LASER TRANSMISSION MICROJOINING TECHNOLOGY FOR … · 2020. 9. 3. · Laser Technology MICROMANUFACTURING 2009, APRIL 1-2, MINNEAPOLIS, MN LASER TRANSMISSION MICROJOINING TECHNOLOGY

Fraunhofer USA Center for Laser Technology

MICROMANUFACTURING 2009, APRIL 1-2, MINNEAPOLIS, MN

LASER TRANSMISSION MICROJOINING TECHNOLOGY

FOR PACKAGING OF MEMS

R. Patwa1, H. J. Herfurth1, S. Heinemann1, Golam Newaz2

1 Fraunhofer USA, Center for Laser Technology, 46025 Port Street, Plymouth, MI 48170, USA

2 Wayne State University, Detroit, MI 48232, USA


Outline

• Introduction - Fraunhofer CLT

• Laser Transmission Microjoining Applications

• Joining Dissimilar Materials

• Results

• Process Characterization

• Joining Similar Materials

• Conclusions


Key Competencies at Fraunhofer CLT

Unbiased Applied R&D in:

Process Development

(from Chips to Ships)

Consulting to Production Validation

Special Optics

Engineering of Advanced Lasers

- Diode Lasers

- Fiber Lasers

Unique Turn-Key Systems


Outline




• Results



• Conclusions


Biomedical Applications

Cochlear Implant to

restore partial hearing

Challenges

• Hermetic sealing

• Localized bonding

• Long term stability

• Biocompatibility

Next-generation retinal

prosthesis Source: California

Institute of Technology

Source: Advanced

Bionics, Corp. Housing of MEMS /

Hermetic sealing

Glass MEMS Device

Silicon base


Laser Transmission Joining Principle

During laser transmission microjoining process -

The laser radiation is transmitted through the partially transparent top material.

It is absorbed at the surface of the bottom material.

The laser radiation is converted into heat energy directly at the interface.

Schematic of sample in fixture Schematic of the sample undergoing

the bonding process


Different Joining Methods

Quasi-simultaneous Mask Simultaneous


Basic Joint Designs

laser beam

transparent

material

absorbing

transparent

material

absorbing

material

laser beam

laser beam

transparent

material

absorbing

material

laser beam

material

transparent

material

absorbing

material


Laser Transmission Joining Setup

Laser Sources

cw Yb- doped fiber laser (JDSU)

• Wavelength : 1110 nm

• Maximum Power : 25 W

• Fiber Size : 9 µm

cw Diode laser (Fraunhofer)




cw Nd:YAG laser (Trumpf)




Sample

Laser

optic

Fixture


Material Combination Matrix

Imid

ex®

Teflo

n®

PE

BA

X®

PV

DF

Poly

ure

thane

PE

EK

Boro

silic

ate

gla

ss

PA

PM

MA

Nitinol X X

Chromium coating X X

Stainless steel X X X

Titanium X X X

Silicon X

Titanium coated glass

X X X

ABS X

PA X

Absorbing

Transparent

Metal - Polymer Ceramic – Metal/Ceramic Polymer - Polymer


Optical Properties of Materials

0

1

2

3

4

5

6

7

8

0 2 4 6 8

Applied Laser Power (W)

Me

as

ure

d L

as

er

Po

we

r (W

)

Cover glass + Imidex

Cover glass + PEEK

No Cover glass & NoPolymer

Transmissivity of Imidex with cover glass = 79.8 %

Transmissivity of PEEK with cover glass = 80.9 %

Absorption (),

Transmission (∆)

Polymer

Silicon

Glass


Process Optimization

Metal-Polymer

Process parameter window is determined to optimize bond formation process.

25

30

35

40

45

50 150 250 350 450 550

Speed [mm/min]

La

ser

po

we

r [W

]

good bond

no bond

temporarily bonded

partially melted

completely melted

Glass-Silicon

0

2

4

6

8

10

12

10 100 1000 10000 100000

(Log) Speed (mm/min)

Laser

Pow

er

(W)

--

no effect

Imidex changes color

Weak Bond

Bond

Strong Bond

Very Strong Bond

Burned


Outline




• Results



• Conclusions


Metal-Polymer Bonding

View

As is bond surface

top view

Titanium - Imidex

Titanium - PVDF

Chromium - PEEK

Nitinol - PEEK

Nitinol - Imidex

Chromium - Imidex Titanium - Polyurethane


Metal-Polymer Bonding

Titanium coated glass/

Imidex bond

Bond line

Stainless steel/PEBAX

bond


Material – Silicon (Top) , Borosilicate Glass (Bottom)

Nd:YAG laser

35 W, 200 mm/min

Diode laser

30 W, 60 mm/min

Fiber laser

Spot Bond

Silicon-Glass Joining


Temperature Control for Plastic Welding

0 50 100 0

5

10

15

20

25

distance [ mm ]

laser

pow

er

[ W

]

