The invention relates to a press for working semiconductor products, in particular lead frames of such products, with high precision, comprising a support, conveying means for conveying and positioning the semiconductor products to be processed relative to the support along a product- processing path, wherein the conveying means are connected to the support, a ram to which at least one tool can be mounted for processing the semiconductor products, drive means for moving the ram relative to the support between a first and a second position, and a programmable control unit wherein a processing operation of the semiconductor products has ended when the ram has arrived in the second position relative to the support .

Such press is known from EP-A-0 655 883. In such press known per se, the drive mechanism typically comprises a crank- sliding mechanism for moving the ram up and down relative to the support. Further, an additional straight guide is present between the ram and the support .

Such known press turns out to entail the drawback that a semiconductor product which has undergone, by means of the press, a processing operation such as for instance the bending of a lead frame, does not properly maintain its processed condition. The bent legs of a lead frame prove to bend back again partially. A further drawback of the known apparatus is that the stroke of the ram is entirely determined by the crank-sliding mechanism. This means that the stroke of the ram can only be changed when the crank-sliding mechanism is adjusted accordingly. This adjustment implies that the length of the crank must be changed. This takes up much time and of course involves an economical drawback, because other guide projections must be purchased. Further, the changing and adjusting of the crank-sliding mechanism takes up much time.

Normally, the known crank-sliding mechanism will perform a relatively small stroke to the order of magnitude of tens of millimeters. However, when it is desired that tools be changed, the ram should be moved relative to the support through a larger distance. As the crank-sliding mechanism does not allow this distance, other provisions are necessary therefor. These provisions, too, entail an economical drawback.

It is the object of the invention to provide a solution to the problems mentioned hereinabove. Accordingly, the press according to the invention is characterized in that the drive mechanism comprises at least one screw spindle which interconnects the support and the ram for moving the ram relative to the support between the first and the second position through rotation around the axis of rotation of the screw spindle in the direction of the axis of rotation of the screw spindle, and at least one motor for driving the screw spindle, wherein the control unit is adapted to stop the ram relative to the support in the second position with a settable duration.

Because, according to the invention, the ram is stopped relative to the support in the second position for a settable duration, the semiconductor product, in particular the lead frame, is retained in its processed condition during this period. During this period, the molecules and atoms of the processed product turn out to be oriented and stabilized relative to each other in such manner that the product retains its shape when the ram is moved relative to the support from the second into the first position again. In other words, this will not involve the above-mentioned legs of the lead frame bending back. Thus, one of the above problems of the known press has been solved.

For making a complete stroke, i.e. moving the ram back and forth relative to the support, the motor makes a reciprocating, rotating movement. Hence, the press stroke directly depends on the angular displacement of the motor.

This implies that the stroke of the press is entirely freely settable. After all, for adjusting the press stroke, the motor need only be controlled in an accordingly adjusted manner for making a reciprocating, rotating movement. For this, no mechanical part have to be changed, as is the case with the known press. When a change of tools is desired, the motor can be controlled in such a manner that the ram is moved away from the support through a large distance. Thus, the space between the ram and the conveying means, where, in use, the semiconductor products to be processed (hereinafter referred to as "the articles to be processed") are located, becomes sufficiently large to enable the tools to be changed easily.

The press according to the invention also has the possibility of optimizing the number of strokes per minute, depending on the processing operation to be performed. When for particular processing operations, it is only necessary to perform a stroke through a relatively short distance, it is possible to control the motor in such a manner that the ram actually performs this short stroke. As a result, it is at the same time possible to choose the number of strokes per minute to be relatively high. A situation in which this occurs is for instance a stroke for performing a cutting movement . On the other hand, if a stroke is intended for performing a stroke for a bending movement, the ram should reciprocate through a relatively greater distance. Simultaneously, the number of strokes per minute, performed by the ram, should be reduced. This can be realized in a simple manner by controlling the motor accordingly for making a reciprocating, rotating movement. Here, too, it is not necessary that parts be changed.

In particular, the control unit is adapted to drive the motor at a constant speed during the period in which the semiconductor products are processed by the tool .

