PTC device
There is provided a PTC device having a sufficient function to detect the possibility of the substrate reaching an extraordinary high temperature more rapidly, and prevent the substrate from reaching such an extraordinary high temperature beforehand. The PTC device 10 includes a layered support 14 that functions as a heat transfer medium and a polymer PTC element 12 disposed thereon wherein the polymer PTC element is disposed on one surface 15 of the layered support (in a thermally connected condition) and the polymer PTC element and the layered support are molded in a resin such that the other surface 15 ′ of the layered support is exposed.
1. A PTC device comprising
a layered support having first and second surfaces, such layered support functioning as a heat transfer medium,
a polymer PTC element disposed on the first surface of the layered support, said PTC element having a trip temperature, and
a potting element formed of a curable resin that coats the PTC element and has a coefficient of linear expansion,
the polymer PTC element and the layered support being molded in a resin such that the second surface of the layered support is exposed and the potting element is between the PTC element and the molded resin, the coefficient of linear expansion of the potting element at the trip temperature of the PTC element being larger than that of the molded resin.
2. The PTC device according to claim 1 wherein the polymer PTC element is disposed on the first surface of the layered support in a thermally connected state.
3. A method of manufacturing a PTC device comprising a layered support and a polymer PTC element disposed thereon comprising the steps of:
disposing the polymer PTC element having a trip temperature on a first surface of the layered support;
surrounding the PTC element with a curable resin by means of potting it prior to molding,
hardening the curable resin to form a potting element,
subjecting the layered support and the polymer PTC element to molding such that a second surface of the layered support is exposed, and said potting element having a coefficient of linear expansion at the trip temperature of the PTC element larger than that of the molded resin.
4. An electrical device comprising a PTC device, said PTC device comprising
a layered support having first and second surfaces, such layered support functioning as a heat transfer medium,
a polymer PTC element disposed on the first surface of the layered support, said PTC element having a trip temperature, and
a potting element formed of a curable resin having a coefficient of linear expansion,
the polymer PTC element and the layered support being molded in a resin such that the second surface of the layered support is exposed and the potting element is between the PTC element and the molded resin, the coefficient of linear expansion of the potting element at the trip temperature of the PTC element being larger than that of the molded resin.
5. The PTC device according to claim 1 , wherein the coefficient of linear expansion of the potting element is not less than 3.0×10 −5 /° C. and not more than 40.0×10 −5 /° C.
6. The PTC device according to claim 1 , wherein the coefficient of linear expansion of the potting element is not more than 30.0×10 −5 /° C.
7. The PTC device according to claim 5 , wherein the coefficient of linear expansion of the potting element is not more than 30.0×10 −5 /° C.
8. The method according to claim 3 , wherein the polymer PTC element is directly or indirectly disposed on the layered support.
9. The electrical device of claim 4 wherein the polymer PTC element is disposed on the first surface of the layered support in a thermally connected state.
10. The method according to claim 3 , wherein the curable resin to be used for potting has the coefficient of linear expansion not less than 3.0×10 −5 /° C. and not more than 40.0×10 −5 /° C.
11. The electrical device of claim 9 wherein the coefficient of linear expansion of the potting element is not less than 3.0×10 −5 /° C. and not more than 40.0×10 −5 /° C.