In the course of a failure investigation, corrosion of the lands was occasionally found in developmental lots of semiconductor bridge (SCB) detonators and igniters. Evidence was found in both detonators and igniters of the gold layer being deposited on top of a corroded aluminum layer, but inspection of additional dies from the same wafer did not reveal any more corroded parts. In some detonators, evidence was found that corrosion of the aluminum layer also happened after the gold was deposited. Moisture and chloride must both be present for aluminum to corrode. A likely source for chloride is the adhesive used to bond the die to the header. Inspection of other SCB devices, both recently manufactured and manufactured about ten years ago, found no evidence for corrosion even in devices that contained SCBs with aluminum lands and no gold. Several manufacturing defects were noted such as stains, gouges in the gold layer due to tooling, and porosity of the gold layer. Results of atmospheric corrosion experiments confirmed that devices with a porous gold layer over the aluminum layer are susceptible to extensive corrosion when both moisture and chlorine are present. The extent of corrosion depends on the level of chlorine contamination, and corrosion did not occur when only moisture was present. Elimination of the gold plating on the lands eliminated corrosion of the lands in these experiments. Some questions remain unanswered, but enough information was gathered to recommend changes to materials and procedures. A second lot of detonators was successfully built using aluminum SCBs, limiting the use of Ablebond{trademark} adhesive, increasing the rigor in controlling exposure to moisture, and adding inspection steps.
Several groups of plastic molded CD4011s were electrically tested as part of an Army dormant storage program. These parts had been in storage in missile containers for 4.5 years, and were electrically tested annually. Eight of the parts (out of 1200) failed the electrical tests and were subsequently analyzed to determine the cause of the failures. The root cause was found to be corrosion of the unpassivated Al bondpads. No significant attack of the passivated Al traces was found. Seven of the eight failures occurred in parts stored on a pre-position ship (the Jeb Stuart), suggesting a link between the external environment and observed corrosion.
An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to joining to alkali barium silicate glass to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr2O3, MnCr2O4 spinel, and SiO2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass-to-metal (GTM) seal behavior. The objectives of this work were to characterize the stainless steel pre-oxidized layer and the glass/oxide/304L interface region after glass sealing. The 304L oxidation kinetics were determined by thermogravimetric (TG) analysis and the glass/metal seals characteristics were studied using sessile drop tests, in which wetting angles were measured and glass adhesion was analyzed. The pre-oxidized layers and glass/metal interface regions were characterized using metallography, focused ion beam (FIB) sectioning, scanning and transmission electron microscopy, and electron probe microanalysis (EPMA). The results show that poor glass sealing behavior is associated with a more continuous layer of SiO 2 at the metal/oxide interface.
Several groups of plastic molded CD4011 were electrically tested as part of an Army dormant storage program. For this test, parts had been in storage in missile containers for 4.5 years. Eight of the parts (out of 1200) failed the electrical tests and were subsequently analyzed to determine the cause of the failures. The root cause was found to be corrosion of the unpassivated Al bondpads. No significant attack of the passivated Al traces was found. Seven of the eight failures occurred in parts stored on a preposition ship (Jeb Stuart), suggesting a link between the external environment and observed corrosion.
An analytical capability is being developed that can be used to predict the effect of corrosion on the performance of electrical circuits and systems. The availability of this ''toolset'' will dramatically improve our ability to influence device and circuit design, address and remediate field occurrences, and determine real limits for circuit service life. In pursuit of this objective, we have defined and adopted an iterative, statistical-based, top-down approach that will permit very formidable and real obstacles related to both the development and use of the toolset to be resolved as effectively as possible. An important component of this approach is the direct incorporation of expert opinion. Some of the complicating factors to be addressed involve the code/model complexity, the existence of large number of possible degradation processes, and an incompatibility between the length scales associated with device dimensions and the corrosion processes. Two of the key aspects of the desired predictive toolset are (1) a direct linkage of an electrical-system performance model with mechanistic-based, deterministic corrosion models, and (2) the explicit incorporation of a computational framework to quantify the effects of non-deterministic parameters (uncertainty). The selected approach and key elements of the toolset are first described in this paper. These descriptions are followed by some examples of how this toolset development process is being implemented.
A physics-based understanding of material aging mechanisms helps to increase reliability when predicting the lifetime of mechanical and electrical components. This report examines in detail the mechanisms of atmospheric copper sulfidation and evaluates new methods of parallel experimentation for high-throughput corrosion analysis. Often our knowledge of aging mechanisms is limited because coupled chemical reactions and physical processes are involved that depend on complex interactions with the environment and component functionality. Atmospheric corrosion is one of the most complex aging phenomena and it has profound consequences for the nation's economy and safety. Therefore, copper sulfidation was used as a test-case to examine the utility of parallel experimentation. Through the use of parallel and conventional experimentation, we measured: (1) the sulfidation rate as a function of humidity, light, temperature and O{sub 2} concentration; (2) the primary moving species in solid state transport; (3) the diffusivity of Cu vacancies through Cu{sub 2}S; (4) the sulfidation activation energies as a function of relative humidity (RH); (5) the sulfidation induction times at low humidities; and (6) the effect of light on the sulfidation rate. Also, the importance of various sulfidation mechanisms was determined as a function of RH and sulfide thickness. Different models for sulfidation-reactor geometries and the sulfidation reaction process are presented.
A methodology has been established to predict the effect of atmospheric corrosion on the reliability of plastic encapsulated microelectronic (PEM) devices. New experimental techniques were developed to directly characterize the Al/Au wirebond interface where corrosion primarily occurs. A deterministic empirical model describing wirebond degradation as a function of environmental conditions was generated. To demonstrate how this model can be used to determine corrosion effects on device reliability, a numerical simulation was performed on a three-lead voltage reference device. Surface reaction rate constants, environmental variables and the defect characteristics of the encapsulant were treated as distributed parameters. A Sandia-developed analytical framework (CRAX{trademark}) was used to include uncertainty in the analysis and directly calculate reliability.