Test cost has become a critical issue for large industrial integrated circuits. Various test compression techniques have been adopted in the industry to reduce test cost. However, appropriate input and output channel counts must be selected to utilize the test compression technology best. This paper presents an efficient and effective method to estimate the test pattern counts under different compression configurations for the Embedded Deterministic Test (EDT) compression technique. In searching for the accurate estimation method, we build mathematical models that reveal the internal relationship among different compression configurations. The models are established based on novel theoretical analysis as well as actual experimental data. Accurate estimation of test pattern counts for a wide range of compression configurations can be obtained based on the results of only two ATPG runs. Experimental results on nine industrial circuits show that the average error rate of pattern count estimation is about 5%, with very few outliers. With the proposed method, a test compression designer can easily pick the best input and output channel configuration to fit the design needs.

Test costs for large industrial designs increase rapidly in recent years. On-chip test compression hardware has become a pragmatic technology to cut down the overall test costs by reducing the test data volume. Determining the input and output channel counts of test compression hardware that results in minimum test data volume is thus a critical issue. In this article, efficient methods to estimate test pattern counts for an extensive range of input/output counts are developed. These methods require only a small number of ATPG runs. The estimation results can then be utilized to determine the test data volume for each input/output configuration. The configuration with the estimated lowest test data volume thus can be determined. The pattern count results of each configuration for a design can also be used to determine the best suitable configuration when the design is to be embedded in an SoC system.

A novel method to efficiently and accurately prognosticate the pattern count at different input compression ratios with the Embedded Deterministic Test (EDT) compression technology is proposed. With this method the total ATPG run time can be significantly reduced compared to the currently used trial-and-error method.

Over the past two decades, test data compression has become a de facto technology used in large industrial designs to reduce the overall test cost. During DFT planning, it is very important to understand the impact of using different numbers of input/output channels on test coverage, test cycles, and test data volume. In this paper, an efficient method to estimate the test data volume with different input channel counts using the Embedded Deterministic Test (EDT) compression technology is proposed. The results can then be used to quickly determine the scan configuration that results in the least or near least test data volume. With this method, the total ATPG run time can be reduced by a factor of more than 10X compared to the currently used trial-and-error method.

System-on-Chip (SoC) designs are increasingly difficult to test using traditional scan access methods without incurring inefficient test time, high planning effort, and physical design/timing closure challenges. The number of cores keeps growing while chip pin counts available for scan remain constant or decline, limiting the ability to drive cores concurrently. With increasingly commonplace tiling and abutment, the scan distribution hardware must be placed inside the cores, making balanced pipelining when broadcasting to identical cores difficult. optimizing test time requires analyzing all the cores and subsequently changing the test hardware in the cores. Internal shift speed constraints may limit the ability to shift data in and out of the chip at high rates. Differences in pattern counts or scan chain lengths between cores tested in parallel can result in padding and increased test time. SSN is a bus-based scan data distribution architecture designed to address all these challenges. It enables simultaneous testing of any number of cores even with few chip I/Os. It facilitates short test time by enabling high-speed data distribution, by efficiently handling imbalances between cores, and by supporting testing of any number of identical cores with a constant cost. It provides a plug-and-play interface in each core that is well suited for abutted tiles, and simplifies scan timing closure. This paper also compares the test cost and implementation productivity of SSN with those of Intel's Structural Test Fabric.

As the complexity of industrial integrated circuits continue to increase rapidly, test data compression has now become a de facto technology for large designs to reduce the overall test cost. During the design for test (DFT) planning, it is critical to understand the impact of using different numbers of input/output test channels on test coverage, test cycles, and test data volume. In this paper, two approaches to predict the test pattern counts and test data volumes with different input channel counts are presented, one with the compression tool able to generate channel-scaling patterns and the other without this capability. The results can be used to determine the scan test configuration that results in the smallest or near smallest test data volume. Experiments on industrial circuits show that the average error rates of pattern count prediction for most circuits are less than 10% for both approaches. The error rates of the predicted smallest data volumes are all less than 3.5%. The total ATPG run time can be reduced by a factor of more than 10X compared to the currently used trial-and-error approach.

This paper proposes an innovative design methodology for layout-friendly decompressor used in EDT compression architecture. A segmented decompressor architecture is proposed, in which each segment drives a subset of scan chains. The EDT input channel injectors are carefully selected to maximize the encoding capacity for all scan chains. Experimental results with several large industrial designs demonstrate that using the proposed technology, the routing congestion introduced by EDT decompressor is reduced significantly with negligible impact on test coverage and improved pattern count.

