lead-free and tin-lead rework development activities within the nemi

LEAD-FREE AND TIN-LEAD REWORK DEVELOPMENT ACTIVITIES
WITHIN 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.
ABSTRACT
With the upcoming European ROHS legislation and
other global movements to lead-free assembly, the
NEMI lead-free rework group investigated and
developed lead-free rework processes for medium to
high-end computer products. The work concentrated on
development of lead-free hot air convection rework for
PBGA, CBGA, and uBGA, and lead-free hand
soldering rework for TSOP and 2512 chip components
on 93mil and 135mil thick test vehicle boards. Leadfree and tin-lead rework profiles along with visual and
X-ray inspection will be presented and discussed.
The lead-free and tin-lead rework was completed
successfully and test boards were submitted for ATC
reliability testing for up to 6,000 cycles from 0°C to
100°C which is ongoing at this time.
INTRODUCTION
Numerous investigations have been performed on the
assembly of lead-free electrical components onto
printed circuit boards using lead-free soldering
materials. Few have explored the reworkability of these
lead-free assemblies. Array packages are one of the
more challenging types of components for rework. For
this work lead-free and tin-lead PBGA, uBGA and
CBGA component were evaluated. The rework process
included removal, site redressing, and part replacement
using hot air convection rework equipment. TSOP and
2512 chip rework components were also evaluated for
tin-lead and lead-free rework on the same boards. The
rework study was performed in two phases.
Phase one emphasized the development of the rework
profile. Both tin-lead and lead-free (SnAgCu)
assemblies on two relatively thick boards (93mil and
135mil) and two surface finishes (Electrolytic NiAu and
Immersion Silver) were evaluated. The rework profile
was developed with consideration of the component,
board, solder paste and standard specifications.
Phase two of the study used the profiles and parameters
developed in Phase 1 to rework test boards at uBGA,
PBGA, CBGA TSOP and 2512 chip locations. Both
reworked and first-pass “as-assembled” assemblies
were subjected to accelerated thermal cycling (from 0°C
to 100°C for 6,000 cycles). Results were compared.
J-STD-020B (Ref.1) required that the lead-free
soldering peak temperatures for large components (>
350Cumm package volume) stay below 245°C and
small components (<350Cumm package volume) stay
below 250°C. This experiment aimed to verify if the
developed rework profiles conformed to this standard.
EXPERIMENTAL
Board and Components Used and Rework Locations
Rework development was conducted on the NEMI
Payette reliability test vehicle. The board is shown in
Figures 1 (topside) and 2 (bottomside). Most of the
components reworked were on the topside. The
bottomside has one PBGA544 component and some
TSOP and 2512 chip components.
Board specifications are shown below:
High Temp Laminate FR4 (Tg: 170°C)
Surface Finish: Imm Ag and Electrolytic NiAu
Board Thickness: 0.093” and 0.135”
Board Dimension: 16.5” x 7.25”
Number of copper layers: 14
Component specifications are shown below:
PBGA544
1mm pitch, 35 x 35mm body size
Ball Alloy: 63Sn37Pb or SnAgCu
Board Location: U29 (Topside), U30 (Bottomside)
UBGA256
1mm pitch, 17mm x 17mm body size,
256 I/O uBGA (Plastic Overmold),
Ball Alloy: 63Sn37Pb or SnAgCu
Board Locations: U40 and U41 (Both Topside)
CBGA 937 I/O
10Sn90Pb alloy spheres
1mm pitch, 32.5 x 32.5 mm body size
4.33 mm thick (die & substrate)
Overall height (including balls) 5.14 mm
SnAgCu alloy spheres
1mm pitch, 32.5 x 32.5 mm package size
1.5 mm thick (substrate only)
Overall height (including balls) 2 mm
Board Locations: U27 and U28 (Both Topside)
The rework process, including component removal, site
redressing, paste deposition and new component
attachment, was evaluated on lead-free assemblies using
new process parameters (i.e. increased processing
temperatures).
