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© 2003, D. C. Hopkins [email protected]

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Courtesy of Curamic Electronics

Excerpt – Direct Bonded Copper

Presented by

Douglas C. Hopkins, Ph.D.312 Bonner Hall

University at BuffaloBuffalo, NY 14620-1900

607-729-9949, fax: 607-729-7129


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Authors thankAuthors thank

Curamik® ElectronicsA member ofA member of

for providing information and photosfor providing information and photos


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DCB Process• Oxygen reduces the melting point of Cu from

1083°C to 1065°C (Eutectic melting temperature).• Oxidation of copper foils or injection of oxygen

during high temperature annealing (1065°C and 1080°C) forms thin layer of eutectic melt.

• Melt reacts with the Alumina by forming a very thin Copper-Aluminum-Spinel layer.

• Copper to copper is fused the same way.• Copper-Aluminum-Nitride (AlN) DBC is possible.

The AlN-Surface must be transformed to Alumina by high temperature oxidation.


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DBC Process

Copper

Ceramic

Copper

Ceramic

O2CopperOxide

Copper

Ceramic

EutecticMelt

Heating

O2 Diffusionand

CoolingCopper

Ceramic

Copper

Copper

Copper

Copper

Copper

Copper

Copper

Copper

1080 -

1070 -

1060 -

1050 -

O2-Concentration in Atom-%0 0.4 0.8 1.2 1.6

Eutectic


END


DBC - Interfaces

Al2O3

Copper

Al2O3

AlN

Copper

Copper


END


Flow Chart of DBC Processing

Substrate Ni + Au surfaceSubstrate Ni plated

Substrate blank copper surface

Control

Shipping to customeras mastercards

Shipping to customeras single parts

Separating mastercardsby breaking

DBC ProcessMasking

Etching

Final Cleaning

Electroless Nickel

Electroless Gold

Laser Scribing


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Masking• High precision screen

printers for high volume• Semiautomatic and fully

automatic with pattern recognition

• Redundant equipment• Photomasking for high

density circuits• Air conditioned clean

rooms


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Etching• Specially designed

precision etchers for thick copper layers

• Automatic chemistry control

• Mask stripping integrated

• 3 separate high volume lines in operation

• Controlled by SPC


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Plating / Final Cleaning• Fully automatic high

volume plating line for electroless Ni + Au

• Controlled by SPC• Final cleaning for Cu

integrated • Parallel backup lines• Solderability and

wire bond testing


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Laser Machining• Fully automatic high

precision CO2 lasers with pattern recognition

• Designed for high volume throughput

• Scribing and drilling• Multiple equipment• Controlled by SPC


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Features of DBC Substrates– Low thermal coefficient of expansion despite relatively

thick copper layers(TCE = 7.2 - 7.4 - 10-6 at 0.3mm / 12mil copper)

– High current carrying capability with thick copper(Copper width 1mm / 40mil, height 0.3mm / 12mil, continuous flow 100amps = temp rise of 14 - 17 °C)

– High peel strength of copper to Al2O3 ≥ 60N/cm;AlN ≥ 45N/cm at 50mm/min peel speed

– High thermal conductivity(Al2O3 = 24W/mK; AlN =170 W/mK)

– Low capacitance between front- and backside copper(Appr. 18pF/cm2 for 0.63mm ceramic thickness)


END


Relative Heat Flux (W/sqm)

•100

•1.000

•10.000

•100.000

•1.000.000

•10.000.000

•100.000.000

•10 •100 •1000 •10000

•Surface of Sun

•Saturn V•Engine•(Case)

•Power Semiconductor Chip

•Logic Chips

•Light Bulb (100 W)

•Hot-Plate

•Heat Loss from Human Body

•Chips need Cooling

Absolute temperature [K] Source: Semikron


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Principal Design of IGBT Power Module

Hard encapsulation Soft encapsulation

Solder joint

IGBT / Diode

Al thick wire bond

Thermal greaseHeat sink

Cu baseplateDBC substrate

Current contactPlastic casing


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IGBTIGBT

DiodeDiode

DBC substrateDBC substrate

Single Switch Module4 Substrates, 4 IGBT‘s and 4 Diodes


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0,4

0,45

0,5

0,55

0,6

0,65

0,7

Ther

mal

resi

stan

ce [K

/W]

10 100 1000 10000 Thermal conductivity[W/mK]

Diamond

Al2O3

AlN

Power Module – Thermal ResistanceThermal Resistance

as a function of Substrate Thermal Conductivity

Chip area = 100mm2; ceramic thickness; 0,635mm; copper baseplate 3mm; power dissipation 100W; solder 0,070mm


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Thermal Mass

0

20

40

60

80

100

120

140

160

Junc

tion

Tem

pera

ture

[°C

]

1E-2 1E-1 1E0 1E1 1E2 1E3ln time [sec]

0,15 mm 0,3 mm 0,6 mm

Influence of copperthickness

Influenceof

Rth static

Cu-thickness (3)

