Abstract:
A surface mount fuse includes a substrate, a fuse element applied to the substrate, first and second terminals applied to substrate, first and second conductors connecting the fuse element electrically with the first and second terminals, and an enclosure coupled to the substrate, the enclosure covering the first and second conductors and defining a cavity overlying at least a portion of the fuse element, the cavity allowing for distortion of the fuse element upon its opening.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 11/537,906, “Fuse with Cavity Forming Enclosure,” filed Oct. 2, 2006, and also claims priority to and the benefit of U.S. Provisional Patent Application “Fuse with Cavity Forming Enclosure,” Ser. No. 60/723,253, filed Oct. 3, 2005. 
     
    
     BACKGROUND 
       [0002]    Printed circuit boards (“PCB&#39;s”) have found increasing application in electrical and electronic equipment of all kinds. The components placed on the PCB control the electronic device. With cellular phones and other handheld electronic devices being designed and manufactured smaller and smaller, the need to save space on the PCB is critical. 
         [0003]    The electrical circuits formed on the PCB&#39;s, like larger scale electrical circuits, need protection against electrical overloads. In particular, circuit boards and other electrical circuits within the telecommunications industry need protection against electrical overload. This protection can be provided by subminiature fuses that are physically secured to the PCB. 
         [0004]    One problem common to most fuses is the potential mechanical distortion of the fuse element upon the opening of the element. Fuses can protect against two type of overcurrent situations, one in which a peak or instantaneous current surpasses a rated peak current of the fuse and another in which an amount of energy due to an overload condition or i 2 R energy surpasses a total energy rating or “let-through” energy rating. Fuse openings caused by instantaneous current surges in particular can lead to fairly severe mechanical distortion of the fuse element. 
         [0005]    For numerous reasons, conductive portions of the fuse need to be insulated electrically. Mechanical distortion of the fuse element can cause the insulation to rupture or fly away from the opened fuse. In a closely spaced PCB environment, such ruptures or projectiles can cause damage to other components of the electronic devices. 
         [0006]    Certain fuses, such as automotive blade fuses or cartridge fuses, provide insulating housings that are sized and configured to provide air gaps or arc barriers, which absorb the energy of an opened fuse or mechanically distorted fuse element. Such air gaps and arc barriers have not been possible to date with surface mount fuses, which have applied insulating coatings directly to the substrate and fuse element. 
         [0007]    Accordingly, a need exists to provide a surface mount fuse having arc-quenching capabilities, and which is able to withstand mechanical distortion and disruption of the fuse element upon an opening thereof. 
       BRIEF SUMMARY 
       [0008]    Described herein are surface mountable fuses that allow for mechanical disruption and distortion of the fuse element upon the openings of the fuse. The fuses can also provide separate arc-quenching features. In one embodiment the fuse which includes a substrate, a fuse element applied to the substrate, first and second terminals applied to substrate, first and second conductors connecting the fuse element electrically with the first and second terminals, and an enclosure coupled to the substrate. The enclosure is configured to cover the first and second conductors. It also defines a cavity overlying at least a portion of the fuse element, the cavity allowing for distortion of the fuse element upon its opening. 
         [0009]    The substrate can be made of any suitable material, such as FR-4, epoxy resin, ceramic, resin coated foil, polytetrafluoroethylene, polyimide, glass and any combination thereof. Any of the fuse elements, first and second terminals, and first and second conductors can be made of at least one material, such as, copper, tin, nickel, silver, gold, alloys thereof and any combination thereof. The terminals, for example, can be plated with multiple conductive layers, such as additional copper layers, nickel layers, silver layers, gold layers, tin layers, and/or lead-tin layers. The fuse element and conductors for example may be formed as a single copper trace, in which the element is thinned or narrowed with respect to the conductors. At least one of the fuse element, first and second terminals, and first and second conductors can be applied to the substrate via a process, such as, etching, metalizing, laminating, adhering and any combination thereof. 
         [0010]    The enclosure can be made of any suitable insulating material. In one preferred embodiment, the material is at least substantially rigid, so that it holds its shape and maintains the advantageous cavity. Suitable materials for the enclosure include hard silicon, polycarbonate, FR-4, or melamine. 
         [0011]    In one embodiment, the enclosure includes a lid portion and a sidewall portion extending from the lid portion. The lid portion has an at least substantially uniform thickness, which is desirable because enough insulation can be assured over the entire are of the lid without having areas of extra, wasted thickness. In one implementation, the extending sidewall portion is coupled to the substrate, e.g., mechanically, chemically, thermally or via any combination thereof. 
         [0012]    In one embodiment, a dissimilar metal, such as tin or tin-lead solder is applied to the fuse element at a location desirable for opening. The tin or tin-lead solder has a lower melting temperature than the copper element, so that upon an overcurrent or overload condition, the lower melting temperature metal melts first, adding heat to the element and quickening its response time. The fuse element in turn opens at that desirable location. 
         [0013]    The enclosure can be sized to have the same footprint (length and width) as the base substrate or have a different footprint than the substrate. If the same, the terminals can be plated onto the edges of both the substrate and enclosure after they have been assembled. If different, the terminals can be plated onto the edges of the substrate before the enclosure and substrate have been assembled. 
         [0014]    The cavity defined by the enclosure can be at least partially filled with a mechanically compliant, arc-quenching material, such as rubbery silicone. The compliant silicone absorbs the energy of a fuse opening. Its compliant nature also enables the element to move without disrupting the enclosure. The compliant silicone or other flexible material can be applied directly to the element in such a manner that a space or gap exists between the silicone and the bottom of the enclosure. Alternatively, the compliant silicone may completely fill the gap. 
         [0015]    The rigid, cavity providing housing may also be employed with surface mount fuses having multiple fuse elements secured to an insulating substrate. U.S. patent application Ser. No. 11/046,367, titled: “Dual Fuse Link Thin Film Fuse,” filed Jan. 28, 2005 and assigned to the eventual assignees of this application, the entire contents of which are incorporated expressly herein by reference, discloses such multiple element fuses. 
