WO1998009322A1

WO1998009322A1 - Method and device for forming a lead frame

Info

Publication number: WO1998009322A1
Application number: PCT/NL1997/000496
Authority: WO
Inventors: Adrianus Wilhelmus Van Dalen
Original assignee: Fico B.V.
Priority date: 1996-08-29
Filing date: 1997-08-29
Publication date: 1998-03-05
Also published as: AU4138497A; NL1003916C2

Abstract

The principle of the method and device focuses on engaging a lead (5) with engaging means (10) and subsequently displacing these engaging means (10) so that the lead (5) is bent without the engaging member displacing relative to the lead. The surface of the lead (5), which is usually provided with a costly and sensitive metal film, is thus prevented from being damaged as a result of a mutual movement of lead and engaging member (10).

Description

METHOD AND DEVICE FOR FORMING A LEAD FRAME

The invention relates to a method and device for bending at least one lead of a lead frame for supporting an electronic component . The lead and the lead frame are also known under the respective names "lead and "lead frame". Such lead frames are much used in semiconductor technology for containing one or more chips wherein the leads take the form of legs for accommodating a lead frame with a chip attached thereto in a larger unit in simple manner. The present methods and devices for bending the leads generally make use of mould-like constructions with which the leads are urged into the correct shape. A drawback hereof is that the surface of the leads can be damaged. Other devices for bending leads are shown in the Japanese patents JP 06252309 and JP 08051175 in which a bending die and a counter-die engage on either side of a lead for bending, both of which are mounted rotatably in a bending device such that on linear displacement thereof die and counter-die rotate. Due to rotation of the die and the counter-die the distance from the point of engagement on the lead to a central part of the lead frame will remain more or less constant. The rotation of die and counter-die is obtained in that the lead exerts a relatively great tensile force on both bending members. Here also there is the danger of the lead being damaged. The present invention has for its object to provide a method and device for bending the leads of a lead frame such that the risk of damage to the leads is further limited. The present invention provides for this purpose a method comprising the following steps of: a. fixing a central part of the lead frame, b. engaging at least one lead for bending, and c. displacing at least one point of engagement of the lead in a manner such that the distance from the point of engagement to the central part of the lead frame remains substantially constant, characterized in that a linear displacement of the point of engagement on the lead while making use of at least one lever results simultaneously in a displacement of the point of engagement on the lead in a direction other than the linear direction. Thus occurs a composite movement of the lead without a rela- tively great tensile force being exerted on the lead.

Thus moving the engaging position results in there being very little danger of damage to the lead.

Through displacement of the point of engagement a part of the lead is preferably urged against a shaping part, which shaping part makes the same movement as the point of engagement. By making use of the shaping part the lead can acquire a more complex final form without a friction force having to be exerted on the lead for this purpose . In another preferred application of the method the fixed part of the lead frame covers a linear path during bending, which linear path encloses an angle with the linear path covered simultaneously by the point of engagement. Instead of the above mentioned curved path through which the lead proceeds, it is also possible to combine two linear movements whereby the relative movement of the lead in relation to the central part is still a curved path. It should be noted here that this can only be realized when one lead, or a plurality of leads situ- ated on the same side of the central part, are bent simultaneously. When however, as occurs frequently in practice, leads have to be bent simultaneously on two sides of the central part, this method is not a feasible option. In this latter case it will be necessary to fall back on the curved path through which the points of engagement of the lead must proceed during bending. The invention also includes a device for bending at least one lead of a lead frame for supporting an electronic component, comprising:

- a frame, - fixation means movable round the frame for fixing a central part of the lead frame,

- an engaging member mounted rotatably in the frame which can be placed in contact with the lead on at least one side, and - drive means for linear displacement of the engaging member relative to the fixation means, characterized in that the rotation shaft of the engaging member with the frame is placed such that a straight line through the rotation shaft and parallel to the direction of linear displacement of the engaging member is located at a distance from the engaging position of the engaging member on the lead.

The distance between the rotation shaft and the engaging position of the engaging member perpendicularly of the direction of linear displacement of the engaging member forms the lever whereby a deformation of the engaging member can be realized with a minimum of tensile forces to be exerted by the lead. This is the case because the described distance forms a lever whereby the force exerted on the lead is reduced. The risk of damage to tti --engaging member is thus reduced considerably.

The engaging member can be embodied such that it engages the lead on one side. It is however also possible to embody an engaging member with at least two parts displaceable relative to each other between which the lead can be clamped. This latter variant has the advantage that the control of the movement of the lead during the bending operation is greater than when the lead is engaged on only one side. Two co-acting engaging members can each be separately mounted for rotation in the frame but it is also possible to place them both on a joint sub-frame. In the latter case the rotation shaft of the sub-frame with the frame is the shaft in relation to which the lever is created.

