ADVERTORIALS Development of aerospace fuses SCHURTER and ESA cooperation


Many years of intensive cooperation in research and development between SCHURTER and the European Space Agency (ESA) has led to the incorporation of new technologies and products for protecting electronic modules in aerospace applications.


measurement values are recorded and handed over in batch documentation along with the delivery to the customer. During requalification processes, that take place every two years, compliance of all technical production measures is checked by the ESA using clearly defined qualification criteria.


In 2004 SCHURTER was asked by the European Space, Research and Technology Center (ESTEC), a sub- organisation of the European Space Agency (ESA), to participate in a development cooperation to manufacture midget fuses for use in aerospace. During a four-year evaluation phase, first the


requirements and potential solutions were developed, which culminated in a generic specification for the qualification, production and delivery of fuses. The subsequent research and development cooperation reached its high point in the MGA-S fuse being listed as an ESAqualified product. SCHURTER documented the general requirements for an aerospace fuse in a White Paper; the detailed specification for the MGA-S is noted in a data sheet. Since 2008 SCHURTER has produced MGA-S fuses according to the agreed upon product requirements. Each individual aerospace fuse undergoes a screening test. At the same time, all


Further development of the technical approaches


Parallel to the series production of the MGA-S, a second phase of the cooperation between SCHURTER and the ESA was started in 2010, in which a solution for the protection of rated currents up to 15 A was to be developed. To this end, an evaluation phase began during which potential variation of designs, particular the most risky as identified, were investigated. This second phase was an integral part of the cooperation and only approachable because of the positive experience from the first phase.


Parallel Circuit of MGA-S


Basically a higher rated current can be achieved through the parallel circuit of selected MGA-S fuses with the same cold resistance. Products that have already been qualified can be used for this purpose. Electrical and thermal analyses of this approach were not


only designed in a theoretical model at SCHURTER, but also measured in experimental set-ups. After extensive testing, however, this approach has some disadvantages. This is due to the increased space requirements for the parallel circuit fuses, as well as a negative impact on the Meantime Between Failure (MTBF).


Increase in the rated current using MGA-S technology


Based on a specification between SCHURTER and the ESA, the rated current range of 5 A to a 15 A, with a voltage of 125 VDC at a breaking capacity of 1000 A, was increased in a further experimental set-up. The mechanical dimensions had to be adjusted accordingly in order to absorb the energy during the high breaking test. With regard to the assembly, the ESA expected compatibility with existing solutions being used, meaning: the solder pads of the new solution had to fit the same connection geometries of the circuit board that had been defined already for the existing product.


This led to a solution using thin film technology, whereby a so-called sputter applies a metal layer of an exactly defined thickness in the micron range to a glass substrate material. Similar to the MGA-S, the device protecting the line is enclosed by a ceramic housing, which guarantees the


stability necessary for the


corresponding operational scenarios in the Too important to fail range.


As an alternative to the thin film technology, which uses the metal sputter process, the application of LIGA technology (stands for: lithography, electroplating, and molding process steps) on established substrate materials of the circuit board industry was also tested during the evaluation phase. The advantages and disadvantages during the evaluation focused on the reliability and long- term stability factors. For example, the carbon compounds generated during combustion were assessed as not sufficiently reliable because of their undefined conductance value.


Accordingly, various models to simulate the change in the cold resistance, the drop in voltage and the change in the temperaturedependent current/time characteristics were developed here for the different potential designs. These models were verified using manufactured and measured prototypes.


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