edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO.4 12 UNVEILING VIA SIDEWALL NANOGAPS: A CASE STUDY OF LOW-TEMPERATURE FAILURES IN A TRANSCEIVER TRANSFORMER DRIVER Angelly Crisar Entice-Gomez Analog Devices Inc. angelly.entice@analog.com EDFAAO (2026) 4:12-20 1537-0755/$19.00 ©ASM International® INTRODUCTION Cold failures are challenging to analyze due to their intermittent or non-reproducible nature, often resulting in inconclusive findings and an unidentified failure mechanism. Unlike catastrophic failures with obvious physical damage, cold failures often leave minimal or no trace, making root cause identification through standard inspection difficult. This article presents a comprehensive failure analysis of a cold temperature anomaly observed in a customer-returned isolated RS-485 transceiver with an integrated transformer driver. Various techniques including backside analysis were effectively employed under controlled conditions to preserve the failure state while performing the fault isolation and facilitating root cause identification. The investigation highlights the critical role of using low acceleration voltage in scanning electron microscopy (SEM) for detecting nanoscale defects, which enabled the identification of a subtle open via anomaly causing the failure. The study underscores the importance of coherent and correlated data in enabling confident decision-making, ultimately leading to successful failure resolution and preventing the mechanism from remaining unidentified. In isolated transceivers, a transformer driver is the internal block that generates a high‑frequency AC signal used to transfer power or data across an on‑chip micro‑ transformer. Because transformers cannot pass DC, the driver converts regulated DC into a high‑frequency waveform that can pass through the isolation barrier. A customerreturned isolated RS-485 transceiver with an integrated transformer driver unit was reported to have no oscillation on the transformer driver at low temperatures (~5°C). Automatic test equipment (ATE) testing confirmed that the unit was failing the transformer driver oscillator frequency parameter test at cold temperatures. During bench testing, the unit showed no oscillation on the transformer drivers (D1 and D2). In addition, a significant decrease in the supply current was observed when the unit was exposed to cold temperatures before power up. Interestingly, the unit eventually recovered and began to oscillate and draw normal supply current once the temperature increased to ambient levels after power up. Additionally, the failure only manifests when the unit is subjected to cold temperatures prior to power up. However, if the unit is powered up at ambient temperature and then exposed to cold temperatures, it functions normally. See Figs. 1 to 3. DIE BACKSIDE FAULT ISOLATION AND CHALLENGES ENCOUNTERED An extensive failure analysis was conducted to identify the mechanism of the failure. The analysis focuses on the transformer driver die of the unit. To achieve a cold environment, a cold spray was applied to the unit to rapidly lower its temperature. However, maintaining a constant failing temperature proved challenging, as the rapid cooling effect of the spray does not provide sustained temperature control. After the temperature reached ambient levels, the part recovered and the failure could no longer be observed. Thus, proper timing was crucial to isolate the failure effectively. Fig. 1 IDD supply current test of the returned unit at ambient and cold temperatures.
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