Gábor Harsányi

Polymer films in sensor applications: a review of present uses and future possibilities

Polymeric materials have gained a wide theoretical interest and practical application in sensor technology. They can be used for very different purposes and may offer unique possibilities. The paper gives a broad summary about the sensor structures and sensing polymer films used in a wide variety of sensors. Finally, the present status and perspectives as well as the advantages of specific polymer based sensors are summarised.

Electrochemical processes resulting in migrated short failures in microcircuits

Metals can exhibit dendritic short-circuits caused by electrochemical migration in conductor-insulator structures, which may result in failures and reliability problems in microcircuits. The classical model of electrochemical migration has been well known for several decades. This process is a transport of metal ions between two metallization stripes under bias through a continuous aqueous electrolyte. Due to the electrodeposition at the cathode, dendrites and dendrite-like deposits are formed. Ultimately, such a deposit can lead to a short circuit in the device and can clause catastrophic failure. A few anomalous and newly discovered phenomena have initiated us to perform some revisions and to add supplementary models to the conventional one. A theoretical review based on practical results is given about the most important possible processes. Material design aspects are also discussed. >

Comparing migratory resistive short formation abilities of conductor systems applied in advanced interconnection systems

Abstract Various metallization types are applied in advanced high-density interconnection systems, pure metals as well as alloys, showing very different abilities for forming migration short circuit failures. There are two conventionally applied empirical possibilities for getting information or comparison about the migration behaviour of a conductor system, the water drop test, and the accelerated climatic tests, such as thermal humidity bias tests and the highly accelerated stress test. The results are generally uncertain showing large spreading and can only be interpreted with difficulties. A third method has also been developed and is presented in the paper for testing metallization systems based on a powerful technique, this is the very well-known cyclic voltammetry (CV) used in electroanalytical chemistry. The results indicate an effective method for making quick comparison between metallization systems in connection with their migration abilities. Moreover, the CV method enables a better understanding of the electrochemical processes that are the bases of the electrochemical migration.

Electrochemical migration behaviour of Cu, Sn, Ag and Sn63/Pb37

The Electrochemical Migration (ECM) behaviour of leaded surface finishes was compared to other surface finishes that are applied in the electronics manufacturing. The studied surface finishes were as follows: bare copper (bCu), immersion tin (iSn), immersion silver (iAg) and Sn63Pb prepared by HASL (Hot Air Solder Leveling). The results were evaluated by Water drop test with the calculation of the Mean Time to Failure (MTTF) and by the investigation of the composition of the dendrites. The results have shown some contradictions relating bare copper and HASL compared to the ECM ranking published previously (Harsányi and Inzelt in Microelectron Reliab 41:229–237, 2001; Yu et al. in J Mater Sci: Mater Electron 17(3):229–241, 2006). The copper and the HASL can change their places in the ECM ranking depending on the technological circumstances of the investigations. This impact can be caused by the composition of lead alloys (eutectic or not), the solubility parameters of the metal hydroxides; the oxidation state of the copper surface, etc. Further and theoretical explanations and the necessary fine adjustment of the migration models are discussed in the paper.

Electrochemical Migration in Thick-Film IC-S

The phenomenon of silver migration in conductor-insulator systems is well known, but it is less known that several other metals can exhibit migration. This paper tries to give a short summary of the phenomenon as applied to thick-film circuits.

Irregular effect of chloride impurities on migration failure reliability: Contradictions or understandable?

Abstract Metals can exhibit dendritic short-circuits caused by electrochemical migration in conductor–insulator structures, which may result in failures and reliability problems in microcircuits. The phenomenon of electrochemical migration has been well known for several decades; the process is a transport of metal ions between two metallization stripes under bias through a continuous aqueous electrolyte. Due to the electrodeposition at the cathode, dendrites and dendrite-like deposits are formed. Ultimately, such a deposit can lead to a short circuit in the device and can cause catastrophic failure. Surface contaminants, especially ionic types, may have significant influences on the overall process. Cl − contaminant has been investigated extensively; however, many contradictory statements were published. The role of these contaminants is rather complicated in influencing the formation of migrated resistive shorts: the various effects act against each other. Theoretical explanations are discussed and strengthened by experimental results in this paper.

