ELEC 6740 Electronics Manufacturing Chapter 4 Substrates ...jevans/elec6740/Chapter4.pdf · Laminate Materials Same as FR-4, but has better strength and electrical properties @ higher

ELEC 6740 Electronics ELEC 6740 Electronics Manufacturing Manufacturing Chapter 4 Substrates for Chapter 4 Substrates for Surface MountingSurface Mounting

R. Wayne JohnsonR. Wayne JohnsonJohnson@eng.auburn.Johnson@eng.auburn.eduedu

SubstratesSubstrates

♦♦ Rigid laminateRigid laminate♦♦ Metal coreMetal core♦♦ Flexible filmsFlexible films♦♦ CeramicCeramic

SubstrateSubstrate

♦♦ Provides electrical interconnect and Provides electrical interconnect and isolationisolation

♦♦ Mounting surface for componentsMounting surface for components–– Must be compatible with assembly processesMust be compatible with assembly processes

Laminate SubstrateLaminate Substrate♦♦ DielectricDielectric

–– Polymer Polymer •• EpoxyEpoxy•• PolyimidePolyimide•• Cyanate Cyanate EsterEster

–– ReinforcementReinforcement•• Glass fabricGlass fabric•• KevlarKevlar•• PaperPaper

♦♦ ConductorConductor–– CopperCopper

Basic Material Property Basic Material Property ConsiderationsConsiderations♦♦ Glass transition Temperature, Glass transition Temperature, TTgg

–– Hard, brittle, glassy Hard, brittle, glassy !! soft, rubberysoft, rubbery

TTgg

♦♦ Above Above TTgg thethe modulus (slope of Force vs. modulus (slope of Force vs. Deformation) decreasesDeformation) decreases

TTgg

♦♦ Above theAbove the TTgg thethe coefficient of expansion coefficient of expansion decreasesdecreases

CTE CTE –– Laminate SubstratesLaminate Substrates♦♦ CTE of polymers typically 50CTE of polymers typically 50--80ppm/80ppm/ooCC♦♦ Reinforcement materials are used to Reinforcement materials are used to

control the CTE in the Xcontrol the CTE in the X--Y planeY plane–– Woven glass fabricsWoven glass fabrics–– KevlarKevlar–– Etc.Etc.

♦♦ CTE in XCTE in X--Y plane typically 14Y plane typically 14--18ppm/18ppm/ooC C to match CTE of Copper (16ppm/to match CTE of Copper (16ppm/ooCC))

♦♦ CTE in ZCTE in Z--direction 100direction 100--200ppm/200ppm/ooCC

Laminate PWB ConstructionLaminate PWB Construction

Effect of Temperature During Effect of Temperature During SolderingSoldering

CTECTE

♦♦ Epoxy: 50Epoxy: 50--80 80 ppmppm//ooCC♦♦ Glass reinforcement: 0.5 Glass reinforcement: 0.5 ppmppm//ooCC♦♦ PWB Dielectric: 14PWB Dielectric: 14--20 20 ppmppm//ooCC♦♦ Copper: 16 Copper: 16 ppmppm//ooCC♦♦ Components: 6Components: 6--2020 ppmppm//ooCC

CTE Effect on ComponentsCTE Effect on Components

Characteristics of Substrate Characteristics of Substrate OptionsOptions

Characteristics of Substrate Characteristics of Substrate OptionsOptions

Characteristics of Substrate Characteristics of Substrate OptionsOptions

Characteristics of Substrate Characteristics of Substrate OptionsOptions

Ceramic SubstratesCeramic Substrates

♦♦ Thick FilmThick Film♦♦ Low Temperature Low Temperature Cofired Cofired Ceramic Ceramic

(LTCC)(LTCC)♦♦ High Temperature High Temperature Cofired Cofired Ceramic Ceramic

(HTCC)(HTCC)

Thermal ConductivityThermal Conductivity

Thermal ConductivityThermal Conductivity

Thick Film ProcessingThick Film Processing

♦♦ Sequential printing and firing of:Sequential printing and firing of:–– ConductorConductor–– DielectricDielectric–– ResistorResistor

layers onto a base ceramic substratelayers onto a base ceramic substrate

Thick Film Screen Printing Thick Film Screen Printing ProcessProcess

Frame

Wire Mesh

Emulsion

SqueegeeInk

Substrate

Conductor PrintConductor Print

Cofired Cofired TechnologyTechnology

♦♦ Cofired Cofired CeramicCeramic–– Firing Temperature:1500 Firing Temperature:1500 -- 16001600ooCC