Junction temperature as function of the dynamic thermal resistance


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Flexural Strength of DBCas a function of copper thickness

300 400 500 600 700 800 900 1000

Alumina Standard DBC dCu=0,20mm DBC dCu=0,25mm DBC dCu=0,30mm

99

9075

63,3

25

10

1

Prob

abili

ty o

f Fai

lure

F [%

]

Flexural Strength [MPa]


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Flexural Strength of HPS DBCCompared with Blank HPS (optimized Alumina) Ceramic

500

550

600

650

700

750

800

850

900

950

1000500

1000

1500

2000

DBC Optimized Alumina

75

99

90

63,3

25

10

1

Prob

abili

ty o

f Fai

lure

F [%

]

Flexural Strength [MPa]


END


Dimple Design

Top view Cross section


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Thermal Cycling ReliabilityStandard Alumina DBC with and w/o Dimples

20 40 60 80 100

200

300

400

500

600

700

800

900

1000

2000

Standard DBC Dimples DBC

99

9075

63,3

25

10

1

Prob

abili

ty o

f Cho

ncho

idal

Fra

ctur

e F

[%]

Number of Temperature Cycles


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Average Life N0 – (Weibull)

050

100150200250300350

800

1000

1200

14001600

18002000

2200

>200

0

>200

0

Num

ber o

f the

rmal

cyc

les

CurStd AlNCurMilCurHP*CurHPI

with Dimples (Copper pattern design for thermal stress relief)

without Dimples

*d(ceramic) = 25 mil, d(Cu) = 12 mil -55°C / 150°C / 15 min.d(ceramic) = 15 mil, d(Cu) = 8 mil -55°C / 150°C / 15 min.


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Special Substrates• Active Metal Brazed (AMB)• Refractory Metallization• Substrates with vias • Substrates with lead offs• 3-Dimensional substrates• DBC Packages• Water cooled substrates


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Via Technology

Both sides flat surface. Ceramic hole diameter min. 1.0mm R<100µΩ

One side flat surface. Ceramic hole diameter min. 1.0mm R<100µΩ

One side flat surface low cost. Ceramic hole diameter 2.5mm (0.3mm copper layer) R<100µΩ


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Vias in DBC Substrates• High current front to

back feed-through• 100 A current• 100 µOhm

• For backside ground-plane or shield

• Both hermetic• Version 1 can be used as

thermal path also


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Integral Terminals• Terminals made of same

copper sheet as circuit• High electrical

conductivity due to solid metal without interface resistance

• Very high reliability


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3-Dimensional DBC• For very high density

circuits• Extremely reliable due

to integral connectors• Base for power• Sidewalls for non-power

components• Assembled flat and bend

up


END


Package Types

Top LeadKovar Frame

2

Kovar Lid

ChipWirebond

Kovar FrameKovar LidSide Lead

ChipWirebond

1

Ceramic Copper 1 Via 2 Direct Bonded Pin


END


Package Types

ChipWirebond

Kovar Lid Kovar FrameSurface Mount

1

Kovar Pin

Kovar LidDown Lead Kovar Frame

ChipWirebond

ChipWirebond

Kovar Lid Kovar FrameGlass to Metal Seals

1

Glass

Ceramic Copper 1 Via 2 Direct Bonded Pin


END


Kovar Frame Brazed on DBC SubstrateGlass Sealed Feed-Through


END


Fluid Cooled DBC• Lowest thermal

resistance of all available solutions for COB

• Rth ranging from 0.08 to 0.02 K/W using Al2O3 or AlN

• Power dissipation up to 3 kW on 2” x 2”

• Extremely compact design

• Modular system assembly


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Liquid flow-through micro channels

BasisElement

Liquid

Ceramic Isolation Layer

Chip Mounting Layer


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Micro Channels

Cut A Cut B


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Micro Channel Water Cooled ModuleHalf bridgeHalf bridge

6 IGBT6 IGBT12 Diodes12 Diodes62 mm Standard 62 mm Standard module sizemodule size450 A450 ACooling water Cooling water temperature up to 80°C temperature up to 80°C possiblepossible


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Rthja as a Function of Water Flow

25

30

35

40

45

50

55

60

65

70

RtH

ja [

mK/

W ]

0 1 2 3 4 5 6 7 Water Flow [ l/min. ]

AlN integ.

Al2O3 integ.

Al2O3 substrate

AlN substrate


END


Module comparisonConventional v. Integrated water cooling

1 →Standard module on closed cooling system (calculation)2 →Module with integrated cooling system

(measurement: soldered Al2O3 ceramics)3 →Module with integrated AlN substrate

100

0

20

40

60

80

Rth

[K/k

W]

Junction -Case

Case-HeatSink

Junction Ambient Junction

Ambient

About 60% reduction of RthJA (flowrate2.5l/min.) 2 → 1

1 2

Heat Sink Ambient

About 60% reduction of RthJA (flowrate2.5l/min.) 3 → 1

3

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