Solder Paste Used for PBGA544 and uBGA256
Tin-Lead: (63Sn37Pb) 90wt% metal content
Lead-free: (Sn3.9Ag0.6Cu) 89.3wt% metal content
Solder Paste Type: No Clean, Type 3
Mini-Stencil used for uBGA256
Thickness: 6mils
Aperture opening: 20mil
Mini-stencil Printing on Component Sphere for
PBGA544
The mini-stencil was cleaned with alcohol and a lintfree wipe after every print to prevent solder paste
clogging. The paste volume used was 2493mils. The
paste volume to print on the ball spheres was based on
the ball diameter.
Solder Paste for Paste Dispense Process (In syringes)
for CBGA933:
63Sn37Pb: No-clean,
87% metal content
Type 4
Sn3.9Ag0.6Cu: No-clean
84% metal content
Type 3
Paste Deposition Equipment for CBGA:
Paste Dispensing System
Localized Hot Air Rework Convection Equipment
For BGA Components
Rework 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
Sn3.9Ag0.6Cu
No-clean cored wire for tin-lead: Sn37Pb
Liquid no-clean rework flux pen
rework:
Redressing Equipment:
Non-contact scavenger system (for CBGA and uBGA)
Manual Solder wick (for PBGA)
Thermocouple Attachment:
Type K Thermocouples – 36 Gauge
Thermally Conductive Adhesive
Kapton Tape (heat resistant tape)
Post Rework Analysis:
Electrical Resistance Measurement
X-Ray System
Visual Inspection
Temperature Profiling Criteria and Thermocouple
Locations
The tin-lead and lead-free rework thermal profiles had
to satisfy the J-STD-020B temperature requirements.
The temperature on the solder ball joint had to be high
enough to guarantee reflow while not exceeding the
maximum temperature allowed on the top of the
component The values for these requirements were
dependent on the solder paste alloy used and the alloy
spheres present on the component. Table 1 summarizes
the rework temperature profiling criteria.
Existing rework equipment used in tin-lead rework was
used for the lead-free rework with higher heater settings
developed to rework lead-free SnAgCu soldered
components.
Thermocouple Calibration and Setup
Prior to the development of any rework profile, the
thermocouples used had to be verified to ensure that
proper temperatures were recorded. A simple test was
performed using boiling water to verify that all
thermocouples used did not deviate more that +/-1°C
from 100°C.
Thermocouples were placed as shown in Figure 3a and
3b for all three types of BGA components.
Thermocouple locations 1 (TC1) and 2 (TC2) were
located on solder joints at the outer corners.
Thermocouple location 3 (TC3) was at the center solder
joint. TC4 and TC5 were attached to the board 150mils
from the package. TC6 was attached to the package top
and TC7 was attached to the package top corner edge.
Solder Wicking Redressing Process
PBGA544
A hand solder wicking method was used to clean and
flatten 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 CBGA933
For both uBGA and CBGA, a vacuum scavenging
system was used that sucked up the residual solder
leaving behind a semi-flat surface for solder print and
part placement. This tool used a nozzle which blowed
hot air to melt the solder while suction was applied by a
vacuum tube at the center of the nozzle. This procedure
was performed without contacting the board. The noncontact approach helped to minimize the potential of
pad damage during site redress.
Figure 4 shows a site with the uBGA removed without
any disturbance to the site and a site after performing
the site redress using the scavenger. It was noted that
for the lead-free operation, the scavenger filter was
more prone to clogging. It was estimated that the filter
would last about 30% longer in the case of tin-lead
solder before requiring cleaning as compared to the case
of lead-free solder redressing.
The choice of rework profile depends on the board
thickness and the type of solder alloy and component in
question.
Paste Printing Process
Three different paste printing techniques were used
depending on the preference of the individual rework
site for the component used.
PBGA544
For the PBGA544, paste was printed onto the
component spheres. Figures 5a thru 5h show the
PBGA544 solder paste printing method.
uBGA256
A mini-stencil operation was used to apply solder paste
to the board. A mini-steel blade was used to screen the
solder through the stencil. Figure 6 shows the
uBGA256 rework site before and after screen printing.
CBGA933
For the CBGA, the solder paste was deposited using a
Paste Dispensing System. The methodology of this
system was to dispense dot by dot a solder paste shot on
each pad of the array by the means of a solder paste
syringe and needle.