This implies that during the processing operation of the product, the ram is moved at a constant speed relative to the support. Surprisingly, it has been established by experiment

that this increases the accuracy of the processing operation considerably. This holds for bending as well as for punching the products to be processed.

Further, it applies that the control unit is preferably adapted to control the conveying means as well. As a result, the press can be applied in a multifunctional manner. Because the control unit is of a programmable design, the press is suitable for processing various types of semiconductor products independently of the shape and dimensions of these semiconductor products to be processed.

In particular, the drive mechanism comprises at least two spindles. In that case, the two spindles are preferably driven by one motor. This has the advantage that all spindles will perform the same rotating movement. As the power transmission by the spindles takes place without hinge point, the construction is rigid and the spindles can serve as straight guides. Preferably, the spindles are constructed as ball circulating screws. These ball circulating screws are not self-braking. This has the advantage that if (in the case of a press driven by several spindles) one of the spindles should move out of position, the mechanical construction will not be damaged. In that case, the non-driven spindle just remains rotating along. The kinetic energy generated during the movement of the ram must decrease to zero in order to bring the press to a stop. Owing to the slight mass inertia of the construction, this is properly possible, and in the event of a product sitting faultily in the tools, the press can also be brought to a stop without damaging the tools.

In particular, the conveying means comprise guide rails for guiding articles, to be processed in successive steps, along the article-processing path in which various tools for processing the articles can be disposed, a number of gripping fingers arranged along the article-processing path for engaging the articles, at least one first conveying motor for moving the guide rails and the gripping fingers back and forth in a direction transverse to the article-processing path, and

at least one second conveying motor for moving the gripping fingers back and forth in the direction of the product- processing path.

It is thus effected that the conveyance of the articles along the product-processing path is also entirely flexible. The conveyance should for instance be set when other products or similar products having different dimensions are to be processed. In other words, the conveyance can readily be adjusted by controlling the motors accordingly. Here, too, it is not necessary to change parts of the mechanism. In particular, the programmable control unit controls both the motor that drives the spindles and the motors of the conveying means. Thus, the entire press can be set for performing the various processing operations, by means of software. European patent application 0 039 532 discloses a press which is likewise provided with spindles. However, the press is entirely unsuitable for processing semiconductor products and hence does not comprise conveying means, controllable by means of a control unit, for conveying and positioning the articles relative to the support along a product-processing path. Moreover, the press does not comprise a control unit adapted to stop the ram for a settable period in the second position relative to the support.

Presently, the invention will be specified with reference to the accompanying drawings. In these drawings:

Fig. 1 shows, in perspective, a possible embodiment of a press according to the invention, in which a ram has been dismounted from the rest of the press and one spindle has been left out; Fig. 2 is a bottom view of the press of Fig. 1, in which the ram has been dismounted and components of the vertical conveyance have been left out;

Fig. 3 is a side elevational view of the apparatus of Fig. 1, in which only the components for controlling the ram are shown; and

Fig. 4 shows a possible embodiment of articles in the form of microchips that can be processed by the press of Fig. 1.

With reference to Figs. 1-3, a possible embodiment of a press according to the invention will now be described. In these Figures, corresponding parts have been provided with identical reference numerals.

In Fig. 1, reference numeral 1 designates a press according to the invention. The press 1 comprises a support 2 and conveying means for conveying and positioning the articles to be processed, consisting of semiconductor products, relative to the support along an article-processing path 4, shown in dotted lines in Fig. 1.

The apparatus further comprises a ram 6 which, in this example, mounts three tools 8.1, 8.2 and 8.3 for processing the articles. The tools 8.1, 8.2 and 8.3 in Fig. 1 are shown separate from the ram, but in use they are connected in a manner known per se to the ram at the bottom side 10 thereof. In this example, each tool 8.i (i = 1, 2, 3) is composed of first tool parts 12. i and second tool parts 14.1. The first tool parts 12. i in this example are mounted in a manner known per se to the support 2 (by means of a master top plate) , and the second tool parts 14.i are each mounted in a manner known per se to the ram at the bottom side 10 thereof (by means of a master bottom plate) . Further, each tool 8.i comprises a straight guide 16. i, which is known per se and provides that the second tool part in this example can be moved back and forth relative to the first tool part in vertical direction only. The straight guide 16.i may for instance consist of a number of pins mounted on the bottom side of a first tool part, whose free ends are received in throughbores provided at the bottom side of the second tool parts, which througbores narrowly enclose the pins. An article located between a tool 8.i can be processed by moving the first part towards the second part. In this manner, for instance cutting and bending

processing operations can be performed on the article in question.

