GB2123122A - Explosive devices - Google Patents

Abstract

A microelectronic circuit package contains explosive material 8 and a microelectronic circuit 6 including a fusible resistor 9 adjacent the material. The resistor may be a thin film element and may form part of an integrated circuit. The package is shielded by a housing 1 and a cover 2 and is preferably arranged so that the resistor can be vaporised using low power on the application of predetermined signals to the circuit, preferably by way of terminal pins 3 extending from the housing. Uses include warheads and demolition charges. <IMAGE>

Description

SPECIFICATION Explosive devices The present invention relates to explosive devices and in particular the initiation of explosives.

Although the invention may have a more general utility, one aspect of it is concerned with a device which in a practical form needs very little energy for the initiation of explosion and yet can readily be made adequately insensitive to stray radio frequency fields.

According to one aspect of the invention, a shielded microelectronic package contains a microelectronic circuit which includes or is in connection with a miniature resistor disposed adjacent explosive material within the package, the resistor being heated to fusion to initiate explosion of the material within the package on the reception of predetermined signals by the microelectronic circuit.

According to another aspect of the invention, an explosive device comprises a shielded package containing explosive material and a substrate bearing a microelectronic circuit adapted to respond to predetermined electrical signals to heat an element disposed on the substrate so as to initiate explosion of the explosive material within the package. The said element may comprise a fusible link which may be constituted by a thin film resistor or a fusible link of the kind which may be employed in programmable read only memories.

The term "miniature resistor" used herein is intended to refer to a resistor which may be fused by the application of a driving current from a microelectronic circuit and in particular a resistor which can be supplied with sufficient energy required to vaporise the resistor and effect initiation of an explosion from a microelectronic circuit which requires a supply voltage of not more than 10 volts.

One benefit of the invention in a preferred form is the facility of incorporating the resistor and its driving circuit in one monolithic integrsted circuit. Moreover, in practice the driving circuit and the resistor or other element can be incorporated in a metallic enclosure, providing the shielding for the package, together with the explosive or pyrotechnic compound.

It is in general feasible to use as the explosive material a comparatively insensitive material, such as TNT or RDX without requiring a more sensitive compound for the purpose of detonation. It may also be feasible to eliminate the necessity for a shutter and safety and arming unit.

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a simplified sectional view of a microelectronic package; and Figure 2 is a diagram of a circuit which may form part of the package shown in Fig.

1.

The device illustrated in Fig. 1 comprises an electrically conductive (preferably metallic) housing 1 which has a cover 2 to form a shielded enclosure. The size of the enclosure may, for example, be similar to that of the "can" of a transistor of T05 size. The housing 1 is pierced by connection pins 3 which constitute electrical terminals for a microelectronic circuit within the package. The pins pass into the interior of the package through apertures which are sealed with an appropriate glass-to-metal seal 4. Within the enclosure is a substrate, preferably a single substrate 5 on which is formed a microelectronic circuit of which one example is given in Fig. 2. The circuit 6 is supported in position by a suitable potting compound 7. Between the substrate 5 and the cover 2 is an explosive compound 8 preferably of the type herein before specified.

The circuit includes or is connected to a fusible element 9 which may be a thin film resistor but might also be a resistor of the kind used as a fusible link in a programmable read only memory. Such a resistor is typically four micrometers by ten micrometers by three hundred and fifty angstroms thick and has a very small thermal mass. Typically such a resistor has a fusion temperature in the region of 1400"C. If a thin film resistor on a glass substrate is used, a typical set of dimensions for the resistor would be one hundred and twenty micrometers by one hundred and twenty micrometers by two hundred angstroms thick, the thin film resistor being thinner but of larger area than the kind of resistor used as a fusible linkage for programmable read only memories.If possible, it is convenient to incorporate the resistor as part of an integrated circuit formed on the substrate. It will be appreciated that the resistors of the kind which are preferred for use in the present invention may be much smaller than the wires used in wire type low energy fuse heads; such wires are typically 6.4 micrometers in diameter and 400 micrometers long.