BGA Rework Process Verification
To reduce the temperature difference between the solder
joint and the top of the component, the topside of the
board was preheated to 150°C by using only the bottom
heaters before the top nozzle was engaged to finish the
remainder of the rework operation.
Multiple trials were performed before finalizing the
rework profiles. With the process developed and
defined, a sample rework operation was performed to
verify the three lead-free rework process steps (remove,
redress, and replace) for the PBGA, CBGA and uBGA
on a 135mil thick NEMI Payette test board.
The reworked PBGA, CBGA and uBGA used for the
verification process had resistance values of the
daisy–chained components measured which were within
the expected value and all reworked components
showed no defects during X-ray inspection. Based on
this, the reworked test boards were thermally and
mechanically tested.
TSOP and 2512 Chip Component Hand Soldering
Rework
For TSOP and 2512 chip components, assembled
components were removed using the Desolder Station.
The component removal locations were then cleaned
using solder wick and the solder station. New
components were then replaced using the supplied leadfree components and solder or tin-lead component and
solder. Reworked components were then inspected
under the microscope at 30X magnification. Electrical
resistance measurements were taken and they were
within the resistance values expected for the daisy
chained parts.
Results and Discussion
Board Profiling
PBGA544
The developed board rework profiles for the PBGA544
component at locations U29 (topside) and U30
(bottomside) for lead-free and tin-lead soldered boards
for both board thicknesses are shown in Tables 2 and 3.
Temperatures were measured on the component and at
the solder joint. Table 2 lists all of the critical lead-free
rework profile parameters and the targets.
All the PBGA package top edge temperature values
exceeded the target of 245°C and one center value was
also exceeded. Usually the component top edge
temperature is not measured. The time above liquidus
temperature of 217°C was near the top end of the target
on all the profiles and was slightly exceeded at the U29
location on the 135mil board for lead-free.
In addition bottomside component temperatures were
measured to see if bottomside PBGA544 component
reflowed during topside PBGA544 rework. The results
indicated the bottomside PBGA544 did not exceed the
lead-free SnAgCu solder melting point.
The SnPb PBGA544 critical rework profile parameters
and targets are listed in Table 3. Package temperature at
the edge of the PBGA top exceeded the target on a
couple of the measurements. The time above liquidus
temperature of 183°C was near the top end of the target
on all the profiles and was slightly exceeded at the U30
location on the 135mil board.
The bottomside tin-lead PBGA did not exceed 183°C
melting point during any of the tin-lead topside 544I/O
PBGA
package
rework
profiling.
The PBGA544 rework profiles for SnPb and SnAgCu
are shown in Figures 7 and 8 for the 135mil thick board.
The board temperatures at 150mils from the reworked
component was above the solder melting temperature in
all cases for tin-lead and lead-free SnAgCu rework.
uBGA256 Rework Profiles
All four rework profiles were created on the 93mil and
135mil thick boards, two for SnPb and two for leadfree. The rework reflow profile parameters are
summarized in Table 4 and were within the target
parameters listed. All top of package temperatures were
at or within the target temperatures for tin-lead and
lead-free processes. For the lead-free assemblies, the
bottom heater’s set-point was set higher to help bring
the solder joint temperature to the target condition and
to keep the top of the package at or below the 245°C
peak temperature target.
In general for the profiles developed, the rework
parameters were normally at the upper end of the target
parameters. The board temperature was also measured
and was typically near or over the melting point for the
tin-lead or lead-free SnAgCu solder alloy.
The board temperatures at 150mils from the component
were above the solder melting temperature in three out
of four cases.
The uBGA256 rework profiles for SnPb and SnAgCu
for 135mil thick boards are shown in Figures 9 and 10.
CBGA933
The results for the SnPb and SnAgCu CBGA rework
profiling on the 93mil and 135mil thick boards are
shown in Table 5.
As expected, the lead-free rework showed more
difficulties than the tin-lead rework process, in part due
to the more stringent temperature requirements for the
lead-free process. It was difficult trying to comply with
the standard J-STD 020B requirements while at the
same time maintaining the minimum solder joint
temperatures to guarantee solder joint reflow.