In this example, the conveying means mentioned comprise two parallel guide rails 18.1 and 18.2, extending along the product-processing path 4 and between first and second tool parts 12. i and 14. i respectively. The parallel guide rails 18.1 and 18.2 are connected to a first beam 22 by means of supporting arms 20. The first beam 22 extends parallel to the guide rails 18. This first beam 22 is supported at its bottom side by two vertical supports 2 . The vertical supports 24 have their bottom sides interconnected via a connecting beam 26. Located in the connecting beam 26 is a throughbore 28 having its inside provided with screwthread. In the throughbore 28, a spindle 30 extends, driven for rotation by, in this example, a motor 32. In a manner known per se, the motor 32 is fixedly connected to the support 2. In this example, this is schematically shown in Fig. 1 by the connection 34.

In this example, the beam 22 has a U-shaped cross section and is hence composed of a bottom part 36 having two opposite sidewalls 38, extending upwards from the bottom part 36. Slidably accommodated in the first beam 22 is a second beam 40. The second beam 40 comprises vertical sidewalls 42 which respectively narrowly connect to the vertical sidewalls 38 extending in the longitudinal direction of the first beam 22. The conveying system further comprises a number of gripper arms 44 which are fixedly connected to the second beam 40. Like the supporting arms 20, the gripper arms 44 extend perpendicularly to the longitudinal direction of the first and second beams. The free ends 46 of the gripper arms 44 are provided with tong-shaped constructions which, in this example, are controlled pneumatically. The free ends 46 are located adjacent the guide rails 18.1 and fit over the guide rails in such a manner that they embrace these rails, as it were.

The second beam 40 is connected to a conveying block 50 via a vertical straight guide 48. The conveying block 50 is provided with a throughbore 52 extending in vertical direction. Located in the throughbore 52 is a fitting bar 54 whose top end is fixedly connected, via a connecting piece 56, to the second beam 40. The conveying means further comprise a second motor 58 which is fixedly connected to the support 2. The motor 58 drives a spindle 60 which extends parallel to the first and second beams and which cooperates with a throughbore 62 provided in the conveying block 50 and having its inside provided with screwthread.

In this example, the ram 6 is provided with four throughbores 64. i (i = 1, 2, 3, 4) . Each of the throughbores 64. i has its inside provided with screwthread 66.i. In each of the throughbores 64. i, a spindle 68. i is provided. In Fig. 1, the spindle 68.3 has been left out for clarity's sake, while the spindle 68.2 is not visible. Each spindle 68.i extends downwards in vertical direction through throughbores 70. i (i = 1, 2, 3, 4) respectively, provided in the support 2. Each of the throughbores 70. i comprises a bearing 72. i bearing-mounting a bottom portion 74.i of the spindle 68.i. For this purpose, the bottom portion 7 . i of each of the spindles 68. i has not been provided with screwthread. The bearings 72.i have the property that the spindles 68. i are connected to the support 2 so as to be immovable, at least substantially immovable, in their longitudinal direction. The spindles can in fact rotate freely in the bearings around their longitudinal axes.

The spindles 68. i extend to below the support 2 and are each provided, adjacent their free ends, with pulleys 76. i. In addition, as can best be seen in Figs. 2 and 3, the apparatus further comprises a motor 78 which is connected to the support 2. Via a belt 80, the motor 78 drives each of the pulleys 76.i and, accordingly, each of the spindles 68. i. The apparatus further comprises a wheel 84, rotatably connected to a plate 86. The plate 86, m turn, is slidably

connected to the support 2. The wheel 84 is likewise driven by the belt 80. By means of a set screw 88, also connected to the support 2, the wheel 84 can be moved towards the belt for tensioning the belt . The apparatus further comprises a control unit 90 controlling the gripping fingers 44, the first motor 32, the second motor 58 and the third motor 78.

The operation of the apparatus is as follows. Fig. 4 shows articles which, in this example, are processed by the press 1. The articles consist of a number of integrated circuits, each circuit being incorporated in a housing 92.j (j = 1, 2, ... , 5) . These housings are connected to a lead frame 94. By means of the tools, the lead frame 94 must successively be subjected to a number of processing operations so as to obtain separated chips whose legs, produced from the lead frame, have a desired shape. These processing operations may consist in, inter alia, bending and cutting and only cutting.

The article to be processed, as shown in Fig. 4, is positioned at a feed side 96 on guide rails 18.1. Next, the control unit 90 controls the gripper arms 44 so that these arms grip the articles. In this example, the distance (pitch) between two successive gripper arms equals the distance between, for instance, the housings 92.1 and 92.3 Then, the control unit controls the motor 32 so that the first beam 22 and, accordingly, the second beam 40 are moved upwards through a predetermined distance. This will involve the bar 54 in the throughbore 52 sliding upwards and thus acting as a straight guide. The upward movement of the first and second beams involves the guide rails 18.1 and 18.2, and the gripping fingers 44, being moved upwards. The articles to be processed are then located at some distance above the first tool parts 12. i . Next, the second motor 58 is driven so that in this example, the conveying block 50 is moved leftwards in the drawing through a distance equal to the distance between two adjacent housings 92.j. As a result, the second beam 40 slides

through the same distance and in the same direction in the first beam 22. This involves the gripping fingers being moved accordingly through the same distance in a horizontal plane. Because the guide rails are connected to the first beam via the supporting arms 20, the guide rails will not move in the horizontal plane. Thus, the articles are moved along the guide rails in the conveying direction 5, in such a manner that between each of the tools 8.1 an article is present. Next, the control unit controls the motor 32 in such a manner that the rails and the gripping fingers are moved downwards through the above-mentioned, predetermined distance, with the articles bedding down on the first tool parts. In this regard, the tool parts may further comprise pins extending in vertical direction, with the articles being provided with openings through which the pins extend when the articles are being moved downwards. As a result, the articles are positioned in the tools 8.1 with great accuracy. Next, the control unit controls the third motor 78. This will cause all spindles 68. i to rotate, in such a manner that the ram 6 is moved relative to the support 2 from a first position into a second position, in other words: the ram 6 is moved downwards. The result is that the second tool parts are moved towards the first tool parts and in this manner, the desired processing operation is performed on the relevant articles. Here, the spindles also act as straight guides in vertical direction between the ram 6 and the support 2. When the pressing movement has thus been carried out by means of the ram, when this ram has arrived in the second position relative to the support, the control unit controls the motor so that the ram is moved upwards again through a slight distance, that is to say it is moved from the first position in the direction of the second position. After this, the control unit controls the gripping fingers 44 for releasing the articles. Then, the control unit controls the second motor 58 so that the gripping fingers are moved backwards, in a direction opposite to the conveying direction, towards their original positions. After this, the gripping

fingers can again be controlled so that they grip the articles again. Next, the control unit controls the motor 32 for moving the rails and the gripping fingers upwards together through the above-mentioned predetermined distance. The articles are then pulled from the pins of the first tools, so that the articles can be moved in the conveying direction 5 again, in order to repeat the entire above-discussed process. For simplicity's sake, the various processing steps have been described hereinabove in such a manner that they do not overlap in time. Preferably, however, the various steps will in fact partially overlap in order to shorten the cycle time. As a matter of fact, when the ram is in such a position that the product still lies across the pins of the bottom part of a tool, the gripping fingers may be open. For the purpose of the operating process, it is better for the pins to take care of the positioning of the product completely (hence, in the lowermost position, the fingers need not be closed) . Hence, the gripping fingers may already open as soon as the products are placed over the pins, and should close as soon as the ram moves upwards and the products have almost been removed from the pins. In the time that the fingers are open, they can move in a direction opposite to the conveying direction. Consequently, the movement of the ram and the horizontal conveyance may overlap (this is very favorable in respect of the cycle time) . As soon as the opposite movement has been carried out, the fingers may close again already (only if the products are almost clear of the pins) . Hence, according to the invention, through rotation around the axis of rotation of the screw spindles, the ram and the support are moved towards and away from each other in the direction of the axis of rotation of the screw spindles. Thus, an up and down movement of the ram is obtained by a movement, inverting each time, of the rotation of the spindles. The repetition frequency and amplitude of the movement performed by the ram can readily be set by programming the control unit accordingly. In this regard, it is not necessary that mechanical parts be changed.

