LEAD-FREE AND TIN-LEAD REWORK DEVELOPMENT ACTIVITIESWITHIN THE NEMI LEAD-FREE ASSEMBLY AND REWORK PROJECT

Jasbir Bath and Mike Wageman, Solectron Corporation;Quyen Chu and Nabel Ghalib, Jabil Circuits;

Alan Donaldson, Intel Corp.;Jose Matias and Eddie Hernandez, Hewlett-Packard Corp.

ABSTRACTWith the upcoming European ROHS legislation andother global movements to lead-free assembly, theNEMI lead-free rework group investigated anddeveloped lead-free rework processes for medium tohigh-end computer products. The work concentrated ondevelopment of lead-free hot air convection rework forPBGA, CBGA, and uBGA, and lead-free handsoldering rework for TSOP and 2512 chip componentson 93mil and 135mil thick test vehicle boards. Lead-free and tin-lead rework profiles along with visual andX-ray inspection will be presented and discussed.

The lead-free and tin-lead rework was completedsuccessfully and test boards were submitted for ATCreliability testing for up to 6,000 cycles from 0°C to100°C which is ongoing at this time.

INTRODUCTIONNumerous investigations have been performed on theassembly of lead-free electrical components ontoprinted circuit boards using lead-free solderingmaterials. Few have explored the reworkability of theselead-free assemblies. Array packages are one of themore challenging types of components for rework. Forthis work lead-free and tin-lead PBGA, uBGA andCBGA component were evaluated. The rework processincluded removal, site redressing, and part replacementusing hot air convection rework equipment. TSOP and2512 chip rework components were also evaluated fortin-lead and lead-free rework on the same boards. Therework study was performed in two phases.

Phase one emphasized the development of the reworkprofile. Both tin-lead and lead-free (SnAgCu)assemblies on two relatively thick boards (93mil and135mil) and two surface finishes (Electrolytic NiAu andImmersion Silver) were evaluated. The rework profilewas developed with consideration of the component,board, solder paste and standard specifications.

Phase two of the study used the profiles and parametersdeveloped in Phase 1 to rework test boards at uBGA,PBGA, CBGA TSOP and 2512 chip locations. Bothreworked and first-pass “as-assembled” assemblieswere subjected to accelerated thermal cycling (from 0°Cto 100°C for 6,000 cycles). Results were compared.

J-STD-020B (Ref.1) required that the lead-freesoldering peak temperatures for large components (>350Cumm package volume) stay below 245°C andsmall components (<350Cumm package volume) staybelow 250°C. This experiment aimed to verify if thedeveloped rework profiles conformed to this standard.

EXPERIMENTALBoard and Components Used and Rework LocationsRework development was conducted on the NEMIPayette reliability test vehicle. The board is shown inFigures 1 (topside) and 2 (bottomside). Most of thecomponents reworked were on the topside. Thebottomside has one PBGA544 component and someTSOP and 2512 chip components.

Board specifications are shown below:High Temp Laminate FR4 (Tg: 170°C)Surface Finish: Imm Ag and Electrolytic NiAuBoard Thickness: 0.093” and 0.135”Board Dimension: 16.5” x 7.25”Number of copper layers: 14

Component specifications are shown below:PBGA5441mm pitch, 35 x 35mm body sizeBall Alloy: 63Sn37Pb or SnAgCuBoard Location: U29 (Topside), U30 (Bottomside)

UBGA2561mm pitch, 17mm x 17mm body size,256 I/O uBGA (Plastic Overmold),Ball Alloy: 63Sn37Pb or SnAgCuBoard Locations: U40 and U41 (Both Topside)

CBGA 937 I/O10Sn90Pb alloy spheres1mm pitch, 32.5 x 32.5 mm body size4.33 mm thick (die & substrate)Overall height (including balls) 5.14 mm

SnAgCu alloy spheres1mm pitch, 32.5 x 32.5 mm package size1.5 mm thick (substrate only)Overall height (including balls) 2 mm

Board Locations: U27 and U28 (Both Topside)

The rework process, including component removal, siteredressing, paste deposition and new componentattachment, was evaluated on lead-free assemblies usingnew process parameters (i.e. increased processingtemperatures).