The temperatures at 150mils away from the reworked
component on the board were over the solder melting
point in most cases.
The CBGA933 SnPb and SnAgCu rework profiles on
135mil thick boards are shown in Figures 11 and 12.
The BGA type reworked components were visually
inspected and examined using 2-D X-Ray Inspection
a n d later subjected to continuity tests (electrical
resistance measurements). An example of the X-ray
image for a lead-free SnAgCu reworked CBGA is
shown in Figure 13. Visual solder joint inspection
images of SnPb versus SnAgCu reworked CBGA
components are shown in Figure 14.
TSOP and 2512 rework
TSOP and 2512 chip rework was evaluated on test
vehicles. During the initial assessments, there was no
difference in the use of SnAgCu versus Sn3.5Ag cored
wire for lead-free hand solder rework in terms of the
solder tip temperature used. The solder tip temperature
used for SnAgCu and Sn3.5Ag was up to 25°F higher
than SnPb to account for the increased melting
temperature of the lead-free solder. Sn3.9Ag0.6Cu
cored rework wire was used in the subsequent reworked
reliability test board builds.
For lead-free SnAgCu solder TSOP and 2512 rework,
the desolder station was set at 800°F to remove parts
from the board and the solder iron station was set at
750°F to reattach new parts to the boards. For tin-lead
solder TSOP and 2512 rework, the desolder station was
set at 750°F to remove parts from the board and the
solder iron station was set at 725° to 750°F to reattach
new parts to the boards. No real issues were
encountered during TSOP or 2512 chip rework with
lead-free or tin-lead solder.
CONCLUSION
For the PBGA544, the rework profiles stayed within all
of the targets. The overall tin-lead and lead-free rework
process for the PBGA544 component went very well on
both 93mil and 135mil thick NEMI Payette boards. No
problems were noticed with either board surface finish.
Rework profile time was around 6 minutes for SnPb
rework and 8 minutes for SnAgCu rework for 135mil
thick boards.
For the uBGA256, the rework profiles for SnPb and
SnAgCu were successfully used to rework various sets
of NEMI Payette assemblies. No major issues were
found for these reworked uBGAs. Rework profile time
was around 7 minutes for SnPb rework and 9 minutes
for SnAgCu rework for 135mil thick boards.
For the CBGA933, lead-free SnAgCu along with SnPb
CBGA rework was feasible. The time taken to preheat
the topside of the board to 150°C using only the bottom
preheat was fairly long. Rework profile time was
around 11 minutes for SnPb rework and 13 minutes for
SnAgCu rework for 135mil thick boards.
The increase in rework profile time for SnAgCu
compared with SnPb rework was due to the higher
times to reach the rework peak temperature for SnAgCu
rework due to its higher melting point and the need to
reach a higher topside board preheat temperature with
the bottomside heater before engaging the topside
nozzle.
For the TSOP and 2512 chip rework, the operators saw
no difference between soldering with lead-free versus
tin-lead soldered joints apart from a difference during
visual inspection, where the lead-free soldered joints
appeared more cratered and resembled what a ‘cold’
solder joint may look like during tin-lead soldering
while the tin-lead reworked joint appeared smooth and
shiny. This would need to be taken into consideration
during solder joint inspection training for lead-free.
Increased solder iron tip temperatures were needed for
lead-free rework, but these were not significantly
higher.
The temperatures in all cases conformed to J-STD-020B
but this work was done by some of the best rework
engineers in the industry with optimized rework
equipment and nozzles with the active support and codevelopment from the rework equipment suppliers. In
addition, rework profiling of thermocoupled boards was
conducted over a period of a few months, calibrating
thermocouples and taking the time to develop the best
rework profiles over multiple rework runs and
reverifying these rework runs. In production, it would
require hours or days to develop rework profiles and
only if a thermocoupled profile board was actually
available. It would be difficult to match this quality and
quantity of rework profiling optimization for the
industry in general.
