Abstract:
A flexible printed circuit (FPC) is provided comprising a base plate and a pair of elongated resin strips disposed on the base plate. The resin strips comprise conductive traces embedded between the resin strips and configured to electrically couple a first unit of an electronic device at a tail end of the resin strips with a second unit of the electronic device at an opposing end of the resin strips. The resin strips have edges having cutouts formed therein adjacent to the tail end.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a flexible printed circuit (FPC) that connects one unit of a device to another unit of the device and, more specifically, to an FPC that inhibits the migration of water along the FPC. 
     Some electronic devices, such as portable computers and flip-type cell phones, are manufactured as two units, which are mechanically connected to each other with a hinge. In order for power and signals to be exchanged between the two units, an FPC may be used to electrically couple the two units.  FIG. 1  is a top perspective view of one end of an FPC  100  connected to, for example, a keyboard case  10 . As illustrated in  FIG. 2A , the FPC  100  may include conductive traces  102  embedded between a pair of resin strips  104  and is bonded to a base plate  106  of the keyboard case  10 . To reduce the possibility of water or other liquid from a spill migrating into the unit  10  to which the FPC  100  is connected, the tail exit of the FPC  100  may be covered with a water-tight film  108 , such as Mylar®. However, as illustrated in the cross-sectional view of  FIG. 2B , there may be gaps  110  at the edge of the water-tight film  108  that can create channels along the edges of the strips  104 , increasing the possibility of intrusion of liquid into the gaps  110  and into the unit  10 . The resin strips  104 , and therefore the gaps  110 , may be about 0.25 millimeters (mm) thick. 
     Therefore, it can be seen that there is a need for a more effective method of reducing liquid migration from the tail exit of an FPC into connected devices. 
     SUMMARY 
     In one aspect, a flexible printed circuit (FPC) connection structure is provided. The FPC comprises a base plate and a pair of resin strips disposed on the base plate. The resin strips comprise conductive traces embedded between the FPC and configured to electrically couple a first unit of an electronic device at a tail end of the FPC with a second unit of the electronic device at an opposing end of the FPC; and edges having cutouts formed therein adjacent to the tail end. 
     In another aspect, a method of manufacturing a flexible printed circuit (FPC) is provided. The method comprises providing a pair of resin strips having a tail end; embedding conductive traces between the resin strips configured to electrically couple a first unit of an electronic device at the tail end of the resin strips with a second unit of the electronic device at an opposing end of the resin strips; forming cutouts in edges of the resin strips adjacent to the tail end configured to increase the effective length of the edges; bonding the resin strips to a baseplate; and overlaying a water-tight film on the resin strips at the tail end. 
     In a further aspect, an electronic device is provided. The electronic device comprises a first unit, a second unit pivotally connected to the first unit, and a flexible printed circuit (FPC) disposed to electrically couple the first unit with the second unit. The FPC comprises a base plate and a pair of resin strips between which conductive traces are embedded and extend the length of the FPC. The conductive traces are configured to electrically couple the first unit at a tail end of the FPC with the second unit at an opposing end of the resin strips, the resin strips having edges. The edges of the resin strips adjacent to the tail end have cutouts formed therein configured to increase the effective length of the edges. The FPC further comprises a water-tight film overlaying the resin strips at the tail end. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a tail exit of prior art FPC on which a water-tight film has been attached; 
         FIG. 2A  is a top view of a prior art FPC; 
         FIG. 2B  is an end cut-away view taken along line A-A of  FIG. 2A ; 
         FIG. 3  is a top cutaway view of an FPC of the present invention illustrating an embodiment of the edges of the resin strips at the tail end of the FPC; 
         FIG. 4  is a top view of an alternative embodiment of the edges at the tail end of the FPC; 
         FIG. 5  is a top view of a second alternative embodiment of the edges at the tail end of the FPC; 
         FIG. 6  is a top view of a third alternative embodiment of the edges at the tail end of the FPC; 
         FIG. 7  is a top view of a fourth alternative embodiment of the edges at the tail end of the FPC; 
         FIG. 8  is a top view of a fifth alternative embodiment of the edges at the tail end of the FPC; 
         FIG. 9  is a side cross-sectional view of a notebook computer in which an embodiment of an FPC of the present invention is installed; 
         FIG. 10  is a cut-away view of a flip-type cell phone in which an embodiment of an FPC of the present invention is installed; and 
         FIG. 11  is a flow chart of a method of producing an FPC of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles, since the scope of the embodiments is best defined by the appended claims. 
     Various inventive features are described below that can each be used independently of one another or in combination with other features. 
     Broadly, exemplary embodiments provide a flexible printed circuit (FPC) that electrically couples one unit of a device to another unit of the device. More specifically, exemplary embodiments provide an FPC that may inhibit the migration of water or other liquid in the FPC. 
