JPH0697635B2 - Partial annealing device for lead frame - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for partially annealing only a stage and inner leads around the stage after pressing a lead frame used for a semiconductor device.

[Conventional technology]

Residual stress staying in a lead frame used for a semiconductor device generally occurs during the next processing history.

i) A process of rolling a metal steel slab into a wide strip of a thin metal plate through hot, cold rolling and heat treatment processing steps. In this process, different residual stresses are formed at the center and both ends of the slab in the width direction.

ii) A process of slitting a wide strip of a thin metal plate into a strip having a required width of a lead frame.

iii) A press working process in which unnecessary portions of the strip material are sequentially removed, and a tie bar that connects and holds the leading end portions of the inner leads is left to form the element mounting stage and the lead frame such as the inner leads and the outer leads into a desired shape.

The lead frame formed by the above process is further assembled in a semiconductor device in a subsequent line. The procedure is to mount an element on the stage of the lead frame, connect the bonding pad of this element and the external lead to each other with a fine wire of a noble metal to form an electrical conduction circuit, and seal them with resin. However, the residual stress generated in the lead frame is released by the heating in the intermediate process until the semiconductor device is assembled. For this reason, deformation such as ups and downs of the leads and deviation of the leads occur at the tip of the inner leads, resulting in defective wire bonding, which is a factor of lowering the yield of semiconductor devices and lacking long-term reliability.

Conventionally, in order to prevent such a problem, the residual stress of the lead frame is removed by using a heat treatment device that indirectly or directly heats the entire strip-shaped or continuous lead frame formed by pressing. It is common practice to apply a treatment.

As the former heat treatment apparatus, a bright annealing apparatus, a vacuum annealing apparatus or the like, which continuously supplies the entire lead frame to a heating atmosphere for preventing oxidation and indirectly heats it, is generally used. In the latter case, there is a direct heating type induction annealing device which directly converts electric energy into heat energy in a metal by utilizing an electromagnetic induction phenomenon.

[Problems to be Solved by the Invention]

However, in the former device, since the heating time is long and the entire device is long in order to secure the heating amount, there is an obstacle in equipment. Further, the adjustment of the heating atmosphere and the temperature control are complicated, and further, in the processing of the strip-shaped lead frame material, a manual alignment process for aligning them in the tray and then carrying them into the heating atmosphere is required. For this reason, there is a problem in terms of cost due to a reduction in work efficiency and the layout and synchronization of the device are also limited, which has been an obstacle to automation.

On the other hand, in the latter device, since the lead frame is continuously conveyed in a narrow heating coil, there is a drawback that vibration causes it to come into contact with the heating coil and damage the lead frame surface such as scratches and lead bending. It was

In addition, since the heat treatment apparatus for indirectly or directly heating heats the entire lead frame, the outer frame of the lead frame, the outer leads, and the dam bar that connects and holds the outer frames are softened. Therefore, there is also a problem that the pitch of the positioning pilot holes provided in the outer frame changes due to the function deterioration of the base material and the deformation due to extension, contraction and the like.

Further, in recent years, the tip portions of the inner leads have become finer due to the diversification of functions of semiconductor devices using a lead frame and the tendency toward more pins. For this reason, the lead width and its interval are further narrowed, and even minute deformation of the inner leads cannot be tolerated, and there has been a demand for a highly accurate partial heat treatment apparatus.

An object of the present invention is to remove a residual stress caused by a processing history only in a necessary area, and to anneal a lead frame that maintains the functions of the lead frame base material and the initial functions such as a positioning reference hole and a pitch accuracy between them. To be able to do it.

[Means for Solving the Problems]

The present invention prevents the oxidation of a lead frame having a residual stress inside due to the processing history such as punching, coining, pressing when a metal strip is pressed into a desired shape of the lead frame. An annealing apparatus for performing heat treatment in an atmosphere to remove the residual stress, comprising a high-frequency heating body for partially heating a lead frame, and a non-heating portion of the lead frame provided around the high-frequency heating body during heating. A mask plate that covers the lead frame and an intermittent transfer mechanism that feeds the lead frame to the high frequency heating body and the mask plate in a non-contact state is provided, and the high frequency heating body is provided in a portion including the inner lead and / or the stage of the lead frame. The feature is that they correspond.

