FR2605827A1 - PROTECTION OF AN ELECTRO-PYROTECHNIC DEVICE FROM ELECTROSTATIC DISCHARGES - Google Patents

Abstract

PROTECTION IS PROVIDED BY A SPARKLER 30 PROVIDING AT LEAST ONE BREAKDOWN BETWEEN EARTH AND EACH OF THE CONNECTION PINS 16, 18 ALLOWING THE ELECTRIC CURRENT SUPPLY OF A RESISTANT ELEMENT 10 PLACED IN CONTACT WITH A PYROTECHNIC COMPOSITION AND DESTINATION TO ALLOW THE FIRE OF IT BY JOULE EFFECT. THE SPARKLER IS CONSTITUTED BY AN INSULATING LAYER 44, 46 SHAPED BY THIN LAYER DEPOSIT OF AN INSULATING MATERIAL ON A CONDUCTIVE SUBSTRATE 32 CONNECTED TO EARTH, AND CONDUCTIVE LAYERS 48, 50 RESPECTIVELY CONNECTED TO THE CONNECTION PINS AND SHAPED IN DIFFERENT ZONES ON THE INSULATION LAYER TO PROVIDE BREAKDOWN ZONES 40, 42 BETWEEN THE SUBSTRATE AND EACH CONDUCTIVE LAYER.

Description

Protection of an electro-pyrotechnic device against

electrostatic discharges.

  The present invention relates to the protection of devices

  electro-pyrotechnic sitives vis-à-vis electrostatic discharges

ticks.

  In an electro-pyrotechnic device, the ignition of the pyrotechnic composition is produced by the heat released by the Joule effect by an initiation circuit comprising at least one resistant element placed in contact with the pyrotechnic composition

  and supplied with electric current by connection pins.

  It is imperative to protect such devices from

  electrostatic discharge screws to prevent improper ignition

  tempestive. Discharges between electrically connected points cause heat production by the Joule effect; We can

  guard against such aggression by using a compound

  pyrotechnic tion having a high auto-ignition temperature or by providing heat dissipation means. On the other hand,

  these protections are ineffective in the case of electro-

  static between electrically isolated points, when these discharges

  cause the formation of an arc within the pyro- composition

  technical. This is why the invention more particularly has for

  object the protection of electro-pyrotechnic devices from

  screw of electrostatic discharges between isolated points.

  To this end, it has been proposed to arrange preferential passages of the arc in an area remote from the pyrotechnic composition. Known solutions consist in connecting a pin of the initiation circuit to the ground of the system, or of interposing between a pin of the initiation circuit and the ground a relatively large resistance compared to that of the resistive element. It has also been suggested to use a thermoplastic or elastomer material made slightly conductive by the incorporation of conductive particles or balls and placed between the ground and the pins of the initiation circuit, or else to arrange small and large spark gaps.

  precision between the ground and the pins of the initiation circuit.

  Although effective, these known solutions have various drawbacks. The creation of resistive paths between the pins of the initiation circuit and the ground is often incompatible with the required isolation conditions. As for the small size and high precision spark gaps used, they are very expensive without always allowing a constancy of the breakdown value over time and in a surrounding medium.

  with varying characteristics.

  Thus, the object of the present invention is to provide

  a means of protection which can be easily integrated into the devices

  electro-pyrotechnic positive and allows at a relatively cost

  low to obtain a constant and invasive breakdown voltage

  reliable. This object is achieved by means of a spark gap protection device providing a breakdown zone at least between each connection pin and the ground, protection device in which, according to the invention, the spark gap comprises a substrate of which at least the surface layer is conductive and is grounded, an insulating layer in one or more parts formed on the substrate by depositing a thin layer of insulating material, -t conductive layers connected respectively to the connection pins and formed in zones different on the insulating layer to arrange said breakdown zones through the insulating layer between the substrate and, respectively, each of the

conductive layers.

  An important feature of the invention is

  in the production of the insulating layer by a deposition process.

