JPH03201387A - Device for partially annealing lead frame - Google Patents

Abstract

PURPOSE:To maintain the initial function of the base material of each lead frame by feeding lead frames while keeping the frames from contact with a high-frequency heating element and a mask plate, and making the high-frequency heating element correspond to the portion of each lead frame including an inner lead and/or a stage. CONSTITUTION:Lead frames 50 intermittently fed from a feed roller 18 are each moved to just above a lower mask plate 8 and a high-frequency induction heating element 9 is stuck to the lower surface of each lead frame 50 and at the same time the lower mask plate 8 covers the ambient of the heating element 9 and each lead frame 50 is sandwiched between the lower mask plate 8 and an upper mask plate 12. Only a stage 51 and the end portion of an inner lead 52 or the area of each lead frame along a damper 53 are subjected to induction heating by the high-frequency heating element 9 and the other area is protected from induction heating by the lower mask plate 8. The lead frame 50 ahead of the line is sandwiched between upper and lower cooling plates 13, 10 and is gradually cooled and annealed by heating treatment and gradual cooling. The initial function of the base material of the lead frames is thereby maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 in a semiconductor device.

[Conventional technology]

Residual stress that remains in a lead frame used in a semiconductor device is generated when the film undergoes the next processing history.

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

il) The process of slitting a wide strip of metal sheet into strips of the required width of the lead frame.

iii) A press working process in which unnecessary portions of the strips are sequentially removed and the tie bars that connect and hold the tips of the inner leads are left behind to form the element mounting stage, inner leads, outer leads, etc. into the desired shape of the lead frame.

The lead frame formed through the above process is further assembled into a semiconductor device in a subsequent line. The procedure is to mount the device on the stage of the lead frame, connect the bonding pad of this device and the external lead with thin precious metal wire to form an electrically conductive circuit, and then seal them with resin. be. However, residual stress generated in the lead frame is released due to heating during an intermediate process before it is assembled into a semiconductor device.

As a result, deformations such as floating or shifting of the leads occur at the tips of the inner leads, resulting in defective wire bonding, which is a factor in lowering the yield of semiconductor devices and lacking long-term reliability.

Conventionally, in order to prevent such problems, residual stress in the lead frame is removed using a heat treatment device that indirectly or directly heats the entire strip-shaped or continuous lead frame formed by press processing. Treatment is generally performed.

As the former heat treatment apparatus, a bright annealing apparatus, a vacuum annealing apparatus, etc., which continuously supply the entire lead frame into an oxidation-preventing heating atmosphere and heat it indirectly, are generally used. Among the latter types, there is a direct heating type high frequency annealing device that uses electromagnetic induction to directly convert electrical energy into thermal energy within the metal.

[Problem to be solved by the invention]

However, in the former device, the heating time is long and the entire device is lengthened to ensure the amount of heating, so there are problems with the equipment. In addition, adjustment of the heating atmosphere and temperature control are complicated, and furthermore, the processing of strip-shaped lead frame materials requires a manual alignment process for arranging them on a tray and then transporting them into the heating atmosphere. For this reason, there are problems in terms of cost due to reduced work efficiency, etc., and there are also restrictions on device layout, synchronization, etc., which has been an obstacle to automation.

On the other hand, in the latter device, the lead frame is continuously conveyed through a narrow heating coil, which has the disadvantage that it comes into contact with the heating coil due to vibrations, causing damage such as scratches on the surface of the lead frame and bending of the leads. Ta.

Further, since the heat treatment apparatus that heats indirectly or directly heats the entire lead frame, the outer frame of the lead frame, the outer leads, and the dam bar that connects and holds them are softened. Therefore, there is a problem in that the pitch of the pilot holes for positioning provided in the outer frame changes due to functional deterioration and deformation due to elongation, contraction, etc. of the base material.

Furthermore, in recent years, with the diversification of functions of semiconductor devices using lead frames and the tendency to increase the number of pins, the tips of inner leads have become smaller. For this reason, the lead width and the spacing between the leads have become narrower, and even minute deformation of the inner leads cannot be tolerated, so there has been a demand for a highly accurate partial heat treatment apparatus.

The purpose of the present invention is to remove residual stress caused by processing history only in necessary areas, maintain the functions of the lead frame base material and the initial functions such as positioning reference holes and mutual pitch accuracy, and The purpose is to enable annealing treatment.

[Means to solve the problem]

The present invention relates to punching when forming a metal strip into the desired shape of a lead frame by press working.

