Hot Bar Reflow

8/9/2019 Hot Bar Reflow

1/27

HOT BAR REFLOW

SOLDERINGFUNDAMENTALSA high quality Selective Soldering Technology


2/27

Content

1. HotBarReflowSolderingIntroduction

2. ApplicationRange

3. ProcessDescriptions

>FlextoPCB

>WiretoPCB

4. DesignGuidelines

5. Equipment6. TroubleshootingGuide

page35

page67

page813

page1422

page23

25

page2627


3/27

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


4/27

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


5/27

ThebenefitsofHotBarReflowSoldering

Suitableformassproduction

Reliableprocessing,

always

equal

process

conditions

Costeffectiveduetothefactthatnothirdcomponentisneededtoconnectflex/wiretothePCB/substrate(connectororACAcanbeavoided)

Multipleconnectionstobemadesimultaneously.Numberofleadsdependonproduct,pitch,design.

Fasttemperaturerampupandcooldown

Closedlooptemperatureandprocesscontrol.

Veryaccuratepositioningoftheparts

HBR

Introduction


6/27

HotBarReflowSolderingApplications

Flexto

Ceramic Component

to

PCB

FlextoPCB WiretoPCB

Application

Range


7/27

HotBarReflowSolderingApplications

FlextoPCB FlextoPCB

LeadframetoPCBWiretoPCB

Application

Range


8/27

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


9/27

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


10/27

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


11/27

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


12/27

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


13/27

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


14/27

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.


15/27

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


16/27

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


17/27

FlexandPCBdesign:ConnectionTypePolyimide flex types

Design

Guidelines


18/27

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


19/27

Designguidelines

TrackandgapofPCBshouldbeboth

50%

of

the

pitch

Trackoftheflexshouldbe80%ofthetrackofthePCB

this

allows

excessive

solder

to

flow

Flextracksshouldbeapprox.0,2mmshorterthanPCBtracks Visualinspectionpossible

Easyalignment

check

Allowexcessivesoldertoflow

Design

Guidelines


20/27

Designguidelines

Thicknessofpolyimideinsolder

areashould

be

as

thin

as

possible

Recommendeddiameterfor

locatingpinsshouldbeatleast1,5

mm

Locatingpinsshouldhavea

minimumdistanceof1,5mm

fromtheoutsidetracks

Design

Guidelines


21/27

Groundplanesand

throughholes

should

be

isolatedfromthetracks

withthermalneckswitha

lengthof2mmanda

widthassmallaspossible

Groundplanesinlayers

belowthesolderingarea

shouldbeminimizedin

sizeand

mass

Designguidelines

Design

Guidelines


22/27

SoldermustbepretinnedonPCBpriortoHotBarprocess

Startpointforscreenprintingisa150micronsthickstencilwithamaskopeningthatresultsina40%padcoverage.

(Afterreflow

oven

approx 40

%

of

thesolderpasteremains)

Forsmallpitchapplicationsitisrecommendedtopretintheparts

byelectro

plating

as

being

the

mostaccuratetechnology.

FlexandPCBdesigns:pretinning

Design

Guidelines


23/27

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.


24/27

MIYACHIEAPRO

Reflow

Soldering

StandaloneSystems


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.


25/27

MIYACHIEAPROReflowSolderingModules


MIYACHIEAPROprovidesarangeof HotBarModulessuitableforyourspecificapplication,suchasBonding

Headsin

different

sizes

and

forces,

adjustable

Thermo

plane

Thermodes,

Interposer

Modules,

Calibration

Toolsandprocessmonitoringtools.ContactourSalesDepartmentformoreinformation.


26/27

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


27/27

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

Documents

Hot Bar Reflow