JP2520486B2 - Method for manufacturing lead frame for semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a lead frame that can assemble a semiconductor device without trouble.

[Conventional technology]

In recent years, with the diversification of functions of semiconductor devices using a lead frame and the tendency toward more pins, the tips of the inner leads forming this lead frame are becoming finer, and the lead width and the spacing between them tend to become narrower. . When manufacturing such a lead frame by a processing method using a press die, the arrangement interval is limited in terms of the strength of the punching tool, and therefore, the punching of the adjacent fine leads is performed at a separated position. It is necessary to shift them.
For this reason, after punching, residual stress remains in the inner leads to cause strain.

In particular, this residual stress is released during the heating step in the semiconductor device assembling process, causing unevenness, overlapping, ups and downs of the lead tips, which leads to poor wire bonding connections and short circuits.

In order to solve the problem that causes deterioration of quality and yield due to the presence of internal stress of the lead frame caused by such punching, various measures have been conventionally proposed.

As one of the measures, for example, as disclosed in JP-A-62-115853, a connecting piece for connecting the lead tips is provided, and the lead tips are fixed and held with tape or resin in the connected state. It has been shown.

However, with this measure, in the semiconductor device assembly process using a lead frame with a large number of lead pins,
In the heat treatment step of this step, the fixing tape is softened, the residual stress fixedly held by the tape is released, and the connection position such as wire bonding becomes defective, resulting in a decrease in yield.

As another measure, as disclosed in Japanese Patent Application Laid-Open No. 59-72754, a strip-shaped lead frame in which the tip of the lead is formed after annealing the entire surface of the lead frame to remove internal stress Alternatively, a method has been proposed in which the continuous body of the lead frame is entirely heat-treated. However, the former measure has a drawback that when arranging the strip-shaped lead frame on the heat treatment jig, it is a manual work, which is inferior in workability, the number of processes is increased, and the incidental equipment such as a vacuum device is expensive. There is. Further, in the latter method, the deformation of the positioning reference holes and the reference hole pitch in the semiconductor device assembly process are changed by thermal deformation such as extension due to heating and slow cooling, shrinkage, etc. Positioning becomes unstable, which causes troubles in assembling the semiconductor device.
Further, since the strength of the entire body is reduced, there is a drawback that when the continuous body of the lead frame is conveyed, the connecting piece having a thin lead tip is deformed or cut.

[Problems to be Solved by the Invention]

The technical problem to be solved in the present invention is to solve the problems associated with the removal of the internal stress after the above-mentioned conventional punching, and the mechanical strength and the positioning accuracy for the post-processing are maintained, and The present invention provides a method for manufacturing a lead frame, which prevents deformation during heating when assembling the device.

[Means for solving the problem]

According to the first aspect of the present invention, unnecessary portions of a strip-shaped thin metal plate are sequentially removed, and a semiconductor element mounting stage and a plurality of inner leads and outer leads radially arranged integrally with the stage are formed to form a continuous lead frame. A press working step, and a plating treatment step of applying a noble metal plating to the wire bonding area at the tip of the inner lead,
In the step of manufacturing the lead frame, which includes a second press working step of forming the tip portion of the inner lead at the same time as cutting the continuous lead frame to a predetermined size,
Between the press working step and the second working step, the continuous lead frame is sandwiched, and only a predetermined portion is heated to a predetermined temperature while being conveyed, and then gradually cooled to remove residual stress. The partial annealing treatment step is further performed between the mask plate in which a plurality of high-frequency heating coils are arranged and the pressing plate for pressing the lead frame against the mask plate to position the mask plate. It is characterized in that it is a step of intermittently transporting the lead frame by a predetermined size.

[Action]

In the lead frame manufacturing method of the present invention, the non-heated portion is masked to partially heat only the required portion such as the inner lead having a high internal residual stress, and the holding frame (side rail) having the outer lead and the reference hole is heated. Since it is not performed, there is no thermal deformation of the holding frame, the reference holes, and the like, and there is no change in the reference holes and the pitch, so that the positioning can be accurately performed during the semiconductor device assembly.

