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Probing Assessment on Fine Pitch Copper Pillar Solder Bumps
Probing Assessment on Fine Pitch Copper Pillar Solder Bumps
June 6 to 9, 2010San Diego, CA USA
Senthil Theppakuttai, PhDBahadir Tunaboylu, PhDJeff HicklinSV Probe, Inc.
Senthil Theppakuttai, PhDBahadir Tunaboylu, PhDJeff HicklinSV Probe, Inc.
June 6 to 9, 2010 IEEE SW Test Workshop 2
Presentation OverviewPresentation Overview
• Introduction• Objectives• Experimental Methodology• Fine Pitch Array Probing Technology• Results of Eutectic Bumps• Results of Lead‐Free Bumps• Results of Cu Pillar Bumps• Summary & Conclusions• Future Work
June 6 to 9, 2010 IEEE SW Test Workshop 3
IntroductionIntroduction• Wafer bumping technology is changing as flip‐chip devices shrink from
150um to ultra‐fine pitch 35um bump arrays
• Fine‐pitch bumps typically have Cu pillar base with solder cap top – This structure offers a solution to the electro‐migration challenges faced by
conventional solder balls, with better thermal & electrical conductivity– Copper pillar bumps also allow for easy under‐fill & flux removal compared
to other solder options
• As the metallurgy of the bump structure changes from eutectic to lead‐free on copper pillars with varying contact geometries, probing very fine‐pitch bumps presents new test, process & precision challenges
• We would like to understand the test challenges on these tiny structures by investigating probe‐bump contacts
June 6 to 9, 2010 IEEE SW Test Workshop 4
ObjectivesObjectives
• Investigate scrub, contact resistance behavior on cu‐pillar bumps as a function of probing conditions for contact reliability.– Scrub Marks Study– Contact Resistance as a Function of Over‐travel, Tip Size
• Study contact behavior of Cu‐pillar bumps at 60μm pitch with various solder cap materials: – Cu pillar with Eutectic Solder Cap– Cu pillar with Lead‐free Solder Cap– Cu Pillars
June 6 to 9, 2010 IEEE SW Test Workshop 5
Test EquipmentTest Equipment• Test Systems for Scrub Mark & Contact Resistance Characterization
Prober: TEL P12 XLn
Keithley Tester & Source Meter
LEO Scanning Electron Microscope
Veeco Profilometer
Nikon Optical Inspection System
Test Wafers: Al, Au, Cu pillar, Cu‐pillar with Pb‐Sn cap, Cu‐pillar with Sn‐Ag cap
Probing Technology: MEMS‐Fine Pitch Vertical Technology (LogicTouch™)
June 6 to 9, 2010 IEEE SW Test Workshop 6
LogicTouchTM Vertical Probing TechnologyLogicTouchTM Vertical Probing Technology
11
33 2244
1. Probes2. Space Transformer (MLC)3. Interposer4. PCB ProbesProbes
Example Layout: 60/30µm Peripheral Layout is Shown Technology Capable of Probing 60µm Arrays Technology Scalable to 40µm Pitch
1. Eutectic Solder Bumps1. Eutectic Solder Bumps
June 6 to 9, 2010 IEEE SW Test Workshop 8
Eutectic Solder Bump WaferEutectic Solder Bump Wafer
60 μm
15 μm
15 ~ 20 μm
60 μm
50 μm
Electroplated Solder Bumps: Cu-pillar with Pb-Sn Cap, after ReflowElectroplated Solder Bumps: Cu-pillar with Pb-Sn Cap, after Reflow
June 6 to 9, 2010 IEEE SW Test Workshop 9
Probe Tips Probe Tips
9 μm Tips 9 x 12 μm Tips
16 μm Tips36 μm Tips
June 6 to 9, 2010 IEEE SW Test Workshop 10
Eutectic Bump ResistanceEutectic Bump Resistance
0.0
0.5
1.0
1.5
2.0
2.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Over Drive (m)
cres
(Ω)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
Cres Stable at 25μm OT ( ~ 3 gf) for All Tip Sizes*Cres is the path resistance including connections from tester to the probe tip.
Cres Stable at 25μm OT ( ~ 3 gf) for All Tip Sizes*Cres is the path resistance including connections from tester to the probe tip.
