JPH0555426A - Manufacture of lead frame for semiconductor device - Google Patents

Abstract

PURPOSE:To improve accuracies of shapes and positions of inner leads by pressing a 42 alloy lead frame and then annealing for a residual stress at a high temperature for a short time. CONSTITUTION:After inner leads 2 of a lead frame 1 for a semiconductor device are plate-retained and punched, it is annealed for residual stress at a high temperature for a short time such as at 700 deg.C for 3-6min. After outer leads 4 of the frame 1 are punched by pressing, it is annealed for residual stress at a high temperature for a short time such as at 700 deg.C for 1min, and Vickers hardness of a material hardness of a burr of the lead 4 is softened to 180-220 deg.C of Vickers hardness. Thus, inner residual stresses of the inner and outer leads generated by punching can be released, and also an inner residual stress due to elongation of a guide rail 3 generated by pressing is alleviated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame used in a semiconductor device, and more particularly to a method for punching a precision thin plate on a lead frame by a progressive die.

[0002]

2. Description of the Related Art In recent years, with the diversification of functions of semiconductor devices using lead frames, the degree of integration has been remarkably increased and the number of internal leads has been increased. Along with this, there is an increasing tendency to miniaturize semiconductor chips, and the spacing between internal leads around the chips is becoming extremely close, and the internal leads themselves are becoming finer.

Therefore, there has been a demand for a lead frame manufacturing method capable of accurately controlling the position and shape of the inner leads by improving the techniques of pressing the plate and pressing.

In order to improve the accuracy of the position and shape of the inner lead, in the press working of the lead frame, a plate pressing structure is adopted when punching the metal strip with a die, but the inner lead is miniaturized. As the pressure increases, the plate pressing pressure tends to increase more and more.

[0005]

42 alloy is used as the material for the lead frame, and in the method of manufacturing the lead frame shown in FIG. 1 from the 42 alloy by the plate pressing structure, the internal leads are miniaturized. Even if a plate holder is used, it is easily affected by the punch press, and the position is likely to change and the shape is likely to be distorted.

Further, not only the inner leads 2 but also the guide rails 3 are pressed. Therefore, when the plate pressing pressure becomes large, the guide rails 3 are stretched and the total pitch is stretched, which causes a problem of affecting the inner leads 2.

Further, since the guide rail 3 is subjected to a plate pressing pressure as well as a marking pressure for identifying the product type, this also causes the guide rail 3 to expand.
In addition, there is a risk of causing meandering due to one-sided extension.

With respect to the elongation of the guide rail 3, a method is adopted in which the elongation due to the plate pressing pressure and the marking pressure is preliminarily estimated when the die is designed.

For meandering due to one-way extension of the guide rail 3, a method is adopted in which V-notch processing is performed on a rail with little extension to balance the extension.

However, in the die design in which the elongation of the guide rail 3 is expected in advance, or in the V notch processing for correcting the meandering, there is a limit in predicting the amount of elongation in advance, and it is difficult to set an accurate amount of elongation. There is a problem to say.

Therefore, it is necessary to remove the influence of the presence of the guide rail 3 from the inner lead 2 after the plate pressing process.

Further, in the press working of the lead frame 1, in addition to the accuracy of the inner lead 2 as described above, there is a problem that the outer lead 4 is roughened or cracked.

That is, the punched side surface of the outer lead 4 is
Since the punch is pulled by the punch, the shoulder portion of the outer lead 4 formed by punching is deformed, the shoulder portion where the punch first hits is rounded, and the shoulder portion where the punch comes out has a burrs with a point. The surface with sagging is called the sagging surface,
The side with the burrs is called the burrs side.

In the final manufacturing process of the lead frame, in the external lead bending process after sealing with the mold resin, there is a difference in quality between bending with the sagging surface outside and bending with the burring surface outside. There is an easy problem. Specifically, roughening is likely to occur on the outer surface of the bent part in the external lead bending process, and this roughening may grow into cracks, but especially when bending with the burial surface outside, the outer side of the bent part Cracks are likely to occur on the surface.