♦♦ Glass/CeramicGlass/Ceramic–– Firing Temperature: 850 Firing Temperature: 850 -- 10501050ooCC

CofiredCofired ProcessProcess

Top Conductor Layer

Via

Second Layer Conductor

Thick Tape

Thin Tape

Glass/CeramicGlass/Ceramic

♦♦ ConductorsConductors–– Au, Ag, Au, Ag, PdAgPdAg, Cu, Cu

♦♦ DielectricsDielectrics–– Crystallizable Crystallizable GlassesGlasses

•• CordieriteCordierite MgOMgO--SiOSiO22--AlAl22OO33

–– Glass Filled CompositesGlass Filled Composites•• SiOSiO22--BB22OO3 3 type glass + Altype glass + Al22OO33

•• PbOPbO-- SiOSiO22--BB22OO3 3 -- CaOCaO type glass + Altype glass + Al22OO33

–– Crystalline Phase CeramicsCrystalline Phase Ceramics•• AlAl22OO33 -- CaO CaO -- SiOSiO22,, MgOMgO -- BB22OO3 3

•• BaSnBaSn(BO(BO33))22

Cofired Cofired CeramicCeramic

♦♦ ConductorConductor–– TungstenTungsten–– Molybdenum/ManganeseMolybdenum/Manganese

♦♦ DielectricDielectric–– 88 88 -- 92% Al92% Al22OO33

Typical Typical Cofired Cofired PropertiesProperties

CofiredCeramic

CofiredGlass/Ceramic

CTE 6.5 ppm/oC 3 to 8 ppm/oC

ThermalConductivity

15-20W/m oC 2-6W/m oC

Camber 1-4 mils/in. Conforms to setter

SurfaceRoughness

10-20 µµµµin 8-10 µµµµin

FlexuralStrength

275-400 MPa 15-250 MPA

Typical PropertiesTypical Properties

CofiredAl2O3

CofiredGlass/Ceramic

Line width (min.) 100µµµµm 100µµµµm

Via Dia. (min.) 125µµµµm 125µµµµm

Number ofLayers

1 - 100 1 - 100

ConductorResistance

8 – 12 mΩΩΩΩ/sq. 3 – 20 mΩΩΩΩ/sq.

DielectricConstant

9 - 10 5 – 8 @ 1MHz

Typical PropertiesTypical Properties

CofiredAl2O3

CofiredGlass/Ceramic

DissipationFactor

5 – 15 x 10-4

@1MHz15 – 30 x 10-4

@1MHzInsulationResistance

> 1014 ΩΩΩΩ-cm 1012 - 1015 ΩΩΩΩ-cm

BreakdownVoltage

550V/25µµµµm 800V/25µµµµm

Resistor Values 0.1 ΩΩΩΩ – 1m ΩΩΩΩ

Cofired Cofired Glass/CeramicGlass/Ceramic

Constrained Core SubstratesConstrained Core Substrates♦♦ Copper/Invar/Copper/Invar/

CopperCopper(Invar (Invar –– Ni/Fe)Ni/Fe)♦♦ Alloy 42Alloy 42♦♦ SiCSiC--Al Al

compositecomposite♦♦ GraphiteGraphite

Compliant LayersCompliant Layers

Selection CriteriaSelection Criteria

Substrate PropertiesSubstrate Properties

Substrate PropertiesSubstrate Properties

Laminate MaterialsLaminate Materials

Same as GSame as G--10, but 10, but can be used to can be used to higher higher temperaturestemperatures

Glass fibersGlass fibersEpoxyEpoxyGG--1111

General purpose General purpose material systemmaterial system

Glass fibersGlass fibersEpoxyEpoxyGG--1010

Punchable Punchable @ or @ or above R.T. XXXP above R.T. XXXP & XXXPC are & XXXPC are widely used in high widely used in high volume single sided volume single sided consumer consumer applicationsapplications

PaperPaperPhenolicPhenolicXXXPCXXXPC

Punchable Punchable @ R.T.@ R.T.PaperPaperPhenolicPhenolicXXXPXXXP

DescriptionDescriptionBase Base MaterialMaterial

ResinResinSystemSystem

Common Common DesignationDesignation

Laminate MaterialsLaminate Materials

Same as FRSame as FR--4, but has 4, but has better strength and better strength and electrical properties @ electrical properties @ higher temperatureshigher temperatures