  Any known deposition method can be used, in particular the methods of forming thin or thick layers in the field of manufacturing semiconductors and integrated circuits. AT

  As an indication, the insulating layer can be produced by evaporation.

  ration, spraying, ion bombardment, chemical or other deposit. The delimitation of the insulating layer or its possible machining are likewise carried out by any known method, for example

  by masking or by chemical or ionic etching.

  The formation of the insulating layer by layer deposition

thin brings several benefits.

  First, the breakdown voltage is easily adjustable on demand by adjusting the thickness of the deposit of the insulating layer. Furthermore, the spark gap is easily adaptable to all

  electro-pyrotechnic devices whatever the devices

  positions and the number of isolated points to protect.

  In addition, it turned out that the electrical characteristics

  spark gap remains unchanged after several sets of

  electrostatic discharges, and that the breakdown voltage is inde-

  depending on the pressure and the nature of the surrounding environment. This

  last point is particularly important in the case of

  electro-pyrotechnic sitives used during space flights or

in a partial vacuum.

  Other particularities and advantages of the pro-

  tection according to the invention will emerge on reading the description

  tion made below, for information but not limitation, in reference to

  Reference to the accompanying drawings in which: - Figure 1 is a schematic and partial sectional view of a first electropyrotechnic device provided with spark gap protection means according to the invention; - Figure 2 is a partial view on an enlarged scale and in section showing more particularly the protection means of Figure I;

  - Figure 3 is a partial top view of the exploded view

  the figure 2; - Figure 4 is a partial view on an enlarged scale and in section of another embodiment of a spark gap usable for the protection of an electro-pyrotechnic device of the type of that of Figure 1; - Figure 5 is a partial top view of the spark gap of Figure 4; - Figure 6 is a schematic and partial sectional view of a second electro-pyrotechnic device provided with protective means according to the invention; - Figure 7 is a top view on an enlarged scale and in section along the plane VII-VII of Figure 6; - Figure 8 is a partial view on an enlarged scale of the spark gap of Figure 7 in section along the plane VIII-VIII; and - Figure 9 is a schematic and partial sectional view showing an alternative mounting of the protection means in an electro-pyrotechnic device such as that of the

figure 6.

  Figure 1 shows an electro-pyrotechnic device which, in known manner, comprises a resistant element 10 in contact with a pyrotechnic composition 12 housed in an envelope

  cylindrical 14. Connection pins 16, 18 allow supply

  electrical indication of the resistant element 10 to cause the pyrotechnic composition to ignite by the heat released

by Joule effect.

  The connection pins 16, 18 pass through an insulating piece 20 to which they are sealed. The pins 16, 18 are connected to the resistant element 10 on the side of the insulating part in contact with the pyrotechnic composition 12 and protrude from the opposite side of the part 20 to be connected to a socket (not shown) allowing linking with a source

of electrical energy.

  The pyrotechnic composition 12 is housed in the cylindrical body 22 of the electro-pyrotechnic device by means of an antistatic skirt 24 which supports the casing 14 and which is itself held inside the body 22. The maintenance of the insulating part 20 is provided by a centering ring 26 also housed in the body 22. The rest of the electro-pyrotechnic device, in particular the lower part of the body 22 which may contain compositions

  specific ignition or detonation, is not shown.

  According to the invention, the protection of the device described above against electrostatic discharges between isolated points (between pins 16, 18 and the metallic mass of the

  device) is provided by a thin layer spark gap.

  In the example illustrated by FIGS. 1 to 3, the spark gap comprises a conductive metal substrate 32 which is placed on the insulating part 20 on the side of the latter opposite to the pyrotechnic composition 10. The substrate 32 is of annular shape and is carried by an internal shoulder 28 of the body 22 to which it is fixed, for example by welding, which ensures the connection of the substrate 32

  to the mechanical and electrical mass of the electro-pyrotechnic device

  fuck. It will be noted that the body 22 is formed in several parts: an upper part carrying the spark gap, an intermediate part

  carrying the skirt 24 and the ring 26 and a lower part containing

  mant the rest of the device, these different parts being assembled

butt welded.

