Transcript No Slide Title

with Reworkable Wafer-Level Underfill
Ken Gilleo - ET-Trends
David Blumel Alpha Metals
[email protected]
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Outline
• The Packaging Revolution
• Flip Chip vs. CSP
• Why Underfill?
• Classes of Underfill
• Final Generation FC; a CSP
• Conclusions
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smaller
faster
cheaper
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Is the KEY to
achieving:
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The
whose time already came!
Faster = more leads
“Can’t be solved by packaging evolution”
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n2 > 4n-4
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1960's
The Entire Packaging History
Hot for the 21st Century
FC-BGA
Flip Chip (C4)
Flip Chip
(re-Engineered)
Lead Frame
Chip-on-Board
SMT
Spider
TCP (TAB)
Feed-thru
mBGA
CSP/FC-BGA
Flip Chip Strip
SMT
Beam Lead Chip
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micro-SMT
• Perimeter Leads
Area Array
• Size: chip scale
• Packaging: minimal
• Packaging: post- and concurrent
• Paths/lead length: shorter
3
2
ULTIMATE
IC
SMT
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COB & TAB
DCA
1
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Translation:
IC to PCB
Perform ance
Enhancem ent
JOINING
WIRING
WIRING
DEVICE
DEVICE
Thermal
Management
Removability
Environmental
Protection
PROTECTION
Standardization
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The Original Flip Chip was a CSP
IBM
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FLIP CHIP 360o REVOLUTION
1963
1990’s
CSP
New bumps, organic
substrate
+
1964
Underfill
High lead, ceramic
substrate
CSP again
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Flip Chip Components
• Under Bump Metallization
• Bumps & bumping
• Joining materials & agents
• Assembly processes
• Underfill
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Bumping Methods
• Attach discrete spheres;
• Print joining mat's;
Au, Cu, Sn/Pb
Sn/Pb or Conductive Adhesive
metal vapor
• Vacuum deposit metal:
• Electrolytic plating;
Au, Cu, Sn/Pb, Ni (cost issue?)
• Electroless plating;
Au, Cu, Ni (NEWER)
• Fluid jet molten metal;
• Stud bump with;
• Material transfer;
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old, still alive
Sn/Pb (VERY NEW)
Sn/Pb, CU or Au (single chip)
Sn/Pb or Cond. Adhes.; paste or film
• Switch to organic substrate
– Causes large thermal mismatch
– Low reliability in thermocycle
• Mismatch must be addressed
– low CTE organic substrate
– columns instead of bumps
– non-fatiguing joints???
– mechanical coupling: chip-to-substrate
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Thermal Mismatch Kills Reliability
Heating
Cooling
CHIP
Sn/Pb
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UNDERFILL Mechanism
Y
Y
p
o
s
i
t
i
o
n
p
o
s
i
t
i
o
n
CTE in
Z-Direction
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CTE in
X-Y plane
Underfill: What You
• A real aggravation
• Added equipment
• Added floor space
• Added cost
• Reduced yield
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Underfill: What You
• Self-Dispensing
• Self-Fluxing
• No added equipment
• No added time required
• Cost-effective
• Reworkable
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Underfill Events
• “Underfill Effect” discovered: 1960’s
• Slow flow, slow cure the norm: early 1990’s
• Fast flow
(>2.5cm/min.),
30 min. cure: 1995
• Pre-dispense flux-fill R&D: mid-1990’s
• Snap flow
(>3 cm/min) /Snap
cure (5 min.): 1997
• Convert FC to SMT: 1998 - 1999
• Wafer-level: coming in 1999 - 2000
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Types of Underfill
APPLIED to
PHASE
PreDispensed
PostDispensed
Liquid
Available
NA
Solid
Available
NA
Liquid
NA
?
Solid
R&D
NA
Liquid
Available
Available
Solid
NA
NA
SUBSTRATE
Chip/Wafer
Chip & Substrate
Concurrently
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Capillary Type
(post dispensed)
• Flow rate is close to max.
