2-5-14 adam giang 2014 flextech inkjet su-8

For Distribution to Flexible & Printed Electronics Conference attendees only. Content remains property of FlexTech Alliance

Fabrication of sub-100µm vias using an ink-jettable, SU-8 based epoxy resist

Adam Giang, Applications Engineer, MicroChem Corp.www.microchem.com • (617)-965-5511 • [email protected]

http://www.microchem.com/

For Distribution to Flexible & Printed Electronics Conference attendees only. Content remains property of FlexTech AllianceAdam Giang 05/01/2023 2

Introduction• A new, thermally cured version of

SU-8 based epoxy resist developed for inkjet

• Via patterns were designed using Adobe Photoshop and imported into a Fuji Dimatix DMP-2800 Materials Printer

• Goal: Combine unique properties of SU-8 with advantages of ink-jet


Introduction• Thin, patterned layers were

created without photomasks• Vias created with additive

process with dimensions smaller than drop size in a single pass


Advantages

• Optically Transparent• High chemical resistance• Excellent thermal stability• Low Young’s modulus

• Maskless Lithography• Rapid prototyping• Reduced material waste• Ability to coat unusual substrates• Reach new applications

• Roll to roll• Large single-format sheet

SU-8 Ink-Jet


Process Flow Traditional Photolithography Ink Jet Print

Spin CoatSoft Bake

ExposePEB

Develop

Print PatternThermal Cure


FTIR Evaluation and Cross-linking

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• FTIR was used to monitor cross-linking reactions in SU-8 and to determine optimal cure temperature

• As bake temp. increases, epoxy absorbance intensity decreases as epoxy is converted to ether and cross-links

• At 200C bake temp, epoxy absorbance is ~0

Cross-linking (acid)HA

Epoxide

Ether

800 850 900 950 1000 1050 1100 1150 1200 1250 1300-0.1

2.77555756156289E-170.10.20.30.40.50.60.70.8

Wavenumber

Absorbance

•65°C•95°C•200°C

Epoxy: 860, 915cm-1


Fluid Properties and Printer Settings

Surface Tension 26.7 Dynes/cmDensity ≈1.03 kg/m3

Filtration 0.2µmViscosity(kinematic)

5.25 cSt

Jetting Voltage 15V - 20VCartridge Size 10pLSubstrate Si, GaAs



Experimental VariablesProcess Controls1) Drop Spacing (DS)

2) Platen Temp

3) Pattern Design

• (Nozzle Temp)

• (Number of Passes)

Pattern Evaluation1) Via Size

2) Via Shape

3) Film Thickness (FT)



DIC Microscopy• Images were obtained

using Differential Interference Contrast (DIC) Microscopy

• Optical technique that accentuates differences in thickness, density, or optical index of a sample

• Color gradients signify changes in thickness


Via

Halo Texture

85µm DS, 45°C, 1x1Pattern 50µm


Process Controls



Drop Spacing• Distance between the

centers of adjacent droplets jetted by printhead

• Overlap between adjacent drops allows material to coalesce

• Decreasing drop spacing allows drops to blend together, and increases film thickness



Drop Spacing and Line Formation• No drop overlap - Separate drops

• Moderate drop overlap – Side-beading effect

• Sufficient drop overlap – Parallel sides



Drop Spacing 75µmDrop Spacing 100µm

Drop Spacing and vias


Temp 45°C • 2x2 Pattern


Drop Spacing – Process Design


Platen Temp 45°C, 4x4 Patterns

60µm DS70µm DS80µm DS

DS Decrease FT Increase Via Size Decrease


Platen (substrate) Temperature• Upon impact with the

substrate, the droplets spread while solvent evaporates

• When heated, the substrate drives of excess solvent more quickly, decreasing drop spread

• Decreased drop spread tends to create thicker films


Increased Temp


Platen Temp: 35°C

Platen Temperature and Vias


Platen Temp: 55°C

85µm DS•1x1 Pattern

Temp Decrease50µm


Platen Temp – Process Design


Drop Spacing: 85µm, 1x1 Pattern

55°C 45°C 35°C

Temp Decrease FT Decrease Via Size Decrease

50µm

50µm

50µm


Digital Pattern Design


• Pixelated images created with Adobe Photoshop• Each pixel corresponds to a location on the wafer• Colored pixels signify drop location


