an innovative high throughput thermal compression … · an innovative high throughput thermal...

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


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


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


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


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


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


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


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


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


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


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


Fluxless-LPC-TCB under Inert Environment for Die Stacking

Without using flux, UPH could be improved significantly


Process Flow for Stacking Die

Stack Die Bonding Molded Underfill

No Flux Cleaning


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

an innovative high throughput thermal compression … · an innovative high throughput thermal...

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