Patent Publication Number: US-7581496-B2

Title: Exploding foil initiator chip with non-planar switching capabilities

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/852,108 filed Oct. 16, 2006, the disclosure of which is hereby incorporated by reference as if fully set forth in detail herein. 

   INTRODUCTION 
   The present disclosure generally relates to detonators and initiation firesets (hereinafter referred to as “initiators”) for initiating an event, such as a combustion, deflagration or detonation event, in an associated charge and more particularly to an exploding foil initiator chip having integrated switching capabilities to provide multiple mode functionality. 
   Initiators utilizing exploding foil initiator (EFI) chips are well known in the art. Briefly, (EFI) chips include a substrate chip (typically a ceramic) onto which a bridge is mounted. The bridge is connected to a power source through two conductive lands or pads or in the alternative a low inductance connection. In a system wherein operation of the exploding foil initiator is initiated by an external trigger (i.e., standard mode operation), the power source can typically be a capacitor whose discharge is governed by a high voltage switch. When the switch closes, the capacitor provides sufficient electric current to convert the bridge from a solid state to a plasma. The pressure of the plasma drives a flyer into contact with an explosive charge, thereby generating a shock wave that can be employed to initiate a desired event (e.g., detonation, deflagration or combustion). 
   Where one or more other modes of operation are desired, it is known in the art to couple the bridge to one or more discrete switch devices. While the discrete switch devices are effective for their intended purpose, it is understood in the art that such discrete switch devices can be both costly and difficult to package into a desired application due to their relative weight, size and spacing. 
   Accordingly, it would be desirable to provide an initiator having multiple mode triggering functionality in manner that is relatively inexpensive, lightweight and compact. 
   SUMMARY 
   In one form, the present teachings provide an initiator that includes a substrate, an exploding foil initiator and a first switch. The exploding foil initiator coupled to the substrate and includes a conductive bridge and a first bridge contact. The first switch has a first contact and a first insulator. The first contact is coupled to the substrate and spaced apart from the first bridge contact by a gap. The first insulator is disposed in the gap. The first switch is operable in an actuated mode in which electrical energy transmitted between the first contact and the first bridge contact is transmitted through the first insulator. 
   In another form, the present teachings provide a method that includes: providing an initiator having an exploding foil initiator and a first switch, the exploding foil initiator including a substrate and a bridge that is coupled to the substrate, the bridge including a first bridge contact, the switch including a first contact, which is spaced apart from the first bridge contact by a predetermined distance, and a first insulator that is received in the first gap; applying electrical energy to the first contact; and directing electrical energy from the first contact through the first insulator to the first bridge contact to thereby actuate the exploding foil initiator. 
   Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       FIG. 1  is a schematic plan view of a detonator constructed in accordance with the teachings of the present disclosure; 
       FIG. 2  is a top plan view of the initiator of  FIG. 1 ; 
       FIG. 3  is a sectional view taken along the line  3 - 3  of  FIG. 2 ; 
       FIG. 4  is a sectional view taken along the line  4 - 4  of  FIG. 2 ; 
       FIGS. 5 through 8  are a top plan views of portions of the initiator of  FIG. 1  illustrating a process for fabricating an initiator in accordance with the teachings of the present disclosure; 
       FIG. 9  is a top plan view of a second initiator constructed in accordance with the teachings of the present disclosure; 
       FIG. 10  is a sectional view taken along the line  10 - 10  of  FIG. 9 ; 
       FIG. 11  is a top plan view of a third initiator constructed in accordance with the teachings of the present disclosure; and 
       FIG. 12  is a sectional view taken along the line  12 - 12  of  FIG. 11 . 
   

   DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS 
   With reference to  FIG. 1  of the drawings, an initiator constructed in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . The initiator  10  can be housed in a hermetically-sealed housing  12  and can be selectively coupled to a source of electrical energy  14  via a plurality of leads or terminals  16 . The initiator  10  can be employed to initiate a detonation event in an appropriate energetic material  18 , such as a primary explosive (e.g., mercury fulminate, lead styphnate or lead azide) or a secondary explosive (e.g., pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), trinitrotoluene (TNT) or hexanitro stilbene (HNS), RSI-007, which is available from Reynolds Systems, Inc. of Middletown, Calif.). 
