Utilizing Printed Electronics Methods for the Fabrication of Multi-layer PC Boards

D. R. HinesLaboratory for Physical Sciences

College Park, MD

John Bolger, Leon LantzDepartment of Defense, Ft Meade, MD

Rich Lewis and Rick Trudeau

KeyW Corporation, Hanover, MD

• Goal: Demonstrate the capability of additive manufacturing to fabricate multi-layer PC boards on demand.

• Utilize a 2-layer power supply design requiring a 1 Amp current carrying capability.

• Print alternating layers of Silver nano-particle (AgNP) and polyimide (PI) inks.

• Populate, functionally verify, and perform reliability testing of 14 boards.

Overview

Requirements

Metal Ink

Dielectric Ink

layer 2layer 1

20 mm

16 m

m

Electrical Current Requirement: 1 Amp

Future Layers : Minimum Feature size & pitch <100 um

Feature Sizes:Biggest 2 – 5 mmSmallest 250 um

Printing Methods

Syringe

Ink-Jet

Aerosol-Jet

Considerations for Materials Selections

Droplet Formation

Substrate Wettability

Drying/Sintering Temperature

Solvent Compatibility Thermal Compatibility

• Polyimide coated SiO2/Si substrate

• Ag nanoparticle ink– Solvents: IPA, Ethylene Glycol– Thermal: requires sintering at 255 ˚C to obtain resistivity 6 x 10-8 Ω m

• Polyimide ink– Solvent: NMP – Thermal: requires thermal cure up to 300 ˚C

• Selected materials are stable to all solvent and thermal processing requirements

Materials

• Ag ink: – Print speed 3 mm/sec– Tip Diameter 150 um tip– Ink Stream Diameter 40 um– 200 pL/sec (est.)

• PI ink:– Print speed 6 - 8 mm/sec – Tip Diameter 300 um tip– Ink Stream Diameter 180 um– 7000 pL/sec (est.)

Print Parameters

• Thermally oxidized Si wafer• Spin coated polyimide (5 um)

– Cure: 255 ˚C, 90 min• First Metal Layer (5 um, 2 Passes) and sinter• Dielectric Layer (10 um, 2 Passes) and cure• Second Metal Layer (5 um, 2 Passes) and sinter• Mount substrate on carrier board• Stencil print conductive adhesive• Pick-and-place• Thermal Cure using reflow oven• Removal from Carrier board• Mounted on test board

Process Flow

Board Fabrication Steps

Component Assembly Steps

Serpentine Fill

Perimeter Fill

BorderFill

Pitch

Pattern Fill SchemaPrinter Process Issues

Aerosol-jet printing requirement for the fabrication of Solid Features

40 mm wideline

200 mm wideline

Polyimide Dielectric layer

Ag nanoparticle Ink Sintered at 255 ˚C

Printed Test Structures

Cartoon of Test Structure

Evaluation of Printed Structures

Printed Interconnected Layers Printed two-layer Structure

Ag

Si PI PISi

Ag

Cross-sectional Measurements

Mea

sure

d W

idth

, mm

0

50

100

150

200

250

0 50 100 150 200 250

12 4 8

Targeted Width, mm

Number of

Print Passes

Evaluation of Printed StructuresWidth Measurements

Number of Print Passes

0

5

10

15

20

25

0 5 10 15 20 25

50 um100 um150 um200 um

1 2 4 8

Mea

sure

d Th

ickn

ess,

mm

Targeted Thickness, mm

TargetedWidth

Evaluation of Printed StructuresThickness Measurements

0

20

40

60

80

100

120

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

CalculatedMeasured

Resis

tan

ce

,

Area-1, um-2

R = r L (1/A) = (6.4 ± 0.1)x10-8 W m

Resi

stan

ce, W

Measured Area-1, mm-2

Calculated

Measured

Evaluation of Printed StructuresResistance Measurements

Evolution of 2-layer Board Design

1st Gen

2nd Gen3rd Gen

1-layer Power Supply Board (Ink-Jet printed)

Bottom Layer Top LayerRequired connections

‘vias’

2-Layer Board Artwork

Metal Layers and Interconnects

Creation of Dielectric layer

Metal Layers overlap Remove overlap at ‘vias’

2-Layer Board Artwork

Bottom Metal Layer Top Metal LayerDielectric Layer

Final Artwork2-layer Power Supply Board

~1 mm

Build up of 2-layer Boards

(26) 2-layer Power Supply Boards Fabricated

and Submitted for

Reliability Testing

2-Layer Board Performance Test Process

• Eight (8) boards in Temperature Cycling – 2000 cycles from 0 to 90 ˚C

• Six (6) boards in HTOL @ 90 ˚C– Over 2200 hours to date

• Six (6) boards to Enter Humidity Testing– 85 ˚C/85% RH

Reliability Evaluation

Performance Test Results

High Temperature Operational Life Testing at 90 ˚C

Total of 18 Individual Voltage Regulators -

After more than 2000 hours at 90 ˚C14 Still Operational

2 Show fluctuations & 2 ‘Dead’

4-Layer Boards - Original Artwork

Dielectric 3 Dielectric 2 Dielectric 1

Metal - Bottom Metal - Sig2 Metal – Sig1 Metal – Top

4-Layer Boards - Direct-write Artwork

Dielectric 3 Dielectric 2 Dielectric 1

Metal - Bottom Metal - Sig2 Metal – Sig1 Metal – Top

• Continue reliability evaluation (2-layer boards)– 85 ˚C/85% RH

• Fabrication of 4-layer boards

Future Work

C = r 0 (A/d)

Material r C (1 mm x 1 mm2)

C (1 mm x 1 cm2)

Polyimide dielectric 3 25 pF 1 nF

Barium Titanate nanoparticle dielectric

40 300 pF 12 nF

Dielectric constants of high-k Materials

SiO2 3.9Al2O3 9HfSiO4 11ZrO2 25HfO2 25Ta2O5 27La2O3 30LaAlO3 30Nb2O5 35TiO2 30–40 (Anatase), 80–100 (Rutile)BaTiO3 1700SrTiO3 2000Pb(Zr,Ti)O3, (Pb,La)(Zr,Ti)O3 2500CaCu3Ti4O12 80 000M. Osada and T. Sasaki, Adv. Mater. 24, 210 (2012)

Printed Capacitors

Integrated Components

Si Capacitors as Substrate

Capacitor Interconnect layer

Power Supply Layers

Hybrid Printed Electronic Device on Kapton

2x4 array of 200 nm Thick Si Semiconductor Elements Transfer Printed onto a Kapton Substrate

Next Step: Add dielectric Layer and Gate Electrode.

Ag Nanoparticle Ink

Source

Drain