In the preferred embodiment the engaging member comprises in addition to a contact surface a material part located in the vicinity thereof, with which material part the lead comes into contact during bending such that the lead shapes itself at least partially to the external form of the material part. In this way the material part forms the shaping part with which a relatively complex final form of a bent lead can be obtained. Assembly of engaging member with shaping part directly ensures that the shaping part also does not exert any friction force on the lead during bending without a complex control of a movement of the shaping part being required, this move- ment being in any case taken over from the engaging member with which the shaping part is assembled.

An advantageous embodiment of the bending device is described in claim 8. An example of this preferred embodiment is shown in the annexed figures. The present invention will be further elucidated with reference to the non-limitative embodiment shown in the annexed figures. Herein: figure 1 shows a cross-section through a bending device with not yet bent lead frame, figure 2 shows a cross-section through the bending device of figure 1 with bent lead frame, figure 3 shows a cross-section through fixation means, engaging means and lead frame as shown in figures

1 and 2 for performing the bending operation, figure 4 shows a cross-section through the elements shown in figure 3 during the bending operation, and figure 5 shows a cross-section through the elements as shown in figures 3 and 4 after completion of the bending operation. Figure 1 shows a bending device 1 in which a lead frame 5 is clamped between an upper fixation column part

2 and a lower fixation column part 3. The fixation column parts 2, 3 are provided with operating means which are not shown in this figure but with which they can be placed at a greater mutual distance so that a lead frame can be placed between fixation column parts 2, 3 or removed after the bending operation. Arranged in the upper fixation column part 2 is a spring 4, the function of which will be shown hereinbelow.

Lead frame 5 is provided with leads 6 situated on two sides of a thickened central part 7 of lead frame 5. Only the central part 7 of lead frame 5 is clamped by fixation column parts 2, 3.

The upper fixation column part 2 is mounted in an upper block 8 and the lower fixation column 3 is mounted on a lower block 9. Both these blocks 8, 9 are preferably provided with the drive means with which fixation column parts 2, 3 can be placed at a greater mutual distance for displacement and removal of lead frame 5. Upper and lower block 8, 9 can be moved still further toward each other after a lead frame 5 is received between fixation column parts 2, 3, as shown in figure 2, without this affecting the fixation column parts 2, 3. Arranged for this purpose is the spring 4 with which the upper fixation column part 2 supports on upper block 8. When upper block 8 is moved further downward the spring 4 will be compressed, which does not influence or hardly influences the clamping of central part 7 of lead frame 5.

Two engaging members 10 are accommodated in upper block 8, which engaging members 10 are mounted pivotally on rotation shafts 11 which are fixed rigidly to upper block 8. Engaging members 10 also support against pins 12 such that the contact surfaces 13 located on the underside of engaging members 10 lie substantially in line with the underside of the upper fixation column part 2. Contact surfaces 13 of engaging members 10 hereby engage on the leads 6 of the non-bent lead frame 5. Pins 12 are held in positions supporting the engaging members 10 by a membrane actuator 14. Rotation of the levers 10 can be controlled by means of the pins 12. A fluid pressure as according to arrow Fl is exerted for this purpose on a membrane 15 to which the pins 12 are rigidly coupled.

The rotation shafts 11 of engaging members 10 are placed to the outside relative to the centre of the device 1 such that there is a considerable distance in horizontal direction to the leads 6, in any case to the position where the contact surfaces 13 of engaging members 10 engage on leads 6. Engaging members 10 thus form levers whereby the forces exerted in horizontal direction on leads 6 can remain limited.

Two engaging members 16 are also accommodated in the lower block 9, both provided with a contact surface 17 for engaging the leads 6 of the non-bent lead frame 5. Engaging members 16 are supported by a membrane actuator 18. A medium pressure F2 is exerted for this purpose on a membrane 19 whereby an upward directed force is exerted on engaging members 16. The latter are both provided with a curved surface 20, both of which surfaces support on internal flat sides 21 of lower block 9. The force re- suiting from engaging members 16 supporting on lower block 9 ensures outward movement of the upper parts, i.e. the contact surfaces 17, of engaging members 16. The contact surfaces 13 of engaging members 10 and contact surfaces 17 of engaging members 16 are herein located such that they engage substantially at corresponding posirt--i ns on opposing sides of the leads 6 of lead frame 5.

Figure 2 shows the bending device 1 in a situation where leads 6 of lead frame 5 are bent. The position of lower fixation column part 3 is unaltered relative to the situation shown in figure 1. The position of upper fixation column part 2 is also unchanged but spring 4 is more compressed than before bending of the leads 6. This compression of spring 4 is realized by moving upper block 8 downward. By moving upper block 8 downward the pivot shafts 11 are also moved downward. During the downward movement of upper block 8 the pins 12 are moved a limited distance upward. This upward movement of pins 12 is realized due to escape of medium from the membrane actuator 14 as according to arrow PI. Further arranged in membrane actuator 14 are springs 22 which, when the medium pressure falls away or decreases, will cause pins 21 to move in upward direction.

