Patent Application
20060266548
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-157350, filed May 30, 2005, the entire contents of which are incorporated herein by reference.
1. Field
One embodiment of the invention relates to a flexible flat cable, a printed circuit board including the flexible flat cable, and an electronic apparatus having an electronic component connected to the printed circuit board by the flexible flat cable.
2. Description of the Related Art
In conventional art, copper wires plated with metal such as tin and lead to decrease the contact resistance and improve the continuity have been used as a conductor used for flexible flat cables. In recent years, it is required not to use lead for various wires used for electronic apparatuses, from the environmental point of view. Therefore, it is considered applying copper wires plated with tin or tin alloy not containing lead.
However, as disclosed in, for Experimental embodiment, Jpn. Pat. Appln. KOKAI Pub. No. 2005-48205, if a flexible flat cable using copper wire plated with tin or tin alloy not containing lead is engaged with a connector, the metal molecules on the surface of the plating are pushed out and grown in a whisker form by stress applied on the engaging portion, that is, whisker is generated and short circuit is caused between conductors.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a flexible flat cable according to the present invention comprises a pair of insulating sheets having flexibility, and a plurality of conductors which are arranged at intervals in lines between the insulating sheets and have at their end portions a connecting portion exposed from the insulating sheets; wherein the conductors contain tin and copper as main components, the connecting portion has a first region containing copper as main component, and a second region which contains tin and copper as main components and is formed on the first region, and at least part of a surface region of the second region is formed of a tin-copper alloy.
Further, a printed circuit board according to the present invention comprises the above flexible flat cable, and comprises a substrate, a conductor pattern provided on the substrate, a connector which has a contact portion provided on the substrate in electrical connection with the conductor pattern and having a tin alloy coating layer, and a housing holding the contact portion and having a fitting port into which a connecting portion of a connecting part is fitted, and the flexible flat cable whose connecting portion is inserted into the fitting port as a connecting part to electrically connect the conductors and the contact portion.
Further, an electronic apparatus according to the present invention has a structure wherein the above printed circuit board is connected to electronic parts by the flexible flat cable.
The conductors containing tin and copper as main components used for the present invention substantially consist of tin and copper, and do not contain lead. They may contain a trace quantity of other elements which do not influence the characteristic of the conductors. Experimental embodiments of the state of the tin and copper in the conductors are a combination of a copper phase and a tin phase formed on the copper phase, a combination of a copper phase and a tin-copper alloy phase formed on the copper phase, and a combination of a copper phase and a tin phase and a tin-copper alloy phase which are formed on the copper phase.
Further, the first region used for the present invention, which contains copper as main component, corresponds to the copper phase, substantially consists of copper and does not contain lead. The first region may contain a trace quantity of other elements which do not influence the characteristic of the first region.
Further, the second region used for the present invention, which contains tin and copper as main components, substantially consists of tin and copper and does not contain lead. The second region may contain a trace quantity of other elements which do not influence the characteristic of the second region. Experimental embodiments of the second region are a combination of a copper phase and a tin-copper alloy phase formed on the copper phase, and a combination of a copper phase and a tin phase and a tin-copper alloy phase which are formed on the copper phase. Therefore, a tin-copper alloy phase exists in at least part of a surface region of the second region.
According to the present invention, a tin-copper alloy phase exists on at least part of a surface region of the connecting portion. This structure prevents occurrence of whisker in the surface region. This structure achieves a flexible flat cable using inexpensive conductors not containing lead, which does not cause short circuit between the conductors, and has a sufficiently low contact resistance with connectors.
Further, using the flexible flat cable achieves a highly reliable connection at low cost with a connector mounted on a printed circuit board, without causing short circuit between conductors.
Further, using the flexible flat cable achieves a highly reliable connection at low cost between a printed circuit board and electronic parts, without causing short circuit between conductors.
The present invention is explained in more detail with reference to the drawings.
