Automated Inspection of Solder Joints for Surface Mount Technology
Electromigration in Solder Joints and Lines - Engineering · Electromigration in Solder Joints and...
Transcript of Electromigration in Solder Joints and Lines - Engineering · Electromigration in Solder Joints and...
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Electromigration in Solder Joints and Lines
K. N. Tu, Xu Gu, Hua Gan, and W. J. ChoiDept. of Materials Science &Engineering, UCLA
Los Angeles, CA 90095-1595
1. Introduction2. Unique behavior or electromigration in solder joints 3. Electromigration of flip chip solder joints
- SnPb vs. Pb-free (SnAgCu)4. Electromigration of solder lines in V-groove
- Temperature, composition, and polarity5. Summary
• Supported by NSF,SRC, IBM, Intel, MotorolaCo-workers : Dr. Everett C. Yeh, Intel, Santa Clara, CA
Prof. C. Y. Liu, National Central University, TaiwanProf. C. Chen, National Chiao Tung University, TaiwanDr. Taek Yeong Lee, Bell Lab. Lucent TechnologiesDrs. P. Elenius & H. Balkan, Flip Chip Technologies
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Peter Elenius, Flip Chip Technologies, (1999)
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Peter Elenius, Flip Chip Technologies, (1999)
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Peter Elenius, Flip Chip Technologies, (1999)
Electronic Thin Film Lab Materials Science & Engineering, UCLA
1. Geometry (Line-to-bump)• Current crowding and local Joule heating
2. Eutectic Composition• No chemical potential gradient as a function of composition• It can lead to a large composition gradient or redistribution
3. UBM dissolution• Fast diffusion of noble and near-noble elements in solder
4. Multiple driving forces• Thermo-mechanical,chemical, electrical
Unique Features of Electromigration in Solder Joints
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Current Density Distribution
2 µm UBM
0.20
0.58
1.66
4.80
13.9
40.0x103 A/cm2
Solder J = I/AAAl<<Asolder
Al line2 µm
e-Current Crowding Position
Electronic Thin Film Lab Materials Science & Engineering, UCLA
0.20
0.58
1.66
4.80
13.9
40.0
x103 A/cm2
(a)
(b)
X
Y
Current D
ensity (x104A
/cm2)
Z
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -
Simulation of current crowding in the solder bump
• Current carried by solder bump : 0.2 Amps• Thickness of Al interconnection : 2 µm• Contact window (opening) : 100 × 100 µm2
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Fig. Sequence of the void propagation at 125 oC, and 2.25×104 A/cm2
(a) 37 hrs (b) 38 hrs (c) 40 hrs (d) 43 hrs
Void Propagation (e-SnPb solder)
(a) (b)
(c) (d)
contact window
e-
e-
e-
Electronic Thin Film Lab Materials Science & Engineering, UCLA
e-
Si
Cu
e-
e-
Void propagation
(c) (b) in fig. 2
Time - Potential Curve
Fig. Potential change of the solder bump due to the electromigration
(b) (c) (d) in fig.2
0 10 20 30 40 50
1
2
3
4
5
6
Pote
ntia
l (V)
Time (hrs)
Resistance does not change much
Electronic Thin Film Lab Materials Science & Engineering, UCLA
* not failed, These MTTF are averaged value of three samples
(hrs)
Mean Time To Failure
= −
ktQexpAjMTTF n n = 1.8, Q = 0.8 eV
(By Flip Chip Technologies)
1.5 A (1.9x104 A/cm2)
1.8 A (2.25 x104 A/cm2)
2.2 A (2.75 x104A/cm2)
Expected Actual Expected Actual Expected Actual
100 oC 380 97 265 63
125 oC 108 573* 79.6 43 55.5 3
140 oC 46 121 34 32 24 1
24 samples tested (three samples for each test condition)8 samples cross-sectioned by W.J.Choi
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Failure Mode in Pb-free (SnAgCu) Solder Bump
Fig. Void propagation and failure at 140 oC and 2.4 Amps (3.0E4 A/cm2)(a) Before current stressing (b) After 14 hours : not failed (c) Magnified picture of (b)
(a)
(b)
(c)
This sample failed after 14.2 hrs
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Failure in SnAgCu Solder bump on Thin Cu/Ni(V)/Al UBM
140 oC , 2.4 Amps
2 hrs21 hrs99 hrs160 oC
14.2 hrs94.5 hrs
132 hrs140 oC
83 hrs112 hrs580 hrs125 oC
2.4 A3.0E4 A/cm2
2.2 A2.75E4 A/cm2
1.8 A2.25E4 A/cm2
0 2 4 6 8 10 12 14 16
1.8
2.0
2.2
2.4
2.6
2.8
3.0
Pote
ntia
l (V)
Time (hrs)
MTTF on SnAgCu solder bump
(b) In last Fig.