Timing exceptions are commonly used to indicate that the timing of certain paths have been relaxed so as to enable the design to meet timing closure. Generating scan-based test patterns without considering timing exceptions can lead to invalid test responses, resulting in unpredictable test quality impact. The existing simulation-based solution masks out unreliable signals after a test pattern is generated. If the signals required for detecting the target fault are unreliable and masked out, the generated test pattern fails to detect the target fault, and it is discarded. To achieve an acceptable test coverage, several iterations of test generation with a randomized decision-making process are typically required where different tests are generated for target faults. In this paper, an innovative deterministic ATPG algorithm called TEA (Timing Exception ATPG) is proposed to prevent the generated test patterns from being impacted by timing exceptions. The deterministic algorithm is compatible with the existing simulation-based approach. In this simulation environment, TEA is complete such that for a target fault, the test pattern generated is guaranteed to detect it. If a test pattern cannot be generated using TEA, the target fault is untestable given the timing exception paths in the design and the existing simulation environment. Compared to the existing simulation-based approach, using TEA can generate a more effective test set, improving test coverage, test pattern count, and the total ATPG run time significantly.

This paper introduces a novel test data compression scheme, which is primarily devised for low-power test applications. It is based on a fundamental observation that in addition to low test cube fill rates, a very few specified bits, necessary to detect a fault, are actually irreplaceable, whereas the remaining ones can be placed in alternative locations (scan cells). The former assignments are used to create residual test cubes and, subsequently, test templates. They control a power-aware decompressor and guide automatic test pattern generation to produce highly compressible test patterns through finding alternative assignments. The proposed approach reduces, in a user-controlled manner, scan shift-in switching rates with minimal hardware modifications. It also elevates compression ratios to values typically unachievable through conventional low-power reseeding-based solutions. Experimental results obtained for large industrial designs illustrate feasibility of the proposed test scheme and are reported herein.

This paper presents several techniques employed to resolve problems surfacing when applying scan bandwidth management to large industrial multicore system-on-chip (SoC) designs with embedded test data compression. These designs pose significant challenges to the channel management scheme, flow, and tools. This paper introduces several test logic architectures that facilitate preemptive test scheduling for SoC circuits with embedded deterministic test-based test data compression. The same solutions allow efficient handling of physical constraints in realistic applications. Finally, state-of-the-art SoC test scheduling algorithms are rearchitected accordingly by making provisions for: 1) setting up time-effective test configurations; 2) optimization of SoC pin partitions; 3) allocation of core-level channels based on scan data volume; and 4) more flexible core-wise usage of automatic test equipment channel resources. A detailed case study is illustrated herein with a variety of experiments allowing one to learn how to tradeoff different architectures and test-related factors.

This paper presents a test data volume (TDV) reduction method for designs utilizing extremely high compression configurations, and it enables reducing the pin count interfacing with the Automatic Test Equipment. Based on the encoding requirements for every test cube, the proposed test compression method changes the number of shift cycles used to load the test stimuli dynamically. No additional pins or modification of the existing scan chains is needed, making the proposed method work seamlessly with existing sequential linear decompressors. Experimental results obtained for industrial designs demonstrate the effectiveness of the proposed method at reducing TDV in high compression configurations.

The paper presents a novel test data compression scheme. The invention follows from a fundamental observation that in a typical test cube only a small portion of the specified positions are necessary to detect a fault, and most of the remaining ones have many alternatives. The necessary assignments are used to form test templates which both control a decompressor to guarantee the necessary assignments and guide ATPG to find alternative assignments to produce highly compressible test cubes. The proposed approach synergistically elevates compression ratios to values typically unachievable through conventional reseeding-based solutions. It also reduces, in a user-controlled manner, switching rates in scan chains with minimal hardware modification. Experimental results obtained for large industrial designs illustrate feasibility of the proposed test scheme and are reported herein.

Due to a production error, an incorrect figure was used for Fig. 8 on p. 1781 in the above paper (ibid., vol. 32, no. 11, pp. 1776-1786, Nov. 2013). The correct figure is presented here.

The paper discusses practical issues involved in applying scan bandwidth management to large industrial system-on-chip (SoC) designs deploying embedded test data compression. These designs pose significant challenges to the channel bandwidth management methodology itself, flow, and tools. The paper introduces several test logic architectures that facilitate preemptive test scheduling for SoC circuits with EDT-based test data compression. Moreover, some recently proposed SoC test scheduling algorithms are refined accordingly by making provision for (1) setting up test configurations minimizing test time, (2) optimization of SoC pin allocation based on scan data volume, and (3) handling physical constraints in realistic applications. Detailed presentation of a case study is illustrated with a variety of experiments that allow one to learn how to tradeoff different architectures and test scheduling.

