Area Array Cobra Probe Card With 5 GHz. Bandwidth Raphael ...

Area Array Cobra Probe Card With 5
GHz. Bandwidth
Raphael Robertazzi
IBM Research
6/12/02
6/12/02 IBM RESEARCH Page [1]

Outline
• Motivation: Test High Speed Area Array ICs In The
Development Stage, At Wafer Level.
– Improve The Bandwidth Of Cobra Probe Cards
For At Speed (10Gb/s) Test.
– Performance Equal To Or Better Than Membrane
Probes, Extension To Higher Frequencies.
• New Hand Wired Space Transformer
Concept / Implementation.
• Experimental Results.
– Rise Time / Bandwidth Measurements.
– 10 Gb/s Serializer/Deserializer Wafer Level BERT
Test.
• Conclusions.
6/12/02 IBM RESEARCH Page [2]

Motivation
• Wafer Level, Developmental Testing Of High
Pin Count Communications ICs.
– Connection To C4 Arrays (Cobra Probe).
– Large Numbers (~100) Of Medium Speed (0.5-1
Gb/S) Data Lines.
– Microwave (10 Gb/S) Data Rates On Selected
Lines.
– Complex, Multiple Power Domains.
– Path To 40 Gb/s Test.
6/12/02 IBM RESEARCH Page [3]

Conventional Cobra Probe Card
Low Speed
Line
Pogo Pin
Pad
Substrate
Space XFM
Cobra Head
6/12/02 IBM RESEARCH Page [4]

High Performance Cobra Probe Card
50 Ohm Micro Coax
Medium Speed Line
High Speed Line
ATE Data Cable
Transition Near
Space XFM
Substrate
Signal/Ground
Twisted Pair
Low Speed
Line
Pogo Pin
Pad
Space XFM
Cobra Head
6/12/02 IBM RESEARCH Page [5]

Probe Card Photo
6/12/02 IBM RESEARCH Page [6]

Space Transformer
100 mm
Micro-Coax
C4 Image
6/12/02 IBM RESEARCH Page [7]

Probe Card On HP83K Test System
Medium Speed Twisted Pair
High Speed Micro-Coax
6/12/02 IBM RESEARCH Page [8]

Probe Card Features
• Space Transformer Manufacturable In 4-6 Weeks.
• Addition Of Medium Speed Differential Lines Capable
Of 3-4 X Bandwidth Of Standard Space Transformer
Lines (92 Ports).
• Addition of High Speed Lines Capable Of 20 X
Bandwidth of Standard Space Transformer (4 Ports).
• Other Improvements Relevant to Microprocessor
Test And Decreased Probe Card Manufacturing
Time.
6/12/02 IBM RESEARCH Page [9]

TDT Characterization
500 Ohm Picoprobe
HP54120B
Cobra Probe
6/12/02 IBM RESEARCH Page [10]

TDT For Medium And Low Speed Lines
6/12/02 IBM RESEARCH Page [11]

Low and Med Speed Line
Rise Time Comparison
Low
Med
τ 20/80
(ps)
980
355
τ 10/90
(ps)
2160
530
6/12/02 IBM RESEARCH Page [12]

TDT For High Speed Lines
6/12/02 IBM RESEARCH Page [13]

High Speed Line Rise Time
τ 20/80
(ps)
40
τ 10/90
(ps)
64
6/12/02 IBM RESEARCH Page [14]

SerDes Output Experiment
HP54120B
Cobra Probe
SerDes IC
τr < 20ps
6/12/02 IBM RESEARCH Page [15]

SerDes Output Data
6/12/02 IBM RESEARCH Page [16]

SerDes BERT Experiment
6/12/02 IBM RESEARCH Page [17]

10 Gb/s Eye Diagram
6/12/02 IBM RESEARCH Page [18]

10 Gb/s BERT Results At Wafer Level
Pattern
Comment
2 7 –1 -> 2 23 –1
2 31 –1
Error Free Over 30
Min. Experiment
Error Rate* =1.3 x 10 -8
* Repairing R x Ground Should Allow
Long Pattern To Run Error Free
6/12/02 IBM RESEARCH Page [19]

Extending Bandwidth
• Bandwidth Of Current Design Limited
By Cobra Head.
– Rise Time Of High Speed Lines
Determined By L/R Time Of Head.
• Paths to Higher Frequencies:
– Redesign Head For 50 Ohm Path From
Coax To Chip.
– Reduce Distance Between Coax And Chip.
6/12/02 IBM RESEARCH Page [20]

TFI Contactor Reduces L/R Time
Substrate
Space XFM
TFI Contactor
Detail
100 µm
Lp = 20 pH, Lp/R = 0.4 ps
6/12/02 IBM RESEARCH Page [21]

Conclusion
• Demonstration Of A New Cobra Probe Card With
Increased Bandwidth:
– 20X Bandwidth Improvement Over Conventional Cobra
Probe Card (Micro Coax).
– 3-4X Bandwidth Improvement Over Conventional Cobra
Probe Card (Twisted Pair And Direct Cable To Card
Connection).
• High Speed Line Bandwidth Limitation Gated By
Cobra Head.
Paths To Higher Frequencies:
– Engineering 50 Ohm Cobra Head.
– Using TFI Contactor.
• New Probe Card Can Be Constructed In 4-6 Weeks.
6/12/02 IBM RESEARCH Page [22]