reballing process controls and cleanliness · reballing process controls and cleanliness ... o...
TRANSCRIPT
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com © 2004 – 2010
Reballing
Process Controls and Cleanliness
DfR Webinar – December 18, 2014
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Reballing is both ball removal and ball attach
o Ball removal melts off the pre-existing solder balls and prepares
the solder pads for new solder balls
o Ball attachment is the placement of new solder spheres on the
pads and reflowing them to form an intermetallic bond
o All reballers studied use comparable methods for ball attach
Introduction: Reballing Techniques
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Reballing Process Controls
o Five reballers employing distinct techniques were
audited during reballing of ball grid arrays
o Reballers identified as A, B, C, D, & E
o This presentation compares observed differences in
o Reballing techniques
o Control of ionic exposure
o Cleaning procedures
o Resulting differences in cleanliness of reballed components
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Test Vehicle Selection
o Two devices which each presented a
unique challenge to reballers
o Fine pitch, low mass
o Large plastic package
o Third component to study the impact of
reballing stresses on 1st level
interconnects1
o Flip chip
1J. Arnold et al, “Impact of Reprocessing Technique on First
Level Interconnects of Pb-Free to SnPb Reballed Area Array Flip
Chip Devices,” iMAPs Device Packaging Conference, 2014.
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Test Vehicle: Dummy CSP
o Fine pitch, low mass CSP
o 97 I/O, 0.4mm pitch
o 5mm square package,
3.2mm die
o Demands precise tooling
o Requires care in handling
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Test Vehicle: Dummy BGA
o Large plastic BGA
o 1156 I/O, 1.0mm pitch
o 35mm square package,
15.2mm die
o Susceptible to warpage
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o Vitesse VSC3312
crosspoint switch
o 196 I/O, 1.0mm pitch
o 15mm square package,
3mm die
Test Vehicle: Active Flip Chip
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o Eight (8) input pair
circuits
o Two 50Ω pull-up
resistors between true
and complement
o Manufacturer specifies
85Ω to 125Ω as
acceptable range
Test Vehicle: Active Flip Chip
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o All measurements for all components within 85Ω and 125Ω range in specification o Five (5)
components probed per population
o Eight (8) probe pairs per component
Results: Electrical Characterization
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Ball Removal Techniques: Melting and Wicking
o Manual
procedure
o Balls melted with
an iron
o Liquid solder
absorbed with
fluxed wick
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
o 1 or 2 passes with the iron
o Used by Reballers B & D
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Ball Removal Techniques: Dissolution in Molten Solder
o Automated
procedure
o SAC305 balls
melted off
package by
contact with SnPb
fountain
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
o Component contacts molten solder
at least twice
o Used by Reballers C & E
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Ball Removal Techniques: Dissolution in Molten Solder
o Automated
procedure
o SAC305 balls
melted off
package by
contact with SnPb
wave
o Hot air knife
leveling
o Reballer A
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
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X-Ray Images After Ball Removal
flip-chip x-ray image with examples of key
features indicated. Solder bumps (first level
interconnects) - yellow circles. Plated
through holes in component substrate - red
arrows. Solder pads from which balls have
been removed - blue dotted circles.
Dressed pads on flip chip; solder visible as radiopacity.
Dark pads on left image indicate thicker coverage than
faintly visible pads on right image.
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Ball Placement and Attachment
All reballers
surveyed
employed stencils
to align new
solder spheres
with dressed pads
Generic stencil and fixture
Ball placement techniques and tooling are
widely considered trade secrets
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Does reballing the second level interconnects (B) damage
first level interconnects (A)?
Focus
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o Upon receipt, components reflowed to simulate assembly
Sample Preparation
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o A contour plot is a graphic representation of the relationships among three numeric variables in two dimensions. Two variables are for X and Y axes, and a third variable Z is for contour levels. The contour levels are plotted as curves; the area between curves can be color coded to indicate interpolated values. (1)
o You can interactively identify, label, color, and move contour levels, and change the resolutions of rectangular grids to get better contouring quality and performance
o The plots on the next slide demonstrate that 95% of the time a resistance reading from the reballed population will overlap with that of the non-reballed population. Each plot indicates reballed and control populations of an I/O pair, and all the plots maintain the same behavior with 95% confidence.
1) SAS Institute Inc.,SAS/INSIGHT User’s Guide, Version 8, Cary, NC: SAS Institute Inc., 1999. 752 pp
What are Contour Plots
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Results: Electrical Characterization, cont.