An annealing device that heats a lead frame in which residual stress remains due to processing history such as coining and pressing in an anti-oxidation atmosphere to remove the residual stress, and partially heats the lead frame. a high-frequency heating body for heating, a mask plate provided around the high-frequency heating body to cover an unheated portion of the lead frame during heating, and intermittent conveyance for feeding the lead frame in a non-contact state with the high-frequency heating body and the mask plate. A mechanism is provided, and the high-frequency heating body is made to correspond to a portion of the lead frame including the inner lead and/or the stage.

[Effect]

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

Since the non-heated areas such as the outer frame of the lead frame and the dam bars that connect and hold the outer leads are masked to prevent heating, the functions of the base material in those areas are maintained and the positioning The initially set pitch of the reference holes is maintained by preventing deformation due to elongation or contraction of the 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 tensile force during transportation, and the feed dimension is stabilized.

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 that area, so the inner lead part expands and contracts toward the semiconductor element mounting stage. Therefore, a stable product can be obtained without being influenced by other areas, causing complicated deformation, and without shifting the lead tip.

〔Example〕

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

In the figure, the casing (
A base 1 is fixed to a pedestal 1a disposed in a container (not shown), and a pass line for a lead frame to be annealed is provided above the base 1. Guide bushes 2a are provided at four corner portions of the base 1, and guide pins 2 are inserted into these so as to be movable in the vertical direction.

An auxiliary plate 3 is connected to the lower end of these guide pins 2, and a top plate 4 is connected to the upper end thereof. An elevating cylinder 5 is connected to the lower surface of the auxiliary plate 3, and its operation causes the auxiliary plate 3 and the top plate 4, which is integrated therewith by a guide pin 2, to move up and down in a direction perpendicular to the pass line.

A backup liner 6 is fixed to the upper surface of the base 1,
Moreover, a holder plate 7 is removably arranged on the entry side of the lead frame.

This holder plate 7 is connected to a backup liner 6 in a direction perpendicular to the pass line of the lead frame in FIG.
Lock 7a provided on the end face
Fixed by Two rows of lower mask plates 8 are arranged on the upper surface of the holder plate 7 in the direction of the pass line as shown in FIG. Four high-frequency induction heating elements 9 are installed in the lower mask plate 8 in the pass line direction.

As shown in FIG. 3, the lower mask plate 8 has high-frequency induction heating elements 9 embedded and fixed at equal pitches, and when a lead frame is placed on it, only the stage and inner lead portions face the high-frequency induction heating element 9. The other portions are configured to cover the lower mask plate 8. In addition,
The high frequency induction heating body 9 includes a dust core 9a and a high frequency heating coil 9b surrounding the dust core 9a.

Furthermore, a lower cooling plate 10 for slowly cooling the lead frame after induction heating is fixed to the upper surface of the holder plate 7 on the exit side of the lead frame. For example, ceramic or the like can be used as a suitable material for the lower cooling plate 10.

On the other hand, an upper holder 11 is incorporated into the lower surface of the top plate 4 so as to be able to be taken in and out in a direction perpendicular to the pass line. This upper holder 11 is also fixed by a lock lla in the same way as the holder plate 7. Then, an upper mask plate 12 is placed at a position corresponding to the lower mask plate 8.
are arranged in two rows, and an upper cooling plate 13 is provided directly above the lower cooling plate 10. These upper mask plate 12 and upper cooling plate 13 are elastically supported by springs 12a and 13a, respectively.

The lead frame 50 is supplied to the line in the form of a strip with four patterns as shown in FIG. In order to supply this lead frame 50, four transport blocks 14 are arranged on a base l with a pass line in between, as shown in FIG.

These transport blocks 14 are guided by rails 1b provided on the base 1, and are moved intermittently back and forth by a drive cylinder 15 that extends and contracts the rods in the direction of the pass line. The conveyance block 14 is provided with an elevating cylinder 14a in the vertical direction.
is provided, and the transport frame 16 is fixed to the rod 14b.

FIG. 4(a) is a schematic plan view of the transport mechanism, and FIG. 4(b) is a side view of the main parts.

As shown in the figure, the transport frame 16 occupies almost the entire width of the bus line, and the frame has four guide rods 16a extending across the pass line. These guide rods 1
6a, there are four gripper holders 16 in the direction of the pass line.
b, 16c, 16d, and 16e are tied together 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, 16e are for the lead frame 50 running on the left side. A rack unit H6f forming a rack is integrated at both ends of each of the gripper holders 16b to 16e. Also, a gripper holder 16b.

