Abstract:
A sole and printed circuit assembly for an article of electrostatic dissipative footwear. The present invention also includes a method of manufacturing a sole for an article of electrostatic dissipative footwear.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to footwear and, more particularly, to footwear constructed to dissipate electrostatic charges.  
           [0003]    2. Description of the Invention Background  
           [0004]    Static electricity is the accumulation of electric charge in an insulated body, most frequently caused by friction, but also by other means, such as induction etc. Electrostatic discharge (ESD) is the transfer of electric charge between two bodies, often accompanied by a visible spark, as in the familiar phenomenon of doorknob shock. While electrostatic discharge per se may not be immediately harmful to a human body, at least at level of voltage less than about 3000 volts, a discharge of much smaller voltage might be damaging to sensitive equipment, such as electronic components for computers and magnetic data carriers. A low volt electrostatic discharge may also ignite explosive gases. Accordingly, protection against ESD is required in the electronics and telecommunications industries and in other industries wherein sensitive electrical components or explosive materials are being handled.  
           [0005]    ESD is of particular concern to the electronics industries. For example, if a quality control inspector carries a static charge during an inspection or testing operation, at a minimum, the accuracy of the test may be affected or, in worse cases, one or more sensitive components may be damaged. One method commonly employed to address this problem is the use of conductive footwear. By wearing a pair of conductive shoes, the person testing the electronic products is electrically grounded and the static charge is therefore eliminated. Various tests have shown that conductivity, more specifically, the impedance of a conductive shoe must be maintained within a certain range. One company in the computer and electronics industry recommends that the impedance of a conductive shoe be maintained within 10 6  ohms to 10 7  ohms. Other forms of grounding have been used to dissipate the electrostatic charge before it builds up to harmful levels. Such grounding measures include installing conductive or dissipative floors or stepping mats and/or wearing conductive wrist straps.  
           [0006]    The efficacy of antistatic devices such as footwear, wrist and heel straps, etc. is typically determined by the electrical resistance of the conducting surface of the device in ohms. This electrical resistance may be affected by various environmental factors, such as humidity, dirt and other contamination, wear and other damage. A variable or unreliable electrical resistance does not provide continuous and reliable protection, as required in many environments with components sensitive to relatively small electrostatic discharges.  
           [0007]    There remains, therefore, a need for footwear with improved electrostatic discharge properties that overcomes the limitations, shortcomings and disadvantages of the previous approaches.  
         SUMMARY OF THE INVENTION  
         [0008]    The invention meets the identified needs, as well as other needs, as will be more fully understood following a review of this specification and drawings.  
           [0009]    One embodiment of the invention comprises an electrostatic circuit for a sole having a conductive outsole, a conductive insole and a nonconductive midsole positioned between the insole and outsole. This embodiment of the electrostatic circuit includes a first substrate that has a first end and a second end. In one embodiment, the substrate is flexible and in another embodiment, the substrate may be relatively rigid and inflexible. The electrostatic circuit may further include at least one conductor path that is attached to the first substrate. Each conductor path has a first exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. Each conductor path also has a second exposed end that is adjacent to the second end of the substrate and that is attachable to the conductive insole. In addition, the circuit includes at least one resistor that is electrically coupled to each conductor path and mounted to the first substrate. In alternative embodiments, each end of the conductive paths may be attached to a corresponding conductive pad to provide an enlarged area for affixing the conductive path to the other components of the sole.  
           [0010]    Another embodiment of the present invention includes an electrostatic circuit for a sole that has a conductive outsole, a conductive insole and a nonconductive midsole between the insole and outsole. In this embodiment, the electrostatic circuit includes a first substrate that has a first end and a second end. A first conductor path is attached to the first substrate. The first conductor path has a first exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. The first conductor path also has a second exposed end that is adjacent to the second end of the first substrate and that is attachable to the conductive insole. A first resistor is supported on the first substrate and is electrically coupled to the first conductor path. In addition, a second conductor path is attached to the first substrate. The second conductor path has a second exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. The second conductor path also has a second exposed end that is adjacent to the second end of the first substrate and that is attachable to the conductive insole. A second resistor is supported on the first substrate and is electrically coupled to the second conductor path. A third conductor path is attached to the first substrate. The third conductor path has a first exposed end that is adjacent to the first end of the first substrate and is attachable to the conductive outsole. The third conductive path also has a second exposed end that is adjacent to the second end of the substrate and that is attachable to the conductive insole. A third resistor is supported on the first substrate and is electrically coupled to the third conductor path.  
           [0011]    Another embodiment of the present invention comprises a sole for a conductive shoe. The sole includes a conductive outsole and a midsole that is adjacent to the outsole. A conductive insole is adjacent to the midsole. The sole further includes a printed circuit that comprises a first substrate and at least one conductor path that is attached to the first substrate. Each conductor path has a first end that is attached to the conductive outsole and a second end that is attached to the conductive insole. At least one resistor is electrically coupled to each conductor path and mounted to the first substrate.  