Independence of A0-AN0 Resistance for Reballed Fl ip Chip Populations
Mean
Std
95.00 100.0096.00 97.00 98.00 99.000.00
2.50
0.50
1.00
1.50
2.00
Independence of A1-AN1 Resistance for Reballed Fl ip Chip Populations
Mean
Std
95.50 100.5096.50 97.50 98.50 99.500.00
2.50
0.50
1.00
1.50
2.00
Independence of A3-AN3 Resistance for Reballed Fl ip Chip Populations
Mean
Std
95.00 100.0096.00 97.00 98.00 99.000.00
2.50
0.50
1.00
1.50
2.00
Independence of A4-AN4 Resistance for Reballed Fl ip Chip Populations
Mean
Std
97.00 102.0098.00 99.00 100.00 101.000.00
2.50
0.50
1.00
1.50
2.00
Independence of A7-AN7 Resistance for Reballed Fl ip Chip Populations
Mean
Std
97.25 102.2598.25 99.25 100.25 101.250.00
2.50
0.50
1.00
1.50
2.00
Independence of A8-AN8 Resistance for Reballed Fl ip Chip Populations
Mean
Std
95.00 100.0096.00 97.00 98.00 99.000.00
2.50
0.50
1.00
1.50
2.00
Independence of A10-AN10 Resistance for Rebal led Fl ip Chip Populations
Mean
Std
95.50 100.5096.50 97.50 98.50 99.500.10
2.60
0.60
1.10
1.60
2.10
Independence of A11-AN11 Resistance for Rebal led Fl ip Chip Populations
Mean
Std
95.00 100.0096.00 97.00 98.00 99.000.00
2.50
0.50
1.00
1.50
2.00
o Contour plots demonstrate overlap between most populations o 95% confidence limit
o Reballer D may be distinguishable from Reballers A and B
o Not distinguishable from Reballers C, E, or control
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Tomographic acoustic micro-imaging (TAMI) performed
o One flip chip per population
o Focused on two interfaces
o Where C4 bumps adhere to pads on the die
o Where C4 bumps adhere to substrate
o No observed gaps, voids, or delamination on reballed or control
components
Results: Scanning Acoustic Microscopy (SAM)
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Results: TAMI-SAM, Die to Bump Interface
A B C
Contr
ol
E D
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
o Computed tomography generates a 3-D model from a
series of x-ray slices
o One flip chip per population
o No cracks or defects observed on reballed or control components
o Some voiding observed at bump to substrate interface
Results: X-ray Computed Tomography (CT)
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o Slices through C4 bumps near substrate provide a
snapshot of voiding in the first level interconnects
o Images were threshold corrected in ImageJ
o Enables estimation of percent voiding
Results: CT, Void Measurement
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o No industry standard for voiding in C4 bumps
o IPC-A-610E allows for 25% voiding in solder balls
o Voiding was well below 25% for all reballers and control
Results: CT, Measured Voiding in C4 Bumps
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BUT WERE THEY CLEAN!!
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handlin
g
Sources of Contamination
Contamination
Flux from ball removal
Flux from ball attach
Handling
Rinse water
During cleaning following ball
removal and ball attach
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal flux
flux
rinse
rinse
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Contamination: Ball Removal Flux
Reballers use flux over surface of BGA
Manual processes brush on
Robotic processes dip
flux
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Ball Removal Flux
IPC J-STD-004
Designator
Flux
Composition
Flux/Flux Residue
Activity Levels Halides
Reballer A ORH1 Organic High Yes
Reballer B ORH0 Organic High No
Reballer C ORH1 Organic High Yes
Reballer D ORH1 Organic High Yes
Reballer E ORM1 Organic Medium Yes
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Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
Reballers use either
tacky flux or solder
paste for ball attach
Solder paste
Squeegeed to pads
through stencil
Tacky flux
Applied over whole surface
of BGA
flux
Contamination: Ball Placement Flux
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Ball Attach Flux
IPC J-STD-004
Designator
Flux
Composition
Flux/Flux Residue
Activity Levels Halides Stencil
Reballer A ORH1 Organic High Yes Yes
Reballer B ORH0 Organic High No No
Reballer C RMA Rosin Moderate ? No
Reballer D RMA-RA Rosin-Resin Moderate-High ? Yes
Reballer E REL0 Resin Low No Yes
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Contamination: Handling
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
ha
nd
ling
o Most reballers
take
precautions to
avoid handling
contamination
o There are
exceptions
Reballer C
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Contamination: Cleaning After Ball Removal
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
o Contamination can be introduced
without proper process controls
o Deionization of
rinse water
o Fresh solvent rinse
Reballer D
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o Same sources as cleaning after ball removal
Contamination: Cleaning After Ball Attach
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
Fagor FI-120W Door Style Dishwasher, Reballer E
rinse
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Cleaning
Performed
Following ball removal
Following ball attach
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
wash
wash
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Cleaning Techniques: Wipe
Manually with isopropyl alcohol
Lintless wipe (i.e. Kimwipe)
Brush
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
wash
wash
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Cleaning Techniques: Rinse