This paper presents novel methods of reducing test time and enhancing test compression for system-on-chip (SoC) designs armed with embedded deterministic test (EDT)-based compression logic. The ability of the proposed scheme to improve the encoding efficiency and test compression, while reducing test application time, is accomplished by appropriate selecting and laying out automatic test equipment channel injectors of every single core EDT-based decompressor as well as appropriate bandwidth management of the entire test procedure combined with new control data optimization techniques. The efficacy of the proposed scheme is validated through experiments on several industrial SoC designs and is reported herein.

This paper presents preemptive test application schemes for system-on-a-chip (SoC) designs with embedded deterministic test-based compression. The schemes seamlessly combine new test data reduction techniques with test scheduling algorithms and novel test access mechanisms devised for both input and output sides. In particular, they allow cores to interface with automatic test equipment through an optimized number of channels. They are well suited for SoC devices comprising both nonisolated cores, i.e., blocks that occasionally need to be tested simultaneously, and completely wrapped modules. Experimental results obtained for large industrial SoC designs illustrate feasibility of the proposed test application schemes and are reported herein.

The paper presents a new channel allocation method for higher Embedded Deterministic Test (EDT) compression in SoC designs comprising isolated cores. It employs a test data reduction technique, which allows cores to interface with ATE through an optimized number of channels. This feature is subsequently used by a new test scheduling and test access mechanisms devised for both the input and output sides. Experimental results obtained for large industrial SoC designs illustrate feasibility of the proposed test application scheme and are reported herein.

This paper introduces a novel Test Access Mechanism (TAM) for chips with multiple isolated identical cores through which all the cores can be tested in parallel and at the same time accurate failure diagnosis can be achieved while requiring similar test resources (tester memory and tester channels) as for a single core. The proposed pipelined architecture relies on forming nonlinear equations on a very limited number of output pins that compress the outputs from the identical cores and solve them off-chip to reproduce the failure information of each core. A very nice feature of the proposed scheme is that the number of observation pins required to achieve a desirable level of diagnostic resolution does not scale with the number of identical cores and can practically be kept constant.

The paper presents a preemptive test application scheme for system-on-chip (SoC) designs with EDT-based compression. It seamlessly combines a new test data reduction technique with a test scheduling algorithm and a novel test access mechanism. It is particularly well suited for SoC devices comprising non-isolated cores, i.e., blocks that occasionally need to be tested simultaneously.

This paper presents a novel low capture power test scheme integrated with EDT (Embedded Deterministic Test) environment. The key contribution of this paper is to generate test vectors that in capture mode mimic functional operation from switching activity point of view. Experimental results presented for industrial circuits demonstrate the effectiveness of the proposed method.

This paper presents a clock control architecture for designs with multiple clock domains, and a novel mix of existing ATPG techniques as well as novel ATPG enhancements. The combination of the ATPG techniques and the clock control hardware lowers the number of test patterns in a fully automated flow, while maintaining the high coverage that is required nowadays by production test. Experimental results are shown for two industrial designs.

This paper presents a novel method to generate test vectors that mimic functional operation from switching activity point of view. The method uses states obtained by applying a number of functional clock cycles starting from the scan-in state of a test vector to fill the unspecified scan cell values in test cubes. Experimental results presented for industrial circuits demonstrate the effectiveness of the proposed method.

High performance designs often use the on-chip device PLLs for accurate test clock generation during testing. The on-chip clock generator is designed in a programmable way to facilitate the test generation process and it in turn creates additional constraints for the automatic test pattern generation (ATPG) tool. This paper describes an efficient and effective method to take the hardware restrictions originated from the on-chip clock generators into account in order to avoid generating clock sequences that cannot be produced by hardware. Experimental results on industrial designs show test pattern reduction and/or ATPG run time reduction when compared with the test generation method that enumerates valid clock sequences explicitly and restricts the test generation within enumerated test sequences.

