Abstract:
An array of ultra-thin metallic foil strips of predetermined thickness electrically connected to a printed circuit board, cables or attached to wires. An associated power source, on the printed circuit board, or attached to the circuit board, cables or wires, directs an electrical current through one or more of the strips in the array of foil strips. Depending upon the use of the circuit board, the foil strips can be used to start or to end an operation. The selection of the foil strip makes use of the electrical properties of the selected metal such as its resistivity as well as the thickness, length and width of the foil strips to provide a strip with characteristics required to achieve a preselected result. As an electric current is provided by a power source, it passes through contacts connected to the one or more foil strips. The application of current through the metallic material can be used to achieve a number of results, such as to act as a heating element.

Description:
This application claims the benefit of the filing date of Provisional Application 60/864,850 entitled MECHANICALLY INTERCONNECTED FOIL CONTACT ARRAY AND METHOD OF MANUFACTURING filed on Nov. 8, 2006. 

   FIELD OF THE INVENTION 
   The present invention is directed to an ultra-thin flexible circuit and specifically to the use of the ultra-thin flexible circuit to control an operation. 
   BACKGROUND OF THE INVENTION 
   Microchip devices have been used for a wide variety of applications. However, these devices have not included ultra-thin metal foils. Simple problems faced in utilizing these ultra-thin foils in microchip devices include handling the foils, as they are susceptible to tearing. More complex problems include assembling the foils to other components of the microchip devices. These methods are required to establish good mechanical contact between the foil and the associated devices, as well as applying normal forces to the foil without damaging it so as to retain it in position once mechanical contact is established. Since the ultra-thin metal foils in microchip devices will carry electrical current, it is also difficult and necessary to clean the surface of the foils of oxides without damaging, tearing or puncturing the foil. 
   Before ultra-thin metal foils can be used as production items for microchips, solutions to these problems must be found. Uses for such ultra-thin foils in microchips are limited because of these problems, but will expand once solutions to these problems are presented. 
   SUMMARY OF THE INVENTION 
   The present invention is an array of metallic foil strips of predetermined thickness electrically connected to a printed circuit board, cables or attached to wires. An associated power source, on the printed circuit board, or attached to the circuit board, cables or wires, directs an electrical current through one or more preselected strips in the array of foil strips. Depending upon the use of the circuit board, the foil strips can be used to start or to end an operation. 
   The selection of the foil strip makes use of the electrical properties of the metal such as its resistivity as well as the thickness and width of the foil strips to provide a strip with characteristics required to achieve a preselected result. As an electric current is provided by a power source, it passes through contacts connected to the one or more foil strips. The application of current through the metallic material can be used to achieve a number of results. For example, the current can cause the temperature of one or more foil strips to increase, due to the resistivity of the selected metal, causing the foil to act as a heating element. 
   There are a number of factors that can be varied to achieve a preselected foil temperature. Certainly, one of the factors is the resistivity of the metallic material selected. The thickness of the foil as well as the width of the metallic material in a strip can also affect the foil temperature. Of course, the current supplied also affects the foil temperature. Thus, by careful selection of the metallic material, foil thickness, foil width and foil length and current supplied, the effective temperature of the foil, and a control device, which may conveniently be included on a printed circuit board, the metal foil an be used as a variable heating element to carefully control the temperature within a confined space. 
   Yet another advantage of the present invention is that the printed circuit board can be used multiple times before replacement by providing the printed circuit board with logic to apply the current to different elements in the array of foil strip elements sequentially or in seriatim. 
   Another advantage of the present invention is that the foil can be used as a coated substrate, the substrate being protected from exposure to an environment until a predetermined temperature is achieved, thereby liberating a coating material on the substrate and exposing the substrate. 
   Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a foil array of the present invention. 
       FIG. 2  is an exploded view of the housing having apertures, a contact adjacent to one of the apertures and a beam of the present invention. 
       FIG. 3  depicts the housing from at top view, in cross-section and a blow-up of an aperture. 
       FIG. 4  is a perspective view of the foil assembly of the present invention being assembled to the housing. 
       FIG. 5  is a schematic depicting the assembly being assembled to a printed circuit board. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides an ultra-thin metallic foil as an array of strips electrically connected to a power supply that provides an electrical current through the metallic foil. As used herein, an ultra-thin metallic foil means a metallic foil having a thickness of 0.005 inches and thinner. Preferably, the ultra-thin metallic foil is connected to a printed circuit board (PCB) that either includes the power supply or is connected to the power supply. Preferably the foil connections are mechanical in nature, although the foil also can function when connected metallurgically, such as by soldering. A foil array  10  is depicted in  FIG. 1 . An exploded view of a housing  12 , a contact  22  and a beam  30  are shown in  FIG. 2 . Housing includes a plurality of apertures  20 . A contact  22  is assembled into the apertures  20 . Depending on the strip, it is not necessary that a contact  22  be assembled into every aperture. However, in order to complete a circuit, it is necessary for a contact to be assembled onto corresponding apertures on opposed sides  13 ,  15  of housing  12 . 
