Layered heater system having conductive overlays
A layered heater includes a resistive layer defining a resistive circuit pattern having at least one bend portion. A conductive overlay is provided on at least one of a top surface and a bottom surface of the bend portion to alleviate the current crowding effect, thereby protecting the electric circuit from premature failure. Methods of manufacturing the layered heater are also disclosed. The overlay may be formed on the bend portion after the resistive layer is formed. The overlay may also be formed on a substrate or a dielectric layer that supports the resistive layer before the resistive layer is formed.
1. A layered heater comprising:
a substrate;
a dielectric layer formed on the substrate;
a continuous resistive layer formed on the dielectric layer, the continuous resistive layer comprising a conductive material separated into an intermediate area and a resistive circuit pattern by a plurality of cuts that extend all the way through the continuous resistive layer, the intermediate area being a part of the continuous resistive layer, the resistive circuit pattern having at least one bend portion, the bend portion having a top surface and a bottom surface;
termination pads electrically connected to the resistive circuit pattern; the intermediate area being electrically inactive;
a conductive overlay disposed on at least one of the top surface and the bottom surface of the bend portion;
wherein the plurality of cuts do not extend longitudinally into the conductive overlay such that the intermediate area does not come into electrical contact with the conductive overlay; and
a second dielectric layer formed over the resistive layer and the conductive overlay.
2. The layered heater according to claim 1 , wherein the overlay is formed on the top surface of the bend portion.
3. The layered heater according to claim 1 , wherein the overlay is formed on the bottom surface of the bend portion.
4. The layered heater according to claim 1 , wherein the overlay is formed on the top surface and the bottom surface of the bend portion.
5. The layered heater according to claim 1 , wherein the overlay is made of the same material as the resistive layer.
6. The layered heater according to claim 1 , wherein the overlay is made of a material different from that of the resistive layer.
7. The layered heater according to claim 6 , wherein the overlay is made of a material comprising 30% Ag, 38% Cu, and 32% Zn.
8. The layered heater according to claim 1 , wherein the overlay has a variable thickness.
9. The layered heater according to claim 1 , wherein the each of the dielectric layer, the continuous resistive layer, the conductive overlay, and the second dielectric layer are formed by a thermal spray process.
10. The layered heater according to claim 1 , wherein the plurality of cuts are formed by a laser.
11. The layered heater according to claim 1 , wherein the plurality of cuts extend through the continuous resistive layer between the conductive overlay and longitudinally into a portion of the conductive overlay.