Dynamic analysis by laser stimulation (DALS) is a method used to analyze temperature-dependent failures. There are cases, however, where the laser alone cannot get devices hot enough to induce an observable change in behavior. This paper examines three such cases and describes how analysts were able to induce and diagnose the underlying failure by using external signals, complex triggering, and resistive heating to compensate for limitations in laser power.

Three failed modules were found during routine inspection of industrial equipment after several years of service. We investigated failure causes of them. As a result of the investigation, we show that there are different failure modes for each type of variable resistors (cermet type, carbon composition type, wire wound type). (1)Cermet type: The wiper was unstable because the wiperfixing was weak already during manufacturing. (2)Carbon composition type: The R12 (resistance between #1 and #2 terminals) was unstable because of extraneous materials in manufacturing or zinc whiskers. (3)Wire wound type: The R13 (resistance between #1 and #3 terminals) was broken by the scratch in manufacturing.

Photon Emission Microscopy (PEM) is one of the commonly used and powerful techniques for fault localization which uses a sensitive camera (like CCD or InGaAs) to detect a light (photon) emission from an electrically biased device. The fault localization of an open anomaly can be a challenge for the failure analysis. This paper discusses a novel technique for localization of an open fault on a thin-film resistor using induced photoemission method. In this proposed method, an emission site is induced at the open fault location on the thin-film resistor. This method was found to be effective and it increases the success rate for an open fault localization on a thin-film resistor.

The focus of this paper is to present an interesting case study involving Vishay wire-wound (WSC model) resistor failures, which affected a significant number of production and fielded assemblies. The failures were considered “mission critical”, which was the primary driver necessitating root cause analysis. A disciplined approach to the failure analysis effort was established, which resulted in root cause determination and the generation of appropriate corrective actions. This paper will highlight a non-conventional decapsulation method used to preserve the integrity of the fragile resistive element and a “lucky break” that was instrumental in linking the supplier’s actions to the failures.

Negative resistance drift in thick film chip resistors in high temperature and high humidity application conditions was investigated. This paper reports on the investigation of possible causes including formation of current leakage paths on the printed circuit board, delamination between the resistor protective coating and laser trim, and the possibility of silver migration or copper dendrite formation. Analysis was performed on a set of circuit boards exhibiting failures due to this phenomenon. Electrical tests after mechanical and chemical modifications showed that the drift was most likely caused by moisture ingress that created a conductive path across the laser trim.

Thick film resistors are widely used in consumer and industrial products such as timers, motor controls and a broad range of high performance electronic equipment. This article provides information on failures due to copper dendrite growth, silver migration, sulfur atmosphere corrosion, variation of temperature, and crack due to molding compound mechanisms. It presents case studies in which a physical analysis plan was developed and executed to investigate these sites of interest on as-manufactured and failed thick film power resistors. The analysis techniques included X-ray inspection, cross-sectioning, decapsulation, and optical and environmental scanning electron microscopy analysis. A table illustrates different failure modes and mechanisms for thick film resistors, and also potential application and manufacturing factors that cause failure mechanisms, which then describe the failure modes. The article is concluded that by preventing the failure of thick film resistors, printed circuit boards can be kept in service for their full lifetime.

Field failures of nichrome thin-film resistors have been investigated recently for several pieces of spaceflight hardware. These failures have involved resistance shifts ranging from a few percent to complete open circuits. Failure analysis and duplication of these failures have revealed that the failures were caused by electrostatic discharge. The failure characteristics and the circuit conditions necessary for failure have been studied for several types of thin-film resistors, including nichrome and tantalum nitride resistive elements. The effects of latent damage and resistive pattern design will also be discussed.