The present invention relates to a method for removing single microchips from a silicon wafer on which a plurality of integrated circuits has been made that is usable in particular in the technology of mounting integrated circuits on a support, the so-called "flip chip", in which the integrated circuits are fixed to a support element with the active side, i.e. the side on which the circuit components are made, facing the support element, to then be electrically connected to other integrated circuits or electric or electronic components. In the integrated circuits, or microchips, manufacturing technique the circuits are made on silicon laminae that are generally circular in shape and are known as "wafers" that, after the creation of the circuits, are divided into parts, so-called "chips", or "microchips", each containing an integrated circuit. In the so-called, "flip chip" mounting technology the single microchips taken from the wafer have to be rotated by 180° before being fixed to the support intended to receive them. Currently, removing the microchips from the wafer, in the aforementioned mounting technology, occurs in the following manner.

The wafer is placed on a substratum, for example a plastic film, with the active part of the microchips facing upwards, and is then cut into the single microchips; the microchips are then removed one at a time, as will be disclosed in greater detail below, and each microchip is transferred to a support to which it is intended to be fixed together with other electric and electronic components.

The time required for the operations of removing and transferring each chip is such that, in the current state of the art, productivity is not greater than 7-8000 microchips per hour. As all the operations of removing the microchip

from the substratum and transferring the microchip to the support to which it is intended to be fixed are mechanical operations, progresses in the art can improve productivity, but not in a significant manner. The present invention is intended to provide a system for removing microchips from a wafer consisting of a plurality of microchips that makes possible much higher productivity than that obtainable with the systems known from the prior art. According to the present invention a system is provided for removing microchips from a wafer placed on a substratum fixed to a movable support element, said system comprising lifting means associated with said movable support element, removing means for removing said microchips from said substratum and transferring means for transferring said microchips, characterised in that said lifting means comprises a plurality of lifting elements suitable for lifting in sequence, or simultaneously, a plurality of microchips and that said removing means comprises a plurality of removing elements suitable for grasping, in sequence or simultaneously, the microchips of said plurality of microchips and delivering them to transferring means, which will then deposit the plurality of microchips in sequence, or simultaneously, on a destination support. Owing to the invention, a significant increase in productivity is obtained in relation to prior-art systems, it being possible to achieve even more than triple productivity, as will be specified below. An example of an embodiment of the invention is disclosed below, with reference to the enclosed drawings, in which:

Figure 1 is a schematic view from above of a wafer of microchips, that illustrates the operation of a microchip removing system according to the prior art; Figure 2 is a diagram that illustrates the movement of the support element of the substratum on which the wafer is

located, in a microchip removing system according to the prior art;

Figures 3, 4 and 5 illustrate the operation of the microchip removing and transferring means; Figures 6 to 9 schematically illustrate the operation of the system according to the invention.

Figure 1 illustrates a microchip removing system 2 according to the prior art. In Figure 1, 1 indicates a silicon wafer, on which a plurality of microchips 2. has been made, represented schematically as squares. The wafer is placed on a substratum 3 of plastics and is weakly fixed thereto through adhesive means, for example a dry adhesive. The substratum 3 is peripherally fixed to an annular element 4, assembled on a support element 5 that is movable on a horizontal plane. The microchips 2 have been preventively separated from one another, for example by cutting the wafer 1 by means of a cutting device.

Below said substratum 3, lifting means is arranged comprising a pushing element 6, for example in the shape of one or more needles that is movable both ways in a vertical direction. When the pushing element 6 is moved upwards, it lifts up a microchip 2 from the substratum 3, overcoming the force of adhesion of the adhesive. Above the wafer 1 removing means 7 is arranged, comprising a gripping element 8, at an end of which a suction cup 10 is arranged; the gripping element 8 is rotatable around a substantially horizontal axis 9, supported on a driving element 15, that is movable in a substantially vertical direction. The removing means 7 is associated with transferring means 11 comprising a further gripping element 12, at an end of which a further suction cup 14 is arranged; the further gripping element 12 is supported on a further driving element 16, which is movable both vertically and horizontally.

At the start of the removing operations the movable support element 5 is positioned in such a way that, for example, a first microchip 2A located near the edge of the wafer 1, in the first row of the microchips located at the top in Figure 1, is aligned with the lifting means 6 and the removing means 7.

