Device for Bonding Wire Leads in Electronic Components

The invention relates to an improved device for bonding wires in electronic components.

Currently available devices for bonding electronic component wires may be basically reduced to two types: a first type, which is called "translatory" type hereiin and is shown diagramatically in FIG. 1, and a second type, called "rotary" type herein and is shown diagramatically in FIG. 2. Both devices perform the same operations under the drive of a single motor, but having different layouts in principle and exhibit different advantages and disadvantages.

For a given installed drive power, the translatory type device of FIG. 1 is slower than the rotary type device of FIG. 2, since larger reciprocating masses are involved therein, but, at the same time, it affords a higher degree of accuracy in bonding than the rotary type device. This is especially true where the bonding points are located at different elevations. In fact, with the rotary device, its capillary movement follows, in use, an arc of a circle which--in view of the minute extent of the movements involved--may be likened to a straight segment of a line. Where the bonding spots are located at different elevations, by contrast, the circular character of the path of movement becomes increasingly more significant as the difference between such elevations increases, and the capillary is positioned offset with respect to the perpendicular to the locus, thus effecting an incorrect soldered joint. The present invention reconciles speed and accuracy of operation. In accordance with the invention a motor is effective to bring, where required, the capillary rapidly as close as feasible to the bonding spot, the capillary being driven through the final portion of its stroke by a cam which can impart the capillary with the motion directly ahead of and during the bonding step. The latter device, having two degrees of freedom, while driving the capillary gently and accurately at a high rate, cannot change the motion in situations that may require it, unless the cam is replaced with another cam having a more appropriate profile to the occasion; this is specially true of instances where successive soldered joints are to be made at different elevations.

It is an object of this invention to provide an improved device for bonding wires leads in electronic components, which can operate at as fast a rate as a device of the rotary type, as accurately as a device of the translatory type, and afford a degree of flexibility in operation such as not even modern cam devices can afford.

This and other objects of the invention will become apparent to be skilled ones from the description which follows and appended claims.

An improved device for bonding electronic components wires, according to the invention, is of a type which comprises a member for fast approaching the capillary to the solder spot, and an ultrasonic transducer including an arm carrying said capillary on one end, said transducer being mounted pivotally on said fast approach member, and is essentially characterized in that associated with said transducer is a linear motor having its field magnet rigidly attached to said fast approach member and its field coil associated with said transducer.

The improved device of this invention is illustrated, by way of example and not of limitation, in the accompanying drawings, where:

FIG. 1, as already referred to in the preamble, shows a conventional device of the translatory type;

FIG. 2, also as referred to in the preamble, shows a conventional device of the rotary type;

FIG. 3 is a diagramatic side view of the inventive device; and

FIG. 4 is a sectional view taken along the line IV--IV of FIG. 3.

Throughout the drawing views, including those showing prior devices, like parts are designated with the same reference numerals.

With particular reference to FIGS. 3 and 4, this device, as generally indicated at 1, comprises a bearing structure 2 whereto a motor 3 is mounted which drives a connecting rod/crank linkage 4 acting on a first frame 5 through roller guides 4'. Said first frame 5 has a pivot point 6 whereat a second frame 7 and third frame 8 are pivotally connected. Rigid with the frame 5 is a static winding 9 of a position transducer, generally indicated at 10, of the Linear Variable Differential Transformer (LVDT) type, as well as a pair of magnets 11 of a linear motor, generally indicated at 12. The moving element 13 of the position transducer 10 and a coil 14 of the linear motor 12 are made associated with the frame 8 which has, at a remote location from the linear motor 12, an arm 15 supporting an electromagnet 16 and related plunger rod 17, and a first portion 18 of a contact 19.

More specifically, the coil 14 has a square or rectangular cross-sectional configuration with the turns lying on parallel planes perpendicularly to the plane of motion of the capillary 23. It follows that, the current and magnetic flux define a plane coincident with that of the capillary 23, thereby the resulting force will be at all times directed into said plane. The magnets 11 have parallelepipedal configurations and extend on parallel planes to said capillary plane of action, and are housed in an iron holder 11' having a middle portion 11" around which the coil 14 is located.

The second portion 20 of the contact 19 is carried on the frame 7 forming a support for an ultrasonic transducer 21 which carries, on a first end thereof, a coil 22, and on the second end thereof, a capillary 23 wherethrough a wire 24 forming the material to be bonded extends. Provided between the frames 7 and 8 is a spring 25 whose function will be explained hereinafter.

In operation, energization of the electromagnet 16 results in its plunger rod 17 moving forward to lock the frame 7 to the frame 8 and close the contacts 18 and 20. The operation of the motor 3, via the connecting rod and crank 4, drives the frame 5 downwards to bring the pivot point 6 level with the bonding spot C. That downward movement of the frame 5 results in a correponding displacement of the frames 7 and 8, owing to the latter being also pivoted at 6 and locked together package-like; such package-like locking is necessary in order to prevent incidental relative movements of the frames 7 and 8 as the capillary 23 is being approached to the bonding spot C and consequent sudden stop at the desired close distance. The electromagnet may be now de-energized to release the frames 7 and 8 which hold, however, the contacts 18 and 20 closed on account of the action of spring 25.

Energization of the linear motor 12 results in a rotation of the frame 8 and, via the spring 25, of the frame 7 as well, thereby causing the capillary 23 to move through the final close up distance. On the capillary 23 contacting the bonding spot C, the contacts 18 and 20 are opened and the spring 25, by resisting the opening of said contacts, provides the required bonding pressure for the capillary 23.

The opening of the contacts 18 and 20 may be used as a signal to energize the coil 22 and effect the bonding by ultrasonic effect. The travel distance of the linear motor 12, and accordingly the rotation of the transducer 21, is controlled by the position transducer 10 which is controlled, in turn, by an electronic unit, of suitable design and known per se, which is not shown and is not pertinent to this invention.

On completion of the bonding at the spot C, the device 1 is conventionally moved over to a second bonding spot C' shown in FIG. 3 at a lower elevation than the spot C. In order to accomodate the difference in elevation between the spots C and C', the motor 3 is again operated to bring the pivot point 6 to a position level with the spot C', and the above-listed sequence of operations are reiterated.

The linear motor 12 controls the movement of the capillary 23, which takes sequentially place as follows:

up to form the loop in the wire;

down to the second bonding region;

up, after completing the second bond, to determine the next wire length to form a ball known as the "tail";

up to pass the electrode under the tail;

down to the following region of first bond.

Through appropriate programming of the electronic unit, it would, of course, possible where necessary to combine the movements controlled by the motors 3 and 12 so as to increase the device rate of operation.