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Laser Drilling For Electrical Interconnection in Advanced Flexible Electronics Applications Timothy E Antesberger Endicott Interconnect Technologies 1093 Clark Street Endicott, NY 13760 [email protected] Acknowledgement: Frank Egitto
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Transcript of 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

    h2h1

    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

    Laser/Material Interactions

    Types of lasers, laser drilling systems, and drilling techniques

    Laser-enabled high-performance electronic components

    Extensions of laser processing technologies

  • Lasing MediumR=100%

    R

  • 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

    Laser/Material Interactions

    Types of lasers, laser drilling systems, and drilling techniques

    Laser-enabled high-performance electronic components

    Extensions of laser processing technologies

  • 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

    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

  • 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

    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

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

    Mask Imaging

    Mask

    x

    x

  • Excimer Laser

    Turning Mirror

    Turning Mirror

    Turning Mirror

    Prism Beam ExpanderBeam Homogenizer

    Lens

    Objective Lens

    Vacuum Chuck / Rotational StageX-Y Positioning Stage

    Mo MaskSubstrate

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

    Contact or Conformal 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

    Contact or Conformal Mask

    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

    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

  • 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

    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

  • 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?