The flat substrates employed in many film-type power resistors are, preferably, thin--being made of a ceramic. It has long been known in the prior art to embed such a substrate, having a resistive film thereon, in a body of synthetic resin, with no thought of any heatsink action. Prior-art power resistors of the type indicated rely, for cooling, solely on passage of air over the synthetic resin body, and on conduction of heat through the leads that are connected to the resistive film. Such prior-art resistors have low power ratings. For many years, the assignee of the present patent application has made and sold large numbers of flat film-type power resistors that are fully encapsulated in a silicone molding compound. These resistors are free-standing, mounted upright (like tombstones) directly on the circuit board, and not mounted in engagement with any chassis (heatsink). Thus, with such resistors, there is no danger of shorting through or arcing to the chassis. such free-standing prior-art power resistor is shown in FIG. 8. A transfer-molded silicone body is shown in phantom lines. An aluminum oxide ceramic chip is the back element (in the drawing), and has a back surface spaced from the back surface of the silicone body. On the front of the chip are screen-printed metalization edge pads, resistive film and glass. The indicated leads are soldered to the edge pads.
USPTO Backgrounds
USPTO Backgrounds