           [0012]    Yet another embodiment of the present invention comprises a method for applying a desired amount of electrical impendence to an electrostatic current passing through a shoe having a conductive outsole, a conductive insole and a nonconductive midsole between the outsole and insole. The method includes affixing one end of a first conductive path formed on a substrate to the conductive outsole and electrically coupling a first resistor having the desired amount of impedance to the conductive path. The method further includes affixing another end of the first conductive path to the conductive insole.  
           [0013]    Another embodiment of the present invention comprises a method of manufacturing a sole for a conductive shoe. The method includes affixing a first conductive path to a substrate such that the first conductive path has a first exposed end and a second exposed end and attaching a first resistor to the first conductive path. The method also includes forming a conductive outsole and a nonelectrically conductive midsole and supporting the nonelectrically conductive midsole on the electrically conductive outsole. The method further includes forming an electrically conductive insole and supporting the electrically conductive insole to the nonelectrically conductive midsole. The substrate is supported within the midsole such that the first exposed end of the first conductive path is in electrical contact with the electrically conductive outsole and the second end of the first electrically conductive path is in electrical contact with the electrically conductive insole.  
           [0014]    Other features and advantages of the invention will become apparent from the detailed description of the embodiments set forth herein and from the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In the accompanying Figures, there are shown present embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein:  
         [0016]    [0016]FIG. 1 is a side elevational view of an item of footwear with an embodiment of a sole of the present invention with portions of the sole shown in cross-section;  
         [0017]    [0017]FIG. 2 is an enlarged partial view of the sole of FIG. 1 showing an orientation of one embodiment of a printed circuit of the present invention;  
         [0018]    [0018]FIG. 3 is a cross-sectional assembly view of the sole of FIG. 1;  
         [0019]    [0019]FIG. 4 is a top view of a midsole and a portion of a printed circuit of the present invention;  
         [0020]    [0020]FIG. 5 is a top view of an embodiment of a printed circuit of the present invention;  
         [0021]    [0021]FIG. 6 is a side elevational view of conductive paths of the printed circuit of FIG. 5;  
         [0022]    [0022]FIG. 7 is a bottom view of the printed circuit of FIG. 5;  
         [0023]    [0023]FIG. 8 is another top view of the printed circuit of FIG. 5, with a moisture barrier applied thereto;  
         [0024]    [0024]FIG. 9 is a cross-sectional exploded assembly view of the printed circuit of FIG. 8 taken along line IX-IX in FIG. 8;  
         [0025]    [0025]FIG. 10 is an enlarged partial view of another sole embodiment showing an orientation of another printed circuit of the present invention;  
         [0026]    [0026]FIG. 11 is top view of a midsole and a portion of the printed circuit depicted in FIG. 10;  
         [0027]    [0027]FIG. 12 is a cross-sectional assembly view of the sole of FIG. 10;  
         [0028]    [0028]FIG. 13 is a top view of the printed circuit depicted in FIGS.  10 - 12 ;  
         [0029]    [0029]FIG. 14 is a cross-sectional exploded assembly view of the printed circuit of FIG. 13 taken along line  14 - 14  in FIG. 13; and  
         [0030]    [0030]FIG. 15 is a side elevational view of the printed circuit of FIGS.  10 - 14 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    Referring now to the drawings for the purpose of illustrating the invention and not for the purpose of limiting the same, FIG. 1 illustrates an embodiment of the present invention in the form of an item of footwear  10  employing an embodiment of a flexible printed circuit  100  of the present invention. As the present Detailed Description of the Invention proceeds, those of ordinary skill in the art will appreciate that the flexible printed circuits  100  may be used in combination with a variety of different types of footwear without departing from the spirit and scope of the present invention. Thus, the protection afforded to the various embodiments of the present invention should not be limited to footwear having the specific cross-sectional shape and configuration depicted in FIG. 1.  
         [0032]    As can be seen in FIG. 1, the item of footwear  10  includes an upper  20  that may be fabricated from a variety of materials such as canvas, leather, etc. The upper  20  may be attached to the sole assembly  30  by conventional footwear assembly processes and techniques. In this embodiment, the sole assembly  30  includes an electrically conductive outsole  40 , a non-electrically conductive midsole  50 , an electrically conductive insole  70  and an electrically conductive sock liner  80 . In addition, as will be described in further detail below, a flexible circuit  100  is supported within the midsole  50  to define at least one electrically conductive path having a desired impedance that extends between the electrically conductive insole board  70  and the electrically conductive outsole  40 . As used herein, the term “electrically conductive” refers to the ability to transmit an electrical current therethrough.  
         [0033]    In this embodiment, the outsole  40  may be fabricated from a polyurethane or similar rubber material that is mixed with carbon powder utilizing known fabrication techniques and processes such that the outsole  40  will conduct an electrical current. In one embodiment, it is desirable for the outsole  40  to have a resistance value of less than 1×10 6  ohms. However, the outsole  40  could conceivably be fabricated from other materials having similar electrically conductive characteristics. As can be seen in FIGS. 1 and 3, the outsole  40  has an upper surface  42  and a lower surface  44  that may have a tread pattern  46  formed thereon.  
