Dragon Group China Bird AC-5K User manual
龙集团 DragonGroup China Limited
BIRD
www.dragongroupchina.com
www.chinaemall.biz
BGAReworkStation AC-5K
DragonGroup ChinaLimited
Address: Fuxin BuildingOffice12DNo.318 FuhuaRoadShenzhen,
China.518000
Telephone: (86)1 379 836 8284 (86)755 83292149 Fax (86)75583292149
Http ://www.dragongroupchina.com www.chinaemall.biz
龙集团 DragonGroup China Limited
BIRD
www.dragongroupchina.com
www.chinaemall.biz
A. BGAReworkStation
1. KnowledgeaboutBGA
BGA isshortfor Ball GridArray.Itisakind of packagemethod whichuseorganic
carrier in IC. Ithasthefollowingfeatures:
Small packagearea.
②Greater functionsand morepins.
③Self-centerizewhile PCB puddle welding, easyto puton tin.
④Morereliable.
⑤Good conductivityand lowoverall cost.
MemorywhichappliesBGA canenlargethememorycapacityby2to3timeswhile the
volume ofmemoryremainsthesame.ComparedwithTSOP,BGA ismuchsmallerand
better atradiatingand conductingelectricity.
2. TypesandFeaturesofBGA
a. Types
Accordingto theencapsulation material,BGA can beclassified into thefollowingtypes:
(1)PBGA（Plastic BGA）
(2)CBGA（CeramicBGA）
(3)CCBGA（CeramicColumn BGA）
(4)TBGA（TapeBGA）
(5)CSP (Chip ScalePackageor MBGA)
b. Features
Compared with QFP, BGA hasthefollowingfeatures:
(1) I/Oterminal spaceisbig(eg.1.0mm, 1.27mm,1.5mm),anditcan accommodatemore
I/O.
(2) Morereliable package,lowrateofweldingdefectsand weldingspotdurable.
(3) Paraposition ofQFPisusuallyobservedwithnakedeyes.Whenthepinspaceis
smallerthan0.4mm,itishard toparapositionandweld. WhilethepinspaceofBGA is
bigger, byapplyingtheparaposition-amplificationdevice,itiseasytoparapositionand
weld.
(4) TheweldingcoplanarityofBGAisbetterthanQFP,becausesoldercanmakeup the
flat error between BGA and PCB after melting.
龙集团 DragonGroup China Limited
BIRD
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(5)Good electricalproperty.Thepinsaresmall,theselfinductanceand mutualinductance
oftheconductivityislow, and thefrequencycharacteristicisgood.
(6)Thetension betweensolderpointsproducesgood self-centrationeffect in
solder-reflow, allowing5% error ofpatch precision.
(7)Compatible withoriginal SMTmounttechnologyand machines.Theoriginal screen
printermachine,mounterand solder-reflowmachineall canbeused. Thecomparison
betweenBGA and QFPisshowninTable1. ThemaindefectofBGA isthenecessityof
X-raydetection after welding.
c.WeldingofBGA
Thesuccess ofweldingBGAisaffectedbytheassemblyofPCB. So3keyfactorsmust
beconsideredin thelayoutofPCB.
Features BGA QFP
PackagesizeS/m2525 1600
Pin space L/mm 1.27 0.50
fault rate ( 10-6/pcs）
0.60 100
(1)ThermalmanagementThermal managementmustbeconsideredwhenwedesignthe
assemblyofPCB. IfmanypiecesofBGA gatheron asmallareaofPCB, itwillcausethe
imbalanceofPCB inthereflowoven. IfmanybigpiecesofBGA gatheronacertainarea
ofPCB, longerheatingperiod willdamagesome oftheBGA.Theareaswithfewer
componentshavereachedtheweldingtemperature,whilethoseareaswithBGA arestill
inlowtemperature.Sotheweldingperiod isoverbeforetheflux paste withdraws from
theweldingspots, thustheremaybepoor solderingor no-meltingofweldingballs.
(2)Rabbet
Thedesignofrabbet on PCB shouldsticktorelevantstandardsstrictly.Anyrabbet
nearBGA weldingpadmustcoverthesoldermaskverywell.Ifnot,theextrawelding
paste will flowfromtheweldingpadtotherabbet,thenleadstoshortcircuit between
weldingpad and rabbetsnearby.
Thegeometricshapeand diameter ofweldingpad:
Thecompactness ofpinshasimmediate impact on thegeometric shapeand diameterof
weldingpad. Similarly,BGA hasdifferentsizes,shapesand complexity.Asthepackage
sizedecreases,thegeometricshapeanddiameteroftheweldingpadcallsfor higher
precision in detection.
龙集团 DragonGroup China Limited
BIRD
www.dragongroupchina.com
www.chinaemall.biz
3. Inspection standards ofBGA
For BGA assembledonPCB, inspection standardisaveryimportantissue.Before
BGA isappliedtothePCB, mostBGA manufacturersdon'tuseX-rayinprocess of
inspection. Instead,theyemploysome traditional methodstotestPCB, suchasautomatic
optical inspection, man-eyeinspection or on-linefunctiontest.However, thesemethods
can'tdetect theinvisibleproblemsveryexactly,suchaspoor soldering,coldweldingand
bridging.TheX-raycandiscovertheseproblemsveryefficiently.Atthesame time,it can
do livemonitoring,guaranteethequality,and realizethein-timefeedbackoftheprocess
control,
a. Evaluation ofX-ray
WhenBGA isfirstusedon BGA,X-raycanevaluate thesolder-reflowaccordingtothe
situation ofun-solder areaor areasaround it. Open-circuit, non-touchingand other similar
situationsshowthesolderpastehasnotreflowenough. Bridgingmayresultfromthefact
that thetemperatureistoohighfor thesoldertoliquefy.Sothesolderflows fromthepad
to theinterval betweenthem, causingshort-circuit.
Poor weldingshouldbeevaluatedobjectively:it isnotsoterrible; thekeypointisthatthe
weldingspotscanstill beweldedon thepad. Theideal situation isno poor welding.Poor
weldingmaybecaused bypollution or theuneven distribution offlux paste. What's more,
warped PCB mayalso lead to poor welding. Open-circuitweldingspotmayexist, too.
Thequantityand sizeofpoor weldingarethekeyfactorstodecidewhetherit will
beaccepted. Generallythesize ofsingle poorweldingshouldbeless than50% ofthe
solderball's diameter. If theballissurroundedbyreflowsolder, BGA isabletowork. It
isaverycriticalstandard.Theelectricalpropertiesmaymeet therequirementsbutthe
mechanicalstrength will beaffected.
PCB withBGA mustuseX-rayevaluation systemsthat candecern holesofless
than100 mdiameter. TheX-raymustbeable toobservefromtop-downandtilt.X-rays
isareliable guaranteeofsuccessfulBGA welding,
b. Proposed inspection criteria
Theinspectioncriteria will helpX-rayinspectionsystem confirmsometypical
weldingproblems,whichisrelatedwiththeuseofBGA device.Itincludesthefollowing
factors:
(1)Poor welding
Poor weldingresultsfromtheexpansion ofcompoundsinsolderduringtheheating
ofBGA.BGA withpoorweldingmaycausesomeproblemssuchasineffectiveness.The
inspection criteriasareasfollows:thesizeofsingle poor weldingshouldbenomorethan
20% ofthesolderball's diameter, withno single poor weldingon thesurface;ifmany
poor weldingmayexist,thetotalshouldbeno morethan20% ofthesolderball's
diameter.
(2)Desolderingspots
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