Method and device for mechanical processing of semiconductor products in a press

The present invention relates to a method and device for mechanical processing of semiconductor products in a press.

In the production of semiconductor products it is usual for a large number of products to be brought together on a carrier in a collective assembly of semiconductor products (which is also referred to for instance as a lead frame or a board). After completion of a part of the production steps of the semiconductor products, such as typically placing of the electronic components on the carrier and encapsulation of the electronic components, the assembled semiconductor products are separated from each other by a separating operation. The punching or stamping of the carrier (for instance in the form of a strip of sheet material) is frequently applied in the production of semiconductors. In addition, other mechanical processes can also be carried out on the electronic components, such as for instance the deforming of the carrier material. During these mechanical processes considerable forces usually have to be exerted locally on the carrier material (in the order of magnitude of thousands of kilos per cm ² ). Another feature of the mechanical processing of the semiconductor products is that this can also produce waste, for instance in the form of slug. The existing presses for mechanical processing of semiconductor products are costly and also noisy during use (a noise pressure well above 90 dB is typical).

The present invention has for its object to provide an improved method and an improved device for mechanical processing of semiconductor products in a press, with which the mechanical processing can be performed relatively cheaply and safely compared to the prior art and with little chance of damage to products and/or press.

The invention provides for this purpose a method for mechanical processing of semiconductor products in a press as according to claim 1. The force limitation of the feed of the products in at least one direction prevents great forces being exerted on the products, the feed means and/or the press such that one or more of these are damaged. In other words, the forces exerted during feed are limited in at least one direction. It is thus possible to prevent products being damaged or the feed means being damaged in the case of for instance stagnation. It is also possible to prevent (considerable) damage

being caused in the case for instance that an erroneous type of component for processing is fed, components do not satisfy minimal specifications or if intrusive factors (dirt, waste, break-off parts etc.) are disruptively present. A further advantage of the force limitation is that it results in increased safety for the operators; if for instance a body part is trapped, injury can thus be prevented. The present invention therefore also results in improved working conditions.

The feed can for instance be embodied such that the feed of the semiconductor products to be processed takes place along a feed path comprising a plurality of mutually differing path parts with movement components which vary, these different movement components being provided with separate force limiters. Envisage here for instance a kangaroo-like feed movement with separate horizontal and vertical movement components. The advantages as already described above of the force limitation of the feed in at least one direction can likewise be realized in multiple directions in the case of more complex feed paths in which the product for feeding is displaced successively in different directions.

The rotating movement is also referred to as a non-uniform rotating movement, i.e. the rotating movement has a non-uniform motion characteristic. By way of further elucidation: a uniform motion (UM) is also defined as a motion in which the ratio of the path covered and the time duration of the motion is constant at any moment, this implying that the speed is also constant at any moment. According to the skilled person in the field the relative movement of the processing elements has heretofore desirably been a smooth one. This is because smooth movements can be realized quickly and reliably compared to non-smooth movements. The individual press parts are preferably displaced substantially linearly relative to each other, and this relative linear displacement is then generally initiated in economic manner by the non-uniform rotating movement of for instance an electric motor.

When a desired relative movement of the press parts does not run smoothly in accordance with a sinusoid (i.e. when the second derivative of the movement in time, d ² x/dt ² , is in any case not discontinuous), there is the (preconceived) notion that this causes problems with an accurate control, and that the mass inertia of the relatively displaceable components results in a limitation in respect of the possible processing

