Laser Drilling For Electrical Interconnection in Advanced ... · EXCIMER LASERS LASER Gas lasing...

Laser Drilling For Electrical Interconnection in Advanced Flexible Electronics Applications

Timothy E AntesbergerEndicott Interconnect Technologies1093 Clark StreetEndicott, NY [email protected]

Acknowledgement:Frank Egitto

Outline

Introduction: Motivation for laser processing and advanced electronics

Laser Fundamentals

Laser/Material Interactions

Types of lasers, laser drilling systems, and drilling techniques

Laser-enabled high-performance electronic components

Extensions of laser processing technologies

Levels of Interconnection

Functions of Rigid and Flexible Electronic PackagingMounting and physical support of electronic components

Protection of devices from environment

Removal of heat from devices

Electrical interconnection of components

Signal distributionPower distribution

Chip

Chip Carrier

Underfill

Conductive Joint

Flip Chip Assembly

Chip

Chip Carrier

EncapsulantWire

Wirebond Assembly

Flex

Wafer

IC Chip

System

Traditional Application of Laser Processing to Flexible Electronics

Annealing of conductors to control electrical properties

LPKF

Exposure of photosensitive materials (e.g., photoresists) for pattern formation

Holemaking for electrical interconnection

SkivingLabeling

SingulationRepair of circuit traces

etc.

Layer 1

Layer 2

Copper Lines Copper Pads

High density elecronic components arecomposed of multiple layers of circuit traces.

A

A'

Land

Plated Through Hole (PTH)

Electrical interconnection between layersis made with drilled and plated holes.

Wiring Planes

External Mounting Planes(No Wiring)

Tycom Microdrills 550 — Diameters .0040" - .0130"

For decades, mechanical drilling has been the conventional means of hole formation and is still a mainstay for most printedcircuit board applications.

Hold down ring

Die

Punch

Mechanical punching has been used extensively for hole formation in thin, flexible, homogeneous materials. Hole diameters on the order 0.002" are achievable, but the process ishighly sensitive to material properties.

FluteLength

Helix Angle

Drill Diameter

Shank

Cutting Edge

Margin Width

Point Angle

Land Width

Web Thickness

Margin Relief

Primary Relief

Secondary Relief

Drill Features

Point Detail

The demand for high-performance, lightweight, portable computing power is driving the industry toward miniaturization of many electronic products and the components that comprise them.

Common examples are laptop computerspersonal digital assistantsdigital camerascellular phones

"Smaller, Lighter, Faster, Cheaper"

Traditional Approaches to Increasing Circuit Density

Smaller lines and spacesSmaller viasBlind and buried (controlled-depth) viasAdded wiring layers

A

A'Use of blind vias increases wiring density.

A

A'

A'

Adding layers increases wiring density

A

To incorporate a greater degree of electronic function into a smaller volume, circuit traces and the holes used to connect them must have smaller physical dimensions.

Microvias are defined as holes used for electrical interconnection and having a diameter less than 0.006 inch (150 m).

hole diameter, dcapture pad diameter, c = d + xline width, lline space, sline-to-pad space, phole pitch, h

d + xd

p

ls

hk

Top View

CrossSection

B

B'

A

A'

2 Lines Per Channel

Hole diameters affect wiring density.

h1

Increased Number of Lines Per Channel

Increase in Wiring DensityWith Reduction in Hole Diameter

h2

h1

Reduced PitchLand on larger hole

Land on smaller hole

Top View

hole diameter, dcapture pad diameter, c = d + xline width, lline space, sline-to-pad space, phole pitch, h

Cross Section

Hole Diameter and Wiring DensitHole Diameter and Wiring Density

Increase in wiring density with decrease in hole diameter by way ofincreased number of lines per channel (pitch constant).

