APPARATUS AND METHOD FOR DAMBAR CUTTING

Description

DESCRIPTION of the industrial invention entitled: “Apparatus and method for cutting "dambar".” in the name of: 1. STMicroelectronics srl 2. STMicroelectronics Sdn. Bhd. there i i- Ml90AOO2 116 The present invention relates to an apparatus and method for cutting a "dambar" of a leadframe of an integrated circuit package after an integrated circuit encapsulation operation. There are several known techniques for encapsulating integrated circuits. In one well-known process, the integrated circuit chip is attached to a conductor structure called a "leadframe," typically made of thin copper strips. During the molding process, a hollow plastic body, the so-called package, is closed around the chip by the top and bottom surfaces of the leadframe and is then filled with a plastic material to create the body of the enclosure. During the molding process, however, the plastic material leaks out of the case into the regions between the leadframe conductors. This can cause jams or otherwise disrupt the equipment used to insert the complete integrated circuit package into a printed circuit board. One solution to the above problem is to create rectangular holes in the leadframe using one or more barrier strips called "dambars" in the leadframe outside the package. During encapsulation, the liquid plastic material fills the holes between the package body and the dambar and does not leak beyond. After encapsulation, the liquid plastic material Dr. Enrico Mittler, who filled these holes, removes the dambar as well. However, removing the dambar is a difficult and expensive operation, especially when the distance between the leadframe conductors is small. A commonly used device for dambar removal involves the use of a special pressure device that forces the dambar toward a suitably shaped cutting insert. During cutting, the integrated device package is supported by a fixed body, and this body must be in contact with the package to avoid damaging it. However, positioning the support too high or too low relative to the package can cause damage to the package and even break its plastic body because the leadframe may not touch the cutting insert during the dambar cutting operation. In view of the state of the art described, the aim of the present invention is to present an apparatus and a method for cutting a "dambar" of a leadframe of an integrated circuit package, after an encapsulation operation of the integrated circuit, which solves the problem described above in such a way as not to cause damage to the package. In accordance with the present invention, this object is achieved by an apparatus for cutting a dambar of a leadframe of an integrated circuit package comprising pressure means for compressing said dambar into cutting inserts, characterised in that it comprises a support device for said package comprising first and second support means between which said package is interposed, said first and second support means being compressed by vertical push mechanisms so as to allow said leadframe of said package to always be in contact with said cutting inserts, and including means for locking said support device in the pressed position. Thanks to the present invention, it is possible to create an apparatus for cutting a "dambar" of a leadframe of an integrated circuit package, after an integrated circuit encapsulation operation, which allows the integrated circuit package to be effectively supported during cutting, by means of a support device adaptable to any working condition during this operation, avoiding possible damage to the package. It is also possible to create a method for cutting a "dambar" of a leadframe of an integrated circuit package, after an encapsulation operation of the integrated circuit, which includes a support phase of said package by means of said support device adaptable to any working condition, avoiding possible damage to the package. The features and advantages of the present invention will become apparent from the following detailed description of a practical embodiment thereof, illustrated by way of non-limiting example in the attached drawings, in which: Figure 1 is a side view of a prior art dambar cutting apparatus; Figure 2 is a plan view of the apparatus of Figure 1; Figure 3 is a side view of the apparatus of Figure 1 with a low support for the package; Figure 4 is a side view of the apparatus of Figure 1 with a tall package support; ». * Figure 5 is a side view of a dambar cutting apparatus according to the present invention; Figure 6 is a side view of the apparatus of Figure 5 with first means for locking the package support device in accordance with the first embodiment of the present invention; Figure 7 is a side view of the apparatus of Figure 5 with second means for locking the package support device according to a variant embodiment of the present invention. With reference to figure 1, a package 1 of an integrated circuit is supported on a fixed support 2. The package 1 is provided with a structure of conductors protruding from the package, called leadframe 10, in which two dambars 5 are inserted. Two vertically movable pressure means commonly indicated with 3 placed on horizontally sliding guides 4 allow the dambars 5 to be forced towards appropriately shaped cutting inserts 6 placed on the sides of the package 1. The cutting inserts 6 have a typical comb shape to allow the cutting of the dambar 5 by pressing the means 3 on the dambar 5 itself, as visible in figure 2. In fact the means 3 are provided with elements 8 which can be inserted between the elements 9 of the inserts 6 so as to allow the horizontal cutting of the dambar 5 only by pressing on it. The fixed support 2 must be substantially in contact with the lower surface of the package so as not to induce damage to it and the leadframe 10 must be in contact with the cutting inserts 6. A support 2 positioned too low with respect to the package 1, as visible in figure 3, can cause damage to the package 1 which also depends on the relative position of the elements 8 of the means of pressure 3 and elements 9 of cutting inserts 6. A support 2 positioned too high with respect to the package 1, as visible in figure 4, can cause the elements 9 of the cutting inserts 6 not to be in contact with the leadframe 10 during the cutting operation of the dambar 5, thus causing damage to the package which can also lead to the breaking of its plastic coating. With current technology, the maximum permitted variation in the distance between package 1 and fixed support 2 is + / - 0.01 mm. Figure 5 shows an apparatus for cutting a dambar 5 according to the present invention which differs from the apparatus of Figure 1 in that it uses a movable support generally indicated by 20 for positioning the package 1 so that its leadframe 10 is in contact with the cutting inserts 6. The movable support 20 is composed of two blocks 11 and 12 loaded by respective springs k1 and k2. Contact between the lower surface of the package 1 and the support block 12 is ensured by the pressure thereon of the spring k2 while the second spring k1 acts on the support block 1 so as to compress the package 1 onto the upper surface of the support block 12. Furthermore, the stiffness of the spring k1 is adjusted so as to be greater than that of the spring k2 to ensure contact of the leadframe 10 of the package 1 with the cutting inserts 6.In this way the stability of the package 1 is guaranteed since the support 20 easily adapts to any different height of the package 1 and furthermore the contact of the leadframe 10 with the elements 9 of the cutting inserts 6 is always ensured during the cutting operation of the dambar 5. However before the cutting operation of the dambar 5 but after the package 1 has been correctly positioned by the support 20, the same package 1 must be blocked in order to prevent any oscillations during the cutting operation of the dambar. Figure 6 shows a first locking device 30 of the package 1 according to the present invention. The locking device 30 comprises bodies 31 connected at the bottom to the guides 4 and provided with inclined lower surfaces 32 to horizontally force movable bodies 33, slidably connected to the cutting inserts 6, against the support block 12 so as to lock it during the cutting operation of the dambar 5. The bodies 31 can also be spring-loaded in a manner not visible in the figure. A second locking device 40 according to a variant of the present invention is described in Figure 7. The locking device 40 comprises a movable body 41 slidably connected to a cutting insert 6 and provided with an inclined surface 42, capable of penetrating into a cavity 43 of the support block 12 which has a shape suitable for receiving the block 41. The penetration of the movable body 41 into the cavity 42 is ensured by a compression mechanism which may consist of a spring. However, the compression force of this mechanism must be less than the compression force given by the difference in the forces associated with the springs k1 and k2. Furthermore, the angle α that the inclined surface forms with a horizontal axis must be suitably chosen so as to prevent the body 41 from sliding during the cutting operation of the dambar 5. The angle α may depend, for example, on the roughness of the surfaces. The apparatus described above lends itself to a different method of operation of cutting a dambar. A method for cutting a dambar 5 of a leadframe 10 of a package 1 of an integrated circuit which includes, before the cutting operation step of the dambar 5, a first and a second step. The first phase involves positioning said leadframe 10 so as to be in contact with cutting inserts 6 by means of a support device 20 of said package 1. The support device 20 comprises a first 11 and a second 12 support means between which said package 1 is interposed with said first 11 and second 12 support means compressed by vertical thrust mechanisms, for example springs k1 and k2. The second phase involves locking said support device 20 by means of appropriate locking means 30, 40 consisting of either at least a first horizontally movable body 33 which is forced against said second support means 12 or at least a second horizontally movable body 41, suitably shaped, which is forced into a shaped cavity 42 of said second support means 12. The penetration of the body 41 into the cavity 42 is ensured by a compression mechanism which may consist of a spring. However, the compression force of this mechanism must be less than the compression force given by the difference in the forces associated with the springs k1 and k2. Furthermore, the body 41 must not slide inside the cavity 42 during the cutting operation of the dambar 5.