Glass fibersGlass fibersEpoxyEpoxyFRFR--55

Same as GSame as G--10, but has 10, but has flame retardantflame retardant

Glass fibersGlass fibersEpoxyEpoxyFRFR--44

Punchable Punchable @ R.T. and @ R.T. and has flame retardanthas flame retardant

PaperPaperEpoxyEpoxyFRFR--33

Same as XXXPC, but Same as XXXPC, but has a flame retardant has a flame retardant (FR) system that (FR) system that renders it selfrenders it self--extinguishingextinguishing

PaperPaperEpoxyEpoxyFRFR--22

DescriptionDescriptionBase Base MaterialMaterial

ResinResinSystemSystem

Common Common DesignationDesignation

Laminate MaterialsLaminate Materials

Controlled dielectric Controlled dielectric laminate. GX has better laminate. GX has better tolerance of dielectric tolerance of dielectric properties than GTproperties than GT

Glass fibersGlass fibersTeflonTeflonGT or GXGT or GX

Better strength & Better strength & demonmstrated demonmstrated stability stability to a higher temperature to a higher temperature than FRthan FR--44

Glass fibersGlass fibersPolyimidePolyimidePolyimidePolyimide

Designed for low Designed for low capacitance or high capacitance or high impact resistance; has impact resistance; has flame retardantflame retardant

Glass fibersGlass fibersPolyesterPolyesterFRFR--66

DescriptionDescriptionBase Base MaterialMaterial

ResinResinSystemSystem

Common Common DesignationDesignation

Highest Continuous Operating Highest Continuous Operating Temperatures (Temperatures (ooCC))

130130130130FRFR--44

220220220220GXGX220220220220GTGT260260260260PolyimidePolyimide105105105105FRFR--66180180170170FRFR--55

105105105105FRFR--33105105105105FRFR--22180180170170GG--1111130130130130GG--1010125125125125XXXPCXXXPC125125125125XXXPXXXP

MechanicalMechanicalElectricalElectricalMaterialMaterial

PWB FabricationPWB Fabrication

PWB FabricationPWB Fabrication

♦♦ Starting Material: Cu clad CoreStarting Material: Cu clad Core

Cu

Epoxy Glass Core

PWB Fabrication:PWB Fabrication:Interlayer ProcessingInterlayer Processing

Shear MarkMat. Bake Drill Reg.

Holes Clean

Strip Resist Etch Develop Photo

PrintDry FilmLamiantion

Inspect Test Clean Oxide Treatment Bake

PWB Fabrication:PWB Fabrication:Apply Dry Film Apply Dry Film PhotoresistPhotoresist

PWB Fabrication:PWB Fabrication:Expose Expose PhotoresistPhotoresist

UV Light

PWB Fabrication:PWB Fabrication:Develop Develop PhotoresistPhotoresist

PWB Fabrication:PWB Fabrication:Etch Copper Etch Copper ––CuClCuCl22//HClHCl, 2:1, 2:1

PWB Fabrication:PWB Fabrication:Strip Strip PhotoresistPhotoresist

PWB Fabrication:PWB Fabrication:Black Oxide TreatmentBlack Oxide Treatment

PWB Fabrication: PWB Fabrication: MultilayerMultilayer ProcessingProcessing

Shear‘B’ StagePrepreg

Lay-up Lamination

Cool downRemove FixtureTrim Flash

PWB Fabrication:PWB Fabrication:LaminationLamination

Release Paper1 oz. CuPrepreg

Prepreg

Inner Layer

1 oz. CuRelease Paper

Top LaminationFixture

Bottom Lam.Fixture

Tooling Holes

PWB Fabrication:PWB Fabrication:MultilayerMultilayer ProcessingProcessing

Mark ID Bake Drill Plated Through Holes

DeburrHole Clean:De-smear

PWB Fabrication:PWB Fabrication:Drill & DeDrill & De--smearsmear

PWB Fabrication:PWB Fabrication:MultilayerMultilayer ProcessingProcessing

Pd Seed ElectrolessCu Plate Clean Photoresist

Application

PhotoPrintDevelopElectroplate

CuElectroplateSn/Pb

Strip Resist Etch StripSn/Pb

PWB Fabrication:PWB Fabrication:Pd Seed & Pd Seed & Electroless Electroless Cu PlateCu Plate

PWB Fabrication:PWB Fabrication:Photo Resist Application, Photo Resist Application, Exposure & DevelopExposure & Develop