Lad's rack unit 16f has a common guide loft 1
6a, and the other gripper holders 16c, 16e are slidably attached to the other set of guide rods 16a. In addition, each Rafuku unit) 1
The pinions 6f are respectively engaged with pinions 16h provided on the output shaft of the motor 16g. And each gripper holder 1
A gripper 17 is attached to each of 6b to 16e.

In such a transport mechanism, when the motor 16g is driven,
Gripper holder 16b on the right side of the pass line.

16c and the left gripper holders 16d and 16e simultaneously expand and contract their respective spacings. In the illustrated case, when the interval is the smallest, the gripper 17 is in a position to hold the edge of the lead frame 50 in the width direction and transport it. And when widening the interval,
At the same time as releasing the hold on the lead frame 50, each of the gripper holders 16b to 16e retreats so as not to interfere with the lowering of the upper mask plate 12 and the upper cooling plate 13.

FIG. 5 is a schematic diagram illustrating the behavior of the gripper 17 with respect to the lead frame 50 on the left side in FIG. The gripper holders 16b and 16c move up and down as indicated by vertical arrows in the figure by the operation of the lifting cylinder 14a. Further, by the operation of the motor 16g, the holder blocks 16b and 16c can be opened and closed toward the left and right edges of the lead frame 50, as indicated by horizontal arrows in the figure. When holding the lead frame 50 by the gripper 17, the holder blocks 16b and 16c are first lowered so that the level of the gripper 17 matches the lead frame 50. Thereafter, the holder blocks 16b and 16c are positioned close to the lead frame 50 and 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 a stroke in which the lead frame 50 located directly above the lower mask plate 8 in FIG. 1 is conveyed to the lower and upper cooling plates 10.13 by intermittent feeding. Further, the transport arm 16 is made long enough to protrude from the entry side to prepare for carrying in the lead frame 50 from the upstream side. A feed roller 1g is provided on the loading side of the lead frame 50 and the unloading side after processing, respectively.
19 are arranged and connected to an external line to form a system that automatically supplies lead freight 50 intermittently.

Here, as shown in FIG. 6, the lead frame 50 is supplied with four patterns, and each pattern is positioned in correspondence with the four high-frequency induction heating elements 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 on which a semiconductor element is mounted is provided at the center, inner leads 52 are formed around the stage 51, and outer leads 54 are further provided with a dam bar 53 as a boundary. In both outer ends of the outer lead 54, reference pin holes 55 are formed at a constant pitch to be used for positioning during annealing, plating, etc.

The annealing area for the lead frame 50 is the area surrounded by the broken line in FIG. That is, the area is along the tip of the stage 51 and the inner lead 52 or the dam bar 53, and the area outside of this is not annealed. For such annealing, the high-frequency induction heating element 9 is set to have a shape equal to the shape surrounded by the broken line, and the lower mask plate 8 is
shall have a shape that can cover the entire area around it. 8th
The figure is a cross-sectional view schematically showing the lead frame 50 during annealing when viewed in the pass line direction, and (a) corresponds to the apparatus shown in FIG. 1. As shown in the figure, the lower mask plate 8 and the high-frequency induction heating element 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. In addition, as shown in FIG. 4B, a high frequency induction heating element 9 can also be incorporated into the upper mask plate 12 to heat it from both sides. In such an arrangement, the high-frequency induction heating element 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 configuration, the lead frame 50 intermittently supplied from the feed roller 18 is held by the gripper 17 lowered by the lifting cylinder 14a, and then lifted to a position slightly higher than the level of the lower mask plate 8. Thereafter, the drive cylinder 15 applies intermittent feeding to the transport block 14, and the lead frame 50 moves directly above the lower mask plate 8 as shown in FIG. Note that, at the same time, the already heated preceding lead frame 50a is held by the gripper 17 and conveyed to just above the lower cooling plate 10.

After the transport block 14 has stopped, the lifting cylinder 14
The transport frame 16 is lowered by a, and the lead frame 50 is placed on the lower mask plate 8 and the preceding lead frame 50a is placed on the lower cooling plate 10. After this, the lead frame 50.50a is gripped by the gripper 17.
At the same time, the motor 16g is used to widen the intervals 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 top plate 4 is lowered from the state shown in FIG. 1 by the lifting cylinder 5, and the upper mask plate 12 and the upper cooling plate 13 are superposed on the lower mask plate 8 and the lower cooling plate NO, respectively.

As explained in FIG. 8(a), the lead frame 50 has the high-frequency induction heating element 9 in close contact with the lower surface thereof, and at the same time, the lower mask plate 8 is placed around it and is sandwiched between the upper mask plate 12 and the lower mask plate 8. Then, only the region surrounded by the broken line in FIG. 7 is induction heated by the high frequency induction heating element 9, and the other regions are suppressed from induction heating by the lower mask plate 8. Therefore, partial heating of the lead frame 50 is performed by the high frequency induction heating element 9. On the other hand, the preceding lead frame 50a has lower and upper cooling plates 10
13 and then slowly cooled, and subjected to heat treatment and annealing by slow cooling.

After a certain period of time has elapsed, the top plate 4 is raised by the lifting cylinder 5 to open the upper surfaces of the lead frame 50 and the preceding lead frame 50a.

Then, the gripper holders 16b to 16 whose spacing was widened
The lead frame 50 and the preceding lead frame 5 after being processed by the gripper 17 are returned to the state shown in FIG. 4(a).
0a, and feed is applied again by the drive cylinder 15. By this feeding, the preceding lead frame 50a is discharged toward the feeding roller 19 side, the lead frame 50 reaches above the lower cooling plate 10, and the succeeding lead frame 50b further reaches above the lower mask plate 8. Thereafter, the lead frame 50 is annealed in the order of heating and slow cooling intermittently according to the above-described procedure.

Note that since the pattern of the lead frame 50 changes variously depending on specifications, the annealing area within the broken line area shown in FIG. 7 also changes. For this reason, the size and arrangement pitch of the high-frequency induction heating element 9 and the upper and lower mask brakes) 8.12
It is also necessary to change the shapes of the upper and lower cooling plates 10 and 13. On the other hand, since the holder plate 7 and the upper holder 11 can be attached to and detached from the backup liner 6 and the top plate 4, respectively, this can be handled without any problem by preparing a mask plate and a cooling plate that match the pattern of the lead frame 50.

FIGS. 9 and 10 show an example of a device installed in a system for feeding lead frames as strips.

Note that the same members as described in the above embodiments will be designated by common reference numerals, and detailed explanation thereof will be omitted.

The strip material 50C of the lead frame has a continuous pattern formed thereon as shown in FIG. 12, and is fed to a processing line as it is to be sequentially processed.

In order to convey such a strip material 50C, a priddle roll 20a is provided on the entrance/exit side of the pass line of the apparatus.

20b is arranged, and a conveying roll 20c for intermittent feeding is provided on the exit side. The stroke of intermittent feed is
As shown in FIG. 2, four high-frequency induction heating bodies 9 are arranged, so the length corresponds to the length of four patterns.

A position detection sensor 21 is provided for positioning the strip material 50C for intermittent feeding by this stroke, and a pilot pin 22 that fits into the reference bottle hole 55 is provided.
Set up.

Further, guide lifters 23 for conveying the strip material 50c in a floating state from the lower mask plate 8 and the like are arranged at a constant pitch on the lower mask plate 8 and the lower cooling plate 10, respectively. FIG. 11 is a detailed view of the guide lifter 23 provided on the lower mask plate 8, and the lower mask plate 8 is provided with a chamber 8a in which the guide lifter 23 can move in and out. A groove 23a is provided at the upper end of the guide lifter 23 so that the edge of the strip material 50c can be inserted and held therein, and a chamber 8 is provided at the lower end.
A flange 23b is provided to prevent it from being pulled out from a.

Further, a coil spring 8b that biases the guide lifter 23 upward is installed in the chamber 8a.

On the other hand, an escape recess 12b is provided on the lower surface of the upper mask plate 12 so as to tightly sandwich the strip material 50c when the upper mask plate 12 is covered with the lower mask plate 8. Note that similar chambers are provided in the lower cooling plate 10 and the upper cooling plate 13, and are shown in FIG. 11 by numbers in parentheses.

In the above configuration, the conveying roll 20c provides intermittent feeding to the strip material 50c, and during this feeding, the guide lifter 23 protrudes upward as shown in FIG. 9, and the strip material 50c moves using its groove 23a as a guide. . And position detection sensor 2
1, after detecting the movement of the strip material 50c, the conveyance is stopped, and the pilot pin 22 is inserted into the reference bottle hole 55 for positioning. Thereafter, the top plate 4 is processed by the lifting cylinder 5, and the upper mask plate 12 and the upper cooling plate 13 are placed on the lower mask plate 8 and the lower cooling plate 10, respectively. At this time, as explained in FIG. 11, the guide lifter 23 enters into the chamber 8a, and the upper and lower surfaces of the strip material 50C are at the upper side.

