laser drilling for electrical interconnection in advanced ...laser gas lasing medium ultraviolet...

Laser Drilling For Electrical Interconnection in Advanced Flexible Electronics Applications

Frank D. EgittoEndicott Interconnect Technologies1701 North StreetEndicott, NY [email protected]

OutlineLaser processing and advanced electronics

Motivation for laser drilling

Lasers

The process of laser "ablation" (vaporization)

Types of lasers, laser drilling systems, and drilling techniques

Laser-enabled high-performance electronic components

Levels of Interconnection

Functions of Rigid and Flexible Electronic Packaging

Mounting and physical support of electronic componentsProtection of devices from environmentRemoval of heat from devicesElectrical 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

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 printed circuit 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 is highly 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"

Microelectronics Advanced Interconnections

Laser via / thin film / z-interconnect based interconnect technology needed to reduce the IC to PWB interconnect gap

HyperBGA is a registered trademark of Endicott Interconnect Technologies, Inc.

Semiconductors versus PackageSmallest features: “parallel paths” for how long?

IC scaling

Time

PWB

PWB w/ buildup layers& Laser vias

Reduced Interconnect

Gap

HyperBGA® Interconnecttechnology

2000’s1990’s 2010’s

Z-interconnect technology

Meso

Micro

Nano??

InterconnectGap

$$F ilte rs A n te n n a s

H

SOPSource:

adapted after Shipley

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

d + xd

p

ls

hk

Top View

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

Cross Section

d + xd

p

ls

hk

Hole Diameter and Wiring DensitHole Diameter and Wiring Density

hole diameter, dcapture pad diameter, c = d + xline width, lline space, sline-to-pad space, phole pitch, h, at one line per channel

h = l + 2p + x + d

hole pitch, h, at two lines per channel

h = 2l + s + 2p + x + d

hole pitch, h, at three lines per channel

h = 3l + 2s + 2p + x + d

In general, for n lines per channel, where n > 1, and n is an integer, the holepitch is

h = nl + (n-1)s + 2p + x + d.

h1

h2

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

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

h = d + k

where k = nl + (n -1)s + 2p + x.

That is, the pitch can be reduced by the same amount that the hole diameter is reduced such that h1 - h2 =

d1 - d2

Wiring density expressed as the number of lines per micron is given by n/h. Percentage increase in wiringdensity, D, with reduced pitch is given by

(n/h2 - n/h1)/(n/h1) = [(d1 + k)/(d2 + k)] - 1For k << d1,d2,

D = (d1/d2) - 1.For k >> d1,d2,

D = 0.

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 + d

n(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'

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).

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).

Mechanically-Drilled Through Via75 m diameter

170 m clearance hole

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

Source: Lambda Physik



LASERS




Excitation of AtomsExcitation of Atoms

E0E1E2

by collision with free electronby collision with free electron

by absorption of lightby absorption of light

E0E1E2

E0E1E2

E = h = E1 - E0

E0E1E2

E0E1E2

E0E1E2

Emission of LightEmission of Light

E = h = E1 - E0

spontaneous emissionspontaneous emission

stimulated emissionstimulated emission

E0E1E2

E0E1E2

E0E1E2

coherent,amplified light

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

Lasing MediumLasing Medium

Pumping MechanismPumping Mechanism

MirrorMirrorR = 100%R = 100%

MirrorMirrorR < 100%R < 100%

Laser Beam OutLaser Beam Out

Elements of a LaserElements of a Laser

IntenseIntenseMonochromaticMonochromatic

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

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

Ultraviolet Visible Infrared400 nm 750 nm

~10,

000

nm -

CO

2

355

nm -

Nd:

YAG

3rd

Har

mon

ic

308

nm -

XeC

l exc

imer

248

nm -

KrF

exc

imer

193

nm -

ArF

exc

imer

157

nm -

F 2

exc

imer

532

nm -

Nd:

YA

G

2n

d H

arm

onic

1064

nm

- N

d:Y

AG

Fun

dam

enta

l

Wavelengths of Selected LasersDetermined Largely By Lasing Medium and Laser Optics



LASERS

THE PROCESS OF LASER "ABLATION" (VAPORIZATION)Beam DeliveryMaterial Absorption



mask

Beam Shaping and Delivery

Photon (Energy) Absorption By Material

Breaking of Chemical BondsPhotochemical ProcessesPhotothermal Processes

Vaporization (Ablation)

Laser Holemaking

Focused Spot

Laser Beam Delivery

Mask Imaging

Mask

Contact or Conformal Mask

Lens

EtchedMetalFoil

200 400 600 800 1000 1200

Wavelength (nm)

00.10.20.30.40.50.60.70.80.9

1

Tota

l Abs

orpt

ion

FR4Matte CuGlass

355

nm -

Nd:

YAG

3rd

Har

mon

ic

308

nm -

XeC

l exc

imer

248

nm -

KrF

exci

mer

532

nm -

Nd:

YAG

2nd

Har

mon

ic

1064

nm

- N

d:Y

AG

F

unda

men

tal

Source: ESI

Absorption Curves

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

Io

Ith, xth

( )

Ix = I0 exp- x

Ablation ceases when Ix < Ith

Io

Ith

xo xth

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 -CF2

Poly(tetrafluoroethylene)

OC N-CO

O C N C O

Abso

rban

ce

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

Rat

e (u

m/p

ulse

)

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



LASERS


TYPES OF LASERS, LASER DRILLING SYSTEMS, AND DRILLING TECHNIQUES

ExcimerCO2Nd:YAG


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 System Used With Projection Mask Used With Projection Mask

