Page 381 - Handbook of Adhesives and Sealants

Adhesive Composition and Formulation 337

TABLE 9.5 Volume Resistivity of Metals, Conductive Plastics and Various Insulation
Materials at 25 C 20
Specific volume
gravity resistivity
3
(gms/cm ) (ohm cm)
Silver 10.5 1.6 10 6
Copper 8.9 1.8 10 6
Gold 19.3 2.3 10 6
Aluminum 2.7 2.9 10 6
Nickel 8.9 10 10 6
Platinum 21.5 21.5 10 6
Eutectic solders — 20–30 10 6
Best silver-filled inks and coatings — 1 10 4
Best silver-filled epoxy adhesives — 1 10 3
Graphite — 1.3 10 3
Low cost silver-filled epoxy adhesives — 1 10 2
2
Graphite or carbon-filled coatings — 10 to 10
14
Oxide-filled epoxy adhesives 1.5–2.5 10 –10 15
14
Unfilled epoxy adhesives 1.1 10 –10 15
Mica, polystyrene & other best dielectrics — 10 16

Figure 9.6 Typical current flow path between metal particles in conductive ad-
hesives. Adsorbed organic molecules and oxide films prevent or impede passage
of electrons across contact points. 20

adhesive must permit high transfer of heat plus electric isolation. Fill-
ers used for achieving thermal conductivity alone include aluminum
oxide, beryllium oxide, boron nitride, and silica. Theoretically boron
nitride is an optimum filler for thermally conductive adhesives. How-
ever, it is difficult to fill systems to greater than 40% by weight with
boron nitride. Beryllium oxide is high in cost and its thermal conduc-