How does scan test work?

How does scan test work?

The scan chains are used by external automatic test equipment (ATE) to deliver test pattern data from its memory into the device. After the test pattern is loaded, the design is placed back into functional mode and the test response is captured in one or more clock cycles.

What is scan DFT?

For any modern chip design with a considerably large portion of logic, design for test (DFT) and in particular implementing scan test are mandatory parts of the design process that helps to reduce the complexity of testing sequential circuits.

What are scan flops?

A scan flip-flop is a D flip-flop with a 2×1 multiplexer added at its input D. one input of the MUX acting as the functional input D when SE/TE=0 and the other input serving as the Scan-In (SI) input when SE/TE=1. Scan/Test Enable (SE/TE) is used to control the MUX i.e used as selection bit.

Why do we need scan chain?

Scan chains are used to detect manufacturing defects present in the combinational logic of the design. ATPG tool generates the test patterns in such a way that all the nodes present in the combinational logic are sensitized and verified for manufacturing defects.

What is at speed scan testing?

At-speed scan test involves loading scan chains at a slow clock rate and then applying two clock pulses at the functional frequency. If the circuit is operational, then the transition will propagate to the end of the path in time and the correct value will be captured.

What are the DFT tools?

Synopsys TestMAX DFT is a comprehensive, advanced design-for-test (DFT) tool that addresses the cost challenges of testing designs across a range of complexities. TestMAX DFT supports all essential DFT, including boundary scan, scan chains, core wrapping, test points, and compression.

What are the scan design rules?

Scan Design Rules

  • Use only clocked D-type of flip-flops for all state variables.
  • At least one PI pin must be available for test; more pins, if available, can be used.
  • All clocks must be controlled from PIs.
  • Clocks must not feed data inputs of flip-flops.

What is scan reorder?

Scan chain reordering is a process used in the design and testing of computing devices that enables the optimization of placing and stitching flip flop registers with a scan chain. It is used to optimize and reorder the scan chain process if it gets detached, stopped or congested.

What is scan segment?

In computer science, a segmented scan is a modification of the prefix sum with an equal-sized array of flag bits to denote segment boundaries on which the scan should be performed.

What is LOC and LOS in DFT?

LAUNCH ON CAPTURE (LOC) and LAUNCH ON SHIFT (LOS) Main transition fault ATPG methodologies are Launch on Capture and Launch on Shift (also known as broadside-load and skewed-load respectively). They both launch transition at the input of combinational block in different way for the same fault detection.

What are DFT techniques?

Design for testing or design for testability (DFT) consists of IC design techniques that add testability features to a hardware product design. The added features make it easier to develop and apply manufacturing tests to the designed hardware.

What are the scan based test techniques in VLSI?

The method of testing a circuit with the scan path is as follows: Set test mode signal, flip-flops accept data from input scan-in. Verify the scan path by shifting in and out test data. Set the shift register to an initial state.

What is scan chain in VLSI?

Scan chain is a technique used in design for testing. The objective is to make testing easier by providing a simple way to set and observe every flip-flop in an IC. The basic structure of scan include the following set of signals in order to control and observe the scan mechanism.

What is scan in VLSI?

The scan path can be tested by shifting a special pattern through the scan path before even beginning to address stuck-at faults in the combinational logic. During the generation of test patterns, the automatic test pattern generation considers the flip-flops as I/O pins.

What is OCC in DFT?

On-chip Clock Controllers (OCC) are also known as Scan Clock Controllers (SCC). OCC is the logic inserted on the SOC for controlling clocks during silicon testing on ATE (Automatic test Equipment).