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An Innovative High Throughput Thermal
Compression Bonding Process
Li Ming 2 September 2015
2 Add Author’s Name Here
Introduction
Throughput improved TCB Process
Liquid Phase Contact (LPC) bonding
Flux-LPC-TCB under inert environment
Fluxless-LPC-TCB under inert environment
Summary
Outline
Mass Reflow vs. Thermal Compression Bonding
40/20 50/25 60 /30 80 Bump Pitch / Diameter (um) Die Thickness (um)
TCB MR
TCB enables interconnects for: • Fine bump pitch, small bump diameter, & small solder volume • Thin & large die: Die warpage • Thin & coreless substrate: Substrate warpage • Stress sensitive ELK : white bumps due to CTE mismatch
TCB major concern:
• Low throughput
75
How to Improve Throughput for TCB Process?
Mechanical approach Process approach
Flux-Liquid Phase Contact (LPC) TCB Flux-LPC-TCB under Inert environment Fluxless-LPC-TCB under Inert environment
TCB
Post-applied underfill (TCB-flux)
Pre-applied underfill (NCP/NCF)
Liquid Phase Contact
(LPC)
Traditional TCB-Flux (Flux-SPC)
Flux-LPC-Inert
(CuOSP)
Fluxless-LPC-Inert
(Ni/Au or SOP)
(localized reflow)
TM
Liquid Phase Contact (LPC)
TCB-flux (SPC & LPC) Process Flow
3. Contact, pulse heating,bonding
and cooling
• To remove OSP
• To remove oxides
• Alignment
• Thermal compensation
• Pulse heating & cooling cover a large portion of bonding cycle time
Flux dipping
1. Applying flux
BH
Heat
Force, heat, Height, time
Heat
BH
Flux printing/spraying
BH
2. Alignment
BH 4. Underfilling &
curing
Pressurized Underfill cure
• Underfill methods: CUF or MUF
Solid Phase Contact (SPC)
Liquid Phase Solder
Solid Phase Solder
Heat Heat
BH Force, heat, Height, time
High UPH of Flux-LPC-TCB Approach
LPC w/o cooling LPC with cooling Flux SPC TCB with cooling Process time 1.0s 1.9s 4.6s
UPH (w/ 2s MHT) 1200 800 600
1.0s 0.9s 1.0s 2.5s 1.0s
Flux-LPC-TCB
Force Force
Temp
Temp
Flux-SPC-TCB
Advantages of Flux-LPC-TCB
Improved throughput Compensation for solder height variation/ better wetting Low substrate temperature & short bonding time Low substrate warpage
Better placement accuracy: align and bond at the
same temperature Good stand-off height control
3~5μm
Bond head 280°C
Bond stage: <100°C
Limitation of Flux-LPC-TCB Process
Solder cap exposed at high temperature Sn oxide formation
Sn oxide affects wetting & causes Open Solution to overcome the issue: Inert environment Flux-LPC-TCB under Inert gas
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Test Vehicles
CoS CoC
Die (5x5 mm)
Bump diameter: Ø60μm Height: 25μmCu/27μm solder Bump pitch: 160μm
Bump diameter: Ø40μm Height: 25μm Cu/17μm solder Bump pitch: 160μm
Bump diameter: Ø40μm Height: 25μmCu/17μm solder Bump pitch: 160μm
Substrate (15.4x15.4mm)
2M layers BT laminate Metallization: CuOSP, Ni/Au Lead width:18μm Pad diameter: Ø80μm Cu lead/pad thickness: 15μm
Si substrate Metalization: Cu Cu pad diameter: Ø60μm Cu pad thickness: 10 μm
Bump -
Lead Pad
Die Cu OSP substrate
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Bonding Parameter Set-up
Temperature, force and position profiles Wetting test
Si
Cu
Si
Cu
Si
Cu
Bonding parameters were not optimized, or temperature was not uniform Bonding parameters were optimized,
and uniform wetting was achieved
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Flux-LPC-TCB : Good Solder joints
45-46 µm 45-46 µm 37-38 µm
BOL BOP C2C
WH T. (0C)
80 80 120
BH T. (0C)
260 260 350
BT (sec)
1 1 1
BOL BOP C2C
Cu
Cu trace Solder
Cu
Cu pad Solder
Cu
Cu pad Solder
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Thermal Aging and Multiple Reflow
Comparison among LPC-TCB, SPC-TCB and MR
150ºC, 4hrs
LPC-TCB MR
3 X reflow
As-bonded
SPC-TCB Cu
Solder IMC
Fracture surface showing solder residual
LPC-TCB Process : Precise stand off height
Initial reference level: Cu pillar touching Cu pad/trace
Final level: The required stand-off height (position control)
Force
Position
Bonding Profile
Temperature
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Solder Height Control
To achieve good solder joint reliability
To facilitate underfill process
Controlling factors
Coplanarity adjustment
Z-direction position control
Thermal compensation
Effect of cooling step
Various solder heights
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Effect of Cooling on Solder Height
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40 45
Solder thickness (um)
Res
torin
g fo
rce
(10-
5N)
Repulsive force
Attractive force
Equilibrium point
Cooling effect on solder height at different bonding levels
Restoring force vs. solder thickness
w/o cooling w/ cooling
4μm
10μm
20μm
z SimulationExperiment
Z
Si
BT
Cu
w/o cooling: Bond head releases the die when solder is still in molten state.w/ cooling: Bond head releases the die after solder solidification.