   With additional reference to  FIG. 2 , the initiator  10  can include a substrate  20 , an exploding foil initiator  24 , a first switch  26  and a second switch  28 . The substrate  20  can be formed of an electrically insulating material, such as ceramic, glass, polyimide or silicon, and can define a surface  20 ′ onto which other components of the initiator  10  can be layered. 
   With reference to  FIGS. 2 through 4 , the exploding foil initiator  24  can include a first bridge contact  30 , a second bridge contact  32 , a bridge  34 , a flyer  36 , and a barrel  38 . The first and second bridge contacts  30  and  32  and the bridge  34  can be formed of an electrically conductive material, such as but not limited to nickel, copper, gold, silver, aluminum and alloys thereof, and can be formed by one or more discrete layers of material. The first and second bridge contacts  30  and  32  and the bridge  34  can be fixedly coupled to the surface  20 ′ of the substrate  20  via any appropriate process, such as metallization. The flyer  36  can be formed of an electrically insulating material, such as polyimide, and can be located in-line with the bridge  34 . The barrel  38  can be formed of an electrically insulating material, such as a polyimide film, can be coupled to the substrate  20  and can define a barrel aperture  38 ′ that can be disposed in-line with both the flyer  36  and the bridge  34 . As will be appreciated by those of ordinary skill in the art, the barrel aperture  38 ′ provides a path along which the flyer  36  may be directed toward an energetic material  18  ( FIG. 1 ) to initiate a reaction in the energetic material. 
   The first switch  26  can include a first insulator  40  and a first switch terminal  42 . The first insulator  40  can be formed of an appropriate electrically insulating material, such as polyimide, and can be layered or bonded onto the first bridge contact  30 . The first switch terminal  42  can be formed of an electrically conductive material, such as but not limited to nickel, copper, gold, silver, aluminum and alloys thereof and can be formed by one or more discrete layers of material. The first switch terminal  42  can be fixedly coupled to the first insulator  40  on a side thereof opposite the first bridge contact  30 . The first switch terminal  42  can be formed in any appropriate process, such as metallization. 
   Similarly, the second switch  28  can include a second insulator  50  and a second switch terminal  52 . The second insulator  50  can be formed of an appropriate electrically insulating material, such as polyimide, and can be layered or bonded onto the second bridge contact  32 . The second switch terminal  52  can be formed of an electrically conductive material, such as but not limited to nickel, copper, gold, silver, aluminum and alloys thereof and can be formed by one or more discrete layers of material. The second switch terminal  52  can be fixedly coupled to the second insulator  50  on a side thereof opposite the second bridge contact  32 . The second switch terminal  52  can be formed in any appropriate process, such as metallization. 
   As will be appreciated, the initiator  10  can be operated in several different modes, including a standard mode, a first breakdown mode, and a second breakdown mode. 
   Operation of the initiator  10  in the standard mode can entail the transmission of electrical energy from an appropriate source of electrical energy  14  ( FIG. 1 ) to the first bridge contact  30 , through the bridge  34  to the second bridge contact  32  and thereafter to an electrical ground. Operation of the initiator  10  in the standard mode may be initiated through an external trigger to thereby electrically couple the bridge  34  to the energy source, which can be a capacitor (not shown) whose discharge is governed by a high voltage switch (not shown). Energy transmitted from the energy source to the bridge  34  is employed to convert the bridge  34  from a solid state to a plasma state. The transformation of the bridge  34  to a plasma state generates pressure that is sufficient to propel the flyer  36  and strike the flyer  36  through the barrel  38  so that it may impact an energetic material  18  ( FIG. 1 ) and generate a shock wave within the energetic material to initiate a desired reaction. It will be appreciated that no energy is transmitted through the first or second switches  26  and  28  when the initiator  10  is operated in the standard mode. 
