Electronics electrically conductive adhesives

Electrically conductive adhesives owe their conductivity as well as their high cost to the incorporation of high loadings of metal powders or other special fillers of the types shown in Table 9.8. If enough metal particles are added to form a network within the polymer matrix, electrons can flow across the particle contact points, making the mixture electrically conductive. Virtually all high-performance conductive products today are based on flake or powdered silver. Silver offers an advantage in conductivity stability that cannot... 

Most unmodified polymeric resins have a very low thermal conductivity. There are certain applications where high levels of thermal conductivity are required. For example, power electronic devices and other heat-generating components are bonded to heat sinks and other metal sources. Metal powder filled adhesives, such as those described above for electrically conductive adhesives, can conduct both heat and electricity. 

In electronics production, two main principles of interconnection are used soldering using metal-based alloys and adhesive bonding with electrically conductive adhesives (Rahn 1993). 

In contrast to soldering, conductive adhesives are used for special electronic applications. Conductive adhesives simultaneously establish mechanical and electrical joints between PCBs and components by means of a particle-filled resin matrix. Whereas the polymer matrix is responsible for the mechanical interconnection, the fiUing particles (silver, palladium, or gold particles) provide the electrical contact between PCB and component. Therefore, in contrast to solder joints, conductive adhesive joints have a heterogeneous structure. 

A second key function for adhesives is to form ohmic contacts or electrical connections between active and passive devices, connectors, leadffames, I/O leads, or other electronic parts to form a circuit. Other applications for electrically conductive adhesives include electrostatic dissipation and electrical grounding connections. 

Electrically conductive adhesives may be isotropic (conduction equally in all directions) or anisotropic (conduction in the z-direction only). Both types are widely used in the assembly and packaging of electronics. 

Although important for structural adhesive bonds, fracture mechanics is not as critical for non-structural low load-bearing adhesives as used in most electronic modules. For the most part, passing minimum specification requirements for peel and tensile strengths both at ambient conditions and accelerated test conditions are sufficient. However, computer-simulated modeling and reliability analysis have been used for evaluating electrically conductive adhesives as used in electronics assembly. ... 

Zwohnski M, Hickman J, Rubon H, Zaks Y. Electrically conductive adhesives for surface mount solder replacement. In Proc. Second Int. Conf. Adhesive Joining Coating Tech, in Electronics Mfg. Stockholm Sweden 1996 333-340. 

Zwolinski, M., Hickman, J., Rubon, H., and Zaks, Y., Electrically Conductive Adhesives for Surface Mount Solder Replacement, Proc. 2 Inti. Conf. on Adhesive Joining Coating Tech. In Electronics Mfg., Stockholm Sweden, pp. 333-340 (1996)... 

Conductive Adhesives. Isotropically electrically conductive adhesives (ICAs) are widely used in the electronics industry when high-temperature soldering processes are unsuitable. Typical applications include silicon die attachment, component attachment in multi-chip modules (MCMs), surface mounted printed circuit board repair, and elec-tromagnetic/radio frequency (EMI/RFI) shielding. 

Y. Fu and J. Liu, Electron Conduction through Nano Particles in Electrically Conductive Adhesives, Micromaterials and Nanomaterials, No. 4, 2004, p 104—109... 

Two-Component Conductive Adhesives Two-component electrically conductive adhesives include products that provide high peel and tensile lap shear strength over a broad temperature range, and silver-filled epoxies recommended for electronic bonding and sealing applications. 

The processes generally employed to fix electronic components on three-dimensional circuit carriers are reflow soldering and electrically conductive-adhesive gluing. The first step in reflow soldering is to print solder paste on to the pads of the circuit trace (Fig. 4.1). The electronic components are subsequently placed in these solder depots. The module, complete with its electronic components, is then heated in a reflow oven, the solder particles of the paste melt, and the molten solder flows over... 

FIGURE 4.1 Process chain of reflow soldering or electrically conductive-adhesive gluing processes with application of the interconnection medium, placement of electronic components, and remelting of the solder or curing of the conductive adhesive... 

Dernevik, M. Sihlbom, R. Axelsson, K. Lai, Z. Liu, J. Starski, P. Electrically conductive adhesives at microwave frequencies. Proceedings of the 48th IEEE Electronic Components and Technology Conference, Seattle, WA, May 1998 1026-1030. 

Wong, C.P. Lu, D. Vona, S. Tong, Q.K. A fundamental study of electrically conductive adhesives. Proceedings of the 1st IEEE International Symposium on Polymeric Electronics Packaging, Norr-koping, Sweden, 1997 80-85. 

Felba, J. Friedel, K.P. Moscicki, A. Characterization and performance of electrically conductive adhesives for microwave applications. Proceedings of the 4th International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing, Helsinki, Finland, June 2000 232-239. 

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