interconnection challenge in wire bonding ag alloy wire · the ag wire easy to cause over etch in...
TRANSCRIPT
Interconnection Challenge in Wire Bonding
– Ag alloy wire
Jensen Tsai / 蔡瀛洲, SPIL, Taiwan
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Content
•Ag Alloy Wire Type Market
•Ag Alloy Wire Benefits
•Workability and Reliability Performance
• IMC behavior and Improvement
•Conclusion
2
Gold Price Trend
800 USD/OZ, Started from 2008/08, Up to now, it grows to ~1400 USD/OZ, growth for 1.75 times
3
Market Application for Wire Selection
Consumer
products
25%
Communication
44%
Memory
20%
Computing
11%
Au wire HVM Pd-Cu wire LVM
Ag alloy wire HVM
Logic: Au wire HVM Pd-Cu wire HVM
Ag alloy wire HVM
Ag wire product characteristics
Quality and Workability: Equal or Better than Pd-Cu wire
Reliability: Meet criteria (up to PCT168, bias-HAST192 passed)
Mass Production: >10kk / month production for normal bond
> 8kk / month production for Die to Die
Ag alloy wire is producible from above factors
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Technology Items Production Available 2013 2014 2015
Ag Wire
Bond Pad Pitch
(um) ≧ 50 ≧ 45 ≧ 45 40 40
Bond Pad Open
(um) ≧ 44 ≧ 40 ≧ 40 35 35
Wire Diameter
(um) 20.3 / 17.8 17.8 15.2 15.2 15.2
Ag composition 88%, 95% 88%, 95% 95%
Low Loop Height (um) ≧ 130 ≧ 100 ≧ 60 -- --
Bonding Method
Pad to Pad (Die to die)
Bond Pitch (um)
-- ≧ 51 ≧ 45 -- --
Ag Alloy Wire Roadmap 5
1. Higher throughput --> lower cost, especially die-to-die
product.
2. WB parameter time --> much shorter than Cu (IMC, Al splash, pad crack…… control)
3. Not necessary to use high end bonder (K&S Iconn, Pro-Cu)
4. Bias-HAST life > 192hrs
5. Bond pad structure is no limitation (same as Au wire)
6. Shelf life of Ag wire is more than Cu wire in factory.
Benefits to choose Ag Alloy Wire 6
Category Control Items Au wire Ag wire Cu wire
Design
Rule Bond Pad Structure No limitation No limitation
Not Recommend Structure (Pad Crack Risk) :
1. None-VIA (B) + Al Thickness < 1.2 um
2. Partial VIA + Al Thickness < 1.2 um
Material Wire Storage
Expiration
Not open
package 1 year 1 year 6 months
Open package NA 20 days 1. Bare : 3 days
2. Pd-Cu : 14 days
Wire
Bond
Cu Wire Kit No Yes Yes
Forming Gas
Type NA 95% N2 + 5% H2 95% N2 + 5% H2
Flow NA Different flow than
Cu
Different flow than Ag
Wire Pull ( Min. ) 0.7 mil ≧ 1.8 gms ≧ 2.0 gms ≧ 3 gms
0.8 mil ≧ 2.0 gms ≧ 2.3 gms ≧ 4 gms
Ball Shear ( Min. ) 0.7 mil ≧ 4.8 gms ≧ 5 gms ≧ 8 gms
0.8 mil ≧ 5.3 gms ≧ 5.7 gms ≧ 10 gms
Appearance Inspection
( Concern after wire bonding ) NA Same Au
Not allowed :
1. Loop neck oxygen or discolor
2. FAB oxidation or strawberry ball
3. Al splash to cause Al wall damaged
High risk pad structure apply Ag wire to avoid pad crack and pad peeling issue.
Ag wire has wider process control of wire shelf life and window
Process Control Comparison (Au/Ag/Cu)
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Crack
Crater test
Pd-Cu wire (None Via, Al thickness < 1.2um)
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Crater test
No Crack
Ag wire (None Via, Al thickness < 1.2um)
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Ag 1N (95%) Pd Cu 2N Au
985 1084 1075
10.5 9 19.2
2.0~7.0 4.0~9.5 4.5~8.5
8.0~12.0 8.0~14.0 2.0~7.0
90 55~75 65~85
70~110 90~120 110~130
Hardness(Hv) FAB 58~62 60~70 41~43
FAB 2~5 2.0~4.0 3.0~4.0
Wire 0.1~3 4.0~8.0 1 5~2 0
3.5 1.8 2.92
310 440 340
0.7 0.7
Wire Type
Melting Point (℃)
Wire Diameter (mil)
HAZ Length (um)
Fusing Current (mA)
Grain Size(um)
Breaking Load(g) Room Temp.
Youngs Modulus (Gpa)
0.7
Resistivity (×10-8Ω.m)
Density (g/㎤)
Elongation(%) Room Temp.