The resistor is in thermally close contact with the explosive material. The resistor is heated so that it vaporises to initiate detonation of the explosive, by the application of electrical power. This may be applied deliberately by means of a suitably protected circuit of which Fig. 2 is a simple example.

The ingress of RF energy which might cause the explosive to detonate prematurely is reduced by the use of an electrically conductive housing and preferably also by the appropriate routing of electrical paths within the housing so as to minimise the effective area enclosed by these paths. This is intended to ensure that the coupling of the electrical paths with an external magnetic field is not hazard ous in the sense of causing detonation.

Fig. 2 is a diagram of a simple electrical circuit including a thin film resistor constituting the heating element for the initiation of explosion. The resistor is connected between the collectors of two transistors T1 and T2 which are connected to four exposed terminals (preferably constituted by pins as described with reference to Fig. 1) such that current will flow in the transistors only if particular conditions exist at the external terminals.

In particular, the terminal 11 is connected by way of a diode 1 5 to the emitter of transistor T2 by way of a resistor 1 6 and to the base of said transistor by way of a resistor 1 7. The base of this transistor is connected by way of a resistor 18 and a diode 1 9 to the terminal 1 3. The terminal 1 2 is connected by way of diode 20 to the base of a transistor T3 by way of resistor 21 and to the emitter of that transistor by way of resistor 22, the base of the transistor being connected by way of resistor 23 to the diode 1 9. The emitter of transistor T3 is connected by way of diode 24 to the base of transistor T1.The base of this transistor is connected to the emitter by way of resistor 25, the emitter being connected to terminal 14 directly. Resistor 23 connects the emitter of transistor T, to the collector of transistor T2.

The particular circuit details are not important. However, in the circuit of Fig. 2 an electric current may flow in transistors T and T2 only if terminals 11 and 1 2 are at a significant positive level with respect to terminal 14 and terminal 1 3 is at or close to the potential of terminal 14. If transistors T1 and T2 are conducting then current will flow through the resistor 9 and so bring about the local heating of the resistor and consequent detonation of the explosive.

Terminal 11 in effect represents an inhibit and antiphase signals are required at terminals 1 2 and 1 3. This set of conditions makes accidental detonation particularly unlikely. Voltage thresholds may be included at terminals 11, 12 and 13 if desired.

The simple circuit shown in Fig. 2 may be modified or augmented in various ways. Some of these ways concern more advanced forms of protection, for example the introduction of digital circuitry to ensure that the circuit will respond only to signals having a correct phase relationship. However, one of the advantages of employing the microelectronic techniques characteristic of the present invention is the facility of including a microprocessor as part of the initiating circuit to provide a unique identity for each initiator. Thus a plurality of initiators may be used in a large assembly and incorporation of a microprocessor facilitates the control or sequence of operation of several parallel initiators whereby the characteristics of a warhead or demolition charge may be controlled or varied.

Claims (8)

1. A shielded package containing a microelectronic circuit which includes a miniature resistor disposed closely adjacent explosive material within the package, the resistor being heated to fusion to detonate the said material.

on the reception of predetermined signals by the circuit;

2. An explosive device comprising a shielded microelectronic package containing explosive material and a substrate bearing a microelectronic circuit adapted to respond to predetermined electrical signals to heat an element disposed on the substrate such as to detonate the explosive material.

3. A device according to claim 2 wherein the element comprises a fusible link.

4. A device according to claim 2 or claim 3 wherein the element comprises a thin film resistor.

5. A package or device according to any foregoing claim in which the circuit and the resistor or element constitute a monolithic integrated circuit.

6. A device or package according to any foregoing claim in which the package comprises a conductive housing constituting an RF shield.

7. A device or package substantially as hereinbefore described with reference to Fig.

1 of the accompanying drawings.

8. A device or package substantially as hereinbefore described with reference to Figs.

1 and 2 of the accompanying drawings.