Solder Paste Used for PBGA544 and uBGA256Tin-Lead: (63Sn37Pb) 90wt% metal contentLead-free: (Sn3.9Ag0.6Cu) 89.3wt% metal contentSolder Paste Type: No Clean, Type 3

Mini-Stencil used for uBGA256Thickness: 6milsAperture opening: 20mil

Mini-stencil Printing on Component Sphere forPBGA544The mini-stencil was cleaned with alcohol and a lint-free wipe after every print to prevent solder pasteclogging. The paste volume used was 2493mils. Thepaste volume to print on the ball spheres was based onthe ball diameter.

Solder Paste for Paste Dispense Process (In syringes)for CBGA933:63Sn37Pb: No-clean,87% metal contentType 4

Sn3.9Ag0.6Cu: No-clean84% metal contentType 3

Paste Deposition Equipment for CBGA:Paste Dispensing System

Localized Hot Air Rework Convection EquipmentFor BGA ComponentsRework Atmosphere: Air (for CBGA and PBGA)Rework Atmosphere: N2 (for uBGA)

Rework Equipment for TSOP and 2512 Chip:Hand soldering iron and desolder station

No-clean cored wire for lead-free rework:Sn3.9Ag0.6CuNo-clean cored wire for tin-lead: Sn37PbLiquid no-clean rework flux pen

Redressing Equipment:Non-contact scavenger system (for CBGA and uBGA)Manual Solder wick (for PBGA)

Thermocouple Attachment:Type K Thermocouples – 36 GaugeThermally Conductive AdhesiveKapton Tape (heat resistant tape)

Post Rework Analysis:

Electrical Resistance MeasurementX-Ray SystemVisual Inspection

Temperature Profiling Criteria and ThermocoupleLocationsThe tin-lead and lead-free rework thermal profiles hadto satisfy the J-STD-020B temperature requirements.The temperature on the solder ball joint had to be highenough to guarantee reflow while not exceeding themaximum temperature allowed on the top of thecomponent The values for these requirements weredependent on the solder paste alloy used and the alloyspheres present on the component. Table 1 summarizesthe rework temperature profiling criteria.

Existing rework equipment used in tin-lead rework wasused for the lead-free rework with higher heater settingsdeveloped to rework lead-free SnAgCu solderedcomponents.

Thermocouple Calibration and SetupPrior to the development of any rework profile, thethermocouples used had to be verified to ensure thatproper temperatures were recorded. A simple test wasperformed using boiling water to verify that allthermocouples used did not deviate more that +/-1°Cfrom 100°C.

Thermocouples were placed as shown in Figure 3a and3b for all three types of BGA components.Thermocouple locations 1 (TC1) and 2 (TC2) werelocated on solder joints at the outer corners.Thermocouple location 3 (TC3) was at the center solderjoint. TC4 and TC5 were attached to the board 150milsfrom the package. TC6 was attached to the package topand TC7 was attached to the package top corner edge.

Solder Wicking Redressing ProcessPBGA544A hand solder wicking method was used to clean andflatten excess solder on all the pads after part removal.Additional flux was put on before the wicking process.A no-clean flux pen was used for this process.

UBGA256 and CBGA933For both uBGA and CBGA, a vacuum scavengingsystem was used that sucked up the residual solderleaving behind a semi-flat surface for solder print andpart placement. This tool used a nozzle which blowedhot air to melt the solder while suction was applied by avacuum tube at the center of the nozzle. This procedurewas performed without contacting the board. The non-contact approach helped to minimize the potential ofpad damage during site redress.

Figure 4 shows a site with the uBGA removed withoutany disturbance to the site and a site after performingthe site redress using the scavenger. It was noted that

for the lead-free operation, the scavenger filter wasmore prone to clogging. It was estimated that the filterwould last about 30% longer in the case of tin-leadsolder before requiring cleaning as compared to the caseof lead-free solder redressing.

The choice of rework profile depends on the boardthickness and the type of solder alloy and component inquestion.

Paste Printing ProcessThree different paste printing techniques were useddepending on the preference of the individual reworksite for the component used.

PBGA544For the PBGA544, paste was printed onto thecomponent spheres. Figures 5a thru 5h show thePBGA544 solder paste printing method.

uBGA256

A mini-stencil operation was used to apply solder pasteto the board. A mini-steel blade was used to screen thesolder through the stencil. Figure 6 shows theuBGA256 rework site before and after screen printing.

CBGA933

For the CBGA, the solder paste was deposited using aPaste Dispensing System. The methodology of thissystem was to dispense dot by dot a solder paste shot oneach pad of the array by the means of a solder pastesyringe and needle.