         [0016]    Here, a single fuse of can protect multiple conductive pathways of a same circuit or multiple different circuits. The fuse elements of the fuse can be rated the same or differently. The multiple elements can be placed in a non-symmetrical relationship with one another, so that it is difficult if not impossible to mount the fuses improperly. Further, certain portions of the insulating substrate can be metallized in addition to the terminal and fuse element metallizations to help balance the fuse during soldering. In that way, potential unequal surface tension forces during soldering due to an unbalanced metallization pattern are balanced. Such additional metallizations can render the multi-element fuses at least somewhat auto-alignable. The terminals are also structured so that diagnostic testing of the fuse can be performed without flipping the fuse, e.g., after the fuse is soldered to a PCB. 
         [0017]    Various multi-element embodiments include fuse links having an X-shaped relationship to one another, a parallel relationship, a perpendicular relationship or a cross-shaped relationship, for example. In one embodiment, each fuse link extends to a unique pair of terminals. In another embodiment, the fuse links share one terminal, namely, a ground or common terminal. 
         [0018]    The multi-element fuses can have upper and lower cavity forming enclosures. The cavity forming enclosures each cover an element and at least portions of the conductors or traces extending from or to the element. The terminals in one embodiment are built-up with multiple conductive layers so as to be at least substantially flush with the upper and lower enclosures. Or, the substrate can be milled or forward, so that the terminal or outside edges of the substrate are raised with respect to the inner, fuse element portion of the substrate. 
         [0019]    In one embodiment, a surface mount fuse includes a substrate, a fuse element applied to the substrate and first and second terminals applied to substrate. The surface mount fuse further includes first and second conductors connecting the fuse element electrically with the first and second terminals and an enclosure coupled to the substrate, the enclosure covering the first and second conductors and defining a cavity overlying at least a portion of the fuse element, the cavity allowing for distortion of the fuse element upon its opening. 
         [0020]    In yet another embodiment, a surface mount fuse includes a substrate, a fuse element applied to the substrate, first and second terminals applied to the substrate and first and second conductors connecting the fuse element electrically with the first and second terminals. The surface mount fuse further includes an enclosure coupled to the substrate, the enclosure having a different footprint from the substrate and defining a cavity overlying at least a portion of the fuse element, the cavity allowing for mechanical distortion of the fuse element upon its opening. 
         [0021]    In still another embodiment, a surface mount fuse includes a substrate, a fuse element surface mount fuse includes a substrate, a fuse element applied to the substrate, first and second terminals applied to substrate, first and second conductors connecting the fuse element electrically with the first and second terminals. The surface mount fuse further includes an enclosure coupled to the substrate, the enclosure defining a cavity overlying at least a portion of the fuse element, the cavity (i) allowing for mechanical distortion of the fuse element upon its opening and (ii) at least partially filled with an arc-quenching, mechanically compliant material 
         [0022]    It is therefore an advantage of the examples disclosed herein to provide an improved surface mountable fuse. 
         [0023]    Another advantage of the examples disclosed herein to provide a surface mount fuse with a cavity providing enclosure that mitigates the effects of the mechanical disruption or distortion of a fuse element upon an opening of same. 
         [0024]    A further advantage of the examples disclosed herein is to provide such surface mount fuse and enclosure, wherein the cavity is further loaded with a mechanically compliant arc-quenching material. 
         [0025]    Still another advantage of the examples disclosed herein is to provide such surface mount fuse and enclosure with a single fuse having multiple fuse links. 
         [0026]    Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0027]      FIG. 1  is a sectioned front elevation view of one embodiment of a surface mount fuse having a cavity forming enclosure, wherein the enclosure has a different footprint than the base substrate of the fuse. 
           [0028]      FIG. 2  is a sectioned front elevation view of another embodiment of a surface mount fuse having a cavity forming enclosure, wherein the enclosure has the same footprint as the base substrate of the fuse, and wherein the cavity is partially filled with a mechanically compliant, arc-quenching material. 
           [0029]      FIG. 3  is a sectioned front elevation view of a further embodiment of a surface mount fuse having a cavity forming enclosure, wherein the enclosure has the same footprint as the base substrate of the fuse, and wherein the cavity is filled completely with a mechanically compliant, arc-quenching material. 
           [0030]      FIGS. 4A to 4C  are top, front and bottom views, respectively, of one embodiment of a fuse having a cavity forming enclosure, and which includes multiple fuse elements having a serpentine arrangement. 
           [0031]      FIGS. 5A to 5C  are top, front and bottom views, respectively, of another embodiment of a fuse having a cavity forming enclosure, and which includes multiple fuse elements having an asymmetrical, parallel relationship. 
           [0032]      FIGS. 6A to 6C  are top, front and bottom views, respectively, of a further embodiment of a fuse having a cavity forming enclosure, and which includes multiple fuse elements having an asymmetrical, X-shaped relationship. 
           [0033]      FIGS. 7A to 7C  are top, front and bottom views, respectively, of yet another embodiment of a fuse having a cavity forming enclosure, and which includes multiple fuse elements having an asymmetrical, cross-shaped configuration. 
           [0034]      FIGS. 8A to 8C  are top, front and bottom views, respectively, of a still further embodiment of a fuse having a cavity forming enclosure, and which includes multiple fuse elements having multiple load terminals fusibly connected to a single or ground or common terminal. 
           [0035]      FIGS. 9A to 9C  are top, front and bottom views, respectively, of yet a further embodiment of a fuse having a cavity forming enclosure and multiple fusible elements of the same or different current rating located on a single side of the fuse. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Referring now to the drawings, and in particular to  FIG. 1 , one embodiment of a fuse having a cavity forming enclosure is shown by surface mount fuse  10   a . Fuse  10   a  includes an insulating substrate  12 . Substrate  12  can be made of any suitable insulating material. In a preferred embodiment, the insulating material is both electrically and thermally insulating. Suitable materials for substrate  12  include FR-4, epoxy resin, ceramic, resin coated foil, polytetrafluoroethylene, polyimide, glass and any suitable combination thereof. 