[Action]

Since the partial annealing apparatus of the present invention is configured as described above, the lead frame formed in the strip shape or the continuous strip shape is lifted between the pair of mask plates which can be opened and closed and conveyed by a required size. Therefore, the lead frame can be transported to a predetermined position without contacting the heating body.

Since the non-heated area such as the outer frame of the lead frame and the dam bar for connecting and holding the outer leads is masked to prevent heating, the function of the base material of that portion is maintained and the positioning is performed by equipping the outer frame. Deformation due to extension or contraction of the reference hole pitch is prevented to maintain the initially set reference hole pitch.

Furthermore, since the mechanical strength of the outer frame portion of the lead frame is maintained, there is no deformation due to the tensile force during transportation, and the feed dimension is stable.

Since the non-heated area is masked and a high frequency is applied to the area corresponding to the inner lead and / or the semiconductor element mounting stage to heat the area, the inner lead portion expands and contracts toward the semiconductor element mounting stage. Therefore, there is no influence of other regions, and a stable product can be obtained in which complicated deformation does not occur and the tip of the lead is not offset.

〔Example〕

FIG. 1 is a partially cutaway front view of the partial annealing apparatus of the present invention, FIG.
The figure is a view seen in the pass line direction of the lead frame.

In the figure, a base 1 is fixed to a base 1a arranged in a casing (not shown) that covers the entire annealing apparatus, and a lead frame pass line for annealing is provided above the base 1. . Guide bushes 2a are provided at the four corners of the base 1, and the guide pins 2 are vertically movably inserted therein. An auxiliary plate 3 is connected to the lower ends of these guide pins 2, and a top plate 4 is connected to the upper ends thereof. An elevating cylinder 5 is connected to the lower surface of the auxiliary plate 3, and by its operation, the auxiliary plate 3 and the top plate 4 integrated with the guide plate 2 are moved up and down in a direction orthogonal to the pass line.

A backup liner 6 is fixed on the upper surface of the base 1,
Furthermore, a holder plate 7 is detachably arranged on the lead frame entry side. This holder plate 7
Can be put in and taken out from the backup liner 6 in a direction orthogonal to the pass line of the lead frame in FIG. 2, and is fixed by a lock 7a provided on the end face. A second lower mask plate 8 is provided on the upper surface of the holder plate 7.
As shown in the figure, two rows are arranged in the pass line line direction. Then, four high-frequency induction heating bodies 9 are incorporated in the lower mask plate 8 in the pass line direction.

As shown in FIG. 3, the lower mask plate 8 is formed by embedding and fixing high frequency induction heating bodies 9 at an equal pitch. When the lead frame is placed, only the stage and the inner lead portions face the high frequency induction heating bodies 9. The other part is configured to cover the lower mask plate 8. In addition,
The high frequency induction heating body 9 comprises a dust core 9a and a high frequency heating coil 9b surrounding the dust core 9a.

Further, a lower cooling plate 10 for gradually cooling the lead frame after induction heating is fixed to the upper surface of the holder plate 7 on the output side of the lead frame. The lower cooling plate 10 can be made of ceramic or the like as a suitable material.

On the other hand, an upper holder 11 is incorporated on the lower surface of the top plate 4 so as to be freely inserted and removed in a direction orthogonal to the pass line.
The upper holder 11 is also fixed by the lock 11a as in the case of the holder plate 7. Then, two rows of upper mask plates 12 are arranged at positions corresponding to the lower mask plate 8, and an upper cooling plate 13 is provided directly above the lower cooling plate 10. These top mask plates 12
And the upper cooling plate 13 are springs 12a and 13a, respectively.
It is elastically supported by.

The lead frame 50 is supplied to the line as a strip having four patterns as shown in FIG. In order to supply the lead frame 50, as shown in FIG. 2, four transfer blocks 14 are provided on the base 1 with the pass line interposed therebetween.
Are arranged. These transfer blocks 14 are guided by rails 1b provided on the base 1 and intermittently reciprocate by a drive cylinder 15 that expands and contracts the rod in the pass line direction. Further, the transfer block 14 is provided with an elevating cylinder 14a in the vertical direction, and the transfer frame 16 is fixed to the rod 14b thereof.

FIG. 4A is a schematic plan view of the transport mechanism, and FIG. 4B is a side view of a main part.

As shown in the figure, the transport frame 16 occupies almost the entire width of the pass line, and four guide rods 16a are bridged across the pass line. These guide rods 16a include four gripper holders 16b, 16c, 16 in the pass line direction.
d and 16e are installed so as to be movable in the width direction. The gripper holders 16b, 16c are for the lead frame 50 running on the right side in FIG. 2, and the other pair of gripper holders 16d, 16c.
e is for the lead frame 50 running on the left side. A rack unit 16f forming a rack is integrated at both ends of each gripper holder 16b to 16e. The rack units 16f of the gripper holders 16b and 16d are slidably attached to the common guide rod 16a, and the other gripper holders 16c and 16e are slidably attached to the guide rods 16a of other sets. Further, each rack unit 16f meshes with a pinion 16h provided on the output shaft of the motor 16g. A gripper 17 is attached to each of the gripper holders 16b to 16e.

In such a transport mechanism, when the motor 16g is driven, the gripper holders 16b, 16c on the right side and the gripper holders 16d, 16e on the left side of the pass line perform an operation of simultaneously expanding or contracting the respective intervals. In the illustrated case, the gap is the smallest, and at this time, the gripper 17 holds the edge of the lead frame 50 in the width direction and can be conveyed. And
When widening the space, the lead frame 50 is released, and the upper mask plate 12 and the upper cooling plate are released.
13 gripper holders 16b to 16e so as not to interfere with the descending of 13
Will evacuate.

FIG. 5 is a schematic diagram for explaining the behavior of the gripper 17 with respect to the left lead frame 50 in FIG. The gripper holders 16b and 16c are moved up and down by the operation of the elevating cylinder 14a as indicated by the vertical arrow in the figure. Also the motor
By the operation of 16g, the holder blocks 16b and 16c can also be opened and closed toward the left and right edges of the lead frame 50, as shown by the horizontal arrows in the figure. When holding the lead frame 50 by the gripper 17, first, the holder blocks 16b and 16c are lowered so that the level of the gripper 17 matches the lead frame 50. After this, the holder blocks 16b, 16
The c is positioned close to the lead frame 50 side and is held by the gripper 17.

The lead frame 50 held by the operation of the gripper 17 is fed by the drive cylinder 15. This feeding is performed by the lower mask plate 8 in FIG.
It is assumed that the lead frame 50 immediately above is conveyed to the lower and upper cooling plates 10 and 13 by intermittent feeding. Further, the transfer arm 16 has a length sufficient to project from the entrance side, and is prepared for carrying in the lead frame 50 from the upstream side. Then, feed rollers 18 and 19 are arranged on the carry-in side and the processed carry-out side of the lead frame 50, respectively, and are connected to an external line to automatically supply the lead frame 50 intermittently.

Here, as shown in FIG. 6, the lead frame 50 has four
It is supplied as having one pattern, and each pattern is positioned so as to correspond to the four high-frequency induction heating bodies 9. FIG. 7 is a plan view showing one pattern formed on the lead frame 50 by press working. In this pattern, a stage 51 for mounting a semiconductor element is provided in the center, an inner lead 52 is formed around the stage 51, and a dam bar 53 is formed.
The outer lead 54 is provided with the boundary as a boundary. Then, reference pin holes 55 used for positioning such as annealing and plating are formed at both ends on the outside of the outer lead 54 at a constant pitch.

The annealing region for the lead frame 50 is the portion surrounded by the broken line in FIG. That is, it is the range along the tip portions of the stage 51 and the inner leads 52 or along the dam bar 53, and the outside thereof is not annealed. Due to such annealing, the high frequency induction heating body 9 is set so as to have the same shape as the shape surrounded by the broken line, and the lower mask plate 8 has a shape capable of covering the entire periphery thereof. FIG. 8 is a sectional view showing the outline of the lead frame 50 during annealing as viewed in the pass line direction, and FIG. 8 (a) corresponds to the apparatus of FIG. As shown in the figure, the lower mask plate 8 and the high frequency induction heating body 9 are in close contact with the lower surface of the lead frame 50, and the upper mask plate 12 is in close contact with the upper surface thereof. Further, as shown in FIG. 7B, the high frequency induction heating element 9 may be incorporated in the upper mask plate 12 to heat from both sides. In such an arrangement, the high-frequency induction heating body 9 is positioned with respect to the lead frame 50 so as to heat the annealing region surrounded by the broken line in FIG.

In the above structure, the lead frame 50 intermittently supplied from the feed roller 18 is held by the gripper 17 lowered by the elevating cylinder 14a and then lifted to a position slightly higher than the level of the lower mask plate 8. After that, the drive cylinder 15 applies intermittent feed to the transfer block 14, and as shown in FIG.
Moves right above the lower mask plate 8. At the same time, the previously heated lead frame 50a is held by the gripper 17 and conveyed to directly above the lower cooling plate 10.

After the transport block 14 is stopped, the transport frame 16 is lowered by the elevating cylinder 14a to move the lead frame 50 onto the lower mask plate 8 and the leading lead frame 50.
Place a on top of lower cooling plate 10. After that, while releasing the restraint of the lead frames 50, 50a by the gripper 17,
A motor 16g is provided to widen the space between the holder blocks 16b to 16e so as not to interfere with the lowering of the upper mask plate 12 and the upper cooling plate 13. Next, the lifting cylinder 5
The top plate 4 is lowered from the state shown in FIG. 1 by superposing the upper mask plate 12 on the lower mask plate 8 and the upper cooling plate 13 on the lower cooling plate 10, respectively.

As described in FIG. 8A, the lead frame 50 is sandwiched between the high-frequency induction heating body 9 and the lower mask plate 8 at the same time as being covered with the lower mask plate 8 and the upper mask plate 12. Then, only the region surrounded by the broken line in FIG. 7 is induction-heated by the high-frequency induction heating body 9, and the other regions are suppressed from being heated by the lower mask plate 8. Therefore, partial heating of the lead frame 50 is performed by the high frequency induction heating body 9. On the other hand, the leading lead frame 50a is sandwiched between the lower and upper cooling plates 10 and 13 to be gradually cooled, and subjected to heat treatment and annealing by slow cooling.

After a certain period of time, the top plate 4 is lifted by the lifting cylinder 5 to open the upper surfaces of the lead frame 50 and the lead frame 50a. Then, the gripper holders 16b to 16e which have been widened are returned to the state of FIG. 4 (a), the processed lead frame 50 and the preceding lead frame 50a are held by the gripper 17, and the feed is given again by the drive cylinder 15. . By this feed, the lead frame 50a is discharged to the feed roller 19 side, the lead frame 50 reaches the lower cooling plate 10, and the subsequent lead frame 50b reaches the lower mask plate 8. After that, the lead frame is intermittently applied according to the above procedure.
Annealing treatment is performed in order of heating and slow cooling of 50.

Since the pattern of the lead frame 50 changes variously depending on the specifications, the annealing region within the broken line area shown in FIG. 7 also changes. Therefore, it is necessary to change the size and arrangement pitch of the high-frequency induction heating body 9 and the shapes of the upper and lower mask plates 8 and 12 and the upper and lower cooling plates 10 and 13. On the other hand, the holder plate 7 and the upper holder 11
Are backup liner 6 and top plate 4 respectively
Since it is removable, it is possible to handle it without any problems by preparing a mask plate and cooling plate that match the pattern of the lead frame 50.