Electronic Thin Film Lab Materials Science & Engineering, UCLA
2002 Electronic Components and Technology Conference
UBM (Under Bump Metallization) Study for Pb-free Electroplating Bumping: Interface Reaction and Electromigration
Se-yeong Jang, Juregen Wolf, Woon-Seong Kwon, Kyung-Wook PaikDept. of Materials science and Engineering
KAIST (Korea Advanced Institute of Science and Technology)
Electronic Thin Film Lab Materials Science & Engineering, UCLA
No chemical potential gradient as a function of composition below the eutectic temperature
Pb-Sn
Ni-Sn
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Failure of SnAgCu Solder Bump on Thick Film UBM
Fig. Failure mode of solder bump on Thick UBM(a) No UBM dissolution(b) Before failure after 261 hrs at 125oC
and 2.0 Amps(c) Failure after at 150oC 25 hrs
at 150 oC and 2.5 Amps• In the same solder on thin film UBM sample,
MTTF is 14.2 hrs at 140 oC and 2.4 Amps
(b)(a)
(c)
50 µm
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Experiment
Experimental Conditions:• Temperature of environment: 100℃• Time of passing electric current:
15min, 30min, 45min, 60min, 75min, 90min, 95min (short) •Current 1.27 A per joint, Current density 2× 104 A/cm2
Chip
PCB
e-
e-
Chip
PCB
e-
e-
Au/Ni/Cu UBM
Cu conducting trace Cu padCu pad
100μm 63Sn/Pb
Flip Chip Solder Ball
100μm 63Sn/Pb
Flip Chip Solder Ball
Current direction, chip side metallurgy (pure Cu), and substrate side metallurgy (Au/Ni/Cu) used in this study.
+-Power Supply
Si Chip
PCBe- e-
e-
Schematic diagram of experimental setup.No current
Electronic Thin Film Lab Materials Science & Engineering, UCLA
From Professor R.Kao
in National Central Univ. in Taiwan
openCu
conducting trace
Cu dissolution
Cu6Sn5IMC
Si Chip
PCB
e-
e-
90mins
Electromigration in SnPb solder bump
I = 1.27A, T = 100℃,
e-15mins
30mins
e-
45mins
0min
Electronic Thin Film Lab Materials Science & Engineering, UCLA
The Top View of the Cu Conducting Trace at Chip Side (solder joint had been polished away carefully)
• The dissolved Cu region was back-filled with solder.
• The failure took place between back-filled solder and Cu conducting trace
Optical micrograph of the top down cross-section at Cu conducting trace
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Proc. 6th Internl. Vacuum Congr. 1974Japan. J. Appl. Phys. Suppl. 2, Pt. 1, 1974
Room Temperature Interaction in Bimetallic Thin Film Couples
King-Ning Tu and Robert RosenbergIBM thomas J. Watson Research Center
Yorktown Hights, New York 10598
PtSn4PtPb4PtPdSn4PdPb2PdNi3Sn4-NiAuSn4AuPb2AuAg3Sn-AgCu6Sn5-Cu
SnPb
Cu, Ag, Au, Ni, Pd, Pt
Si, Ge, Sn, PbInterstitial Diffusion
Table. Intermetallic compounds formed at room temperature
Electronic Thin Film Lab Materials Science & Engineering, UCLA
0 day
4 days
8 days
8 days
SiO2(0.12µm)
Cr or Ti (0.05µm)
Cu(1µm)
100µm
69.4µm
Si V-groove
Cu wireCu wire
Si (001)(a)
(b)
Polished Surface
IMC
Electromigration inV-Groove Line
SEM Images
J = 2.8 x 104 amp/cm2
T = 150 oC
Electronic Thin Film Lab Materials Science & Engineering, UCLA
~0.5(Eutectic)
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Room Temperature Electromigration in Eutectic SnPb solder on V-groove
67.42 %66.76 %68.11 %-69.63 %23.6
68.42 %79.95 %-86.02 %86.49 %13.8
69.34 %86.00 %86.04 %89.33 %91.66 %0
18013590450
Polishing from anode to cathode sidePolishing down from the surface
(µm)
Fig. Electromigration phenomenon in Eutectic SnPb solder line stressed by a current density 5.7x104A/cm2 at RTfor 4 days, 8 days, and 12 days
Electronic Thin Film Lab Materials Science & Engineering, UCLA
The Polarity Effect of Electromigration The Polarity Effect of Electromigration on Intermetallic Compound (IMC) Formationon Intermetallic Compound (IMC) Formation
in Solder Vin Solder V--groove Samplesgroove Samples
• Experiment and Results–Morphology change of IMC: polarity effect–Thickness change of IMC: polarity effect
• Analysis and Discussion
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Polarity Effect of EM on IMC Thickness
Cu Cu
100µm
PCB
Si chip
Soldere-
IMC
Solder 10hr
Cu
IMC
Solder
Cu
10hr e-
Anode
Cathode
3.2x104 A/cm2, 180oC
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Sample Preparation
<110>
Solder line
Cu wireSi Wafer • Advantage of V-groove sample:
- Comparable dimension and current density as real flip chip solder joints - Easy to make and observe- Higher current density comparing with traditional samples
• Advantage of V-groove sample:- Comparable dimension and current density as real flip chip solder joints - Easy to make and observe- Higher current density comparing with traditional samples
SiO2 (0.1 µm)
Cr or Ti (0.05 µm)
Cu (1 µ
100 µm
Cu (1µm)
69.4 µm69.4 µm
Au (0.05µm)
Solder
Electronic Thin Film Lab Materials Science & Engineering, UCLA
• Width of solder line: ~ 100µm
• Length of solder line: ~ 600-800µm
• Width of solder line: ~ 100µm
• Length of solder line: ~ 600-800µm
Typical Sample View
Solder V-groove sample after reflow Polished sample ready for EM test
Si wafer
Cu Cu
CuCu
Solder line Solder line
Si wafer
e-Cu Cu
Cu
Cathode Anodee- e-
Cu
IMC
Solder
Electronic Thin Film Lab Materials Science & Engineering, UCLA
Comparing of Morphology Change
Cathode(4x104 A/cm2, 150oC)
Anode(4x104 A/cm2, 150oC)
No Current(150oC)
157hr0min
0min
0min
35min
35min
Electronic Thin Film Lab Materials Science & Engineering, UCLA
EM effect on Thickness Change of IMC
0 hr
Anode (3.2x104 A/cm2, 180oC) Cathode (3.2x104 A/cm2, 180oC)
10hr
e-
Anode Cathode
e-0 hr
10hr
Cu6Sn5
Cu6Sn5
Anode
Anode(a)
(b)
Cu
Cu
Solder
Solder
0 hr
10hr
Cu6Sn5
Cu6Sn5
Cathode
Cathode(d)
(c)
Cu
Cu
Solder
Solder
Electronic Thin Film Lab Materials Science & Engineering, UCLA
EM effect on Thickness Change of IMC (cont.)
e-
Anode Cathode
e-
Anode (3.2x104 A/cm2, 180oC) Cathode (3.2x104 A/cm2, 180oC)
21 hr
87hr
Cu6Sn5
Cu3Sn
Cu6Sn5
Anode
Anode
Cu
Cu
(b)
(a) Solder
Solder
21 hr
87hr
87hrCu3Sn
Cathode
Cathode
Cu
Cu
(d)
(c)Solder
SolderVoid
Cu6Sn5