Testing of Digital Systems - Introduction 1
Testing of Digital Systems
Zebo Peng and Petru Eles
Embedded System Laboratory (ESLAB)
Linkping University
http://www.ida.liu.se/~zebpe/teaching/test/index.html
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 2
Contents
Basic principles and practice of digital system testing.
Design for testability techniques.
Integration of test consideration with system synthesis.
Testing of system-on-chip.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 3
Course Organization
General lectures.
- Lecture notes and selected papers.
Seminars and discussions, led by the participants.
- M. Abramovici, M. A. Breuer and A. D. Friedman, Digital System
Testing and Testable Design, Computer Science Press, 1990.
- Seminar notes by the participants.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 4
Lecture I: Introduction
1. Basic definition and terminology
2. Classification of test
3. Test process
4. Test cost and its reduction
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 5
Design versus Test
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 6
What is Testing?
Process of exercising a product and analyzing its resulting response to
check whether faults are introduced during the manufacturing or opera-
tion phase.
Process of exercising a product and analyzing its resulting response to
check whether it functions correctly.
Process of determining whether a product functions correctly.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 7
Hardware Life Cycle
Specification Validation
Verification Test
Design Review Preparation
Inspection
Simulation
Implementation
Manufacturing
Production Test
System Integration Testing
System Test
Operation and
Maintenance
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 8
Causes of Incorrect Function of Digital Systems
Design errors usually consistent
Fabrication (manufacturing) errors
- often consistent, e.g., wrong components
- usually operator errors
Fabrication (manufacturing) defects Physical faults
- inconsistent, e.g., impurity of materials
Physical failures
- wear-out
- environmental factors
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 9
Classification of Physical Faults
Permanent always present after their occurrence.
Intermittent existing only during some intervals.
Transient a one-time occurrence cased by a temporary change in
some environmental factor.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 10
Another Classification
Logic (functional) faults the logic function of CUT (circuit under test)
is wrong.
Parametric the magnitude of a CUT parameter is changed (e.g.,
power and current).
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 11
Principles for Digital Test
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 12
A Board Testing Example
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 13
Test Head Fixtures
Edge-connector via the normal input/output pins.
Bed of nails.
Wafer prober a set of micro-probes arrange so as to make contact
with the bonding pads of a chip.
- Bare chip test for known-good die (for MCM application).
- Wafer-level screening.
Probes:
- Mechanical probe.
- Electron-beam probe.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 14
Main Difficulties in Testing
Miniaturization -> Physical access difficult or impossible.
Increasing complexity -> Large amount of test data.
Number of access ports remains constant -> Long test application time.
High speed -> High demand on testers driver/sensor mechanism and
more complicated failure mechanism.
-> Testing accounts up to 50% of product development efforts.
The key to successful testing lies in the design process.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 15
Design for Testability (DFT)
To take into account the testing aspects during the design process so
that more testable designs will be generated.
The design is changed to make it more testable.
Advantages of DFT:
- Reduce test efforts.
- Reduce cost for test equipments (ATE).
- Shorten turnaround time.
- Increase product quality.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 16
Test vs. Diagnosis
Test Detection of faults.
Diagnosis Detection and location of faults (fault site and fault type).
- Repair.
- Manufacturing process optimization (reduce manufacturing errors).
- Re-design.
Cause-effect analysis (external fault location):
- Build a fault dictionary.
- Use dictionary look-up to determine the possible faults.
Effect-cause analysis (internal fault location): based on the erroneous
response, determine directly the faults that could produce it.
- Ex. guided-probe testing.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 17
Types of Testing
Production (manufacturing) test test individual products to check
whether faults are introduced during the manufacturing phase.
System test test a product in its operating environment to ensure that
it works correctly when interconnected with other components.
Operation and maintenance test test a product in the filed for diagno-
sis or "preventive" purpose.
Prototype test testing to check for design faults during the system
development phase. Diagnosis is required.
Different levels: chip, board, or system.
On-line, off-line, or concurrent testing.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 18
Types of Testing (Contd)
Functional test validating the correct operation with respect to its
functional specification.
Structural test testing of structural defects, such as open, stack-at,
and short-circuit.
Static v. at-speed testing.
In-circuit test the tester gains access to the internal nodes.
Parametric test testing of technology-dependent parameters, such
as power consumption.
IDDq test testing the entire circuit by making analog measurements
of IDD which is the current flows in a CMOS circuit when all nodes are
in the quiescent state.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 19
Test Classification
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 20
Test Classification (Contd)
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 21
A Typical Testing Process
Test Strategy
Selection
Test Generation
Test Evaluation
Test Application
Manufacturing
Analysis and Design
Diagnosis
Test Mechanism
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 22
Composition of Testing Costs
Cost of test equipment (hardware):
- A test controller (usually a computer).
- Interface drivers/receivers and cable-connections.
- System of probe-contacts.
- A controlled environment.
Cost of software supports:
- Test pattern generation programs.
- Test evaluation procedures (fault simulation and analysis).
Testing time
- Test development time.
- Test application time (maybe very long for "burn-in" purpose).
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 23
Cost of Finding Defects (Rule of Tens)
>$500.00
$50.00
$5.00
$0.50
Chip Board System Field
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 24
Methods for Test Cost Reduction
DFT simplifies/automates test pattern generation, which decreases de-
velopment cost and lead times.
DFT facilitates more efficient production test, i.e., lower fault levels and
shorter test application times.
BIST can reduce the need for expensive test equipment and supports
field test.
Better design verification reduces the need for functional test which has
long test application time.
Statistics-based methods reduces overall test cost.
Zebo Peng, ESLAB, LiTH
Testing of Digital Systems - Introduction 25
Summary
Testing is an expensive and complex task, and is becoming more diffi-
cult with the development of more complex chips, especially systems-
on-chip.
It takes typically 30% of the total production cost.
Hardware testing is mainly used to find physical faults introduced dur-
ing the manufacturing and operation phases.
Testing does not guarantee the absent of faults!
Zebo Peng, ESLAB, LiTH