This paper presents a new and comprehensive low-power test scheme compatible with a test compression environment. The key contribution of this paper is a flexible test-application framework that achieves significant reductions in switching activity during all phases of scan test: loading, capture, and unloading. In particular, we introduce a new on-chip continuous-flow decompressor. Its synergistic use with a power-aware scan controller allows a significant reduction of toggling rates when feeding scan chains with decompressed test patterns. While the proposed solution requires minimal modifications of the existing design for test logic, experiments indicate that its use results in a low switching activity which reduces power consumption to or below a level of a functional mode. It resolves problems related to power dissipation, voltage drop, and increased temperature. Our approach integrates seamlessly with test logic synthesis flow, and it does not compromise compression ratios. It fits well into various design paradigms, including modular design flow where blocks come with individual decompressors and compactors.

This paper presents a new and comprehensive power-aware test scheme compatible with a test compression environment. The key contribution of the paper is a flexible test application framework that achieves significant reductions in switching activity during all phases of scan test: scan loading, unloading, and capture.

This paper presents X-Press - a new two-stage test-response compactor that can be easily integrated with a multiple scan-chain environment. This compactor preserves all benefits of spatial compaction and offers, due to its overdrive sequential section, compression much higher than the ratio of scan chains to compactor outputs. X-Press is also capable of handling a wide range of unknown (X) state profiles by deploying a two-level scan-chain-selection mechanism. In addition to a new compactor architecture, original contributions of this paper include a detailed analysis of two-level error masking caused by X states and a new algorithm to both rank scan chains and then to determine, in per-pattern mode, scan-chain-selection rules used to suppress X states. Experimental results obtained for a variety of designs show feasibility and efficiency of the proposed compaction scheme, altogether with actual impact of X states on a test-pattern count. Finally, diagnostic capabilities of the proposed scheme accompanied by further experimental results are also analyzed.

Timing-aware ATPG [1] has been shown to be an effective method for generating high-quality test sets that detect small delay defects through the longest paths. However, this method usually results in a much higher test pattern count than the traditional transition fault test generation. In this paper, we propose a new criterion that identifies a subset of transition faults to be targeted by the timing-aware ATPG in order to reduce test pattern count while minimizing the impact on the overall delay test quality. The new criterion utilizes the minimal static slack to classify certain transition faults as timing-critical. The test pattern count reduction is achieved by restricting the timing-aware ATPG to targeting the timing-critical transition faults while using traditional transition fault test generation for the remaining transition faults. The experimental results for the industrial circuits show the effectiveness of the proposed method.

Generating test patterns without considering timing exceptions and constraints can lead to invalid test responses, resulting in false failures on the tester or yield loss. A path-oriented approach to handle timing exception paths with setup violations during at-speed test generation has been presented in [1]. This paper presents a unified and complete algorithm for computing test responses in the presence of timing exceptions with both setup and hold violations, and Boolean timing constraints. The new algorithm analyzes all possible effects of glitches in the circuit. It resolves pessimism in the case of multiple interacting timing exception paths. The new method significantly reduces the number of unknowns in the test responses, resulting in improved test coverage and test compression. The new method can be applied to 1) any fault model, 2) any test pattern, 3) any simulation environment, and/or 4) any test generator.

In order to generate correct at-speed scan patterns, the effect of timing exceptions and constraints needs to be considered during test generation. A path-oriented approach to handle timing exception paths during at-speed ATPG has been presented in (Vorisek et al., 2006). The new method has been applied to and tested on many example circuits at Semiconductor Technology Academic Research (STARC). This paper presents a sample of these test cases, and illustrates how the proposed method generates correct-by-construction at-speed patterns on these circuits without pessimism

In this paper, a new ATPG methodology is proposed to improve the quality of test sets generated for detecting delay defects. This is achieved by integrating timing information, e.g. from standard delay format (SDF) files, into the ATPG tool. The timing information is used to guide the test generator to detect faults through the longest paths in order to improve the ability to detect small delay detects. To avoid propagating faults through similar paths repeatedly, a weighted random method is proposed to improve the path coverage during test generation. During fault simulation, a new fault-dropping criterion, named dropping based on slack margin (DSM), is proposed to facilitate the trade-off between the test set quality and the test pattern count. The quality of the generated test set is measured by two metrics: delay test coverage and SDQL. The experimental results show that significant test quality improvement is achieved when applying timing-aware ATPG with DSM to industrial designs

Before on-chip scan compression, it was possible to use different EDA tool vendors to do scan insertion, pattern generation, and diagnosis. On-chip scan compression changed that use model since each tool vendor supplied a different type of scan compression logic and had tool-specific ways to pass necessary information from scan insertion to pattern generation and from pattern generation to diagnosis. OCI (open compression interface) is a standardization of how the necessary data is passed from test logic insertion to pattern generation to diagnosis such that different vendors can be used for each step independent of the on-chip scan compression logic used. This document discusses the need for OCI and gives a conceptual overview of the OCI standard