Thus, the horizontal and vertical conveyance by the first and the second motor 32, 58 can also be set by programming the control unit accordingly. Also when a different setting is desired, no parts have to be changed. Hence, the major advantage is that all movements to be performed by the press can be set by means of software. When it is desired that the tools be replaced by other tools, the control unit can control the third motor 78 in such a manner that the ram is moved upwards relative to the support through a large distance of, for instance, 10-50 cm. As a result, the space between the ram and the guide rails becomes properly accessible to enable easy changing of the tools. By the drive mechanism of the vertical conveyance, the guide rails can be moved upwards so far (more than the distance that is normally necessary) that it is possible to remove the lowermost tools without disassembling the rails. When the tools have been installed, the control unit can be programmed accordingly. If, for performing a processing operation, the first and second tool parts of the newly installed tools for instance have to be moved up and down relative to each other through only a relatively small distance, the up and down movement to be performed by the ram can be adjusted accordingly. Because the movement is relatively small, the repetition frequency of the up and down movement of the ram can be increased accordingly. This, too, can be programmed in the control unit in a simple manner.

As stated, the drive mechanism of the press is suitable for moving the ram relative to the support between the first and the second position. A processing operation of the semiconductor products has ended when the ram, relative to the support, has arrived from the first position into the second position. In particular, _^ the control unit is adapted to stop the ram relative to the support in the second position for a settable duration. In particular in the case of bending, this has the advantage that the bent product is retained in its bent position for some time. It appears that in that case, the molecules and atoms of the product have the opportunity of

being reoriented and in particular of stabilizing relative to each other. This stabilization involves the bent shape of the products being maintained when the ram is moved relative to the support from the second position in the direction of the first position. In other words, when the products are released by the tools.

In particular, the control unit is adapted to drive the motor 78 at a constant speed during a period when semiconductor products are processed by the tool. This has as a result that the tools are driven at a linear speed when processing the semiconductor products. This proves to increase the accuracy of the processing operation. Also, the processed product again proves to be particularly stable and to maintain its shape, obtained through the processing operation, also after the processing operation. Hence, according to the invention, it applies in particular that during the processing of the product, the ram is moved relative to the support at a constant speed and that when the processing operation has ended, i.e. when the ram has arrived in the second position relative to the support, the ram is retained in this second position for some time. By means of the programmable control unit, this period can be programmed. As it is possible to set this period, this period can entirely be adapted to the product to be processed and to the processing operation to be performed.

Preferably, the period when the ram is stopped in the second position relative to the support is 1 ms - 0.5 s, in particular 2 ms - 0.25 s.

The invention is by no means limited to the above- described exemplary embodiments. For instance, the motors may form part of a servosystem. The motors used here are alternating-current motors which are characterized by very high dynamics and a long lifetime (no carbon brushes) and are controlled digitally. These characteristics are essential for realizing short cycle times. Direct-current motors can be applied as well. It is also possible to vary the number of

spindles. The apparatus could also be provided with for instance one spindle. In that case, however, additional vertical straight guides between the ram and the support are in fact necessary. Also, in principle, it is not impossible that the third motor 78 is mounted on the ram. In that case, the throughbores 70. i of the support 2 are provided with a screwthread capable of cooperating with the spindle 66.i. The bearings 72.i will then be mounted on the ram itself. In this example, the ram comprises bushes 64. However, it is also possible that the ram is constructed as a flat plate having throughbores with a screwthread being provided in the throughbores themselves.

Such variants are all understood to fall within the framework of the invention.