Download - Micro mechatronics 1nefr0001/ENSMMlessonsFJN/... · Micro mechatronics 1 part 7: bonding Halbleiterkontakti erung Die- and wire bonding Prof. Fritz J. Neff Director of the Laboratory

Micro mechatronics 1part 7: bonding

HalbleiterkontaktierungDie- and wirebonding

Prof. Fritz J. NeffDirector of the Laboratory for Micro mechatronics and Hybrid integrated thick film circuitSat the University of AppliedSciences Karlsruhe (FH), 16. August 2004

Prof. Fritz J. Neff, Steinbeis TZ Mechatronik-Karlsruhe 2

Definition BondingBonding is the electrical or mechanical connectionbetween the pads of a semiconductor and those of the substrateDie bonding is the mechanical connection betweena semiconductor with the substrateWire bonding is the electrical connection betweenthe semiconductor and the substrateFlip-chip-bonding is the only bonding technology which allows same time in one step to realize themechanical and the electrical connection between a semiconductor and the substrate


Use of bare dies


Parameter: thick film metalisation

AgPd- and AgPt-films are fit forbonding withAl-wire with d > 150 µm

Au-films are fit for bonding withAlSi1- and Au-wire d < 50 µm


Parameter: surface profile

Influences of the pad surface to the bond:

- peak-to-valley-hight,- adhesion of printed film/layer,- thickness of metallisation,- homogenity of layer,- impurities in the layer (killing particles!),- components of the paste like organic binder,

yield of metall and frit


Parameter: composition of printed film

Less organic binder means higher yield of metal and therefor low values of peak-to-valley-hight

Repeating of the fireing process will cause better surface

Very thin film contain less organic binderand therefor better surface.


Parameter: intermetallic connections

Homogenious connections will not cause anyproblemsHeterogenious connections are causing migrationof particles and therefor the formation of intermetallic connections.

Aluminium - Wedge - Bond

AuAl2

Au - Schicht

Substrat

Au Al5 2

Kirkendall - Voids


Parameter: intermetallic connections

thermal and mechanical stability over long time of use only is possible by homogenious connections[Au/Au oder Al/Al]but:most used Au/Cu- or Au/Al-connections and

therefor the result areintermetallic connection,

problems are causing the Kirkendall-Voids; holeswhich are formating because of different diffusionconstants of the different materials


Diebonding with glueing

most used technology to connect the rear side of the die/chip with the prepared diepad on thesubstrate; the advantage is also to compensaterelative elongations between the different materials with help of the elasticity of the glue.

Elektrisch leitenderZwei-Komponenten-Klebstoff

Die

BondpadDiepadKeramiksubstrat


Diebonding

Die bonder inLaminar flow box

class100


Die BondingLow pressuregripperoverhead thesubstrate


Pad surfaces

aluminiumgold copper


Wire bonds

Ball-wedge-bonding (left)with Au-wire

Wedge-wedge-bonding (rigth)with Au- or Al-wire


Wire bonding

Thermo compression bonding, TC(Temperature T and bond force N) withAu-Draht

Thermo sonic bonding, TS (Temperature T,bond force N and ultra sonic US)with Au- (Cu-, Pd-) wire

Ultra sonic bonding, US (Ultra sonic US and bond force N) with Al- (Au-) wire


Micro-friction solderingby ultra sonic power

one of the two friction partners have to have a higher plasticity (wire)

the surfaces of the partners should not becontaminated or oxidated

the force/energy of friction soldering is higherthan the linkage force and therefor result an approach of the two different lattice and so several new local connections


Ball-wedge-bonding

Thermosonic bondingfor only gold wires

diameters 25 µm - 32 µm

Capillary tubeGold wire

Wire grip

Wedge-bonding point

Ball-bonding point


Ballbond and tool

thermal energyand

nominal forceand

ultra sonic energyresult in

friction and plasticflow of the wire


Ball-Wedge-BondingBond parameters for dAu = 25 µm

Substrate temperature: ≤ 150°Cnominal force: 300....1000mNultra sonic energy: 0,1......1Wsoldering time: 40.......60ms

each new combination of materials and tools will cause new parameter values!


Ball-Wedge-Bonding sequence

El. dischargeto form the ball

Loop forming


Ideal Ball-Wedge-Bonds


Ball-wedge-bonding

Ball-wedge-bonderin LMHS

in theLaminar Flow Box

class 100


Wafer Bumping= FCB-preparation

tchnologies forwafer bumpingPrinting of solderby- stencil or- stamp printingBall bumping by- ball bonder

LM 324


Ball-Wedge-Bonding

ball bondson LM324


Wedge-Wedge-Bonding

Ultra sonic bondingfor AlSi1-wires;diameters 25µm - 32µm

Wedge-tool Wire grip

Al-wire

First wedge bond

Scond wedge bond


Wedge-bonding tool

nominal force andultra sonic energy result in friction and plastic flow of the wire material


Bond tools and materials

For Al-wires, tools made of tungsten carbideFor gold wires, tools made of titanium carbide orosmide.

30°

60°

45°

a.) b.) c.)


Wedge-Wedge-BondingBond parameters for dAlSi1 = 25µm

Substrate temperature: ~ 20°Cnominal force: 25 ...40 cNultra sonic energy: 0,5 ...1 Wsoldering time: 30....50 ms

each new combination of materialsand tools will cause new parametervalues!


sequence of wedge-wedge-bonding


perfect wedge-wedge-bonds


Wedge-Wedge-Bonding

Wedge-Wedge-Bonderin LMHS

inLaminar Flow Box

class 100


Wedge-bond on die bond-pad


Materials for wires

goldaluminiumpalladium

copper


Physikal properties of wire materialsPhys. properties Dimension Au

99,99Cu Pd Al 99,99 AlMg0,5 AlSi1

Melting point °C 1063 1083 1554 660 650 -659

655 -660

Elasticity module kN/mm² 78 126 121 71 69 66

Shearing module kN/mm² 28 38 50 27 27 27

therm. conductivity at 20°C

W/mK 312 390 75 230 198 195

therm. Expansion coefficient

10-6K-1 15,3 17,6 11,5 25,3 25,1 25

El. resistance Ωmm²/m 0,022 0,017

0,099

0,029 0,03 0,03

therm. resistancecoefficient

10-3K-1 3,72 4,07 3,97 4,14 3,98 3,95

Length resistance at 25µm and 20°C

Ω/m 44,8 34,6 201,7

57,073 61,2 61,15


Gold wires

used for bei- US-Ball-Bonding,- US-Ball-Bumping,- TS-Wedge-Wedge-Bondingwire diameters7,5µm < d < 100µm, Standard 25µm and 32µm


Gold wiresrequirements:- minimale hardness and hardness

increase- free of oxide- chemical inerteimportant features:- max tension force- max elongationcomponents of the alloy:- Y, Fe, Cu, Ag,...with < (0,01-0,02)%


Gold wires

Important is therecristallisation

important therefor theused alloy- increase of tension- increase of elongation.


Aluminium wiresused for- US-wedge-wedge-bonding,wire diameters- thin wires 7,5µm < d < 100µm,

alloy of AlSi1 or AlMg0,5Standard 25µm and 32µm

- thick wires 100µm < d < 500µm (pure Al)


Aluminium wiresrequirements:- minimale hardness and hardness

increase- free of oxide- chemical inerteimportant features:- tension- elongationcomponents of the alloy:- Si, Mg


Aluminium wiresAlSi1 Al


Length of bonding wire


Problems with increaseof packing density


Resistance of Bonding wires

d = diameter of wireσ = el. resistancelges = length

[ ]Ω∗

=d

lR gesges σ1


Induktivity of bonding wires


Induktivitybetweenparallelbondingwires


Flip-Chip-Bonding

4 circuits on same 2“ x 2“ –Al2O3-Substrate,LM 324 is prepared with Au-ball-bumpsfor flip-chip-bonding.


Au-Ball-Bumping

1. Au-ball- as result of el. discharge2. Au-ball-bumping steps

1

2


Au-Ball-forms


•Printing of Ni/Au Bumps on the wafer(UBM Under Bump Metalisation)

•Printing of solder paste

•Melting of solder paste (Reflow)

•Washing of the wafer

Wafer Bumbing (Pac Tech)


Flip Chip Bonding with LM324 amplifier

• dimensions: 65 Mil x 62 Mil, ca. 1625 µm * 1550 µm • max. temperature: 150°C

• thickness of chip/die: 15 Mil

• Bonding Pads : 4 x 4 Mil

• Tolerance : ± 10%

1 Mil = 25 µm

Important values


LM324 without and with Au-Bumps


Flip-Chip-Bonding

die positioningwith help of image treatment by 2 cameras