For h, p, x, l, and s, constant,

h = nl + (n -1)s + 2p + x + dn(l + s) = - d + q , where q = h + s - 2p - x

n2(l + s) = - d2 + q , where d2 is the smaller diameter hole

n1(l + s) = - d1 + q , where d1 is the larger diameter hole

(n2 -n 1)(l + s) = d1 - d2

n2 - n1 = (d1 - d2) / (l + s).

That is, the increase in the number of lines per channel, n2 - n1 , is equal to the ratio of thechange in hole diameter, d1 - d2 , to the line pitch, l + s. Again, n2 - n1 must be an integer. Forexample, if d1 - d2 < l + s , there is no increase in wiring density. If (l + s) < (d1 - d2) < 2(l + s) ,lines per channel increase by 1. If 2(l + s) < (d2 - d1) < 3(l + s), lines per channel increase by 2,and so on.

B

B'

A

A'

2 Lines Per Channel

PTHs consume real estate, blockingchannels that could be used for wiring.

Cross Section

B

B'

A

A'C'

B

B'

A

A'

PTHBlind Via

Space available for wiring

Increase In Wiring Density With Blind Vias

Increase In Wiring Density Blind Via vs PTH

Use of blind vias Increases wiring density.

Mechanical drills and punches are not suited to formation of blind microvias.

A

AA'

A'

blind via through via

buried via

Microvia

A blind, buried, or through via that is on the order of 150 m or smaller in diameter.

Definition often limited to blind vias for high density interconnect structures (HDIS).

Layer Interconnection with Controlled-Depth Vias

Layer Interconnection with Plated Thru Holes Lines must go around PTH's

Controlled-depth vias don't block lines

Increase In Wiring Density With Controlled-Depth Vias

40 m and 75 m laser-drilled vias in cores

0S/1P Joining Core

2S/1P Core

0S/1P Joining Core

2S/1P Core

0S/1P Joining Core

Electrically Conductive

Paste

Increase In Wiring Density WithControlled-Depth Vias

Blind Via

ElectricallyConductivePaste

40 m and 75 m laser-drilled vias in cores

Mechanically-Drilled Through Via75 m diameter

170 m clearance hole

Laser-Drilled and Plated Through HoleNd:YAG 355 nm Gaussian Beam

Drilled Through Epoxy-Glass and Cu Foil (Top and Bottom)

Epoxy-Glass3.0 mil diameter6.0 mil thickness

Laser Micromachining of a Human HairUsing an Excimer Laser at 193 nm

Source: Lambda Physik

Outline

Introduction: Motivation for laser processing in advanced electronics

Laser Fundamentals





Lasing MediumR=100%

R<100%

1

2

3

4

6

5

LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of RRadiationadiation

Source: Engineering Technology Institute

Laser Wavelengths For Processing

100 nm

Excimer Nd:YAG CO2

Laser Type

Wavelength

248 nm 1064 nm

VISIBLE INFRAREDULTRAVIOLET

1000 nm 10,000 nm

400 nm 750 nm

10,600 nm

Lasing MediumLasing Medium

Pumping MechanismPumping Mechanism

MirrorMirrorR = R = 100%100%

MirrorMirrorR < R < 100%100%

Laser Beam OutLaser Beam Out

Elements of a Elements of a LaserLaser

IntenseIntenseMonochromaticMonochromatic

Continuous Wave (CW) or Pulsed (High Energy Bursts) Outputs

Pulsed Mode Used For Clean Holemaking With a Minimum of Thermal Damage

Outline

Introduction: Motivation for laser processing in advanced electronics

Laser Fundamentals





mask Beam Shaping and Delivery

Photon (Energy) Absorption By Material

Breaking of Chemical BondsPhotochemical ProcessesPhotothermal Processes

Vaporization (Ablation)

Laser Holemaking

Laser Material Interaction

• Homogeneous– Consistent material

cross-section – No Cu planes – No glass fillers

• Non-Homogeneous– Fiber reinforced

• FR4 typical circuit board material

– Particle filled• Build-up materials for

HDI packaging

– Cu planes– Mixed materials

200 400 600 800 1000 1200

Wavelength (nm)

