Critical Barriers Associated with

Copper Bonding Wire

William (Bud) Crockett Jr.

w-crockett@ml.tanaka.co.jp

May 2015

1980s, wire bonding was supposed to be replaced by

tape automated bonding (TAB)

In Global Electronics the most emphasizedIn Global Electronics the most emphasized

precious metal is Goldprecious metal is Gold

VehiclesMobile phones

PCsLCD TVs

etc.

RuRu

PtPt

Au

RhRh

AgAg

Pd

Electrical properties, high corrosion resistance

Electronic devices

Preciousmetal

Question is how to cut the device cost while using Gold (Au) metal?

11Reduce the thickness of Au plating on the substrate

Reduce the material cost of PKGReduce the material cost of PKG

Target is to optimize the combination between the Surface finish material and Wire bond material

22Use alternative metals instead of Au wire

Bonding Wire Transition Gold => Copper

Copper vs. Gold

Challenges of Bare Copper Wire

Challenges of Bare Copper Wire

� Copper Wire is Hard

� Die pad crack

� Al pad splash

� Narrow process windows (Short tail, fish tail, lifted bonds)

� FAB (Forming Gas N2H2)

� Capillary life

� Reliability (PCT/HAST Failures, Oxidation)

Au/Cu/PCC Hardness & Compression Comparisons

PCC

PCC

First Bond Second Bond

High ParametersNarrow Range

Cu Wire ParametersNarrow Range

Low ParametersWide Range

Std ParametersWide Range

Bo

nd

ing

Pa

ram

ete

rs

Parameter Range

Low

High

Au

Cu

Cu Wire Bonding Process Window Comparison

1) Copper wire is harder than Gold wire2) Copper processes have work hardening issues

Bondin

g P

ara

mete

rs

Parameter Range

Low

High

Cu Optimum Parameters

Low Parameters

High Parameters

Existing Common problem in Cu bonding

Short tail / No tail issue

Cu

Bondin

g P

ara

mete

rs

Parameter Range

Low

High

Optimum Parameters

Low Parameters

High Parameters

Aluminum splashingshorting to adjacent pad

Lifted Metal

More Common problems in Cu bonding

1) Lifted metal occurs at lower side of optimum parameters

How to Achieve Process Window Closer to Au Wire and Solve Oxidation Issues?

Palladium Coated

Copper Wire (PCC)

(Gen I) Palladium Coated(Gen I) Palladium Coated Wire: CLRWire: CLR--11

CCopper bonding wire, opper bonding wire, LLong life & ong life & RRobust stitch bondobust stitch bond

Comparison with Bare Copper wire

Advantage DisadvantageLonger Spool Lengths (1km – 5km/spool)

Wider 2nd bond window/Higher 2nd bond pull

Chemical Stability

Better HAST (BGA)

Longer shelf life; 6 months after

manufacturing date, 1 month after opening

package (bare Cu 1-week after opening)

Price is higher than bare copper

(Au relative value 1.0, bare Cu 0.2,

PdCu 0.4 in HVM)

FAB is harder (possible pad damage)

Capillary Life

Comparison with Bare Copper wire

Advantage DisadvantageLonger Spool Lengths (1km – 5km/spool)

Wider 2nd bond window/Higher 2nd bond pull

Chemical Stability

Better HAST (BGA)

Longer shelf life; 6 months after

manufacturing date, 1 month after opening

package (bare Cu 1-week after opening)

Price is higher than bare copper

(Au relative value 1.0, bare Cu 0.2,

PdCu 0.4 in HVM)

FAB is harder (possible pad damage)

Capillary Life

4N Bare Cu wire

Thin Coated layer

4N Bare Cu wire

Thin Coated layer

CLR-1 φ20umCLR-1 φ20um

Storage Resistance Comparisons Copper Wire

**No Packing, stored in open environment (office)

Manufacturing Process Comparison Copper Wire

Palladium CoatedPalladium Coated wire: CLRwire: CLR--1A1A

Compare with CLR-1 (Gen I)

