Partially based on Prof . Vishwani D. Agrawal lecture VLSI Testing
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Transcript of Partially based on Prof . Vishwani D. Agrawal lecture VLSI Testing
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Partially based on Prof. Vishwani D. Agrawal lecture VLSI Testing
and book by S. Mourad, Y. Zorian, "Principles of Testing Electronic Systems”
ECE 617 - Fault Testable DesignDr. Janusz Starzyk
School of EECSOhio UniversityAthens, OH, 45701
http://www.arltesting.com/
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IC Testing Machine
(IC81-0444-467)
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3360-P VLSI Test System
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Definition ofTesting
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Outline
Reliability and testingDesign ProcessVerification & testingFaults and their detectionFault coverageTypes of testsTest applicationsDesign for TestTest economics
0.18u VLSI silicon neuronshttp://www.ini.uzh.ch/node/21083
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Reliability and Testing
Reliability of electronics systems is no longer limited to military, aerospace or bankingUsed by almost everyone in the workplaceApplied to smaller and smaller devicesHave continually new failure modesReliability depending on being error freeFailures in both software and hardwareHere we concentrate on hardware
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The goal over time is to reduce the cost of manufacturing the product by reducing the per-part recurring costs:
- reduction of silicon cost by increasing volume and yield, and by die size reduction (process shrinks or more efficient layout)
- reduction of packaging cost by increasing volume, shifting to lower cost packages if possible (e.g., from ceramic to plastic), or reduction in package pin count
Test Objective
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- reduction in cost of test by:- reducing the vector data size- reducing the tester sequencing complexity- reducing the cost of the tester- reducing test time- simplifying the test program
Test Objective
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Controller(algorithm)
RAM
UDL UDL
RAM
DSP(Netlist)
Micropro.(Layout)
Interface Block(RT Level )
FPGA
A System on a Chip
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Verification and Testing
Testing a circuit prior to fabrication is known as design verificationVerification is certainly done at various stages of the design processMost viable design verification is through simulationTesting is identifying that the fabricated circuit is free from errorsNeed to specify what errors testing is looking for
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BehaviouralDescription
BehavioralDFT
Synthesis
RTL Description
LogicDFT
Synthesis
Gate Description
Test PatternGeneration
FaultCoverage?
Manufacturing
Good Product
Test Application
Product
TechnologyMapping
Layout
ParameterExtraction
Gate
Libraries
Libraries
low high
DFT Cycle
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Test Programming
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Types ofLogic Faults
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Types ofPhysical Faults
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Faults and their Detection
Physical failures are manifested as electrical failures and are interpreted as faults on the logic levelSeveral physical defects may be mapped into few fault typesThe main fault type is Stuck-at FaultA fault is detected by a test patternTest pattern is an input combination that confirms the presence of the fault
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ZB
A R 1
R 2
RL
BA Z
ZA
A Z
(a) (b)
Possible Defects
Two technologies, two physical defects map into the same stuck-at zero faultNotation used - A SA0, A@0, or A/0
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Inputs FF Faulty ResponseAB Response A/0 B/0 Z/0 A/1 B/1 Z/100 0 0 0 0 101 0 0 0 0 110 0 0 0 1 111 1 0 0 1 1
A
BZ
Detecting Stuck-at Faults
Fill in the blanks in faulty response A/0 and A/1
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Inputs FF Faulty ResponseAB Response A/0 B/0 Z/0 A/1 B/1 Z/100 0 0 0 0 0 0 101 0 0 0 0 1 0 110 0 0 0 0 0 1 111 1 0 0 0 1 1 1
A
BZ
Detecting Stuck-at Faults
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Detecting Stuck-at FaultsA
BZ
Inputs Fault Free Faulty ResponsesAB Response A/0 B/0 Z/0 A/1 B/1 Z/100 0 0 0 0 0 0 101 0 0 0 0 1 0 110 0 0 0 0 0 1 111 1 0 0 0 1 1 1
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Sequential CircuitR
S
QA
2
1
Inputs FF Faulty ResponseSR Response A/0 S/0 R/0 A/1 S/1 R/1
01 0 0 0 X 0 0 100 0 1 0 X 1 0 110 1 1 0 1 0 1 111 0 0 0 1 1 1 1
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Types ofTesting
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Types of Tests
The exhaustive test used to detect the faults on a 2-input AND gate is not practical for circuits with 20 or more primary inputsPseudo-exhaustive: exhaustive for components in the circuits
segmentation or partitioning
A random test is also viable to detect faults, but pseudo-exhaustive tests are more realistic for Stuck-at FaultsDeterministic or fault oriented tests
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Functional Testing
Exhaustive & pseudo-exhaustive testing :
Partial dependence circuits:-a circuit in which primary outputs (PO)
depend on all the primary inputs (PI)- each output tested using 2ni inputs
(ni < n shows inputs affecting PO)
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Functional Testing
Example :
Exhaustive & pseudo-exhaustive testing
Exhaustive test for each gate
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Functional Testing
the circuit is partitioned into segments such that each segment has small number of inputseach segment is tested exhaustivelyusually inputs & output of each segment are not PIs or POs so we need to control segment inputs using PIs and observe its outputs using PO - this lead to sensitizing partitioning
Exhaustive & pseudo-exhaustive testing Partitioning technique :
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Functional Testing
Example : Consider the following circuit :
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Functional Testing
Example: the following shows 8 input vectors to test exhaustively h.