BGA Rework Process Verification

To reduce the temperature difference between the solderjoint and the top of the component, the topside of theboard was preheated to 150°C by using only the bottomheaters before the top nozzle was engaged to finish theremainder of the rework operation.

Multiple trials were performed before finalizing therework profiles. With the process developed anddefined, a sample rework operation was performed toverify the three lead-free rework process steps (remove,redress, and replace) for the PBGA, CBGA and uBGAon a 135mil thick NEMI Payette test board.

The reworked PBGA, CBGA and uBGA used for theverification process had resistance values of thedaisy–chained components measured which were withinthe expected value and all reworked componentsshowed no defects during X-ray inspection. Based onthis, the reworked test boards were thermally andmechanically tested.

TSOP and 2512 Chip Component Hand SolderingReworkFor TSOP and 2512 chip components, assembledcomponents were removed using the Desolder Station.The component removal locations were then cleanedusing solder wick and the solder station. Newcomponents were then replaced using the supplied lead-free components and solder or tin-lead component andsolder. Reworked components were then inspectedunder the microscope at 30X magnification. Electricalresistance measurements were taken and they werewithin the resistance values expected for the daisychained parts.

Results and DiscussionBoard ProfilingPBGA544The developed board rework profiles for the PBGA544component at locations U29 (topside) and U30(bottomside) for lead-free and tin-lead soldered boardsfor both board thicknesses are shown in Tables 2 and 3.Temperatures were measured on the component and atthe solder joint. Table 2 lists all of the critical lead-freerework profile parameters and the targets.

All the PBGA package top edge temperature valuesexceeded the target of 245°C and one center value wasalso exceeded. Usually the component top edgetemperature is not measured. The time above liquidustemperature of 217°C was near the top end of the targeton all the profiles and was slightly exceeded at the U29location on the 135mil board for lead-free.

In addition bottomside component temperatures weremeasured to see if bottomside PBGA544 componentreflowed during topside PBGA544 rework. The resultsindicated the bottomside PBGA544 did not exceed thelead-free SnAgCu solder melting point.

The SnPb PBGA544 critical rework profile parametersand targets are listed in Table 3. Package temperature atthe edge of the PBGA top exceeded the target on acouple of the measurements. The time above liquidustemperature of 183°C was near the top end of the targeton all the profiles and was slightly exceeded at the U30location on the 135mil board.

The bottomside tin-lead PBGA did not exceed 183°Cmelting point during any of the tin-lead topside 544I/OP B G A p a c k a g e r e w o r k p r o f i l i n g .

The PBGA544 rework profiles for SnPb and SnAgCuare shown in Figures 7 and 8 for the 135mil thick board.The board temperatures at 150mils from the reworkedcomponent was above the solder melting temperature inall cases for tin-lead and lead-free SnAgCu rework.

uBGA256 Rework Profiles

All four rework profiles were created on the 93mil and135mil thick boards, two for SnPb and two for lead-free. The rework reflow profile parameters aresummarized in Table 4 and were within the targetparameters listed. All top of package temperatures wereat or within the target temperatures for tin-lead andlead-free processes. For the lead-free assemblies, thebottom heater’s set-point was set higher to help bringthe solder joint temperature to the target condition andto keep the top of the package at or below the 245°Cpeak temperature target.

In general for the profiles developed, the reworkparameters were normally at the upper end of the targetparameters. The board temperature was also measuredand was typically near or over the melting point for thetin-lead or lead-free SnAgCu solder alloy.

The board temperatures at 150mils from the componentwere above the solder melting temperature in three outof four cases.

The uBGA256 rework profiles for SnPb and SnAgCufor 135mil thick boards are shown in Figures 9 and 10.

CBGA933The results for the SnPb and SnAgCu CBGA reworkprofiling on the 93mil and 135mil thick boards areshown in Table 5.

As expected, the lead-free rework showed moredifficulties than the tin-lead rework process, in part dueto the more stringent temperature requirements for thelead-free process. It was difficult trying to comply withthe standard J-STD 020B requirements while at thesame time maintaining the minimum solder jointtemperatures to guarantee solder joint reflow.

The temperatures at 150mils away from the reworkedcomponent on the board were over the solder meltingpoint in most cases.

The CBGA933 SnPb and SnAgCu rework profiles on135mil thick boards are shown in Figures 11 and 12.

