JPH03114249A - Lead frame for semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a lead frame for semiconductor devices in such a way that front end sections of leads are not deformed even when the leads become free at the time of heating the front end sections for assembling a semiconductor device and wire bonding can be performed accurately by performing partial annealing to the inner lead section provided with a wire bonding area so as to remove residual stress. CONSTITUTION:This lead frame 10 is constituted of a plurality of outer leads 1, tie bars 2 for connecting and holding the leads 1, inner leads 3 radially arranged toward the center in corresponding to the leads 1, semiconductor element mounting stage 6 supported by support bards 4, etc., formed by press work. When the front end sections of the inner leads 3 are formed, much of such work stress as torsion, etc., produced in the front end sections at the time of the press work remains in the front end sections, since the width of the sections is narrow. Since such work stress is released and gives adverse influences to wire bonding, etc., when the sections are heated for assembling a semiconductor device, annealing is performed to the inner leads 3 and semiconductor element mounting stage 6 only by high-frequency heating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame and a method for manufacturing the same, which allow semiconductor devices to be assembled without any trouble.

[Conventional technology]

In recent years, with the diversification of functions of semiconductor devices using lead frames and the trend toward multi-bin usage, the tips of the inner leads that make up this lead frame have become smaller, and the lead width and spacing between them have become narrower. . When manufacturing such a lead frame using a press mold processing method, there are restrictions on the spacing between the punching blades due to their strength, so adjacent fine leads are punched out at separate locations during the process. It is necessary to shift the Therefore, after punching, residual stress remains in the inner lead and causes distortion.

In particular, this residual stress is released during the heating stage of the semiconductor device assembly process, causing deviation, overlapping, and ups and downs of the lead tips, which can lead to poor wire bonding connections and
This will lead to a short circuit.

Various countermeasures have been proposed in the past in order to solve the problem of deterioration in quality and yield due to internal stress banding in lead frames caused by such punching.

As one of the measures, for example, JP-A-62-1158
As disclosed in Japanese Patent No. 53, a connecting piece is provided to connect the leading ends of the leads, and the leading ends are fixedly held with tape, resin, etc. in the connected state.

However, with this method, in the semiconductor device assembly process using a lead frame with a large number of lead pins, the fixing tape softens in the heat treatment process of the process, and the residual stress held fixed by the tape is released, and the wire This resulted in poor connection positions such as bonding, which was a factor in lowering yield.

In addition, as another measure, as disclosed in Japanese Patent Application Laid-Open No. 59-72754, after annealing is applied to the entire surface of the lead frame to remove internal stress, a strip-shaped lead frame is formed to form the tip of the lead. Alternatively, a method has been proposed in which the entire continuous body of the lead frame is subjected to heat treatment. However, the former method requires manual work when arranging the strip-shaped lead frames on the heat treatment jig, which is poor in workability, increases the number of steps, and has the drawbacks that the cost of ancillary equipment such as vacuum equipment is high. There is. Furthermore, in the latter method, thermal deformation such as elongation and shrinkage due to heating and slow cooling causes deformation of the positioning reference holes and changes in the reference hole pitch in the semiconductor device assembly process, resulting in changes in the semiconductor device assembly process in the subsequent process. Positioning becomes unstable, which causes trouble when assembling semiconductor devices. Furthermore, since the overall strength of the lead frame is reduced, there is a drawback that the thin connecting piece at the tip of the lead may be deformed or broken when the continuous body of the lead frame is transported.

[Problem to be solved by the invention]

The technical problem to be solved by the present invention is to solve the above-mentioned problems associated with removing internal stress after punching, while maintaining mechanical strength and positioning accuracy for post-processing. The present invention provides a lead frame that prevents deformation during heating during device assembly, and a method for manufacturing the lead frame.

[Means to solve the problem]

The lead frame for a semiconductor device of the present invention is made up of a semiconductor element mounting stage and a plurality of inner leads and outer leads arranged radially from the stage, by sequentially removing unnecessary parts of a strip-shaped thin metal plate. Therefore, when assembling a semiconductor device using the lead frame, internal residual stress is selectively removed only from required portions of the inner lead having the wire bonding area and/or the element mounting stage.

The above lead frame for a semiconductor device is manufactured by sequentially removing unnecessary portions of a strip-shaped metal thin plate material to continuously form a semiconductor element mounting stage and a plurality of inner leads and outer leads arranged radially from the stage. After the first press working process, the plating process of applying precious metal plating to the wire bonding area of the tip of the inner lead, and the second press process of forming and cutting the tip of the inner lead to a fixed size, high frequency heating is performed. A continuous body of lead frames is intermittently conveyed by a predetermined distance between a mask plate on which a plurality of coils are arranged and a pressing plate that presses and positions the lead frame against the mask plate, and the continuous body of lead frames is held therebetween. Then, the non-heated parts of the lead frame are masked, and a high-frequency current of 15 KHz to 500 KH is applied to the required parts of the lead frame, which is heated by induction and then slowly cooled to remove residual stress. It is a form of smoothing.

[Effect]

In the lead frame of the present invention, non-heated parts are masked and partial heating is applied only to required parts such as inner leads with high internal residual stress.Since the outer leads and the holding frame (site rail) having reference holes are not heated, There is no thermal deformation of the frame, reference holes, etc., and no change in the pitch of the reference holes, allowing for accurate positioning during assembly of semiconductor devices.

Furthermore, the inner lead part that has the wire bonding area is partially annealed to remove residual stress, so even if the lead tip is free, it will not deform when heated during semiconductor device assembly. Wire bonding can be performed accurately at a predetermined position without any trouble.

〔Example〕

FIG. 1 shows an embodiment of the lead frame of the present invention, in which only the portion 7 including the inner lead 3 and the semiconductor mounting stage 6 is selectively annealed by high-frequency heating to remove residual stress from the semiconductor. FIG. 2 is a perspective view showing a lead frame 10 for a device.

Referring to the figure, a lead frame 10 is supported by a plurality of outer leads 1, tie bars 2 that connect and hold them together, inner leads 3 arranged radially toward the center corresponding to the outer leads 1, and a support par 4. It is constructed by pressing a semiconductor element mounting stage 6 and an outer frame 9 having a reference pilot hole 8 for positioning in a subsequent process.

In forming a thin part in a predetermined wire bonding area at the tip of the inner lead 3 and forming the tip of the inner lead 3, the inner lead 3
Since the tip width is narrow, a large amount of processing stress such as torsion during press processing remains.

The inner lead 3 and the semiconductor element mounting stage 6 are annealed using high-frequency heating to remove this processing stress, which is released by heating during semiconductor device assembly and adversely affects wire bonding, etc., and is a factor in reducing quality and yield. Partial annealing is applied to only certain parts.

FIG. 2 shows another embodiment of the invention.

As shown in this figure, a lead frame for a semiconductor device is provided in which only the inner leads 3 of a lead frame 20 are annealed by high-frequency heating to remove residual stress.

In the above embodiment, the inner lead 3 is entirely covered, but it may be applied to a portion such as the tip of the inner lead 3.

That is, it also includes selectively annealing portions where processing residual stress has occurred due to the processing history of the lead frame.

FIGS. 3<a> to 3(d) show the manufacturing process of the lead frame of the present invention using an induction annealing device.

FIG. 3(a) shows the first press working step, in which a thin metal sheet strip M of a required width is unwound from an unwinding device 51, and an intermittent conveying device 52 with a tensioning device is used to unwind a thin metal sheet material M to a pressing device 57.
It is intermittently conveyed at a required pitch to a progressive mold 58 attached to the mold.

The strip material M that has been intermittently conveyed has reference pilot holes 8 formed at predetermined positions in the outer frame 9 at both ends of the strip material M by the progressive die 58 . Next, the tip portions of the outer leads 1 and the inner leads 3, the tie bars 2, and the support leads 4 are punched out to create a desired shape for the lead frame, forming a continuous body F of the lead frame, and winding it up in the winding device 53.

The tip of the inner lead 3 is connected to a connecting part (not shown) via an intermediate piece (not shown) extending from the inner lead 3, and the inner leads 3 are connected to each other and formed integrally,
Furthermore, coining is performed to form a thin part of the wiring area at the tip of the inner lead where the electrode of the semiconductor element and the inner lead 3 are connected by the noble metal wire.

FIG. 3(b) shows a high-frequency annealing process in which residual stress from the above processing is removed by annealing only required portions of the lead frame.

Referring to the same figure, the continuous body F of the lead frame formed in the first pressing step of (a) is mounted on the unwinding device 54 having a tension adding function, and the continuous body F of the lead frame formed in the first press working step of (a) is mounted on the unwinding device 54 having a tension adding function, and the continuous body F of the lead frame is placed on the high frequency heating section 511 by the intermittent conveying device 55. The lead frame is dimensionally conveyed to heat only a required portion of the lead frame, and then conveyed to a post-cooling section 512 where it is gradually cooled and partially annealed, and then wound up by a winding device 56 having a tension adding function.

Heating section 511 for induction annealing process. Details of the annealing device for the cooling section 512 are shown in FIG.