   In the first breakdown mode the second bridge contact  32  can be coupled to an electrical ground, while the first switch terminal  42  can be coupled to a source of electrical energy. Electricity can be transmitted through the first insulator  40  in a direction that can be generally perpendicular to the surface  20 ′ of the substrate  20  when a sufficiently large electric potential is applied to the first switch terminal  42  to thereby supply energy to the bridge  34 . It will be appreciated that the electricity may or may not follow a path through the first insulator  40  that is generally perpendicular to the surface  20 ′ of the substrate  20  but rather that the electricity can pass vertically through the layers that are deposited onto the surface  20 ′. 
   In the second breakdown mode the first bridge contact  30  can be coupled to an electrical ground, while the second switch terminal  52  can be coupled to a source of electrical energy. Electricity can be transmitted through the second insulator  50  in a direction that can be generally perpendicular to the surface  20 ′ of the substrate  20  when a sufficiently large electric potential is applied to the second switch terminal  52  to thereby supply energy to the bridge  34 . It will be appreciated that the electricity may or may not follow a path through the second insulator  50  that is generally perpendicular to the surface  20 ′ of the substrate  20  but rather that the electricity can pass vertically through the layers that are deposited onto the surface  20 ′. 
   In some instances it can be desirable for the first and second switches  26  and  28  to be identically configured. It may be desirable in other situations to configure the first and second switches  26  and  28  differently from one another. For example, the first and second insulators  40  and  50  can be formed of the same insulating material but have different thicknesses so that the magnitude of the electric potential that is needed to pass energy through the first switch  26  is different from the magnitude of the electric potential that is needed to pass energy through the second switch  28 . 
   As those of ordinary skill in the art will appreciate from this disclosure, the transmission of electrical energy between a switch (e.g., the first switch  26 ) and an associated bridge contact (e.g., the first bridge contact  30 ) in a vertical direction through one or more dielectric layers has numerous advantages. For example, an initiator constructed in accordance with the teachings of the present disclosure can have significant levels of functionality (e.g., switching modes) while being packaged in a relatively small volume. Furthermore, as the various terminals and contacts can be sealed between one or more layers of an insulating material, the switches are not affected by foreign particles. Moreover, the insulation of the terminals and contacts can facilitate the transmission of energy having a relatively high electric potential while the terminals and contacts are in relatively close proximity without concern that the electric energy will be inadvertently misdirected (i.e., jump) between the terminals and/or switches. 
   With reference to  FIGS. 2 and 5  through  7 , a process for forming an initiator  10  in accordance with the teachings of the present disclosure is provided. With specific reference to  FIG. 5 , the first and second bridge contacts  30  and  32  and the bridge  34  can be coupled to the surface  24  of the substrate  20  to form a first subassembly  100 . A first mask (not shown) can be employed to define a first predetermined area over which the first and second bridge contacts  30  and  32  and the bridge  34  extend. The first and second bridge contacts  30  and  32  and the bridge  34  can be applied to this predefined area in a desired manner, such as through metallization. Alternatively, one or more layers of metal may be applied to the surface  20 ′ of the substrate  20 , a first mask (not shown) may be employed to apply a “resist” to the layer of metal and the portions of the layer of metal that are not coated by the resist may be removed in an etching process in a manner that is similar to the formation of a printed circuit board. The resist may be subsequently removed or may be employed to form the first layer of insulating material  102  ( FIG. 6 ) described below. 
   With specific reference to  FIG. 6 , a first layer of insulating material  102  can be applied to a second predefined area over a desired portion of the first subassembly  100  ( FIG. 5 ) to thereby form a second subassembly  104 . In the particular example provided, portions of the first and second bridge contacts  30  and  32  are not covered to facilitate the electrical connection of the exploding foil initiator  24  ( FIG. 2 ) to one or more external devices (not shown). A mask (not shown) of the type that is employed in the formation of a printed circuit board can be employed to control the deposition of insulating material onto the first subassembly  100  ( FIG. 5 ). 