Advantage DisadvantageWider 2nd bond window/Higher 2nd bond pull

Slightly softer FAB

Reduce capillary drag

Fine pitch applications

SSB bonding

**Same Cost as CLR-1 (Gen I)

New Qualification

PCN

Compare with CLR-1 (Gen I)

Advantage DisadvantageWider 2nd bond window/Higher 2nd bond pull

Slightly softer FAB

Reduce capillary drag

Fine pitch applications

SSB bonding

**Same Cost as CLR-1 (Gen I)

New Qualification

PCN

4N Bare Cu wire

Pd Coated layer

Thin Au layer

CLR-1 (Gen I)

(Gen II)(Gen II)

+

PCC Wire (FAB Schematic Image)

PCC 1

PCC 2

FAB make

・Wire: PCC 1, PCC 2 φ20um

・FAB: φ38um

・Bonder: UTC-3000

・EFO: 80mA, 0.12ms

・Gas: N2+5%H2, 0.5L/min

・Measurement count n=3

Molded by epoxy resin

Polish and buff

EPMA-1600

SHIMADZU

FAB EPMA Mapping

1) Pd remains more on the FAB surface of PCC 1 than that of PCC 2 wire type2) Pd element diffused in FAB which makes it harder. Pad damage risk3) Pd element on perimeter of ball more effective for retarding Halogen attack??

PCC

Reliability

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200

Time(h)

Failu

re r

atio (

%)

Failu

re=in

itia

l re

sis

tannce×

20%up

CLR-1A

CLR-1

Wire E (ref)

K&S　MaxumPlus

PCC Comparisons

HTS 220deg C, QFP, Halogen resin

Bonder：K&S Maxum Plus

Forming Gas ：N2-5%H2, 0.5l/min

Die-Pad ：Al-0.5%Cu （t=0.8um）

(Hitachi 6mm□ Al-Cu0.5%)

Capillary ：SPT SI-25130-385E-ZS36

(H:25, T:130, CD:38, FA:8, OR:30)

Wire Dia.：20um

FAB Dia.：40um

Squashed Ball Dia.：50um

TD PCC

PCC 1

PCC 2

0

10

20

30

40

50

60

70

80

90

0 200 400 600 800 1000 1200

Time(h)

不良数（Ω20%up)

PCC Comparisons

HTS 200deg C, QFP, Green resin

Bonder：K&S KnS ICONN

Heat Stage Temperature=200℃

Die-Pad ：Al-0.5%Cu-1%Si / SiO2 / Si

(Renesas DG001□ t=0.8um)

Capillary ：SPT SU-25080-385F-ZU34TP

(H25,CD38,T80)

Wire Dia.：20um

FAB Dia.：X=39.5um,Y=36

Squashed Ball Dia.：

X=50.5um , Y=50.0 , Z=10.0

X

Y

【1st B’g Parameter】

Tip=7.0(mils) ,CV=0.3(mils/msec)

Contact Threshold=70%、Constant Current

Contact Defect Mode=V Mode

USG Current=85(mA) 、USG Profile=Square

USG Bond Time=10(ms)、

USG Pre Bond=60(mA)、

Force=15(gf)、Force Profiling=On

Init‘l Force=45(gf)、Init'l Force time=33(%)

Force Ramp Time=10%

X-Scrub=3(um) , Y-Scrub=0(um)

Scrub Cycles=2 ,Scrub Phase=90(deg)

1st Scrub mode=Pre USG

▲▲▲▲:PCC 1 ,N2-5%H2 ,90mA (1.60mil)

△△△△:PCC 1 ,N2 ,90mA (1.69mil)

▲▲▲▲:TD PCC ,N2-5%H2 ,90mA (1.65mil)

△△△△:TD PCC ,N2 ,90mA (1.69mil)

1135h （Next page）

1135h （Next page）

HTS 200deg C, QFP, Green resin1135h

Observation is no corrosion in 1st bond cross section

TD

PC

CN

290m

AT

D P

CC

N2H

290m

AP

CC

2N

290m

AP

CC

1

N2H

290m

A

0

10

20

30

40

50

60

70

80

90

0 200 400 600 800 1000 1200

Time(h)

不良数（Ω20%up)

UHAST 130deg C 85%rh, QFP, Halogen resin

Bonder：K&S KnS ICONN

Heat Stage Temperature=200℃

Die-Pad ：Al-0.5%Cu-1%Si / SiO2 / Si

(Renesas DG001□ t=0.8um)

Capillary ：SPT SU-25080-385F-ZU34TP

(H25,CD38,T80)

Wire Dia.：20um

FAB Dia.：X=39.5um,Y=36

Squashed Ball Dia.：

X=50.5um , Y=50.0 , Z=10.0

【1st B’g Parameter】

Tip=7.0(mils) ,CV=0.3(mils/msec)

Contact Threshold=70%、Constant Current

Contact Defect Mode=V Mode

USG Current=85(mA) 、USG Profile=Square

USG Bond Time=10(ms)、

USG Pre Bond=60(mA)、

Force=15(gf)、Force Profiling=On

Init‘l Force=45(gf)、Init'l Force time=33(%)

Force Ramp Time=10%

X-Scrub=3(um) , Y-Scrub=0(um)

Scrub Cycles=2 ,Scrub Phase=90(deg)

1st Scrub mode=Pre USG

●●●●:PCC 1 ,N2-5%H2 ,45mA (1.52mil)

○○○○:PCC 1 ,N2 ,45mA (1.61mil)

●●●●:TD PCC ,N2-5%H2 ,45mA (1.55mil)

○○○○:TD PCC ,N2 ,45mA (1.67mil)

1085h

1085h

UHAST 130deg C 85%rh, QFP, Halogen resin1085h

TD

PC

CN

245m

AT

D P

CC

N2H

245m

AP

CC

1N

245m

AP

CC

1

N2H

245m

ACorrosion? alloy layer?

Introduction: Alternative alloy Bonding Wires (Cu & Ag)

FAB Compression Test Comparisons

Au>Ag>Cu>PCC

Ag Alloy

Al Splash Comparisons

Ag alloy

Ag alloy

4N Au

Crystal Observation (Vertical Section)

Heat Affected Zone

Heat Affected Zone

Ultra low Loop & Reverse Bonding is possible for Ag alloy wire

Ag/Au/Pd

Ag/Pd

4N Au 4N Au

Ag alloyAg alloy

Ag Wire Reliability

Reliability Comparisons

4N bare Cu vs. Cu Alloy

Cu alloy

Cu alloy

Gold Ag alloy Cu alloy Copper PCC

Material Cost High Medium Low Low Medium

Forming Gas － N2 N2+H2 N2+H2

N2+H2

N2

Chip Damage Low Low Med Med High

Process window 1st

Wide Med Med Med Narrow

Process window 2nd

Wide Med Wide Med Med

HTS 2000+hr

ReliabilityPoor Excellent Excellent Fair Fair

Wire Types Summary

Bonding wires material cost can be summarized as:Cu>>Cu alloy>>PCC>>Ag alloy>>Au (LGP used $1200)

Closing Remarks

Alternative (Ag_Cu) alloy wires show good potential as

they offers several advantages compared to bare copper and palladium coated copper wires; good bonding performance and superior reliability.

Alternative (Ag_Cu) alloy wires may not work for all

applications but they can certainly help support many application areas where cost and performance define a product

Ag & Cu alloy wire usage is expected to increase in the next few years in both the LED and Semiconductor industry.

Thank you

Tsutomu Yamashita

Tanaka Denshi Kogyo K.K.