Copper may destroy chip-level reliability: handle with care-mechanism and conditions for copper migrated resistive short formation

Although copper has a number of advantageous parameters in comparison with aluminum, and therefore, is expected to become the metallization of future high-speed, high-density silicon devices, its application introduces a new failure mechanism into the systems which has never occurred with aluminum; this is the electrochemical migration (not equal to the electromigration) resulting in short circuit formation between adjacent metallization stripes under DC bias. A great alert signal must be given for semiconductor producers in order to perform lifetime tests before introducing copper into the everyday fabrication process, otherwise the reliability of future electronic systems may dramatically be destroyed.

Investigation of intermetallic compounds (IMCs) in electrochemically stripped solder joints with SEM

Abstract In this work we compare the microstructures of intermetallic compounds (IMCs) in electrochemically stripped solder joints created by two different soldering methods (vapor phase soldering (VPS), and selective laser soldering with a CO2 laser). After the selective removal of the Sn phase with amperometry, the microstructure and structural composition of the IMC can be revealed in a detailed way, which is unlike any other previously published methods. The differences between the IMC microstructures of the technologically different solder joints were analyzed with optical microscopy and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) measurements were utilized to identify the different intermetallic phases (Ag3Sn, Cu6Sn5). Significant differences were observed in the IMC structures of solder joints prepared by different technologies.

Fractal description of dendrite growth during electrochemical migration.

The electrochemical migration (ECM) is an important physical-chemical failure mechanism which limits the realization of fine pitch structures in the manufacturing technology of printed wiring boards (PWB). The cause of ECM is the material transport that leads to dendrite formation. Electrical shorts will grow between pads or leads in fine pitch applications. The mechanism of ECM can be described by electrochemical principles. Dendrites are treatable as a fractal phenomenon because these special formations are in accordance with the most significant criteria of the fractal theory. We have observed in pursuance of our experiment-series that there is relationship between the materials of selective surface finishes of printed wiring boards, mean time to failure (MTTF) done to the migration process and the shape and form of dendrites grown on the top of the substrates in lateral arrangement. If the result of failure analysis is shortage caused by ECM in form of dendrite structure then it is worth to examine the shape and form of dendrites. According to our conclusion the reason of failure can be found with simply and cheap methods and the most efficient protection can be applied if we apply the above-mentioned relationship.

Conducting Polymer Based Electrochemical Sensors on Thick Film Substrate

New types of electroconducting conjugated polymer (ECP) based enzymatic and gas sensors were developed by using thick film technology. In order to prepare a stable polymeric film which is suitable for the enzyme immobilization and for gas detection itself, a special conducting salt (sodium dodecyl sulfate, SDS) was used. This combination resulted in sensors with favorable properties, i.e., higher sensitivity and longer operation stability. In the case of the ECP based uric acid biosensor a new layout was developed for the measurement of the current difference between the polymer and the enzyme electrode by using two working electrodes identically prepared (sensor and polymer electrodes) at the same time in the same solution. The sensor gives an easily measurable stationary response in the physiological concentration range of uric acid. Using a similar electropolymerization method, a selective ECP based sensor was prepared as part of a sensor array for intelligent gas monitoring. The changes in conductivity of the polypyrrole film in the presence of different gases were registered. A reversible sensor response of about 30 % in saturated methanol=air mixture and 50 % at 1000 ppm ammonia in air was obtained at room temperature. For NH3 a linear response in the 40‐1000 ppm concentration range could be registered while almost no response was obtained for ethanol, NO and CO. The sensor proved to be insensitive for H2.