The BGA type reworked components were visuallyinspected and examined using 2-D X-Ray Inspectiona n d later subjected to continuity tests (electricalresistance measurements). An example of the X-rayimage for a lead-free SnAgCu reworked CBGA isshown in Figure 13. Visual solder joint inspectionimages of SnPb versus SnAgCu reworked CBGAcomponents are shown in Figure 14.

TSOP and 2512 reworkTSOP and 2512 chip rework was evaluated on testvehicles. During the initial assessments, there was nodifference in the use of SnAgCu versus Sn3.5Ag coredwire for lead-free hand solder rework in terms of thesolder tip temperature used. The solder tip temperatureused for SnAgCu and Sn3.5Ag was up to 25°F higherthan SnPb to account for the increased meltingtemperature of the lead-free solder. Sn3.9Ag0.6Cucored rework wire was used in the subsequent reworkedreliability test board builds.

For lead-free SnAgCu solder TSOP and 2512 rework,the desolder station was set at 800°F to remove partsfrom the board and the solder iron station was set at750°F to reattach new parts to the boards. For tin-leadsolder TSOP and 2512 rework, the desolder station wasset at 750°F to remove parts from the board and thesolder iron station was set at 725° to 750°F to reattachnew parts to the boards. No real issues wereencountered during TSOP or 2512 chip rework withlead-free or tin-lead solder.

CONCLUSIONFor the PBGA544, the rework profiles stayed within allof the targets. The overall tin-lead and lead-free reworkprocess for the PBGA544 component went very well onboth 93mil and 135mil thick NEMI Payette boards. Noproblems were noticed with either board surface finish.Rework profile time was around 6 minutes for SnPbrework and 8 minutes for SnAgCu rework for 135milthick boards.

For the uBGA256, the rework profiles for SnPb andSnAgCu were successfully used to rework various setsof NEMI Payette assemblies. No major issues werefound for these reworked uBGAs. Rework profile timewas around 7 minutes for SnPb rework and 9 minutesfor SnAgCu rework for 135mil thick boards.

For the CBGA933, lead-free SnAgCu along with SnPbCBGA rework was feasible. The time taken to preheatthe topside of the board to 150°C using only the bottompreheat was fairly long. Rework profile time wasaround 11 minutes for SnPb rework and 13 minutes forSnAgCu rework for 135mil thick boards.

The increase in rework profile time for SnAgCucompared with SnPb rework was due to the highertimes to reach the rework peak temperature for SnAgCurework due to its higher melting point and the need toreach a higher topside board preheat temperature withthe bottomside heater before engaging the topsidenozzle.

For the TSOP and 2512 chip rework, the operators sawno difference between soldering with lead-free versustin-lead soldered joints apart from a difference duringvisual inspection, where the lead-free soldered joints

appeared more cratered and resembled what a ‘cold’solder joint may look like during tin-lead solderingwhile the tin-lead reworked joint appeared smooth andshiny. This would need to be taken into considerationduring solder joint inspection training for lead-free.Increased solder iron tip temperatures were needed forlead-free rework, but these were not significantlyhigher.

The temperatures in all cases conformed to J-STD-020Bbut this work was done by some of the best reworkengineers in the industry with optimized reworkequipment and nozzles with the active support and co-development from the rework equipment suppliers. Inaddition, rework profiling of thermocoupled boards wasconducted over a period of a few months, calibratingthermocouples and taking the time to develop the bestrework profiles over multiple rework runs andreverifying these rework runs. In production, it wouldrequire hours or days to develop rework profiles andonly if a thermocoupled profile board was actuallyavailable. It would be difficult to match this quality andquantity of rework profiling optimization for theindustry in general.

Data from the rework project was supplied to the J-STD-020C standards committee and helped toformulate the temperatures and conclusions developedin this new standard (Ref.2). In recognition of the factthat lead-free rework presented unique issues in termsof reducing component top temperature, J-STD-020Cwas adopted, which indicates that any size of lead-freecomponent that was not rated to 260°C based on itspackage volume and thickness has to be tested by thecomponent supplier to at least one reflow pass at 260°Cpeak to account for lead-free rework. This is shown inTable 6 which compares the ‘old’ J-STD-020B with the‘new’ J-STD-020C with the current JEITA standard forlead-free component temperature testing.

The temperature measured on the board at 150mils fromthe reworked component (PBGA, uBGA, CBGA) wasin many cases above the melting temperature of thesolder used on the board (tin-lead or lead-free SnAgCu).

