JPH0261330B2 - - Google Patents

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a method for reducing residual strain in a metal strip, and more particularly, it relates to a method for reducing residual strain in a metal strip, and more particularly, to This invention relates to a new technique proposed for the purpose of reducing the shear strain remaining in the strip, thereby improving the processing accuracy of the strip in subsequent processes.

"Prior Art and Its Disadvantages" As a means of manufacturing a sufficiently thin metal strip (this is a general term for thin and flexible metal strip-shaped materials, and is also called a metal ribbon), it is necessary to prepare a desired product sheet in advance. A commonly used method is to apply a slitting shear to a wide metal strip that has been expanded to a certain thickness, and then shear it in the longitudinal direction to obtain a plurality of narrow metal strips. When a metal strip is manufactured by shearing a metal strip in this way, the shear strain imparted by the slitting shear remains in the metal structure of the slit edge of the metal strip. . That is, the edge of the sheared metal strip has a first
As shown in a of the figure, significant elongation deformation has occurred, and when the distribution of residual stress due to this elongation deformation in the sheet width direction is observed, it can be seen that large compressive stress has been generated as shown in b. If this strain is left to remain, depending on the use of the metal strip, it may become an obstacle that disturbs the processing accuracy in subsequent steps.
For example, as shown in FIG. 2, a metal strip 10 supplied as a punching material for a lead frame for an integrated circuit element has an aluminum strip 10 of a predetermined width attached to the center of the surface of a metal base material 12 made of 42% nickel steel. By punching and bending this metal strip 10, a lead frame 16 having the shape shown in FIG. 3 is obtained. In this case, if a metal strip containing significant residual strain at the edge of the slit is used as the processing material as described above, the leads 18 formed on the lead frame 16 will be deformed in the width direction as the residual strain is released. However, this results in a situation where the distance dimensions a ₁ and a ₂ between the opposing ends of each lead 18 become non-uniform. If the spacing between the lead ends becomes uneven in this way, it becomes difficult to automatically position the aluminum lead wires (not shown) of the integrated circuit chip so that they face the aluminum cladding of the lead ends. This will seriously impede the bonding work.

Therefore, in order to easily observe the tendency of internal strain remaining at the edge of the metal strip, the metal strip was photoetched to form comb-like strips in the longitudinal direction, and each strip was The degree and distribution of strain was determined based on the degree of deformation. First, when the sheared metal strip 10 was subjected to the photoetching process, as shown in FIG. When released, they each exhibited a tendency to curve inwardly toward each other. In view of the fact that the strain remaining at the edge of the metal strip affects the finishing accuracy of the product in the subsequent process, low-temperature annealing methods, for example, have been implemented as a means to remove the harmful strain. There is. However, this low-temperature annealing method requires an expensive continuous bright annealing furnace for annealing in a stream of reducing or non-oxidizing gas, and has the disadvantage of increasing equipment costs. In addition, the melting point of aluminum, which is used as a cladding for the lead frame material of integrated circuit devices, is as low as 660°C, and when exposed to temperatures of 550°C or higher, the interface between aluminum and 42% nickel steel base material will melt. The problem is that an intermetallic compound of aluminum and iron is formed, and this compound exhibits significant brittleness and causes cracks during post-processing. For this reason, annealing must be performed at a temperature of 550°C or lower, but at a temperature of 550°C or lower,
This is not sufficient to reduce residual strains inherent in the metal strip. Therefore, there is a need to establish a method for reducing shear strain at or near room temperature without exposing the metal strip to high temperatures.

Therefore, as a result of various studies in view of the above-mentioned request, the inventor of the present application found that if a metal strip with residual strain as shown in FIG. It was found that the residual strain was canceled out by the stress of 100 mL, and was significantly reduced to a practically negligible extent.

``Object of the Invention'' Therefore, the present invention reduces the shear strain remaining at the edge of a metal strip at room temperature without using any special equipment, and improves the finishing accuracy during post-processing of the metal strip. The purpose is to improve.

"Means for Solving the Problems" In order to overcome the above-mentioned drawbacks and achieve the intended purpose, the method for reducing residual strain in a metal strip according to the present invention involves shearing a wide metal strip in the longitudinal direction. When you do,
In order to reduce the shear strain remaining at the edge of the metal strip obtained by shearing, the metal strip is cut by a pair of cemented carbide rolling rolls whose rotating axes are aligned vertically. It is characterized by rolling at a reduction rate of 3 to 14%.

Further, in order to similarly achieve the above object, a method for reducing residual strain in a metal strip according to another invention of the present application is such that when a wide metal strip is sheared in the longitudinal direction, the resulting metal strip is In order to reduce the shear strain remaining at the edge, the metal strip is rolled twice at a reduction rate of 3 to 10% using a pair of forged steel rolling rolls whose rotating axes are aligned vertically. Characterized by rolling.

Next, a method for reducing residual strain in a metal strip according to the present invention will be described with reference to preferred embodiments.

Example 1 A metal strip made of 42% nickel steel, which is suitably used as a material for lead frames for integrated circuits, was sheared in the longitudinal direction by slitting shear to a width of 23.1 mm.
A metal strip with a thickness of 0.31 to 0.25 mm was obtained. Next, this metal strip was rolled by being passed between a pair of upper and lower cemented carbide rolling rolls made of, for example, tungsten carbide sintered with cobalt. The rolling reduction ratio at this time was adjusted appropriately to a value sufficient to cancel out the strain remaining at the edge of the slit of the metal strip, and was set in the range of 3 to 14% as described later. It was found to be suitable (by the way, the rolling reduction ratio is calculated as follows: When the thickness of the rolled material at the roll entrance is h ₁ and the thickness at the exit is h ₂ ,
(expressed as an index of (h ₁ − h ₂ )/h ₁ (%)). In other words, the reduction rate of the metal strip on the rolling roll is 3 to 14%.
When the metal strip was rolled once in the range of , and the photo etching was applied to the metal strip,
As shown in FIG. 4b, the distribution of residual stress became very small, and no bending deformation was observed in the comb-like strips at the edge portions of the strip 10. Also, using this metal strip, a lead frame for an integrated circuit element as shown in Fig. 3 was created, and the difference in spacing between the lead ends (a ₁
-a ₂ ) and the rolling reduction ratio, a curve shown as a solid line in FIG. 5 was obtained. This curve clearly shows that the rolling reduction rate that can suppress the gap size difference (a ₁ -a ₂ ) as low as possible is within the range of about 3 to 14%.

Note that when this rolling reduction rate is further increased to exceed 14%, the cross section of the metal strip 10 shown as a rectangle in a of FIG. 6 is expanded in the width direction as shown in b, and both ends are There is a marked tendency for rounding (radius R) at the edges. As a result, metal strip 1
In the vicinity of both end edges of 0, the elongation in the length direction becomes smaller by the amount of expansion in the width direction, resulting in an elongation distribution shown in c in Fig. 6, and d in Fig. 6.
As shown in the figure, the distribution is such that tensile stress remains at the edges. When this metal strip is photo-etched, the strips at both end edges exhibit outward bending deformation, as shown in FIG. It turns out that this method is not effective in reducing residual distortion.

Example 2 The same 42% nickel steel metal strip used in Example 1 was sheared in the longitudinal direction using a slitting shear to obtain a metal strip with a width of 23.1 mm and a thickness of 0.29 to 0.25 mm. Next, this metal strip was passed between a pair of upper and lower forged steel rolling rolls, and rolled at a reduction ratio of 3 to 10%. However, when the photoetching was applied to a metal strip that had been passed through a rolling roll once within the range of the rolling reduction ratio and the residual stress distribution was observed, the strips at both end edges were It was found that each was bent inward and the residual strain was not reduced. This is because the Young's modulus of the forged steel rolling roll is low, so the roll surface itself curves during rolling, causing an edge drop phenomenon in the metal strip. In other words, as shown in FIG.
As shown in FIG. 7B, a large so-called edge drop occurs, and this edge drop portion A is stretched excessively in the length direction and compressive residual stress is generated therein, resulting in the bending phenomenon shown in FIG. 7A.
Therefore, in order to avoid the above-mentioned bending phenomenon, when the edge was passed through the forged steel rolling roll again with an area reduction rate of 3 to 10%, the edge drop part B was also rolled down uniformly as shown in Fig. 8c, and the strain was reduced. The distribution in the sheet width direction became uniform. Then, in this way, 3
When the photoetching was applied to the metal strip after passing it twice at a rolling reduction rate of ~10%, the result was shown in Fig. 7b.
As shown in the figure, the bending deformation of the strip at both end edges was eliminated. In addition, this metal strip was used to stamp and form a lead frame for an integrated circuit element as shown in Figure 3, and the correlation between the gap size difference (a ₁ - a ₂ ) between the lead ends and the rolling reduction ratio was determined. When I plotted, the fifth
A curve indicated by a broken line in the figure was obtained. That is, this curve shows that in order to reduce the residual shear strain using a forged steel roll, it is sufficient to pass the roll twice at a rolling reduction of 3 to 10%.

In Example 1 described above, a roll made of cemented carbide was used as the rolling roll, and in Example 2, a roll made of forged steel was used as the rolling roll. As described above, the reason for selectively using cemented carbide rolling rolls and forged steel rolling rolls is that the latter can be manufactured at a much lower cost than the former, and high-precision rolls can be manufactured easily. It is required that it is possible. That is, by using forged steel as the material, manufacturing costs can be suppressed and high-precision rolls can be easily manufactured, so if these points are taken into consideration, the latter has greater advantages than the former. However, in terms of durability, the former cemented carbide roll is overwhelmingly superior to the latter forged steel roll. Therefore, both
The most appropriate use is determined by weighing the various matters mentioned above.

In both the first and second embodiments, either cold rolling or warm rolling can be suitably employed as the rolling method.

As explained in detail above, according to the method of the present invention, the shear strain remaining at the slit edge of a metal strip manufactured by shearing a metal strip can be canceled out by applying stress during rolling. It can be reduced to an almost negligible level in processing. Therefore, inconveniences such as the residual strain being released during processing in the subsequent process and impairing finishing accuracy can be avoided, and the process can be carried out at room temperature without the need for expensive and special dedicated equipment. It has many beneficial advantages.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing elongation deformation and residual stress distribution occurring at the edge of a sheared metal strip;
Figure 2 is a perspective view of a metal strip coated with aluminum, Figure 3 is a perspective view of a lead frame for an integrated circuit element, and Figure 4 is a metal strip coated with comb-like strips by photoetching. Fig. 5 is a graph showing the correlation between the difference in lead spacing of the lead frame and the rolling reduction rate, and Fig. 6 is a graph showing the correlation between the lead frame lead spacing difference and the rolling reduction rate, and Fig. 6 is a graph showing the relationship between the lead frame and the rolling reduction ratio of 14% or more. FIG. 7 is an explanatory diagram for determining the bending deformation state similar to FIG. 4, and FIG. 8 is an explanatory diagram of the edge drop phenomenon.

Claims (1)

[Claims] 1. When a wide metal strip is sheared in the longitudinal direction,
In order to reduce the shear strain remaining at the edge of the metal strip obtained by shearing, the metal strip is cut by a pair of cemented carbide rolling rolls whose rotating axes are aligned vertically. A method for reducing residual strain in a metal strip, characterized by rolling the metal strip at a reduction rate of 3 to 14%. 2 When a wide metal strip is sheared in the longitudinal direction,
In order to reduce the shear strain remaining at the edge of the metal strip obtained by shearing, the metal strip is rolled down using a pair of forged steel rolling rolls whose rotating axes are aligned vertically. A method for reducing residual strain in a metal strip, which comprises rolling twice at a rate of 3 to 10%.