         [0034]    The midsole  50  of this embodiment may be fabricated from a non-conductive material such as polyurethane or EVA. As used herein, the term “non-conductive” means having an electrical impedance value that is greater than 1×10 7  ohms. However, the midsole  50  may be fabricated from other suitable materials that essentially do not conduct electrical current. In one embodiment, the midsole  50  has a resistance that is greater than 1×10 7  ohms. As can be seen in FIGS. 3 and 4, a cavity  52  is provided through the midsole  50  to enable the printed circuit  100  to extend therethrough and thereby be supported by the midsole  50  as will be discussed in further detail below. Also in this embodiment, the insole  70  and the conductive sock liner  80  may be fabricated from polyurethane or similar material that contains a carbon powder to provide these elements with the ability to conduct an electrical current. Also in this embodiment, the insole  70  and the sock liner  80  have a resistance value that is less than 1×10 6  ohms. Thus, in this embodiment, the outsole  40  has an electrical impedance, the midsole  50  has an electrical impedance that is greater than the electrical impedance of the outsole  40 , and the insole  70  has an electrical impedance that is less than the electrical impedance of the midsole.  
         [0035]    One embodiment of a printed circuit  100  of the present invention is depicted in FIGS.  5 - 9 . In this embodiment, the printed circuit  100  includes at least one electrically conductive path or conductor path. As can be seen in FIGS. 5 and 6, this embodiment of the printed circuit  100  includes a first electrically conductive path  110 , a second electrically conductive path  120  and a third electrically conductive path  130 . The paths  110 ,  120 ,  130  may be formed from copper foil or similar material utilizing conventional chemical milling techniques. In this embodiment, the electrical conductive paths  110 ,  120 ,  130  may be approximately 25 μm thick. However, copper foil or similar materials having other thicknesses could conceivably be used.  
         [0036]    The electrically conductive paths  110 ,  120 ,  130  may be attached to a first substrate  140  with a commercially available adhesive  149  such as that adhesive supplied by King Her Chemical Industrial Corporation of No. 38, 18 th  RD., Industrial Park, Taichung, Taiwan, R.O.C. However, other similar adhesives may be employed. In this embodiment, the first substrate may comprise a polyimide sheet material and having a thickness of 18 μm. However, other flexible sheet materials may also be used. The first substrate has a first end  142  and a second end  144  and a first side  146  and a second side  148 . The first electrically conductive path  110 , the second electrically conductive path  120  and the third electrically conductive path  130  are attached to the first side  146  of the first substrate  140  such that a first end  112  of the first path  110  is adjacent the first end  142  of the first substrate and the second end  114  of the first path . 10  is adjacent the second end of the first substrate, the first end  122  of the second path is adjacent the first end  142  of the first substrate  140 , the second end  124  of the second path  120  is adjacent the second end  144  of the first substrate  140 , the first end  132  of the third path  130  is adjacent to the first end  142  of the first substrate  140  and the second end  134  of the third path  130  is adjacent to the second end  144  of the first substrate  140 . See FIGS. 5 and 7. The paths  110 ,  120 ,  130  may be attached to the first side of  146  of the first substrate  140  by a layer of commercially available adhesive  149 , such as that adhesive described above.  
         [0037]    Also in this embodiment, a first resistor  116  is electrically coupled to the first path  110 . A second resistor  126  is electrically coupled to the second path  120 . A third resistor  136  is electrically coupled to the third path  130 . The resistors  116 ,  126 ,  136  may comprise commercially available 6.8M-ohm resistors that extend through the first substrate  140  and are electrically coupled (soldered, etc.) to their respective path. In this embodiment, second substrate  150 , in the form of polyimide sheet may be attached to the first side  146  of the first substrate and the central portions  118 ,  128 ,  138  of the first, second and third paths  110 ,  120 ,  130 , respectively by a second layer of commercially available adhesive  151  of the type described above. In particular, the central portion  118  of the first path, the central portion  128  of the second path  120  and the central portion  138  of the third path are encapsulated between the first substrate  140  and the second substrate  150 . As can be seen in FIGS. 5 and 7, the second substrate only covers the central portions of the paths such that the first ends  112 ,  122 ,  132 , of the first, second and third paths  110 ,  120 ,  130 , respectively are exposed. See FIG. 7. In this embodiment, the printed circuit  100  is assembled under pressure and may have an overall thickness of approximately 80-90 μm. An overall thickness of less than 3 mm should also work well. However, the printed circuit  100  may have a variety of other thicknesses that afford the circuit  100  the flexibility to be positioned within the sole assembly  30  as will be further discussed below. Thus, as used herein, the term “flexible” means that at least one portion of the circuit  100  may be bent or positioned relative to another position of the printed circuit such that those portions are not coplanar with respect to each other without damaging the printed circuit or its components (i.e., without hampering or destroying the ability of the first, second and third paths  110 ,  120 ,  130 , respectively to conduct electrical current). The skilled artisan will appreciate that such construction enables the flexible printed circuit to be installed in a variety of advantageous configurations. It is conceivable, however, that the conductive paths  110 ,  120 ,  130 , etc. may be affixed to a relatively rigid substrate that that has been preformed to a desired shape for installation in the manner described herein. Therefore, while the flexible substrates and circuits described herein are capable of flexing with the sole, it is conceivable that rigid substrates could also be employed. Thus, the protection afforded to the printed circuit herein should not be limited to circuits formed on flexible substrates, but should also encompass rigid printed circuits.  