0

100

200

300

400

500

600

tem

pera

ture

[°C]

0 50 100 0

5

10

15

20

25

distance [ mm ]

Laser

pow

er

[ W

]

0

100

200

300

400

500

600

tem

pera

ture

[°C]

Diode laser; 5 m/min

signal processor

temperature

detector

laser beam

focussing

lens

focussing

lens

workpiece

filter

laser power

detector

optical fibre

T

TL

L

L

temperature

radiation

Custom optic for

temperature control


Joint Characterization – Failure Load Limit

0

1000

2000

3000

4000

5000

6000

0 0.2 0.4 0.6 0.8 1

Displacement (mm)

Lo

ad

(g

ram

s)

Nitinol/Imidex

Chromium/Imidex

Chromium/PEEK

Nitinol/PEEK

Titanium/Imidex

Polymer-Polymer Metal-Polymer

400

600

800

1000

1200

1400

0.0 1.0 2.0 3.0 4.0

Speed (m/min)

Failu

re L

oad

(N

)

Thickness - 3.1mm

Thickness - 2.4mm

Thickness - 1.9mm


Joint Characterization – Shear Pull Strength

0

5

10

15

20

3 4 5 6 7 8 9 10

Laser Power (W)

Pu

ll S

tre

ng

th (

N/m

m2

)

Nitinol/PEEK

0

5

10

15

Niti

nol/I

mid

ex

Niti

nol/P

EEK

Chr

omiu

m/P

EEK

Chr

omiu

m/Im

idex

Titani

um/Im

idex

Ma

xim

um

Pu

ll S

tre

ng

th (

N/m

m2

)

Metal-Polymer


Joint Characterization –Degradation in Cerebrospinal fluid (CSF)

Material combination:

Glass: Pyrex 7740 Ti-coated

Imidex: 0.177 mm thick

Laser: Fiber laser

Average failure load as bonded: 21.5 N/mm2

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Weeks in CSF Solution at 37 oC

Fa

ilu

re L

oa

d (

N/m

m2)


Joint Characterization – Pressure Testing

Sample

Titanium: 3 mm x 5 mm; hole diameter = 1 mm

Imidex: O. D. 2 mm

Pressure test setup Result

Burst pressure: 80 bar

Tensile strength: 8 N/mm2


Helium detector/

Mass

spectrometer

Helium

Vacuum

Laser Bond

Laser: Fiber laser

Power: 4.2 W

Speed: 100 mm/min

Polyimide to Titanium

Substrate: 2.6 x 10-6 Std. cc/sec/cm2

Bond: 3.4 x 10-6 Std. cc/sec/cm2

Leak rate slightly higher

Joint Characterization – He-Leak Testing


Joint Characterization – SEM Analysis


Joint Characterization –XPS Analysis

Titanium Surface

Ti2p lines

XPS Signal

Collection Area

Material combination:

Imidex/Titanium Bond

Lines

C1S lines


Competing Technologies

• Laser Micro-joining

Advantages

- Highly localized

- Precise bond lines

- Heat affected zone (HAZ) confined to very small volume of material

- Encapsulation design flexibility

- Non-contact process

• Ultrasonic Welding

Advantages

- Lower initial equipment cost

• Adhesive Bonding

Advantages

- Good for area bonds


Outline




• Results



• Conclusions


Butt Joint (33 W, 100 mm/min) Cross-section

Material: Glass wafer

(Pyrex 7740)

Thickness: 0.5 mm

Laser: Pulsed CO2

(Rofin SC x10)

Power: 65 W

Speed: >25.0 m/min

Multiple scans

Glass-to-Glass Welding


T - Joint Fillet Edge Joint

0.25 mm

0.25 mm

Fillet Edge Joint

Cross-section Cross-section

Glass-to-Glass Welding


Conclusions

• Laser transmission microjoining of similar and dissimilar material

combinations has been successfully achieved.

• The results demonstrate the similarities and differences between the different

material systems and underscored the importance of laser microjoining

technology for such applications.

• This study provides a database of novel joining combinations that can be

commercialized for industrial applications.

• This technology clearly exhibits a high potential for laser joining processes to

address the increasing demand for packaging applications.


Thank you for your attention!

CONTACT-

Rahul Patwa

[email protected] .com

www.clt.fraunhofer.com

Fraunhofer Center for Laser Technology

46025 Port Street

Plymouth, Michigan 48170

LASER TRANSMISSION MICROJOINING TECHNOLOGY FOR … · 2020. 9. 3. · Laser Technology MICROMANUFACTURING 2009, APRIL 1-2, MINNEAPOLIS, MN LASER TRANSMISSION MICROJOINING TECHNOLOGY

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