PWB Fabrication:PWB Fabrication:Electroplate CuElectroplate Cu

Copper ThicknessCopper Thickness

Barrel CrackingBarrel Cracking

Barrel CrackingBarrel Cracking

PWB Fabrication:PWB Fabrication:Electroplate Electroplate SnSn//PbPb

PWB Fabrication:PWB Fabrication:Strip Strip Photoresist Photoresist & Etch Cu& Etch Cu

PWB Fabrication:PWB Fabrication:Strip Strip SnSn//PbPb

PWB Fabrication:PWB Fabrication:MultilayerMultilayer ProcessingProcessing

SoldermaskApplication & Cure

Legend Print& Cure

Hot Air SolderLevel

CleanDrill Non-PlatedHoles

Route &Bevel

Final Electrical &Mechanical Test

PWB Fabrication:PWB Fabrication:Solder Mask ApplicationSolder Mask Application

Solder MasksSolder MasksTypes of Soldermask

Temporary

PeelableWashable

Aqueous Solvent

Permanent

Solder MaskSolder MaskPermanent

Dry Film

Aqueous Solvent

Wet Screened

Photoimageable

WetScreen

Curtain Coat ScreenedUVCure

Thermal Cure

Hole Tenting with Dry FilmHole Tenting with Dry Film

PWB Fabrication:PWB Fabrication:Hot Air Solder LevelHot Air Solder Level

Hot Air Leveled Process Hot Air Leveled Process (HASL)(HASL)♦♦ Solder dip and hot air solder leveling is a common Solder dip and hot air solder leveling is a common

PCB surface finish for solder attachment.PCB surface finish for solder attachment.–– Sn/Pb coating is applied after the solder mask Sn/Pb coating is applied after the solder mask

application, coating only the contact areas, plated application, coating only the contact areas, plated holes and contact padsholes and contact pads

–– Coated boards are cleaned, fluxed and dipped into Coated boards are cleaned, fluxed and dipped into molten solder. molten solder.

–– While the alloy is still in the liquid state, excess While the alloy is still in the liquid state, excess material is blown off the contact surface with hot material is blown off the contact surface with hot air, leaving a solder coated surface finish.air, leaving a solder coated surface finish.

Issues related to HASLIssues related to HASL

♦♦ Uneven surface platingUneven surface plating♦♦ Crowning of solder on fine pitch and CSP sitesCrowning of solder on fine pitch and CSP sites♦♦ Solder paste uniformitySolder paste uniformity♦♦ Tin/Copper intermetallic migrationTin/Copper intermetallic migration♦♦ Extreme Thermal shock Extreme Thermal shock

–– Board warpBoard warp–– DelaminationDelamination–– Damage to the plated holesDamage to the plated holes–– Defects that may effect long term reliability.Defects that may effect long term reliability.

Ni/Au Ni/Au ElectrolessElectroless ProcessProcess

♦♦ Electroless Ni is applied over the exposed bare Electroless Ni is applied over the exposed bare copper after solder mask coating processcopper after solder mask coating process..–– The fabricator will typically use the Sn/Pb plated The fabricator will typically use the Sn/Pb plated

circuit pattern as an etch resist and strip the circuit pattern as an etch resist and strip the SnSn//PbPbafter etching.after etching.

–– Exposed attachment sites and holes are plated with Exposed attachment sites and holes are plated with the Ni using the Ni using electrolesselectroless plating process followed by a plating process followed by a layer of gold by immersion process as well.layer of gold by immersion process as well.

–– TypicalTypical•• ElectrolessElectroless Ni thickness : 125 Ni thickness : 125 -- 200 µ in200 µ in•• Immersion Gold thickness : 3 Immersion Gold thickness : 3 -- 8 µ in8 µ in

–– Ni improves plated through hole reliabilityNi improves plated through hole reliability

Ni/Au Electroplating ProcessNi/Au Electroplating Process

♦♦ Electroplated Ni/Au is applied after hole Electroplated Ni/Au is applied after hole plating. plating.

