MXPA99008177A - High impedance semiconductor bridge detonator - Google Patents

Abstract

A detonator (10) contains an SCB initiator assembly (35) in initiation relation to an ignition charge (18). The SCB initiator assembly (35) contains an initiator element (36) having a bridge (60) of semiconductor material between two conductive lands (62a, 62b). The bridge (60) provides a resistance of at least about 50 oms and has a volume between 48,600 cubic microns and 600,000 cubic microns with a typical thickness of two microns. A firing current of more than 200 milliamp provided to the initiator assembly (35) via input leads (26a, 26b) causes the bridge (60) to initiate the ignition charge (18).

Description

HIGH IMPEDANCE SEMICONDUCTOR BRIDGE DETONATOR BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to detonators of the semiconductor bridge. In particular, the invention relates to that detonator having a thin-film bridge of high impedance with certain electrical characteristics for special applications. BACKGROUND OF RELATED PROCEDURES Detonators are used to initiate various types of explosive charges, for example, to initiate auxiliary detonators for explosive charges located at the bottom of a borehole in blasting activities. A conventional detonator comprises an elongated shell or shell with one end closed and the other open. An explosive exit charge is placed on the closed end of the frame. A transmission line with initiating signal is passed through the open end of the frame and is operatively connected to the output load, so that the initiating signal of the signal transmission line can be transferred to the output load to trigger the signal. detonator. Some detonators comprise electric start charging elements, such as a thermal wire, a thin metallic wire that explodes or a semiconductor bridge (SCB) that initiates the output load. The elements of the initiating charge extend between electrical contacts which receive an electrical activation signal by means of conducting wires. The element of the initiating charge emits the energy of the electric activation signal to initiate the explosive material of the detonator. The amount of energy emitted is related to the electrical resistance of the electric element of the initiating charge and the current that passes through the element of the initiating charge at the time of initiation. U.S. Pat. 4,708,060 granted to Bickes, Jr. et al., dated November 24, 1987, discloses the existence of elements of the ignition device of the SCB, which are described as consisting of an electrical semiconductor material disposed on a non-conductive substrate. The semiconductor material can be, for example, a n-type silicon layer that has been adulterated with phosphorus. As indicated in this patent, other semiconducting and adulterating materials with a similar effect can be used. The resistivity of the adulterating material varies with the level of adulteration, as is well known in that field. Normally, the semiconductor material is placed on the non-conductive substrate by a process of chemical vapor deposition by which the thickness of the material can be precisely controlled. The surface of the non-conductive substrate is generally covered during the deposition process in such a way that the layer of semiconductor material has the shape of an hourglass, that is, it forms two relatively large pieces joined by a small bridge. Then, two pieces of conductive material are placed on the large pieces of the semiconductor material and separated with the bridge of semiconductor material between them. The resistivity of the semiconductor material and the dimensions of the semiconductor bridge that is between the conductive parts determines the effective resistance that the semiconductor bridge provides between the conductive parts. The patent indicates that there is a preference for low resistance SCBs, for example, no greater than 10 ohms, for safety reasons, i.e., in case the SCB is used with an ignition charge with electrostatic sensitivity (see column 7, lines 44-50) and for a reduction in resistivity with an increase in the size of the SCB (see column 7, lines 53-55). The activation data provided correspond to electrical initiation signals of high amperage (for example, 10 amps and more) and short duration, less than 100 microseconds in duration (see column 5, row 62 to column 6, row 3). The comparative data in Table 2 are difficult to interpret because SCB1 and SCB2 differ not only in terms of strength but also in thickness (2 microns vs. 4 microns).

U.S. Pat. 5,179,248 granted to Hartman and collaborators, dated January 12, 1993, is related to a Zener diode for the protection of the SCB.

