Interconnection Challenge in Wire Bonding Ag alloy wire. Jensen Tsai / 蔡瀛洲, SPIL, Taiwan

Transcription

1 1 Interconnection Challenge in Wire Bonding Ag alloy wire Jensen Tsai / 蔡瀛洲, SPIL, Taiwan

2 2 Content Ag Alloy Wire Type Market Ag Alloy Wire Benefits Workability and Reliability Performance IMC behavior and Improvement Conclusion

3 3 Gold Price Trend 800 USD/OZ, Started from 2008/08, Up to now, it grows to ~1400 USD/OZ, growth for 1.75 times

4 4 Market Application for Wire Selection Memory 20% Computing 11% Consumer products 25% Au wire HVM Pd-Cu wire LVM Ag alloy wire HVM Communication 44% 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

5 5 Ag Alloy Wire Roadmap Technology Items Production Available Ag Wire Bond Pad Pitch (um) Bond Pad Open (um) Wire Diameter (um) / Ag composition 88%, 95% 88%, 95% 95% Low Loop Height (um) Bonding Method Pad to Pad (Die to die) Bond Pitch (um)

6 6 Benefits to choose Ag Alloy Wire 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.

7 7 Process Control Comparison (Au/Ag/Cu) 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 Open package NA 1 year 1 year 6 months 20 days Cu Wire Kit No Yes Yes 1. Bare : 3 days 2. Pd-Cu : 14 days Type NA 95% N 2 + 5% H 2 95% N 2 + 5% H 2 Forming Gas Flow NA Different flow than Cu Different flow than Ag Wire Bond Wire Pull ( Min. ) Ball Shear ( Min. ) Appearance Inspection ( Concern after wire bonding ) 0.7 mil 1.8 gms 2.0 gms 3 gms 0.8 mil 2.0 gms 2.3 gms 4 gms 0.7 mil 4.8 gms 5 gms 8 gms 0.8 mil 5.3 gms 5.7 gms 10 gms 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

8 8 Pd-Cu wire (None Via, Al thickness < 1.2um) Crater test Crack

9 9 Ag wire (None Via, Al thickness < 1.2um) Crater test No Crack

10 10 Wire Properties Comparison Wire Type Ag 1N (95%) Pd Cu 2N Au Wire Diameter (mil) Melting Point ( ) Density (g/ cm3 ) Breaking Load(g) Room Temp. Elongation(%) Room Temp. Youngs Modulus (Gpa) HAZ Length (um) ~ ~ ~ ~ ~ ~ ~75 65~85 70~110 90~ ~130 Hardness(Hv) FAB 58~62 60~70 41~43 Grain Size(um) FAB 2~5 2.0~ ~4.0 Wire 0.1~3 4.0~ ~2 0 Resistivity ( 10-8 Ω.m) Fusing Current (ma) 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

11 11 Ag Alloy Wire Workability (Normal Bond) - Wire Bond Process Comparison for Normal Bond Items Wire Type Au 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 VIA No 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

12 12 Ag Alloy Wire Workability (Pad-to-Pad) - Die to Die bonding has obvious benefits Items Wire Type Au 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 VIA No Limitation Maturity Mass Production Mass Production Mass Production Die 2 Die Die 1 Die 1 Die 2 Bond Pad Ag alloy wire Obviously higher throuhput than Pd-Cu wire

13 13 Ag Alloy Wire Workability Comparison - Wire Pull Data Wire Type Au wire Cu wire Ag wire - Ball Shear Data Wire Type Au wire Cu wire Ag wire - 1 st and 2 nd Bond Photos Criteria Sample Size Max Min Avg STD Cpk 2pcs/all wire > 2.7g 2pcs/all wire pcs/all wire Criteria Sample Size Max Min Avg STD Cpk 2pcs/all ball > 8.5g 2pcs/all ball pcs/all ball 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

14 14 Ag Alloy Wire Workability Comparison - IMC & Crater Comparison Wire type Criteria Condition IMC Sample Size Result Criteria Sample Size Cratering Result Au wire > 80% 0 hr 0/2 90% 82% No Crack 0/3 No crack No crack Cu wire > 80% 0 hr 0/2 No 0/3 Crack 92% 90% No crack No crack Ag wire > 80% 0 hr 0/2 93% 92% No Crack 0/3 No crack No crack Ag alloy wire IMC and Bond pad crater could meet product criteria