Future WorkPBGAThe rework machine did an acceptable job of reworkingall of the tin-lead and lead-free SnAgCu boards, but thetime above liquidus was at the high end of thespecification. The bottom heater was often used tocreate the rework profiles and subsequently took alonger time to cool down. Higher bottom heater settingsreduced the amount of topside nozzle heat neededwhich reduced the delta T between the solder joint andthe component top. This was also the case for the uBGAand CBGA components.

uBGA

Future work would need to address higher bottom sideheating capabilities (as for PBGA and CBGA) andimprovements to the scavenger redressing device toreduce increased clogging encountered for lead-freeSnAgCu compared to tin-lead solder.

CBGAThe rework system could be improved to accelerate theboard preheating stage. The system took too long toreach the desired topside temperature of 150°C duringthe NEMI Payette board rework for both 93 and 135milthick boards. Some improvements should be made tothe machine for better rework thermal performance andcontrol.

The paste dispensing system for the CBGA worked wellwith tin-lead solder paste but it showed more issuesduring the lead-free SnAgCu solder paste dispensing.Improvement of the paste dispensing system would beneeded to better handle the different amount of solderpaste required in the paste dispense process for the newcollapsing Pb-free SnAgCu CBGAs.

ACKNOWLEDGEMENTThe authors would like to thank all the partners of theNEMI rework sub-group for their advice and support.Recommendations and support from the reworkmachine manufacturers, solder paste suppliers and thebackup technical staff at the individual rework sites aregratefully acknowledged. The authors would like toacknowledge Terri Zee of Solectron Corp., Rich Parkerof Delphi, Jerry Gleason of Hewlett-Packard Corp. andRon Gedney of NEMI (National ElectronicsManufacturing Initiative) for critically reviewing thispaper.

REFERENCES1. IPC/JEDEC J-STD-020B July 2002:

Moisture/Reflow Sensitivity Classification forNonhermetic Solid State Surface MountDevices.

2. IPC/JEDEC J-STD-020C July 2004:Moisture/Reflow Sensitivity Classification forNonhermetic Solid State Surface MountDevices.

Table 1: Profile ParametersSn37Pb SnAgCu

Minimum temperature for solder ball 200°C 230°CMaximum package temperature top center 220°C 245°CMaximum temperature delta between solder ball thermocouples (corner tocenter)

10°C 10°C

Temperature delta between lowest temperature solder ball and package top 15°C 15°CTime above liquidus (seconds) 45-90 45-90Heating rate (°C/second) 0.5-2.5 0.5-2.5Cooling rate, machine dependent (to be monitored and reported)Soak time (to be monitored and reported)/ sec 120-183°C 150-217°C

Table 2 PBGA 544Lead-free Rework ParametersProfile Parameters Target 0.135”

U290.135”U30

0.093”U29

0.093”U30

Minimum Temperature forSolder Ball [°C]

>230°C 232.3°C 232.6°C 236.6°C 234.1°C

M a x i m u m P a c k a g eTemperature [°C]

245°C T: 245.1°CE: 246.7°C

T: 244.0°CE: 249.7°C

T: 244.5°CE: 245.1°C

T: 244.7°CE: 248.5°C

Maximum Temperature DeltaBetween Solder Ball TC(_Tx-y) [°C]

10°C 6.2°C 4.7°C 4.8°C 3.9°C

Temperature Between LowestSolder Ball & Package Top(_Tz) [°C]

15°C T: 12.8°CE: 14.4°C

T: 11.4°CE: 17.1°C

T: 8.5°CE: 7.9°C

T: 10.6°CE: 14.4°C

Time Above Liquidus (TAL)[sec]

45-90sec 93.3sec 85.0 sec 88.0sec 74.9sec

Heating Rate [°C/sec] 0.5-2.5°C/sec

0.8°C/sec 0.8°C/sec 1.2°C/sec 1.1°C/sec

Cooling Rate [°C/sec TBD -0.7°C/sec -0.8°C/sec -1.1°C/sec -1.1°C/secSoak Time (150-217°C) [sec] TBD 108.2sec 103.0sec 91.4sec 96.9sec“T” indicates top center of the component (TC6).“E” indicates the edge of the component top (TC7).Bolded Temperatures and Times indicated a value above the target.Table 3 SnPb PBGA 544 Rework Profile ParametersProfile Parameters Target 0.135”

U290.135”U30

0.093”U29

0.093”U30

Minimum Temperature forSolder Ball [°C]

