Thermal pen tip

Claim 1

A thermal pen tip comprising: an insulating substrate having a flat surface and side surfaces slanting away from said flat surface; a heat reserve layer having one surface formed on said flat surface of said substrate, side surfaces and a second convex surface opposite said one surface, said second surface including a flat center portion having a predetermined width and end portions curving to merge with said side surfaces of said heat reserve layer, said side surfaces being slanted relative to said second surface whereby no sharp edge is formed therebetween; a resistance layer having a first thickness formed only on said flat portion of said second surface and including electrical terminal means; and a thermally conductive and electrically nonconductive layer having a second thickness formed on said resistance layer, said protective layer including a flat center portion having a predetermined width and end portions curving to conform to said heat reserve and resistance layers, the radius of curvature of said end portions of said protective layer being at least twice the sum of said first and second thickness, whereby a line drawn by said thermal pen tip will have a width corresponding to said predetermined width of said flat center portion of said protective layer.