15 15 Wire Material IMC Comparison Wire type 2N Au Pd Cu Ag alloy HTSL 150C/1000 hrs IMC thickness 6.3um 0.7um 3.56um IMC growth rate: Au wire > Ag alloy wire > Pd-Cu wire

16 16 Ag Alloy Wire Reliability Performance - Ag Wire Reliability Test Result Test item Read point Sample Size SAT F/T Cross-Section Moisture Sensitivity Test MSL3 (30 /60%RH/192hrs) Pressure Cooker Test (PCT) Thermal Shock Test (TST) Temperature Cycling Test (TCT) Bias High Acc. Stress Test (bias-hast) High Temperature Storage Life Test (HTSL) (Without precondition) 0 hour 0/180 0/180 Precondition 0/180 0/180 >168 hours NA 0/45 500cycles NA 0/ cycles NA 0/45 >192 hours NA 0/ hours NA 0/45 Reliability test conditions follow JESD STD and PASS.

17 17 Ag Alloy wire b-hast Testing - Lead Frame Package PKG Wire B-HAST(hrs) Bias Type Dia (mil) Voltage (V) BOM MQFN 5*5 / 40 95% Ag 0.8 F/T Passed F/T Passed VDD33 : 3.6V VDD12 : 1.32V Ag L/F MQFN 8*8 / 68 95% Ag 0.9 O/S Passed O/S Passed PS :1.2V,3.3V Ag L/F - Substrate Package PKG Wire B-HAST(hrs) Bias Type Dia (mil) Voltage (V) PBGA 27*27 / % Ag 0.7 O/S Passed O/S Passed PS1: 3.3V PS2: 1.8V PS3: 1.5V PS4: 0.9V BOM Au Finger TFBGA 18*18 / % Ag 0.7 F/T Passed F/T Passed VDD12 :1.2V VDD25 : 2.5V VDD33 : 3.3V Au Finger Ag wire can pass bias-hast 168hrs w/ Substrate and lead frame base

18 18 De-Cap Capability 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

19 19 Ag Alloy Wire Project 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)

20 20 Ag Alloy Wire Project (Die-to-Die) 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 BOM Substrate: 240.7*76.3mm Die Attach : Hxx FILM FH*** Bonding Wire : 0.7mil Ag wire Compound : Sxx G*** Solder Ball : 0.3mm Quality check item _PASS Item Measured Method Criteria Unit Wire-pull WP tester >2 gw Ball-shear BS tester >5 gw Ball- Thickness Cratering Microscope 500X 10um min um Microscope 200X Not allow Crack IMC Microscope 500X >70% 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

21 21 Ag Alloy Wire Production Volume - Package type majorly are TSOP, QFN, LQFP, TFBGA, MCMTFBGA, SVFBGA Ship out Q'ty (Mpcs) Q1'12 Q2'12 Q3'12 Q4'12 Q1'13 Q2'13 The average volume has reached 53M pcs/month

22 22 1N Ag Alloy Wire Suppliers Vendor A B C D E Ag Capacity (km) 2013 July -60K 2013 Aug -80K 60K 2013 Aug -20K 2013 Sept -50K 60K 45K Site KOREA TW TW KOREA CHINA KOREA CHINA Status Production Production Qualification Qualification Qualification A & B vendors are Qualified and under high volume production C, D and E vendors are Under Qualification

23 23 IMC Growth Behavior for Au/Ag Wire As bonded assembly HTSL HTSL1000 4N Au wire Kirkendall void Au5Al3 Au5Al3 Au4Al1 IMC AuAl2 AuAl2 Kirkendall void Au4Al1 HTSL1000 Kirkendall void Al IMC thickness :4~5um 2N Au wire Pd IMC Au5Al3 AuAl2 AuAl2 Au5Al3 Pd rich layer Au4Al1 Au4Al1 Pd rich layer Al IMC thickness :3~4um 1N Ag wire IMC Ag3Al Ag3Al (Ag,Pd)3Al Ag3Al (Ag,Pd)3Al (Ag,Pd)2Al Ag3Al No void Al IMC thickness :2~3um 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

24 24 Conclusion 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

25 25 Q & A