The Zener diode, which is connected through the terminal areas of the SCB, serves to prevent premature energization of the explosive as a result of electrostatic discharge or other voltages greater than the activation voltage. The patent specifies a bridge strength not greater than 1 ohm, since greater resistance would have a detrimental effect on the heating of the explosive (see, for example, column 5, lines 60-66). RP 67 publication of the American Petroleum Institute (API), entitled "Recommended Practices for Oilfield Explosives Safety ", Recommended Practices for the Safety of Explosives for Oil Fields, First Edition, March 1, 1994, provides recommended safety practices for electric detonators used in applications at the bottom of oilfield explosive drilling. Since these practices correspond to detonators with thermoelectric wires and SCB, they require that the detonator have a minimum resistance of 50 ohms DC and a minimum current of non-activation of 200 milliamps ("miliamps" or "ma"), that is, the detonator must have a minimum threshold of 2 watts. Most detonators used in the oil and gas industry currently have resistors to meet these requirements, that is, they usually contain a 1 ohm thermal wire and two 25 ohm separate resistors that are electrically connected in series with a thermal thread of little resistance. The separated resistors are normally located in the detonator frame between the closing bushing for the open end of the detonator and an internal rubber plug, and the resistors and the internal rubber plug represent a significant portion of the total length of the detonator. Although the thin metallic wire of explosion and the detonators with metal and explosive initiating charge, which do not need resistors, are currently commercially available in the oil and gas market, their costs are considerably higher and are not directly compatible with the standard inductor activation systems because they require specialized activation or ignition equipment. GENERAL OBJECTIVES The present invention relates to a semiconductor bridge initiating charge element comprising an electrically carrier substrate. The semiconductor material is placed on top of the substrate. In the substrate there are two conductive terminal zones in contact with the semiconductor material with a bridge of semiconductor material, i.e., a semiconductor bridge (SCB) extending between them. The SCB has a resistance of at least almost 50 ohms. The SCB can have a volume ranging from about 13,160 to 600,000 cubic micrometers ("μm3"), for example 76,000 μm3 'In addition, the SCB can have a length-to-width ratio in the order of about 1: 2 to 1: 4. . The invention also provides an initiator charging module comprising a non-electrically conductive base, a pair of connector terminals mounted on the base, and a semiconductor bridge initiating charge element, as indicated above, mounted on the base at the that each connector terminal is electrically connected to a conductive fixed attenuator in the initiating charge element of the semiconductor bridge. The invention also provides a detonator comprising a housing, an outlet charge in the housing and an initiator assembly for initiating the exit charge. The initiator assembly is composed of the initiator charge module described above. The detonator may comprise an ignition charge in the housing. Preferably the ignition mixture comprises a composition not sensitive to static. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view of an already patented term wire detonator that includes a pair of internal resistors; Figure 2 is a schematic cross-sectional view of a detonator according to the physical embodiment of the present invention; Figure 3 is an enlarged perspective view of the initiator charge set of the detonator of Figure 2; Figure 4A is an enlarged vertical view of the semiconductor bridge initiating charge element (SCB) of the initiator charge assembly of Figure 3; and Figure 4B is a view of the initiating charge element of the SCB of Figure 4A taken along line 4B-4B. DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED PHYSICAL MATERIALIZATIONS OF THE INVENTION With reference to Figure 1, a detonator with already patented thermal wire 110 and which is currently used in oil and gas activities is schematically illustrated.

The detonator 110 comprises a metal detonator frame or housing 112 which generally has a cylindrical configuration with a closed end 112a and an open end 112b. At the closed end 112a, the housing 112 contains a base load 14 composed of a secondary explosive material.

For oil and gas applications, explosive materials that are useful at high temperatures, such as RDX or HNS (hexanitrostilbene), are preferred over others such as PETN (pentaerythritol tetranitate).