Further, since the inner lead portion having the wire bonding area is partially annealed to remove the residual stress, even if the lead tip portion becomes free, it is deformed by the heating during the semiconductor device assembly. Without this, wire bonding can be accurately performed at a predetermined position.

〔Example〕

FIG. 1 shows an embodiment of a lead frame manufactured by the manufacturing method of the present invention, in which only the portion 7 including the inner lead 3 and the semiconductor mounting stage 6 is selectively subjected to high frequency heating to be annealed and left. FIG. 1 is a perspective view showing a semiconductor device lead frame 10 from which stress is removed.

Referring to FIG. 1, the lead frame 10 is supported by a plurality of outer leads 1 and tie bars 2 for connecting and holding the outer leads 1, inner leads 3 radially arranged toward the center corresponding to the outer leads 1, and a support bar 4. The semiconductor element mounting stage 6 and the outer frame 9 having the positioning reference pilot hole 8 in the subsequent process are formed by pressing.

When forming a thin portion of a predetermined wire bonding area on the tip of the inner lead 3 or forming the tip of the inner lead 3, since the tip width of the inner lead 3 is narrower than that of the outer lead 1, twisting during press working A lot of machining stress such as glue remains.

This processing stress is released by the heating of the semiconductor device assembly and adversely affects the wire bonding and the like, and annealing by high frequency heating that removes the processing stress that causes a reduction in quality and yield is achieved by the inner lead 3 and the semiconductor element mounting stage 6. Only the part is partially annealed.

 FIG. 2 shows another embodiment of the lead frame.

As shown in the figure, the present invention provides a lead frame for a semiconductor device in which only the inner leads 3 of the lead frame 20 are high-frequency heated and annealed to remove residual stress.

Although the above embodiment is applied to the entire inner lead 3, it may be a part of the inner lead 3 such as the tip. That is, it also includes selectively annealing a portion where a processing residual stress is generated due to the processing history of the lead frame.

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

FIG. 3 (a) shows the first press working step, in which a thin sheet metal material M having a required width is unwound from the unwinding device 51 and is attached to the press device 57 by the intermittent transfer device 52 with a tension applying device. It is conveyed to the mold 58 intermittently with the required pitch.

For the strip material M that has been intermittently conveyed, the reference pilot holes 8 are formed at predetermined positions of the outer frame 9 at both ends of the strip material M by the progressive die 58. Next, the outer lead 1, the inner lead 3 and the tie bar 2 and the support lead 4 are punched out to create a required shape of the lead frame A, form a continuous lead frame F, and wind it up on the winding device 53.

The tip portion of the inner lead 3 is connected to a connecting portion (not shown) via an intermediate piece (not shown) that extends the inner lead 3, and the inner leads 3 are mutually connected to be integrally formed. Coining is performed to form a thin portion of the wiring area at the tip of the inner lead connecting the electrode of the semiconductor element and the inner lead 3 with the noble metal wire.

FIG. 3 (b) shows an induction annealing step in which only the required portion of the lead frame is annealed to remove the residual stress of the above processing.

Referring to the figure, the continuous lead frame F formed in the first press working step of (a) is attached to the unwinding device 54 having a tension adding function, and the intermittent transfer device 55 sets the high frequency heating unit 511 to a predetermined size. It is conveyed to heat only a required portion of the lead frame, conveyed to the post-cooling unit 512, gradually cooled, partially annealed, and wound on a winding device 56 having a tension adding function.

FIG. 4 shows the details of the annealing device for the heating part 511 and the cooling part 512 in the induction annealing process.

As shown in the figure, a plurality of high-frequency heating units 41 (four in this embodiment) in which a heating coil 42 is attached to a dust core 43.
An array fixed mask plate 44 and cooling plate 48,
A guide pin 47, which is detachably fixed to the support plate 45, is provided with a guide roller 47 in which the continuous lead frame F is vertically arranged with respect to the conveying direction between the guide plate 49 mounted in a state of being movable back and forth by the actuator 212. Mount and carry the required pitch. Next, the actuator 212
Is operated to press and position the continuous lead frame F against the mask plate 44 by the pressing plate 211, mask the non-annealed portion, and heat only the required portion of the lead frame by high frequency. In addition, actuator 21
The operation 2 is released and the high-frequency-heated lead frame is conveyed at a predetermined pitch, and is pressed and positioned by the cooling plate 48 in conjunction with the operation to gradually cool the heated portion.