   With specific reference to  FIG. 7 , a second layer of insulating material  106  can be applied to a third predefined area over a desired portion of the second subassembly  104  ( FIG. 6 ) to thereby form a third subassembly  108 . In the particular example provided the flyer  36  ( FIG. 2 ) is relatively thicker than the first and second insulators  40  and  50  ( FIG. 3 ) and as such, the insulating material  106  is deposited over the bridge  34  to ensure that the flyer  36  ( FIG. 2 ) is formed to a desired thickness. A mask (not shown) of the type that is employed in the formation of a printed circuit board can be employed to control the deposition of insulating material onto the second subassembly  104  ( FIG. 6 ). 
   With specific reference to  FIG. 8 , the first and second switch terminals  42  and  52  can be coupled to the third subassembly  108  ( FIG. 7 ) to thereby form a fourth subassembly  110 . A mask (not shown) can be employed to define a fourth predetermined area over which various elements, including the first and second switch terminals  42  and  52  are to extend. The first and second switch terminals  42  and  52  can be applied to this predefined area in a desired manner, such as through metallization. Alternatively, one or more layers of metal may be applied over the third subassembly  108  ( FIG. 7 ), a mask (not shown) may be employed to apply a “resist” to the layer of metal and the portions of the layer of metal that are not coated by the resist may be removed in an etching process in a manner that is similar to the formation of a printed circuit board. The resist may be subsequently removed or may be employed to form the third layer of insulating material  60  described below. 
   With reference to  FIG. 2 , a third layer of insulating material  60  can be applied to a fifth predetermined area to thereby cover portions of the first and second switch terminals  42  and  52 . In the particular example provided, portions of the first and second bridge contacts  30  and  32  and the first and second switch terminals  42  and  52  are not covered to facilitate the electrical connection of the exploding foil initiator  24 , the first switch  26  and/or the second switch  28  to one or more external devices (not shown). A mask (not shown) of the type that is employed in the formation of a printed circuit board can be employed to control the deposition of insulating material onto the fifth subassembly. It will be appreciated that each of the above-described layers of insulating materials may be deposited in one or more discrete layers (i.e., sub-layers) and that the individual layers need not be of equal thicknesses. Moreover, while the individual layers are formed of the same material in the particular example provided, it will be appreciated that one or more of the individual layers (or sub-layers) may be formed of a material that differs from another of the individual layers (or sub-layers). 
   With reference to  FIGS. 8 and 9 , a second initiator constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   a . The initiator  10   a  can be generally similar to the initiator  10  of  FIG. 1  except as noted below. The first switch terminal  42   a  can be mounted onto the surface  20 ′ of the substrate  20  and can be spaced apart from the first bridge contact  30   a  by a first gap  200 . Similarly, the second switch terminal  52   a  can be mounted onto the surface  20 ′ of the substrate  20  and can be spaced apart from the second bridge contact  32   a  by a second gap  202 . One or more layers of insulation  210  can be applied over the first and second bridge contacts  30   a  and  32   a , the bridge  34  and the first and second switch terminals  42   a  and  52   a  such that the insulation  210  can be received in the first and second gaps  200  and  202 . First and second trigger contacts  214  and  216 , respectively, can be layered over the insulation  210 . In the example provided the first and second trigger contacts  214  and  216  are generally similar and as such, only the first trigger contact  214  will be discussed in detail herein. The first trigger contact  214  can include a terminal portion  220 , which can be adapted to be coupled to a source of electrical energy (not shown) and a projection  222 . The projection  222  can extend from the terminal portion  220  and can overlie the insulation  210  over the first gap  200 . Optionally, the projection  222  can also overlie portions of the first bridge contact  30   a  and/or the first switch terminal  42   a.    
   In operation, the initiator  10   a  can be employed in a breakdown mode or a trigger mode. In the breakdown mode, the second bridge contact  32   a  can be electrically coupled to an electrical ground and the first switch terminal  42   a  can be electrically coupled to a source of electric power having an electric potential that is sufficient to transmit electric energy through the insulation  210  that is disposed in the first gap  200 . 