         [0038]    As was described above, the flexible printed circuit  100  is provided with three paths or conductors  110 ,  120 ,  130  that have a corresponding resistor  116 ,  126 ,  136  attached thereto. The total amount of resistance through the flexible printed circuit  100  is determined by the quantity and size of resistors employed. For example, the total impedance for the three 6.8M ohm resistors may be calculated as follows:  
           R1   ×   R2   ×   R3         R1   ×   R2     +     R1   ×   R3     +     R2   ×   R3         =       2.267                 M                 ohms     =     2.267              ×     10   6                     ohms   .                               
 
         [0039]    If one of the three resistors fails, the total impedance value for the flexible circuit board of this embodiment will be:  
           R1   ×   R2       R1   +   R2       =       3.4                 M                 ohms     =     3.4              ×     10   6                     ohms   .                               
 
         [0040]    As indicated above, at least one major company in the computer industry recommends that the impedance of a conductive shoe be maintained within 10 6  ohms to 10 7  ohms. Thus, in this embodiment, even if two resistors fail, the total impedance value will be at 6.8×10 6  ohms, which is still below the upper limit of 10 7  ohms.  
         [0041]    Those of ordinary skill in the art will appreciate that the impedance of the flexible circuit board may be varied by altering the number of paths (conductors) and resistors to achieve a desired amount of impedance in accordance with standard electrical engineering formulas (i.e., “Ohm&#39;s Law”). For example, series arrays or combination arrays may be used and their total impedance may be calculated as follows: 
         [0042]    One resistor:  
         [0043]    R (total resistance value)=R 1   
         [0044]    Two resistors (Combination Arrays):  
         R        (     total                 resistance                 value     )       =       R1   ×   R2       R1   +   R2                             
 
         [0045]    Three resistors (Combination Arrays):  
         R        (     total                 resistance                 value     )       =       R1   ×   R2   ×   R3         R1   ×   R2     +     R1   ×   R3     +     R2   ×   R3                               
 
         [0046]    Series Arrays:  
         [0047]    R (total resistance value)=R 1 +R 2 +R 3 +. . .  
         [0048]    In this embodiment, a moisture resistant barrier  180  may be wrapped over the resistors  116 ,  126 ,  136  to retard and prevent the infiltration of moisture into the points where the resistors  116 ,  126 ,  136  are coupled to the paths  110 ,  120 ,  130 , respectively. The moisture barrier  180  may comprise a wrapping of conventional electrical insulation tape. However, the moisture resistant barrier  180  may be formed with other materials such as sealant, glue or the like.  
         [0049]    The flexible printed circuit  100  may be installed in the footwear as shown in FIGS. 1, 2,  3  and  4 . As can be seen in FIGS. 2 and 4, the midsole  50  has a hole or passageway  52  therethrough sized to receive a portion of the flexible circuit  100 . In addition, an undercut  58  area may be provided in the bottom surface  57  of the midsole  50  to accommodate the resistors  116 ,  126 ,  136  when the circuit  100  is supported in the midsole  50  as shown. See FIG. 2. As can be seen, such arrangement permits the circuit  100  to be oriented such that the first end  112  of the first path  110 , the second end  122  of the second path  120  and the third end  132  of the third path  130  to be in electrical contact with the conductive outsole  40  to transmit electrical current thereto. Similarly, the second end  114  of the first path  110  and the second end  124  of the second path  120  and the second end  134  of the third path  130  are supported in electrical contact with the conductive insole board  70  to receive electrical current therefrom. If desired, the first end  142  of the circuit  100  may be attached to the underside  57  of the midsole with double-sided adhesive tape  159  or other commercially available conductive adhesive. A variety of different types of adhesives or adhesive tapes may be used. For example, the double-sided tape manufactured by the 3M Company under Model No. 467 may be employed. Similarly, the second end  144  of the circuit  100  may be affixed to the upper surface  59  of the midsole by another section of such double-sided adhesive tape  159  or other commercially available adhesive. The reader will appreciate that when the flexible circuit  100  is installed as shown in FIGS. 1, 2,  3 , and  4 , the exposed ends  112 ,  122 ,  132 , of the paths  110 ,  120 ,  130 , respectively remain exposed to contact the conductive outsole  40  and the exposed ends  114 ,  124 ,  134  of the paths  110 ,  120 ,  130 , respectively are exposed to contact the conductive insole board  70 . In this embodiment, the end  142  of the flexible circuit  100  that contains the exposed ends  112 ,  122 ,  132  may be fastened to the outsole  40  with commercially available ESD conductor glue  170  that has a resistance range of 5×104˜10 6  Ohms. The midsole  50  is attached to the outsole  40  by commercially available conductive cement. Similarly, the insole board  70  is attached to the midsole  50  by commercially available conductive cement. In this embodiment, the sock liner is not attached to the insole board. Thus, when installed as shown in FIGS. 1 and 2, the exposed ends  114 ,  124 ,  134  of the paths  110 ,  120 ,  130 , respectively contact the conductive insole board  70  and the flexible circuit  100  extends through the opening  52  in the midsole  50  and the exposed ends  112 ,  122 ,  124  of the paths  110 ,  120 ,  130 , respectively, contact the conductive outsole  40 . Therefore, such arrangement permits a static charge to pass from the foot through the conductive sock liner  80 , through the conductive insole board  70 , through the paths  110 ,  120 ,  130  and resistors  116 ,  126 ,  136  to provide an impedance of 2.267×10 6  ohms. This charge then passes from the paths  110 ,  120 ,  130  to the conductive outsole  40  such that the charge is safely dissipated to the floor surface. In this embodiment, by way of example only, the impedance of the respective parts of the sole assembly is: sock liner  80 : 2.5×10 4 -2×10 5  ohms; insole board  70 : 10 4 -10 5  ohms; resistors  116 ,  126 ,  136 : 6.8×10 6  ohms (each); midsole  50 : 10 11 -10 12  ohms; conductive outsole  40 : 10 4 -3×10 4  ohms; and conductive adhesive: 10 4 -10 5  ohms.  
