Low temperature curable polyimide for advanced package

Takahiro Sasaki Asahi Kasei E-Materials Corporation

Outline

1. Introduction of Asahi Kasei E-Materials 2. Requirements for advanced package and our solutions 3. Introduction of PIMELTM BL-301 4. Conclusion

1. Introduction of Asahi Kasei E-Materials 2. Requirements for advanced package and our solutions 3. Introduction of PIMELTM BL-301 4. Conclusion

Home & Construction Materials

Electronics

Health Care

Chemicals& Fibers

Asahi Kasei Chemical

Asahi Kasei Fiber

Asahi Kasei E-materials

Asahi Kasei Micro Device

Asahi Kasei Homes

Asahi Kasei Construction Materials

Asahi Kasei Pharma

Asahi Kasei Medical

ZOLL Medical

Saran Wrap™ cling

film

Hebel Haus™

SUNFORT™ (dry film photoresist)

HIPORETM (lithium-ion battery separator)

Introduction of Asahi Kasei Group

FY2014 Net sales USD 16.3 billion

PIMELTM （photosensitive polyimide/PBO precursor)

Plastic Optical fiber Reflective Polarizer WGFTM

Products of Asahi Kasei E-materials

Dry Film Photoresist SUNFORT TM

Glass fabric insulation material for package circuit board

LIB separator (Lithium-ion battery) HIPORE TM

Latent hardener NOVACURE TM

Photomask Pellicles

Liquid Photopolymer APR TM

Epoxy resin AER TM

Photosensitive Material PIMEL TM

1. Introduction of Asahi Kasei E-Materials 2. Requirements for advanced package and our solutions 3. Introduction of PIMELTM BL-301 4. Conclusion

Roadmap of package

WB - BGA

WL - CSP

FC - BGA(C4)

混合 混合

Fan - out

WB - stacked

Multi - chip PKG

FC - BGA(Cu piller )

混合 混合

Si interposer

FO - P on P

TSV - stacked

Chip on Chip(WB )

“ Super Chip ”

Stack DRAM

SSD Memory card

DRAM etc.

SiP

CPU 、 GPU High - end chip

For Mobile Thin and Small

Wire - bond PKG

Bump PKG

Low - K CPU

DRAM

MPU Logic

Moore’s law

Advanced packaging technology

For dielectric material Curing with low heat resistive materials Low temperature cure is needed Chip becomes thinner Low stress is needed

getting harder and harder

Miniaturization

We believe “LOW TEMPERATURE CURE & LOW STRESS products provide the customer satisfaction.”

Necessity of low temperature curability for dielectric material

1995 1990 2000 2005 2010

PI：Negative tone/ Solvent developable

PBO： Positive tone/ Aqueous developable

1985

Phenol： Positive tone/ Aqueous developable

2015

For Bump PKG

For Wire bonding

For Power device

Low temperature cure Low stress Good Cu compatibility Good Chemical resistance Excellent reliability

Low temperature cure Low stress Low CTE High resolution

High resolution Excellent electrical properties

BL-300series BM-300series

AM-270series

MA-1000series

History and R&D roadmap of PIMELTM

Improving the reliability of electronic devices

Dielectric for advanced package

Low temperature cure and low stress

Stable in TCT Relaxation of drop impact Imidization

adhesion on Cu

Summary of requirements for advanced package and our solutions

We think TCT(Thermal Cycle Test) is major concern in advanced package. We compared Polyimide(PI) and Polybenzoxazole(PBO), which is more stable in TCT by experiment.

The result showed us stability of PI is much better than it of PBO.

1. Our solution for ‘Stable in TCT’

Test chip of TCT

Chip layer image

- Al pad: 1 um - Oxide passivation (PE-CVD): 1 um - 1st dielectric polymer: 7 um - RDL (TiW/Cu sputtering +Cu

plating): 3 um - 2nd dielectric polymer: 7 um - UBM: Ni 5 um, Au 100 nm - UBM diameter: 235nm - Solder ball size :250um (SAC 305)

N

O

X N

O

PI(Polyimide)

PBO(Polybenzoxazole)

Imide ring

Oxazole ring

N

C

C

C

C

O

O

O

O

XN

PI or PBO

Test board and chamber of TCT

TCT data is collected using an ESPEC TSD 100. The test conditions for the AATC (air to air thermal cycling) are shown as below.

2 Chambers (ESPEC TSD 100) Lower Temp: -55deg.C for 30min Higher Temp: +125deg.C for 30min

Cooperation with Fraunhofer IZM

Chips are mounted here

Chip size UF

Cycle times

Fail rate by different dielectric (%) PI PBO

3×3mm No 100 0 0 250 0 0 500 0 40

9×9mm Yes 100 0 0 500 0 0

1000 0 5

The results of TCT

Observation of failure sample(PBO) Solder breakage occur at interface between solder

and PCB. PBO breakage is also found under a bump edge. RDL metal layer breakage is also found on some of

chips.

S-S curve under low temperature

PI has very stable mechanical property at -55deg.C. On the other hand, PBO elongation at -55deg.C is much lower than

the elongation at 25deg.C. It is supposed that the PBO material tends to cause breakage at low

temperature.

PI is much more stable than PBO in TCT

PI PBO

25deg.C 25deg.C

－55deg.C －55deg.C

2. Our solution for ‘Relaxation of drop impact’

We think drop impact is also major concern in advanced package, especially for mobile electronic devices. We studied what factor is effective for relaxation of drop impact by finite element analysis (FEA).

