Most Asked DFT Interview Questions in 2024
Design for testability is a design methodology that involves adding additional circuitry to a chip to make testing it easier and more affordable. The controllability and observability of the internal fault nodes are enhanced with the aid of DFT techniques.
What makes DFT significant?
Technology advancements have resulted in the dense packing of billions of transistors into a tiny chip, creating new challenges and increasing the likelihood of defects. To make sure the product is of high quality, testing is necessary. There could be a variety of defects during the fabrication process, which could lead to the chip’s transistors being destroyed in part.
What is DFT?
DFT, or Design for Test, enhances testability by incorporating features in the design. It includes scan chains, test points, and built-in self-test (BIST) structures to facilitate testing.
What is the difference between verification and DFT?
Verification ensures design meets specifications, while DFT focuses on making it testable. Verification checks functionality, whereas DFT enhances testability through features like scan chains and test points.
Difference between defect, fault, and failure?
Defects deviate from design specs, faults cause errors within the design, and failures are observable incorrect outputs. Defects lead to faults, which can cause failures during operation.
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What is observability and controllability?
Observability lets us observe internal signals during testing, while controllability allows us to control internal signals. Both are essential for effective testing and fault detection.
What is scan?
Scan is a testing technique where the circuit is reconfigured to facilitate observation and manipulation of internal states. It involves converting flip-flops into shift registers to enable serial access to internal nodes for testing.
How can we perform a scan operation?
Scan operations are performed by loading test patterns into scan chains and applying them to the circuit. This allows for observation and manipulation of internal states during testing.
What is serial and parallel loading?
Serial loading shifts test patterns bit by bit into the scan chain, while parallel loading loads test patterns in parallel into the scan chain. Serial loading is slower but requires fewer pins, while parallel loading is faster but requires more pins.
What is the difference between sequential and combinational ATPG?
Sequential ATPG generates test patterns considering the circuit’s sequential behavior, while combinational ATPG generates patterns without considering sequential elements. Sequential ATPG tests for faults affecting sequential behavior.
What is ATPG?
ATPG, or Automatic Test Pattern Generation, generates test patterns to detect faults in a design using algorithms to create efficient and effective fault detection patterns.
What is DRC violation?
DRC violation, or Design Rule Check violation, occurs when a design violates specified rules for layout, timing, or other design aspects, indicating potential issues affecting functionality or manufacturability.
What is a fault model?
A fault model defines types of faults considered during testing, such as stuck-at faults, bridging faults, and transition faults, among others.
How many fault models are there?
Various fault models include stuck-at faults, bridging faults, transition faults, and delay faults, among others, used in testing to detect different fault types.
What is scan stitching?
Scan stitching connects multiple scan chains to form a longer scan chain, allowing testing of larger designs without increasing the number of required pins.
What is BIST?
BIST, or Built-In Self-Test, integrates test circuitry into the design for automatic generation and application of test patterns without external test equipment.
What is BISA?
BISA, or Built-In Self-Alignment, aligns test patterns automatically with the circuit under test, ensuring accurate testing despite manufacturing variations.
What is BSCAN?
BSCAN, or Boundary Scan, adds test circuitry to the boundary of integrated circuits for testing interconnects and logic inside the chip without physical access to internal nodes.
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