Paddled in the housing 112 adjacent to the base load 14, and therefore in relation to the signal transfer thereof, there is an intermediate load 16 which is usually composed of a primary explosive material, such as a plumbate azide. Together the base charge 14 and the intermediate charge 16 form the detonator output charge. The output charge generates the explosive detonation output that leaves the housing 112 and provides the detonator output signal. Beside the intermediate charge 16 there is an ignition charge 18 which preferably consists of a material not sensitive to static, such as for example a mixture of boron and ferric oxide. A typical mixture of this type, which is composed of about 15 percent boron by weight, is mentioned in U.S. Pat. 4,484,960 issued to Rucker on November 27, 1984. As is well known in the field, other reactive mixtures, such as TÍH1.65 / KCIO4; B / BaCr04, etc. they can become relatively insensitive to static electricity too. Inside the ignition charge 18 there is an initiating charge element consisting of a thermal wire 20. The wire extends between a pair of thermal wire conductors 22a, 22b. The ignition charge 18 is fixed and held by an internal plug or bushing 24, through which the thermal wire conductors 22a and 22b pass.

The electrical input conductors 26a, 26b enter the interior of the housing 112 through an open end 112b and there are held by a locking bushing 28. This closing bushing 28 is held within the open end 112b of the housing 112 by a flange 30, which also serves to seal the interior of the housing 112 against the bushing 28, and thus helps to protect against the entry of environmental contaminants agent, such as water and oil into the interior of the housing 112. Inside the housing 112, between the Closing bushing 28 and the inner bushing 24, the input conductors 26a, 26b are connected to the thermal conductor conductors 22a, 22b through resistors 32a, 32b. Normally, each of the resistors 32a and 32b provide twenty-five ohms of resistance and, therefore, meet one of the safety criteria recommended by the American Petroleum Institute. When in operation, the input conductors 26a, 26b carry an electrical initiating signal to the thermal wire 20 through the resistors 32a, 32b and the thermal wire conductors 22a, 22b. The current of the initiating signal generates sufficient heat in the thermal wire 20 to initiate the firing charge of boron and ferric oxide 18, and therefore to initiate the detonator. The duration of the initiating signal, which in the oil and gas industry is applied as applied voltage with ramp, is usually not less than 100 milliseconds and can last for 3 seconds and, as indicated below, The current level of the initiating signal is small. In an effort to improve the field of detonators for oil and gas applications, the Applicant attempted to replace conventional thermal wire 20 with a semiconductor bridge initiating charge module (SCB) consisting of an initiating loading element of the SCB.

In attempting to select an initiating charge element of the SCB for a detonator such as the detonator 110, the applicant discovered that an initiating charge element of the SCB consisting of a conventional 1 ohm SCB measuring 17X36X2 microns (which has been used successfully to initiate ignition loads that comprise, for example, BNCP) could not safely start a boron / ferric oxide ignition charge when it received the 800 milliampere current stipulated by industry standards as current for all types of activation in oil and gas applications. The applicant discovered that approximately 50 percent more current (ie, about 1200 milliamperes) was required for that type of SCB to initiate the boron / ferric oxide ignition charge, for a 1.4 watt ignition power. The current needed to provide 1.44 watts could be reduced by increasing the resistance of the semiconductor bridge. For example, to meet the corresponding security requirements of the API, the conventional 1 ohm SCB, 17 X 36 X 2 microns could be adulterated to provide a 50 ohm resistor, but then the ignition threshold potential of 1.44 watts would be find it with a non-activating current of only about 170 milliamperes, which is lower than the safety requirement of 200 milliamperes. The present invention arises from the general theoretical knowledge that among SCBs having the same thickness and the same electrical resistance, the larger SCBs require more current to initiate the boron / ferric oxide ignition charge than the smaller SCBs. In other words, the power needed to start the ignition charge varies depending on the size of the SCB. The experiments carried out by the applicant revealed that there is a specific relationship between the size limits of the SCBs and the ignition threshold currents that were not previously known or suggested in the field. The applicant's conclusions in this regard are summarized in the following BOX I, which illustrates the ignition threshold and power current (W = I2R) for four SCB sizes of 1 ohm (designated A, B, C and D). The "length" dimension indicated in FIGURE I is measured between the conductive terminal zones of the SCB element, ie from one end to the other; The "width" dimension is measured from side to side, that is, at right angles to the length measurement. If the SCB were adulterated so that they have the resistivity necessary to provide a resistance of 50 ohms, they would provide the indicated threshold power with less current, as also indicated in TABLE I. TABLE I 1 ohm SCB Dimensions threshold lit for (micrometers B / Fe203 Current (μm3)) Threshold current ratio of (2μm thick) approx. of Power 50 ohms SCB Length X Width Length: nw (Amps) (Watts) (Amps) A 17 36 1: 2 1.21 1.5 0.173 B 47 140 1: 3 1.51 2.3 0.214 C 90 270 1: 3 2.07 4.3 0.29 D 100 380 1: 4 2.37 5.6 0.33 The data in TABLE I allow the applicant to identify critical size limits for 50 ohm SCBs that have activation or ignition characteristics that meet API requirements. Specifically, the data in TABLE I show that a 50 ohm SCB must have a volume of at least about 47X140X2 μm = 13,160 microns cubic so that it has an ignition threshold current that exceeds the security criterion of the non-activation API at 2 watt, 200 milliamps. The extrapolation of this data indicates that SCB of 50 ohms of a maximum of about 600,000 cubic microns can be used. SCBs with more than 600,000 cubic microns will require more than 800 milliamperes to initiate the boron / ferric oxide ignition charge, a current level that exceeds a useful trigger limit current of the detonator. Preferably, as indicated in TABLE I, the SCBs of the present invention have a thickness of about 2 μm and a length-width ratio of the order of about 1: 2 to 1: 4. A SCB detonator according to the present invention is schematically illustrated in Figure 2. The detonator 10 consists of a housing 12 which has, generally, a cylindrical configuration with a closed end 12a and an open end 12b and contains the same output load as a conventional detonator 110 (Figure 1), ie a base load 14 and an intermediate load 16. An optional ignition charge 18, preferably not sensitive to static, is freely placed in the housing 12 next to the intermediate charge 16. The input conductors 26a and 26b extend into the interior of the housing 12 and are fixed there by a locking bushing 28 and a flange 30. The input conductors 26a and 26b carry an electric initiating signal to an initiating charging module 34. The initiating charging module 34 comprises a charge initiating charging element. semiconductor bridge 36, which is illustrated and described in greater detail in Figures 3 to 4 b and in the text attached thereto. When the electric initiating signal is transferred via the input conductors 26a and 26b to the initiating charge module 34, the initiating charge element of the SCB 36 initiates the ignition charge 18 and thereby initiates the detonator output charge. Overall, the bushing 28 (with the conductors 26a, 26b thereof) and the initiating charge module 34 form an initiating charge assembly 35. In other physical embodiments of the invention, the ignition charge can be omitted and the SCB can initiate directly the intermediate load. As indicated above, the initiating charge element of the SCB 36 is a high impedance component that is manufactured to provide a resistance. less around 50 ohms, that is 55 ± 5 ohms. Accordingly, the detonator 10 complies with the safety requirement promulgated by the American Petroleum Institute without any need to place a resistor on the initiator charge element, ie add a separate resistor or more than one resistor to the circuit of the initiator. detonator, as has been done in other known inventions. Therefore, with reference to the already patented detonator 110 (Figure 1), resistors 32a and 32b are not necessary in detonator 10 (Figure 2) according to the present invention. In the absence of the resistors 32a and 32b, the internal bushing 24 is no longer necessary. The elimination of the resistors 32a and 32b and the internal bushing 24 allows the detonator 10 to be considerably shorter than the already known and patented detonator 110, since the initiator charge module 34 occupies much less space in the detonator housing than the detonators. resistors 32a, 32b and the internal bushing 24. All this produces greater manufacturing efficiency, lower costs and greater flexibility in the design of other devices with which the detonator will be used. Optionally, it can be said that one aspect of the invention excludes separate resistors from the detonator circuit. The method of the initiating charge 34 and the bushing 28 (which, in combination with the input conductors 26a, 26b comprise an initiating charge assembly) are illustrated in greater detail in Figure 3. The bushing 28 has an upper portion 28a within which the connecting bolts 38a and 38b are placed. . The bushing 28 is preferably made of a synthetic and elastic polymeric material. The upper portion 28a of the bushing 28 is cylindrical, generally, and has a diameter that corresponds approximately to the inner diameter of the detonator housing (not shown), for example, about 0.233 inch (5.9 mm). The rest of the bushing 28 is divided into the joint 40 to facilitate insertion of the exposed ends of the electrical conductors 26a and 26b into the open ends of the connector bolts 38a and 38b. The clamp ring 42 exerts a clamping pressure on the upper portion 28a of the bushing 28 to help secure the conductors 26a and 26b in the connector bolts 38a and 38b, respectively. The initiator charge module 34 consists of a non-conductive pill 44, generally cylindrical in shape, which may be made of a polymeric material, for example, an epoxy resin. The connector terminals 46 and 48 extend through the pill 44 to the upper surface 34a and the lower surface 34b. Near the bottom surface 34b, the connector terminals 46 and 48 form the coupling notches 46a, 48a, which are dimensioned and configured to engage the connector bolts 38a and 38b in the bushing 28. The initiator charge element of the SCB 36 is adhered to the upper surface 34a of the pill 44, preferably between the connector terminals 46 and 48, in any convenient manner, for example, by an epoxy adhesive. Two 5 mil (0.005 inch) aluminum bond wires 52, 54 extend between the exposed ends of the connector terminals 46 and 48 and the associated conductive attenuators (not shown) of the initiator charge element of the SCB 36 and they can be fixed by sonic welding to each end, using a procedure well known in the field. Like the bushing 28, the pill 44 is cylindrical, generally, and has a diameter D corresponding to the internal diameter of the detonator housing (not shown). Preferably, the connecting bolts 38a, 38b and the coupling notches 46a, 48a are configured such that once the bolts 38a and 38b are inserted in the notches 46a, 48a, they will be securely fastened therein, for example , by means of a latching mechanism of the type of a retainer with flexible leaf spring in the bolts 38a, 38b and the corresponding grooves in the coupling notches 46a, -48a. Thus, the initiating charge module 34 and the bushing 28 (including the conductors 26a, 26b) will be joined together to build the initiator charge assembly 35 and to provide electrical continuity between the conductors 26a, 26b and the tie wires 52, 54 The initiating charge assembly 35 allows the transmission of an initiating signal from an external device to the interior of the detonator and, in particular, to the ignition charge. Now, with respect to Figures 4A and 4B, it is noted that the initiating charge element of the SCB is composed of an electrically non-conductive substrate 56 which may consist of a silicon base 56a with a silica shell 56b. (In this field it is known that sapphire can be used to use it as a substrate, as other materials such as aluminum oxide could also be used, silicon is preferred because of its favorable thermal properties). In the silica layer 56b there is a thick layer of 2 microns of semiconductor material 58 which may consist of a semiconductor layer of polysilicon adulterated with phosphor in an hourglass configuration having two fixed attenuators set apart by a space 58a, 58b, ( Figure 4B) joined by a thin film bridge 60. The bridge 60 has a width 60a, a length 60b and a thickness equivalent to the thickness of the layer 58. The typical thickness of the semiconductor layer 58 is two microns. The level of adulteration of layer 58, which determines the resistivity of the semiconductor material, is coordinated with the predicted length 60b (Figure 4B) and the width 60a and the thickness of the semiconductor bridge 60 that will extend between the metallized end areas to provide the desired resistance between them. The typical size of the semiconductor according to the present invention is about 100 (length) x 380 (width) x 2 microns (volume = 76,000 microns cubic). The electrically conductive metalized terminal areas 62a and 62b (which are partially separated in Figure 4B for purposes of illustration) respectively cover the fixed attenuators 58a, 58b of the semiconductor layer. The electrically conductive bonding wires 52, 54 (Figure 3) are connected to the metallized end regions 62a and 62b, respectively. The electrical resistance between the bond wires 52, 54 is basically equivalent to the electrical resistance provided by the bridge 60 between the terminal areas 62a and 62b. The resistance provided by the bridge 60 is the resistance attributed to the element of the initiating charge of the SCB. The initiating charge element of the SCB 36 can be manufactured by well-known procedures involving photolithographic masking, chemical vapor deposition, etc., to precisely control the thickness, configuration and concentration of adulteration of each layer of material, which it produces a very uniform yield of large amounts of SCB. At the indicated resistance of 50 ohms, the applicant discovered that for the SCB measuring 100 x 380 x 2 microns, about 0.34 amperes of current, or 5.6 watts of power, is needed for this element of the SCB to start in sure the ignition charge. This current requirement is congruent with the industry standard requirement for a current of -no activation of 200 milliamperes. It is also congruent with the industry requirement for an activation-only current level of 800 milliamperes or less. For about ten SCB test elements according to the present invention, an activation current of only 670 milliamperes and a non-activating current of 430 milliamperes was discovered. Based on the applicant's findings indicated in TABLE I above, bridge 60 of the 50 ohm SCB element is believed to be about 13,160 μm and preferably has a volume of 48,600 to 300,000 μm3 or better still, about 76,000 μm3, to start the ignition charge while complying with the desired non-activation current criterion. In order to ensure compliance with the minimum resistance, the semiconductor layer 58 may be manufactured such that the bridge 60 provides a DC resistance of 55 ± 5 ohms. In the manufacture of the detonator 10, the base load 14 and the intermediate load 16 are tamped in the empty housing 12. The ignition charge 18 is freely positioned within the housing 12 above the intermediate load 16, but is not compacted therein. . Separately, the input conductors 26a and 26b are fixed in the bushing 28 and the initiator module 34, which is manufactured in the manner described above, is fixed to the bushing 28 by inserting the bolts 38a and 38b into the coupling notches. 46a, 48a to form the initiator charge assembly. Next, the initiator charge assembly is inserted into the housing at a depth where the initiating charge element of the SCB 36 comes into contact with the ignition charge 18 with a minimum of compressive force. Typically, a maximum pressure of approximately 1,000 psi is applied to the initiator charge assembly. When this assembly is well placed in place, the rim 30 is formed in the housing 12 to retain the bushing 28 in place. When an electrical initiating signal of sufficient amperage is received from the conductors 26a and 26b, the bridge 60 (FIG. 4B) vaporizes and initiates the ignition charge 18, which in turn ignites the detonator 10. While it has been described in detail the invention, referring to the particular physical materializations thereof, to read and understand all of the above it will become clear that those who understand the field will come up with numerous variants for the physical materializations described above, and we have by intent to include such variants within the scope of the appended claims.