Wire Properties Comparison 10
Hardness Cu > Ag > Au
Lower hardness allow lower force applied on bond pad reduce the risk of pad crater General wire bonder can handle Ag wire
Wire Type
ItemsAu Pd-Cu Ag Alloy
Forming gas kits No need Need Need
Machine setting time Short Long Middle
Through put 1 ~ 0.9 ~ 0.95
Pad Structure
(Pad Crack Concern )No Limitation
Can not apply to
None VIA, Partial VIANo Limitation
Maturity Mass Production Mass Production Mass Production
Ag alloy wire
Shorter machine setting time and higher throughput than Pd-Cu wire
No bond pad structure limitation, but Pd-Cu does
Ag Alloy Wire Workability (Normal Bond)
- Wire Bond Process Comparison for Normal Bond
11
Wire Type
ItemsAu Pd-Cu Ag Alloy
Forming gas kits No need Need Need
Machine setting time Short Long Middle
Through put 1 ~ 0.85 ~ 0.9
Pad Structure
(Pad Crack Concern )No Limitation
Can not apply to
None VIA, Partial VIANo Limitation
Maturity Mass Production Mass Production Mass Production
Die Die 1 Die 1 Die 2
_ _ _ Die 2_
_ _
Bond Pad
Ag alloy wire
Obviously higher throuhput than Pd-Cu wire
Ag Alloy Wire Workability (Pad-to-Pad)
- Die to Die bonding has obvious benefits
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- Wire Pull Data
- Ball Shear Data
- 1st and 2nd Bond Photos
Criteria Sample Size Max Min Avg STD Cpk
2pcs/all wire 5.5 3.5 4.530 0.338 1.807
2pcs/all wire 12.1 7 8.714 0.845 2.373
2pcs/all wire 10.8 5.7 8.064 0.942 1.897
Wire Type
Au wire
> 2.7gCu wire
Ag wire
Criteria Sample Size Max Min Avg STD Cpk
2pcs/all ball 35.30 19.50 28.343 3.759 1.759
2pcs/all ball 40.10 27.70 32.997 2.075 3.935
2pcs/all ball 39.57 25.23 32.689 2.399 3.361
Wire Type
Au wire
> 8.5gCu wire
Ag wire
Au Cu Ag
1st
2nd
Wire pull and ball shear data are close to Cu wire and better than Au wire
Ag wire has less Aluminum splash effect than Cu wire
Ag Alloy Wire Workability Comparison 13
Wire
type
IMC Cratering
Criteria Condition Sample
Size Result Criteria
Sample
Size Result
Au wire > 80% 0 hr 0/2 No
Crack 0/3
Cu wire > 80% 0 hr 0/2 No
Crack 0/3
Ag wire > 80% 0 hr 0/2 No
Crack 0/3
90% 82%
93% 92%
92% 90% No crack No crack
No crack No crack
No crack No crack
Ag alloy wire IMC and Bond pad crater could meet product criteria
Ag Alloy Wire Workability Comparison
- IMC & Crater Comparison
14
IMC growth rate: Au wire > Ag alloy wire > Pd-Cu wire
Wire type 2N Au Pd Cu Ag alloy
HTSL 150C/1000 hrs
IMC thickness 6.3um 0.7um 3.56um
Wire Material IMC Comparison 15
Reliability test conditions follow JESD STD and PASS.
Test item Read point Sample Size
Cross-Section SAT F/T
Moisture Sensitivity Test
MSL3
(30℃/60%RH/192hrs)
0 hour 0/180 0/180
Precondition 0/180 0/180
Pressure Cooker Test
(PCT) >168 hours NA 0/45
Thermal Shock Test
(TST) 500cycles NA 0/45
Temperature Cycling Test
(TCT) 1000cycles NA 0/45
Bias High Acc. Stress Test
(bias-HAST) >192 hours NA 0/45
High Temperature Storage Life Test
(HTSL) (Without precondition) 1000 hours NA 0/45
Ag Alloy Wire Reliability Performance
- Ag Wire Reliability Test Result
16
Ag wire can pass bias-HAST 168hrs w/ Substrate and lead frame base
Ag Alloy wire b-HAST Testing
- Lead Frame Package
- Substrate Package
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Bias
Type Dia (mil) 96 168 Voltage (V)
MQFN
5*5 / 4095% Ag 0.8
F/T
Passed
F/T
Passed
VDD33 : 3.6V
VDD12 : 1.32V Ag L/F
MQFN
8*8 / 6895% Ag 0.9
O/S
Passed
O/S
PassedPS :1.2V,3.3V Ag L/F
PKGWire B-HAST(hrs)
BOM
Bias
Type Dia (mil) 96 168 Voltage (V)
PBGA
27*27 / 48495% Ag 0.7
O/S
Passed
O/S
Passed
PS1: 3.3V
PS2: 1.8V
PS3: 1.5V
PS4: 0.9V
Au Finger