♦♦ Ni/Au is resistant to the acid used to etch away Ni/Au is resistant to the acid used to etch away copper.copper.–– This replaces the plating and subsequent stripping This replaces the plating and subsequent stripping

of Sn/Pb.of Sn/Pb.♦♦ This method can furnish finer lines and spaces.This method can furnish finer lines and spaces.♦♦ TypicalTypical

–– Electroplated Ni thickness : 100 Electroplated Ni thickness : 100 -- 150 µ in150 µ in–– Electroplated AU thickness : 3 Electroplated AU thickness : 3 -- 5 µ in5 µ in

A word of caution…A word of caution…

♦♦ The gold plating volume within the solder joint The gold plating volume within the solder joint should be less than 3% and preferably less than should be less than 3% and preferably less than 1% to avoid1% to avoid embrittlementembrittlement of the joint andof the joint andintermetallicintermetallic formation.formation.–– Gold thickness will depend on solder volumeGold thickness will depend on solder volume

♦♦ Current industry issue with Current industry issue with ElectrolessElectrolessNi/Immersion Au. Ni/Immersion Au. –– Low occurrence rate of failures in Low occurrence rate of failures in

mechanical shock related to the immersion mechanical shock related to the immersion gold processgold process

Solder Ball with Crack at Solder Ball with Crack at Pad InterfacePad Interface

Courtesy:Bruce HoughtonCelestica

Black PadBlack Pad

Courtesy:Bruce HoughtonCelestica

ElectrolessElectroless Ni/Immersion AuNi/Immersion Au

♦♦ Root cause (current theory): nickel is Root cause (current theory): nickel is attacked or excessively corroded in the attacked or excessively corroded in the gold bath.gold bath.–– Somewhat design dependentSomewhat design dependent–– Somewhat chemistry dependentSomewhat chemistry dependent–– Not related to phosphorous content in NiNot related to phosphorous content in Ni

Ref: F. D. Bruce Houghton, “Solving the ENIG Black Pad Problem: An ITRI Report on Round 2,” Future Circuits International, 2000, pp.121-128.

Pd or Ni/Pd (Pd or Ni/Pd (electrolesselectroless) ) PlatingPlating♦♦ Pd coatings have been developed as an Pd coatings have been developed as an

alternative to solder and Ni/Au.alternative to solder and Ni/Au.♦♦ Process is relatively new, but proven to be Process is relatively new, but proven to be

compatible with solder attachment processes.compatible with solder attachment processes.♦♦ Pd is applied to the exposed circuit features Pd is applied to the exposed circuit features

using electroless plating method and is using electroless plating method and is compatible with either Ni alloy as a base compatible with either Ni alloy as a base plating or the bare Cu alloy surface.plating or the bare Cu alloy surface.

♦♦ Low cost, low stress processLow cost, low stress process♦♦ Pd metal cost is highPd metal cost is high

Immersion AgImmersion Ag

♦♦ Provides a Provides a solderable solderable coatingcoating♦♦ Ag dissolves into molten solderAg dissolves into molten solder♦♦ Growing in popularity Growing in popularity

Immersion or White TinImmersion or White Tin

♦♦ Good initial Good initial solderabilitysolderability♦♦ SnSn--Cu Cu intermetallicintermetallic formation and formation and

oxidation limit use with multiple oxidation limit use with multiple soldering cyclessoldering cycles

Alternatives to Alloy PlatingAlternatives to Alloy Plating♦♦ As an alternative to plating, many companies As an alternative to plating, many companies

have had success and economic advantage as have had success and economic advantage as well as a flat attachment surface with organic well as a flat attachment surface with organic preservatives or prepreservatives or pre--flux coatings over bare flux coatings over bare copper.copper.

♦♦ As a means of retarding oxide growth on the As a means of retarding oxide growth on the bare copper attachment sites and via/test pads, bare copper attachment sites and via/test pads, a preservative or inhibitor coating is applied to a preservative or inhibitor coating is applied to the board. Organic/Nitrogen coatings such as, the board. Organic/Nitrogen coatings such as, Benzotriazole or Imidazole are used instead of Benzotriazole or Imidazole are used instead of alloy finishes.alloy finishes.

Advantages of OSPAdvantages of OSP

♦♦ Multiple exposure capabilityMultiple exposure capability♦♦ Ease of visual inspection of deteriorated Ease of visual inspection of deteriorated

copper (if any)copper (if any)♦♦ Excellent pad coplanarityExcellent pad coplanarity♦♦ Consistent solderabilityConsistent solderability

Concerns of OSP Coated Concerns of OSP Coated BoardsBoards♦♦ Degrades in high humidity/temperatureDegrades in high humidity/temperature♦♦ Limited (6Limited (6--12 months) shelf life12 months) shelf life♦♦ Physical contact can degrade coatingPhysical contact can degrade coating♦♦ Exposed copper will (in time) tarnishExposed copper will (in time) tarnish