Silver-glass adhesive

The most important additive in an adhesive formulation is the filler. Fillers such as metal particles are used to render adhesives both electrically and thermally conductive while electrically insulative fillers such as metal oxides are used to provide thermal conductivity alone. Regardless of whether they are electrically conductive or not, fillers provide numerous simultaneous benefits, including the following  

The processing and surface preparation of silver particles is critical to their performance as a filler. The first step in manufacturing silver flakes is to produce silver powder. Powdered silver may be produced by chemical precipitation, electrolytic precipitation, or melt atomization. Most commercially available silver powders are precipitated by reducing silver from a silver nitrate solution. Particle sizes of powdered silver range from submicron to 5 Silver powders are selected based on size and morphology 

Material Specific Gravity (gm/cm Volume Resistivity (ohm-cm) Thermal Conductivity (W/mK) 

Boron nitride and sihca filled modified cyclo-olefin thermo set - - 1.0 

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The main advantages of silver-glass adhesives are their very high thermal conductivities and thermal stabilities compared with filled polymer resin formulations. Thermal conductivities of 65 W/mK to over 80 W/m K are reported. ... 

By virtue of their high silver content, silver-glass adhesives have high electrical conductivities, typically 1.3 x 10 ohm-cm. Other typical properties are flexural modulus of 350 kpsi, die shear adhesion of 900 psi, and CTE of 20 ppm/°C. ... 

Applications for silver-glass adhesives are primarily for the attachment of power semiconductor die, LEDs, and devices near the engine in automobiles. 

Molded plastic. of packages to processing temp. >350 C (if silver-glass adhesives are used) High strength, low-temperature Silver-filled epoxy, modified... 

In another evaluation, silver-glass, polyimide, and silicone adhesives were analyzed for residual stress. The silver-glass adhesive showed the greatest deflection the silicone, the lowest and the polyimide was intermediate. This order is explained by the high modulus of the silver-glass and the low modulus of the silicone relative to the polyimide. ... 

Cases 6a and 6b show the importance of properly curing (processing) the silver-glass adhesive. The high carbon dioxide and moisture content of Case 6a indicates that the polymer binder or other organic constituents of the silver-glass were not completely burned off. After a second cure cycle was used, good RGA results were obtained (Case 6b). 

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