldering
systems.
Typical
examples
are
LCD
repairsystems,turntable
systemsforquality
connectionsbetween
PCBs,flexfoils,LCD's
andothercomponents
andfullyautomated
productionlines.
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MIYACHIEAPROReflowSolderingModules
HotBarReflowSolderingEquipment
MIYACHIEAPROprovidesarangeof HotBarModulessuitableforyourspecificapplication,suchasBonding
Headsin
different
sizes
and
forces,
adjustable
Thermo
plane
Thermodes,
Interposer
Modules,
Calibration
Toolsandprocessmonitoringtools.ContactourSalesDepartmentformoreinformation.
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HotBar
Reflow
Soldering
Troubleshooting
Guide
TroubleshootingGuide
Problem PossibleCauses PossibleRootCauses PossibleSolutions
Opensolderjoints Notenoughheatintheleads Toolowprocesstemperature IncreaseHotBartemperature
Theseopensolderjointscanbe: Increaseprocesstime
>random ImproveflatnessofHotBaralignment
>alwaysleftofright IncreaseHotBarwidth
>alwaysonespecificjoint Improvesupportonalljoints
>alljoints Reducesupportheatadsorbtion
>attheedgesorthecentre Reduceamountofflux
Theseallcanhavedifferentcauses. Increasefluxdryingtime
Pleaseconsultanexpertforthis. Differentheatabsorbtionperlead Improveproductdesign
Improvefixturedesign
Notenoughpressureontheleads Notenoughforce Increaseforce
ReduceHotBarwidth
Forcenotdistributedevenlyenough Improvesupportonalljoints
ImproveflatnessofHotBaralignment
Improveflatnessofpart
Improvethicknessevenessofpart
CleanHotBar
Surfacenotwettableenough Wrongflux Changetodifferenttypeofflux
Toolittleflux Increaseamountofflux
Fluxtooold Changetofresherflux
Fluxdispensedtoolongago Applyfluxagain
Fluxnotdistributedevenly Improvedistributionofflux
Fluxnotactivated Increasefluxactivationtime
Toomuchoxidation ReduceoxidationofleadsandPCB
WrongflexandPCBsurfaces Changetoothersurfacetreatments
Notenoughsolder Notenoughsolder Increaseamountofsolder
Improvesolderposition
Improvesoldershape
Gaptobebridgedtoolarge Improvesupportonalljoints
IncreaseHotBarwidth
IncreaseHotBarpressure
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Problem PossibleCauses PossibleRootCauses PossibleSolutions
Solderbridging Toomuchpressureonthelead Toomuchforce Reduceforce
Distributepressurebetteroveralljoints Improveflatness
ImproveHotBaralignment
Toomuchsolder Toomuchsolder Reduceamountofsolder
Changepositionofsolder
Changeshapeofsolder
Notenough
space
for
the
solder Reduce
Hot
Bar
width
IncreasebevelHotBar
Increaseflexibilityofflex
Isolationsurfacetoowettable Notenoughseperationroom Decreasepadwidth
Solderballing Toomuchvapourpressurefromflux Fluxnotdry Longertimeafterfluxdispensing
Longerupslope
Usefluxactivationstage
Toomuchflux Reduceamountofflux
Wrongflux Changetodifferenttypeofflux
Toomuch
solder
for
the
available
space Improve
available
space
Increase
pad
width
Increasepadlength
ReduceHotBarwidth
Increaseflexibilityofflex
Reduceamountofsolder Reduceamountofsolder
Changepositionofsolder
Changeshapeofsolder
Toomuchvapourpressurefrompolutions Removepolutions Cleanpartbeforeusage
Avoidpartpolution
Burning Toohigh
temperature Hot
Bar
too
hot Lower
Hot
Bar
temperature
IncreasewidthHotBar
Redcueprocesstime
Notenoughheatdissipation Increasepressure
Increaseflatness
Wrongmaterials Materialnottemperatureresistant Changematerials
Changetothinnermaterials
HotBar
Reflow
Soldering
Troubleshooting
Guide