00.10.20.30.40.50.60.70.80.9

1

AbsorptionFR4Matte CuGlass

355 nm - Nd:YAG 3rd Harmonic

308 nm - XeCl excimer

248 nm - KrF excimer

532 nm - Nd:YAG 2nd Harmonic

1064 nm - Nd:YAG Fundamental

Source: ESI

Absorption Curves

Focused Spot

Laser Beam Delivery

Mask Imaging

Mask

Contact or Conformal Mask

Lens

EtchedMetalFoil

Io

Ith, xth

( )

Ix = I0 exp- x

Ablation ceases when Ix < Ith

Io

Ith x

oxth

x

shallow absorption moderate absorption deep absorption

Ix = I0 exp- x

I0 = I1 I0 = I2 > I1 I0 = I3 > I2

Rate(Etched Depth Per Pulse)

I1 I2 I3 I0

moderate deeper absorptionhigh rate

low little or no absorptionlow rate

Ix = I0 exp- x

1 2 3

high strong but shallow absorptionlow rate

321

I0 I0 I0

Rate(Etched Depth Per Pulse)

Ith = k (1/ n)

200 300 400 500

BPDA-PDA Polyimide

CF2 -CF2Poly(tetrafluoroethylene)

OC

N-CO

OC

NCO

Absorbance

Wavelength (nm)

Absorbance of PTFE and Polyimide

C.R. Davis, F.D. Egitto, and S.L. Buchwalter, Appl. Phys. B54, 227 (1992).

PTFE

0.1 1 10 100% Polyimide in PTFE

0

1

2

3

4

5

Etch Rate (um/pulse)

BPDA-PDA Polyimide

Doping of PTFE With Polyimide

F.D. Egitto and C.R. Davis, Appl. Phys. B55, 488 (1992).

~ 102 cm-1

OC

CO

N

OC

CO

N

CF2 -CF2

~ 105 cm-1

Outline


Laser Fundamentals





EXCIMER LASERSLASER

Gas lasing mediumUltraviolet (UV) emissione.g., 308 or 248 or 193 nmSeveral hundred pulses per second

LASER SYSTEMBroad beamLaser spot is shaped using a projection mask

TYPICAL ATTRIBUTESBest suited to etching of polymersNot well-suited to removal of metalsTapered wall profile

75 m via in polyimide made with an excimer laser at 308 nm.

Mask Imaging

Mask

Cu at base of via

Excimer Laser

Turning Mirror

Turning Mirror

Turning Mirror

Prism Beam ExpanderBeam Homogenizer

Lens

Objective Lens

Vacuum Chuck / Rotational StageX-Y Positioning Stage

Substrate

Mask

Example of Excimer Laser SystemExample of Excimer Laser SystemUsed With Projection MaskUsed With Projection Mask

Mask Imaging

Mask

x

y

stationary

Excimer Laser

Turning Mirror

Turning Mirror

Turning Mirror


Lens

Objective Lens


Substrate

Mask

Example of Excimer Laser SystemExample of Excimer Laser SystemUsed With Projection MaskUsed With Projection Mask

Stationary Beam, Scanning Mask and SubstrateStationary Beam, Scanning Mask and Substrate

Mask Imaging

Mask

x

x

Excimer Laser

Turning Mirror

Turning Mirror

Turning Mirror


Lens

Objective Lens


Mo MaskSubstrate

Example of Excimer Laser SystemExample of Excimer Laser SystemUsed With Contact MaskUsed With Contact Mask


Lens

Etched Metal Foil

y

x

LASERGas Lasing MediumIR emission (around 10.6 m)

LASER SYSTEMFocused beam (50-75 m minimum diameter) or metal contact mask

TYPICAL ATTRIBUTESHighest powerBest suited to drilling of polymers, some thermal damageHigh reflectance from metal surfacesBest when speed (not small size) is importantUsed in about 80% of microvia applications

CO2 LASERS

Focused Spot Contact or Conformal Mask

Lens

EtchedMetalFoil

CO2 Laser Processing of Woven Glass/Epoxy Resin Using a Conformal Mask. Cu-Plated 6 mil Via.