         [0037]    Applied to substrate are conductors  34   a  and  34   b  and fuse element  50 , which in one embodiment are or include copper traces. Conductors and element  50  can be formed from a single copper trace, which is narrowed and/or thinned at one portion to form the element. The copper traces are etched onto substrate  12  via any suitable etching or metalizing process. One suitable process for etching the metal onto substrate  12  is described in U.S. Pat. No. 5,943,764 (“the &#39;764 patent”), assigned to the eventual assignee of the present application, the entire contents of which are incorporated herein by reference. Another possible way to metalize substrate  12  of fuse  10   a  is to adhere conductors  34   a  and  34   b  and element  50  to substrate  12 . One suitable method for adhering the conductors  34   a  and  34   b  of fuse  10   a  to substrate  12  is described in U.S. Pat. No. 5,977,860, assigned to the eventual assignee of the present application, the entire contents of which are incorporated herein by reference. Alternatively, conductors  34   a  and  34   b  and element  50  are copper, tin, nickel, silver, gold, alloys thereof and any combination thereof. 
         [0038]    As discussed, conductors  34   a  and  34   b  are narrowed and/or thinned as they extend towards each other. The narrowed/thinner portion of conductors  34   a  and  34   b  is the most likely the place for the pathways to open upon an overcurrent or overload condition. This portion is therefore termed the fuse element  50 . 
         [0039]    In the illustrated embodiment, a dissimilar metal deposition  51  is placed on fuse element  50 . Deposition  51  in an embodiment includes pure tin, nickel or a combination of tin and lead, e.g., solder. Deposition  51  has a lower melting temperature than does the copper traces of the conductors  34   a ,  34   b  and fuse element  50 . To that end, deposition  51  can be any metal or alloy having a lower melting temperature than the conductors  34   a ,  34   b  and fuse element  50 . The addition of deposition  51  helps to ensure that the corresponding fuse element  50  opens at the narrowed location. When the deposition  51  heats-up due to an overcurrent condition, the alloy melts and causes an increased point of heat transfer on fuse element  50 , which in turn melts before other points along the conductors  34   a  and  34   b . In this way, the point at which fuse  10   a  opens is controllable and repeatable. 
         [0040]    Conductors  34   a  and  34   b  communicate electrically with terminals  40   a  and  42   a . As discussed in the &#39;764 patent, it may be desirable to place multiple conductive layers on one or more of the terminals  40   a  and  42   a . The conductive layers of terminals  40   a  and  42   a  can include any number and combination of layers of copper, nickel, silver, gold, tin, lead-tin and other suitable metals. The terminals can have the same or different numbers and types of conductive layers. 
         [0041]    An at least semi-rigid, cavity forming enclosure  53   a  is fixed to substrate  12 . Enclosure  53   a  includes a lid portion  61  and a sidewall portion  63  extending downwardly from lid portion  61 . Lid portion  61  has an at least substantially uniform thickness, which is desirable because it ensures that a proper level of insulation is provided without providing an unnecessary amount of insulation in any area. Enclosure  53   a  is made of any suitably rigid, insulating material, such as silicone, polycarbonate, FR-4 or melamine. 
         [0042]    Lid portion  61  and sidewall portion  63  form a cavity  57   a . The sidewalls portion  63  extend away from the lid portion  61  to create a gap or cavity of the same height. 
         [0043]    Cavity  57   a  provides room for element  50  to move or deform upon an opening of element  50 , without in turn deforming or dislodging enclosure  53   a . Sidewall portion  63  is fastened to substrate  12  via any suitable method, such as mechanically, adhesively and/or thermally or in any other suitable manner. Enclosure  53   a  covers all of element  50 , deposition  51  and conductors  34   a  and  34   b  in the illustrated embodiment. Terminals  40   a  and  40   b  remain exposed. Enclosure  53   a  of device  10   a  has a smaller footprint (length and width) than does substrate  12 . Accordingly, terminals  40   a  and  40   b  are formed on substrate  12 , e.g., before enclosure  53   a  is attached to substrate  12 . 
         [0044]    Fuse  10   a  can be rated for any suitable surface mount peak current and let-through energy rating. 
         [0045]    In  FIG. 2 , an at least semi-rigid cavity forming enclosure  53   b  is fixed to substrate  12 . Enclosure  53   b  includes a lid portion  61  and a sidewall portion  63  extending downwardly from lid portion  61 . Lid portion  61  has an at least substantially uniform thickness, which is desirable as described above. Enclosure  53   b  is made of any suitably material listed above. All of the materials and methods for making enclosure  53   a  of  FIG. 1  are applicable to enclosure  53   b  of  FIG. 2 . Except, as discussed below, enclosure  53   b  has the same footprint as substrate  12 . 
         [0046]    Lid portion  61  and sidewall portion  63  form a cavity  57   b . Cavity  57   b  provides room for element  50  to move or deform upon an opening of element  50 , without in turn deforming or dislodging enclosure  53   b . Further, a mechanically compliant, arc-quenching material  59   b , such as silicone is applied to fuse element  50 , deposition  51 , a portion of terminals  34   a  and  34   b  and a portion of substrate  12 . An air gap still exists, however, between material  59   b  and the inner surface of lid portion  61  of enclosure  53   b.    
         [0047]    Arc-quenching material  59   b  absorbs energy from the opening of fuse element  50 . Its rubbery or compliant nature however enables element  50  to deform without deforming or rupturing enclosure  53   b . The open space  57   b  around arc-quenching material  59   b  also enables the material and the element to move upon an opening of element  50 . 