         [0050]    To test the effectiveness of the above-mentioned design, two different items of footwear manufactured in accordance with the above-mentioned embodiment of the present invention were tested as outlined below by Fowler Associates, Inc. of 3551 Moore-Duncan Highway, Moore, S.C. 29639:  
         [0051]    Iron Age® Women&#39;s Style 492M, SIZE 7M Steel Toe Hiker  
         [0052]    Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2 
         [0053]    Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc, 100 vdc, 500 vdc  
         [0054]    Electrodes: 2½ in. aluminum cylinder, aluminum plate, aluminum foil  
         [0055]    Laboratory conditions: 73° F., 12% RH  
                                                                                         Resistance of Individual to Ground-Ohms           Laboratory conditions: 73° F., 12%                After 3 mins. of Wear   After 5 mins. of Wear            Test Sample   10 v   100 v   10 v   100 v               Style 492M       Both   2.69 × 10 6     1.83 × 10 6     2.50 × 10 6     1.73 × 10 6         Left   4.23 × 10 6     3.18 × 10 6     4.15 × 10 6     3.13 × 10 6         Right   4.43 × 10 6     3.41 × 10 6     4.23 × 10 6     3.35 × 10 6                          Resistance of Shoe to Ground per ESD S9.1-Ohms           25 lbs. lead shot in Shoe       Test Sample   100 v               Style 492M           Left   4.17 × 10 6         Right   4.81 × 10 6                            
 
         [0056]    Iron Age® Women&#39;s Style 492M, SIZE 6M Steel Toe Hiker  
         [0057]    Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2  
         [0058]    Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc, 100 vdc, 500 vdc  
         [0059]    Electrodes: 2½ in. aluminum cylinder, aluminum plate, aluminum foil  
         [0060]    Laboratory conditions: 73° F., 12% RH  
                                                                                         Resistance of Individual to Ground-Ohms           Laboratory conditions: 73° F., 12%                After 3 mins. Of Wear   After 5 mins. of Wear            Test Sample   10 v   100 v   10 v   100 v               Style 492M       Both   2.32 × 10 6     1.44 × 10 6     2.21 × 10 6     1.47 × 10 6         Left   3.86 × 10 6     2.80 × 10 6     3.87 × 10 6     2.88 × 10 6         Right   3.49 × 10 6     2.56 × 10 6     3.40 × 10 6     2.55 × 10 6                          Resistance of Shoe to Ground per ESD S9.1-Ohms           25 lbs. lead shot in Shoe       Test Sample   100 v               Style 492M           Left   4.12 × 10 6         Right   3.01 × 10 6                            
 
         [0061]    Iron Age® Women&#39;s Style 492M, SIZE 6M Steel Toe Hiker  
         [0062]    Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2  
         [0063]    Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc, 100 vdc, 500 vdc  
         [0064]    Electrodes: 2½ in. aluminum cylinder, aluminum plate, aluminum foil  
         [0065]    Laboratory conditions: 73° F., 12% RH  
                                                                                         Resistance of Individual to Ground-Ohms           Laboratory conditions: 73° F., 50%                After 3 mins. Of Wear   After 5 mins. of Wear            Test Sample   10 v   100 v   10 v   100 v               Style 492M       Both   3.48 × 10 6     1.50 × 10 6     3.25 × 10 6     1.60 × 10 6         Left   5.16 × 10 6     2.84 × 10 6     4.22 × 10 6     3.05 × 10 6         Right   5.26 × 10 6     2.90 × 10 6     4.05 × 10 6     2.96 × 10 6                          Resistance of Shoe to Ground per ESD S9.1-Ohms           25 lbs. lead shot in Shoe       Test Sample   100 v               Style 492M           Left   3.21 × 10 6         Right   2.78 × 10 6                            
 
         [0066]    As can be appreciated from the foregoing description, the various embodiments of the present invention represent a vast improvement over prior footwear designs that are constructed to dissipate static electricity. In particular, the flexible circuit board embodiments of the present invention are relatively compact and require minimal space to install. Furthermore, because they are flexible, they are not as susceptible to damage as the conventional resistors used in other shoe designs. The resistors provide a series of load bearing contact surfaces for more uniform distribution of the weight pressure from the insole to the outsole, and thus result in reduction of the pressure in each resistor. The impendence dimensions of the resistors employed by the present invention are generally smaller and more stable than such prior resistor arrangements and, therefore, they can typically resist more pressure. Furthermore, if one or two of the resistors of the present invention fail, the total impedance value will be below 10 7  ohms. Furthermore, because the flexible circuit board determines the major part of the impedance of the sole, the impendence of the sole materials employed is less critical. Therefore a wider range of materials can be used to fabricate the sole. Manufacturing costs can thus be greatly reduced without affecting quality requirement because the impedance of the resistor components in the midsole is very stable and will not change in a wet environment such as perspiration from the wearer&#39;s foot or a wet floor surface, the total impedance of the sole can still be maintained within a desired range of impedance.  