Claims (11)

1. CLAIMS 1. An initiating charge element of the semiconductor bridge, comprising: a carrier substrate that does not conduct electricity; a semiconductor material placed on the substrate; and two conductive terminal zones in contact with the semiconductor material and with a bridge of semiconductor material (SCB) -which extends between them, in which the SCB has a resistance of at least about 50 ohms. The element of claim 1 wherein the SCB has a volume in the order of about 13,160 μm3 to about 600.00 μm3 '3. The element of claim 2 wherein the SCB has a thickness of around 2 μm. The element of claim 1, claim 2 or claim 3 wherein the SCB has a length-to-width ratio ranging from about 1: 2 to 1: 4. The element of claim 1, the claim 2 or claim 3 wherein the SCB has a volume of about 76,000 μm3"6. An initiating charge module consisting of: a non-electrically conductive base; a pair of connector terminals mounted on the base; and a semiconductor bridge initiating charge element of claim 1, claim 2, claim 3, or claim 4 mounted on the base; wherein each connector terminal is electrically connected to a conductive fixed attenuator in the semiconductor bridge element. 7. The initiating charge module of the claim 6 comprises a SCB with a volume of about 76,000 μm3 ' 8. In a detonator having a housing, an output charge in the housing, and an initiating charge assembly for igniting the output charge, the improvement comprising the initiator charge assembly with an initiating charge module that responds to what is described in FIG. claim 6. The detonator of claim 8 wherein the SCB has a volume of about 76,000 μm3 '10. The detonator of claim 6 further comprising an ignition charge in the housing between the initiator and charge set. the output load. 11. The detonator of claim 10 comprising an ignition composition not sensitive to static.