         [0048]    Sidewall portion  63  is fastened to substrate  12  via any suitable method, such as mechanically, adhesively and/or thermally. Enclosure  53   b  covers all of fuse element  50 , deposition  51  and conductors  34   a  and  34   b . Enclosure  53   b  of device  10   b  has the same footprint (length and width) as base  12 . Accordingly, terminals  40   a  and  42   b  are formed on substrate  12  and enclosure  53   b  in one embodiment, e.g., after enclosure  53   b  is attached to substrate  12 . 
         [0049]    Fuse  10   b  can be rated for any suitable surface mount peak current and let-through energy rating. 
         [0050]    In  FIG. 3 , an at least semi-rigid cavity forming enclosure  53   c  is fixed to substrate  12 . Enclosure  53   c  includes a lid portion  61  and a sidewall portion  63  extending downwardly from lid portion  61 . Lid portion  61  has an at least substantially uniform thickness, which is desirable as described above. Enclosure  53   c  is made of any suitably material listed above. 
         [0051]    Lid portion  61  and sidewall portion  63  form a cavity, which in the illustrated embodiment is filled completely with arc-quenching material  59   c . The cavity provides room for fuse element  50  to move or deform upon an opening of fuse element  50 , without in turn deforming or dislodging enclosure  53   c . Further, mechanically compliant, arc-quenching material  59   c  absorbs energy from the opening of fuse element  50 . Its rubbery or compliant nature however enables fuse element  50  to deform without deforming or rupturing enclosure  53   c.    
         [0052]    Sidewall portion  63  is fastened to substrate  12  via any suitable method, such as mechanically, adhesively and/or thermally. Enclosure  53   c  covers all of element  50 , deposition  51  and conductors  34   a  and  34   b . Enclosure  53   c  of device  10   c  has the same footprint (length and width) as base  12 . Accordingly, terminals  40   a  and  40   b  are formed on substrate  12  and enclosure  53   c  in one embodiment, e.g., after enclosure  53   c  is attached to substrate  12 . 
         [0053]    Fuse  10   c  can also be rated for any suitable surface mount peak current and let-through energy rating. 
         [0054]    Any of fuses  10   a  to  10   c  can be provided in any desirable surface mount size, such as, for example an 0402, 0604, 0805 and/or 1206 packages. Conductors  40   a ,  42   a ,  40   b ,  42   b ,  40   c ,  42   c  may be arranged according to any applicable industry standards. 
         [0055]    Referring now  FIGS. 4A to 4C , one embodiment of a dual fuse link surface-mountable fuse having upper and lower cavity forming enclosures  53   d  and  55   d , respectively, is illustrated by fuse  10   d . Fuse  10   d  includes a substrate  12  that has a top  14  and a bottom  16 . Substrate  12  also has a front  26 , a back  28 , a left side  30 , and a right side  32 . Fuse  10   d  includes separate conductive pathways or fuse links  34 ,  36  attached to the top and bottom surfaces  14 ,  16 , respectively. Fuse link  34  includes separate conductive pathways  34   a  and  34   b  (referred to collectively as fuse link  34 ). 
         [0056]    A metal deposition  51  is placed on the interface between conductive pathways  34   a  and  34   b , which is approximately in the middle of fuse link  34 . Likewise, fuse link  36  includes two separate pathways  36   a  and  36   b  (referred to collectively as fuse link  36 ). A metal deposition  52  is placed on the interface between pathways  36   a  and  36   b , approximately in the middle of fuse link  36 . First fuse link  34  and metal deposition  51  are located on top  14  of substrate  12 . Second fuse link  36  and metal deposition  52  are located on the bottom  16  of substrate  12 . 
         [0057]    Fuse links  34  and  36  in one embodiment are or include copper traces. The copper traces are etched or adhered to substrate  12  via any suitable etching or metalizing process, such as those described above for fuse  10   a . The metal depositions  51  and  52  in an embodiment include a combination of tin and lead, e.g., solder, as described above and operate the same as described above. Namely, the addition of metal depositions  51  and  52  helps to ensure that the corresponding fuse link opens at the narrowed location e.g., at tin-lead spots  50  and  52 . 
         [0058]    As illustrated, conductive pathway  34   a  extends to a terminal  40  located at one of the corners of substrate  12 . As seen in  FIG. 4A , conductive pathway  34   b  extends to a second terminal  42  located at a different corner of substrate  12 . As seen in  FIG. 4C , terminals  40  and  42  of fuse link  34  in one embodiment extend from the top  14 , down sides  30  and  32  and cover a portion of the bottom  16  of substrate  12 . Extending the terminals along multiple surfaces of the substrate enables each of the fuse links to be tested diagnostically from one side of the fuse or without having to flip the fuse, e.g., after it has been mounted to a parent printed circuit board (“PCB”). 
         [0059]      FIG. 4C  illustrates the terminals  44  and  46  of second serpentine shaped fuse link  36  having second metal deposition  52 . As seen in  FIG. 4C , conductive pathway  36   a  extends to terminal  44 , which is located at a third corner of substrate  12 . Conductive pathway  36   b  extends to terminal  46 , which is located along the back  28  of substrate  12 . As seen in  FIGS. 4A and 4B , terminal  44  extends up side  30  and front  26  and along a portion of top  14  of substrate  12 . Likewise, terminal  46  extends up back  28  and along a portion of top  14  of substrate  12 . 
         [0060]    As seen in  FIGS. 4A to 4C , fuse links  34  and  36  do not extend to one of the four corners of substrate  12 . Nevertheless, that fourth corner is metalized along a portion of the top  14 , front  26 , side  32  and bottom  16  of substrate  12 . That is, a fourth terminal  48  is provided that does not connect electrically to either of the fuse links  34  and  36 . 
         [0061]    Separate terminal  48  is provided for multiple reasons. First, a metallization at the fourth corner of substrate  12  enables fuse  10   d  to be soldered properly to the parent PCB. Enabling all four corners of fuse  10   d  to be soldered (e.g., reflow soldered) to the parent PCB helps to ensure that fuse  10   d  is mounted flushly on the PCB and is not tilted or angled upward from one or more sides or corners of fuse  10   d . Dummy terminal  48  balances surface tension forces when fuse  10   d  is soldered to the PCB, so that fuse  10   d  is aligned correctly in a X-Y or planar direction along the surface of the parent PCB. Terminal  48  also enables fuse  10   d  to be secured at all four corners to strengthen the connection between fuse  10   d  and the parent PCB. Terminal  48  may also help diagnostically. 
         [0062]    A further reason to metalize the fourth corner with dummy terminal  48  is to streamline the manufacturing process. As discussed in the &#39;764 patent, one of the last steps in manufacturing fuse  10   d  is to dice or cut individual fuses from a large sheet of multiple fuses. A process very similar to that described in the &#39;764 patent can be used to produce fuse  10   d . Accordingly, fuse  10   d  at a point in the manufacturing step is adjacent to up to eight other fuses (four lateral and four diagonal). The quarter circle at dummy terminal  48  is adjacent to quarter circles of three terminals of three other fuses. The four quarter circles of four fuses together form a bore or hole. It is easier to plate the entire hole than it is to not plate the dummy terminal  48  portion and plate instead only three-quarters of the hole for actual terminals of the other fuses. For multiple reasons, dummy terminal  48  is desirable. 
         [0063]    As discussed above, it may be desirable to place multiple conductive layers on one or more of the terminals  40 ,  42 ,  44 ,  46  and  48 . The conductive layers of terminals  40  to  46  can include any number and combination of layers of copper, nickel, silver, gold, tin, lead-tin and other suitable metals. The terminals can have the same or different numbers and types of conductive layers. 
         [0064]    The configuration of the terminals in  FIGS. 4A to 4C  is advantageous for multiple reasons. First, fuse links  34  and  36  and associated metal depositions  51  and  52  are thermally decoupled from one another. For one reason, metal depositions  51  and  52  are placed on opposite sides of substrate  12  from one another. Also, metal depositions  51  and  52  are misaligned laterally or in a planar direction with respect to each other. That is, the elements are not placed directly above and below one another. Instead, the spacing or arrangement of elements  51  and  52  is offset as seen in top and bottom views, respectively, of  FIGS. 4A and 4C . Spacing the elements  51  and  52  apart in three directions helps to insulate the elements from one another to prevent false triggering. 
         [0065]    Another advantage of the fuse link configuration shown in  FIGS. 4A to 4C  is that fuse links and metal depositions may be sized or structured differently to produce a differently rated fuse link. For example, fuse link  34  (including separate pathways  34   a  and  34   b ) and metal deposition  51  located on the top  14  of substrate  12  may be rated differently, e.g., ten amps, than is bottom side fuse link  36  (including pathways  36   a  and  36   b ) and metal deposition  52 , which could be rated for five amps or fifteen amps. Generally, either of the fusible links and associated metal depositions can be rated for any suitable amperage and let-through energy. 
         [0066]    The non-symmetrical arrangement of the fuse links on the top  14  and bottom  16  of fuse  10   d  makes an improper mounting of fuse  10   d  more difficult. That is, the mounting footprint of terminals  40  and  42  of the fuse link  34  and metal deposition  51  is different than (e.g., will not mate or mount to mounting pads that mate with terminals  44  and  46 ) the mounting footprint of fuse link  36  and terminals  44  and  46  located on the bottom  16  of fuse  10   d . The reverse is also true. That is, the mounting pads of a parent PCB that mate with terminals  44  and  46  of fuse link  36  will not mate with and cannot mount to terminals  40  and  42  of fuse link  34 . The configuration of fuse links  34  and  36  on fuse  10   d  therefore prevents or tends to prevent an assembler from placing an improperly rated fuse in a circuit or improperly mounting fuse  10   d.    
         [0067]    As seen in  FIG. 4B , fuse  10   d  includes cavity forming enclosures  53   d  and  55   d . Enclosures  53   d  and  55   d  include lid and sidewall portions as described above. The sidewall portions are fixed to substrate  12  via any method described above. Enclosures  53   d  and  55   d  form gaps or cavities that enable the elements (located at depositions  51 ,  52 ) to deform upon opening without deforming or dislodging enclosures  53   d  and  55   d . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material, such as silicone, as described above. 
         [0068]    Enclosures  53   d  and  55   d  are also shown in phantom in  FIGS. 4A and 4B . As seen, the enclosures  53   d  and  55   d  cover portions of links  34   a  and depositions  51  and  52 . Enclosures  53   d  and  55   d , like enclosures  53   a  to  53   c , inhibit corrosion and oxidation of the fusible links  34  and  36  as well as metal depositions  51  and  52 . The enclosures also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  10   d , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  10   d . The enclosures as discussed also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0069]    As illustrated in  FIG. 4B , terminals  44  and  48  are built-up via multiple metal layers  44   a / 44   b  and  48   a / 48   b , respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  53   d  and  55   d , respectively. This enables fuse  10   d  to be properly surface mounted. Terminals  40  and  42  are likewise built-up. 
         [0070]    In an alternative embodiment, top  14  and bottom  16  of substrate  12  are machined, milled, etched, formed initially or otherwise formed to have an inner depressed or recessed area, which is then covered by enclosure  53   d  and  55   d . The enclosures  53   d  and  55   d  when added to fixed substrate  12  reside at least substantially flush with the outer terminal portions of substrate  12 . 
         [0071]    The teachings previously described with respect to fuse  10   d  of  FIGS. 4A to 4C  are applicable to the remaining fuses discussed herein. The remaining fuses differ primarily in the configuration and arrangement of the fuse links, metal depositions and associated terminals. Each of the materials discussed above for the substrate, fusible links, terminals and metal depositions is applicable to each of the remaining fuses. For ease of illustration, those materials, methods of fabrication or application are not repeated in all cases for each of the foregoing fuses. 