     Referring to  FIG. 3 , according to exemplary embodiments, an FPC  300  may include a base plate  302  and pair of resin strips  304  between which conductive traces are embedded and extend the length of the resin strips  304 . The conductive traces may electrically couple a first unit of an electrical device at a tail end of the FPC with a second unit of the electrical device at the opposite end of the FPC. The conductive traces may include a variety of types of thin and flexible interconnection circuits, such as an etched cupper conductive pattern sandwiched by a pair of polyimide resin strips, or a silk screen printed conductive pattern sandwiched by a pair of polyethylene terephthalate (PET) resin strips. A water-tight film  306  such as Mylar® or other sealing material may overlay the resin strips  304  to seal the edges  304 A of the resin strips  304 . Nonetheless, gaps or channels between the water-tight film  306  and the resin strips  304  may remain. 
     Referring also to the flow chart  1100  of  FIG. 11 , in contrast to the straight edges  104 A of the prior art resin strips  104 , according to one embodiment, the resin strips  304  may be provided (step  1102 ) and conductive traces may be embedded between the resin strips  304  (step  1104 ). Small cutouts  304 B may be formed in their edges  304 A near the tail exit  300 A of the FPC  300  (step  1106 ) and the resin strips  304  may be bonded to the base plate  302  (step  1108 ). The cutouts  304 B may increase the effective length of the edges  304 A of the resin strips  304 . Consequently, the path a liquid  20  must take through the channels between the resin strips edges  304 A and the water-tight film  306  is lengthened and the time it takes for the liquid  20  to travel along the edges  304 A may be increased. A water-tight film may overlaid on the resin strips  304  to provide an initial sealing barrier to liquid (step  1110 ). 
     According to one embodiment, the cutouts  304 B in the edges  304 A of the resin strip may be formed as notches, such as V-shaped notches  304 C. According to another embodiment, the cutouts  304 B in the edges  304 A of the resin strips may be formed as oblong chambers  304 D with narrow openings. When a liquid  22  enters the gaps, it may travel along the edges  304 A and fill the chambers  304 D. The pressure of the liquid  22  within the chambers  304 D may then retard further liquid  22  flow along the edges  304 A. 
     According to still another embodiment, the resin strips  304  may have both notches  304 C and chambers  304 D formed in an alternating pattern in the edges  304 A near the tail exit  300 A of the FPC  300 . In this configuration, the effects on the flow of liquid by the notches  304 C and by the chambers  304 D may reinforce each other. 
     In one demonstration, a prior art FPC  100  having resin strips  104  with straight edges  104 A was connected to a keyboard. The length of time it took for water to enter the gaps  110  and travel along the edge channels to reach the keyboard was about five minutes. In contrast, the length of time it took for water to reach the keyboard increased to about twenty minutes when the resin strips  304  with alternating notches  304 C and chambers  304 D were used. Any water that remains in the channels after water is removed from the outside of the FPC may eventually evaporate and not cause damage. 
       FIGS. 4-8  illustrate some edge configurations that may be used with the FPC  300 . It will be appreciated that the illustrated edge configurations are representative and not exhaustive and that other configurations may be used.  FIG. 4  illustrates a resin strip tail  400  with a single squared notch  402  cut into each edge. The notches  402  may be about 6 millimeters (mm) wide and about 6 mm deep. 
       FIG. 5  illustrates a resin strip tail  500  with multiple squared notches  502  cut into each edge. The notches  502  may be about 3 mm wide, about 6 mm deep, and spaced about 3 mm apart along each edge. 
       FIG. 6  illustrates a resin strip tail  600  with a set of squared notches  602  cut into each edge. Each notch  602  may have rough sides  604 . The notches  602  may be about 1.5 mm wide, about 6 mm deep, and spaced about 1.5 mm apart along each edge. 
       FIG. 7  illustrates a resin strip tail  700  with a set of oblong chambers  702  cut into each edge. Each chamber  702  may have a narrow opening  704 . The chambers  702  may be about 3 mm wide and about 5 mm deep. The openings  704  may be spaced about 5 mm apart along each edge. 
       FIG. 8  illustrates a resin strip tail  800  with a set of oblong chambers  802  cut into each edge. Each chamber  802  may have a narrow opening  804  and be separated from the adjacent chamber by a notch  806 . The chambers  802  may be about 3 mm wide and about 5 mm deep and the notches may be about 1.5 mm wide and about 6 mm deep. The openings  804  may be spaced about 5 mm apart along each edge. 
       FIG. 9  is a side cross-sectional view of a notebook computer  900 . A keyboard unit  902  may be mechanically connected to a display unit  904  with a hinge  906  to enable the two units  904 ,  906  to pivot relative to each other. The two units  904 ,  906  may be electrically coupled to each other with an embodiment of an FPC  908  of the present invention to inhibit the migration of water or other liquid along the edges of the resin strips. 
       FIG. 10  illustrates a top cut-away view of a cell phone  1000 . A keyboard unit  1002  may be mechanically connected to an display unit  1004  with a hinge  1006  to enable the two units  1002 ,  1004  to pivot relative to each other. The two units  1002 ,  1004  may be electrically coupled to each other with an embodiment of an FPC  1008  of the present invention to inhibit the migration of water or other liquid along the edges of the resin strips. 
     It should be understood, of course, that the foregoing relate to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.