9 and 10 show an example of an apparatus installed in a system for feeding a lead frame as a strip-shaped material. The same members described in the above embodiment are designated by common reference numerals, and detailed description thereof will be omitted.

The strip-shaped material 50c of the lead frame is formed by continuously forming patterns as shown in FIG. 12, and this is directly flown to the processing line and sequentially processed. Such a strip 50c
In order to convey the sheet, bridle rolls 20a and 20b are arranged on the entrance side and the exit side of the pass line of the apparatus, and a conveyor roll 20c for intermittent feeding is provided on the exit side. The intermittent feed stroke corresponds to the length of the four patterns because four high frequency induction heating elements 9 are arranged as shown in FIG. Then, the position detection sensor 21 is provided for positioning the strip member 50c with respect to the intermittent feed due to this stroke, and the pilot pin fitted into the reference pin hole 55.
Install 22.

Further, guide lifters 23 for transporting the belt-shaped material 50c in a state of being floated from the lower mask plate 8 and the like are arranged on the lower mask plate 8 and the lower cooling plate 10 at a constant pitch. Figure 11 shows the lower mask plate 8
3 is a detailed view of the guide lifter 23 provided in FIG. 1, in which the lower mask plate 8 is provided with a chamber 8a in which the guide lifter 23 can be retracted. A groove 23a is provided at the upper end of the guide lifter 23 so that the edge portion of the strip member 50c can be inserted and held therein, and a flange 23b is provided at the lower end so as not to be pulled out from the chamber 8a. In addition, a coil spring that biases the guide lifter 23 upward is provided in the chamber 8a.
It incorporates 8b. On the other hand, the lower surface of the upper mask plate 12 has a strip-shaped material when it covers the lower mask plate 8.
A recess 12b for escape is provided so as to tightly sandwich 50c. The lower cooling plate 10 and the upper cooling plate
A similar chamber is also provided at 13, which is indicated in Figure 11 by the numbers in parentheses.

In the above configuration, the feeding roll 20c is intermittently fed to the belt-shaped material 50c, and during this feeding, the guide lifter 23 projects upward as shown in FIG. 9 and the groove 23a is used as a guide to guide the belt-shaped material 50c.
Moves. Then, the band-shaped material is detected by the position detection sensor 21.
After detecting the movement of 50c, the conveyance is stopped, and the pilot pin 22 is inserted into the reference pin hole 55 and positioned. After that, the top plate 4 is processed by the elevating cylinder 5, and the upper mask plate 12 is put on the lower mask plate 8 and the upper cooling plate 13 is put on the lower cooling plate 10, respectively. At this time, as explained in FIG. 11,
The guide lifter 23 enters the chamber 8a, and the strip 50
The upper and lower surfaces of c are tightly sandwiched between the upper and lower mask plates 8 and 12.

The heating by the high frequency induction heating body 9 thereafter is exactly the same as in the case of the above-mentioned embodiment, and only the stage 51 and the inner leads 52 within the broken line shown in FIG. 7 are heated. On the other hand, the leading portion of the strip 50c sandwiched between the lower and upper cooling plates 8 and 13 is gradually cooled in synchronization with the heating of the trailing portion. When the heating process is completed, the lift plate 5 raises the top plate 4 to raise the upper mask plate 12 and the upper cooling plate 13, respectively, and accordingly, the guide lifter 23 projects as shown in FIG. 11 (a). The strip 50c is lifted from the lower mask plate 8 and the lower cooling plate 10. Then, in this state, feeding by the transport roll 20c is given, and thereafter, similar processing is repeated.