         [0072]    For purposes of illustration, each of the fuses is given a name that is descriptive of the shape or relative configuration of the fuse links and metal depositions on the respective fuses. Accordingly, fuse  10   d  described in  FIGS. 4A to 4C  is labeled a serpentine fuse because of the serpentine shape of fuse link  36 . Fuse  60  discussed in  FIGS. 5A to 5C  is accordingly labeled an asymmetrical, parallel fuse. 
         [0073]    In  FIGS. 5A to 5C , symmetrical, parallel fuse  60  includes many of the same components described above for the serpentine fuse  10   d  of  FIGS. 4A to 4C . In particular, fuse  60  includes an insulating substrate  62  having a top  64 , bottom  66 , back  68 , sides  70  and  72  and a front  76 . Fuse links  84  and  86  are plated, etched, adhered or otherwise secured to substrate  62 . Fuse link  84  includes conductive pathways  84   a  and  84   b  that extend to terminals  90  and  92 , respectively. Fuse link  86  includes conductive pathways  86   a  and  86   b  that extend to terminals  94  and  96 , respectively. A metal deposition  100  is placed on fuse link  84  to help provide a definite point at which fuse link  84  opens upon an overcurrent condition. Likewise, a metal deposition  102  is placed on fuse link  86  to provide a definite point at which fuse link  86  will open. 
         [0074]    Fuse links  84  and  86  are sized (thickness and width) to open at a set and desired overcurrent level. Fuse links  84  and  86  may be rated the same or differently from one another. Given the parallel and symmetrical arrangement of the fuse links and terminals of fuse  60 , it may be desirable for the fuse links to have the same rating, so that the fuses are mounted properly no matter which surface  64  or  66  of substrate  12  is placed onto the parent PCB. 
         [0075]    As seen in  FIGS. 5A to 5C , terminals  90  to  96  each extend down/up respective sides  70  and  72 , front  76  and rear  68  of substrate  62 . The terminals further extend along a portion of the opposite top  64  or bottom  66 , respectively. Unlike the fuse  10   d  of  FIGS. 4A to 4C , all four corners of fuse  60  are consumed by terminals  90  to  96 , which each extend from one of the fusible links  84  and  86 . Accordingly, fuse  60  of  FIGS. 5A to 5C  does not need a dummy terminal. 
         [0076]    In the parallel, symmetrical arrangement of fuse  60 , or with any of the fuses described herein, it is expressly contemplated to provide two substrates  62  that sandwich an inner metallic layer having a third fusible link and element, third set of conductive pathways that extend to a third set of terminals. The third set of terminals (not illustrated) in one embodiment are metallized on the outside of the two substrates  62 , for example at front  76  and back  68  or otherwise away from the corners where terminals  90  to  96  are located. In this way, the present invention provides for more than two fuse links and metal depositions per assembly. The present invention also includes the provision of any suitable number of insulating substrates and conductive layers located between the insulating layers. Each of the separate fusible links extends to a terminal located on at least one outer surface of the fuse. The three or more terminals may each be rated the same, some rated differently, each rated differently or any combination thereof. 
         [0077]    As seen in  FIG. 5B , fuse  60  includes cavity forming enclosures  83  and  85 . Enclosures  83  and  85  include lid and sidewall portions as described above. The sidewall portions are fixed to substrate  62  via any method described above. Enclosures  83  and  85  form gaps or cavities that enable the elements (located at depositions  100 ,  102 ) to deform upon opening without deforming or dislodging enclosures  83  and  85 . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material as, such as silicone, described above. 
         [0078]    Enclosures  83  and  85  are also shown in phantom in  FIGS. 5A and 5B . As seen, the enclosures cover portions of links  84  and  86  and depositions  100  and  102 . 
         [0079]    Enclosures  83  and  85  inhibit corrosion and oxidation of the fusible links and metal depositions  100  and  102 . The enclosures also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  60 , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  60 . The enclosures as discussed also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0080]    As illustrated in  FIG. 5B , terminals  94  and  96  are built-up via multiple metal layers  94   a / 94   b  and  96   a / 96   b , respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  83  and  85 , respectively. This enables fuse  60  to be properly surface mounted. Terminals  90  and  92  are likewise built-up. In an alternative embodiment, substrate  62  is machined or formed as described above in connection with  FIG. 4B , so that enclosures  83  and  85  reside at least substantially flush with the outer terminal portion of substrate  62 . 
         [0081]    Refer now to  FIGS. 6A to 6C , a third fuse  110  is illustrated. Fuse  110  includes many of the same components as fuses  10   d  and to  60  described above. Fuse  110  for apparent reasons is called an X-shaped, symmetrical fuse. X-shaped, symmetrical fuse  110  includes a substrate  112 . Substrate  112  is made of any of the materials described above. Substrate  112  includes a top  114 , a bottom  116 , sides  120  and  122 , a front  126  and aback  118 . 
         [0082]    A fuse link  134  including conductive pathways  134   a  and  134   b  is placed on the top  114  of fuse  110  via any of the methods described above. Likewise, fuse link  136  including conductive pathways  136   a  and  136   b  is placed on the bottom  116  of substrate  112  via any of the methods described herein. Fuse links  134  and  136  include metal depositions  150  and  152 , respectively. 
         [0083]    Conductive pathways  134   a  and  134   b  of fuse link  134  extend to terminals  144  and  142 , respectively. Likewise, pathways  136   a  and  136   b  of fuse link  136  extend to terminals  140  and  146 , respectively. Terminals  140  to  146  cover each of the corners of substrate  112 . Accordingly no dummy terminal, like the one shown in  FIGS. 4A to 4C , is provided. Terminals  140  to  146  extend down/up the front, back and sides of substrate  112  and cover a portion of the surface opposite of their respective fuse links, as has been described herein. 
         [0084]    X-shaped, symmetrical fuse  110  is well suited to have an inner third or forth etc., metal layer, comprising additional fuse links and metal depositions. Also, due to the symmetrical nature of fuse  110 , it may be desirable for fuse links  134  and  136  to have the same current ratings so that fuse  110  may be mounted in multiple directions, without fear of protecting a circuit with an improperly rated overcurrent protection device. 