Data from the rework project was supplied to the JSTD-020C standards committee and helped to
formulate the temperatures and conclusions developed
in this new standard (Ref.2). In recognition of the fact
that lead-free rework presented unique issues in terms
of reducing component top temperature, J-STD-020C
was adopted, which indicates that any size of lead-free
component that was not rated to 260°C based on its
package volume and thickness has to be tested by the
component supplier to at least one reflow pass at 260°C
peak to account for lead-free rework. This is shown in
Table 6 which compares the ‘old’ J-STD-020B with the
‘new’ J-STD-020C with the current JEITA standard for
lead-free component temperature testing.
The temperature measured on the board at 150mils from
the reworked component (PBGA, uBGA, CBGA) was
in many cases above the melting temperature of the
solder used on the board (tin-lead or lead-free SnAgCu).
Future Work
PBGA
The rework machine did an acceptable job of reworking
all of the tin-lead and lead-free SnAgCu boards, but the
time above liquidus was at the high end of the
specification. The bottom heater was often used to
create the rework profiles and subsequently took a
longer time to cool down. Higher bottom heater settings
reduced the amount of topside nozzle heat needed
which reduced the delta T between the solder joint and
the component top. This was also the case for the uBGA
and CBGA components.
uBGA
Future work would need to address higher bottom side
heating capabilities (as for PBGA and CBGA) and
improvements to the scavenger redressing device to
reduce increased clogging encountered for lead-free
SnAgCu compared to tin-lead solder.
CBGA
The rework system could be improved to accelerate the
board preheating stage. The system took too long to
reach the desired topside temperature of 150°C during
the NEMI Payette board rework for both 93 and 135mil
thick boards. Some improvements should be made to
the machine for better rework thermal performance and
control.
The paste dispensing system for the CBGA worked well
with tin-lead solder paste but it showed more issues
during the lead-free SnAgCu solder paste dispensing.
Improvement of the paste dispensing system would be
needed to better handle the different amount of solder
paste required in the paste dispense process for the new
collapsing Pb-free SnAgCu CBGAs.
ACKNOWLEDGEMENT
The authors would like to thank all the partners of the
NEMI rework sub-group for their advice and support.
Recommendations and support from the rework
machine manufacturers, solder paste suppliers and the
backup technical staff at the individual rework sites are
gratefully acknowledged. The authors would like to
acknowledge Terri Zee of Solectron Corp., Rich Parker
of Delphi, Jerry Gleason of Hewlett-Packard Corp. and
Ron Gedney of NEMI (National Electronics
Manufacturing Initiative) for critically reviewing this
paper.
REFERENCES
1. IPC/JEDEC J-STD-020B July 2002:
Moisture/Reflow Sensitivity Classification for
Nonhermetic Solid State Surface Mount
Devices.
2. IPC/JEDEC J-STD-020C July 2004:
Moisture/Reflow Sensitivity Classification for
Nonhermetic Solid State Surface Mount
Devices.
Table 1: Profile Parameters
Minimum temperature for solder ball
Maximum package temperature top center
Maximum temperature delta between solder ball thermocouples (corner to
center)
Temperature delta between lowest temperature solder ball and package top
Time above liquidus (seconds)
Heating rate (°C/second)