Due to the combined downward movement of rotation shafts 11 and the upward movement of support pins 12 the engaging members 10 will pass through a complex movement whereby the contact surfaces 13 of engaging members 10 will cover a downward and inward directed path.

The contact surfaces 17 of engaging members 16 accommodated in lower block 9 will also cover a nonlinear path. This movement is realized by reducing the medium pressure on the membrane 19 of membrane actuator 18 by allowing medium to escape from actuator 18 as according to arrow P2. Membrane 19 will consequently move downward and a support construction 23 connected rigidly to membrane 19 will therefore likewise move downward. Engaging members 16 are pivotally connected to support construction 23 with interposing of pivot shafts 24. Due to the downward directed movement of support construction 23, and thus also of pivot shafts 24, the engaging members 16 will also be moved downward. The curved surface portions 20 of engaging members 16 are thereby released from the flat sides 21 of lower block 9. The downward movement of engaging members 16 likewise results in the contact surfaces 17 of engaging members 16 running through a movement directed toward the fixation column part 3. The working applied by the bending device 1 as shown in figures 1 and 2 is shown in more detail in figures 3- 5. Figure 3 herein shows the situation in which engaging members 10, 16 engage the leads 6 by means of contact surfaces 13, 17 prior to the leads being bent. The fixa- tion column parts 2, 3 engage on the central part 7 of lead frame 5.

Figure 4 shows an intermediate position in which leads 6 are partially bent. Contact surfaces 3, 17 of engaging members 10, 16 are herein moved downward through a limited distance but are also moved toward the lower fixation column part 3.

Finally, figure 5 shows the situation wherein leads 6 are fully bent. For this purpose the contact surfaces 13, 17 are moved even further downward and likewise even further toward the lower fixation column part 3. Also shown is that a side wall part 25 of lever 10 also determines the final form of the bent lead 6.

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Claims

1. Method for bending at least one lead of a lead frame for supporting an electronic component by the following steps of: a. fixing a central part of the lead frame, b. engaging at least one lead for bending, and c. displacing at least one point of engagement of the lead in a manner such that the distance from the point of engagement to the central part of the lead frame remains substantially constant, characterized in that a linear displacement of the point of engagement on the lead while making use of at least one lever results simultaneously in a displacement of the point of engagement on the lead in a direction other than the linear direction.

2. Method as claimed in claim 1, wherein by displac- ing the point of engagement a part of the lead is urged against a shaping part, which shaping part makes the same movement as the point of engagement .

3. Method as claimed in claim 1 or 2 , wherein the point of engagement covers a non- linear path during bending of the lead.

4. Method as claimed in claim 1 or 2 , wherein the fixed part of the lead frame covers a linear path during bending, which path encloses an angle with the linear path covered simultaneously by the point of engagement .

5. Device for bending at least one lead of a lead frame for supporting an electronic component, comprising:

- a frame,

- fixation means movable round the frame for fixing a central part of the lead frame, - an engaging member which is mounted rotatably in the frame and which can be placed in contact with the lead on at least one side, and

- drive means for linear displacement of the engaging member relative to the fixation means, characterized in that the rotation shaft of the engaging member with the frame is placed such that a straight line through the rotation shaft and parallel to the direction of linear displacement of the engaging member is located at a distance from the engaging position of the engaging member on the lead.

6. Bending device as claimed in claim 5, wherein the engaging member consists of at least two parts dis- placeable relative to each other for clamping a lead between the parts.

7. Bending device as claimed in claim 5 or 6 , wherein the engaging member comprises in addition to a contact surface a material part located in the vicinity thereof, with which material part the lead comes into contact during bending such that the lead shapes itself at least partially to the external form of the material part.

8. Bending device as claimed in any of the claims 5- 7, wherein the engaging means are formed by two levers, both provided with a contact surface, which surfaces are located mutually opposite for engaging the flat side of a lead, wherein: a first lever is supported pivotally at a first position by a pivot point and is supported at a second position by a displaceable stop, whereby, while applying a pressure force on the contact surface, the rotation position of the—iev-er is determined subject to the position of the adjustable stop, a second lever is supported pivotally at a first position by a pivot point and provided at a second position with a curved surface part, whereby a rotational force is exerted on the lever when the second lever is supported by the curved surface, and the drive means are formed by a press construction whereby first and second lever are linearly displaceable relative to each other, in addition to a linear drive for displacing the displaceable stop of the first lever and a linear drive for displacing the pivot point of the second lever.