Low voltage lithographic fuses: Preliminary results of breaking capacity and cyclic load tests

High breaking capacity fuse of low rated current is one of the most difficult fuses to design and build. The fuse element is of such small dimensions that its mechanical fragility is too high. Besides the fuse filler, usually quartz sand could deteriorate the element after the assembling, mainly during the filling process. In order to solve this difficulty the fuse-on-substrate technique has been in use from the 1980 decade. Initially rigid substrate materials were used, such as alumina, silica, glass-polytetrafluoroethylene (PTFE), solidified quartz sand, etc. Also extra cooling was provided through a metallic plate applied to the other substrate face. Lately, lithographic techniques in use for printed circuit construction were extended for fuse manufacturing on flexible substrates. The offset printing technique on flexible substrate added to the use of new conductive inks, allows the manufacturing of good accuracy dimension fuses. The lithographic fuses could find an excellent application field on the protection of small size semiconductors. Several fuse samples on three dissimilar flexible substrate materials were manufactured, having rated current from 0.1 to 1 A. Rated current and temperature rise tests do not represent a problem due to the low current values. However the main manufacturers´ concerns are related with cyclic long duration overload behavior and high current breaking performance. The paper presents the results of a limited number of cyclic loading, and high current breaking tests. The high current tests correspond to duties l₁ and I₂ specified by IEC 60127, carried out in a circuit with 230 V ac and currents of about 1,500 A. It is preliminarily concluded that fuses using one of the tested substrates present a reasonably good performance, no far away from the conventional HBC fuse. Further research is necessary especially on the fuse material dimensions accuracy and on substrate material behavior under arcing conditions.