Abstract:
Fluid-based switches and methods for producing the same are disclosed. In one embodiment, a method for producing a switch comprises depositing a first alignment pad on a first substrate, depositing a second alignment pad on a second substrate, depositing solder on at least one of the alignment pads, depositing a switching fluid on the first substrate, and mating the first substrate to the second substrate by aligning the alignment pads and heating the solder, the substrates defining therebetween a cavity holding the switching fluid, the cavity being sized to allow movement of the switching fluid between first and second states.

Description:
BACKGROUND OF THE INVENTION 
     Fluid-based switches, such as liquid metal micro switches (LIMMS) have been made that use a liquid metal, such as mercury, as the switching element. The liquid metal may make and break electrical contacts. Alternately, a LIMMS may use an opaque liquid to open or block light paths. To change the state of the switch, a force is applied to the switching fluid, which causes it to change form and move. 
     Substrates used to manufacture the LIMMS may be held together with adhesives, such as polymers. The adhesives used may not withstand some assembly conditions (e.g., soldering temperatures). Additionally, polymers may absorb gases and/or moisture and may outgas during use, which may cause chemical contamination of the interiors of the package. Polymers also do not seal hermetically, so additional sealing is required to create a hermetic switch. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method for producing a switch is disclosed. The method comprises depositing a first alignment pad on a first substrate. A second alignment pad is deposited on a second substrate. Solder is then deposited on at least one of the alignment pads. A switching fluid is also deposited on the first substrate. The substrates are mated together by aligning the alignment pads and heating the solder. A cavity holding the switching fluid is defined between the two substrates, the cavity sized to allow movement of the switching fluid between first and second states. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative embodiments of the invention are illustrated in the drawings in which: 
     FIG. 1 illustrates an exemplary plan view of a substrate including switching fluid and alignment pads; 
     FIG. 2 is an elevation view of the substrate shown in FIG. 1; 
     FIG. 3 illustrates an exemplary plan view of a substrate including a switching fluid channel and alignment pads; 
     FIG. 4 is an elevation view of the substrate shown in FIG. 3; 
     FIG. 5 illustrates an elevation view of the substrates shown in FIGS. 1-4 soldered together to form a switch; 
     FIG. 6 illustrates a method to create the switch of FIG. 5; 
     FIG. 7 illustrates an elevation view of a second exemplary embodiment of the substrates shown in FIGS. 1-4 soldered together to form a switch; 
     FIG. 8 illustrates an elevation view of the substrate shown in FIG. 6 after heating; 
     FIG. 9 illustrates a perspective view of a first exemplary embodiment of a hermetically sealed switch; AND 
     FIG. 10 illustrates a perspective view of a second exemplary embodiment of a hermetically sealed switch; 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 illustrate a first substrate  100  for a fluid-based switch, such as a LIMMS. By way of example, the first substrate  100  may be ceramic, glass, ceramic-coated metal, or a combination of these materials. Other suitable materials may also be used. 
     Deposited on the substrate  100  are a plurality of wettable pads  102 ,  104 ,  106 , possibly serving as electrical contacts. Switching fluid  118  is deposited on the wettable pads  102 - 106 . Switching fluid  118  may be a liquid metal, such as mercury, and may be used to make and break electrical contacts or open and block light paths. 
     Also deposited on the substrate  100  are alignment pads  110 ,  112 . Alignment pads  110 ,  112  may be made of a wettable material, such as metal or metal alloys, and may be used to align and mate substrate  100  with a second substrate used to form a switch. It should be appreciated that alternate embodiments may include a different number of alignment pads  110 ,  112  and/or wettable pads  102 ,  104 ,  106  than that depicted in FIGS. 1 and 2. 
     Solder  114  is deposited on each alignment pad  110 ,  112 . By way of example, solder  114  may be a solder with a high-melting point. Solder  114  may be used to mate the first substrate  100  to a second substrate used in the formation of the switch. In alternate embodiments, solder  114  may alternately or additionally be deposited on alignment pads located on the second substrate. 
     Seal ring  120  is deposited on at least a portion of the perimeter of the first substrate  100 . By way of example, seal ring  120  may be made of a wettable material, such as metal or metal alloys. As will be described in further detail below, seal ring  120  may be used to hermetically seal the switch. Sealing ring  120  may not be included in alternate embodiments. 
     FIGS. 3 and 4 illustrate a second substrate  300  used in a fluid based-switch. The second substrate  300  includes a switching fluid channel  304 , a pair of actuating fluid channels  302 ,  306 , and a pair of channels  308 ,  310  that connect corresponding ones of the actuating fluid channels  302 ,  306  to the switching fluid channel  304 . It is envisioned that more or fewer channels may be formed in the substrate  300 , depending on the configuration of the switch in which the substrate is to be used. For example, the pair of actuating fluid channels  302 ,  306  and pair of connecting channels  308 ,  310  may be replaced by a single actuating fluid channel and single connecting channel. Additionally, it is envisioned that in alternate embodiments, channels or portions of channels may be formed in the first substrate  100  used to construct the switch. 
     In some embodiments, substrate  300  may comprise multiple layers that are used to form the channels of the substrate  300 . The layers may provide a gap between seal rings  120 ,  340  for solder to flow into to hermetically seal the switch. The layers may also provide better control of cavity volumes during manufacturing. By way of example, the layers may be glass, ceramic, ceramic-coated metal, a combination of these materials, or other suitable materials. The layers of the substrate  300  may be assembled together by anodically bonding or fusion bonding them together. This may provide a more robust bond able to withstand other assembly conditions, such as soldering, and may reduce or eliminate the risk of chemical contamination. However, in alternate embodiments using multiple layers, adhesives or other bonding methods may also be used. 
     The substrate  300  also includes seal ring  340  deposited on at least a portion of the perimeter of the substrate  300 . By way of example, seal ring  340  may be made of a wettable material, such as metal or metal alloys. As will be described in further detail below, seal ring  340  may be used to hermetically seal the switch. It should be appreciated that in alternate embodiments, substrate  300  may not include seal ring  120 . 
     Substrate  300  further includes alignment pads  320 ,  322 . Alignment pads  320 ,  322  may be made of a wettable material, such as metal or metal alloys, and may be used to align and mate substrate  300  with a first substrate  100  to form a switch. It should be appreciated that alternate embodiments may include a different number of alignment pads. It should also be appreciated that solder  114  may alternately, or additionally, be deposited on one or more of the alignment pads  320 ,  322  on the second substrate  300 . 
     Seal belts  332 ,  334 ,  336  may also optionally be deposited on substrate  300 . They may be made of a wettable material, such as metal or metal alloys. The use of seal belts within a switching fluid channel  304  may provide additional surface areas to which a switching fluid may wet. This not only helps in latching the various states that a switching fluid can assume, but also helps to create a sealed chamber from which the switching fluid cannot escape, and within which the switching fluid may be more easily pumped (i.e., during switch state changes). It should be appreciated that alternate embodiments may not include seal belts  332 - 336 . 
     FIG. 5 illustrates a fluid-based switch that may be formed by soldering together substrates  100 ,  300 . As illustrated by FIG. 6, the switch may be made by forming  600  at least two substrates  100 ,  300 , so that the substrates mated together define between them portions of a number of cavities. Each substrate may include a seal ring  120 ,  340  deposited on a portion of the perimeter of the substrate that may be used to hermetically seal the switch. In alternate embodiments, seal rings  120 ,  340  may not be included. 
     Next, alignment pads  110 ,  112  are deposited  605  on the first substrate and alignment pads  320 ,  322  are deposited  610  on the second substrate. Solder  114  is deposited  615  on at least one of the alignment pads  110 ,  112 ,  320 ,  322 . Additionally, switching fluid  118  is deposited  620  on one of the substrates  100 . It should be appreciated that the switching fluid  118  and the alignment pads  110 ,  112 ,  320 ,  322  may be deposited in any order. In alternate embodiments, before depositing switching fluid  118  or alignment pads  110 ,  112  on the substrates  100 ,  300 , one or both of the substrates may be made flat and smooth (e.g., by lapping, polishing, or chemical mechanical polishing) to aid in the bonding of the substrates. 
     Finally, the first substrate  100  is mated  625  to the second substrate  300  by aligning  630  their respective alignment pads  110 / 320 ,  112 / 33 , and heating  635  the solder  114 . The substrates  100 ,  300  may be brought into close contact with each other by pressing the substrates together during the heating of the solder  114 , which may improve switch performance by minimizing leakage of gases and/or liquids passing between the substrates. It should be appreciated, that by using an adhesive-free method to bond the substrates together and create the switch, the risk of chemical contamination to the interior of the switch may be reduced or eliminated. Additionally, the solder  114  may be better able to withstand other assembly conditions. 
     FIGS. 7 and 8 illustrate a second exemplary embodiment of a switch that is hermetically sealed. The switch comprises substrates  100 ,  300  mated together so that portions of a number of cavities are defined between the substrates. Each substrate  100 ,  300  includes a seal ring  120 ,  340  deposited on a portion of the perimeter of the respective substrate. By way of example, seal rings  120 ,  340  may be a wettable material, such as metal or metal alloys. Substrate  300  further includes seal belts  332 ,  334 ,  336  to provide additional surface area for switching fluid  118  to wet. Alternate embodiments may not include seal belts  332 - 336 . 
     The substrates  100 ,  300  may be soldered  114  together as previously described. A hermetic seal may then be created by dispensing a solder paste with epoxy flux  702  on at least one of the substrates. The solder paste may then be heated to wet the solder  804  to the seal rings  120 ,  340  and create the hermetic seal. In one embodiment, solder  114  used to assemble the substrates may have a higher melting point than the solder  804  used to create the hermetic seal, which may prevent the solder  114  from melting during the creating of the hermetic seal. Epoxy flux  802  surrounds at least a portion of the solder  804  and may protect the solder from vapors created by the switching fluid  118 . It should be appreciated that alternate embodiments may not include epoxy flux  802 . 
     FIG. 9 illustrates a first exemplary embodiment of a fluid-based switch including a hermetic seal  930 . The switch  900  comprises a first substrate  902  and a second substrate  904  mated together. Substrates  902 ,  904  may be soldered together as described previously in this application. The switch may then be hermetically sealed as described with reference to FIGS. 7 and 8. By using an adhesive-free method to assemble the substrates, the risk of chemical contamination to the interior of the switch may be reduced or eliminated. It should be appreciated that in alternate embodiments, the switch  900  may not include the hermetic seal  930 . 
     The substrates  902  and  904  define between them a number of cavities  906 ,  908 , and  910 . Exposed within one or more of the cavities are a plurality of electrodes  912 ,  914 ,  916 . A switching fluid  918  (e.g., a conductive liquid metal such as mercury) held within one or more of the cavities serves to open and close at least a pair of the plurality of electrodes  912 - 916  in response to forces that are applied to the switching fluid  918 . An actuating fluid  920  (e.g., an inert gas or liquid) held within one or more of the cavities serves to apply the forces to the switching fluid  918 . 
     In one embodiment of the switch  900 , the forces applied to the switching fluid  918  result from pressure changes in the actuating fluid  920 . The pressure changes in the actuating fluid  920  impart pressure changes to the switching fluid  918 , and thereby cause the switching fluid  918  to change form, move, part, etc. In FIG. 9, the pressure of the actuating fluid  920  held in cavity  906  applies a force to part the switching fluid  918  as illustrated. In this state, the rightmost pair of electrodes  914 ,  916  of the switch  900  are coupled to one another. If the pressure of the actuating fluid  920  held in cavity  906  is relieved, and the pressure of the actuating fluid  920  held in cavity  910  is increased, the switching fluid  918  can be forced to part and merge so that electrodes  914  and  916  are decoupled and electrodes  912  and  914  are coupled. 
     By way of example, pressure changes in the actuating fluid  920  may be achieved by means of heating the actuating fluid  920 , or by means of piezoelectric pumping. The former is described in U.S. Pat. No. 6,323,447 of Kondoh et al. entitled “Electrical Contact Breaker Switch, Integrated Electrical Contact Breaker Switch, and Electrical Contact Switching Method”, which is hereby incorporated by reference for all that it discloses. The latter is described in U.S. patent application Ser. No. 10/137,691 of Marvin Glenn Wong filed May 2, 2002 and entitled “A Piezoelectrically Actuated Liquid Metal Switch”, which is also incorporated by reference for all that it discloses. Although the above referenced patent and patent application disclose the movement of a switching fluid by means of dual push/pull actuating fluid cavities, a single push/pull actuating fluid cavity might suffice if significant enough push/pull pressure changes could be imparted to a switching fluid from such a cavity. Additional details concerning the construction and operation of a switch such as that which is illustrated in FIG. 9 may be found in the afore-mentioned patent of Kondoh. 
     FIG. 10 illustrates a second exemplary embodiment of a switch  1000 . The switch  1000  comprises a substrate  1002  and a second substrate  1004  mated together. Substrates  1002 ,  1004  may be soldered together as previously described. Switch  1000  may then be hermetically sealed as described with reference to FIGS. 7 and 8. In alternate embodiments, switch  1000  may not include hermetic seal  930 . It should be appreciated that by using an adhesive-free method to assemble the substrates, the risk of chemical contamination to the interior of the switch  1000  may be reduced or eliminated and the bonding between the substrates  902 ,  904  may be better able to withstand other assembly or operating conditions than adhesives. 
     The substrates  1002  and  1004  define between them a number of cavities  1006 ,  1008 ,  1010 . Exposed within one or more of the cavities are a plurality of wettable pads  1012 - 1016 . A switching fluid  1018  (e.g., a liquid metal such as mercury) is wettable to the pads  1012 - 1016  and is held within one or more of the cavities. The switching fluid  1018  serves to open and block light paths  1022 / 1024 ,  1026 / 1028  through one or more of the cavities, in response to forces that are applied to the switching fluid  1018 . By way of example, the light paths may be defined by waveguides  1022 - 1028  that are aligned with translucent windows in the cavity  1008  holding the switching fluid. Blocking of the light paths  1022 / 1024 ,  1026 / 1028  may be achieved by virtue of the switching fluid  1018  being opaque. An actuating fluid  1020  (e.g., an inert gas or liquid) held within one or more of the cavities serves to apply the forces to the switching fluid  1018 . 
     Additional details concerning the construction and operation of a switch such as that which is illustrated in FIG. 10 may be found in the aforementioned patent of Kondoh et al., and patent application of Marvin Wong. 
     While illustrative and presently preferred embodiments of the invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.