Abstract:
An array of 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 L-shaped contacts to one or more of the strips in the array of foil strips. The foil strips are in contact with horizontal legs of the L-shaped contacts. 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 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 60/864,804 entitled MECHANICALLY INTERCONNECTED FOIL CONTACT ARRAY HAVING L-SHAPED CONTACTS AND METHOD OF MAKING 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 L-shaped contacts mechanically connected, and therefore electrically connected, to the one or more foil strips. The L-shaped contacts are inserted into a housing and the foil strip is captured between the L-shaped contacts and a beam that is ultrasonically welded to the L-shaped housing. 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 as part of the foil selection process. 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. 
   An 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 a partial view of the housing having pockets, an L-shaped contact assembled into one of the pockets in accordance with the present invention. 
       FIG. 3  depicts an L-shaped contact of the present invention. 
       FIG. 4  is a partial schematic of the foil assembled to the housing to form an assembly in accordance with the present invention. 
       FIG. 5  is a perspective view of one embodiment of a beam of the present invention. 
       FIG. 6  is a perspective view of the foil assembly of the present invention being assembled to the housing. 
       FIG. 7  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 enlarged view of a portion of housing  12  with an inserted L-shaped contact  22  is shown in  FIG. 2 . Housing includes a plurality of apertures  20  and a plurality of pockets  66 . An L-shaped contact  22  having a horizontal leg  24  is assembled into the pocket  66 .  FIG. 3  depicts the L-shaped contact  22  having a vertical leg  23  and a horizontal leg  24 . The vertical leg  23  of each contact  22  is assembled into an aperture  20  of the housing so that the vertical leg  23  extends from the bottom of the housing, shown in  FIG. 4 , while the horizontal leg  24  of each L-shaped contact  22  is assembled into one of the pockets  66  formed in a top surface  68  of the housing, so that the horizontal leg  24  of the contact  22  seats in the pocket  66 . A top surface  70  of the horizontal leg  24  assembled in the pocket  66  is either flush with or sits just below the top surface  68  of the housing  12 . Depending on the foil array  10  that includes strips  14 , it is not necessary that a contact  22  be assembled into every aperture  20 . 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 . 
     FIG. 4  depicts the assembly comprising housing  12 , a plurality of L-shaped contacts  22  assembled to the housing  12  so that the vertical legs  23  of the L-shaped contacts  22  extend from the bottom of housing  12 , foil array  10  comprising a plurality of strips  14  assembled over the contacts  22  so that the strips are in contact with the horizontal legs  24  of the contacts and captured between the legs  24  and beam  30 , one beam  30  assembled to the opposed sides  13 ,  15  of the housing. 
   Referring again to  FIG. 3 , each contact  22  includes a vertical leg  23  and a horizontal leg  24 , the vertical leg  23  being assembled into aperture  20  of housing  12 . In order to facilitate the assembly of foil array  10  comprising a plurality of strips  14  over the horizontal leg  24 , housing  12  includes guides to assist in guiding the thin strips over the horizontal legs of aperture  20 . The guide feature can take many forms. Simply designing the housing and the L-shaped contacts so that the top surface  70  of the horizontal legs of the contacts are below the housing top surface allows the housing pocket above the legs to act as a guide. In this circumstance, beam  30  can be designed as shown in the partial cross section in  FIG. 5 . Beam  30  includes a plurality of ribs  72  projecting downward from a bottom surface  74  of the beam. The bottom surface of the beam is a mirror image of housing top surface  68 , the ribs  72  fitting into the housing pockets  66  to capture the plurality of strips between the horizontal legs  68  and the beams  30 . Beam bottom surface  74  contacts housing top surface  68 . The beam is secured by any convenient method. In a preferred embodiment, both the beam and housing being comprised of a polymeric material, the beam and housing are secured by ultrasonic welding. However, the present invention contemplates any other form of securing the beam to the housing to capture the strips between beam  30  and horizontal legs  24  including the use of an adhesive or mechanical fastening such as latches. 
   The plurality of guides are not limited to the use of the pockets, which may be considered a negative guide. The guides may include positive projections extending from housing top surface  68 . These guides facilitate the assembly of the strips between these projections. The projections can extend across only a part of the housing so that beams  30  can be assembled to the housing to capture strips  14  without interfering with the projections. Alternatively, the beams may include apertures to accept the projections. Again, any variety of arrangements can be used to assemble the beams  30  to the housing  12  in order to capture the strips between the beam and the horizontal leg  24 , thereby securing the mechanical connection between the strips and the horizontal leg, the above examples being illustrative of some of the arrangements. 
   The vertical leg  23  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 through the contact to the vertical legs  23  at the other. The vertical legs  23  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 . 
   Foil array  10  is assembled to housing  12  as depicted in  FIG. 4 . Foil array  10  comprises a plurality of strips  14  that span 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 ,  FIG. 1 , 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 . After insertion of L-shaped contacts  22  into housing  12 , foil array  10  is assembled across the housing  12  and guided into position by guides, either positive or negative so that the strips  14  of foil array  10  are in contact overlying horizontal leg  24  of contact  22  on opposite sides  13 ,  15  of housing  12 , the foil array between the opposite sides  13 ,  15  of housing  12 . Next, a pair of beams  30  is provided. The beams  30  capture the strips  14  of foil array  10  and secure the strips against the horizontal arms of contacts  22 . Ideally, beams  30  are designed to matingly engage with the housing  12  so that beam bottom surface  74  contacts housing top surface  68 . Thus, the housing and the beams include features that correspond to allow them to mate. Contact between not only the beams and the metallic foil, but also between the bottom surface of the beam and the top surface of the housing allows for the establishment of a reliable and secure assembly. Although beams  30  are shown individually as a separate pair, it will be understood that beams  30  can be provided as a single piece that can be assembled to housing  12 . 
   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. 6 . In the embodiment shown in  FIG. 6 , positive guides  17  project upward from housing top surface  68 . The beams  30  include apertures corresponding the positive guides, the apertures in the bottom surface of beams  30  and not visible in this view. The beams  30  apply a normal force to each strip  14  of the plurality of strips securing them against the horizontal leg  24  of contact  22 . Beams are secured in contact with the housing  12 , by any convenient means as discussed above. If desired, the beams  30  may include a latch feature such as depicted in  FIG. 6 , on at least one end of each beam  30 , and preferably a latch  36  at each end of the beam  30 , as an alternate or additional method of securing the beam 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 as a mating feature to correspond to the latch feature  36  of the beam  30 . Any other suitable mechanism may be used to secure beams  30  to housing  12 . 
   The mandrel  50  provides support for the foil array  10  as the beams  30  are moved downward against the foil array  10  and housing  12 . After securing beams  30  against housing  12  of foil array  10  into the contacts on a first side of housing  12  using a beam  30 , thereby capturing foil array  10  between horizontal legs  24  of contact  22  and beam  30  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. On removal of the mandrel, the plurality of strips  14  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 . 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. During assembly, 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. Then the beams are assembled, capturing the foil strips  14  as described above. Also increasing the length of the strips 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  once assembled to the housing  12 , as described above, is firmly captured between beams  30  and horizontal legs  24  of contacts  22 , the lower legs  23  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. 7 , 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.