Challenges in

Material Applications for SiP

Sze PeiLimRegional Product Manager for Semiconductor Products

Indium Corporation

9/25/2017

Indium Corporation

Customer Recognition:

• Intel (Preferred Quality Supplier Award)

• Celestica (Total Cost of Ownership Award)

• Samsung (Superior Vendor Award)

• Shinwa (Best Supplier Awards)

Materials Supplier:

• SMT solder pastes

and fluxes

• Power semiconductor

die-attach

• Semiconductor fluxes

• SiP solder pastes

• TIMs

• Engineered solders

• Specialty compounds

• NanoFoil®

• Introduction

• Challenges

• Solder Paste

• Flip-Chip Flux

• Acknowledgements

• Q & A

Outline/Agenda

• Heterogeneous integration in SiP

– Increased functionality in a single package,

higher performance

– Faster time to market

– Lower cost

• Miniaturization for SiP passives

– Current 01005

– 008004

• (ASE: 2017/2018)

– 0050025

• (2019/2020)

Introduction of SiP

• Solder Paste

– Smaller stencil aperture, tighter gap between pads

– More critical solder paste printing requirements

– Jetting paste?

• Flip-Chip Flux

– Cross contamination of flip-chip flux with solder paste

• Cleaning

– Solder paste and flux cleanability

– Water wash vs. solvent wash

– How clean is clean?

• CUF/MUF

– Flowability

– Compatibility with no-clean flux

9/25/2017

Challenges in Material

Solder Paste: Powder Size

Powder Size (IPC J-STD-005) vs. Minimum Stencil Aperture

• Minimum of 5-6 solder particles across the aperture

• Increase in powder surface area will require more flux or flux with a

better oxidation barrier to protect the powder from surface oxidation

TypeLess than 0.5%

larger than

10% Max.

between

80% Min.

Between

10% Max. Less

than

Minimum

Stencil

Aperture (um)

Approximate

Powder Surface

Area (times)

1 160 150-160 75-150 75 NA NA

2 80 75-80 45-75 45 NA NA

3 60 45-60 25-45 25 270 1.0

4 50 38-50 20-38 20 230 1.2

5 40 25-40 15-25 15 150 1.9

6 25 15-25 5-15 5 90 3.7

7 15 11-15 2-11 2 66 5.6

9/25/2017

High Volume Powder (SAC305)

Type 5 Type 6 Type 6-SG

Type 6-SG Solder Paste Printing

• Water-soluble Indium3.2HF

• 0.1mm aperture

• 50µm-thick stencil

Solder Paste: Flux Types

Standard No-Clean SMT

Paste

Ultralow Residue No-

Clean Water-wash

Typical Flux

Residue (%w/w of

flux) 40-60% 4-10%

Zero after cleaning /

drying

Cleaning Process

Not needed for standard

SMT, but can be solvent-

cleaned Not needed

DI water clean or

aqueous solvent

MUF/CUF

compatibility

Poor if not cleaned

(delamination and

solder bridging)

Usually good if all

solvent removed during

reflow or post-

processing

Excellent if residue

completely cleaned and

dried

• Paste rheology

• Slump behavior

• Stencil life

Solder Paste

Minimum slump or bridging down to 50µm gap

9/25/2017

Printing Performance

125µm x 150µm pad and 50µm gap distance

X (µm) Y (µm) Stencil Thickness (µm)