         [0067]    Another printed circuit  200  embodiment of the present invention is depicted in FIGS.  10 - 15 . In this embodiment, the printed circuit  200  includes at least one electrically conductive path or conductor path. As can be seen in FIG. 12, this embodiment of the printed circuit  200  includes a first electrically conductive path  210 , a second electrically conductive path  220  and a third electrically conductive path  230 . The paths  210 ,  220 ,  230  may be formed from copper foil or similar material utilizing conventional chemical milling techniques. In this embodiment, the electrical conductive paths  210 ,  220 ,  230  may be approximately 25 μm thick. However, copper foil or similar materials having other thicknesses could conceivably be used.  
         [0068]    The electrically conductive paths  210 ,  220 ,  230  may be attached to a first substrate  240  with a commercially available adhesive  249  such as that adhesive supplied by King Her Chemical Industrial Corporation of No. 38, 18 th  RD., Industrial Park, Taichung, Taiwan, R.O.C. However, other similar adhesives may be employed. See FIG. 13. In this embodiment, the first substrate  240  may comprise a polyimide sheet material and having a thickness of 18 μm. However, other flexible sheet materials may also be used. The first substrate  240  has a first end  242  and a second end  244  and a first side  246  and a second side  248 . The first electrically conductive path  210 , the second electrically conductive path  220  and the third electrically conductive path  230  are attached to the first side  246  of the first substrate  240  such that a first end  212  of the first path  210  is adjacent the first end  242  of the first substrate and the second end  214  of the first path  210  is adjacent the second end  244  of the first substrate  240 , the first end  222  of the second path is adjacent the first end  242  of the first substrate  240 , the second end  224  of the second path  220  is adjacent the second end  244  of the first substrate  240 , the first end  232  of the third path  230  is adjacent to the first end  242  of the first substrate  240  and the second end  234  of the third path  230  is adjacent to the second end  244  of the first substrate  240 . See FIGS. 12 and 13. The paths  210 ,  220 ,  230  may be attached to the first side of  246  of the first substrate  240  by a layer of commercially available adhesive  249 , such as that adhesive such as that adhesive supplied by King Her Chemical Industrial Corporation of No. 38, 18 th  RD., Industrial Park, Taichung, Taiwan, R.O.C. However, other similar adhesives may be employed.  
         [0069]    Also in this embodiment, a first resistor  216  is electrically coupled to the first path  210 . A second resistor  226  is electrically coupled to the second path  220 . A third resistor  236  is electrically coupled to the third path  230 . The resistors  216 ,  226 ,  236  may comprise commercially available 6.8M-ohm resistors that are electrically coupled (soldered, etc.) to their respective path. In this embodiment, a second substrate  250 , in the form of polyimide sheet may be attached to the first side  246  of the first substrate and the central portions  218 ,  228 ,  238  of the first, second and third paths  210 ,  220 ,  230 , respectively by a second layer of commercially available adhesive  251  of the type described above. In particular, the central portion  218  of the first path  210 , the central portion  228  of the second path  220  and the central portion  238  of the third path  230  are encapsulated between the first substrate  240  and the second substrate  250 . As can be seen in FIG. 13, the second substrate  250  only covers the central portions of the paths such that the first ends  212 ,  222 ,  232 , of the first, second and third paths  210 ,  220 ,  230 , respectively are exposed.  