         [0085]    Links, terminals and elements  150  and  152  are made of any of the materials described above. Metal depositions  150  and  152  as shown are aligned with one another with respect to an axis extending out of the page. It may be desirable for thermal coupling reasons to alternatively offset the placement of the metal deposition. 
         [0086]    As seen in  FIG. 6B , fuse  110  includes cavity forming enclosures  153  and  155 . Enclosures  153  and  155  include lid and sidewall portions as described above. The sidewall portions are fixed to substrate  112  via any method described above. Enclosures  153  and  155  form gaps or cavities that enable the elements (located at depositions  150 ,  152 ) to deform upon opening without deforming or dislodging enclosures  153  and  155 . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material, such as silicone, as described above. 
         [0087]    Enclosures  153  and  155  are also shown in phantom in  FIGS. 6A and 6C . As seen, the enclosures cover portions of links  134  and  136  and depositions  150 ,  152 . 
         [0088]    Enclosures  153  and  155  inhibit corrosion and oxidation of the fusible links and metal depositions  150  and  152 . The enclosures  153  and  155  also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  110 , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  110 . The enclosures as discussed also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0089]    As illustrated in  FIG. 6B , terminals  144  and  146  are built-up via multiple metal layers  144   a / 144   b  and  146   a / 146   b , respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  153  and  155 , respectively. This enables fuse  110  to be properly surface mounted. Terminals  140  and  142  are likewise built-up. In an alternative embodiment, substrate  112  is machined or formed as described above. 
         [0090]    Referring now to  FIGS. 7A to 7C , a further alternative fuse  160  is illustrated. Fuse  160  includes a substrate  162  and fuse links  184  and  186 . Fuse link  184  is placed on the top  164  of substrate  162 . Fuse link  186  is placed on the bottom  166  of substrate  162 . Substrate  162  also includes sides  170  and  172 , front  176  and rear  168 . 
         [0091]    Fuse  160  is different from the other fuses shown and described herein because the corners of substrate  162  are not metallized, rather the inner portions of sides  170  and  172 , front  176  and rear  168  are metallized. The centers of those portions are shown having semi-circular cut-outs or bores. The bores are originally completely circular when a plurality of fuses  160  are made in a sheet, before the fuses  160  are separated or diced into the individual fuses  160 . Nevertheless, because each front, back and side of fuse  160  includes a terminal or metallization, fuse  160  is solderable to a parent PCB without experiencing unbalanced surface tension forces and is or tends to be auto-alignable without additional dummy terminals. 
         [0092]    Fuse  160  for apparent reasons is called a cross-shaped symmetrical fuse. Fuse links  184  and  186  may be rated the same or differently. In one embodiment because fuse  160  is symmetrical and fuse links  184  and  186  are rated for the same ampage so that the fuse may be soldered in multiple configurations without fear of improper mounting. Fuse links  184  and  186  include metal depositions  200  and  202 , respectively, which may be of any the types described herein. 
         [0093]    It should be appreciated from the foregoing examples that the fuses and substrates of the present invention can have many different shapes, fuse link configurations and terminal configurations. The fuses and substrates are also be sized to support a fuse having any suitable desired rating. The overall dimensions of the fuses can be an order of 1/16 inch (1.59 mm) and be generally square in shape or have rectangular dimensions. The thickness of the substrate or fuse can be on the order of a 1/64 inch (0.40 mm). In alternative embodiments, the dimensions of the fuse are bigger or smaller than the listed dimensions as desired and/or thicker than the thickness listed. The thickness of the traces in one embodiment is on the order of 0.005 inch (0.13 mm). 
         [0094]    As seen in  FIG. 7B , fuse  160  includes cavity forming enclosures  183  and  185 . Enclosures  183  and  185  include lid and sidewall portions as described above. The sidewall portions are fixed to substrate  162  via any method described above. Enclosures  183  and  185  form gaps or cavities that enable the elements (located at depositions  200 ,  202 ) to deform upon opening without deforming or dislodging enclosures  183  and  185 . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material, such as silicone, as described above. 
         [0095]    Enclosures  183  and  185  are shown covering portions of links  184  and  186  and depositions  200 ,  202  in  FIGS. 7A and 7B . 
         [0096]    Enclosures  183  and  185  inhibit corrosion and oxidation of the fusible links and metal depositions  200  and  202 . The enclosures  183  and  185  also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  160 , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  160 . The enclosures as discussed also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0097]    As illustrated in  FIG. 7B , terminals  194  and  196  are built-up via multiple metal layers  194   a / 194   b  and  196   a / 196   b , respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  183  and  185 , respectively. This enables fuse  160  to be properly surface mounted. Terminals  190  and  192  are likewise built-up. Alternatively, substrate  162  can be machined or formed as discussed above. 
         [0098]    Referring now to  FIGS. 8A to 8C , an alternative embodiment of the surface mount use of the present invention is illustrated by fuse  210 . Fuse  210  as illustrated includes a single ground or common terminal  242  that connects electrically via separate fuse links  234  and  236  to load terminals  240  and  244 . 
         [0099]    Fuse  210  includes an insulating substrate  212 . Insulating substrate  212  includes a top  214 , a bottom  216 , sides  220  and  222 , a front  226  and a rear  218 . A fuse link  234  is placed on the top  214  of substrate  212 . Fuse link  234  includes a first conductive pathway  234   a  that extends to load terminal  240 . Fuse link  234  includes a second conductive pathway  234   b  that extends to ground or common terminal  242 . 
         [0100]    Fuse link  236  is placed on the bottom  216  of substrate  212  of fuse  210 . Fuse link  236  includes a first conductive pathway  236   a  that extends to load terminal  244 . Fuse link  236  includes a second conductive pathway  236   b  that extends to ground or common terminal  242 . 