June 6 to 9, 2010 IEEE SW Test Workshop 11
Scrubs on Eutectic BumpsScrubs on Eutectic BumpsScrub Length
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b Le
ngth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
• 16 μm Tips + 50 μm OT– Scrub Mark ~ 17 x 15 μm– Scrub Depth ~ 15 μm
• 36 um Tips + 50 μm OT– Scrub Length is 33 x 35 μm– Scrub Depth is 8 μm
Scrub Depth
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b D
epth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
Scrub Width
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b W
idth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
June 6 to 9, 2010 IEEE SW Test Workshop 12
Scrub Marks with 16 μm Tips at 50 μm OTScrub Marks with 16 μm Tips at 50 μm OT
16 μm16 μm Scrub Mark ~ 18 x 17 μmScrub Depth ~ 15 μmScrub Mark ~ 18 x 17 μmScrub Depth ~ 15 μm
June 6 to 9, 2010 IEEE SW Test Workshop 13
Scrub Marks with 36 μm Tips at 50 μm OTScrub Marks with 36 μm Tips at 50 μm OT
Scrub Mark ~ 35 x 36 μmScrub Depth ~ 8 μmScrub Mark ~ 35 x 36 μmScrub Depth ~ 8 μm
2. Sn‐Ag (Lead Free) Solder Bumps2. Sn‐Ag (Lead Free) Solder Bumps
June 6 to 9, 2010 IEEE SW Test Workshop 15
Sn‐Ag Solder Bump WaferSn‐Ag Solder Bump Wafer
60 μm50 μm
Electroplated Solder Bumps: Cu-pillar with Sn-Ag Cap, after ReflowElectroplated Solder Bumps: Cu-pillar with Sn-Ag Cap, after Reflow
June 6 to 9, 2010 IEEE SW Test Workshop 16
Sn‐Ag Bump ResistanceSn‐Ag Bump Resistance
0.0
0.5
1.0
1.5
2.0
2.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Over Drive (m)
cres
(Ω)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
Cres stable at 25 μm OT ( ~ 3 gf) for All Tip SizesCres stable at 25 μm OT ( ~ 3 gf) for All Tip Sizes
June 6 to 9, 2010 IEEE SW Test Workshop 17
Scrubs on Sn‐Ag BumpsScrubs on Sn‐Ag Bumps
• 16 μm Tips + 50 μm OT– Scrub Mark ~ 17 x 16 μm– Scrub Depth ~ 16 μm
• 36 μm Tips + 50 μm OT– Scrub Mark ~ 29 x 28 μm– Scrub Depth is 7.5 μm
Scrub Length
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b Le
ngth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
Scrub Width
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b W
idth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
Scrub Depth
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b D
epth
( m
)
9 um Tips 12 um Tips 16 um Tips 36 um Tips
June 6 to 9, 2010 IEEE SW Test Workshop 18
Scrub Marks with 16 μm Tips at 50 μm OTScrub Marks with 16 μm Tips at 50 μm OT
Scrub Mark ~ 17 x 16 μmScrub Depth ~ 16 μmScrub Mark ~ 17 x 16 μmScrub Depth ~ 16 μm
June 6 to 9, 2010 IEEE SW Test Workshop 19
Scrub Marks with 36 μm Tips at 50 μm OTScrub Marks with 36 μm Tips at 50 μm OT
Scrub Mark ~ 29 x 27 μmScrub Depth ~ 7.5 μmScrub Mark ~ 29 x 27 μmScrub Depth ~ 7.5 μm
30 m
3. Copper Pillar3. Copper Pillar
June 6 to 9, 2010 IEEE SW Test Workshop 21
Cu‐Pillar WaferCu‐Pillar Wafer
June 6 to 9, 2010 IEEE SW Test Workshop 22
Copper Pillar ResistanceCopper Pillar Resistance
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Over Drive (m)
cres
(Ω)
9 um Tips 12 um Tips
• Cres with 12 μm Tips >> 9 μm Tips
• For 9 μm Tips, Cres Stable at 50 μm OT (5~6 gf)
June 6 to 9, 2010 IEEE SW Test Workshop 23
Scrubs on Copper PillarsScrubs on Copper PillarsScrub Length
012
34567
89
10
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b Le
ngth
( m
)
9 um Tips 12 um Tips
• 9 μm Tips + 50 μm OT– Scrub Mark ~ 7 x 9 μm– Scrub Depth is 1.75 μm
• 12 μm Tips + 50 μm OT– Scrub Mark ~ 7 x 12 μm– Scrub Depth is 1.15 μm
Scrub Width
0
2
4
6
8
10
12
14
16
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b W
idth
( m
)
9 um Tips 12 um Tips
Scrub Depth
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Over Drive (m)
Scru
b D
epth
( m
)
9 um Tips 12 um Tips
June 6 to 9, 2010 IEEE SW Test Workshop 24
Scrub Marks with 9 μm Tips at 50 μm OTScrub Marks with 9 μm Tips at 50 μm OT
Scrub Mark ~ 8 x 9 μmScrub Depth ~ 1.75 μmScrub Mark ~ 8 x 9 μmScrub Depth ~ 1.75 μm
June 6 to 9, 2010 IEEE SW Test Workshop 25
Summary & ConclusionsSummary & Conclusions• We have demonstrated probing fine‐pitch solder bumps at
60um pitch arrays using LogicTouchTM technology.• Larger tips (> 16 μm) were effective for solder bump probing
while smaller tips were recommended (< 9 μm) for copper pillar probing. Since copper pillar surface is harder to penetrate, a sharper tip is required for effective probing.
• Contact behavior of Copper Pillar bumps with solder caps were studied with four different tip sizes.– The Cres behavior on eutectic or lead‐free bumps were very similar for all
four tip sizes as a function of overtravel. However, the scrub signature of 36um‐tip was distinctly different than the rest. We have not observed any appreciable difference in probing performance between eutectic solder & lead‐free bumps.
– Copper pillar probing shows a parallel to copper pad probing. Cres stabilizes at higher OT compared to solder bumps.
– No damage was observed after multiple probing on all bump types studied.
June 6 to 9, 2010 IEEE SW Test Workshop 26
Future WorkFuture Work• Cres Behavior on Contacts on Different Locations on Solder Bumps• Life Test on all Three Bump Materials including the Bump Height
Variation vs. Probing Performance
• Effect of Current on Scrub, Cres & Cleaning
Acknowledgements– Authors gratefully acknowledge the support from Son Dang, Joseph Martin, & Ivan Pipps