Bondability analysis of bond pads by thermoelectric temperature measurements

To reduce cost and enhance reliability for microelectronics applications, a complete understanding of the thermosonic bonding process is required. In particular, the question of whether melting, diffusion, or significant heating occurs along the interface during friction has often been raised. We present results obtained with a new device based on thermoelectric temperature measurements to determine the temperature at the bond interface. In addition to the temperature information, the data characterizes the bonding process in real time on a micrometer scale. The basic principle of the developed apparatus is temperature measurement by an Au-Ni thermocouple fixed within the inside chamfer of a bonding capillary. Different bond substrates with high and low bond contact quality have been investigated. The thermoelectric temperature measurements very precisely determines the bonding behavior of the bond pads. A few nanometers surface contamination on a bond pad significantly reduces the temperature rise at the bond interface and therefore impairs bondability of the substrate. These results demonstrate the sensitivity and accuracy of the measurement principle. The apparatus is a powerful tool to measure the tribology of the bond system and to characterize the bondability of different bond pads.     

Charge ahead [ultracapacitor technology and applications]

Ultracapacitors, also known as electrochemical double-layer capacitors (EDLCs) or supercapacitors have been around for decades and first appeared as low-power, low-energy, long-life backup devices, but until recently had few other applications. This article outlines the technology behind ultracapacitors and presents a variety of current applications, including backup power supplies, power boosters in portable electronics, and automobile electronics. Also briefly discussed are cost issues and possible future developments.     

Layout modeling and construction procedure for the arrangement of exhibition spaces in a fair

This paper tackles a subset of layout problems that is not a subject of the scientific research to date: the arrangement of the exhibition spaces in a fair. A fair is a large‐scale exhibition for goods and services; for example a trade fair or a regional fair. The layout problem of fairs consists in finding an acceptable layout for both the exhibitors, the visitors, and the organizer of the fair. A model for representing the layout of fairs is presented: the adjacency model. Based on the adjacency model, a construction procedure is developed that leads to the generation of alternative layout solutions. Numerical results for the layout of a real fair are reported.     

Influence of surface contamination on metal/metal bond contact quality

The influence of surface cleanliness of Au/Ni coated multichip materials (MCMs), Ag plated Cu lead frames, and Al bond pads on semiconductor chips on the strength of Au wire bond contacts has been investigated. A clean surface is important for good adhesion in any kind of attachment process. Investigations by means of x-ray photoelectron spectroscopy have been performed on the bond substrates to determine the chemical composition, the nature as well as the thickness of the contamination layer. The influence of contamination on bond contact quality has been examined by pull force measurements, which is an established test method in semiconductor packaging industry for evaluating the quality of wire bonds. The results clearly show that a strong correlation between the degree of contamination of the substrate and pull strength values exists. Furthermore, a contamination thickness limiting value of 4 nm for Au and Ag substrates was determined, indicating good wire bond contact quality. The effect of plasma cleaning on wire bondability of metallic and organic (MCMs) substrates has been examined by pull force measurements. These results confirm the correlation between surface contamination and the strength of wire bond contacts for Au/Ni coated MCMs and Ag plated Cu lead frames. Atomic force microscopy measurements have been performed to determine the roughness of bond surfaces, demonstrating the importance of nanoscale characterization with regard to the bonding behavior of the substrates. Finally, bonding substrates used in integrated circuit packaging are discussed with regard to their Au wire bonding behavior. The Au wire bonding process first results in a cleaning effect of the substrate to be joined and secondly enables the change of bonding energy into frictional heat giving rise to an enhanced interdiffusion at the interface.     

A method for measuring the muon capture ratio A(HZ) in a H2 + Z gas mixture

A method is proposed for measuring the $\text{A(}\text{H}\text{Z}\text{)}$ capture ratio of muons in a H₂ + Z gas mixture making use of the transfer of muons captured in hydrogen to the heavier element Z.