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C. Steuer, K. Gehm, E. Reinhold

VON ARDENNE ANLAGENTECHNIK GmbH

D-01324 Dresden, Germany

e-mail: steuer.christoph@vonardenne.biz

AIMCAL 2005Myrtle Beach, SC

Copper Coating On Polyimide Films

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Copper Coating On Polyimide Films - Content

1. Introduction and Motivation

2. Coating Task

3. Tools & Processes

Ÿ Quality Assurance

Ÿ Experiments at FOBA 600w Tool Comparison

w Experimental Results

w Comparison Of Technological Variants

w Limitations & Consequences

Ÿ Experiments of Copper EB-PVD

Ÿ Summary

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Introduction FOBA 600

Ÿ Web coater FOBA 600:w plastic web (6... 100 µm) & thin metal foil ( ...100 µm)

w 600 mm web width

w 1 ... 1.000 m/min web speed

w EB-gun with 200 kW / 60 kV and 2 magnetrons

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Motivation

Ÿ Productsw FPB flexible printed boards

n used e.g. in printers, cell phones

w FCC flexible conducting circuits

n reducing weight

n less space

w Tasks to product

n Has to withstand many bending cycles

n Even at very small bending radii

n Rough climatic changes in short time (temperature, humidity)

n Keep conducting / working in corrosive surroundings (sea climate; sweat)

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Coating Task

Ÿ Copper seed layer coatingw onto polyimide (PI) web by PVD technologies

w very good adhesion has to be achieved

w some hundred nanometers layer thickness copper before galvanic layer increase to some micrometers thickness

Ÿ Known Problems & Add-onsw adhesion between PI & copper most critical point

w hard test conditions [peel force test after pressure cooker test]

w polyimide contains remarkable amounts of water & gases

w needs sophisticated experimental programs

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Layer Stack

Ÿ Layer stackw Polyimide

w Adhesion layer

w Thin copper layer (some hundred nm), PVD

w Thick copper layer (some µm), galvanic

x µm copper, galvanic

x 100 nm copper, PVD

x nm adhesion layer, PVD

x 10 µm Polyimide

x µm copper, galvanic

x 100 nm copper, PVD

x nm adhesion layer, PVD

x 10 µm Polyimide

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Technological Development At Von Ardenne Anlagentechnik

Ÿ Main technology: Magnetron sputtering of interface and seed layer

Ÿ Main focus of effortsw intensive pretreatment of web

w search for appropriate technological steps and parameters

Ÿ Additional studies: substituting technology for increasing copper layer

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Tools & Processes l

Ÿ IR back side heaterw Purpose: outgassing web,

removal of water vapor

w Free span arrangement

Ÿ MF Glow discharge on layer sidew Purpose: surface activation,

add. removal of water + gases

w Immediately coating after glow discharge necessary

w Glow discharge chamber is pumped via slits to winder chamber

w Web on cooling drum

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Tools & Processes ll

Ÿ Linear ion source LION 600w surface activation

Ÿ DC sputtering SDM 900w adhesion layer

w thin metal layer NiCr

Ÿ MF sputtering copper SDM 900w copper seed layer

w power up to 14 kW

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Quality Assurance - Layer Test Procedures

Ÿ Part 1: w galvanic Cu deposition (> 25 µm)

w Peel Force Test

Ÿ Part 2:w galvanic Cu deposition (> 8 µm)

w Pressure Cooker Test: 168h @ 2bar, 121°C, 100% relative humidity

w galvanic Cu deposition (> 25 µm)

w Peel Force Test

Ÿ Peel Force Test IPC-TM - 650:w Tension on Cu layer perpendicular

to substrate

w Measurement of peeling force

Ÿ Additionally:w Investigation of pulled layer and

substrate under microscope

w Which was weakest connection?

PI

Cu

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Experiments at FOBA 600 - Tool Comparison

Ÿ MF glow discharge:w gases and mixtures

w gas flow => pressure => voltage & current => power

Ÿ LION 600w gases and mixtures

w gas flow

w power

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Experiments at FOBA 600 IIl

Ÿ DC sputtering, SDM 900

w Thin metal layer NiCr

w Achieved dyn.dep.rate ca. 57 nm*m/min

Ÿ MF sputtering copper SDM 900

w Achieved dynamic deposition rate: ca. 150 nm*m/min

w Scale process via optical transmission + ramp up / down web speed

w Example simulation „copper 35 nm on PET“: characteristic peak near 590 nm

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Experimental Results & Comparison Of Technological Variants l

Ÿ Technology 1:w IR Heating

w MF Glow Discharge (MF GD)

w DC-Sputtering NiCr

w MF Sputtering Cu

Ÿ Technology 2:w IR Heating

w Ion Bombardment LION

w DC-Sputtering NiCr

w MF Sputtering Cu

Ÿ Results after PCT:w technology 1: good adhesion at all samples

w technology 2: ablations at all samples

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Experimental Results & Comparison Of Technological Variants ll

Ÿ Peeling force measurements:

1,56,5Ion source N2/O2 + high power

1,66,4Ion source N2/O2 + low power

1,45,6Ion source N2 + high power

1,16,3Ion source N2 + low power

4,39,7MF GDC N2 + high power

4,47,8MF GDC N2 + low power

after PCT / N/cm²

before PCT / N/cm²

Sample

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Experimental Results & Comparison Of Technological Variants lll

1. Peel force test before PCT is not significant for adhesion after PCT.

2. Samples produced with MF GD provide best adhesion values after PCT.

3. Particle energy of MF GD is sufficient for surface activation.

4. Particle energy of ion source is too high and damages polyimide.

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Limitations & Consequences

Ÿ Lab Coaterw Copper deposition rate dominates web speed

w 1 magnetron equipped with copper Þ low web speed

w For production machine: some additional magnetrons possible Þ higher web speed Þ higher productivity

Ÿ Measure & Testw PFT + PCT at a cooperation partner

w Tests are intensive by time

w No adhesion values available close after experiment Þ long feedback time

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Following Coating Step

Ÿ Steps afterwards w thick copper deposited commonly by galvanic technologies =>

wet chemistry

Ÿ Are there alternatives to galvanic coating?

Ÿ Possibility: Electron Beam PVD with copperw advantage:

n PVD technology, sustrate keeps „dry“

n can be done immediately after sputter run at same vacuum cycle

n No wet chemistry & electrolysis =>

- minimized chemical hazard

- no costs for chemical waste removal

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Ÿ Executed Experimentsw Evaporation of Cu from hot crucible

w Coating Cu on thin steel foil

w Coating Cu on PET web

Ÿ Measurementw Layer thickness of Cu by coulometry (inhouse)

w Electrochemical process

Ÿ First successesw Deposition rate about 4.000 nm*m/min

w Stable EB process

w Crucible capacity provides long cycle time

w Process not optimized on PI - higher rates still expected due to acceptable heat load

Starting Experiments of Copper EB-PVD

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EB PVD Cu - Open Tasks

Ÿ Experiments started on PET

Ÿ Next step: technology transfer to PI

Ÿ because of some µm layer thickness w Þ minimization of tension over web width necessary

Ÿ Optimization of cooling efficiency because of high condensation heat load

Ÿ Reducing conditioning time for copper evaporation

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Ÿ Coating technology for interface and seed layer developed successfully

Ÿ Several pretreatment tools tested

Ÿ Use of MF glow discharge provides best results

Ÿ PFT after PCT necessary for evaluation

Ÿ First steps in EB PVD of copper

Special thanks to the team members for their work.

Summary - Copper On Polyimide

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FOBA 600

FOBA 600

Thank you for your attention.

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