Area Ratio

150 125 35 0.97

150 112.5 35 0.92

150 100 35 0.86

125 70 35 0.64

125 65 35 0.61

120 60 35 0.57

150 125 50 0.68

150 112.5 50 0.64

150 100 50 0.60

125 70 50 0.45

125 65 50 0.42

120 60 50 0.40

Print down to 0.42 area ratio

9/25/2017

Printing Performance

0.64AR0.62AR0.57AR0.45AR0.42AR0.40AR

1 80

1 60

1 40

1 20

1 00

80

60

40

20

0

Dat

a

Boxplot of Different Aspect Ratio using Paste C

Cpk Cp

0.45AR 2.11 2.33

0.42AR 2.19 2.36

0.40AR 2.03 2.21

0.64AR 2.74 2.91

0.62AR 2.82 3.05

0.57AR 2.42 2.62

Box Plot of Different Aspect Ratios

Powder size comparison T6-SG vs. T7-SG

• T7-SG has smaller standard deviation

Printing Performance

0.40AR T7SG0.40AR T6SG0.42AR T7SG0.42AR T6SG0.45AR T7SG0.45AR T6SG

1 80

1 60

1 40

1 20

1 00

80

60

40

20

0

Data

Boxplot of Volume T6SG vs T7SG

Substrate support system: pallet vs. vacuum

• Vacuum support shows better consistency

Printing Performance

Support Aspect Ratio Cpk Ppk Cp

Pallet 0.68 2.52 1.07 3.20

Pallet 0.64 2.70 1.10 2.97

Pallet 0.60 2.39 1.11 2.61

Vacuum 0.68 2.82 1.29 3.37

Vacuum 0.64 2.91 1.60 3.27

Vacuum 0.60 2.73 1.38 3.19

Next Generation

Water-Soluble Indium3.2HFA SiP Printing Paste

A A

Voiding Performance

Solder Paste for Jetting

• Jetting can dispense dots close to pad and high above the pad

• Faster than dispensing; higher frequency

• Ability to achieve smaller deposits

• Ability to dispense additional paste to increase volume

• Ability to dispense paste in cavity on a substrate

9/25/2017

Jetting Performance

MEMS Lid-Attach

• Consistent rectangles for MEMS

lid-attach with no gaps

Flip-Chip Flux Application Processes

Emerging Flip-Chip Challenges

• Package Design Changes

– Pitch: Shrinking to 100 microns and below

– Die-substrate clearances: Down to 60 microns

and below

– Substrates thin (coreless): Subject to warping

– Logic die: Down to 50 microns thick and

memory (DRAM) down to <20 microns thick

• Flux Cleaning Challenges

– Pitch reduction limits ability to completely

remove water soluble flux residues:

• Corrosive residues left behind

• Block flow of CUF and MUF leading to underfill voiding

• Interfere with CUF and MUF adhesion causing delamination

– Cleaning process:

• Increases substrate warpage after reflow and before underfill

– Die damage

– Cracked solder joints

• Adds costs

Answer:

Move to

no-clean flux

TGA Comparison:

ULR and Standard Residue Fluxes

Standard

reflow peak

maximum

Low-Residue Flux for Mass Reflow

• Flip-Chip Flux NC-26S

• Flip-Chip Flux NC-26-A

• Flip-Chip Flux NC-699

– Different rheology or viscosity is required based on process

and product type

Flip-Chip Flux NC-26S

Flip-Chip Flux NC-26-A

Flip-Chip Flux NC-699

Viscosity (kcsp) 20 4 1.5

Residue Level* 7~8% ~4% <1%

* Residue level was measured by gravimetric method before and after reflow using typical

lead-free SAC profile with convection oven.

ULR Flux:

Importance of Rheology

• High viscosity

– Bridging

– Inability to remove die from tray

• Low viscosity

‒ Flux wicking and

die-surface contamination

‒ Inability to hold die in place

‒ Poor joint strength

Printing Comparison:

TACFlux® 10 and Flip-Chip Flux NC-26S

Flip-Chip Flux NC-26S TACFlux ® 10

40µm-thick

stencil

95mil

(diameter)

175mil

(pitch)

Fluxes were printed on a smooth

copper surface, which makes

slump easier than on a PCB.

12mil diameter

(largest circle)

4mil width

(smallest square)

Fluxes were printed on an ENIG

surface with a solder mask on a

PCB

Parameter setting:

• Kneading: 100 strokes

• Separation: 1mm/sec

• Pressure: 2kg per 8-inch squeegee

Two stencils with different aperture openings:

• Both are 40µm thick

• TACFlux® 10 slumped while Flip-Chip Flux NC-26S did not.

• Flip-Chip Flux NC-26S provided better printing compared to TACFlux® 10

Compatibility with Underfill

Flux and Underfill Materials

Fluxes and Reference Underfill

Low-Residue FluxFlip-Chip Flux NC-026S (NC-26S)

G355

U8410-73C

Flip-Chip Flux NC-026-A (NC- 26-A)

749-17-B (Compatibility Improved Flux)

ReferenceTACFlux 7 (Regular Residue Flux)

Blank (No Flux Applied)

Molded Underfill (G355)

Shear Strength

• G355‐Blank gives best shear strength; next best is 749‐17‐B

• NC-26-A and NC-26S provide similar and proper compatibility

• TACFlux® 7 is worse than others

• After humidity and high temperature (HT) treatment, shear strength

became lower as expected

3500.0

3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0G355 G355 with

HTG355 with G355 with G355 with N-26A NC-26-A and 749-17-B

HT

G355 with 749-17-B

and HT

G355 with NC-26S

G355 with G355 with G355 with NC-26S and TACFlux 7 TACFlux 7 and

HT HT

Sh

are

Str

en

gth

(p

si)

G355

Capillary Underfill (U8410-73C)

• 749‐17‐B, NC-26-A, and NC-26S gives similar or even higher shear

strength in some cases than U841073‐Blank (no flux residue)

• U8410‐73C provides good compatibility with no-clean low-residue flux

• TACFlux® 7 is worse than others

• No-clean low-residue fluxes provide good compatibility.

U8410-73C4000.0

3500.0

3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0U8410-73C U8410-73C U8410-73C

and HT 749-17- B B and HT and HT TACFlux 7

U8410-73C

with TACFlux 7

and HT

Sh

ea

rS

tre

ng

th (

psi)

U8410-73C U8410-73C U8410-73C U8410-73C U8410-73C U8410-73C

Blank Blank with HT with NC-26-A with NC-26-A with with 749-17- with NC-26S with NC-26S with

Shear Strength

9/25/2017

Flip-chip, MR,

and TCBFlip-chip MR,

and TCB

Flip-chip, TCB

Wafer-bumping

Wafer-bumping

Flux jetting

Reflow and sintering

Vacuum reflow

and sinteringReflow

Cleaning flux and

die-attach paste

Cleaning flux and

die-attach paste

Solder paste

jetting

Solder paste

jetting

Equipment and Materials Partners*

Thank you!