By repeating the above operation in sequence, it is possible to obtain a continuous lead frame F in which only the required portions of the lead frame are continuously annealed. The heating and gradual cooling performed in the above-mentioned one step may be carried out by a multi-step method in which the heating and gradual cooling are divided into several steps depending on the material and shape.

Returning to FIG. 3, FIG. 3 (c) is a process diagram showing a plating process in which a required portion of the partially annealed continuous lead frame F is plated.

According to this process drawing, this continuous lead frame F
Is attached to the unwinding device 51, is sequentially conveyed to the plating device 513, and is subjected to pre-treatment, plating treatment and post-treatment in order, and a continuous lead frame F where the required portion is plated
Can be obtained.

FIG. 3 (d) is a drawing showing a step of forming a strip-shaped lead frame by forming the leading end portions of the inner leads of a continuous lead frame F, which is plated on a required portion.

According to this process diagram, a continuous lead frame F having a required portion plated is mounted on the unwinding device 51, and is intermittently conveyed by the feeding device 52 to the progressive die 518 mounted on the pressing device 517 in sequence. , The inner lead is formed to a predetermined length by removing the connecting portion including the intermediate piece connecting the leading end of the inner lead, and the continuous body is cut to a required length to obtain a strip-shaped lead frame. be able to.

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

Furthermore, in this embodiment, the tandem system in which each process is divided is used, but it may be performed in a continuous process in which a plurality of processes are connected.

〔The invention's effect〕

The present invention effectively utilizes the electromagnetic induction phenomenon, which is a feature of high frequency induction heating, and causes heat to be generated directly inside the metal. Therefore, the following effects can be achieved as compared with the conventional connection smoothing.

(1) Since it is directly heated, the thermal efficiency is good, the processing time is short, the generation of oxide film is extremely small, and the work efficiency is improved.

(2) Since partial heating can be performed, it is possible to select an annealed portion, mask the non-annealed portion to prevent thermal effects, and maintain the performance of the non-annealed portion.

(3) It is easy to control heating conditions, and a fine temperature can be provided.

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

(5) The annealing depth can be adjusted depending on the frequency setting.

(6) The working environment is good and the pollution is low.

It is possible to achieve a high-quality lead frame that achieves the initial purpose such as high yield.

[Brief description of drawings]

The attached drawings show embodiments of the present invention. 1 and 2 show examples of lead frames manufactured by the manufacturing method of the present invention. 3 and 4 are views showing an embodiment of the manufacturing process of the lead frame of the present invention. 1: Outer lead, 2: Tie bar, 3: Inner lead, 4: Support bar 6: Semiconductor mounting stage, 8: Reference pilot hole, 9: Outer frame 10: Lead frame, 44: Mask plate, 45: Support plate 55: Intermittent Conveyor device, 56: Winding device, 57: Press device, 5
8: Progressive die 211: Press plate, F: Continuous lead frame

Claims (1)

(57) [Claims] 1. A continuous lead frame in which an unnecessary portion of a strip-shaped metal thin plate is sequentially removed to form a semiconductor element mounting stage and a plurality of inner leads and outer leads integrally and radially arranged from the stage. 1, a press working step, and a plating processing step of applying a noble metal plating to the wire bonding area at the tip of the inner lead,
In a lead frame manufacturing process having a second press working step of cutting the continuous lead frame at a predetermined size at the same time as forming the tip portion of the inner lead, the first press working step and the second working step are performed. Between,
The continuous lead frame is sandwiched, and only a predetermined portion is heated to a predetermined temperature while being conveyed, and then a partial annealing treatment step of gradually cooling to remove residual stress is interposed, and the partial annealing treatment step is performed. A step of intermittently transporting the continuous lead frame by a predetermined size between a mask plate having a plurality of high-frequency heating coils arranged and a pressing plate for pressing the lead frame against the mask plate for positioning. And a method for manufacturing a lead frame for a semiconductor device.