6/4/01 IBM RESEARCH Page [1]

Area Array Probe Card Interposer

Raphael RobertazziIBM Research

6/4/01

6/4/01 IBM RESEARCH Page [2]

Outline

• Motivation:– Probe Cards for Testing Complex ICs in the

Developmental Stage.– Hand Wired Space Transformer Limitations.– Bandwidth / Power Supply Bypassing

for High Speed / High Current Parts.• Interposer Concept / Implementation.• Experimental Results.• Conclusions.

6/4/01 IBM RESEARCH Page [3]

Motivation• Developmental Testing of Complex ICs.

Space XFM Required.– Probe Cards Need to be Manufactured Quickly

(<12 weeks). Ceramic Modules Not an Option.– Membrane Probe Technology Still Too Immature

for Complex Area Arrays of Ports.– Needle Cards Unusable.

Only Viable Option is Hand WiredSpace Transformer / Cobra Probes

6/4/01 IBM RESEARCH Page [4]

Hand Wired Space Transformer Limitations

• Bandwidth < 600 MHz– Rise time > 2nS

• Current < 30 Amps• Prone to Net List Errors

6/4/01 IBM RESEARCH Page [5]

Requirements For Two ICs Under Development

• Microprocessor Part– More Than 7000 Ports.– Probe Card #1 Accessed 866 Ports.– Current Draw 100 Amps At Full Speed– Clock Line Bandwidth > 1GHz.

• Communications Part– 10 Gb/s Input Port– High Quality RF By Pass.– Power Net Diagnostics (Noise).

6/4/01 IBM RESEARCH Page [6]

Desirable Performance Enhancements

• High Speed I/O Lines ( 1-10 GHz and Beyond).

• High (100 Amp) Current Drive, More Power Pins, and Low Inductance By Pass.

• Power Grid Diagnostics.• Lithographic Implementation of the Power

Net.• Ability to Repair Nets.• Decreased Probe Card Fabrication Time.

6/4/01 IBM RESEARCH Page [7]

Cobra Probes

Head

Magnet Wire

SpaceXFM

Pogo Pin Pad

Substrate

Hand Wired Space Transformer Cobra Probecard

6/4/01 IBM RESEARCH Page [8]

Application of the Interposer

J971 COBRA HEAD

VESPAL SPACE TRANSFORMER

COBRA WRIRESPACE TRANSFORMER LEAD

NORMAL CONFIGURATION

WITH KAPTON INTERPOSERHIGH SPEED LINE

BUMP

VESPAL SPACE TRANSFORMER

J971 COBRA HEAD

BUMP

HIGH SPEED LINE

DETAIL

HIGH SPEED CONNECTOR

MICROSTRIP TRACE

6/4/01 IBM RESEARCH Page [9]

Interposer Features

By Pass Capacitor

(4-1)

VDD Plane

GND Plane

High Speed Line

Low Inductance Ground Connection for High Speed Line and Supply By Pass

Through Connection toWire Bundle

Port to Port Connection

Bump

Cobra Probe

Wire

6/4/01 IBM RESEARCH Page [10]

Interposer Photo(Standard Flex Process)

Through Connection

High Speed Line

VDD Plane

Kapton Substrate

6/4/01 IBM RESEARCH Page [11]

Interposer Photo(Micro-Via Flex Process)

Through Connection

VDD Plane

25 µm Via

Kapton Substrate

6/4/01 IBM RESEARCH Page [12]

Interposer Schematic

MicrostripTrace

SMBJack

Kapton SheetMounting Frame

6/4/01 IBM RESEARCH Page [13]

Interposer on Test System

6/4/01 IBM RESEARCH Page [14]

TDR Characterization

HP54120BCobra Probe

6/4/01 IBM RESEARCH Page [15]

TDR Results

2 nS/Div 500 pS/Div

TDR With Interposer Mounted,

τ = 250 pS.

TDR of J971 Cobra Card,

τ = 1.15 nS.

6/4/01 IBM RESEARCH Page [16]

TDT Characterization

HP54120B

Cobra Probe

500 Ohm Picoprobe

6/4/01 IBM RESEARCH Page [17]

TDT Results

500 pS/Div 500 pS/Div

TDT of Interposer Alone,

τ = 214 pS.

TDT of Interposer + Cobra Head,

τ = 246 pS.

6/4/01 IBM RESEARCH Page [18]

S - Parameter Characterization

HP8753BCobra Probe

50 Ohm ThroughQuartz Substrate

6/4/01 IBM RESEARCH Page [19]

S – Parameter Results

0 1 2 3 4 5 6

0.0

0.2

0.4

0.6

0.8

1.0

50%@0.65 GHz

Quartz Substrate Through50% @2.45 GHz

CPCI Installed Hand Wired Cobra Alone

S21

f (GHz)

6/4/01 IBM RESEARCH Page [20]

Cobra Head Bandwidth Estimates

0 1 2 3 4 5 6

0.2

0.4

0.6

0.8

1.0

(20/80) % Rise Time = 56 pS4 GHz BW

Estimated S21 For Cobra Head Correcting For Connector and Microstrip Losses

Cobra Head, Probe Separation 11 mils.

Extra

pola

ted

|S21

|

f (GHz)

6/4/01 IBM RESEARCH Page [21]

Interposer For Biasing

Current Injection

Current Collection

X-Section: About 225#36 Wires at 1 InchFor 1 Oz. Copper.

Kapton Interposer

Chip C4s

6/4/01 IBM RESEARCH Page [22]

Current Capacity

• #36 (5 mil) Magnet Wire = 19.6 Mils.– 350 Wires 6900 Mils.

• 1Oz Cu = 1.4 Mils Thick– @1 inch diameter 4400 Mils.

• Calculated Resistance = 0.19 mΩ, Injecting on a 10 Inch Circle and collecting On a 1 Inch Circle, for 1.8 µΩ−cm, 1 Oz. Copper.

1 Oz Plane Can Provide at Least 64% of the Capacity of a Large (350 wire) Power Net

6/4/01 IBM RESEARCH Page [23]

Bias Experiment

Current Injection, 10 Amps

Current Collection

Copper Plane On Interposer

2.3

2.5

2.7

8.54.83.1

Potential, mV

6/4/01 IBM RESEARCH Page [24]

Conclusion

• Demonstrated 4X Bandwidth Improvement Over Hand Wired Space XFM Alone.

• Bandwidth Limitation Gated by Connector, Not Cobra Head.

• Interposer Can Add Extra Current Supply Capacity and High Quality, Low Inductance By Pass Capacitance.

• Interposer Provides a Quick Repair / Reroute Capability for Probe Card.