   In the trigger mode, the second bridge contact  32   a  can be electrically coupled to an electrical ground, the first switch terminal  42   a  can be electrically coupled to a source of electric power having an electric potential that is not sufficient (by itself) to transmit electric energy through the insulation  210  that is disposed in the first gap  200 , and the terminal portion  220  of the first trigger contact  214  can be selectively coupled to a voltage source. Application of electric power to the terminal portion  220  can affect the field about the first gap  200  to effectively lower the electric potential that is necessary to cause energy to be transmitted through the insulation  210  and across the first gap  200  (i.e., so that the electric potential of the energy applied to the first switch terminal  42   a  is sufficient to transmit electric energy through the insulation  210  and across the first gap  200 ). 
   In an alternative trigger mode, the second bridge contact  32   a  can be electrically coupled to an electrical ground, the first switch terminal  42   a  can be electrically coupled to a source of electric power having an electric potential that is not sufficient (by itself) to transmit electric energy through the insulation  210  that is disposed in the first and second gaps  200  and  202 , and the terminal portion  220  of the second trigger contact  216  can be selectively coupled to a voltage source. Application of electric power to the terminal portion  220  of the second trigger contact  216  can affect the field about the second gap  202  to effectively lower the electric potential that is necessary to cause energy to be transmitted through the insulation  210  and across the first and second gaps  200  and  202  (i.e., so that the electric potential of the energy applied to the first switch terminal  42   a  is sufficient to transmit electric energy through the insulation  210  and across the first and second gaps  200  and  202 ). 
   With reference to  FIGS. 10 and 11 , a third initiator constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   b . The initiator  10   b  can be generally similar to the initiator  10  of  FIG. 1  except that a trigger contact  214   b  has been substituted for the second switch  28  ( FIG. 2 ). The trigger contact  214   b  can be formed of a conductive material, such as but not limited to nickel, copper, gold, silver, aluminum and alloys thereof, and can be formed by one or more discrete layers conductive material. The trigger contact  214   b  can be disposed vertically between two or more discrete layers ( 52   b   1 ,  52   b   2 ) of insulating material  52   b  between the first bridge contact  30  and the first switch terminal  42 . The trigger contact  214   b  can include a terminal portion  220   b , which can be adapted to be coupled to a source of electrical energy (not shown) and a projection  222   b . The projection  222   b  can extend from the terminal portion  220   b  and can be disposed vertically between the first bridge contact  30  and the first switch terminal  42 . In the particular example provided, the first bridge contact  30  is coupled to the surface  20 ′ of the substrate  20 , a first layer of insulating material  52   b   1  is deposited over the first bridge contact  30 , the trigger contact  214   b  is coupled to the first layer of insulating material  52   b   1  on a side opposite the first bridge contact  30 , a second layer of insulating material  52   b   2  is deposited over the projection  222   b  of the trigger contact  214   b , the first switch terminal  42  is coupled to the second layer of insulating material  52   b   2  and a third layer of insulating material  60  is deposited onto a portion of the first switch terminal  42 . 
   The initiator  10   b  can be employed in a standard mode, a breakdown mode or a trigger mode. Operation of the initiator  10   b  in the standard and breakdown modes can be generally similar to the operation of the initiator  10  ( FIG. 1 ) in these modes and as such, need not be discussed in further detail. Operation of the initiator  10   b  in the trigger mode can include electrically coupling the second bridge contact  32  to an electrical ground, electrically coupling the first switch terminal  42  to a source of electric power having an electric potential that is not sufficient (by itself to transmit electric energy through the insulating material  52   b  (i.e., vertically through the first and second layers of insulating material  52   b   1  and  52   b   2  to the first bridge contact  30 ) and selectively coupling the terminal portion  220   b  of the trigger contact  214   b  to a voltage source, such as a negative voltage source. Application of electric power to the terminal portion  220   b  can affect the field between the first bridge contact  30  and the first switch terminal  42  to effectively lower the electric potential that is necessary to cause energy to be transmitted through the insulating material  52   b  (i.e., so that the electric potential of the energy applied to the first switch terminal  42  is sufficient to transmit electric energy through the insulating material  52   b  to the first bridge contact  30 ). As will be appreciated, electrical energy that is received by the first bridge contact  30  can be transmitted through the bridge  34  and the second bridge contact  32  as described above. 
   While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims.