Patent Application
20060226199
The present invention relates generally to soldering of a flat flexible cable (“FFC”) to an electrical substrate and more particularly to the soldering of an FFC to an electrical substrate using a lead-free solder.
Generally, FFCs have a conductive member enclosed in a polymer sheath. When soldering an FFC to a substrate, the temperature required to melt the solder may damage the polymer sheath. Currently, FFCs are being soldered to the substrate using lead-alloy solders. However, the industry trend is towards the use of lead-free solders which have a higher melting temperature. Because of the higher melting temperature, there is a greater risk of damaging the polymer sheath of the FFC. Therefore, there exists a need for a solution that allows for the soldering of FFC to a substrate using a lead-free solder that will minimize or eliminate damage to the polymer sheath.
In overcoming the drawbacks and limitations of the known technologies, a method and the resulting product of soldering a FFC to an electronic substrate using lead-free solder is disclosed. The substrate includes conductive traces embedded within the substrate and through holes or slots extending through the thickness of the substrate adjacent to the conductive traces. By having the slots extend through the thickness of the substrate, electrical and physical access to the copper traces is possible. The FFC includes a conductive strip encapsulated by a non-conductive sheath and an exposed end portion which is inserted into the slot. A lead-free solder bonds and electrically connects the exposed end portion to the conductive trace of the substrate.
In order to solder the FFC to an electronic substrate using lead-free solder, the exposed end portion of the flat flexible cable is inserted into the slot of the substrate such that the exposed portion passes through the entire depth of the substrate creating a target area. The flat flexible cable is then heating to a temperature of about 100° C. Finally, molten lead-free solder is applied to the target are for approximately 5 to 9 seconds.
These and other advantages, features and embodiments of the invention will become apparent from the drawings, detailed description and claims, which follow.
Referring now to
The substrate 12 is made from at least one of polyimide, polyethylene naphthalate (“PEN”), polyethylene terephthalate (“PET”) and flame retardant Type 4 (“FR4”) epoxy based substate. Alternatively, any other non-conductive polymer can be used as is known in the industry or later developed. Generally, the substrate 12 is rigid, but it may be made to be flexible. The copper traces 14 are typically made of copper, but may be made of any conductive material.
Referring now to
The previous paragraphs described an end product of a method. The following paragraphs will describe the method for making the end product.
Referring now to
A soldering device 40 has a solder pot 42 which contains molten solder 44. The molten solder 44 is preferably a lead-free type. More specifically, the molten solder 44 includes tin with at least one of: silver and copper. The soldering device 40 further includes a pump 46 and a tube 48. The pump 46 is placed near the bottom of the solder pot 44 so that the pump 46 is immersed in the molten solder 44. The pump 46 pumps molten solder 44 through the tube 48 and out through an opening 52 at an end 53 of a nozzle 54. When in operation, the molten solder 44 pumped out the opening 52 will, by force of gravity, trickle down the end 53 of the nozzle 54 and return to the solder pot 42.
The target area 29 will then be situated near the opening 52 of the nozzle 50 such that the molten solder 44 that is flowing through the opening 52 will contact the target area 29. The force exerted on the molten solder 44 by the, pump 46 and capillary action will force an amount of molten solder 44 between end portion 26 and the copper trace 14. After about 5 to 9 seconds, the target area 29 is removed from the opening 52 of the nozzle 50 such that the molten solder 44 that is flowing through the opening 52 is not in contact with the target area 29.
The heating element 30 is then removed from the FFC 20 and the remaining solder 56 is allowed to cool. The remaining solder 56 bonds and electrically connects the end portion 26 of the FFC 20 to the copper trace 14.
The foregoing description of the embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Numerous modifications or variations are possible in light of the above teaching. The embodiment discussed was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
