edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 3 18 integration of artificial intelligence significantly enhances the efficiency of the FA process. Informed Design Decision-Making: The third domain, which is the primary focus of this work, empowers designers to make informed decisions during the design phase. This involves being well-versed in the compatibility of designs with physical inspection methods. One approach is to develop compatibility profiles or predictions, enabling designers to anticipate potential inspection challenges. Another strategy involves creating simulated projections of x-ray images even before the actual fabrication of the chip, thus allowing for preemptive design adjustments. PROPOSED X-RAY COMPATIBILITY METRIC With the broader concept of DFI established, the focus now shifts to a specific aspect of this approach: the x-ray compatibility metric, named CMx-ray. This metric is a vital component of the co-design branch of DFI, designed to synergize pre-silicon verification with post-silicon validation in IC manufacturing. The placement of CMx-ray within the manufacturing flow serves as a crucial bridge linking pre-silicon verification to post-silicon validation. This strategic positioning is key to understanding how CMx-ray can enhance the overall efficiency and effectiveness of the IC manufacturing process. Developing the CMx-ray metric involves a thorough and systematic analysis of both IC packaging specifications and x-ray imaging parameters. Central to this process is a focus on a set of parameters specific to the design-for-inspection approach. These DFI parameters might include, but are not limited to, the distance between bumps and RDL, inter-RDL separation, bump-to-bump pitch, and TSV pitch. It’s crucial to note that the particular DFI parameters selected for consideration are contingent on the specific packaging technology employed for the chip under examination. These parameters have been recognized as critical factors influencing the observability of features in x-ray imaging. In parallel, the CMx-ray development also takes into account various x-ray imaging specifications. These encompass resolution and other imaging and reconstruction parameters that define the capabilities and limitations of the x-ray inspection systems in use. By amalgamating these DFI parameters with the x-ray imaging specifications, a comprehensive metric is proposed. This metric quantitatively evaluates the compatibility of a chip design with x-ray inspection techniques. THE DFI X-RAY COMPATIBILITY FRAMEWORK The authors propose a two-step framework (Fig. 6) for developing and implementing the x-ray compatibility metric. The first step is to determine the DFI parameter thresholds that are specific for a particular type of IC package. The DFI evaluator block in Fig. 6 represents the process of determining the DFI thresholds by taking into account the design specifications of the advanced IC package, the specifications of the x-ray imaging equipment to be used, and the results from collecting sample images, and performing modelling and simulation. To establish the compatibility metric, an experimental analysis is conducted involving a collection of IC samples. These samples represent a range of chip designs with varying DFI parameter values. For each sample, x-ray images are acquired and meticulously observed, and analyzed for visibility and distinguishability of the fine-pitched features. Secondly, a simulation environment needs to be set up to predict how the image of a test package sample will look like. This is discussed in greater detail later in this section. Through this analysis, critical thresholds are identified for the DFI parameters, which represent the minimum values required to ensure adequate observability through x-ray inspection. These thresholds are determined based on certain DFI heuristics that govern the visibility and distinguishability levels necessary for reliable detection and assessment of the fine-pitched features. After the DFI thresholds are set for a sample package type, a test package design is evaluated based on how many and to what extent the DFI parameters of the test design conform to the preset thresholds. A numerical value is determined to Fig. 6 The framework for the proposed DFI x-ray compatibility metric.
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