Wireworking – Crimping
Patent
1995-09-07
1998-02-10
Larson, Lowell A.
Wireworking
Crimping
B21F 4500
Patent
active
057158720
DESCRIPTION:
BRIEF SUMMARY
The invention concerns method and apparatus for forming lead-outs of integrated circuits.
Integrated circuits (ICs) are mainly constructed on support strips and are injection molded with a plastic casing. The structures of the leads are formed, by etching or punching, on the support strip which consists of a metal band. The leads are arranged in a common plane at the sides of the casing. In order to solder the integrated circuits onto a circuit support board, the leads, initially in a level position, must be bent into a suitable shape. At that point the casings are still connected via bridges at their corners to the support strip. The greater the number of leads on the integrated circuit and the closer these leads are arranged to each other, the greater are also the precision requirements during the bending process, since even very small deviations from the required bending angles and lopsided positions of the leads will result in faulty contacts on the circuit support board. The bending tools for the leads are therefore precision tools. Modern highly integrated circuits having far more than one hundred leads require a very high precision of the bending tools.
The leads are mostly bent into Z-shapes having two approximately right angles. In order to obtain this, the leads are usually clamped, close to the casing, against a bending matrix and are initially bent downwards in a sloping manner at an angle of approximately 45 degrees by means of a bending die, against the complementary bending surface of the matrix. The integrated circuits, still connected to the lead frame, are then guided to an adjacent swage where the leads are bent between a bending matrix and slanting bending dies into their final position. In order to obtain this, the bending matrix has a form accommodating the desired Z-shape of the leads; an upper die, its tip positioned towards the apex of the bending matrix form, pushes from above in a slanting manner into the bending matrix form, thereby pushing the leads into the indentation of the matrix' bending form. It is inevitable that during this process a relatively high surface compression between the leads and the bending tool as well as friction resulting from the relative movement between the leads and the tool results in a rubbing-off of tin, which at this point is already coating the leads prior to the subsequent soldering process. The rubbed-off tin is deposited on the tool, with the result that the tool, costing more than DM 100,000.00 has to be changed and cleaned already after a relatively short time, i.e. after a few thousand strokes of the tool. At a working speed of two strokes per second, 1000 strokes take only 8 minutes, so that several operators are constantly required for each machine in order to clean the tool, as well as several sets of tools. This results not only in high personnel and machinery costs, but also in relatively long standstill periods due to the frequent changes of tools; therefore resulting in a considerably more expensive manufacture of chips, quite apart from the fact that each change of tools may lead to damage of the integrated circuits or of the tool itself, due to possible faulty adjustment during assembly. If greater tin deposits on the bending tool are tolerated so as to avoid a too frequent change of tools, the precision of the bending process will be affected with the result that not all the bent ends of the leads are positioned in a common plane, which is absolutely necessary for soldering them onto a circuit support board. Furthermore, in the case of the already-known bending devices, it is possible that during the bending process itself individual leads, groups of leads or even all the leads may be bent in a way not vertical to the original common plane of the leads, but slanting towards it, especially when the leads, formed by etching, have a profile deviating from the usual rectangular shape. This results in a faulty position of the bent ends of the leads, especially an inadequate coplanarity as well. It is not possible to compensate for this
REFERENCES:
patent: 4977442 (1990-12-01), Suzuki et al.
patent: 5094982 (1992-03-01), Suzuki et al.
patent: 5158121 (1992-10-01), Ishii
patent: 5283946 (1994-02-01), Simmons et al.
IBM Technical Disclosure Bulletin, vol.28 No. 7, Dec. 1985, "Integrated Circuit Lead-Forming Mechanism".
Larson Lowell A.
Micro)n Technology, Inc.
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