Conference Review

Material Sciences for the Future _________ Henry Brown Society for the Advancement of Material and Process Engineering INTRODUCTION

Thirty-seven sessions on materials and processes, most of them projecting future directions, were presented at the 31st International SAMPE (Society for the Advancement of Material and Process Engineering) Symposium and Exhibition, April 7-10, 1986, in Las Vegas. The sessions were as diverse as materials advances in Japan, automated manufacturing, high temperature resins, computer modeling of composite processes, space materials, adhesive materials, and electronic materials and processes. Computer modeling of composite processes was especially interesting because composite activity has long been dominated by design methods and fractography. The thrust of the future will be in manufacturing and using closed loop computer control of cure cycles rather than cure cycles empiricially determined from past experience, and on using material conservative processes. Another set of interesting sessions were those on electronic materials and processes. These sessions were interesting because many of the problems discussed are the same basi.c problems encountered by metal bonders and composite fabricators many years ago. Some of the problems are unique because of small size and fragility, but most are well recognized in other fields--adhesion, corrosion, thermal expansion stresses, etc. Solutions for electronics problems should come relatively fast because of the extensive background available from other fields. Common electronics materials and

process concerns are defined by papers presented at this conference. The "problem statement," corrosion, shielding, assembly and thermal expansion damage were all addressed. PROBLEM STATEMENT

The end user, especially the military end user, is constantly pushing the electronics designer for smaller, higher density packages and higher reliability. Unfortunately, higher density in a smaller package frequently leads to lower reliability. Many of the causes of reduced reliability are known and are being approached as engineering problems rather than simple manufacturing problems. Corrosion. Metal corrosion and polymer degradation is always a problem when moisture is present. One paper dealt entirely with measuring corrosion resistance of EMI seals. The author points out that galvanic corrosion must be considered. The seal assembly, not component parts, must be tested. A similar phenomenon can happen with EMIIRFI shielding materials when conductive plastics are used. The author projects only pure silver filler will have a 20-year life, as required for military applications. Other fillers will corrode and become ineffective. Shielding. The shielding market is huge because virtually all digital equipment, in all countries, must be shielded. Plastics are so readily and inexpensively formed to complex and aesthetic shapes that a great deal of activity involves making plastics electrically conductive. One paper" describes "chatter machined" fibers

which are mixed with ABS plastic and injection molded. "Chatter machining" is an inexpensive process of chipping fragments (fibers) from a turning metal bar. The paper describes aluminum and brass fibers and size effects of each. Size is a factor because surface oxidation (corrosion) can reduce shielding effectiveness. Assembly. Assembly under microscopes is common for very sophisticated high density devices. Even then, handling problems exist. One paper describes non-conductive lead frames which hold leads in position during handling and processing, including wave soldering and degreasing. A fiber glass/epoxy frame and acrylic adhesive were found acceptable. PWB often create problems because of high thermal expansion which causes solder joints and fine leads to break. One paper describes a recently emerging resin type, semiIPN (semi-Inter Penetrating Network) combined with DuPont Kevlar (registered trademark) woven fabric. The system has low thermal expansion and good environmental resistance. 1223 cycles of two-hour duration between 55 and 125°C failed to cause any solder cracks at all. SAMPE will hold special electronics meetings, starting in 1987, because of the very widespread need for better understanding of assembly materials and processes in the electronics industry.

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HA VE YOU MOVED? It you have recently moved or changed employers, TMS would like to know your new address so we can keep you up to date on all the latest Society activities. Please complete and return the Mailing Address Update card included in this issue of Journal of Metals, so you don't miss any of your membership benefits! JOURNAL OF METALS· June 1986

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