kbg ken gilleo - et-trends david blumel alpha metals with reworkable wafer-level underfill...
TRANSCRIPT
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Ken Gilleo - ET-Trends David Blumel Alpha Metals
with Reworkable Wafer-Level Underfill
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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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smallersmallersmallersmaller
fasterfaster
cheapercheaper
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Is the KEY to achieving:
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Smaller
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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Flip Chip Strip
Spider
Chip-on-Board
BGA
Lead Frame
TCP (TAB)
(re-Engineered)
1960'sHot for the 21st Century
SMT
Flip Chip (C4)
micro-SMT
TB
GA
SM
T
Feed-thru
Beam Lead Chip
FC-BGA
CSP/FC-BGA
The Entire Packaging HistoryThe Entire Packaging History
Flip Chip
BGA
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• Perimeter Leads Area Array
• Size: chip scale
• Packaging: minimal
• Packaging: post- and concurrent
• Paths/lead length: shorter
SMT
3
COB & TAB
2
DCA
IC 1ULTIMATE
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Is Flip Chip a True PACKAGE?
Is Flip Chip a True PACKAGE?
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DEVICEDEVICE
JOIN
ING
JOIN
INGW
IRIN
GW
IRIN
G
PROTECTION
the
PerformanceEnhancement
Removability
ThermalManagement
Translation:IC to PCB
Standardization
EnvironmentalProtection
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IBM
The Original Flip Chip was a CSP
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FLIP CHIP 360o REVOLUTIONFLIP CHIP 360o REVOLUTION
1963
1964
1990’sCSP
High lead, ceramic substrate
New bumps, organicsubstrate
+Underfill
CSP again
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Flip Chip Components
• Under Bump Metallization
• Bumps & bumping
• Joining materials & agents
• Assembly processes
• Underfill
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metal vapor
Bumping Methods• Attach discrete spheres; Au, Cu, Sn/Pb
• Print joining mat's; Sn/Pb or Conductive Adhesive
• Vacuum deposit metal: old, still alive
• Electrolytic plating; Au, Cu, Sn/Pb, Ni (cost issue?)
• Electroless plating; Au, Cu, Ni (NEWER)
• Fluid jet molten metal; Sn/Pb (VERY NEW)
• Stud bump with; Sn/Pb, CU or Au (single chip)
• Material transfer; Sn/Pb or Cond. Adhes.; paste or film
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• 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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H e a t i n g C o o l i n g
Thermal Mismatch Kills Reliability
CHIP
Sn/Pb
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UNDERFILL Mechanism
Y
posi tion
cons
train
ed
Y
posi tion
CTE inZ-Direction
CTE inX-Y plane
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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
SUBSTRATE
Chip/Wafer
APPLIED to
Liquid Available
Solid
PHASEPre-
DispensedPost-
Dispensed
Chip & SubstrateConcurrently
Liquid
Solid
Liquid
Solid
Available
Available Available
NA
NA
NA
?
R & D NA
NANA
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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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1994 1995 1996 1997 1998
Year
0
500
1000
1500
2000
Cure Time in min.
UNDERFILL PRODUCTIVITY TIMECure: min.
Year Cure Time
1994 1800 min.1995 301996 151997 61998 4.5
Chronological Time vs. Flow Time
1994 1995 1996 1997 19980
10
20
30
40
50
60
70
Flow time sec/2.5mm
Sec.flow
UNDERFILL PRODUCTIVITY
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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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Not Assembled
Pre-Assembled
Pre-Dispensed
Post-Dispensed
UnderfillUnderfill
Flux/UnderfillFlux/Underfill
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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?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.
ACA film has a built-in underfill and is the 1st example of pre-dispensed solid underfill.
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• Wafer-level applied
• Self-fluxing
• Dry solid
• Integral to Flip Chip
• True SMT process
• Transparent to assembler
• Can be reworkable
Pre-Dispense Solid on Chip
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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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RamificationsRamifications:RamificationsRamifications:• FC becomes a std. SMT process.
• FC becomes CSP if reworkable.
• Underfill becomes a semiconductor process.
• The ready-to-bond FC becomes the most cost-
effective 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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TIME in Solder Reflow Oven
TEMP
Melts; flux activates, begins to bond to substrate
Melts; flux activates, begins to bond to substrate
Solder joints form, underfill properties generated
Solder joints form, underfill properties generated
Flux has deactivated, material is now an underfill
Flux has deactivated, material is now an underfill
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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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Solid Flux
FLIP CHIPINTEGRTATED/FLUXFILL
Type 1 - Single material converts from flux to
underfill during reflow
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FLIP CHIP INTEGTRATED FLUX/UNDERFILL
Solid Flux
Solid ThermoplasticUnderfill
Type 2 - Two separate materials
Many variationsMany variations
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Status
TechnologyTechnology 2-LAYER 1-LAYER
MATERIALS
WAFER COATING
DICING
FC ASSEMBLY
RELIABILITY
complete being optimized
selection stagebeing optimized
Feasibilityconfirmed
to bedetermined
confirmed
to bedetermined
to bedetermined
to bedetermined
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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
Delco is not a sponsor or participant
Delco is not a sponsor or participant
Copper sheet
Flux/underfill after heating
Purchased quartz FC with Sn/Pb bumps
Phase 1 Test Platform
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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 UltimateMicro Package
Everything should be made as simple as possible but not simpler.
Albert EinsteinJust add heat; some assembly required.
Just add heat; some assembly required.