As shown in the figure, a heating coil 42 is attached to the dust core 43.
A plurality of high-frequency heating units 41 (in this embodiment, four
The continuity of the lead frame is between the mask plate 44 and cooling plate 48 which are arranged and fixed, and the press plate 211 which is attached to a guide bin 49 which is detachably fixed to the support plate 45 so as to be movable forward and backward using an actuator 212. The body F is attached to guide rollers 47 arranged vertically with respect to the conveyance direction and conveyed at a required pitch. Next, actuate the actuator 212 to press the press plate 211.
Press and position the lead frame continuum F against the mask plate 44, mask the non-annealed part,
Only required portions of the lead frame are subjected to high frequency heating.

Furthermore, the actuator 212 is deactivated and the high-frequency heated lead frame is conveyed at a predetermined pitch.
In conjunction with the above operation, the cooling plate 48 is pressed and positioned to slowly cool the heated portion.

By sequentially repeating the above operations, it is possible to obtain a continuous body F of the lead frame in which only the required portions of the lead frame are continuously annealed. The heating and slow cooling performed in the above-mentioned stages may be performed by a multi-stage method in which the material is divided into several stages depending on the material and shape.

Returning to FIG. 3, FIG. 3(C) is a process diagram showing a plating process in which required portions of the continuous body F of the partially annealed lead frame are subjected to plating treatment.

According to this process diagram, the continuous body F was mounted on the unwinding device 51 and sequentially conveyed to the plating device 513, where it was sequentially subjected to pre-treatment, plating treatment, and post-treatment, and plating was applied to the required portions. A series F of lead frames can be obtained.

FIG. 3(d) is a drawing showing the process of forming the tip of the inner lead of the continuous body F of the lead frame, which has undergone plating treatment on required portions, to obtain a strip-shaped lead frame.

According to this process diagram, a continuous body F of a lead frame, which has been plated at required portions, is mounted on an unwinding device 51, and is sequentially and intermittently conveyed by a feeding device 52 to a progressive mold 518 mounted on a press device 517. Then, the connecting portion including the intermediate piece connecting the tips of the inner leads is removed to form the inner leads to a predetermined length, and the continuous body is cut to the required length to form a lead frame in the form of a strip. can be obtained.

In the process of this embodiment, the process of adhesion of the insulating resin tape for fixing the inner leads is omitted, but a tape adhesion process may be added depending on the shape of the inner leads, the number of leads, and the conveying means.

Furthermore, although this embodiment used a tandem method in which each step was divided, it may be performed in a continuous step in which a plurality of steps are connected.

〔Effect of the invention〕

The present invention makes effective use of the electromagnetic induction phenomenon, which is a feature of high-frequency induction heating, and generates heat directly inside the metal, so it can achieve the following effects compared to conventional indirect annealing.

(1) Direct heating provides good thermal efficiency and short processing time.
The generation of oxide film is extremely small, improving work efficiency.

(2) Since partial heating is possible, the annealing portion can be selected, and the non-annealed portion can be masked to prevent thermal effects, and the performance of the non-annealed portion can be maintained.

(3) Heating conditions can be easily controlled and precise temperatures can be provided.

(4) Since it is pressed and fixed and then heated, there is less deformation and the accuracy of positioning in the semiconductor assembly process is improved.

[5] Depending on the frequency setting, the annealing depth can be adjusted.

(6) The working environment is good and there is little pollution.

etc., it is possible to achieve the initial objectives and provide a high-quality lead frame with a high yield.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying figures illustrate embodiments of the invention. FIGS. 1 and 2 each show an embodiment of the lead frame of the present invention. FIGS. 3 and 4 are diagrams showing an embodiment of the lead frame manufacturing process of the present invention.

Claims (1)

[Claims] 1. Sequentially removing unnecessary parts of a strip-shaped metal thin plate material,
A lead frame for a semiconductor device comprising a stage on which a semiconductor element is mounted and a plurality of inner leads and outer leads arranged radially from the stage, the lead frame for a semiconductor device having internal residual stress removed only from required portions of the lead frame. . 2. Sequentially remove unnecessary parts of the strip-shaped metal sheet material,
A first press processing step in which a semiconductor element mounting stage and a plurality of inner leads and outer leads arranged radially from the stage are continuously formed; and a plating step in which precious metal plating is applied to the wire bonding area at the tip of the inner lead. In a lead frame manufacturing process that includes a second press working process of forming and cutting the tip end of the inner lead to a specified size, during the manufacturing process, the continuous body of the lead frame is held and transported to a predetermined size. 1. A method for manufacturing a lead frame for a semiconductor device, comprising a partial annealing process in which only a portion is heated to a predetermined temperature and then slowly cooled to remove residual stress. 3. In the description of claim 2, the partial annealing process includes a mask plate in which a plurality of high-frequency heating coils are arranged;
A method for manufacturing a lead frame for a semiconductor device, which comprises a step of intermittently conveying a continuous body of the lead frame by a predetermined dimension between a press plate that presses and positions the lead frame against the mask plate.