  The annular substrate 32 is crossed by the pins 16, 18 and sufficient clearance is provided between the pins 16, 18 and the wall of the central passage of the substrate 32 so that the intervals between these parts cannot constitute paths

  preferential arcing in the event of electrostatic discharge.

  ? é0 ú Indeed, these preferential paths are constituted by breakdown zones 40, 42 arranged on the substrate 32 to provide protection against electrostatic attacks

  between ground and, respectively, pins 16, 18.

  Each breakdown zone is located within an insulating layer formed by a thin layer deposition of an insulating material on the conductive substrate 32. The insulating layer may be in a single part common to the two breakdown zones or, as in the example illustrated, in two parts 44, 46 formed in different zones of the surface of the substrate 32 (see in particular FIG. 3). Conductive layers, or electrodes 48, 50, are formed on the insulating layer or layers 44, 46 also by depositing a thin layer of a conductive material. The electrical connections between the electrodes 48, 50 and, respectively, the pins 16, 18 are provided by conductive filaments 52, 54 welded at one end to the electrodes 48, 50, respectively, and at the other end to conductive rings elastic 56, 58 enclosing

pins 16, 18, respectively.

  As already indicated, the insulating layers 44, 46 are deposited by any known method of deposition in a thin or thick layer used in the technology for manufacturing semiconductors and integrated circuits, for example by evaporation, sputtering, ion bombardment or chemical deposition. Likewise, the design of the insulating layer or layers is obtained by any known method of masking or etching. The formation of the conductive layers 48, 50 on the insulating layers 44, 46 is also carried out by any process.

  known deposit of thin or thick conductive layers.

  The production of the insulating layer or layers 44, 46 by a thin layer deposition technique makes it possible to precisely adjust the breakdown voltage by adjusting the thickness of the deposited insulating layer. By way of example, layers of silicon dioxide with a thickness equal to 2.5 microns made it possible to obtain breakdown voltages of approximately 800 V. In addition to the ease and precision of voltage regulation breakdown device, the protection device seloh the invention has other advantages. It is first of all quite apparent that its integration into the electro-pyrotechnic device is easy to carry out. In addition, not only can a precise breakdown voltage be obtained, but this breakdown voltage retains its value after several series of electrostatic discharges and

  despite modifications to the environment of the device (notably

  pressure and nature of the surrounding environment).

  Of course, different embodiments of the dis-

  positive protection of Figures 1 to 3 may be considered.

  Thus, the breakdown zones can be formed on any face of the substrate 32. Furthermore, it is possible to use for the spark gap an insulating substrate, for example the insulating part.

  itself, on which is deposited a metallic layer conduc-

  connected to the mechanical and electrical mass of the device

  Electro-pyrotechnics. The insulating layer (s) and the electr

  conductive trodes defining the breakdown zones are then

  formed on this surface metal layer.

  Another variant of the spark gap is

  illustrated by figures 4 and 5. The common elements with the dis-

  positive of Figures 1 to 3 bear the same references.

  In this embodiment, the breakdown zones are arranged on the face of the substrate 32 facing the insulating part 20. Each breakdown zone, for example 40 ′, is formed by a thin insulating layer 44 ′ deposited on the conductive substrate 32 and

  a conductive layer or electrode 48 'deposited on the layer 44'.

  The electrical connection between the electrode 48 'and the pin 16 is made by a metallic coating 52' deposited on the insulating part 20 and forming a conductive path between the area of

  the part 20 which comes into contact with the electrode 46 'and a metal-

  Bearing 56 'of the hole 16a formed in the insulating part 20 for the passage of the pin 16. As shown in FIG. 4, the covering 52' can be formed in a countersink of the insulating part 20. The surface of the covering 52 'is polished at the same time as that of the part 20 so as to be in the same plane and not to have any roughness liable to damage the insulating layer 44 '. The electrical contact between the pin 16 and the metallization 56 'is ensured by the sealing of the pin in the hole 16a. The electrical contact between the electrode 48 'and the coating 52' is ensured by the pressure exerted on the mounting of the device between the skirt 24, which is supported by its lower edge on the underside of the envelope 14 of the pyrotechnic composition 12, and the shoulder 28 which rests on the upper face of the substrate 32. The permanence of this pressure contact can be ensured by elastic means, for example an elastomer layer 28a interposed between the shoulder

28 and the substrate 32.