Further, cracks in the bent portion are likely to occur when the external leads extend in a direction perpendicular to the rolling direction of the material of the lead frame. Therefore, in the lead bending shape of the lead frame of the QFP type semiconductor device, cracks often occur when the external lead extending in the direction perpendicular to the metal strip rolling direction is bent.

When a plate pressing structure is adopted during punching of the lead frame 1, the surface roughness and cracks during the external lead bending process described above are further increased. This is because when the plate pressing structure is adopted, the pressing force becomes significantly large in the lead bending process, and the burrs surface becomes 10% or more of the initial hardness due to work hardening.

When a crack is generated in the bent portion of the lead, the lead strength is significantly deteriorated, and the solder-plated surface for electrical connection on the substrate of the QFP type semiconductor device and the back surface of the external lead is peeled off.
Furthermore, a crack is generated in the mold resin portion, and the function as a semiconductor device is significantly deteriorated.

In order to prevent this, it is necessary to change the working conditions of the bending die, but this is complicated.

Therefore, according to the present invention, in the punch press working of the inner lead which is the final manufacturing process of the lead frame,
The purpose is to improve the accuracy of the shape and position of the inner lead.

Another object of the present invention is to provide a method for easily and reliably preventing cracks that may occur in the external leads in the external lead bending step, which is the final manufacturing step of the lead frame.

[0021]

In order to achieve the above object, in the method of manufacturing a lead frame for a semiconductor device of the present invention, in order to homogenize internal stress after the lead of the 42 alloy lead frame is pressed. The residual stress annealing is performed at high temperature for a short time.

According to one aspect of the present invention, after the inner lead of the semiconductor device lead frame is punched by pressing the plate, the residual stress annealing is performed at a high temperature for a short time. The high temperature short time here is, specifically, a temperature of 700 ° C. for 3 to 6 minutes.

According to another aspect of the present invention, after the outer lead of the 42 alloy lead frame is punched out by pressurization, residual stress annealing is performed at high temperature for a short time to change the material hardness of the burring face of the outer lead to Vickers hardness of 180 to 220. Soften. The high temperature short time here is a time of longer than 0.5 minutes but shorter than 1.5 minutes at a temperature of 700 ° C. Particularly, it is preferable that the residual stress annealing is performed at a temperature of 700 ° C. for 1 minute.

[0024]

When the lead frame for a semiconductor device is manufactured by the manufacturing method constructed as described above, not only the internal residual stress of the internal lead caused by punching is moderated by the residual stress annealing at high temperature for a short time, but also Since the internal residual stress due to the elongation of the guide rail generated in the press working step is also alleviated, the influence on the internal lead adjacent to the guide rail can be prevented.

Therefore, if the lead frame for a semiconductor device is taken out and cut into a sheet after the residual stress annealing,
Inner leads are finished to desired dimensions. Further, when performing the residual stress annealing, it is possible to correct the meandering by applying an appropriate tensile force to both ends of the metal strip to balance the tensile force.

When the material hardness of the burring surface of the external lead is softened to a Vickers hardness of 180 to 220, the tensile strength increased in the press working process is lowered and the elongation is increased and recovered. Therefore, peeling of the solder plating, cracking of the mold resin portion, etc. can be prevented at the time of external lead bending processing which is the final manufacturing process of the lead frame, and in the present invention, since the material is heated for a short time, a crystal grain growth phenomenon is observed in the material. Since it is not present, it is possible to prevent the surface of the lead bent portion from being rough.

[0027]

EXAMPLES Examples will be described with reference to the drawings.

[Example 1] In a process of punching a lead frame metal strip made of 42 alloy material having a plate thickness of 0.25 mm by a progressive die, when the internal lead processing step is completed, the metal strip is reeled. It was wound into a shape and run in a reducing hoop furnace having a furnace temperature of 700 ° C. and a furnace length of 6 m at a feed rate of 1 to 2 m / min to perform residual stress relief annealing.
During the annealing, an appropriate tensile force of 3 to 4 kg is applied to both ends of the metal strip.
f was added. The elongation (μm) of the total pitch of the metal strips emitted from the hoop furnace was measured. The results are shown in A of Table 1.

[Comparative Example 1] In the same manner as in Example 1, in punching a metal strip for a lead frame by a progressive die, when the internal lead processing step was completed, residual stress relief annealing was not performed and the total pitch was reduced. Elongation (μm) was measured. The results are shown in B of Table 1.

It is clear that the elongation of the total pitch can be suppressed by performing the residual stress removing annealing.

[0031]

[Table 1]

[Example 2] When a metal strip of 42 alloy material having a plate thickness of 0.25 mm was punched by external leads, it was found to be work-hardened by the pressure of the plate pressing during punching. This was subjected to a residual stress relief test under the conditions shown in Table 2. All atmospheres were reducing. The evaluation of the test results is shown in Table 2.

From the evaluation of Table 2, it can be seen that the best softening is obtained under the annealing condition of 700 ° C. for 1 minute.

By this annealing, the surface layer on the burring surface of the outer lead is softened to Vickers hardness of 180 to 220. Therefore, it is possible to prevent the occurrence of defects in the lead bending process which is the final step of the lead frame. Further, the bending conditions can be kept constant, and a stable lead frame member can be provided.

[0035]

[Table 2]

[Embodiment 3] A lead made of 42 alloy having a thickness of 0.15 mm and elongated in a direction perpendicular to the rolling direction was annealed at 700 ° C. for 1 minute in Embodiment 2, and then a lead bending measuring machine was used. One end of the lead was fixed to the, and a predetermined load was applied to the other end of the lead to perform a bending fatigue test.

The results are shown as A in Table 3.

[Comparative Example 3] A lead made of 42 alloy having a thickness of 0.15 mm, which was elongated in a direction perpendicular to the rolling direction, was fixed at one end of the lead to a lead bending measuring machine without annealing. A bending fatigue test was performed by applying a predetermined load to the end.

The results are shown in Table 3B.

[0040]

[Table 3]

In the non-residual stress-removed annealed product (B), there was a difference in fatigue strength depending on the lead surface specification and sag surface specification of the lead, and the fatigue surface specification was low in fatigue strength.

In the residual stress relief annealed product (A), there was no difference in the fatigue strength depending on the lead surface specification and the sag surface specification of the lead. This is a result of the material of the lead surface of the lead being softened by the residual stress removing annealing, and the fatigue strength of the lead surface specification being improved.

[0043]

Since the present invention is constructed as described above, it has the following effects.

Since the accuracy of the shape position of the inner lead generated in the step of pressing the lead frame is improved and the bending crack of the outer lead is reduced, the yield in the semiconductor assembly work using the lead frame is improved.

[Brief description of drawings]

FIG. 1 is a plan view of a lead frame to which the present invention is applied.

[Explanation of symbols]

 1 lead frame 2 inner lead 3 guide rail 4 outer lead

Claims (5)

[Claims] 1. A method of manufacturing a lead frame for a semiconductor device, which comprises performing high-temperature short-time residual stress annealing for homogenizing internal stress after press working the leads of a 42 alloy lead frame for a semiconductor device. 2. The method of manufacturing a lead frame for a semiconductor device according to claim 1, wherein after the inner leads of the lead frame for a semiconductor device are punched out by pressing the plate, high temperature and short time residual stress annealing is performed. 3. The residual stress annealing is performed at a temperature of 700 ° C. for 3 to 6
The method of claim 2, wherein the method is performed for minutes. 4. A method of softening the material hardness of the burring surface of the outer lead to a Vickers hardness of 180 to 220 after press-punching the outer lead of the 42 alloy lead frame for a semiconductor device, followed by high temperature and short time residual stress annealing. A method for manufacturing a lead frame for a semiconductor device, comprising: 5. The residual stress annealing is 0.5 at a temperature of 700 ° C.
The method of claim 4, wherein the method is performed for a time longer than a minute but shorter than 1.5 minutes.