how to test complex vlsi/soc - yonsei universitytera.yonsei.ac.kr/class/2010_1/lecture/topic 12...
TRANSCRIPT
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How to Test Complex VLSI/SoC
2010
Sungho Kang
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OutlineWhat is Testing? Faults, ATPG & Fault SimulationAd-HocScanLogic BIST & Memory BISTP1149.1 & P1500Conclusion
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Determine requirements
Write specifications
Design synthesis and Verification
Fabrication
Manufacturing test
Chips to customer
Customer’s need
Test development
VLSI Implementation
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Design Constraints
Area
Speed
Power
Testability
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Testing Defect
Physical deviation from some specified properties
Test An experiment whose purpose is to detect the presence of detectsand to diagnose the source of defects
Byproduct of testing Reliability measurement of the product and processQuality assuranceAssistance to verification and validation
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Testing ProcessRule of thumb: spend 5-10% die area on DFT (10% of die is state and scan is 50% overhead per state!)
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Verification vs TestingVerification
Correctness of designSimulation, Emulation and Formal verificationPerformed once before manufacturingResponsible for quality of design
TestingCorrectness of manufactured hardwareTest generation and test applicationPerformed every manufactured devicesResponsible for quality of devices
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Testing Costs To detect problems early (Rule of Ten)
Test Failure CostChip Test Component Failure $0.3Board Test Board Failure $3System Test System Failure $30Field Test Field Failure $300
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Test Cost vs Manufacturing Cost
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VLSI Chip Yield
A manufacturing defect is a finite chip area with electrically malfunctioning circuitry caused by errors in the fabrication processA chip with no manufacturing defect is called a good chipFraction (or percentage) of good chips produced in a manufacturing process is called the yield
WaferDefects
Faulty chips
Good chips
Unclustered defectsWafer yield = 12/22 = 0.55
Clustered defects (VLSI)Wafer yield = 17/22 = 0.77
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Bathtub Curve
Failure Rate
Time
EarlyFailures
WearoutFailures
Infant Mortality
Working Life
Wearout
Random failure
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Test Process
TestProcess
Parts forManufacturing Line
Bad partswhich fail Test
(BF)
Good partswhich pass Test
(GP)
Bad partswhich pass Test
(BP)
Defect Level =BP
GP + BP
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Quality of TestQuality of Test
Y : YieldDL: Defect Leveld : defect coverageDL = 1 - Y 1-d
Consider a 0.5 yield processTo achieve 0.01 defect level, 99% coverage is requiredTo achieve 80% coverage, 0.2 defect level
1.0
0.8
0.6
0.4
0.2
0.00 20 40 60 80 100
defect level (%)
fault coverage (%)
Y = 0.01
Y = 0.1Y = 0.25
Y = 0.5
Y = 0.75
Y = 0.9
Y = 0.99
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Design for TestabilityRefers to those design techniques that make test generation and test application cost-effective
Why need?Difficulty in preparing test patterns
AdvantagesTest generation is easyHigh quality testing
DisadvantagesArea overheadTiming overhead
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How Much Testing Is Enough?
40
30
20
10
0
0 20 40 60 80 100Testability of a Circuit (%)
Test Development Time as a Percentage of Total
Design Time
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Test Costs vs Manufacturing Costs
Additional silicon areaOverhead for test purposes
costs
No specialtest provision
Total costs
Processing costs
Packaging costs
Testing costs
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Current Situation Increase of complexity
Moore’s LawNo. of transistors doubles every 18 months
Increase of speed30% increase per year
Timing and signal integrity Increase of test cost
30-40% of overall costIncrease of ATE performance
12% increase per yearTime to Market
Exhaustive testing is no good8080 takes 1020 years at one million tests per second
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Test Cost Factors
Low costexternal ATE
RF/AnalogCore
User Defined
Core
User DefinedCore
DRAM
IP
ROM
IP
IP
UDL
BIST Mem BISTTest AccessSoC Test Controller
IO Pad
IO Pad
Design for Testability
Test Equipment
TestEngineering
Test CAD Tools
TestMethodology
Spec.Design MethodologyLow Cost Test
Equipment
Efficient TestEngineering
Sound TestMethodology
AppropriateDFT
Powerful TestCAD Tools
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Manufacturing Defects
In fabrication, defects get introduced from many sources:ContaminationMetalization DefectImplant DefectWafer DefectOxide DefectInterconnect Defect
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Logical Fault ModelsGate Level Faults
Stuck-atShort between signal and ground or power
Bridging Short between two signals
Transistor Level FaultsShort
Connecting points not intended to be connectedOpen(break)
Breaking a connectionStuck-on (stuck-short)Stuck-open (stuck-off)
Delay FaultsTemporary Faults
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Single Stuck-at Fault (SSF)Only one line in the circuit is faulty at a timeThe fault is permanent (as opposed to transient)The effect of the fault is as if the faulty node is tied to either Vcc (s-a-1), or Gnd (s-a-0)The function of the gates in the circuit is unaffected by the fault
A B C
0 0 00 1 01 0 01 1 1
Fault-Free Gate
Vcc
A
BC
Fault: A s-a-1
A B C
0 0 00 1 11 0 01 1 1
Faulty Gate
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Relative Performance of Fault Models
at-speedfunctional
slow functional
stuck-at scan
at-speedscan
0 80
0
0 5
190 22
02
4 6
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HP(1996) : 25K std. cell design, 0.8micronFull scan : 1497FFs, 33MHzFunctional pattern : 83.7% fault coverageStuck-at fault coverage : 99% with 284 patternsTransition fault coverage : 99.4% with 554 patterns
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Fault Coverage and Efficiency
Fault coverage =
Fault efficiency
# of detected faultsTotal # faults
# of detected faultsTotal # faults -- # undetectable faults=
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Fault Simulation
FaultSimulator
Circuit
FaultCoverage
FaultList
TestPatterns
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ATPG
FaultList
ATPGCircuit Tests
FaultModel
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ATPG ExampleG output s-a-1 A
BCD
E
F
G
H
J
IK
0/1
A
111
E
F
G
H
J
IK
0/1
0
0
0
Fault Excitation
X
111
F
G
H
J
IK
0/1
0
0
0
0/1
10
Fault Propagation
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Sequential ATPG
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DFT Rule Checking
Scan Design, Boundary Scan DesignMemory BIST Design, Logic BIST Design
DFT Rule CheckingStatic Timing Analysis
Test Pattern Generation
Logic SimulationTest Vector Translation
DFT Rule Checking
Full Timing Simulation
DFT Rule Checking
Test Synthesis
Verilog/VHDL Netlist
ATPG
DFT Flow
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Classification of DFTAd-Hoc Design
InitializationAdding extra test pointsCircuit partitioning
Structured DesignScan designBoundary ScanBuilt-in Self Test
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PartitioningPhysically divide the system into multiple chips or boardsOn board-level systems, use jumper wires to divide subunitsCan have performance penalties
Module 2
Module 3
Module 1System
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Test Point InsertionEmploy test points to enhance controllability and observabilityLarge demand on extra I/O pins Example
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Sequential Circuit
FF
FF
FF
Combinational
logic
PI PO
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Adding Scan Structure
FF
FF
FF
Combinational
logic
PI PO
SCANOUT
SCANIN
Test/Normal
A MUX is added
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Automated Scan Design
Chip layout: Scan-chain optimization,timing verification
Behavior, RTL, and logicDesign and verification
Gate-levelnetlist
Scan design
rule audits
CombinationalATPG
Scan hardwareinsertion
Scan sequenceand test program
generation
Design and testdata for
manufacturing
Rule violations
Scannetlist
Combinationalvectors
Scan chain order
Mask dataTest program
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Sources of DFT Rule ViolationReset/preset violations
Controllability through PIs or disabled during testClock rule violations
Controllability/gatingTristate bus violations
Ensures there is no contentionBidirectional I/O violations
Controls direction to avoid contentionsLatch violations
Ensures transparency during test modeShift constraint violations
Ensures proper shifting of data through the scan chain
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Scan Chain ReorderingTo reduce the routing congestionsTo reduce the hold-buffer insertion during placement
May need skew-based optimization
Before After
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Built In Self Test Capability of a product to carry out an explicit test of itself
Test patterns are generated on-chipResponses to the test patterns are also evaluated on chipExternal operations are required only to initialized the built-in tests and to check the test results (go/no-go)
Pattern Generator
Logic BISTController
Response Analyzer
CUT
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Linear Feedback Shift RegisterThe state of shift register depends only on the prior state
= 1
D Q D QD QD Q
c2c1c1 cn
cn-1
Q1 Q2 Q3 Qn
a-1 a-2 a-n+1 a-n
am am-1 am-2 am-n+1 am-n
Next State
Current State
= 1
D Q D QD QD Q
c2c1c1cn
cn-1
Q1 Q2 Q3 Qn
am-1 am-2 am-nCurrent State
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LFSR ExampleCharacteristic Polynomial : 1+x2+x3
Initial condition (1,0,0) : xQ1 : x / (1+x2+x3)Q2 : x2 / (1+x2+x3)Q3 : x3 / (1+x2+x3)
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LFSR ExampleWhen initial state is 100
Q1 Q2 Q31 0 00 1 01 0 11 1 01 1 10 1 10 0 11 0 00 1 01 0 1
When initial state is 000Q1 Q2 Q30 0 00 0 0
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MISRMultiple input signature analysis
...
D Q D Q D Q D Q+ + +...Q1 Q2 Q3 Qn
Cn-2 C1Cn-1Cn
+
D1 D2 D3 Dn
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Test patterns are applied to CUT every clock cycleAdditional logic and delay are required between the input FF and CUTBILBO like type: Cannot perform compression and pattern generation concurrentlyEntire test is scheduled and divided into sessionsComplex test control unit is required
Test-per-Clock
PRPG
MISR
CUT
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STUMPS
PRPG
Logic BISTcontroller
MISR
Scan chain
Scan chain
Scan chain
Scan chain
Self Testing Using MISR and Parallel SRSGCentralized and separate BISTMultiple scan paths
Reduction in test timeLower overhead than BILBO but takes longer to apply
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Complete Fault CoverageHybrid test pattern generation
Combination of pseudo-random test and deterministic testDeterministic test pattern generation
Store-and-generate schemeTest set embedding scheme
Bit-flipping or Bit-fixingLFSR reseeding or multiple-polynomial reseeding
Hybrid BIST trade-off ( random deterministic)
TimeTime
Short test timeShort test timeHeavy H/W overheadHeavy H/W overhead
TimeTime TimeTime
Long test timeLong test timeLight H/W overheadLight H/W overhead
Optimal test timeOptimal test timeOptimal H/W overheadOptimal H/W overhead
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Multiple Seed / Reseeding
LFSR
CUT
MISR
Seed0Seed1Seed2
BISTController
SeedROM
Testclock
vvv
v
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SequentialCUT
t0 t1 … ... tL-1 s0 s1 … ... sn-1
Scan chain
Bit FlippingCircuit
… ...
SignatureAnalyzer
Bit Fixing/Bit Flipping Method
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Today’s SoC environments Large and complex VLSI circuitsNeed an enormous amount of test data
Limitations of ATE based test methodsChannel width and memory sizeModified or more expensive ATE must be required
Reducing test data by eliminating useful test patternsCan be reduced for the size of the ATE memory Deceases the accuracy of testing
Why Need Test Compression ?
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Compress the test input sequencesNeed a decompression units to make original test sequencesCan be reduced for both limitations of ATE
The size of ATE memoryThe width of ATE channel
Can be reduced test application time
Test Compression
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Embedded Memory Testing
Source: ITRS 2001 – Percentage of Logic Forecast in SoC Design
9442352014
9098702008
7113161002005
5216321302002
2016641801999
% Area Memory
% Area Reused Logic
% Area New Logic
Node(nm)
Year
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Memory Functional Model
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MBIST Basic ArchitectureFault Model
Stuck-at FaultAddress Decoding FaultCoupling FaultPattern-Sensitive Fault
Memory Test AlgorithmsMarch TestCheckerboardZero-One
Embedded RAM
ModuleMUX
Normal Inputs
BIST Pattern Generation &
Response Comparison
TestOutputs
TestInputs
BISTMODE
NormalOutputs
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Concept of Boundary ScanImprove testability by reducing the requirements placed on the physical test equipmentAlso called
• JTAG (Joint Test Action Group) Boundary Scan Standards• IEEE P1149.1
Why use it?• Testing interconnections among chips• Testing each chip• Snapshot observation of normal system data
Why testing boards?• To test board is easier than to test systems
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IEEE 1149.1 Device Architecture
IDCODE Register
Instruction register
Bypassregister
TAP
MUX
BS Test bus circuitry
TDO
TCK
TDI
TMS
I/O Pad Boundary-scan cell
Boundary-scan path
GlueLogic
S out
TRST
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The Principle of BS Architecture
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SOC Design EvolutionEmergence of very large transistor counts on a single chipMixed technologies on the same chipCreation of Intellectual Property (IP)Reusable IP-based design
Data Path
CPUCore
DSP Core
DRAM
IP Core
ROM
IP Core
IP Core
UDL
Logic BIST Memory BISTT̀est AccessBoundary Scan TAP Controller
IO Pad
IO Pad
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IEEE P1500
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ChipOutputs
User Defined Test Access Mechanism
Core 1
Standard P1500
Core Test Wrapper
Core N
Standard P1500
Core Test Wrapper
P1500 WIP
Wrapper control
WSO1 WSIN
WSI1 WSON
TAM-In TAM-InTAM-Out TAM-Out
TAM-Source TAM-Sink
ChipInputs
System ChipTAM Source/SinkFrom chip I/O, test bus/rail/port, BIST, etc..
TAM In/Out0 to n lines for parallel and/or serial test data, or test control
P1500 Wrapper Interface Port(WIP)From chip-level TAP controller, chip I/0, …
System Chip with P1500 Wrapped Cores
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Test Access
No Direct Physical Access MethodTest access mechanism is required
Today’s chip is tomorrow’s core
Test Control Interface
Test Control I/F
Test Control I/F
3rd Generation Core
2nd Generation Core
1st GenerationCore
Test Access
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Core Level Testing Summary
RF/AnalogCore
User Defined
Core
User DefinedCore
DRAM
IP
ROM
IP
IP
UDL
BIST Mem BISTTest AccessSoC Test Controller
IO P
ad
IO P
ad
Low costexternal ATE
• Memory test algorithm• Memory BIST, BISR
• Testable design
• Analog Fault modeling• Mixed signal Built-In Self Test
• Built-In Self Calibration
• Testable core design• Logic BIST• Test reuse• Hierarchical testing
• Core access architecture• Parallel access & bypass• Core isolation
• IP-system test interface
• Test spec.• Test hardware
control• Test
scheduling
• Automatic test pattern • Fault simulation• Testability measure• Scan insertion & synthesis
• BIST circuit synthesis• Boundary scan insertion & synthesis
Test Automation
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Test ChallengesTest quality
Test cost reduction
At-speed test
Reduction of design efforts
Test design reuse