Sponsored by: EPD Process Fundamentals Committee, MSD Thermodynamics & Phase Equilibria Committee, Japan Institute of Metals
Program Organizers: Prof. R.Y. Lin, University of Cincinnati; Prof. Y. Austin Chang, University of Wisconsin-Madison; Prof. R. Reddy, University of Navada-Reno and Dr. C.T. Liu, Oak Ridge NL
Monday, PM Room: B2
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: A. Mikula, Institut fur Anorganische Chemie, Universitat Wien, Wahringerstrasse 42, A-1090 Vienna, Austria; S.K. Wu, Institute of Material Science & Engineering, National Taiwan University, Taipei, Taiwan
2:00 pm Invited
FUNDAMENTALS OF BONDING BY ISOTHERMAL SOLIDIFICATION FOR HIGH TEMPERATURE SEMICONDUCTOR APPLICATIONS: Rainer Schmid-Fetzer, Techn. Universitat Clausthal, AG Elektronische Materialien, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfield, Germany
Isothermal solidification can be used to form strong bonds at low temperatures which remain solid at much higher temperatures. The exploitation of this principally known technique for new high temperature processing steps and applications in electronic assemblies is the aim of this study. Three basically different variants of this bonding process are given. A comprehensive metallurgical screening is performed and the feasibility of binary material systems is given on a quantitative scale. Very attractive systems are spotted that have never been studied before. Detailed examples for the realization of bonding with complex ternary and multilayer systems are given. A highly innovative example is the chip stack or wafer bonding of unmetallized Si or SiC at 250[[ring]]C. The proposed bond remains stable above the melting point of Si and enables entirely new semiconductors manufacturing steps. An improved die bonding process was proposed and verified experimentally.
2:25 pm
INFRARED JOINING OF SILICON CARBIDE FORMATION AT THE JOINT DURING INFRARED BONDING OF SILICON CARBIDE: Randall A. Blue, Ray Y. Lin. Department of Materials Science and Engineering, M.L. #12, University of Cincinnati, Cincinnati, OH 45221-0012
Joining of Silicon Carbide with infrared using a mixture of Si - 30 wt.%C as the brazing material has been investigated. Joining was performed at a temperature of 1500=B0C in a flowing argon atmosphere for processing times ranging from 5 to 60 seconds. Cross section examinations of the joined parts have shown that all joints are nearly void free with excellent wetting between the base SiC and the brazing material. Silicon carbide has been identified as the reaction product in the joining zone with a transmission electron microscope (TEM) and selected area diffraction (SAD) analysis. At 1500=B0C with a holding time of 60 seconds, a nearly homogenous SiC joint forms, producing strengths comparable to other brazing techniques. A kinetic model of forming SiC from liquid silicon and carbon will be presented.
2:50 pm
ON THE METALLURGY OF ACTIVE BRAZING OF SILICON NITRIDE: J.K. Kivilahti, M. Paulasto, F.J.J. van Loo, Helsinki University of Technology, Dept. of Materials Science and Engineering, FI- 02150 Espoo, Finland
Advanced ceramics like silicon nitride are increasingly used as structural components in demanding high temperature applications as well as in electronics industry. Complex, multicomponent structures for engineering applications generally. The interfacial microstructures formed when Si3N4 is brazed with Ag-Cu-Ti braze alloys have been discussed in several recent studies. In order to resolve which chemical reactions are possible under various joining conditions and thereby to be able to control the brazing of Si3N4 the reactions in brazing has to be studied using both microstructural and thermodynamics. In this work the earlier determined ternary Ti-Ag-Cu and Ti-Is-N systems have been applied to the brazing of silicon nitride with AgCuTi alloys. Using direct brazing experiments at various temperatures and thermodynamic analyses performed by combining the most recent available thermodynamic data and experimental information the chemical reactions controlling the brazing process are determined and a description of the am is presented. It is shown that the miscibility gap found in the ternary Ti-Ag-Cu system exists during brazing and divides the liquid braze into Ag-rich (Ll) and Ti- and Cu-rich (L2) liquid. The liquid L2 segregates at the ceramic interface and reacts with the silicoa quaternary Ti-Si-Cu-N compound.