The paper presents a two-stage test response compactor with an overdrive section and scan chain selection logic. The proposed solution is capable of handling a wide range of X state profiles, offers compaction much higher than the ratio of scan chains to compactor outputs, and provides excellent diagnostic resolution

Transition delay fault (TDF) testing has become a necessary test method in very deep sub micron (VDSM) technologies due to the presence of resistive defects that cause subtle timing failures. The transition delay fault model is based on a slow-to-rise and slow-to-fall fault at each node in the circuit. Some resistive defects such as resistive vias actually induce both faults and the TDF test set can contain unnecessary test patterns for proper screening of this type of defect. The inline resistance fault (IRF) model more accurately represents this defect type and is studied in depth in This work. ATPG experimental results show that IRF patterns can be generated 1.4 to 1.8 times faster with 45% to 58% fewer patterns than traditional TDF patterns. IRF and TDF pattern test results are presented and show that the more expensive TDF remains a more comprehensive test than IRF as expected, but that the quality impact of using only the IRF test set is minimal, especially when combined with effective IDDQ outlier screening such as statistical post processing. Additionally, a methodology is presented for the determination of the number of delay defects that behave according to each model from the test data alone, which is necessary to accurately determine delay defect coverage from multiple test coverage metrics.

Growing ASIC design sizes and advanced deep sub-micron technologies require new fault models and more test vectors to meet high test quality goals. To realize these goals within given test resources and cost constraints, new DFT techniques must be used. This paper reports test quality metrics and the test cost of industrial designs for different fault models using three DFT techniques: ATPG for deterministic patterns, Logic BIST for pseudo-random patterns, and EDT for compressed deterministic patterns. It is shown how these techniques can be used to achieve the high quality goals within the test resources currently available for stuck-at tests.

This paper presents a novel test-data volume-compression methodology called the embedded deterministic test (EDT), which reduces manufacturing test cost by providing one to two orders of magnitude reduction in scan test data volume and scan test time. The presented scheme is widely applicable and easy to deploy because it is based on the standard scan/ATPG methodology and adopts a very simple flow. It is nonintrusive as it does not require any modifications to the core logic such as the insertion of test points or logic bounding unknown states. The EDT scheme consists of logic embedded on a chip and a new deterministic test-pattern generation technique. The main contributions of the paper are test-stimuli compression schemes that allow us to deliver test data to the on-chip continuous-flow decompressor. In particular, it can be done by repeating certain patterns at the rates, which are adjusted to the requirements of the test cubes. Experimental results show that for industrial circuits with test cubes with very low fill rates, ranging from 3% to 0.2%, these schemes result in compression ratios of 30 to 500 times. A comprehensive analysis of the encoding efficiency of the proposed compression schemes is also provided.

This paper introduces embedded deterministic test (EDT) technology, which reduces manufacturing test cost by providing one to two orders of magnitude reduction in scan test data volume and scan test time. The EDT architecture, the compression algorithm, design flow, experimental results, and silicon implementation are presented.

This paper discusses practical issues involved in applying logic built-in self-test (BIST) to four large industrial designs. These multi-clock designs, ranging in size from 200 K to 800 K gates, pose significant challenges to logic BIST methodology, flow, and tools. The paper presents the process of generating a BIST-compliant core along with the logic BIST controller for at-speed testing. Comparative data on fault grades and area overhead between automatic test pattern generation (ATPG) and logic BIST are reported. The experimental results demonstrate that with automation of the proposed solutions, logic BIST can achieve test quality approaching that of ATPG with minimal area overhead and few changes to the design flow.

This paper presents an efficient and novel method for sequential learning of implications, invalid states, and tied gates. It can handle real industrial circuits, with multiple clock domains and partial set/reset. The application of this method to improve the efficiency of sequential ATPG is also demonstrated by achieving higher fault coverages and lower test generation times.

This paper demonstrates how fault simulation of building blocks found in data-path architectures can be performed extremely efficiently and accurately by taking advantage of their simple functional models and structural regularity.This technique can be used to accelerate the simulation of those blocks in virtually any fault simulation environment, resulting in fault simulation algorithms that can perform fault grading in a very demanding BIST environment.

A novel highly efficient fault simulation technique targeted for circuits produced through high-level synthesis is presented. The technique combines hierarchical and functional fault simulation of commonly used building blocks that have regular structures. Comparison with gate-level simulation demonstrates the advantage of using this technique for this class of circuits.