• Cure time is close to min.
• Still adds
– equipment
– space
– time
– cost
• Result: FC = SMT
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Cure: min.
2000
UNDERFILL PRODUCTIVITY TIME
Year Cure Time
1994 1800 min.
1995
30
1996
15
1997
6
1998
4.5
1500
1000
500
0
1994
1995
1996
CureYear
Time in min.
1997
Sec.
flow
70
60
1998
UNDERFILL PRODUCTIVITY
Chronological Time vs. Flow Time
50
40
30
20
10
0
1994
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1995
1996
Flow time sec/2.5mm
1997
1998
Pre-Dispensed Liquid
• Process control is critical
• Requires dispenser/printer
• Solder reflow oven provides cure
• Enables FC = SMT
• Result: next generation underfill
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Pre-Dispensed
Flux/Underfill
Not Assembled
Post-Dispensed
Underfill
Pre-Assembled
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Pre-Dispense Solid on Substrate
• Film-on-PCB
– Special, expensive equipment
– Not an SMT process
– Doesn’t address underfill problems
An old
concept?
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Anisotropic Conductive Adhesive
ACA film has a built-in underfill and is
the 1st example of pre-dispensed solid
underfill.
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Pre-Dispense Solid on Chip
• Wafer-level applied
• Self-fluxing
• Dry solid
• Integral to Flip Chip
• True SMT process
• Transparent to assembler
• Can be reworkable
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Liquid polymer-based composition is coated onto Flip
Chips at wafer-level and then converted to a SOLID that:
(1) Permits a bumped wafer to be diced into Flip Chips.
(2) Provides flux for assembly.
(3) Liquefies to a thermoplastic underfill during reflow.
(4) Polymerizes and wets substrate during reflow step .
(5) Remains reworkable after reflow stage cure.
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Ramifications:
• FC becomes a std. SMT process.
• FC becomes CSP if reworkable.
• Underfill becomes a semiconductor process.
• The ready-to-bond FC becomes the most costeffective minimal package.
• Success can make this package the dominant
micropackage.
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Assembly Process
• Pick & Place FC from any format
• Reflow
• flux melts/activates
• underfill liquefies/wets
• solder melts/forms joint
• underfill solidifies
• Test
• Rework if required
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Solder joints form,
underfill properties
generated
T
E
M
P
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Melts; flux
activates, begins
to bond to
substrate
Flux has
deactivated,
material is now
an underfill
TIME in Solder Reflow Oven
Issues & Challenges
• Materials; single or multiple?
• Shelf life, what is required?
• What wafer Coating process?
• Dicing with polymer in place?
• Assembly
– voiding, filleting, adhesion
– process sensitivity
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FLIP CHIP
INTEGRTATED/FLUXFILL
Type 1 - Single material
converts from flux to
underfill during reflow
Solid Flux
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FLIP CHIP
INTEGTRATED FLUX/UNDERFILL
Type 2 - Two separate materials
Solid Thermoplastic
Underfill
Solid Flux
Many variations
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Status
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Technology
2-LAYER
1-LAYER
MATERIALS
complete
being optimized
WAFER COATING
being optimized
selection stage
DICING
Feasibility
confirmed
FC ASSEMBLY
confirmed
RELIABILITY
to be
determined
to be
determined
to be
determined
to be
determined
Phase 1 Test Platform
Transparent 12 mm x 12 mm Flip Chip Bonded
to Copper with single-layer Flux/Underfill by
running through an IR reflow oven at 220oC
Copper sheet
Purchased quartz FC with Sn/Pb bumps
Flux/underfill after heating
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Delco is not a
sponsor or
participant
Conclusions
• Today’s underfills impede FC
• FC = SMT: required for max. success
• Underfill can be a semicon process
• FC will become a CSP again
• Result: best micropackage solution
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The Ultimate
Micro Package
Everything should be made as simple as
possible but not simpler.
Albert Einstein
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Just add heat;
some assembly
required.