  We have considered above the case of an electro-

  pyrotechnic including a single resistant element. The invention is similarly applicable to electro-pyrotechnic devices

  comprising, for reasons of redundancy, two resis-

  aunts. Such a device with two resistant elements is illustrated

by Figures 6 and 8.

  In the same way as in the device of FIG. 1,

  each resistant element 110, 111 is located in contact with a

  pyrotechnic position 112 housed in a cylindrical enclosure 7--

  114. Connection pins 116, 118 are provided for the power supply.

  tation of the resistive element 110, as well as

  pins 117, 119 for supplying the resistive element 111.

  Electrical energy is supplied via a connector 101 fixed laterally to the upper part of the body 122 of the electro-pyrotechnic device. The circuits 116-110-118 and 117-111-119 are connected in parallel on the terminals 102 and 103 on connector 101, the connections between the pins 116 to 119 and the terminals 102, 103 being produced by flexible conductors 104 to 107 The pins 116 to 119 pass through an insulating part 120 to which they are sealed and which is placed in contact with the pyrotechnic composition 112. Maintaining this composition 112 and the insulating part 120 in the body 122 of the electro-pyrotechnic device is ensured by means of an antistatic skirt 124 and a ring 126, as in the embodiment of 'a

figure 1.

  According to the invention, the protection of the device described above against electrostatic discharges is ensured by means of a thin layer spark gap. In the example illustrated, the spark gap 130 provides six breakdown zones between the connection pins and the mass of the device, as well as between connection pins connected to different resistant elements. It should be noted that three breakdown zones could be sufficient due to the parallel connection of the connection pins. The choice of six different breakdown areas is

dictated here for the sake of redundancy.

  The spark gap 130 shown in FIGS. 6 to 8 comprises a metallic annular substrate 132 placed on the insulating part 120 and crossed by the pins 116 to 119. The conductive substrate 132 is fixed by welding to an internal shoulder 128 of the body 122, this which ensures its connection to the mechanical and electrical ground of the device. Breakdown zones 140, 141, 142, 143 between the mass and, respectively, the pins 116, 117, 118 and 119 are formed on the substrate 132. For this purpose, the latter is coated with an insulating layer 144 formed by a thin layer deposition of an insulating material. Conductive layers or electrodes 148, 149, 150, 151 are formed by depositing a thin layer of a conductive material on the insulating layer 144 in different zones distributed around the periphery of the spark gap (see in particular FIG. 8). Conductive filaments 152, 153, 154, 155 connect the electrodes 148 to 151 respectively to elastic conductive rings 156, 157, 158,

  159 enclosing pins 116 to 119. Note that the iso- layer

  lante 144 may be formed into several separate parts bearing

  each one a particular electrode.

  Two additional breakdown zones 240 and 242 are

  formed on spark gap 130 to protect against electrical attack

  trostatic between connection pins 116 and 117 respectively and between connection pins 118 and 119, i.e.

  between pins connected to different resistive elements.

  The breakdown zones 240, 242 are arranged by forming insulating layers 244, 246 by depositing a thin layer of insulating material on the electrodes 148, 150 connected to the pins 116, 118. Conductive layers, or electrodes, 249, 251 are formed on the insulating layers 244, 246 by depositing a thin layer of a conductive material. The electrodes 249, 251 are electrically connected to the pins 117, 119. For this purpose, it is possible to use conductive filaments connecting the electrodes 249, 251 respectively to the rings 157, 159. Another solution consists, as in the example illustrated, in extending the conductive layers 249, 251 until at least partially covering the electrodes 149, 151. The conductive filaments 153 and 155 which provide the connection

  with pins 118 and 120 can then be soldered to the elec

trodes 249, 251.

  As a variant, the additional breakdown zones between connection pins could be formed on the electrodes 149,

  151 instead of being on electrodes 148, 150.

