Epoxy attachment materials

In ceramics, the heat flow is primarily due to phonon generation, and the thermal conductivity is generally lower than that of metals. Crystalline structures, such as alumina and beryllia, are more efficient heat conductors than amorphous structures such as glass. Organic materials used to fabricate printed circuit boards or epoxy attachment materials are highly amorphous electrical insulators, but tend to be very poor thermal conductors. 

The ideal die attach material has a short cure time at a relatively low-cure temperature, exhibits low moisture absorption, provides good adhesion to multiple surfaces, contributes low stress to the die and can be processed within a very tight tolerance. Many epoxies are now available meet some of these demands to a high degree, yet each material has limitations. 

Figure 44 Package constructions used to evaluate the thermal transfer properties of the die attachment materials and substrates. TO-3 steel package is composed of steel case la, OFHC copper 2a, nickel film 3, soft solder 4a, and integrated circuit 5. TO-3 aluminium package is formed of aluminium header lb plated with nickel 3 on the top of which a silver-filled epoxy adhesive 4b is employed to bond the semiconductor device 5. The 24-lead CERDIP package is based on nickel-plated alumina substrate Ic with soft solder bonded silicon chips. In 40-lead plastic package, integrated circuits 5 are bonded to leadframes 2b by using silver-filled epoxy adhesive 4b and then encapsulated in moulding...

The aliphatic components of SOM, derived from various sources, tend to persist in soil (Almendros et al. 1998 Lichtfouse et al. 1998a Lichtfouse et al. 1998b Mosle et al. 1999 Poirier et al. 2000). The principal source of aliphatic materials in soil is plant cuticular materials, especially cutin, an insoluble polyester of cross-linked hydroxy-fatty acids and hydroxy epoxy-fatty acids (Kolattukudy 2001). Some plant cuticles also contain an acid and base hydrolysis-resistant biopolymer, comprised of aliphatic chains attached to aromatic cores known as cutan (Tegelaar et al. 1989 McKinney et al. 1996 Chefetz 2003 Sachleben et al. 2004). 

Contact materials and confignrations nsed in TSC experiments vary widely and depend on the particnlar application. Metal electrodes can be attached to the sample by evaporation or by application of condnctive pastes (silver paint or epoxy) or metal-organic compounds. Typical contact configurations are shown in Fig. 1.5. 

Epoxy networks may be expected to differ from typical elastomer networks as a consequence of their much higher crosslink density. However, the same microstructural features which influence the properties of elastomers also exist in epoxy networks. These include the number average molecular weight and distribution of network chains, the extent of chain branching, the concentration of trapped entanglements, and the soluble fraction (i.e., molecular species not attached to the network). These parameters are typically difficult to isolate and control in epoxy systems. Recently, however, the development of accurate network formation theories, and the use of unique systems, have resulted in the synthesis of epoxies with specifically controlled microstructures Structure-property studies on these materials are just starting to provide meaningful quantitative information, and some of these will be discussed in this chapter. 

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