Pattern Design - Vias Insert Small Logo Here

1x1 2x2

3x3 4x4



100µm DS, 45°C, 1x1 100µm DS, 45°C, 4x4


4x4

1x1


• Larger design patterns allow closer drop spacing• Larger design patterns give thicker layers at similar features

sizes• Larger patterns allow easier shape tuning

Smaller Drop Spacing Thicker film Easier shape control

Larger Drop Spacing Thinner film



80µm DS, 45°C, 1x1 60µm DS, 45°C, 4x4


Pattern Evaluation



Via Size• Drop Spacing

• Platen Temp

• Pattern Design

• Minimum dimensions <50µm


Wafer 6 1x1 85DS 45C

50µm


Via Shapes• Pattern shape is determined by how much individual

drops coalesce around the via

• As drops start to come together, they form a ‘star’ shape

• As the drops continue to blend together, the corners come together into square and round shapes, until finally the feature collapses

• Because these shapes depend on the degree of drop overlap, not all shapes are possible at all sizes (for a single formulation)



Via Shape

95µm DS


Platen Temp 45C, 1x1 Pattern

90µm DS 85µm DS50µm

50µm

50µm


Pattern Design and Shape• Smaller void patterns create shapes more sensitive

to process changes

• Large designs create straight sides more easily


50µm


Thickness Control

• Drop Spacing

• Substrate Temp

(Nozzle Temp)

(Formulation)


60µm 70µm 80µm 85µm35°C .438µ

m.373µm

.313µm

.264µm

45°C .463µm

.402µm

.332µm

.277µm

55°C .5µm .413µm

.336µm

.284µm

Drop Spacing

Subs

trate

Tem

p


DOE• Test multiple combinations

of DS and Platen temp

• Select combinations for appropriate thickness

• Test combinations several different pattern designs (i.e. [1x1],[4x4])


60µm 70µm 80µm 85µm35°C .438µ

m.373µm

.313µm

.264µm

45°C .463µm

.402µm

.332µm

.277µm

55°C .5µm .413µm

.336µm

.284µm

Drop Spacing

Subs

trate

Tem

p


Process Design Insert Small Logo Here

Course Adjustmen

t?

Design Pattern

s

Set/Test Drop

Spacing

Adjust Platen Temp

Finish

Size and shape off?

Size or shape off?

Thickness off only

Adjust Platen

Temp or Reformula

te

Start

Y

N

YY

N N


Shape Distortion• DMP 2800 printer uses a 16

nozzle printhead

• Larger Patterns Require multiple passes

• Discontinuity between passes causes unequal pull on the via

• Shapes printed close to these borders can be distorted



Shape Distortion Insert Small Logo Here

• DMP 2800 printer uses a 16 nozzle printhead

• Larger Patterns Require multiple passes

• Discontinuity between passes causes unequal pull on the via

• Shapes printed close to borders can be distorted

For Distribution to Flexible & Printed Electronics Conference attendees only. Content remains property of FlexTech Alliance 05/01/2023 33

Conclusion• SU-8 based epoxy resist suitable for use with inkjet

printing

• Drop spacing, platen temp, and pattern design controlled via size and shape, and film thickness

• Vias fabricated with an additive process

• Both round and square vias were demonstrated

• Features created were smaller than drop size

Adam Giang



Conclusion• Thermal-cure procedure does not require photomask or

exposure, allowing rapid prototyping

• Inkjet process reduced material waste

• Higher viscosity inks, photo-cure (lower temperature) also available

Adam Giang



AcknowledgementsDaniel J. Nawrocki, Director of Development and Engineering, MicroChem Corp.

Michael Stan, Applications Engineering Manager, MicroChem Corp.

Tom Sutter, Global Business Development Manager, MicroChem Corp.

George J. Cernigliaro, Ph.D., Vice President and Chief Technology officer, MicroChem Corp.

Fuji Dimatix Sales/Customer ServiceAdam Giang


For Distribution to Flexible & Printed Electronics Conference attendees only. Content remains property of FlexTech Alliance

Questions?

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www.microchem.com (617)[email protected]

http://www.microchem.com/

2-5-14 adam giang 2014 flextech inkjet su-8

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