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In addition to its use as a protective coating for monolithic integrated circuits, Silicafilm with Boron is an ideal material for use as a passivating coating on thin film circuits such as nichrome-gold films on glass or alumina substrates. The particularly attractive features of the coating, in addition to its ease of application, is the degree of impermeability of the film to water vapor and oxygen, thereby eliminating the low reliability which nichrome resistors exhibit under load in high humidity environments.

Application of the Film
1. The substrates need no exotic cleaning procedures. The substrates should be free of grease or hydrocarbon contamination. Simple degreasing followed by a rinse in alcohol and water is all that is necessary.

2. Silicafilm with Boron may be applied by spinning, dipping, or spraying. However, the most uniform film thickness will be achieved by spinning. The following film thicknesses will be observed for each of the various spin speeds:

3000 rpm 1500 angstroms
2000 rpm 2000 angstroms
1000 rpm 2500 angstroms

Silicafilm with Boron as delivered is free of particulate matter. However, if the bottle is frequently opened, the accumulation of liquid on the mouth of the bottle and its subsequent drying will yield glassy film-like particles which drop into the liquid and do not dissolve. Should this occur, the material may be freed of this material by filtering through a hypodermic syringe with a pvc filter holder and a membrane that is insoluble in alcohol.

The quantity of solution applied to the substrate prior to the start of spinning must be determined by experiment. In general, about 5 drops will adequately cover a 2 1/2" x 2 1/2" substrate.

The length of time of spinning will depend upon the spin speed. An adequate spinning time can be determined by noting when the interference colors stop changing.

Heat Treatment
After spinning, the film should be baked. The criteria for the optimum temperature and time for the bake cycle should be the maximum consistent with the allowable temperature for the substrate. Silicafilm with Boron will harden on standing at room temperature. However, the film will not exhibit its maximum hardness and density. Heating to higher temperatures will yield a denser film. For the protection of nichrome resistors, heating temperatures in the range of 250oC to 300oC for times of the order of 1 hour are adequate.

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Material Safety Data Sheet