LASERSolid Lasing MediumInfrared (IR) Fundamental Emission (1064 nm)Visible (532 nm) or UV (355 or 266 nm) emission with nonlinear crystalsUp to 100,000 pulses per second

LASER SYSTEMFocused beam (12 to 25 m diameter, depending on wavelength and optics) or shaped beam for blind via drilling.Trepanning for holes having diameters greater than beam diameter

TYPICAL ATTRIBUTESCapable of drilling variety of materials (polymers, glass, metals)Most versatileWell-suited to holes with small diameter, high aspect ratioUsed in about 20% of microvia applications

Nd:YAG LASERS

Mask Imaging

Mask

Focused Spot

Trepanning

Top View

Beam

Via

Punching

Nd:YAGQ-Sw

BBO2nd

BBO3rd

Arc Lamp orDiode Pump

OutputCoupler

BeamSplitter

BeamDump

355 nmOutput

1064 nm

532 nm

355 nm

HRMirror

355 nm Laser Rail Layout355 nm Laser Rail Layout

Source: ESI

Trepanning

Top View

Beam

Via

PunchingBeam Profiles

Gaussian

"Top Hat"

Radial Pitch

Beam Diameter

Bite Size

Spiral Tool

Beam Diameter

Bite Size

Trepan Tool

multiple revolutions(programmable) laser beam turns

on and off

Beam PositioningBlind Via DrillingThrough Via Drilling

Blind via on pad

Buried via throughclearance hole

Registration Requirements

Clearance hole

Panel BorderToolpath File Border

Design Data Locations Drilled Hole

Locations

Four Point AlignmentToolpath File %(ESI 5100)T1 8T0 996 G0X112710.0 Y94580.0X112710.0 Y661160.0X504510.0 Y661160.0X504510.0 Y94580.0

T1 1T0 101 G0T2 101.6X71119.0 Y80690.0Y83230.0Y85770.0Y88310.0Y90850.0X80010.0 Y89580.0X78739.0 Y80690.0X76199.0X73659.0X81279.0X118109.0 Y88310.0X72389.0 Y128950.0X214629.0 Y88310.0X237490.0 Y89580.0X261644.9 Y102852.0Y104122.0Y105392 0

Designed location of alignment markers

Designed location of drilled holes

Hole Diameter in m

Design Alignment Targets

Measured Alignment Targets

RegistrationX-Ray Image of 75 m Vias Through 125 m Clearance Holes

Typical microvia Multilayer viaSkip microvia

Via on via withconductive fill

Staggered via

Blind Via FormationVarious Blind Via Structures

Source: TechSearch International, Inc.

Dielectric

Mask Imaging

Mask

Focused Spot


Lens

EtchedMetalFoil

Blind Via Drilling:

Cu surface mask

or, without Cu mask

Laser-Drilled and Plated Blind ViaNd:YAG 355 nm Gaussian Beam, Trepanned, No Surface Cu Mask(Similar hole quality possible using shaped beam in punching mode)

Top Diameter = 4.2 milsBottom Diameter = 3.0 mils

In Focus, High Fluence*For High Intensity

Through Metal Stop on Metal

Out of Focus or ORLow Fluence For Low Intensity

"Shaped" UV orIR to Reflect From Metal

* fluence = energy per unit area per pulse

Control of Etch Selectivity By Adjustment of Fluence or Wavelength

Pass 1: Remove surface Cu.

Nd:YAG Laser.........Two-Pass ProcessGaussian Beam Profile

Trepan or Spiral

Pass 2: Remove dielectric.