TFBGA
18*18 / 40995% Ag 0.7
F/T
Passed
F/T
Passed
VDD12 :1.2V
VDD25 : 2.5V
VDD33 : 3.3V
Au Finger
PKGWire B-HAST(hrs)
BOM
The Ag wire easy to cause over etch in FA decap procedure
Molding compound type have limitation for selection
In order to meet FA decap, need to select below molding compound types with difference packages
1. Single die + leadframe package with A compound
2. Single die + substrate package wtih B compound
De-Cap Capability 18
Customer: ****
• Package : TSOP
• Pin count : 54L
• Chip size : 127x92 mil
• Pad open : 51X71 um
Quality check item _PASS
Item Measured Method Criteria Unit
Wire-pull WP tester >2.3 g
Ball-shear BS tester >5.7 G
Ball-Thickness Microscope 500X 10 min um
Cratering Microscope 200X Not allow Crack
IMC Microscope 500X >70%
BOM
• Lead frame :
145x110mil/Stamping/A42
• Die Attach : Hxx 49***
• Bonding Wire : 0.8mil Ag wire
• Compound : Sxx G***
• Solder Plating : 100% Sn
FT Result
• FT yield is compatible to Au wire
product
Reliability Test Items
• MSL : Level 3 ( 30ºC / 60%RH / 192hours)
Bias-HAST 200, PASS (45/45 units)
PCT 216, PASS (45/45 units)
TST 500, PASS (45/45 units)
TCT 1000, PASS (45/45 units)
• HTSL 1000, PASS (45/45 units)
Ag Alloy Wire Project 19
Customer: **** • Package : MCM-TFBGA 13X13
• Pin count : 454
• Application: Mobile BB
• Chip size : 157X155 / 109X191 mil
• Pad size : 55X49 / 51X44 um
• Al pad thickness: 1.45um
Quality check item _PASS
BOM
• Substrate: 240.7*76.3mm
• Die Attach : Hxx FILM FH***
• Bonding Wire : 0.7mil Ag wire
• Compound : Sxx G***
• Solder Ball : 0.3mm
Reliability Test Items
• MSL : Level 3 ( 30ºC / 60%RH / 192hours)
PASS (200/200 units)
TCT 1000
HTSL 1000
HAST 168
FT yield is compatible to Au wire product
Item Measured Method Criteria Unit
Wire-pull WP tester >2 gw
Ball-shear BS tester >5 gw
Ball-
Thickness Microscope 500X
10um
min um
Cratering Microscope 200X Not allow Crack
IMC Microscope 500X >70%
Ag Alloy Wire Project (Die-to-Die)
20
The average volume has reached 53M pcs/month
Ag Alloy Wire Production Volume
- Package type majorly are TSOP, QFN, LQFP, TFBGA, MCMTFBGA, SVFBGA
21
47
65
102
142 143
160
0
20
40
60
80
100
120
140
160
180
Q1'12 Q2'12 Q3'12 Q4'12 Q1'13 Q2'13
Ship out Q'ty (Mpcs)
A & B vendors are Qualified and under high volume production
C, D and E vendors are Under Qualification
Vendor A B C D E
Ag Capacity
(km)
2013 July -60K
2013 Aug -80K60K
2013 Aug -20K
2013 Sept -50K60K 45K
Site KOREA TW TWKOREA
CHINA
KOREA
CHINA
Status Production Production Qualification Qualification Qualification
1N Ag Alloy Wire Suppliers 22
Al
IMC
Au5Al3
AuAl2
Au5Al3
AuAl2 Au4Al1
As bonded assembly HTSL HTSL1000
4N Au wire Kirkendall void
Au4Al1
Kirkendall void
Al
IMC
Au5Al3
AuAl2
Au5Al3
AuAl2 Au4Al1
2N Au wire
Au4Al1 Pd
Pd rich layer
Al
IMC Ag3Al
1N Ag wire
(Ag,Pd)3Al
Ag3Al Ag3Al
4N Au wire has kirkendall void after HTSL 1000hrs
2N Au wire has Pd rich layer to reduce void and enhance corrosion resistance
1N Ag wire has slow IMC growth and no kirkendall void in IMC layer
(Ag,Pd)3Al
(Ag,Pd)2Al
Ag3Al
IMC thickness :2~3um
IMC thickness :3~4um
IMC thickness :4~5um
Kirkendall void
No void
Pd rich layer
HTSL1000
IMC Growth Behavior for Au/Ag Wire 23
Ag Alloy already be proven good workability and reliability and has been in production for more than one year
The benefits of Ag alloy wire
Good bonding workability
Shorter machine parameters setting time
Higher throughput in manufacturing (Lower cost)
No limitation for bond pad structure
Not necessary to use K&S Iconn, Pro-Cu high end bonders
Good storage time
Conclusion 24
Q & A
25