200°C 200.5°C 203.8°C 203.3°C 201.6°C

M a x i m u m P a c k a g eTemperature [°C]

220°C T: 216.3°CE: 219.8°C

T: 217.2°CE: 225.0°C

T: 215.0°CE: 218.1°C

T: 216.5°CE: 222.0°C

Maximum Temperature DeltaBetween Solder Ball TC(_Tx-y) [°C]

10°C 5.1°C 3.6°C 2.2°C 5.5°C

Temperature Between LowestSolder Ball & Package Top(_Tz) [°C]

20°C T: 15.8°CE: 19.3°C

T: 13.5°CE: 21.2°C

T: 11.7°CE: 14.8°C

T: 14.9°CE: 20.4°C

Time Above Liquidus (TAL)[sec]

45-90sec 84.9sec 90.6sec 83.8sec 79.3sec

Heating Rate [°C/sec] 0.5-2.5°C/sec

1.3°C/sec 1.1°C/sec 1.3°C/sec 1.3°C/sec

Cooling Rate [°C/sec TBD -1.0°C/sec -0.9°C/sec -1.0°C/sec -1.2°C/secSoak Time (120-183°C) [sec] TBD 80.8sec 83.6 sec 90.0sec 86.6sec“T” indicates top of the component (TC6).“E” indicates the edge of the component (TC7).Bolded Temperatures and Times indicated a value above the target for the PBGA.

Table 4 Rework Reflow Profile Parameters (uBGA256)

Bolded Temperatures and Times indicated a value above the target for the uBGA.

Table 5 Rework Reflow Profile Parameters (CBGA933)

Bolded Temperatures and Times indicated a value above the target for the CBGA.

Table 6 ‘Old’ J-STD020B compared with ‘New’ J-STD-020C versus Existing JEITA standard for lead-freecomponent temperature testing

Target Parameters Target Target93mil 135mil 93mil 135mil

Solder Ball Min. Temp (°C) 200 203 199 230 230 229Package Max. Temp (°C) 220 213 210 245 245 245Max. Temp. Delta Between Solder Ball TCs (°C) 10 0 2 10 1 1Temp. Between Lowest Solder Ball and Pkg Top (°C) 20 10 11 15 15 16Avg. Time over Liquidous (TAL) -sec 45 to 90 86.7 75 45 to 90 93.3 85.3Avg Joint & Package Heating Rate (°C/sec) 0.5 to 2.5 2.12 1.22 0.5 to 2.5 2.2 1.8Board Temp. 150mils Away from Comp. (°C) <183°C 192 183 <217°C 208 218

SnPb Lead-free SnAgCu

Target Parameters Target Target93mil 135mil 93mil 135mil

Solder Ball Min. Temp (°C) 200 199 201 230 239 235Package Max. Temp (°C) 220 201 202 245 239 238Avg. Time over Liquidous (TAL) for Solder Joint -sec 45 to 90 69 75 45 to 90 59 66Avg. Time over Liquidous (TAL) for Package Top Center -sec 74 74 64 71Board Temp. 150mils Away from Comp. (°C) <183°C 184 206 <217°C 257 212

SnPb Lead-free SnAgCu

Figure 1 Primary Board Side (Top)

Figure 2 Secondary Board Side (Bottom)

Figure 3a Thermocouple Locations 1-3

Figure 3b Thermocouple Locations 4-7

Figure 4 uBGA Site Before and After Redressing

Figures 5a thru 5h shows the PBGA544 solder paste printing method

Figure 6 uBGA Site Before and After Screen Printing

Figure 7: PBGA544 SnPb rework profile for the 135mil thick board.

Figure 8: PBGA544 SnAgCu rework profile for the 135mil thick board.

Figure 9: uBGA256 SnPb rework profile for the 135mil thick board.

Figure 10: uBGA544 SnAgCu rework profile for the 135mil thick board.

Figure 11: CBGA933 SnPb rework profile for the 135mil thick board (Temp {°C} versus Time {sec}).

Figure 12: CBGA933 SnAgCu rework profile for the 135mil thick board(Temp {°C} versus Time {sec}).

Figure 13: SnAgCu CBGA933 X-Ray Image After Rework**Note: Corner joints which show a slightly bigger diameter is actually a visual distortion due to its distance fromthe center.

Figure 14: Visual solder joint inspection images of SnPb (left) versus SnAgCu (right) reworked CBGAcomponents