Cooling rate, machine dependent (to be monitored and reported)
Soak time (to be monitored and reported)/ sec
Sn37Pb
200°C
220°C
10°C
SnAgCu
230°C
245°C
10°C
15°C
45-90
0.5-2.5
15°C
45-90
0.5-2.5
120-183°C
150-217°C
Table 2 PBGA 544Lead-free Rework Parameters
Profile Parameters
Target
0.135”
0.135”
0.093”
U29
U30
U29
Minimum Temperature for >230°C
232.3°C
232.6°C
236.6°C
Solder Ball [°C]
Maximum
P a c k a g e 245°C
T: 245.1°C
T: 244.0°C
T: 244.5°C
Temperature [°C]
E: 246.7°C
E: 249.7°C
E: 245.1°C
Maximum Temperature Delta 10°C
6.2°C
4.7°C
4.8°C
Between Solder Ball TC
(_Tx-y) [°C]
Temperature Between Lowest 15°C
T: 12.8°C
T: 11.4°C
T: 8.5°C
Solder Ball & Package Top
E: 14.4°C
E: 17.1°C
E: 7.9°C
(_Tz) [°C]
Time Above Liquidus (TAL) 45-90sec
93.3sec
85.0 sec
88.0sec
[sec]
Heating Rate [°C/sec]
0.50.8°C/sec
0.8°C/sec
1.2°C/sec
2.5°C/sec
Cooling Rate [°C/sec
TBD
-0.7°C/sec
-0.8°C/sec
-1.1°C/sec
Soak Time (150-217°C) [sec] TBD
108.2sec
103.0sec
91.4sec
“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 Parameters
Profile Parameters
Target
0.135”
0.135”
0.093”
U29
U30
U29
Minimum Temperature for 200°C
200.5°C
203.8°C
203.3°C
Solder Ball [°C]
Maximum
P a c k a g e 220°C
T: 216.3°C
T: 217.2°C
T: 215.0°C
Temperature [°C]
E: 219.8°C
E: 225.0°C
E: 218.1°C
Maximum Temperature Delta 10°C
5.1°C
3.6°C
2.2°C
Between Solder Ball TC
(_Tx-y) [°C]
Temperature Between Lowest 20°C
T: 15.8°C
T: 13.5°C
T: 11.7°C
Solder Ball & Package Top
E: 19.3°C
E: 21.2°C
E: 14.8°C
(_Tz) [°C]
Time Above Liquidus (TAL) 45-90sec
84.9sec
90.6sec
83.8sec
[sec]
Heating Rate [°C/sec]
0.51.3°C/sec
1.1°C/sec
1.3°C/sec
2.5°C/sec
Cooling Rate [°C/sec
TBD
-1.0°C/sec
-0.9°C/sec
-1.0°C/sec
Soak Time (120-183°C) [sec] TBD
80.8sec
83.6 sec
90.0sec
“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.
0.093”
U30
234.1°C
T: 244.7°C
E: 248.5°C
3.9°C
T: 10.6°C
E: 14.4°C
74.9sec
1.1°C/sec
-1.1°C/sec
96.9sec
0.093”
U30
201.6°C
T: 216.5°C
E: 222.0°C
5.5°C
T: 14.9°C
E: 20.4°C
79.3sec
1.3°C/sec
-1.2°C/sec
86.6sec
Table 4 Rework Reflow Profile Parameters (uBGA256)
Bolded Temperatures and Times indicated a value above the target for the uBGA.
Target Parameters
Solder Ball Min. Temp (°C)
Package Max. Temp (°C)
Max. Temp. Delta Between Solder Ball TCs (°C)
Temp. Between Lowest Solder Ball and Pkg Top (°C)
Avg. Time over Liquidous (TAL) -sec
Avg Joint & Package Heating Rate (°C/sec)
Board Temp. 150mils Away from Comp. (°C)
Target
200
220
10
20
45 to 90
0.5 to 2.5
<183°C
SnPb
93mil
135mil
199
203
213
210
0
2
10
11
86.7
75
2.12
1.22
192
183
Target
230
245
10
15
45 to 90
0.5 to 2.5
<217°C
Lead-free SnAgCu
93mil
135mil
229
230
245
245
1
1
16
15
93.3
85.3
2.2
1.8
218
208
Table 5 Rework Reflow Profile Parameters (CBGA933)
Bolded Temperatures and Times indicated a value above the target for the CBGA.
Target Parameters
Solder Ball Min. Temp (°C)
Package Max. Temp (°C)
Avg. Time over Liquidous (TAL) for Solder Joint -sec
Avg. Time over Liquidous (TAL) for Package Top Center -sec
Board Temp. 150mils Away from Comp. (°C)
Target
200
220
45 to 90
<183°C
SnPb
93mil
135mil
199
201
201
202
69
75
74
74
184
206
Target
230
245
45 to 90
<217°C
Lead-free SnAgCu
93mil
135mil
239
235
239
238
59
66
64
71
257
212
Table 6 ‘Old’ J-STD020B compared with ‘New’ J-STD-020C versus Existing JEITA standard for lead-free
component temperature testing
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 from
the center.
Figure 14: Visual solder joint inspection images of SnPb (left) versus SnAgCu (right) reworked CBGA
components