Harry K. Charles

The Influence of Contamination on Aluminum-Gold Intermetallics

The uncontrolled formation of aluminum-gold intermetallics such as purple plague (AuA12) has not been considered a major semiconductor and/or hybrid reliability problem for several years, due to the advent of dependable lower temperature assembly processes which include: thermosonic gold ball bonding, ultrasonic aluminum wedge bonding, and epoxy attachment of both die and substrates. Today, however, intermetallics are beginning to appear again even in the lower temperature production environment. Isolated instances of ball bond lifting after long burn-ins at 125°C are being noted in high reliability programs. Rapid intermetallic consumption of second or tail bonds has been reported in hybrids with aluminum substrate metallization and gold thermosonic bonding. These processes are definitely accelerated by the 125°C thermal exposure, but have occurred so rapidly that contamination appears to be the principal driving source. A case study is presented in which a switch in substrate attach epoxy caused a catastrophic acceleration of intermetallic formation and widespread bond failures after the hybrids were exposed to a thermal testing environment. Details of the failure investigation process are presented including: impurity searches using energy dispersive X-ray, scanning Auger microprobe, and secondary ion mass spectrometry; epoxy cure cycle validations using residual gas analysis methods; the empirical use of the wire bond pull as the process validation method; and the analysis of sealed package ambient both pre and post burn-in.

Advanced Wire Bonding Technology: Materials, Methods, and Testing

Wirebonding is the most dominant form of first-level chip or integration circuit interconnect method used throughout the world-wide electronics industry today. Many trillion of wirebonds are made annually using automated machines. Wirebonding is reliable, flexible, and low cost when compared to other forms of first-level microelectronic interconnection. Failures are typically at the single digit parts per million level or below. As the number of interconnections on the integrated circuit grows with increased functionality, the bonding pads are becoming much smaller and closer together. Similarly rigid inorganic substrates and package structures have given way to their more flexible organic counterparts. Everywhere in the microelectronic industry new applications, materials, and structures are appearing and challenging the performance and, hence, the dominance of wirebonding.

Precision bone and muscle loss measurements by advanced, multiple projection dexa (AMPDXA) techniques for spaceflight applications

An advanced, multiple projection, dual energy x-ray absorptiometry (AMPDXA) scanner system is under development. The AMPDXA is designed to make precision bone and muscle loss measurements necessary to determine the deleterious effects of microgravity on astronauts as well as develop countermeasures to stem their bone and muscle loss. To date, a full size test system has been developed to verify principles and the results of computer simulations. Results indicate that accurate predictions of bone mechanical properties can be determined from as few as three projections, while more projections are needed for a complete, three-dimensional reconstruction.

Electronics and its impact on energy and the environment

Technologys impact on human health has been a concern for at least 200 years. These concerns ranged from the waste and pollution due to mining and heavy manufacturing to emissions from the automobile and fossil fuel power plants. Now the proliferation of electronics products, their manufacture and disposal are posing additional threats to the fragile balance of the Earths eco systems. Nevertheless, electronics can also be the solution to many of our current and future environmental and energy related problems. The environmental threats from electronics can be significantly reduced or eliminated through consciously environmentally responsible choice of materials, technology, design, manufacture, distribution, usage, and end-of-life disposal. In a similar way the application of electrical and electronics technologies and devices for power generation, electric and hybrid automobiles and solid-state lighting can significantly positively contribute to reducing mankinds carbon footprint and improve our environment. Thus, consciously and demonstrably, electronics technologies, devices and applications are making major contributions through the removal of toxins and pollutants; innovative materials enable reduction in use of other materials; new electronics energy sources will become the long-term major sustainable sources; solid state lighting is decreasing the consumption of energy whilst providing improved illumination. Nano-electronics products now enable more efficient use of energy in many walks of life

The Reflow Attachment and Reliability Testing of Ceramic Chip Carriers

The results of an extensive program for the solder reflow attachment and reliability testiny of ceramic chip carriers for use in space satellites, implantable biomedical electronics, and underwater instrumentation are discussed in detail. The program was divided in three major parts; 1) the packaging of integrated circuit chips in ceramic carriers; 2) the selection and qualification of solders, reflow methods and cleaning processes; and 3) the validation of the chip carrier-substrate system for high reliability applications. Military Standard environmental testing of ceramic chip carriers alone and carriers attached to thin film and thick film (multilayer) ceramic substrates, glass, sapphire, and various printed wire circuit boards has been conducted. Test results are presented for various carrier-substrate-solder combinations along with discussions of associated failure modes and fabrication problem areas.

Laser-based electro-optic testing of multichip module structures

Laser-based electro-optic probing is a proven noninvasive technique for testing high-speed microwave circuits on substrates such as gallium arsenide (GaAs) and indium phosphide (InP). We have extended this technique to probe circuit structures on doped and poled polyimide substrates that are useful in high-density packaging applications such as multichip modules (MCMs). Our results demonstrate the potential to improve the testability of MCMs by probing circuit structures that are buried in the central layers of an MCM. In addition to direct, point-by-point electric field measurements in representative MCM structures, we have investigated the poled polyimide dielectric efficacy both as a dielectric circuit layer and as a suitable electro-optic material.

Ultra-thin, and flexible physiological monitoring system

An ultra-thin and flexible physiological monitoring system has been designed that is suitable for use in a wide range of applications from sports training and performance assessment to the home health monitoring of the worlds aging population. Key aspects of the design include: embedded garment sensors with a simplified 1-wire bus structure; a miniaturized ultra-thin, self contained electronics/controller module; and a wireless interface for the real-time remote data monitoring and analysis.

The Practical Implementation of Voltage Contrast as a Diagnostic Tool

The various modes of voltage contrast, their basic theory of operation, and the techniques and equipment necessary for their practical implementation in a small multipurpose scanning electron microscope (SEM) are described in detail. The voltage contrast modes considered include: static, dynamic, quasistatic, clock stretching, synchronous, stroboscopic, and full quantitative. Details of SEM mounts and signal interconnection schemes both internal and external are presented. Techniques for mounting dual inline packages and ceramic chip carriers (C3) have proven particularly useful and are easily adaptable to most SEM types. The selection of the proper operating parameters necessary to achieve successful voltage contrast operation and micrographs is presented in detail. For example, investigations of dynamic range, voltage sensitivity, and the little described floating ground levels were performed in the case of static voltage contrast. Similarly, the effects of changing frequency and device ground level were explored for the synchronous voltage contrast modes. Experimental devices ranged from simple transistors where the bias and signal flows could easily be understood to more complex integrated circuit chips with their multiplicity of current paths and dynamic signal patterns. The extension of the theory, fixturing and operation to even more complex devices such as LSI and VLSI circuits is discussed.

Multiple projection DEXA scanner for precision bone and muscle loss measurements and analysis during prolonged spaceflight

Bone structural information derived from DEXA data is shown to be relevant in explaining BMD loss versus strength-related observations in both aging populations and individuals exposed to microgravity for prolonged periods. Commercial DEXA instruments are limited (and not optimized) to make these critical structural measurements. Progress on the development of a multiple projection DEXA scanner system for making precision bone and muscle loss measurements and their resultant implications on bone strength and fracture risk is described.