〔The invention's effect〕

In the present invention, since a pair of mask plates having a high-frequency induction heating element can be opened and closed and the lead frame is conveyed between the mask plates in a floating state, the heating element or the like does not come into contact with the lead frame and the surface thereof is not scratched. Does not damage. Further, since the annealing area extends to the inner lead, the initial function of the outer frame of the lead frame and the base material such as the outer lead and the dam bar can be maintained, and the initially set reference hole pitch for positioning can be maintained. Therefore, the positioning in the semiconductor device assembling process can be accurately performed, and the yield is improved.

Furthermore, compared to conventional equipment, the working environment is better, there is no pollution, the heating conditions can be easily controlled by setting the frequency, and the size is reduced, so it can be easily connected to the press equipment, plating equipment, etc. As a result, it is possible to provide a lead frame that has a remarkable effect such that a one-step line can be configured, improves the quality and yield of semiconductor devices, and maintains long-term reliability.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing a main part of a partial annealing apparatus of the present invention, FIG. 2 is a side view seen in a pass line direction, and FIG. 3 (a) is a lower mask plate of a high frequency induction heating body. FIG. 3 (b) is a sectional view taken along the line II of FIG. 3 (a), FIG. 4 (a) is a schematic plan view of the transport mechanism, and FIG. FIG. 5 is a side view of the main part, FIG. 5 is a schematic view for explaining the holding of the lead frame by the behavior of the gripper, FIG. 6 is a schematic perspective view showing the arrangement of the heating part with respect to the strip-shaped lead frame, and FIG. FIG. 8 is a plan view of a lead frame pattern for showing an annealed region, FIG. 8 is a schematic cross-sectional view of a heating portion and upper and lower mask plates for the lead frame, and FIG. 9 is a case where the strip material of the lead frame is processed. Partially cutaway front view, Figure 10 is a side view seen in the pass line direction, and Figure 11 (a) is a FIG. 11 (b) is a schematic diagram showing the floating conveyance of the lead frame by the lifter, FIG. 11 (b) is a schematic diagram showing the sinking of the guide lifter, and FIG. 12 is a schematic perspective view showing the relationship between the strip-shaped material of the lead frame and the heating portion. . 1: Base, 1a: Base 1b: Rail 2: Guide pin, 2a: Bushing 3: Auxiliary plate, 4: Top plate 5: Lifting cylinder, 6: Backup liner 7: Holder plate, 7a: Lock 8: Lower mask plate 8a: Chamber, 8b: Coil spring 9: High frequency induction heating body 9a: Dust core, 9b: High frequency heating coil 10: Lower cooling plate 11: Upper holder, 11a: Lock 12: Upper mask plate 12a: Spring, 12b: Recess 13: Upper cooling plate 13a: Spring, 13b: Recessed portion 14: Transport block, 14a: Lifting cylinder 14b: Rod 15: Drive cylinder 16: Transport frame 16a to 16e: Gripper holder 16f: Rack unit 16g: Motor, 16h: Pinion 17: Gripper , 18, 19: Feed rollers 20a, 20b: Bridle roll 20c: Conveyor roll 21: Position detection sensor, 22: Pilot pin 23: Guide lifter, 23a: Groove 23b: Flange 50: Lead frame 50a: Lead lead frame 5 0b: Subsequent lead frame 50c: Band material 51: Stage, 52: Inner lead 53: Dam bar, 54: Outer lead 55: Reference pin hole

Claims (1)

[Claims] 1. A stamping, coining, and the like for forming a lead frame into a desired shape by pressing a metal strip.
An annealing device for removing the residual stress by subjecting the lead frame, which has residual stress inside due to processing history such as press working, in an antioxidation atmosphere to remove the residual stress. A heating body, a mask plate provided around the high-frequency heating body and covering a non-heated portion of the lead frame during heating, and an intermittent transfer mechanism for feeding the lead frame to the high-frequency heating body and the mask plate in a non-contact state A partial annealing apparatus for a lead frame, comprising: a part including the inner lead and / or the stage of the lead frame, the high frequency heating element being associated with the part.