         [0070]    In this embodiment, the printed circuit  200  is assembled under pressure and may have an overall thickness of approximately 80-90 μm. An overall thickness of less than 3 mm should also work well. However, the printed circuit  200  may have a variety of other thicknesses that afford the circuit  200  the flexibility to be positioned within the sole assembly  30  as will be further discussed below. Thus, as used herein, the term “flexible” means that at least one portion of the circuit  200  may be bent or positioned relative to another position of the printed circuit such that those portions are not coplanar with respect to each other without damaging the printed circuit or its components (i.e., without hampering or destroying the ability of the first, second and third paths  210 ,  220 ,  230 , respectively to conduct electrical current). The skilled artisan will appreciate that such construction enables the flexible printed circuit to be installed in a variety of advantageous configurations. It is conceivable, however, that the conductive paths  210 ,  220 ,  230 , etc. may be affixed to a relatively rigid substrate that that has been preformed to a desired shape for installation in the manner described herein. Therefore, while the flexible substrates and circuits described herein are capable of flexing with the sole, it is conceivable that rigid substrates could also be employed. Thus, the protection afforded to the printed circuit herein should not be limited to circuits formed on flexible substrates, but should also encompass rigid printed circuits.  
         [0071]    Also in this embodiment, a first attachment pad assembly  300  is attached to a first end  290  of the printed circuit  200  and a second pad assembly  320  is attached to a second end  292  of the printed circuit  200 . Such attachment pad assemblies provide an increased area for accommodating adhesive for attaching the ends of the printed circuit to portions of the sole assembly. More specifically and with reference to FIGS.  12 - 14 , the first pad assembly  300  of this embodiment may comprise, for example, a first pad member  302  and a primary pad member  304 . In this embodiment, the first and primary pad members  302 ,  304  are fabricated from a commercially available conductive EVA material. However, other conductive materials may be employed. In this embodiment, the first and primary pad members  302 , 304  afford a relatively large area for attachment to the other sole components as will be discussed in further detail below. For example, the first and primary pad members  302 ,  304  may be approximately 1.5 inches (38 mm)×approximately 1.25 inches (31.75 mm) and 0.0625 inches (1.6 mm) thick. However, it is conceivable that the first and primary pad members  302 ,  304  may be made in other suitable sizes and that the sizes of the first and primary pad members  302 ,  304  may be dissimilar.  
         [0072]    The first ends  212 ,  222 ,  232  of the conductive pathways  210 ,  220 ,  230 , respectively may be affixed to the first pad member  302  by a conductive adhesive  306  of the type described above. Similarly, a portion of the first substrate  240  may be attached to the primary pad member by another layer of the conductive adhesive  306 . The conductive adhesive  306  may also serve to join the first pad member  302  to the primary pad member  304 . In addition, the first ends  212 ,  222 ,  232  of the conductive pathways  210 ,  220 ,  230 , respectively may be joined to the first and primary pad members  302 ,  304  by stitches  310  which extend through the first end of the printed circuit  200  and the first and primary pad members  302 ,  304 . The stitches  310  may be formed from a conductive or non-conductive thread or similar material.  
         [0073]    Likewise, the second pad assembly  320  of this embodiment may comprise, for example, a second pad member  322  and a secondary pad member  324 . In this embodiment, the second and secondary pad members  322 ,  324  may also be fabricated from conductive EVA material. The second and secondary pad assemblies afford a relatively large area for attachment to the other sole components as will be discussed in further detail below. For example, the second and secondary pad members may be approximately 1.5 inches (38 mm)×approximately 1.25 inches (31.75 mm) and 0.0625 (1.6 mm) thick. However, it is conceivable that the second and secondary pad members  322 ,  324  may be made in other suitable sizes and that the sizes of the second and secondary pad members  322 ,  324  may be dissimilar.  
         [0074]    The second ends  212 ,  222 ,  232  of the conductive pathways  210 ,  220 ,  230 , respectively may be affixed to the second pad member  322  by a conductive adhesive  306  of the type described above. Similarly, the end  244  of the first substrate  240  may be attached to the secondary pad member  324  by another layer of the conductive adhesive  306 . The conductive adhesive  306  may also serve to join the second pad member  322  to the secondary pad member  324 . In addition, the first ends  212 ,  222 ,  232  of the conductive pathways  210 ,  220 ,  230 , respectively may be joined to the second and secondary pad members  322 ,  324  by stitches  330  which extend through the second end  292  of the printed circuit  200  and the second and secondary pad members  322 ,  324 . The stitches  330  may be formed from conductive or non-conductive thread or similar material.  
         [0075]    As was described above, the flexible printed circuit  200  is provided with three paths or conductors  210 ,  220 ,  230  that have a corresponding resistor  216 ,  226 ,  236  attached thereto. The total amount of resistance through the flexible printed circuit  200  is determined by the quantity and size of resistors employed. For example, the total impedance for the three 6.8M ohm resistors may be calculated as set forth above and may equal 2.267 M ohms=2.267×10 6  ohms. If one of the three resistors fails, the total impedance value for the flexible circuit board of this embodiment will be 3.4 M ohms=3.4×10 6  ohms. As indicated above, at least one major company in the computer industry recommends that the impedance of a conductive shoe be maintained within 10 6  ohms to 10 7  ohms. Thus, in this embodiment, even if two resistors fail, the total impedance value will be at 6.8×10 6  ohms, which is still below the upper limit of 10 7  ohms.  