Mask Imaging

Mask

xy

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 System Used With Contact Mask Used 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

BBO 2nd

BBO 3rd

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

Rep Rate. Tthe number of laser pulses delivered to the workpiece per unit time.Focus Height (or Z Offset). Positions the beam out of focus relative to the surface of the part by the specified amount.Average Power. The energy per pulse multiplied by the rep rate.Tool Diameter. The desired final diameter of the via.Pulses. The number of times the laser fires into a given gole in the punch mode.Bite Size. The distance between laser pulses, center to center, in the trepan or spiral mode.Velocity. The speed at which the beam moves across the work surface, in the trepan or spiral mode.Repetitions. The number of times the path of the beam is traced, in the trepan or spiral mode.Effective Spot Size. What the computer believes the diameter of the beam on the material to be. A large value for

effective spot size prompts the laser software to trace a tighter spiral or trepanning loop.Inner Diameter. The inside diameter of the first spiral.Revolutions. The number of spiral revolutions per hole.Radial Pitch. The distance between spiral revolutions.

Radial Pitch

Beam Diameter

Bite Size

Spiral Tool

Beam Diameter

Bite Size

Trepan Tool

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 G0 X112710.0 Y94580.0 X112710.0 Y661160.0 X504510.0 Y661160.0 X504510.0 Y94580.0T1 1T0 101 G0T2 101.6 X71119.0 Y80690.0 Y83230.0 Y85770.0 Y88310.0 Y90850.0 X80010.0 Y89580.0 X78739.0 Y80690.0 X76199.0 X73659.0 X81279.0 X118109.0 Y88310.0 X72389.0 Y128950.0 X214629.0 Y88310.0 X237490.0 Y89580.0 X261644.9 Y102852.0 Y104122.0 Y105392.0%

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

Beam PositioningBlind Via DrillingThrough Via Drilling

esi_blind_via.wmvesi_through_via_drilling.wmv esi_53xx_laser_drilling.wmv

Typical microvia Multilayer viaSkip microvia

Via on via with conductive fill

Staggered via

Blind Via FormationVarious Blind Via Structures

Source: TechSearch International, Inc.

CuDielectric

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 ProcessChemically etched copper "mask"

Ablate dielectric with IR beam

Combination Nd:YAG & CO2 Laser Process

Trepan or Spiral

Other Means of Microvia Formation

LaserMechanical DrillPhotosensitive Polymers (Photo-vias)Chemical Etching

Wet Etching

Plasma Etching

Punch

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

Maskless Imaging Using a Rastered Laser Beam

S. Corbett, J. Strole, K. Johnston, E.J. Swenson, and W. Lu, "Laser Direct Exposure of Photodefinable Polymer Masks Using Shaped-Beam Optics," IEEE Transactions of Electronic Packaging Manufacturing, 28(4), 312 (2005).

O* CO, CO 2, etc.

Plasma Wet Chemical

Chemical Etching

Photoresist

Immerse In or Spray WithWet Chemical Etchant

Strip Photoresist

Plasma Etch

RF

Plasma+

Blocking Capacitor

Ground Shield

Vacuum Chamber

To Vacuum PumpGas Inlet Quartz PlateSample

++++

++

O*

O*

O*

O*

O*

O*

O*

Cu Cathode

Sample Plasma Etch SystemReactive Ion Etching (RIE)

Isotropic EtchingIsotropic Etching

Anisotropic EtchingAnisotropic Etching

Ray Fillion

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

ThousandsVia Count / Side

0

500

1000

1500

2000

2500

Num

ber o

f Sid

es /

(Day

- M

achi

ne)

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

Cos

t Per

Pan

el

Laser

Plasma

Laser Drilling vs Plasma EtchingRelative Cost

0.002" 0.004" 0.006" 0.008" 0.010"

Via Diameter

Cos

t Per

Via

LaserMechanical

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

10A

spec

t Rat

io

Source: Electro Scientific Industries, Inc.

ESI's Via Technology Roadmap

UVYAG

Mechanical Drill

Blin

d Vi

as

Thro

ugh

Vias

CO2

Photovia



Lasers



LASER-ENABLED, HIGH-PERFORMANCE ELECTRONIC COMPONENTS

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

HyperBGAHyperBGA R

90 m Blind Via

Chip

Solder Underfill

50 m Through Via

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

Layer Interconnection with Controlled-Depth Vias

Layer Interconnection with Plated Thru HolesLines must go around PTH's

Controlled-depth vias don't block lines

Sequential Build-Up Process (SBU)Benefits of Blind Vias and Added Layers

Fabricate Core

Fabricate 1st Build-up Layers on Core

Fabricate 2nd Build-up Layers on Existing Layers

Etc.

Stacked Blind Vias Staggered Blind Vias

or

Fabricate All Layers Separately

Join & Interconnect Layers

Parallel Process for Z-Axis InterconnectAs Alternative to SBU

A means of forming electrical joints between adjacent cores is required.

Advantages of Parallel Lamination for Z-Axis Interconnect vs SBU

Shorter cycle timeIndividual layers (cores) built in parallel

Higher yieldOpportunity to inspect and sort cores, prior to lamination, to optimize composite yield

Selected cores with multiple pieces

Good alignedwith good

Scrap aligned with scrap

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 CoreElectrically Conductive

Paste

Increase In Wiring Density With Controlled-Depth Vias

Blind Via

ElectricallyConductivePaste

40 m and 75 m laser-drilled vias in cores

Summary

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

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

Thanks to ESI for providing video files.Thanks for your attention.

laser drilling for electrical interconnection in advanced ...laser gas lasing medium ultraviolet...

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