Spray wash with warm deionized water
Automated technique
Spray
“Swish”
May or may not include a detergent
Requires a bakeout
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
wash
wash
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Cleaning: Post Ball Removal
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
wash
Cleaning agent Manner Cleaning Motion Temperature
Reballer A IPA manual wipe room
Reballer B
(time sensitive)IPA manual wipe room
Reballer B
(time insensitive)DI H2O manual wipe warm
Reballer C
(large batch)DI H2O automated spray warm
Reballer C
(small batch)IPA manual brush room
IPA manual wipe room
DI H2O, detergent automated rinse, spray warm
Reballer E DI H2O automated swish warm
Post Solder Sphere Removal
Reballer D
(all devices
cleaned twice)
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Cleaning: Post Ball Attach
Device
needs
reballing
Ball
placement
Ball attach
Reballing
complete
Ball
removal Ball
removal Ball
removal
wash
Cleaning agent Manner Cleaning Motion Temperature
Reballer A DI H2O automated rinse, spray warm
Reballer B
(time sensitive)IPA manual wipe room
Reballer B
(time insensitive)DI H2O manual wipe warm
Reballer C IPA manual brush room
Reballer D DI H2O, detergent automated rinse, spray warm
Reballer E DI H2O, detergent automated spray warm
Post Ball Attach
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Cleanliness: Ion Chromatography
Metrohm Modular Ion
Chromatography System
IPC-TM-650, 2.3.28
Includes ionic extraction in
diluted isopropanol at 80°C
for 1 hour
Volume of extract limited by size of component
Avoids over-dilution of sample material
CSPs yielded sufficient extract to measure anions
BGAs yielded sufficient extract to measure anions and weak
organic acids
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Component Cleanliness: CSP
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Component Cleanliness: CSP
(μg/in2) Br- Cl- F- NO3- NO2
- PO43- SO4
2-
Reballer A - 8.07 - 6.08 - - 1.67
Reballer B - 4.18 - 7.37 - - 7.30
Reballer C - 5.04 - 9.56 - - 4.25
Reballer D - 3.27 - 10.37 - - 10.05
Reballer E - 3.55 - 7.66 - - 7.07
Upper Control
Limit 10 2 1 4 4 4 4
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Component Cleanliness: BGA
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Component Cleanliness: BGA
(μg/in2) Br- Cl- F- NO3- NO2
- PO43- SO4
2- WOA
Reballer A - 5.80 - 0.51 0.40 - - 19.30
Reballer B 6.50 1.90 - 0.57 - - 0.42 21.36
Reballer C 1.81 1.27 - - - - 0.06 24.91
Reballer D - 2.30 0.84 - - - 0.10 35.09
Reballer E 1.18 0.63 - 0.49 0.46 - 0.42 6.13
Upper
Control Limit 10 2 1 4 4 4 4 50
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Sources of Contaminants: Chloride (Cl-)
o Incompletely deionized rinse water
o Added to municipal water to control bacterial growth
o Unprotected handling
o Flux residue
o Non “halide-free” fluxes only
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Sources of Contaminants: Nitrate (NO3-)
o Incompletely deionized rinse water
o Ammonium nitrate and urea fertilizer run-off
o Manufacturing residue
o Substrate etched with ammonium nitrate
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Sources of Contaminants: Sulfate (SO42-)
o Incompletely deionized rinse water
o Acid rain
o Manufacturing residue
o Substrate etched with sodium or ammonium persulfate
o Solder mask
o Contact with paper, plastic, or rubber
o Sulfur a part of, or added to, many materials
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Conclusions
o Undesirable concentrations of halides were measured on
final reballed components from all studied suppliers
o Flux selection correlates best to ionic contamination
o Consistent with chloride as most common contaminating species
o Consistent with use of halide containing fluxes
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CSP Cleanliness and Flux
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BGA Cleanliness and Flux
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Conclusions, cont.
o Reballers with poor handling control do not exhibit most
elevated contamination
o Reballers with poor control over cleaning procedures do
not exhibit most elevated contamination
o Cleaning technique appears to have little impact
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
CSP Cleanliness and Cleaning
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BGA Cleanliness and Cleaning
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Impact
o Contaminants present on reballed components will enter
assembly procedure
o Flux residues will have another opportunity to activate
o Cause of voiding in assembled joints
o X-ray inspection post-assembly revealed no voiding exceeding
IPC-A-610E (25%)
o Can be present as ionic contamination in final product
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Impact, cont.
o What’s most concerning is that reballers think they are
performing sufficient cleaning to remove ionic residues
o ROSE measurement of rinse water does not represent on-part
contamination
o Choose higher activity fluxes with false confidence
© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Acknowledgements
This work was supported by a Small Business Innovation
Research grant from the Office of the Secretary of
Defense.
The author also wishes to thank the participating
reballers for their warm welcome and insight into the
reballing process.