Claims

CLAIMS 1. Apparatus for cutting a dambar (5) of a leadframe (10) of a package (1) of an integrated circuit comprising pressure means (3) for compressing said dambar (5) into cutting inserts (6), characterized in that it comprises a support device (20) of said package (1) comprising a first (11) and a second (12) support means between which said package (1) is interposed, being said first (11) and second (12) support means compressed by vertical thrust mechanisms (kl, k2) so as to allow said leadframe (10) of said package (1) to always be in contact with said cutting inserts (6), and comprising locking means (30; 40) of said support device (20) in compressed position.

2. Apparatus according to claim 1, characterized in that said thrust mechanisms (kl, k2) consist of springs.

3. Apparatus according to claim 1, characterized in that said locking means (30) comprise at least one horizontally movable body (33) which is forced against said second support means (12) before the cutting operation of said dambar ( 5).

4. Apparatus according to claim 1, characterized in that said locking means (40) comprise at least one horizontally movable shaped body (41) which is forced into a shaped cavity (43) of said second support means (12) before the operation of cutting said dambar (5).

5. Apparatus according to claim 4, characterized in that said at least one shaped body (41) must be housed in said cavity (42) in a manner not sliding.

6. Apparatus according to claim 4, characterized in that said shaped body (42) is forced into said cavity (42) by means of a mechanism whose compression force must be less than the difference in the compression forces of the thrust mechanisms (kl, k2) associated respectively with said first (11) and second (12) support means 7. Method for cutting a dambar (5) of a leadframe (10) of a package (1) of an integrated circuit, characterized by providing a first step of positioning said leadframe (10) in contact with cutting inserts (6) by means of a support device (20) of said package (1), said support device (20) comprising a first (11) and a second ( 12) support means between which said package (1) is interposed, said first (11) and second (12) support means compressed by vertical thrust mechanisms (kl, k2), and a second locking step of said device support in compressed position by means of suitable locking means (30, 40).

8. Method according to claim 7, characterized in that said thrust mechanisms (kl, k2) consist of springs. Method according to claim 7, characterized in that said locking means (30) comprise at least one horizontally movable body (33) which is forced against said second support means (12). Method according to claim 7, characterized in that said locking means (40) comprise at least one horizontally movable shaped body (41) which is forced into a shaped cavity (42) of said * 1 second support means (12).

11. Method according to claim 10, characterized in that said at least one shaped body (41) must be housed in said cavity (42) in a non-sliding way. Method according to claim 10, characterized in that said shaped body (42) is forced into said cavity (42) by means of a mechanism whose compression force must be less than the difference in the compression forces of the thrust mechanisms (kl, k2) associated respectively with said first (11) and second (12) support means. ittler