         [0101]    A metal deposition  250  is placed fuse link  234 . A metal deposition  252  is disposed on fuse link  236 . Fuse links  234  and  236  are secured to substrate  212  via any of the embodiments discussed above. Likewise, metal depositions  250  and  252  are made according to any of the embodiments discussed herein. Metal depositions  250  and  252  as well as fuse links  234  and  236  can be rated the same or differently. The fuse links are separated from one another in three dimensions for thermal decoupling. The non-symmetrical relationship between fuse links  234  and  236  also makes fuse  210  well suited for different current ratings because the fuse  210  is difficult to mount improperly. 
         [0102]    As seen in  FIGS. 8A and 8C , three of the four corners of substrate  212  are metallized via terminals  240 ,  242  and  244 . For reasons discussed above, dummy terminal  246  is provided in one preferred embodiment. As further illustrated, each of the terminals extends around portions of three different sides of substrate  212 . Terminals  240  to  246  can each be plated with multiple conductive layers, such as multiple copper layers, nickel, silver, gold or lead-tin layers as can the terminals of any of the fuses discussed herein. 
         [0103]    Fuse  210  protects multiple load lines that lead to a single ground or common terminal. It should be appreciated that it is also possible to provide two substrates  212  sandwiching an internal metal layer, which enables three or more load terminals to be fusibly connected to a single ground or common terminal  242 . Fuse  210  protects multiple load devices having a common negation or ground line. 
         [0104]    As seen in  FIG. 8B , fuse  210  includes cavity forming enclosures  253  and  255 . Enclosures  253  and  255  include lid and sidewall portions as described above. The sidewall portions are fixed to substrate  212  via any method described above. Enclosures  253  and  255  form gaps or cavities that enable the elements (located at depositions  250 ,  252 ) to deform upon opening without deforming or dislodging enclosures  253  and  255 . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material as described above. 
         [0105]    Enclosures  253  and  255  are shown covering portions of links  234  and  236  and deposition  250 ,  252  in  FIGS. 8A and 8C . 
         [0106]    Enclosures  253  and  255  inhibit corrosion and oxidation of the fusible links and metal depositions  250  and  252 . The enclosures also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  210 , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  210 . The enclosures also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0107]    As illustrated in  FIG. 8B , terminals  244  and  246  are built-up via multiple metal layers  244   a / 244   b  and  246   a / 246   b , respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  253  and  255 , respectively. This enables fuse  210  to be properly surface mounted. Terminals  240  and  242  are likewise built-up. Alternatively, substrate  212  can be machined as discussed above. 
         [0108]    Referring now to  FIGS. 9A and 9C , a further alternative embodiment of the present invention is illustrated by fuse  260 . In each of the previous embodiments, the fuse links and metal depositions were thermally insulated from one another by being placed on opposite sides of the insulating substrate. Also described herein, the fuse links and metal depositions can be separated by multiple substrates, for example, when three or more fuse links are provided and in an X-Y or planar direction. Fuse  260  on the other hand illustrates an alternative embodiment where multiple fuse links  284  and  286  each having a metal deposition  300  and  302 , respectively, are placed on a same surface  264  of substrate  262  of fuse  260 . It is possible that a planar separation between fuse links  184  and  186  can be made large enough to provide both links on the same surface of the substrate. It is therefore contemplated to place multiple fuse links on multiple surfaces, for example, to provide four total fuse links in one device. 
         [0109]    Fuse  260  includes a substrate  262  as mentioned. Substrate  262  includes a top  264 , a bottom  266 , sides  270  and  272 , a front  276  and a rear  268 . As discussed, fuse links  284  and  286  are placed on the same top surface  264  of fuse  260 . Fuse links  284  and  286  and their respective metal depositions  300  and  302  are rated the same or differently as desired. The fuse links and metal depositions are applied via any of the methods discussed above and include any of the different materials disclosed herein. 
         [0110]    Fuse link  284  includes a conductive pathway  284   a  that extends to terminal  290 . A conductive pathway  284   b  of fuse link  284  extends to terminal  292 . Likewise, conductive pathway  286   a  of fuse link  286  extends to terminal  294 , while conductive pathway  286   b  of fuse link  286  extends to terminal  296 . Terminals  290  to  296  each extend along three sides of substrate  262  as seen in  FIGS. 9A and 9C .  FIG. 9B  further illustrates that the terminals can be plated with multiple conductive layers as discussed above. 
         [0111]    Because fuse  260  is relatively symmetrical, the surface tension forces created during soldering should be balanced, making the mounting of fuse  260  to a parent PCB a process that is at least somewhat auto-aligning. The fuse is alternatively configured non-symmetrically, for example, when providing fuse links with different current ratings. 
         [0112]    As seen in  FIG. 9B , fuse  260  includes cavity forming enclosure  283 . Enclosure  283  includes lid and sidewall portions as described above. The sidewall portions are fixed to substrate  262  via any method described above. Enclosure  283  forms gaps or cavities that enable the elements to deform upon opening without deforming or dislodging enclosure  283 . The cavities may be partially or fully filled with a mechanically compliant, arc-quenching material as described above. 
         [0113]    Enclosure  283  inhibits corrosion and oxidation of the fusible links and metal depositions. The enclosures also protect those items from mechanical impact and aid in the distribution and manufacture of fuse  260 , for example, by providing a surface on which a tool can apply a vacuum to pick and place fuse  260 . The enclosures as discussed also help to control the melting, ionization and arching that occur when one of the fusible links opens upon an overload condition. 
         [0114]    As illustrated in  FIG. 9B , terminals  294  and  296  are built-up via multiple metal layers, respectively, so that the outer layers of the terminals are at least substantially flush with the top and bottom of enclosures  283  and  285 , respectively. This enables fuse  260  to be properly surface mounted. Terminals  290  and  292  are likewise built-up. 
         [0115]    At least one of the tops of enclosures  283  and  285  includes marking or branding indicia  304 , which includes any suitable information, such as fuse rating information, manufacturer information and the like. Any of the embodiments discussed herein can have indicia  304 . 
         [0116]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.