2-5-14 adam giang 2014 flextech inkjet su-8
TRANSCRIPT
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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]
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
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Introduction• Thin, patterned layers were
created without photomasks• Vias created with additive
process with dimensions smaller than drop size in a single pass
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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
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Process Flow Traditional Photolithography Ink Jet Print
Spin CoatSoft Bake
ExposePEB
Develop
Print PatternThermal Cure
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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
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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
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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)
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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
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Via
Halo Texture
85µm DS, 45°C, 1x1Pattern 50µm
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Process Controls
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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
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Drop Spacing and Line Formation• No drop overlap - Separate drops
• Moderate drop overlap – Side-beading effect
• Sufficient drop overlap – Parallel sides
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Drop Spacing 75µmDrop Spacing 100µm
Drop Spacing and vias
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Temp 45°C • 2x2 Pattern
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Drop Spacing – Process Design
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Platen Temp 45°C, 4x4 Patterns
60µm DS70µm DS80µm DS
DS Decrease FT Increase Via Size Decrease
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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
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Increased Temp
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Platen Temp: 35°C
Platen Temperature and Vias
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Platen Temp: 55°C
85µm DS•1x1 Pattern
Temp Decrease50µm
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Platen Temp – Process Design
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Drop Spacing: 85µm, 1x1 Pattern
55°C 45°C 35°C
Temp Decrease FT Decrease Via Size Decrease
50µm
50µm
50µm
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Digital Pattern Design
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• Pixelated images created with Adobe Photoshop• Each pixel corresponds to a location on the wafer• Colored pixels signify drop location
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Pattern Design - Vias Insert Small Logo Here
1x1 2x2
3x3 4x4
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Pattern Design - Vias Insert Small Logo Here
100µm DS, 45°C, 1x1 100µm DS, 45°C, 4x4
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4x4
1x1
Pattern Design - Vias Insert Small Logo Here
• 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
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Pattern Design - Vias Insert Small Logo Here
80µm DS, 45°C, 1x1 60µm DS, 45°C, 4x4
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Pattern Evaluation
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Via Size• Drop Spacing
• Platen Temp
• Pattern Design
• Minimum dimensions <50µm
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Wafer 6 1x1 85DS 45C
50µm
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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)
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Via Shape
95µm DS
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Platen Temp 45C, 1x1 Pattern
90µm DS 85µm DS50µm
50µm
50µm
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Pattern Design and Shape• Smaller void patterns create shapes more sensitive
to process changes
• Large designs create straight sides more easily
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50µm
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Thickness Control
• Drop Spacing
• Substrate Temp
(Nozzle Temp)
(Formulation)
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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
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DOE• Test multiple combinations
of DS and Platen temp
• Select combinations for appropriate thickness
• Test combinations several different pattern designs (i.e. [1x1],[4x4])
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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
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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
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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
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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
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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
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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
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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
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Questions?
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www.microchem.com (617)[email protected]