  FIG. 9 finally illustrates another mounting of a protection device according to the invention for a device

  electro-pyrotechnic with two insulating elements.

  The device of FIG. 9 differs from that of FIGS. 6 to 8 essentially in that the spark gap 130 ′ constitutes a cover closing the body 122 at its upper end. The metal substrate 132 'is connected to the mechanical and electrical ground, for example by screwing onto the body 122, while the breakdown zones are arranged on the underside of the substrate 132'. For the rest, the spark gap is identical to that

  described with reference to Figures 6 to 8.

  Of course, other provisions of the spark gap in the electro-pyrotechnic device could be adopted insofar as they contribute to creating breakdown areas

  distant from the pyrotechnic composition.

Claims (6)

  1. Protection device against electric discharges   three of an electro-pyrotechnic device comprising a component   pyrotechnic sition (12; 112), at least one resistant element (10; 110) adjacent to the pyrotechnic composition and connection pins (16, 18; 116, 117, 118, 119) connected to the element   resistant, to allow the ignition of the pyro-   technique by the heat given off by the Joule effect by the resistant element when it is supplied with electric current via the connection pins, said protection device comprising at least one spark gap (30; 130) providing at least one zone of breakdown between each connection pin and the ground of the electropyrotechnic device and being characterized in that: the spark gap (30; 130) comprises a substrate (32; 132) of which at least the surface layer is conductive and is connected to ground, an insulating layer (44, 46; 44 ', 144) in one or more parts formed on the substrate by depositing a thin layer of an insulating material, and conductive layers (48, 50; 48', 50 '; 148, 149, 150, 151) connected respectively to the connection pins (16, 18; 116, 117, 118, 119) and formed in different zones on the insulating layer to provide breakdown zones (40, 42;, 141, 142 , 143) between the substrate and, respectively, each conductive layers.   2. Protective device according to claim 1, characterized in that the electrical connection between a connection pin (16, 18; 116, 117, 118, 119) and the corresponding conductive part of the spark gap (30; 130) is produced by means of a conductor (52, 54; 152, 153, 154, 155) welded to said conductive part and to a conductive ring (56, 58; 156, 157, 158,   159) enclosing the connection pin.   3. Protective device according to claim 1, characterized in that the electrical connection between a pin of   connection (16) and the corresponding conductive part of the screen   tor is produced by means of a conductive deposit (52 ′, 56 ′) which is formed on an insulating piece (20) through which the connection pin passes and which is in contact with the connection pin and with   the corresponding conductive part of the spark gap.   4. Device according to any one of the claims   above, for the protection of an electro-pyrotechnic system comprising two resistant elements (110, 111), each connected to two connection pins, characterized in that the spark gap (130) also provides at least one additional breakdown zone (240, 242) between a connection pin (116, 118) connected to one of the resistive elements and a connection pin (117, 119) connected to   the other resistant element, the or each additional breakdown zone   being closed by two conductive parts (148-249, 150-   251) connected respectively to the corresponding connection pins   dantes (116-117, 118-119) and an insulating part (244, 246) which is interposed between the conductive parts and which is formed by depositing an insulating material in a thin layer on one of these conductive parts.   5. Device according to claim 4, characterized in that the spark gap comprises a common substrate (132), a first insulating layer (144) formed on the substrate in one or more parts, first conductive layers (148-151) formed different zones on the first insulating layer for arranging first breakdown zones (140-143) between the substrate and, respectively, each first conductive layer, a second insulating layer (244, 246) formed by deposition in thin layer on one at less first conductive layers, and a second conductive layer (249, 251) formed on the second insulating layer to provide at least a second breakdown zone (240, 242) between a first and a second conductive layer, the latter being electrically connected respectively to a connection pin of a resistant element and a connection pin of the other resistant element.   6. Device according to any one of the claims   previous, characterized in that the spark gap (30; 130) and the or each resistant element (10; 110, 111) are arranged on two opposite sides of an insulating piece (20; 120) which, like   the spark gap, is crossed by the connection pins.