Trepan or Spiral

160 m Laser-Drilled Blind Via In Epoxy/GlassUsing 355 nm Nd:YAG Gaussian Beam

Spiral Mode, Two Pass Process

CO2 Laser..........Two-Step Process Chemically etched copper "mask"

Ablate dielectric with IR beam

Combination Nd:YAG & CO2 Laser Process

Trepan or Spiral

UV UV

Cu Pad

Apply

Expose

Develop

Photomask

Photosensitive Dielectrics

Positive Negative

UV UV

Cu PadPositive Photoresist Negative Photoresist

Apply Resist

Expose

Develop

Photomask

Photolithography

O* CO, CO 2, etc.

Plasma Wet Chemical

Chemical Etching

Photoresist

Immerse In or Spray WithWet Chemical Etchant

Strip Photoresist

Plasma Etch

0 10 20 30 40 50 60 70 80 90 100 110

ThousandsVia Count / Side

0

500

1000

1500

2000

2500

Number of Sides / (Day - Machine)

Laser, 300 vias/secLaser, 80 vias/secPhoto process

Panel Throughput: Photo-vias vs Laser

50,000 100,000

150,000 200,000

250,000

Number of Vias Per Panel

Cost Per Panel

Laser

Plasma

Laser Drilling vs Plasma EtchingRelative Cost

0.002" 0.004" 0.006" 0.008" 0.010"

Via Diameter

Cost Per ViaLaserMechanical

Laser Drilling vs Mechanical DrillingRelative Cost

Photo-via42.0%

Laser via43.0%

Plasma3.0%

Drill9.0% Punch

3.0%

December 19961

Photo-via34.0%

Laser via60.0%

Plasma1.0%

Drill4.0% Punch

1.0%

August, 19981

1Estimates: N.T. Information, Ltd., charts courtesy of Electro Scientific Industries.

2The Electronics Industry Report 2002, Prismark Partners LLC.

Packaging and HDI Production

Laser vias used for 90% of HDI applications in 2002.2

0 2 4 6 8 10 12 14Via Diameter (mils)

0.1

1

10

Aspect Ratio

Source: Electro Scientific Industries, Inc.

ESI's Via Technology Roadmap

UVYAG

MechanicalDrill

Blind Vias Through Vias

CO2Photovia

Outline


Laser Fundamentals





HyperBGAHyperBGAR

90 m Blind Via

Chip

Solder Underfill

50 m Through Via

Standard Build-up 3-2-3CoreEZ 2-4-2

X Section Comparison

Both packages use 50υ blind viasCoreEZ core vias are 4x smallerCoreEZ is ½ as thickCore EZ’s core is 6 times as denseCoreEZ can fully route signals on both sides of the core

2 times the wiring density with fewer layers

CoreEZCoreEZ R

HyperZ

• Coreless structures for maximum wiring density– 40um and 65um vias

R

R. Fillion, E. Delgado, P. McConnelee, and R. Beaupre, "A High Performance Polymer Thin Film Power Electronics Packaging Technology," Advancing Microelectronics, 30(5), 7 (2003).

GE Power Overlay

Ray Fillion

Outline


Laser Fundamentals





Embedded Resistor Trimming

• Resistors formed through etching thin film resistor foil

• Resistor value designed low for etching process

• Laser used to trim up to nominal value

• Tighter control

Laser Direct Imaging

• Laser Direct Imaging of Photoresist– Real-time registration adjustment– Mask savings v. traditional photoprocessing– Falls inline with existing equipment infastructure

Laser Direct Ablation of Dielectric

• Laser Direct Ablation– Laser system used to

form trenches in dielectric

– Trenches are plated with via fill plating technology

– Surface material is removed leaving circuit traces embedded in dielectric

SummaryLaser processing is key to providing portable and high performance computing power.

Technology is changing rapidly with new enabling applications being consistently being discovered.

Abundant opportunity for process control through variation of laser beam parameters (e.g., wavelength and fluence) and material properties.

Thanks for your attention.QUESTIONS?

Laser Drilling For Electrical Interconnection in Advanced ... · EXCIMER LASERS LASER Gas lasing...

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