Simultaneously, the transferring means 11 is positioned in such a way as to be aligned vertically with the removing means 7. The lifting means 6 lifts the microchip 2A from the substratum, so that it can be grasped and removed by the suction cup 10 of the gripping element 8. Subsequently, the gripping element 8 rotates by 180° around the axis 9, positioning itself with the suction cup 10 facing upwards. The microchip 2 grasped by the suction cup 10 thus has its inactive face pointing upwards. At this point, the further gripping element 12 of the transferring means 11 descends until the further suction cup 14 grasps the microchip 2, which is simultaneously released by the suction cup 10 of the gripping element 8.

Lastly, the transferring means 11 transfers the microchip 2 to a support on which it is intended to be fixed, depositing it on the support with the active face turned toward the support. In the meantime, the removing means 7 rotates again by 180°, returning to its initial position and the support element 5 moves to align a second microchip 2B, adjacent to the microchip 2A, with the lifting means 6 and the removing means, so that the microchip 2B can be removed by the removing means 7.

The sequence of operations is repeated until all the microchips of a row have been removed, after which the support element 3 moves to align the first microchip 2C of the next row with the lifting means 6 and the removing means 7, and so on.

The movements of the support element 5 are schematised in Figure 2. The operation of removing the microchips ends when the last microchip 2D of the last row of microchips has been removed. In Figures 6 to 9 there is illustrated the microchip removing system 2 according to the invention. In this system, the lifting means associated with the support element 5 comprises a plurality of lifting elements 6, four in the example in Figures 6 to 9, arranged in a preset configuration, for example at the vertices of a square.

Also the removing means 7 comprises a plurality of gripping elements 8. The number of the gripping elements 8 is the same as the number of the lifting elements 6 and each gripping element 8 is aligned vertically with a corresponding lifting element 6.

The transferring means 11 also comprises a plurality of further gripping elements 12, that may be independent of one another or be part of a transferring device provided with a plurality of further gripping elements 12 that are not independent of one another, i.e. that move together to transfer the microchips 2 to the supports on which they have to be mounted. In this case, the transferring device my comprise a number of further gripping elements 12 that is the same as the number of gripping elements 8 of the removing means 7, each further gripping element 12, being aligned vertically with a corresponding gripping element 8. Furthermore, the transferring device may comprise a number of further gripping elements 12 that is the same or different from the number of the gripping elements 8 of the removing means 7, but arranged in such a way as to be able to deposit the microchips in the correct preset position with a single depositing movement. Lastly, the transferring means 11 may comprise two or more transferring devices, each of which is provided with a plurality of further gripping elements 12.

At the start of microchip removing operations 2, the support element 5 is positioned in such a way that at least a microchip 2 is aligned with a first lifting element 6 and a first gripping element 8. At this point, the microchip 2 can be removed from the first gripping element 8 and be delivered to a first further gripping element 12. Whilst the first gripping element 8 transfers the microchip 2 to the further first gripping element 12, the support element 5 moves to position a second microchip 2 at a second lifting element 6 and at a second gripping element 8, so that the second microchip 2 can be removed by the second gripping element 8 and delivered to a second further gripping element 12. Said movement of the support element 5 can start as soon as the suction cup 10 has removed and lifted up the chip and the lifting element 6 has descended to the initial position. The sequence of the movements of the- support element 5 can be studied in order to minimise the total distance travelled. If the transferring means 11 comprises a plurality of further gripping elements 12 that are independent of one another, during removing of the second microchip 2, the first further gripping element 12 transfers the first microchip 2 to the support on which it has to be mounted and then returns to align itself with the first gripping element 8, whilst waiting to receive another microchip 2 from it. In this way downtime is substantially eliminated in microchips 8 removing and transferring operations. If the transferring means 11 comprises a transferring device provided with a plurality of further gripping elements 12 that are not independent of one another, transferring the microchips 2 to the respective supports occurs only after all the further gripping elements 12 of _. the transferring device have received a microchip 2 from the gripping elements 8 of the removing means 7. If the removing device is provided with a different number of further gripping elements 12, for example a greater number, than the number of gripping

elements 8 of the removing means 7, after removing the first microchip 2 and delivering it to a first further gripping element 12, the transferring device moves to position on the second gripping element 8 a second further gripping element 12. As already said, only when the transferring device has all the further gripping elements 12 full, does it move to go and deposit the microchips 2 on the support to which they have to be fixed, and any second removing device with its further gripping elements 12 removes the microchips from the various gripping elements 8 of the removing means 7. The various further gripping elements. 12 of the transferring device are not linked to the single gripping elements 8, so that, if a gripping element 8 does not remove the microchip 2 from the wafer 1, either because it is a faulty chip or because the gripping element 8 is outside the wafer 1, the transferring device positions itself on a subsequent gripping element 8.

