Electric heating – Inductive heating – Metal working
Reexamination Certificate
1999-04-19
2001-05-22
Walberg, Teresa (Department: 3742)
Electric heating
Inductive heating
Metal working
C029S854000
Reexamination Certificate
active
06236029
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for soldering the core end of an electrical wire to a contact terminal of a connector by means of a soldering sleeve, said soldering sleeve being a shrinkable tube including meltable soldering material, and said method comprising the steps of:
positioning said core end onto said contact terminal;
positioning said soldering sleeve so as to cover said core end and said contact terminal; and
heating said soldering sleeve in order to melt the soldering material included therein and so to solder said core end to said contact terminal.
Such a method is already known in the art, e.g. from “
Operating and Maintenance Manual”
of the AA-400 Super Heater-Mark III heating gun of the Raychem Corporation™—Electronics Group, located at 300 Constitution Drive, Menlo Park—Calif. 94025. Therein is described the above method that consists of positioning, by an operator, the electrical wire on a positioning tool in order to bring the core end of the wire into contact with the contact terminal while covering the whole with the shrinkable soldering sleeve. At the same time, the operator heats the soldering sleeve with a heating gun. By this heating, the solder of the sleeve melts and provides a soldered connection between the contact terminal and the core end of the wire. Secondly the sleeve shrinks over the soldered connection.
In this known method, the positioning of the core end of the wire onto the contact terminal must be very precise and, because it is covered by the soldering sleeve and thus no longer visible, it is very difficult for an operator to maintain this position during the whole soldering process. The result is thus very dependent of the ability and experience of the operator.
The quality of the resulting soldered connection and of the shrinked down sleeve is also very much influenced by the human factor. Indeed, the heating with a heating gun is a relatively long and fastidious operation during which it is not easy to obtain a uniform heat. Generally only the side near to the gun gets the necessary calories to heat the connection. This is particularly true with hot air guns that also have the particularity that the heating resistors thereof degrade slowly whereby, as result, it becomes rapidly harder to get the same result even if the gun is still in the calibration tolerance. As a consequence, the operator has to adapt to the changing performance of the heating gun.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a soldering method as described above but wherein the human ability is of less importance, whereby the reproducibility may be increased as well as the quality of the soldered joint.
According to the invention, this object is achieved due to the fact that said method further includes the step of pre-soldering said core end of the electrical wire to said contact terminal prior to positioning said soldering sleeve over said core end and said contact terminal.
In this way, during the pre-soldering operation, the operator only has to position the core end of the electrical wire onto the contact terminal, without taking into account the shrinkable soldering sleeve. The pre-soldered joint is continuously visible and the pre-soldering operation is relatively fast. This operation is thus easy to reproduce with a constant quality.
The next heating of the soldering sleeve is also facilitated because the core end and the contact terminal are then already interconnected and well positioned.
Since the human ability is of minor importance in the present process, the reproducibility is very high.
The quality of the resulting soldering is also increased with respect to that of the above known method. Indeed, in the known method, it has been found by metallographic investigation that solder from the soldering sleeve is located between the contact terminal and the core end. With the present method however, the contact terminal and the core end are in contact with each other and are imbedded in the solder in a homogenous way. This provides a better electrical contact.
Another advantage of the pre-soldering operation is that it is reversible. This means that the core end of the electrical wire may be de-soldered and correctly repositioned onto the contact terminal if necessary.
The pre-soldering operation of the present invention is further facilitated in that said contact terminal has a spoon plated with a meltable soldering material and to which said core end is pre-soldered.
Preferably, said spoon is a tinplated spoon.
Another characteristic feature of the present method is that said step of pre-soldering said core end to said contact terminal is realized according to the soldering by resistance method wherein an electrical current flows via said core end and said contact terminal pressed against each other.
The ‘soldering by resistance’ method is known as giving good results and suits perfectly to the pre-soldering step of the present soldering method.
Also another characteristic feature of the present invention is that said soldering sleeve is heated by induction heating.
Induction heating is known as providing the most homogenous soldering.
Preferably, the inductive heating is provided in an oven wherein said connector is inserted with the electrical wire already pre-soldered to the contact terminal.
In a more general application of the present method, said connector is provided with a plurality of contact terminals to which core ends of different electrical wires are successively pre-soldered and soldered.
In more detail, said connector is a rectangular flat connector provided with a plurality of contact terminals arranged in a row and to which core ends of different electrical wires are pre-soldered and soldered according to the present method.
It is to be noted that the heating by induction can not be applied to the above known method where three items have to be positioned with respect to each other prior to the soldering operation for each of the contact terminals of the connector.
Yet another characteristic feature of the present invention is that said soldering sleeve is constituted by a tube that includes the solder material and that is adapted to shrink over the joint core end and contact terminal during the step of heating said soldering sleeve.
By using the present method, the risk of altering the structure of the shrinkable tube of the sleeve is much lower than by using a heating gun, especially when the latter degrades as discussed above.
The present invention also relates to a soldering apparatus for soldering the core end of an electrical wire to a contact terminal of a connector by means of a soldering sleeve, said contact terminal being plated with a meltable soldering material and said soldering sleeve being a shrinkable tube also including meltable soldering material, said apparatus comprising:
a pre-soldering fool with pressure means adapted to press said core end and said contact terminal together, and with electrical means adapted to provide an electrical current flowing via said joint core end and contact terminal, so as to pre-solder them together according to the soldering by resistance method; and
an inductive soldering tool adapted to heat by induction said soldering sleeve covering the pre-soldered core end and contact terminal in order to melt the soldering material included in said soldering sleeve and to shrink the shrinkable tube.
Such an apparatus is especially designed for operating according to the method of the present invention.
In more detail, the present apparatus is characterized in that said pressure means comprises electrical fingers adapted to press together said core end and said contact terminal, and in that said fingers are electrically conductive so that said current also flows through said fingers.
The fingers may for instance be driven by an engine so that a constant and repetitive pressure may be exerted on each core end and contact terminals of the connector.
The best pre-soldering is obtained with electrical fingers that have a relatively
Alcatel
Sughrue Mion Zinn Macpeak & Seas, PLLC
Van Quang
Walberg Teresa
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