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Functional Testing
Example: Add vectors 5 - 8 to test exhaustively g and 9 -10 to test exhaustively y
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Functional Testing
Example: Add missing combinations to vectors 4 and 9 to test exhaustively x
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Types of Testing
Verification testing, characterization testing
Verifies correctness of design and correctness of test procedureMay require correction of either or both
Manufacturing testingFactory testing of all manufactured chips for parametric and logic faults, and analog specificationsBurn-in or stress testing
Acceptance testing (incoming inspection)User (customer) tests purchased parts to ensure quality
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Verification Test
Very expensiveApplied to selected partsUsed prior to production or manufacturing test
May comprise:Scanning Electron Microscope testsBright-Lite detection of defectsElectron beam testingArtificial intelligence (expert system) methodsRepeated functional tests
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Manufacturing TestDetermines whether manufactured chip meets specificationMust cover high % of modeled faultsMust minimize test time (to control cost)No fault diagnosisTest at rated speed or at maximum
speed guaranteed by supplier
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Burn-in or Stress TestProcess:
Subject chips to high temperature and over-voltage supply, while running production tests
Catches infant mortality casesThese are damaged or weak (low reliability) chips that will fail in the first few days of operation Burn-in causes bad devices
to fail before they are shipped to customers
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Manufacturing Test Scenarios
Wafer sort or probe test Done before wafer is scribed and cut into chipsTest devices are checked with specific patterns to measure:• Gate threshold• Polysilicon field threshold• Poly sheet resistance, etc.
Packaged device tests
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Types of TestsParametric – measures electrical properties of pin electronics – delay, voltages, currents, etc. – fast and cheapFunctional – used to cover very high % of modeled faults – test every transistor and wire in digital circuits – long and expensive
http://www.ece.unm.edu/~jimp/vlsi/slides/c1_intro-8.gif
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Functional TestATE and Manufacturing World – any vectors applied to cover high % of faults during manufacturing testAutomatic Test-Pattern Generation World – testing with verification vectors, which determine whether hardware matches its specification – typically have low fault coverage (< 70 %)
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Levels of testing
LevelsChipBoardSystem
• Boards put together• System-on-Chip (SoC)
System in field
Cost – Rule of 10It costs 10 times more to test a device as we move to higher levels in the product manufacturing process
Mixed Signal VLSI Circuit
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Levels of testing
Other ways to define levels – these are important to develop correct “fault models” and “simulation models”
TransistorGateRTLFunctionalBehavioralArchitecture
Focus: Chip level testing – gate level design
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Typical Test Program
1. Probe test (wafer sort) Catches gross defects
2. Contact electrical test3. Functional & layout-related test4. DC parametric test5. AC parametric test
Unacceptable voltage/current/delay at pin Unacceptable device operation limits
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Rise/fall Time Tests
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Set-up and Hold Time Tests
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Propagation Delay Tests
1. Apply standard output pin load (RC or RL)2. Apply input pulse with specific rise/fall3. Measure propagation delay from input to
output Delay between 5 ns and 40 ns (ok) Delay outside range (fails)
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Circuit UnderTest
Checker
EncodedOutputN N
N
P
On Line Testing
Embedded checkers – error detectionPeriodic diagnostic programsWatchdog checkers
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Analog
Logic
RAM
Embedded testExternal test
High BandwidthLow Bandwidth
Source/sink
Logic
RAM
Analog
Embedded testExternal test
High Bandwidth
On- vs Off-Chip Testing
Off chip test On chip test
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Test Specifications & Plan
Test Specifications:Functional CharacteristicsType of Device Under Test (DUT)Physical Constraints – package, pin numbers, etc.Environmental Characteristics – power supply, temperature, humidity, etc.Reliability – acceptance quality level (defects/million), failure rate, etc.
Test plan generated from specificationsType of test equipment to useTypes of testsFault coverage requirement
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Test Data Analysis
Uses of ATE test data:Reject bad DUTsFabrication process informationDesign weakness information
Devices that did not fail are good only if tests covered 100% of faultsFailure mode analysis (FMA):
Diagnose reasons for device failure, and find design and process weaknessesImprove logic and layout design rules
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Testers cost over $1 000 000
Cost of Testing
VLSI Test System TS600
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Cost of Testing
Design for testability (DFT)Chip area overhead and yield reductionPerformance overhead
Software processes of testTest generation and fault simulationTest programming and debugging
Manufacturing testAutomatic test equipment (ATE) capital costTest center operational cost
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Cost of Manufacturing Testing
Example test cost:0.5-1.0GHz, analog instruments,1024 digital pins: ATE purchase price
= $4.272M
Running cost (five-year linear depreciation)= Depreciation + Maintenance + Operation
= $0.854M + $0.085M + $0.5M= $1.439M/year
Test cost (24 hour ATE operation)= $1.439M/(365 x 24 x 3,600)= 4.5 cents/second
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Good
Bad
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PCB for 16 channel pin
card for IC tester henning-eng.com/pcb800.htm
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Time in Months
Reve
nues
TTime toMarket
Loss ofRevenues
Time to Market
Test Economics
The life cycle of a product is shorter than its design cycleTime to market needs to be shortenTesting is necessary for reliability and for improving yield
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VLSI Defects
Faulty chips
Good chips
Unclustered defectsWafer yield = 12/22 = 0.55
WaferDefects
Clustered defects (VLSI)Wafer yield = 17/22 = 0.77
Smaller dies
Wafer yield = 78/88 = 0.88
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Yield and Defect Level
Defect Level
1
0.1
0.01
0.001
%
TT%
DPM
10000
5000
1000
500
100
50
10
.01 0.1 1 1099.99 99.9 99 90
Y=50% Y=90%
C%
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Fault coverage
Test transparency
Yield
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Multi-site Testing
One ATE tests several (usually identical) devices at the same timeBoth probe and package testDUT interface board has > 1 socketsUsually tests 2 or 4 DUTS at a time Usually test 32 or 64 memory chips at a timeLimits: # instruments available in ATE, type of handling equipment available for package
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Example VLSI Test Systems
Advantest T3347BLow-cost Parallel Testing of Four High-end MCU and Testing of Large ASIC
40 MHZ testing speed. Accommodates up to 512 I/O pins. Simultaneous testing of up to four devices per station.
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ADVANTEST Model T6682 ATE
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T6682 ATE Block Diagram
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T6682 ATE Specifications
Uses 0.35 mm VLSI chips in implementation1024 pin channelsSpeed: 250, 500, or 1000 MHzTiming accuracy: +/- 200 psDrive voltage: -2.5 to 6 VClock/strobe accuracy: +/- 870 psClock settling resolution: 31.25 psPattern multiplexing: write 2 patterns in one ATE cyclePin multiplexing: use 2 pins to control 1 DUT pin
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T6682 Pattern Generation
Sequential pattern generator (SQPG): stores 16 M vectors of patterns to apply to DUT, vector width determined by # DUT pins
Algorithmic pattern generator (ALPG): 32 independent address bits, 36 data bits
Scan pattern generator (SCPG) supports JTAG boundary scan, greatly reduces test vector memory for full-scan testing
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T6682 Test Data Analysis
Uses of ATE test data:Reject bad DUTSFabrication process informationDesign weakness information
Devices that did not fail are good only if tests covered 100% of faultsFailure mode analysis (FMA)
Diagnoses reasons for device failureFinds design and process weaknessesAllows improvement of logic & layout design rules
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T6682 Probe Card
Probe card – custom printed circuit board (PCB) on which DUT is mounted in socket
may contain custom measurement hardware
Probe needles come down and scratch the pads to stimulate/read pins
Membrane probe – for unpackaged waferscontacts printed on flexible membrane, pulled down onto wafer with compressed air
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LTX FUSION HF ATE
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Specifications
Intended for SOC test digital, analog, and memory test supports scan-based test
Modular can be upgraded with additional instruments
enVision Operating Systemmaximum 64 M vectors memory storage
1 or 2 test heads per tester, maximum of 1024 digital pins, 1 GHz maximum test rateAnalog instruments:
DSP-based synthesizers, digitizers, time measurement, power test, radio frequency source and measurement capability (up to 4.3 GHz)
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ADVANTEST Model T2000 ATEScalable Architecture
Microsoft Windows 2000
C++(Microsoft Visual Studio Professional)
OTPL(Open Architecture Test System Programming Language)
Re-configurable Program Structure for test data and algorithm
T2000 System Software Emulator
Wave Tool (Logic Analyzer, Oscilloscope).
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ADVANTEST T6577
Tests SoC/Mixed-Signal
Devices Supports for a maximum of 1024 logic and/or I/O channels. Performs parallel test of up to 32 devices Supports baseband, DVD read channel, and jitter test At-speed test of high-speed memory interfaces Test rates of up to 667 Mbpsmaximum of eight channels