   The housing is depicted in  FIG. 3 .  FIG. 3A  depicts a top view of the housing  12 , while  FIG. 3B  depicts a cross section of the housing  12 , while  FIG. 3C  depicts a detailed view of a housing aperture  20 . The housing  12  includes a plurality of apertures  20 . A contact  22  is assembled into apertures  20  on opposed sides  13 , 15  of housing  12 , the spacing of the assembled contacts  22  corresponding to the spacing of the strips in the foil array  10 . 
   Referring again to  FIG. 2 , each contact  22  includes an upper U-shaped portion  24  having a pair of arms  26  connected to a lower leg  28 . The upper U-shaped portion  24  of each contact is sized to reside in the upper portion  21  of aperture  20 . The upper portion  21  of aperture  20  is preferably slightly wider than the upper U-shaped portion  24  of contact. Similarly, the lower portion  23  of aperture  20  is slightly wider than the lower leg  28  of contact  22 . This allows contacts  22  to float within the housing  12  thereby allowing forces on the strip to reach equilibrium. The lower leg  28  of each contact  22  extends through housing  24 , allowing the assembly to be connected to form a complete circuit by establishing a connection between the strips  14  at one end and the legs  28  at the other. The lower leg extending through the housing is clearly depicted in  FIG. 4 . The foil array  10  assembled to a housing  12  having contacts  22  utilizing a beam  30  constitutes an assembly  38 . While  FIG. 2  illustrates a preferred geometry for contact  22 , other contact configurations that establish a reliable connection between the contact  22  and the foil to establish a circuit through assembly  38  are also contemplated by the invention. 
   Foil array  10  is assembled to housing  12  as depicted in  FIG. 4 . Foil array  10  comprises a plurality of strips  14  that span the housing  12  laterally. The strips are connected longitudinally, perpendicular to the direction that the plurality of strips  14  span the housing, by attachment to a longitudinal band  16  at each end of each strip  14 . Each of the strips in the plurality of strips spans the same distance about the housing  12 . The longitudinal bands  16  may be attached to a ribbon (not shown) wider than a strip positioned at each end of the foil array  10  parallel to the plurality of strips. The longitudinal bands  16  and ribbons are provided to assist in handling the foil array and may be removed after assembly is completed. The foil array  10 , which can be fabricated as a roll that includes a plurality of separable foil arrays, is assembled to the housing  12 . The foil array  10  is assembled across the housing  12  and guided by guide ribs  17  in the housing so that the array of strips correspond to contacts  22  in the apertures  20  on opposite sides  13 ,  15  of housing  12 . Next, a pair of beams  30  is provided. The beams  30  include a plurality of fingers  32  extending away from beam top surface  34 , each finger sized to be assembled into an aperture  20  that includes a contact  22 . Although beams  30  are shown individually as a separate pair, it will be understood that beams  30  can be provided as a single piece having a plurality of fingers  32  corresponding to apertures  20  extending away from a top surface. 
   A mandrel  50  is provided to support the foil array  10  during assembly. The mandrel  50  is a small surface area mandrel that contacts the plurality of strips on the underside, that is, on the side opposite of the beam top surface  34  as shown in  FIG. 4 . As the beams  30  are inserted into the apertures, each of the fingers  32  applies a normal force to the portion of each strip  14  of the plurality of strips that it contacts, urging it downward and into the upper U-shaped portion  24  of contact  22 , slightly deflecting the arms  26  of contact  22  outwardly within the aperture toward the walls of the housing. This is possible as the upper portion  21  of aperture  20  is slightly larger than the U-shaped portion  24  of the contact  22 . The thin foil is self-centered in the U-shaped portion  24  of contact  22 , and thus captured in the aperture by the upper U-shaped portion  24  between the arms  26  and the finger  32 , the finger exerting a force on the both the arms  26 , placing the arms in tension and a normal force on the foil strip  24  adequate to break any oxides on the metal foil. A two-point contact between the foil strip  14  and the contact  22  is established by this arrangement. If desired, the beams  30  may include a latch feature such as depicted in  FIG. 2 , on at least one end of each beam  30 , and preferably a latch  36  at each end of the beam  30 , for retaining the beam and contacts in housing  12 . This can be a male latch device in the beam and a female latch receiving mechanism in the housing. In this circumstance, the housing includes at least one corresponding structure, here a latch-receiving aperture  40  as a mating feature to correspond to the latch feature  36  of the beam  30 . The latch feature  36  is depicted in  FIG. 2  as a shouldered protrusion, and the mating feature in the housing is a slot  40  that captures the shoulder on the protrusion. However, these configurations may be reversed. These are preferred embodiments, and any other suitable locking mechanism may be used. 
   The mandrel  50  provides support for the foil array  10  as the beams  30  are pushed downward. After the assembly of foil array  10  into the contacts on a first side of housing  12  using a beam  30 , thereby trapping the foil array  10  on the first side of the housing, the foil is draped over small area mandrel  50  and maintained in contact with the mandrel  50  as the free end of the foil array is identically assembled into the opposite side of the housing  12 , after which mandrel  50  can be removed. At this point the plurality of strips  10  are in compression, which is evident since a slight radius exists in the strips across the span between the apertures  20  in the housing  12 . A mandrel  50  is inserted as described between the opposed sides  13 ,  15  of housing against the foil array until the strips spanning the mandrel are taut. In a preferred embodiment, the mandrel should be sized to contact about 50% or less of each strip of the plurality of strips between apertures on either side of the housing as the assembly proceeds. Preferably, the mandrel should be sized to contact about 25% or less of each strip of the plurality of strips between apertures on either side of the housing as the assembly proceeds. Most preferably, the mandrel should be sized to contact about 10% or less of each strip of the plurality of strips between apertures on either side of the housing as the assembly proceeds. Then the beams are assembled, capturing the foil strips  14  in the contacts as described above. Upon removal of the mandrel  50 , any applied tensile stresses in the strips between opposed sides  13 ,  15  are removed. In an alternate embodiment, the strips may be sufficiently long to allow them to be looped around convoluted or arcuate areas in which substantially straight strips cannot be utilized. In this circumstance, no mandrel  50  is required to assemble the foil array to the housing. Also increasing the length of the arc will vary the resistance of the strip, thereby permitting further control of heat capacity of the strip. Thus, by carefully controlling the length of the strips and the geometry of the foil, the arc length of the assembled foil can be varied as desired. 
   The foil array  10  when joined to the housing  12 , as described above, is firmly seated in the upper U-shaped portion  24  of contacts  22 , the lower leg  28  of contacts protruding through the bottom of housing  12  constitutes an assembly. With the plurality of strips  14  captured in apertures  20  on either side  13 ,  15  of the housing, the foil material  62  extending outwardly beyond the housing is removed by any convenient method. Preferably, a trimming tool can be used to remove the excess foil in a single operation. A circuit exists running from the lower leg  28  of contact  22  extending below housing  12 . The plurality of strips form an arch  64 , the strips relaxing to a compressive state on removal of the mandrel. The strips thus do not form a plane across the sides of housing  13 ,  15 , but rather form an arch that extends slightly above a plane that would include the top surface of the housing  12 . Preferably, the apex of the arch formed by each strip is a point, such that these points formed by the apex of each strip form substantially a straight line. As used herein, the term “form substantially a straight line” is governed by good manufacturing practice. The circuit runs through the contact, across strip  66  to the contact on opposed side of housing  13  to the lower leg  28 . A plurality of separate circuits are thus provided. Clearly, if no strip is provided in the foil array at a position across opposed contacts on the housing, no circuit is available at this position. Alternatively, if contacts are omitted in apertures on one or both sides of the housing, again no circuit is available. Thus it is possible to tailor the final assembly to a predetermined configuration, if desired. This can be particularly useful if a circuit is not desired or required across each and every pair of apertures. This assembly  38  can then be connected to a power source, such as being plugged into a PCB  60  as depicted in  FIG. 5 , in a preferred embodiment. A controller can be provided as required, and may readily be included as part of the PCB or as a separate component. The controller can be configured and programmed to allow a flow of current across a single strip in the foil array  10 , or over a plurality of strips  14  in the array  10 , as desired 
   In operation, each strip  14  in the foil array  10  is designed to allow passage of a preselected amount of current. The PCB can be designed so that the preselected current passes through each strip only once, if so desired. There are a number of uses for such a device. For example, each strip can be designed so that a strip fails if the current exceeds a predetermined level. Alternately, the PCB can be designed so that when a predetermined current level is reached, additional strips automatically can be switched in to the circuit to provide additional current to meet a demand. A material of high conductivity should be provided for this application, such as copper. The strip can also be designed so that the current passing through it results in the strip reaching a preselected temperature, at which temperature a physical event occurs, such as the melting of an applied material The strips can be designed to provide heat, in which the material selected should have a high resistivity, allowing each strip to be a resistance heater. One such material is stainless steel, such as a high chromium stainless such as a 300 series stainless steel, and preferably a 304 stainless steel. Not only do such steels form good resistors, but also resist oxidation/corrosion at elevated temperatures. This can allow precision heating of a small space by carefully controlling the heat input into the space. Clearly, the use of the foil will dictate its design, and the design is within the skill of the artisan once the use is known. Thus, a preselected temperature or current carrying capability can be achieved by proper selection of material, strip width and strip thickness. The material selected for the foil can have a high resistivity or high conductivity, depending on the application. For most applications, the foil thickness is about 0.0005 inches (about 12 microns) although thicknesses as thick as 0.005 inches and as low as about 0.0001 inch can be utilized. The only limitation on the minimum thickness is the ability to manufacture foil of sufficient thickness. The most cost effective method for manufacturing foil is by rolling it to the desired thickness and then slitting it into the desired array pattern. The configuration of the foil can also be achieved by chemical etching or laser cutting. Stamping of the configuration may also be possible. However, it may be possible to achieve micron or even submicron foil thicknesses by electrochemical etching or vapor deposition methods, although such methods will substantially increase the cost and require special handling precautions to prevent damage to the foil. 
   While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.