speed. A known preferred value for further specifying the smooth movement according to the prior art is that the jerk of the processing elements in time must have a constant progression, or still more preferably is limited to values lower than 200 m/s ³ . In addition, the skilled person assumes that the movement characteristic of the press parts, which is already sinusoidal-like as a result of the usual conversion of a uniform rotating drive to a linear displacement, results in a gentle closure of the press parts. In combination with the force limitation of the feed of the products, the present invention provides the advantages of a non-uniform rotating drive of the press parts particularly when, as the individual press parts approach the shortest mutual distance, an even greater deceleration occurs than with the sinusoidal-like movement characteristic of the press parts. The contact moment of the press parts is in practice not located in the dead centre (i.e. not at the peaks or valleys of the movement characteristic) but at some distance from the dead centre position. This is caused by the fact that the tools connected to the press parts must also make an "operating stroke". During punching for instance the punching elements must thus still be urged into the punching plate. The result hereof is that, at the moment that the press parts - or (what is equivalent in this application) the entering into mutual contact of the tools forming part of the press parts or coupled thereto - come into mutual contact they can still have a considerable linear speed. Not only does the feed of the products for processing take place in controlled manner, the further processing thereof also takes place under conditioned circumstances, which together results in a highly controllable processing of the products.

It is particularly advantageous if the movement characteristic is now specifically modified because, before the dead centre of a sinusoid is reached, there is already a need - more than according to the usual sinusoid - for increased deceleration. The variation in the rotation speed of the drive occurs more particularly under conditions in which the average speed of successive operations is the same. That is, a particular effort is made to both decelerate and accelerate within a single processing cycle. More specifically, this relates not so much to a change in rotation speed over a plurality of successive processing cycles, but to deceleration and acceleration within a single cycle of movement. The peaks of the movement characteristic can thus be "widened". Unexpectedly, the press is found to thus run much more quietly (a sound reduction of more than 20 dB is found to be feasible in practice). The drawbacks of a non-uniform

rotating drive are not found to offset the advantages which this can provide, particularly in conditions where the sound impact in the vicinity of a press represents an important factor. Standards set for working conditions must be particularly taken into account here. Another important advantage is that, because the press closes at less speed, it runs "more smoothly", which reduces wear of the tools. This is because the tools forming part of the press parts come into mutual contact at a lower than usual speed. Reduced wear is of course advantageous because the tools thereby require less maintenance, but also because the effective operating time of the press thereby increases. In addition, the present invention also allows higher speeds because of the combination with the force limitation of the feed, which provides a very significant advantage in respect of productivity. An increase in productivity of 30-50% is found to be feasible.

The invention also provides a method for mechanical processing of semiconductor products in a press, wherein during the relative displacement of the individual press parts during performing of the mechanical processing of semiconductor products waste is created which is collected in a container, wherein exceeding of at least one filling level of the container is automatically monitored. This is possible for instance by means of determining the weight of the container with content. It is important that the container is emptied on time. Unnecessary work is carried out if a container is emptied before it contains a determined minimum quantity of waste. Emptying of a container which has exceeded a determined filling level can on the other hand result in undesirable working conditions and/or in the operation of the press being impeded. An automatic detection of the degree of loading of the container can provide a solution here. Because the container is generally exchangeable and because small contamination (dust) is usually present among other contaminants in the container, a weight detection forms a particularly reliable solution for the provision of such a detection.

In another preferred method the force of the movement of the press parts directed toward each other is monitored by means of a safety system in order to thus prevent damage occurring to the device (for instance the press parts or the tools forming part of the press parts) in the case of wrongly placed products.

It is further advantageous that the change in product-dependent settings, for instance via rapid-action couplings, is only possible in preferred positions. The chance of errors due to for instance incorrect adjustment is thus limited, and rapid operation can take place.

In order to limit the sound pressure it is advantageous that the press parts connect to each other via a resilient material part. Such a connection is then made in co-action with a form-retaining (accurately dimensioned) stop which defines the final size; the resilient material part then provides for damping, while a precise final size is nevertheless defined.

The present invention also provides a press device for mechanically processing semiconductor products as according to claim 8. With such a device which is provided with a feed means for semiconductor products to be processed which connects to the press parts, feed means can be driven via a force limiter. The advantages as already indicated above can thus be realized. The force limiter can for instance be formed by a restorable release coupling (such as for instance a magnetic coupling, a clamp coupling, a slip coupling or another type of safety) which disconnects when a maximum force to be transmitted is exceeded. It is advantageous if, after being disconnected, the coupling can be easily restored to the coupled position, although it is also possible to envisage a used release segment having to be replaced for this purpose by a new release part.

