INTERMETALLIC COMPOUNDS

Intermetallic compounds are materials composed of two or more types of metal atoms, which exist as homogeneous, composite substances and differ discontinuously in structure from that of the constituent metals. They are also called, preferably, intermetallic phases. Their properties cannot be transformed continuously into those of their constituents by changes of composition alone, and they form distinct crystalline species separated by phase boundaries from their metallic components and mixed crystals of these components. It is generally not possible to establish formulas for intermetallic compounds on the sole basis of analytical data, so formulas are determined in conjunction with crystallographic structural information.

The term alloy is generally applied to any homogeneous molten mixture of two or more metals, as well as to the solid material that crystallizes from such a homogeneous liquid phase. Alloys may also be formed from solid-state reactions. In the liquid phase, alloys are essentially solutions of metals in one another, although liquid compounds may also be present. Alloys containing mercury are usually referred to as amalgams. Solid alloys may vary greatly in range of composition, structure, properties, and behavior.


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PHYSICAL AND MECHANICAL PROPERTIES OF INTERMETALLIC
COMPOUNDS COMMONLY FOUND IN SOLDER JOINTS


ABSTRACT

Three intermetallic compounds (Cu6Sn5, Cu3Sn, and Ni3Sn4) commonly found in solder joints have been prepared by gas atomization and then consolidated into bulk forms with microstructures similar to those observed in actual joints. Physical and mechanical properties relevant to the performance of joints have been measured for these materials. These data are evaluated in light of previously reported results, appropriate theories, and with regard to their applicability to actual layers in solder joints.


INTRODUCTION

In every solder joint, between the solder and the substrate, a layer is present containing one or more intermetallic compounds [1,2,3]. This layer formed at the moment the joint was made, and was responsible for the resulting strong bond. It may also be responsible for problems in solderability [4,5] and may compromise the future reliability of the joint [1,2,6]. These layers are usually 1 to 5 micrometers thick and, depending upon conditions, may thicken with time [3]. As solder joints are made ever smaller, the intermetallic occupies an ever greater proportion of the whole joint. The day when the intermetallic layers represent 10-20% of the joint is fast approaching.


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Intermetallic compound

Chemical compound


IIntermetallic compound, any of a class of substances composed of definite proportions of two or more elemental metals, rather than continuously variable proportions (as in solid solutions). The crystal structures and the properties of intermetallic compounds often differ markedly from those of their constituents. In addition to the normal valences of their components, the relative sizes of the atoms and the ratio of the total number of valence electrons to the total number of atoms have important effects on the composition of intermetallic compounds. See also [You must be registered and logged in to see this link.].