         [0076]    Those of ordinary skill in the art will appreciate that the impedance of the flexible circuit board  200  may be varied by altering the number of paths (conductors) and resistors to achieve a desired amount of impedance in accordance with standard electrical engineering formulas (i.e., “Ohm&#39;s Law”) that were set forth above. In this embodiment, a moisture resistant barrier  280  may be wrapped over the resistors  216 ,  226 ,  236  to retard and prevent the infiltration of moisture into the points where the resistors  216 ,  226 ,  236  are coupled to the paths  210 ,  220 ,  230 , respectively. The moisture barrier  280  may comprise a wrapping of conventional electrical insulation tape. However, the moisture resistant barrier  280  may be formed with other materials such as sealant, glue or the like.  
         [0077]    The flexible printed circuit  200  may be installed in the footwear as shown in FIGS. 10 and 11. As can be seen in those Figures, the midsole  50  has a hole or passageway  52  therethrough sized to receive a portion of the flexible circuit  200 . In addition, an undercut  58  area may be provided in the bottom surface  57  of the midsole  50  to accommodate the resistors  216 ,  226 ,  236  and the first pad assembly  320  when the circuit  200  is supported in the midsole  50  as shown. Likewise, an upper notch  58 ′ may be provided in the upper surface  59  of the midsole  50  to accommodate the second pad assembly  320 . See FIG. 12. As can be seen, such arrangement permits the circuit  200  to be oriented such that the first pad assembly  302  is in electrical contact with the conductive outsole  40  to transmit electrical current thereto. Similarly, the second pad assembly  320  is supported in electrical contact with the conductive insole board  70  to receive electrical current therefrom. If desired, the first pad assembly may be attached to the underside  57  of the midsole with a conductive adhesive such as a commercially available ESD conductor glue  170  that has a resistance range of 5×10 4 ˜10 6  Ohms or other similar glues or adhesive mediums. Similarly, the second pad assembly  320  may be affixed to the upper surface  59  of the midsole by another such conductive adhesive. The midsole  50  is attached to the outsole  40  by commercially available conductive cement. Similarly, the insole board  70  is attached to the midsole  50  by commercially available conductive cement. In this embodiment, the sock liner  80  is not attached to the insole board. Thus, when installed as shown in FIGS. 10 and 11, the second conductive pad assembly  320  is affixed to the conductive insole board  70  and the flexible circuit  200  extends through the opening  52  in the midsole  50  and the first conductive pad assembly  300  is attached to the conductive outsole  40 . Therefore, such arrangement permits a static charge to pass from the foot through the conductive sock liner  80 , through the conductive insole board  70 , through the second conductive pad assembly  320 , through paths  210 ,  220 ,  230  and resistors  216 ,  226 ,  236  to provide an impedance of 2.267×10 6  ohms. This charge then passes from the paths  210 ,  220 ,  230  through the first conductive pad assembly  300  to the conductive outsole  40  such that the charge is safely dissipated to the floor surface. In this embodiment, by way of example only, the impedance of the respective parts of the sole assembly is: sock liner  80 : 2.5×10 4 -2×10 5  ohms; insole board  70 : 10 4 -10 5  ohms; resistors  116 ,  126 ,  136 : 6.8×10 6  ohms (each); midsole  50 : 10 11 - 10   12  ohms; conductive outsole  40 : 10 4 -3×10 4  ohms; and conductive adhesive: 10 4 -10 5  ohms. This embodiment would also have results similar to those test results set forth above.  
         [0078]    As can be appreciated from the foregoing description, the various embodiments of the present invention represent a vast improvement over prior footwear designs that are constructed to dissipate static electricity. In particular, the flexible circuit board embodiments of the present invention are relatively compact and require minimal space to install. Furthermore, because they are flexible, they are not as susceptible to damage as the conventional resistors used in other shoe designs. The resistors provide a series of load bearing contact surfaces for more uniform distribution of the weight pressure from the insole to the outsole, and thus result in reduction of the pressure in each resistor. The impendence dimensions of the resistors employed by the present invention are generally smaller and more stable than such prior resistor arrangements and, therefore, they can typically resist more pressure. Furthermore, if one or two of the resistors of the present invention fail, the total impedance value will be below 10 7  ohms. Furthermore, because the flexible circuit board determines the major part of the impedance of the sole, the impendence of the sole materials employed is less critical. Therefore a wider range of materials can be used to fabricate the sole. Manufacturing costs can thus be greatly reduced without affecting quality requirement because the impedance of the resistor components in the midsole is very stable and will not change in a wet environment such as perspiration from the wearer&#39;s foot or a wet floor surface, the total impedance of the sole can still be maintained within a desired range of impedance.  
         [0079]    Whereas particular embodiments of the invention have been described herein for the purpose of illustrating the invention and not for the purpose of limiting the same, it will be appreciated by those of ordinary skill in the art that numerous variations of the details, materials and arrangement of parts may be made within the principle and scope of the invention without departing from the invention as described in the appended claims.