This enables total microchip 2 removing and transferring time to be noticeably reduced, because also in this case downtime is substantially eliminated from transferring of the microchips 2 from the wafer 1 to the support on which they have to be fixed, with a significant increase in productivity. In an advantageous version of the present invention, the distance between two adjacent lifting elements 6, and correspondingly, the distance between two adjacent gripping elements 8 is advantageously the same as a multiple of the dimensions of a microchip. In this case, when a lifting element 6 and a gripping element 8 are aligned on a microchip 2, also the other lifting elements 6 and the other gripping elements 8 will be aligned on respective microchips 2, so that the first gripping means 7 can simultaneously remove a plurality of microchips to then transfer them to the transferring means 11, whilst the wafer 1 moves to position another plurality of microchips 2 at the lifting

elements 6 and then the gripping elements 8 for the next removal.

If for any reason, for example the presence of a defective microchip 2 or one of the gripping elements 8 positioned outside the wafer, or something else, one of the gripping elements 8 cannot remove a microchip 2, it performs no movement and memorises the lack of the microchip in that position so that the corresponding further gripping element 12 of the transferring means 11 does not become activated for the transfer of the microchip.

The productivity obtainable with this version of the invention is a multiple of the productivity which is obtainable with the prior-art systems, because at each removal operation of the microchips 2 the system removes from two to four microchips 2 simultaneously, depending on the positioning of the wafer 1.

In Figure 6 the position of the removing means 7 at the start of the microchip 2 removing cycle is illustrated. The position of the first gripping elements 8 of the removing means 7 in relation to the wafer 1 has been indicated in an extremely schematic manner by checks of a dark colour. In this position three of the four gripping elements 8 are substantially aligned on a microchip 2, whilst a fourth gripping element 8 is located outside the wafer 1 and, therefore, in an inactive position.

In Figure 7 an intermediate position of the removing means 7 is shown, in which all four gripping elements 8 are in an active position, i.e. near a microchip 2 to be removed. Figure 8 illustrates a second intermediate position of the removing means 7- in which only two gripping elements 8 are in an active position, i.e. at a microchip 2 to be removed, whereas the other two gripping elements 8 are in an inactive position. In Figure 9 a final position of the removing means 7 is illustrated in which three gripping elements 8 are in an active position.

All the microchip 2 removing and transferring operations are monitored by microcameras, one for each gripping element 8 and further gripping element 12, that monitor the presence of the microchip 2, its position and any marks with which the defective microchips 2 are identified. The plan of the wafer 1, indicating the position of the efficient microchips 2 and of the defective ones, can be stored in an electronic file that is usable by a command and control device that manages movements of the support element 5, of the removing means 7 and of the transferring means 11.

The percentage of the removing cycles in which one or more of the gripping elements 8 are inactive depends on the diameter of the wafer 1. The current tendency of silicon manufacturers to constantly increase the diameter of wafers 1 means that the percentage of the removing cycles in which a gripping element 8 is in an inactive , position tends to decrease. Furthermore, if the dimensions of the wafer- 1 increase the number of gripping elements 8 of the removing means 7 and of the further gripping elements 12 of the transferring means 11 can be increased, with a further increase in productivity.

In the case of a wafer 1 that is 8 inches in diameter that can contain about 50000 microchips, if the removing means 7 comprises four gripping elements 8, as in the illustrated example, in fewer than 1% of the positions that the removing means 7 can adopt in relation to the wafer 1 there are only two gripping elements 8 active; in about 22% of the positions three gripping elements 8 are active and in about 77% of the positions all four gripping elements 8 are active.

This makes possible a productivity increase that is approximately 370% in relation to prior-art systems, in which only one gripping element is used. It is naturally possible to use removing means 7 with more than four gripping elements 8, thereby increasing productivity still further.

It is furthermore possible to use a removing system that involves the removing of the microchips 2 from two wafers 1 simultaneously, by two removing means 7, one for each wafer, with a multiplicity of lifting and removing devices for each wafer.

In the practical embodiment, the materials, the dimensions and the constructional details may be different from those indicated but be technically equivalent thereto, without thereby leaving the scope of legal protection of the present invention.