Electrical ignition and method for its production

The invention relates to an electrical ignition element with a ceramic body as the ignition bridge carrier, which is contained in a metallic outer sleeve and has one or more bores into which contact pins are fitted as current leads, between which an ignition bridge is located, and a method for producing an electrical ignition element.

Such an igniter is described in US-A-3,659,527.

With such an ignition element, however, it can - similarly as with ignition elements described in DE-C-2 020 016, DE-A-2 816 300, DE-A-2 840 738 or FR-A-2 090 579 are described - leakage occurs when there is a change in temperature. The strict requirements that are placed, for example, on the reliability of ignition means that are to be used in airbags or in defense equipment, are difficult to meet with the known ignition elements.

The invention has for its object to make an electrical ignition element available, which does not have the disadvantages of the previously known constructions, is mechanically highly resilient and is sealed even after repeated thermal cycling. At the same time, a method for producing this ignition element is to be developed, which can be carried out comparatively easily without complex post-processing, but with great certainty with regard to the process products and their properties.

The solution to the problem is an electrical ignition element of the type mentioned, which is characterized in that the outer sleeve and the contact pins are connected gas-tight to the ceramic body by brazing or glazing.

Stainless steel, which can also be used as a material for the contact pins, has proven particularly useful as a material for the metallic outer sleeve. However, it is also possible to use other metallic materials for the metallic outer sleeve and / or the contact pins, for example aluminum, copper, nickel and their alloys, titanium, zirconium, tantalum and other heat-resistant and high-melting metals and alloys, especially those under the Description KOVAR known cobalt-nickel-iron alloy.

A wide variety of ceramic materials can be used as the material for the ceramic body, in particular those based on aluminum oxide, silicon dioxide, silicon nitride, silicon carbide and zirconium dioxide.

The tight and firm connection or edging between the metallic outer sleeve and the ceramic body on the one hand and between the ceramic body and the contact pins on the other hand takes place by brazing or by glazing. The materials known to any person skilled in the art, with which metallic materials and ceramic materials are tightly connected, can be used for the glazing. In this context, alkali and alkaline earth silicate glasses, glasses based on borosilicate and glasses containing rare earth oxides have proven particularly useful. A glass of the following composition can be used as an example of a glass which is suitable for this glazing connection between metallic and ceramic material:<tables id="tabl0001" num="0001"><img file="EP0248977B1_D0001.tif" /></tables>

However, it is also possible to use ceramic pastes, for example the pastes shown below in their composition:<tables id="tabl0002" num="0002"><img file="EP0248977B1_D0002.tif" /></tables>

Silicon or silicon alloys mixed with quartz powder, glass powder and clay can also be used to permanently bond the ceramic with the metallic materials.

The conductive layer applied in the form of a sheet around the contact pins is generally a thin or thick film layer applied in a customary manner, which has been produced, for example, by screen printing or by electroplating. The noble metals and noble metal alloys of group VIII of the periodic table, in particular platinum or palladium and their alloys also with silver and / or gold, have proven themselves as materials for this conductive layer.

The actual ignition bridge between the contact pins or the conductive layers enclosing them in the form of a surface can either be formed by a wire, as can be seen, for example, from FIG. 4, which will be explained in detail later. However, it has been shown that the application of the ignition bridge also has special advantages in screen printing technology; resistance ranges from 1 to 100 ohms can be achieved in this way. However, it is also possible to apply the ignition bridge as a thin film in an atomization process known per se or by vapor deposition in a vacuum. The wire-shaped ignition bridges are either soldered or welded on.

Precious metal materials, as already mentioned above, have also proven particularly useful as materials for these ignition bridges. These resistance bridges, which are specially applied using screen printing technology, have an already sharply defined resistance range after heat treatment, but if desired, it is possible to achieve resistance values ​​of even smaller fluctuation ranges by post-processing in the laser trimming method known to the person skilled in the art.

It is particularly advantageous when using screen printing technology to produce the ignition bridge that the ceramic body does not require any special pretreatment, but rather can be used directly with the roughness depth of N 5, for example, which occurs in production. In addition, screen printing technology is an easy-to-use process that also provides ignition bridges that are far more economical than mechanical wire bridges in terms of their mechanical resilience.

The invention is explained below with reference to the drawings.

Figure 1 shows in section the metallic outer sleeve 1 with the fitted ceramic body 2 in the form of a ceramic blank with here, for example, two contact pins 3. The ceramic body 2 is tightly connected to the metallic outer sleeve 1 on the one hand and the contact pins 3 on the other hand, by brazing or by blowing using the glasses or pastes given above as examples in their composition.

FIG. 2 shows a simplified top view of the ignition element of FIG. 1, only the contact pins 3 with the conductive layers 4 surrounding them in the form of a surface and the ignition bridge 5, which here, like the conductive layers 4, have been applied using the screen printing process, being shown for better clarity .

FIGS. 3 and 4 show a variant of the ignition element shown in FIGS. 1 and 2 according to the invention, in which the ignition bridge is formed by a wire 5a which establishes the conductive connection between the contact pins 3.

It is of course possible to use a larger number of contact pins in the ceramic body, in which case the corresponding larger number of ignition bridges must of course also be applied.

The method for producing the electrical ignition element according to the invention is characterized in that a ceramic body having one or more bores is fitted into a metallic, geometrically shaped outer ring and is connected to the metallic outer ring by brazing or glazing, whereupon the metallic contact pins are fitted into the bores of the ceramic body and are also connected to the ceramic body by brazing or glazing and then either wire-shaped ignition bridges between the contact pins are produced by soldering or welding, or preferably ignition bridges are produced by sputtering or vapor deposition technology in a vacuum or screen printing process.

Preferably, in the screen printing method, an electrically conductive layer is first applied in the form of a surface around the contact pins, and the connection between the contact pins and the ignition bridge is then established via this.

The ignition element with the ceramic body according to the invention is distinguished from the previously known embodiments in that, owing to the higher compressive strength of the ceramic materials, a far higher mechanical strength can be achieved than was possible with glass leadthroughs. In addition, the ceramic materials have a higher thermal conductivity than normal glasses, which has proven extremely favorable, for example, in the first-time production of 1A / 1W ignition elements. However, the prerequisite is that the outer sleeve and the contact pins have been connected to the ceramic body in a gastight manner by brazing or by glazing.