7~8μm
7~8μm
7~8μm
3.7~4.5μm
10.7~12.0μm
21.0~22.0μm
• Without a cooling step, an equilibrium height will be achieved
• With a cooling step, solder height could be controlled by a pre-determined level
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Effect of Cooling Temperature on Solder Height
220ºC 180ºC
Solder solidification
Signal indication for cooling temperatures
Solid
Liquid
Cu
Cu
Zone I: Solder in a solid state (a position controlled height) Zone II: Solder in a solid/liquid mix state Zone III: Solder in a molten state (an equilibrium height)
Bonding head releases at
Zone I Zone II Zone III
September 7, 2015 ASM Pacific Technology Ltd. © 2015 page 17
BH Temp (DegC)
BS Temp (DegC)
Bond Time (ms)
Bond Force (g)
Cooling Temp. (DegC) UPH Process Control
300 80 350 300g Without Cooling
1800 Hot pick, Force mode change to position mode control, pull back 10um, without
cooling
300°C
300gm
10μm
350ms
Flux-LPC on Embedded Trace Substrate with Hot Pick & No Cooling Process (with 10um pull back)
September 7, 2015 ASM Pacific Technology Ltd. © 2015 page 18
Left
Middle
Right
Flux-LPC on ETS : Hot Pick & No Cooling Process (with 10um pull back)
Die Size (mm) 10 x 8
Die thickness (um) 760um
Bump Size (um) 50um
Bump Height (um) ~45um Cu / ~17um SnAg
Bump Pitch (um) 110/55
No of Bump 1637
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A New TCB Approach: Fluxless-LPC-TCB under Inert Environment Fluxless bonding
No flux is needed (no dipping, no cleaning) Receiving pads: Ni/Au Advantages for Fluxless process
Improving UPH significantly No flux residual Lower cost of maintanence
APT ASM PT Ltd. © 2015
Substrate with Ni/Au surface finish Si die with Cu/Ni/Au Metalization
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Effect of N2 Protection (C2S)
Excellent Wetting Solder thickness: 5-6um
Non Wetting observed in some bumps solder thickness: 5-6um
Inert environment improves the solder wetting significantly for fluxless-LPC-TCB process
With N2
APT ASM PT Ltd. © 2015
Without N2
Cu
Cu Ni Solder
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Fluxless-LPC-TCB under Inert Gas for C2C
Sample Bond Head Temp (0C)
Bond time (sec)
Work Holder Temp (0C)
Bond Force (g)
Cooling
1 350 0.5 120 500 No
2 300 0.5 160 200 No
Solder height 3.0 um 3.5 um 4.2 um
Solder height 8.6 um 7.3 um 6.4 um
Sample 1
Sample 2
Good joints formed under different bonding conditions
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Fluxless-LPC-TCB under Inert Environment for Die Stacking
Without using flux, UPH could be improved significantly
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Process Flow for Stacking Die
Stack Die Bonding Molded Underfill
No Flux Cleaning
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Conclusions
Inert Thermocompression Bonding Technology
bonding technology
Flux-LPC-TCB under Inert environment provides an improved throughput and reliable Interconnection method to address fine pitch/small solder volume, thin die and/or coreless substrate packages
Fluxless-LPC-TCB under Inert environment is a suitable process for 3D TSV stacking die packages with high throughput and no flux residual
TM