Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2003-07-14
2004-11-30
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S580200
Reexamination Certificate
active
06824630
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for connecting a flexible flat cable using an ultrasonic welding machine and to a horn of the ultrasonic welding machine.
2. Description of the Related Art
A flexible flat cable has a conductive element, such as a copper foil with a thickness of about 35 &mgr;m. The foil is covered by an insulation coating layer made, e.g. of a PET (polyethylene terephthalate). The flexible flat cable can be connected to a member, such as a busbar, by ultrasonic welding. More particularly, the conductive element is exposed by stripping the insulation coating layer over a specified range. The flexible flat cable and the member to be connected then are placed between an anvil and a horn of an ultrasonic welding machine so that the exposed surface of the conductive element contacts the upper surface of the member to be connected. An ultrasonic vibration is given to the horn while the flexible flat cable and the member to be connected are pressurized, thereby bringing metal atoms of the conductive element and the member to be connected into contact and connecting the two by an inter-atomic attraction.
The base material of the conductive element has a fairy low strength, and the strength of the base material tends to decrease due to damage caused by welding with the ultrasonic welding machine. Thus, it is difficult to ensure sufficient strength for a connecting portion of the conductive element of the flexible flat cable and the busbar or the like. There has been a problem that the conductive element of the flexible flat cable will break at the connecting portion, for example, due to a tensile force on the flexible flat cable.
Japanese Unexamined Patent Publication No. 2000-294332 discloses a process of connecting flexible wires to form conductive patterns while being held between a pair of insulation coating layers. One side of each insulation coating layer is removed to expose one surface of each wire. The stripped portions then are disposed between an anvil and a horn of an ultrasonic welding machine with the exposed surfaces of the wires put together and held in contact. An ultrasonic vibration is transmitted from the horn to conductive elements via the insulation films while the stripped portions are pressurized. Thus, ultrasonic welding is applied to the conductive element of one flexible wire and that of the other flexible wire to connect the two flexible wires while the outer surfaces of the conductive elements are covered by the insulation coating layers.
The above-described process connects the conductive portions while the outer surfaces of the connecting portion are covered by the insulating coating layers. The breaking strength of the connecting portion against an external load logically should be improved by the reinforcing action of the insulation coating. However, the ultrasonic welding is applied by transmitting the ultrasonic vibration to the horn while the horn is pressed in contact with the insulation coating that covers the outer surfaces of the conductive elements. Vibration energy applied during ultrasonic welding is absorbed by the insulation coating. As a result, proper ultra sonic welding of the conductive elements is difficult, and the conductive elements ultra sonically welded by this process have a low break strength.
FIGS. 11 and 12
show an ultrasonic welding machine
30
with a horn that has truncated pyramidal protrusions
32
that are intended to improve the breaking strength of ultra sonically welded parts. The protrusions
32
are formed at a specified interval on the bottom surface of the horn
31
. The ultrasonic welding machine
30
also has an anvil
33
. A flexible flat cable
1
and a member to be welded, such as a busbar
2
, are introduced between the horn
31
and the anvil
33
of the ultrasonic welding machine
30
. The protrusions
32
of the horn
31
bite into an insulation coating layer
5
that covers the outer surface of the flexible flat cable while the insulation coating layer
5
is molten by vibration energy transmitted to the horn
31
. A conductive element
4
of the flexible flat cable is welded ultrasonically to the busbar
2
or the like with the leading end surfaces of the protrusions
32
pressed in contact with the conductive element
4
of the flexible flat cable
1
.
Coating material that is molten during ultrasonic welding may clog the spacings between the protrusions
32
, and may cause a connection failure. Thus, leading end surfaces of the protrusions
32
cannot be pressed into contact with the conductive element
4
when the coating material clogs the spaces between the protrusions
32
. Thus, the vibration energy transmitted to the conductive element
4
decreases and proper ultrasonic welding cannot be performed.
In view of the above, it is an object of the invention to enable a flexible flat cable to be connected easily and properly to a member such as a busbar.
SUMMARY OF THE INVENTION
The invention relates to a flexible flat cable connecting method for welding a flexible flat cable. The flexible flat cable has a conductive element made of, e.g. a copper foil that is covered by an insulation coating layer. The connecting method employs an ultrasonic welding machine to connect the flexible flat cable with a member to be connected. The method comprises stripping the insulation coating layer from a connecting surface of the flexible flat cable to expose the conductive element. The method then includes introducing the flexible flat cable and the member to be connected between a horn and an anvil of the ultrasonic welding machine so that the connecting surface of the flexible flat cable is held in contact with the member to be connected. Elongated projections are provided on a press-contact surface of the horn. The projections have a tapered cross section and preferably are pressed in contact with the insulation coating layer of the flexible flat cable. The method then comprises transmitting an ultrasonic vibration to the horn. Thus, the elongated projections bite into the insulation coating layer to ultrasonically weld the conductive element to the member to be connected.
Accordingly, a connection strength between a flexible flat cable and a member to be connected such as a busbar is improved since a vibration energy can be transmitted efficiently to the conductive element while the leading ends of the elongated projections are pressed in contact with the conductive element. Moreover, the overall strength of the connection can be improved by the remaining insulation coating in the connection area.
The elongated projections on the press-contact surface of the horn preferably extend substantially in the longitudinal direction of the flexible flat cable.
Ultrasonically welding is repeated by causing the elongated projections of the horn to bite in the insulation coating layer of successive flexible flat cables. Coating material molten by the vibration energy during the first ultrasonic welding does not adhere to the press-contact surface of the horn and hence does not clog spaces between the elongated projections. Thus, vibration energy is transmitted efficiently to the conductive element during the next of the ultrasonic welding because the leading ends of the elongated projections are pressed in contact with the conductive element. Therefore, the conductive element can be welded ultrasonically to the member to be connected, while the outer surface of the conductive element is covered by the insulation coating layer and the conductive element and the member to be connected can be connected securely.
An exposing step of the method may further comprise partly stripping the insulation coating layer at a side opposite from the connecting surface of the flexible flat cable to expose the conductive element. With this method, the operation of ultrasonically welding the conductive element to the member to be connected can be repeated at the non-stripped portion of the insulation coating layer at the outer side of the flexible flat cable by causing t
Kihara Takeshi
Oishi Akinori
Casella Anthony J.
Hespos Gerald E.
Sumitomo Wiring Systems Ltd.
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