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IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 1
Overview
How To Peel Ultra Thin Dies From Wafer Tapep
Stefan Behler, Besi Switzerland [email protected]
Stefan Behler, Besi Switzerland AG
Overview
How To Peel Ultra Thin Dies From Wafer Tapep
Introduction: 4 key properties Multidisc Die Ejector FEA Model
1. Wafer foil bulk peel force2. Wafer foil edge peel force
d
Stefan Behler, Besi Switzerland AG
3. Bending stress: ejector types, FEA simualtions, comparison
4. Die strength: overview, examples
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 2
Four Key Properties
• handling thin dies with carrier foils is still state of the art• typical die bonder data sheet specification:
«min. die thickness 20 m»
(3) die bending stress
wafer foil (2) edge peel force
(4) die strength
die
• this specification is too simple!
ejectorsystem
(1) bulk peel force
ejector discs at different heightsvacuum holes
Multidisc Die Ejector
5B
3B
4B
7B
1
2B
3B
2F
5F
…
6B
6F
7F
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 3
Multidisc Die Ejector: Disc Move
¼ of a die
Multidisc Die Ejector: Die Peeling Simulation
pre‐defined geometries, pseudo‐dynamic8um peel/step (47steps)disc height 300umcolor code: bending stress
¼ of a die
color code: bending stressz‐axis 4X
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
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Die attach film adhesivepeel front
overhang
peeled length
FEA Model: Geometry
silicon die
waferfoil
h0vacuum
h
peel speed model
disc move
disc height peel length
L1t1
time
h1
1. run simulation for static geometry
FEA Model: Dynamics
L1
simulation G
L2 = L1 + L1
t1
t2
simulation G
L3 = L2 + L2t3
h1
h2
h3
E
DG Z
2
2
2. convert stress at peel front to peel energy G (D = adhesive thickness, E = adhesive modulus)
3. convert peel energy to peel speed
h4
simulation G
L4 = L3 + L3t4
… etc.
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 5
Four Key Properties
Introduction: 4 key properties Multidisc Die Ejector FEA Model
1. Wafer foil bulk 2. Wafer edge peel force
d3. Bending stress: ejector types, FEA simualtions, comparison
4. Die strength: overview, examples
1. Wafer foil «bulk» peel force | data sheets
Label Foil Type Peel speed[mm/s]
Peel energy[J/m2]
15
peel speed
peel energy
[J/m2][mm/s] [J/m ]
A Lintec LE4728
UV 5.0 2.0
B Hitachi HR Series
UV 1.0 0.43
C Ablestik ATB-100US1
UV 1.7 5.2
D NittoEM-310J-P
UV 5.0 4.8
- Nitto non-UV
5.0 70.0
5
10
A
C D
peel speed
model for FEA (*)
[J/m ]
SWT-20P+ UV
)cos1( b
Fenergypeel
* approximates trend in data from Saiki et al, Tokoyo Institute of Technology
00.1 1.0 10.0 100.0
A
peel speed [mm/s]
B
peel force peel angle
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 6
2. Wafer foil «edge» peel force
• adhesion at die edge (point load)
• typical range 0.1 … 1.5 N
• must be < 0.3 N for thin dies
example: step cut
• value depends on dicing method
• can be reduced by step cut, DBG, ..
2. Wafer foil «edge» peel force
• single cut shows 2x higher edge peelforce due to local heating by blade
• Hitachi HR-9070-GT1
(A) single cut
(B) DBG, DAF laser cut
1 mm
e P
eel F
orce
[N
]
0.2
0.4
0.6
0.8
Edg
e
0.0100 300 100 300
(A) single cut (B) DBG
UV dosage [mJ/cm2]
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
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3. Bending Stress | Ejector types
Multi Stage Multi Disc Multi Needle
3. Bending Stress | 2D FEA models
die wafer foil
vacuum
disc 1disc 2
stage 1stage 2ejector surface
Multi Stage
Multi Disc
[mm]
needle top
10
Multi Needle
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
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3. Bending Stress | Multi Stage
40 um
total time 700 ms
up speed 1 mm/s
stage width 2 mm
Stefan Behler, Besi Switzerland AG
3. Bending Stress | Multi Disc
40 um
total time 200 ms
down speed 3.8 mm/s
disc width 0.8 mm
Stefan Behler, Besi Switzerland AG
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 9
3. Bending Stress | Multi Needle
20 um
needle diameter 0.7 mm
needle distance 3 mm
(dynamic simulation not possible in 2D)
Stefan Behler, Besi Switzerland AG
3. Bending Stress | Peel propagation
3 3
Multi Stage
20 um die can not be peeled
Multi Disc
400
600
800
0
1
2
peel length [mm]
40um
20um
400
600
800
stage 2stage height [um]
0
1
2peel length [mm]
target peel length
disc height [um]
0
200
400
0 50 100 150 200 2500
200
400
0 200 400 600 800[ms]
stage 1
[ms]
disc 1 disc 2
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
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3. Bending stress | Comparison
maximum bending stress [MPa]
600
• thinner die more bending stress
• tensile stress on surface (compressive stress only for multi needle)
100
200
300
400
50040 um
20 um• smallest bending stress by multi disc
• with assumption/settings in this model, 20um dies cannot be picked with multi stage
0Multi
NeedleMulti Stage
Multi Disc
4. Die strength
• material property, (almost) independent of thickness
• measured by bending test
th i i f diff t t ththree main regions of different strength:• surface (active structure)• backside (grinding, polishing...)• edges (dicing)
die strength [MPa] measured by 3-point bending
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 11
4. Die strength | example
Ultra‐Thin Chips ‐ A New Paradigm in Si Technology [BURGHARTZ] 2012
4. Die strength | example: blank vs. TSV
• wafer preparation & strength measurement by IMEC
• IMEC’s standard 5x50 µm via-middle TSV
• die size 10x10x0.05 mm | stealth dicing
Pro
babi
lity
[%
] TSV
blank
CDS
Fra
ctur
e
MDS
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 12
4. Die strength | overview
wafer processing CDS [MPa]
conventional backgrind #320 80 backgrinding grit sizeconventional backgrind, #320
conventional backgrind, #2000 800
DBG, CMP 1’000 – 15’000
DBG, CMP, thickness 100 um 440
DBG, CMP, thickness 30 um 1’433
DBG, blank 20 um 1000
DBG, metal tracks and bondpads 800
size effect
backgrinding grit size
effect
structure effect, p
Stealth dicing, with TSV’s 930
• large variation, 2 orders of magnitude!
4. Die strength vs. bending stress
• typical ranges are very close
• risk of die cracking
• «min. die thickness 20 m»
this specification is too simple!
1000
1500
40 um
20 um
max bending stress
[Mpa]
characteristic die strength
0
500
Multi Needle
Multi Stage
Multi Disc
20 um
var. processing methods
IEEE Electronics Packaging SocietySCV Chapter
December 7, 2017
www.cpmt.org/scv 13
Summary
• Introduction of the key properties
• Wafer foil bulk & edge peel force
• Bending stress: ejector types, FEA model, comparison
• Die strength: overview
Acknowledgements
• Thanks to Shotaro Kato and co-workers (Hitachi Chemical) for providing test wafers
• Thanks to W. Teng, A. Podpod (IMEC, Belgium) for providing strength data for TSV dies