3:15 pm Invited
BONDING OF THIN COPPER DISCS TO SAPPHIRE BY A CUPROUS OXIDE INTERLAYER: G.P. Martins, Wen-Ming Chen, Carlos A. Silva, Colorado School of Mines, Golden, CO 80401
Joining of metal/metal, ceramic/ceramic systems can be effected by a transient liquid phase (TLP) scheme or an adaptation of it. The bonding of copper to Al2O3 ( alumina or sapphire) by this technique has been of interest during the last twenty years in the electronics industry. In general, the process can be conveniently analyzed by identifying three distinct stages which lead to the formation of a joint-member whereby an interlayer is completely consumed. The research conducted was devoted to a primary effort on the development of mathematical models describing the behavior of three stages associated with the process. A secondary effort was focused on bonding of copper disk (screens or washers) to sapphire lenses. Several bonded parts were successfully manufactured in the laboratory scale equipment which incorporated an isothermal cell as a critical system component. However, only a cursory analysis was conducted on one assembly in regard to the interfacial bond region between the copper and sapphire. The predictions obtained are the first known quantification of the time scales related to the mechanisms associated with TLP bonding of copper to sapphire by use of a cuprous-oxide interlayer.
3:40 pm BREAK
4:00 pm Invited
INFRARED JOINING OF TiAl TO TiAl WITH ALUMINUM FOILS: Sunil K. Annaji, Ray Y. Lin, Department of Material Science & Engineering, University of Cincinnati, M. L. 12, Cincinnati, OH 45221-0012; S. K. Wu, Institute of Material Science & Engineering, National Taiwan University, Taipei, Taiwan
It has been shown that when liquid Al is in contact with Ti there is the formation of an intermetallic TiA13 phase. This is the basis for the brazing of TiAl using aluminum foils. In this study, infrared joining of TiAl was investigated at temperatures between 1050deg.C and 1350deg.C in a flowing argon environment for times varying between 15 seconds to 60 seconds. The growth of TiAl3 in the joint appears to be diffusion controlled with aluminun being the dominant moving species. Cross sectional studies on the joined specimen have shown different degrees of reaction depending on the temperature and time of holding. Microhardness studies across the joint show a gradual decrease in the hardness as the indentations are made towards to the center of the joint. However, it is observed that at higher temperatures of processing and longer periods of time, the hardness values towards the center increase considerably as compared to the increase at the periphery of the joint. TEM studies have been done to identify the TiAl3 phase.
4:25 pm
THERMODYNAMICS AND PHASE DIAGRAM OF NEW SOLDER MATERIALS: S. Karlhuber, A. Mikula, Institut fur Anorganische Chemie, Universitat Wien, Wahringerstrasse 42, A-1090 Vienna, Austria
The unique physical and mechanical properties have made the Pb-Sn solders attractive for low temperature joining of electronic parts. But since lead in the solder became a great environmental problem and a health concern, it is safer and more economical instead of cleaning up the waste dumps to replace lead in the solder materials. This idea has caught on and a lot of research and development efforts are going on to replace lead in the soft solder materials. Some of these materials are ternary tin alloys and not much is known about the thermodynamics and the phase diagram of these alloys. We investigated (Ag, Au, Cu)-Sn-Zn systems and determined the thermodynamic properties over the whole composition range and did some work on the phase diagrams in the Sn-rich corner.
4:50 pm
PERIODIC LAYER FORMATION DURING SOLID STATE REACTION: M.R. Rijnders, A.A. Kodentsov, F.J.J. van Loo Lab, Solid State Chem. & Mat. Sci., Eindhoven Univ., of Tech., P.O. Box 513, 5600 MB Eindhoven, the Netherlands
A periodic layered morphology of the reaction zone has been observed in several annealed solid/solid diffusion couples. This morphology is characterized by a regular array of bands of particles embedded in an intermetallic matrix phase. An understanding of the mechanism underlying periodic layer formation is important in predicting the long-term high temperature stability of joints. From experimental observations we will show that various factors like widely different mobility's of components, high vacancy fluxes, particle coarsening, dislocation movement, shifting phase interfaces and development of stresses should be included in a comprehensive theory concerning this type of reaction.
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