As shown in
As shown in
The exposed conductor layer 1 of the connecting portions 5 is obtained by arranging copper wires in lines at intervals on the insulating belt-like sheet 3, then plating the copper wires with a tin layer, and annealing at least the connecting portions at 220 to 300° C. Thereby, the tin-copper alloy phase is formed on the copper phase, such that at least part of the tin-copper alloy phase reaches the surface region. In the model diagram of
A printed circuit board 30 comprises an insulating substrate 32, a conductor pattern 33 provided on the insulating substrate 32, a connector 20 that is electrically connected to the conductor pattern 33, and a flexible flat cable 10 inserted in and connected to the connector 20. The connector 20 and the conductor pattern 33 can be electrically connected by soldering a terminal 9 of the connector 20 to a terminal (not shown) connected to the conductor pattern 33.
The connector 20 has a contact portion 7 having a tin alloy coating layer, and a housing 6 holding the contact portion 7 and having a fitting port 31 into which a connecting portion of connecting parts are fitted.
Experimental embodiments of the tin alloy used for the contact portion are tin-silver alloy, tin-copper alloy such as Sn-Su2 alloy, tin-bismuth alloy, and tin-lead alloy.
In the printed circuit board 30, a flexible flat cable 10 having the same structure as illustrated in
A portable computer is explained herein as the electronic apparatus. As shown in
In the housing 14, a keyboard 19 is provided in a central portion of the top cover 14a.
A front end portion of an upper surface of the top cover 14a forms a palm rest portion 12. A touch pad 24 and a click button 16 are provided in almost the center of the palm rest portion 12.
Further, speakers (not shown) are accommodated in the right and left of the front end portion in the housing 14.
The display unit 13 comprises a housing 18 having a flat and rectangular box shape, and a liquid crystal display panel 20 accommodated in the housing 18. The liquid crystal display panel 20 is exposed to the outside through a display window 21 formed in the housing 18. The housing 18 has a pair of leg portions 22 projecting from one end thereof. The leg portions 22 are rotatably supported by the rear end portion of the housing 14 by hinge portions (not shown). This structure enables the display unit 13 to rotate between a closed position where the display unit 13 is laid down to cover the keyboard 19 from above, and an open position where the display unit 13 stands in the rear of the keyboard 19.
The present invention is described in detail with reference to Experimental embodiments.
Copper wires were subjected to tin plating, and thereby a tin plating layer was formed on the copper wires. Thereafter, the wires were subjected to rolling, and thereby copper wires having a thickness of 0.035 mm were obtained. The copper wires were introduced into an infrared heating device whose surface heating temperature was set to 220° C., heated therein for 1 minute, and then taken out of the infrared heating device and made stand to cool.
The copper wires were arranged, by a laminator, at regular intervals on an insulating belt-like sheet having a thickness of 0.0475 mm and formed of heat-resistant polyethylene terephthalate, and thereby an insulating belt-like sheet with conductors was obtained.
Thereafter, the tin-plated copper wires were subjected to surface analysis by a scanning electron microscope.
As a result, the copper wires were proved to have a tin-copper alloy phase existing on a copper phase and reaching the surface. However, a tin phase remained in some parts of the surface.
Table 1 below illustrates the obtained result of Experimental embodiment 1.
Tin-plated copper wires were heated in the same manner as in Experimental embodiment 1, except that the respective surface heating temperatures were set to 240, 260, 280, and 300° C. Then, the compositions of the wires were checked in the same manner.
As a result, it was proved that a tin-copper alloy phase existed on a copper phase and reached to the surface, in the cases of using the surface heating temperatures of 240° C. and 260° C. However, a tin phase remained in some parts of the surface. Further, in the cases of using the surface heating temperatures of 280° C. and 300° C., a sufficient amount of tin-copper alloy phase existed on the copper phase, and little tin phase existed.
Table 1 below illustrates the obtained results of Experimental embodiments 2 to 5.
Tin-plated copper wires were heated in the same manner as in Experimental embodiment 1, except that the respective surface heating temperatures were set to 200 and 320° C. Then, the compositions of the wires were checked in the same manner.
As a result, in the case of using the surface heating temperature of 200° C., only a tin phase existed on a copper phase, and no tin-copper alloy phase existed.
On the other hand, in the case of using the surface heating temperature of 320° C., a sufficient amount of tin-copper alloy phase existed on a copper phase, and little tin phase existed. However, cracks occurred on the surface.
Table 1 below illustrates the obtained results of Comparative Experimental embodiments 1 and 2.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-157350 | May 2005 | JP | national |