The feed means can be embodied such that they cover a plurality of path parts with differing movement components. The forces to be exerted on the different path parts can advantageously be individually limited. Envisage here for instance a horizontal and a vertical path part with movement components which together require a composite "kangaroo-like" feed movement. As already stated above, such a limitation of the maximum forces to be exerted results in a reduced chance of damage to the device (and the products), and also provides the advantage of a greater safety for the operator. Less mechanical wear will also occur to the specific moving parts of the device.

In a preferred variant the device also comprises: a container for collecting waste from the semiconductor products and detection means for detecting at least one filling level of the waste container. Such waste containers are generally releasable so as to enable easy emptying thereof. Detection of the degree of filling can prevent that a container

becomes so full that it becomes too heavy for (manual) emptying or that it becomes so full that it will begin to impede proper operation of the press. In addition to the advantage that the danger of being emptied too late can be reduced, it is also possible to control the maximum weight of a container to be removed by an operator. This measure therefore also results in improved working conditions.

In a preferred embodiment the detection means for detecting at least one filling level of the waste container comprise a weight detector for the container. This can advantageously be assembled with the frame of the press. Because the waste is dusty, visual detection is for instance difficult. It is also the case that excess weight is a factor which can have an adverse effect on working conditions, and so in this way the value which is important is measured. By assembling the detector with the frame an exchangeable container can be embodied in simple manner, and the reliability of the device is enhanced.

In yet another advantageous embodiment variant at least one of the press parts is safeguarded via a detection system with feedback to the rotating drive. Such a detection can take place via safety pins. It is stated here once again for the sake of clarity that the term "press part" is understood to mean the non-exchangeable machine part in combination with an exchangeable tool part connected thereto. The chance of damage to the press parts is further reduced by the safety.

In yet another preferred embodiment the device is provided with at least one rapid- action coupling for displacing a product-dependently adjustable component of the device. In similar manner it is advantageous that the device is provided with at least one rapid-action coupling for exchanging a product-dependent component of the device. These measures simplify conversion of the device, which can result in time-saving as well as being an advantageous for working conditions. A further advantage is that the reliability of correct settings hereby increases without having to depend to a considerable extent upon the expertise and skill of the relevant operators.

Yet another preferred variant of the press is characterized in that at least one of the press parts is provided with a stop on a side directed toward another press part, this stop being provided on the contact side with a resilient material part. This resilient material part is

desirably placed here in a form-retaining recess, and further consists of a full material part which is provided on the sides adjoining the form-retaining material part with sides chamfered to a position under the form-retaining material part. The usual prior art central opening in the resilient material part is therefore absent. The edge(s) of the resilient material part in this construction still provide some space for deformation of the resilient material part in the space left clear by the form-retaining material part. The resilient material part is however preferably so large that it is not forced completely into the space left clear by the form-retaining material part. This prevents the form-retaining material at any time defining the final size of the stop, due to a precise control of the form and the volume of the resilient material part. In addition to thus reducing the sound pressure, a resilient material part without central opening has the advantage that such a resilient material part has a longer lifespan than the material parts with a central opening.

The present invention will be further elucidated on the basis of the non- limitative exemplary embodiments shown in the following figures. Herein: figure 1 shows a perspective view of a device according to the invention, figures 2A and 2B show perspective views of components of the device as shown in figure 1, particularly components relating to the driving of the device, figures 3 A and 3B are perspective views of components of the device as shown in figure 1 , particularly components for removing waste, and figures 4A and 4B are perspective views of a prior art resilient stop part provided with a central opening placed in a form-retaining recess and a resilient stop part according to the invention.

Figure 1 shows a perspective view of a press device 1 for mechanical processing of semiconductor products, provided with a feed conveyor 2 along which the products for processing are supplied and a discharge conveyor 3 along which the processed, generally separated products are discharged. Discharge conveyor 3 is provided with a fast-action closure 4 with which access can be gained to discharge conveyor 3 with a single operation, for instance in order to remove a jammed product or put it back in line. Using fast-action closure 4 the discharge conveyor 3 can then be returned once again to a protected position with a single operation. Figure 1 further shows an electric motor 5 connected to one of the press parts 6, 7; this will be elucidated in more detail below

with reference to figures 2 A and 2B. Different processing elements (not shown) can be coupled to press parts 6, 7; device 1 is used particularly in combination with a punch and punch plate. Drive 5 is visible because a door 8 is shown in an open position. Waste container 9, which is provided with a handle 10, is therefore also visible in figure 1. Waste can be discharged to container 9 during for instance punching and separating of products. As soon as it is full, an operator must open the door 8 and replace or empty container 9. This will be further elucidated with reference to figures 3A and 3B. Press parts 6, 7 are protected from the outside world by means of a hood 11, opening of which activates a sensor which stops operation of device 1. Door 8 and all other components are assembled with a frame 12.

Figure 2A shows a perspective view of a part of the drive and press parts 6, 7 taken from frame 12 as these form part of device 1 as shown in figure 1. Electric motor 5 is coupled via a drive roller 26 and a drive belt 20 to a drive wheel 21 which, via eccentrics 22 (see figure 2B herefor), drives the vertical displacement of the upper press part 7. The coupling of eccentrics 22 to press part 7 can be safeguarded by a detection system (not shown) whereby it is possible to intervene in electric motor 5. Using a second drive 27 a feed element, not shown in detail here, is moved intermittently via a drive belt 28 and at least one mechanism following cam 24 with a force-limited coupling. Such a coupling can for instance take a magnetic form such that the magnetic coupling is released when a determined load is exceeded. The components then only have to be placed together again in order to restore the coupling. Another option is to hold a connecting pin with a determined bias in a coupling position. If the bias on the pin is exceeded by a load, the pin is pressed out of the coupling position and the drive is thus uncoupled from press part 7. A force-limited drive can otherwise also be applied for other forced movements in device 1. Figure 2A further also shows schematically the control 25 of electric motors 5 and 27 with which for instance the non-uniform rotation of motor 5 can be controlled as according to the present invention.

Figure 3 A shows a perspective view of waste container 9 with handle 10 which supports on a weighing strip 30. As also shown in figure 3B, weighing strip 30 is assembled with frame 12 of device 1, whereby the weight of container 9 with content can be monitored. If desired, an underpressure can be generated in the container by connecting a suction device to an overflow 31 connected to container 30. Subject to circumstances, such as

the sensitivity of the products for processing, the quantity and type of the small particles released, locally applicable standards and so forth, it is also possible to opt to allow overflow 31 to communicate freely with the environment.

Figure 4A shows a first stop 40 according to the prior art which is formed by a form- retaining base 41 with a contact side 42 ground accurately to size. A resilient material part 43 is held by form-retaining base 41 in a manner such that it protrudes above contact side 42. A central recess 44 is provided in resilient material part 43. When first stop 41 comes into contact with an opposite second stop 45 it is possible, also because of the central opening 44 in resilient material part 43, for the resilient material part 43 to be compressed so far that second stop 45 comes into contact with the contact side 42 ground to size; the stop size is thus precisely determined. A drawback of the central opening 44 in resilient material part 43 is that it limits the lifespan and the deformability of resilient material part 43, although more important is that this stop 40 contributes toward the sound production of a press device.

The stop as shown in cross-section in figure 4B shows a full resilient material part 46, the sides 48 of which adjoining a form-retaining stop part 47 are chamfered such that they extend to a position below the furthest protruding sides 49 of form-retaining material part 47. However, a central part 50 of the contact side of resilient material part 46 protrudes further than the furthest protruding sides 49 of form-retaining material part 47. The advantage of stop 51 as shown in figure 4B is that the sound of the closing of the press parts can hereby be reduced without losing stop accuracy. A condition here is however that the volume of the resilient material part 46 is chosen such that it can never be forced fully into the form-retaining material part 47 and the final size is determined by form-retaining material part 47; the stop is after all formed by resilient material part 46. The accuracy of the form of resilient material part 46 here of course forms a critical size.