The result showed the suitable modulus corresponding to thickness of dielectric is important.

The drop impact of WLCSP package without UF is calculated with FEA using a zooming technique [1].

The acceleration and the velocity of the board level model is used the value obtained from the global model.

Approach to the solution of drop impact

1. M. Fujita, “ A Finite Element Analysis of Board Level Drop Reliability Test and Analysis of Stress Buffer Effect of Polyimide,” in Proc. IEEE CPMT Symposium, Kyoto, Japan, Nov. 11-13, 2013.

Board level model as a detailed model

Global level model as a simplified model

h = 40cm

Stand-off

Drop test table

Buffer

Rigid base

Mounting board

Acc

eler

atio

n, a

/ G

15

00G

Time, t / s 0.5ms

Si die

Polyimide

Solder Cu pad

Large mass cubic

Standoff

Input-G

v0 Symmetry center

Relation between dielectric layer parameter and principal stress

Principal stress of position at bump edge (Position 1)

Principal stress of position at pad area (Position 2)

The principal stress change by dielectric layer thickness and modulus shows inverse correlation between bump edge and pad area.

Position 2

Position 1

Response surface of interaction

Most minimized stress condition line

In the case of thickness of dielectric is around 20um (10um*2), the suitable modulus is around 3GPa.

High reliability of PI come from polyimide structure, not precursor. But, in general, imidization needs high temperature. So, we studied to complete imidization with low temperature cure condition.

The acidity control of amine unit of precursor is very effective.

3. Our solution for ‘Imidization at low temperature’

Amine unit Acid unit C N

COOR

H O

N

H O

C

ROOC

Acid unit C

O

ROOC

Amine-B Amine-A

Acidity

Low temp. Cure type PI

Conventional PI

High

Low

Imidization temperature

High

Low

Lower acidity of amine unit makes imidization temperature lower. Some kinds of bases are often used as catalyst for imidization. But,

it might be cause of side effects. On the other hand, control acidity of amine has less side effects.

The relation between acidity of amine unit and imidization temperature

C

O

C

O

O

N

H

R1

R2

CN

C

O

O

R1Cure

Imidization reaction

Absorbance 1380cm-1

Absorbance 1500cm-1

Imide Index =

Benzene

imide

Definition of imide index

The effect of acidity of amine unit

Amine A (lower acidity amine) is effective to imidization at low temperature cure condition.

In advanced package, redistribution metal is almost Cu. So, adhesion on Cu is very important. Actually, delamination between dielectric layer and Cu often becomes big issue.

We found the ‘effective additive’ for adhesion on Cu.

4. Our solution for ‘Strong adhesion on Cu’

N R2 N

R2 N R2

Cu surface Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu

Additive A Additive A Additive A Additive A

Polyimide

N R2 N

R2

Additive A

Coordinate bond

Hydrogen bond

Adhesion mechanism on Cu

We are using very effective chemical ‘Additive A’ for adhesion on Cu. ‘Additive A’ makes hydrogen bond with polyimide and coordinate

bond with Cu surface.

Method : Substrate :

Cure condition :

After High Temperature Storage Additive A

No Yes

Adhesion strength (Breakage mode)

40 MPa (Cu-PI)

> 70MPa (Epoxy)

Sebastian method Cu 200deg.C/2h/N2

High Temperature Storage condition : 175deg.C / 270hours

Pull

PI

Substrate

Pin

Epoxy

Cu

Effect of ‘Additive A’ at severe condition

‘Additive A’ is very effective for adhesion on Cu.

Improving the reliability of electronic devices

Dielectric for advanced package

Low temperature cure and low stress

Stable in TCT Relaxation of drop impact Imidization

adhesion on Cu

Summary of requirements for advanced package and our solutions

Polyimide structure

Suitable modulus

Acidity of Amine unit

Effective additive

1. Introduction of Asahi Kasei E-Materials 2. Requirements for advanced package and our solutions 3. Introduction of PIMELTM BL-301 4. Conclusion

PIMELTM BL-301 Today’s topics

General Polymer structure - Polyimide ☺ Condition Cure temperature deg.C 200 350 Structure Imidization % 100 100 ☺

Thermal Glass transition point (Tg) deg.C 200 260 Internal thermal stress MPa 19 29 ☺

Electrical Dielectric constant (@1GHz) - 3.3 3.3

Mechanical

Tensile strength MPa 130 150 Elongation (@25deg.C) % 50 50 ☺ Elongation (@-55deg.C) % 45 45 ☺ Young's modulus (E') GPa 3.5 3.4 ☺

Adhesion @ 121deg.C, 2atm,

100hrs

on Si MPa >70 >70 on Cu MPa >70 >70 ☺

Chemical resistance

-Photoresist stripper -Metal etchant -Flux

- Excellent Excellent ☺

Properties of PIMELTM BL-301

PIMELTM BL-301 shows excellent properties in 200deg.C cure. PIMELTM BL-301 shows wide margin on cure temperature. PIMELTM BL-301 get good reputations from many customers.

1. Introduction of Asahi Kasei E-Materials 2. Requirements for advanced package and our solutions 3. Introduction of PIMELTM BL-301 4. Conclusion

Conclusion

Low temperature cure dielectric material is suitable for advanced package.

To achieve the role as dielectric even at low temperature cure, we showed our solutions for the requirements.

PIMELTM BL-301 meets these requirements and is widely used / evaluated by many customers.

PIMELTM HP: http://www.asahi-kasei.co.jp/ake-mate/pimel/en/index.html

Thank you for listening !