It is tightly sandwiched by the lower mask plate 8.12.

The subsequent heating by the high-frequency induction heating element 9 is exactly the same as in the previous embodiment, and only the stage 51 and inner leads 52 within the broken line shown in FIG. 7 are heated. On the other hand, the strip material 5 sandwiched between the lower and upper cooling plates 8°13
The leading portion at 0C is gradually cooled in synchronization with the heating of the succeeding portion. When the heat treatment is completed, the top plate 4 is raised by the lifting cylinder 5, and the upper mask plate 12 and the upper cooling plate 13 are respectively raised, and accordingly, the guide lifter 23 protrudes as shown in FIG. 11(a), The strip material 50c is lifted off the lower mask plate 8 and the lower cooling plate 10. Then, in this state, feeding is applied by the conveying roll 20c, and the same processing is repeated thereafter.

〔Effect of the invention〕

In the present invention, a pair of mask plates each having a high-frequency induction heating element can be freely opened and closed, and the lead frame is transported between them in a floating state, so that the lead frame does not come into contact with the heating element, etc., and the surface is free from scratches, etc. No damage will be caused. In addition, since the annealing area extends to the inner leads, it is possible to maintain the initial functions of the base materials such as the outer frame of the lead frame, outer leads, and dam bars, and maintain the initially set reference hole pitch for positioning. Therefore, positioning in the semiconductor device assembly process can be performed accurately, and the yield can be improved.

Furthermore, compared to conventional equipment, the working environment is better, there is no pollution, heating conditions can be easily controlled by setting the frequency, and since it is smaller, it can be easily connected to pressing equipment, plating equipment, etc. As a result, it is possible to provide a lead frame that has remarkable effects such as being able to configure a single process line, improves the quality and yield of semiconductor devices, and maintains long-term reliability.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway front view showing the main parts of the partial annealing apparatus of the present invention, Fig. 2 is a side view as seen in the pass line direction, and Fig. 3 (
a) is a plan view showing the arrangement of the high-frequency induction heating element on the lower mask plate, FIGS. 3 to 3) are cross-sectional views taken along the line II in FIG. A schematic plan view, FIG. 4(b) is a side view of the main parts, FIG. 5 is a schematic diagram for explaining how the lead frame is held by gripper behavior, and FIG. FIG. 7 is a plan view of the lead frame pattern to show the annealing area, FIG. 8 is a schematic cross-sectional view of the heating section and upper and lower mask plates for the lead frame, and FIG. 9 is a schematic cross-sectional view of the lead frame pattern. A partially cutaway front view when the frame is used for processing strip material, FIG. 10 is a side view seen in the pass line direction, and FIG. 11(a) is a schematic diagram showing floating conveyance of the lead frame by a guide 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 material of the lead frame and the heating section. 1: Base la: Base 1b: Rail 2 guide pin 2a: Push 3: Auxiliary plate 4 Ni dot plate 5: Elevating cylinder 6: Back up ply reach 7; Holder plate 7
a: 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 lla: lock 12; upper mask plate 12a spring 12b two recesses 13; upper cooling plate 13a; spring 13b: recess 14: transport block 14a: lifting cylinder 14b:
Rod 15: Drive cylinder 16: Conveyance frame 16a to 16e Nigelipper holder 15f Niggly lifter 16g; Motor 16h; Binion 17; Gripper 18.19: Feed roller 20a 20b Nibridle roll 20C: Conveyance roll 21; Position detection sensor 22: Pilot pin 23 Nigui lifter 23a ; Groove 23b; Flange 50; Lead frame 50a: Leading lead frame 50b: Following lead frame 50C: Letter material 51: Stage 52: Inner lead 53: Dam bar 54: Outer lead 55: Reference bottle hole

Claims (1)

[Claims] 1. The lead frame, in which residual stress remains internally due to the processing history such as punching, coining, and pressing when forming the metal strip into the desired shape of the lead frame, is placed in an oxidation-preventing atmosphere. An annealing device that performs heat treatment to remove the residual stress, the device comprising: a high-frequency heating element that partially heats the lead frame; and a mask that is provided around the high-frequency heating element and covers the unheated portion of the lead frame during heating. plate, and an intermittent transport mechanism that feeds the lead frame to the high frequency heating body and the mask plate in a non-contact state, the high frequency heating body being made to correspond to a portion of the lead frame including the inner lead and/or the stage. A lead frame partial annealing device characterized by: