The Importance of LBIST: Enhancing Testability in Semiconductor Design

The Importance of LBIST: Enhancing Testability in Semiconductor Design

In the present-day scenario, the design complexity and size of the SOC are expanding at an alarming rate. Designers are likewise shifting to lower technology nodes in order to meet greater performance goals. There may be flaws that arise during the device’s field usage. Infield failures are mostly caused by latent flaws, which may not be visible or easily detected during manufacture testing but may grow over time or during real-time field application due to environmental circumstances. To detect latent faults, the device must include a mechanism that allows it to do routine self-tests utilizing software or LBIST-based approaches. The logic built-in self-test (LBIST) reduces testing complexity by an order of magnitude. Logic- BIST is integrated circuitry in the chip that performs scan-based structural testing of the design. This approach measures fault coverage with the fewest vectors and helps us overcome the shortcomings of the previous strategies.

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What is LBIST?

Logic Built-In Self-Test, commonly referred to as LBIST is a DFT methodology integrated into the core logic of an IC. The logic may be checked without any outside involvement. In other words, an integrated circuit has hardware and/or software for self-testing. Core logic refers to any type of hardware (logic gates, memory, etc.) that can constitute a part or the entire chip. The STUMPS (Self-Test Using MISR and PRPG) architecture is used to construct a general LBIST system.

LBIST involves embedding a set of test circuits and control logic that enable the IC to self-diagnose and evaluate its own. By leveraging LBIST, engineers can perform comprehensive tests on the IC without relying on external test equipment and thereby reducing both test costs and time.

Applications of LBIST 

Infield Test Safety

LBIST testing is commonly used for essential applications, particularly automotive. It is used for frequent testing of SOCs in the field (or “in-system” testing) to guarantee that a satellite, medical equipment, or automobile works as intended. For example, when a car’s electronically-controlled braking system is turned on, LBIST testing is performed. If the device has a problem and the output signature is incorrect, it shows the logic has some flaws. In that instance, the car’s electronic controls can notify the driver that there is a problem with the system and that it may be unsafe to drive the vehicle.The testing may be used for end-of-life identification as a device reliability test by assessing the amount of frequent failures that the device exhibits over time.

Logic BIST for Scan Testing 

Scan testing is a widely employed technique in the semiconductor industry for detecting faults and ensuring the functionality of digital circuits. However, for designs with large sizes and extensive scan vectors,the  tester memory requirement can be challenging. In such cases, Logic BIST may be used to provide test coverage without requiring a large amount of tester memory. Then, on top of that, scan patterns are constructed to obtain the remaining coverage that random ATPG cannot achieve. However, it has its own set of issues; failure diagnosis with LBIST are not as straightforward as with standard scan patterns. Diagnostics need the inclusion of additional hardware in the design.

Automotive Electronics

LBIST plays a vital role in ensuring the reliability and safety of automotive electronics. As vehicles become increasingly complex and rely on numerous semiconductor components, the need for robust testing methodologies is paramount. LBIST enables thorough testing of critical automotive systems, such as engine control units (ECUs), advanced driver-assistance systems (ADAS), and infotainment systems. By integrating LBIST into these systems, manufacturers can detect faults, ensure proper functionality, and meet stringent safety standards.

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Field-Programmable Gate Arrays (FPGAs)

FPGAs are programmable devices that allow for flexible hardware configurations. LBIST is utilized in FPGA testing to evaluate the functionality of programmable logic resources and configurable interconnects. By integrating LBIST circuits into FPGA designs, engineers can perform self-testing at different levels, including the internal logic blocks, interconnects, and input/output interfaces. This aids in identifying faults and verifying correct programming of FPGAs, ensuring their proper operation in diverse applications like telecommunications, aerospace, and industrial automation.

Benefits of LBIST

LBIST has numerous distinct features that make it desirable, particularly in safety-critical designs such as those used in vehicles and airplanes. LBIST has several benefits, which are stated below:

  1. LBIST enables self-testing logic within the chip, allowing the chip to test itself without external control or interference.
  2. This enables testing at higher frequencies, significantly lowering test time.
  3. LBIST can run when the chip is operational on the field. As a result, it is extremely beneficial in safety-critical applications because flaws developed in the field may be quickly detected at startup before the device enters functional mode.

Conclusion:

In the ever-evolving semiconductor industry, LBIST has emerged as a crucial technique for enhancing testability, reducing test time and cost, and improving overall product quality. Similarly, there are a plethora of topics to be discovered about the semiconductor industry. And if you are interested in this field, then Chipedge is the perfect place for you. It is one of the best training and placement institutes in Bangalore that offers various courses including VLSI Course, VLSI Physical Design Course, and VLSI online course with certificate in Bangalore both for freshers as well as professionals. Contact us to know more.

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