JPS62158525A - Residual deflection adjusting method for metal strip piece - Google Patents

Abstract

PURPOSE:To reduce the residual deflection in the metal organization and to improve the finishing accuracy of a lea frame by press-fitting a dissimilar metal to a metal strip piece within the range lower than the curve that each coordi nate of the limited roll surface roughness value and the rolling reduction rate value is plotted. CONSTITUTION:The metal strip piece that the dissimilar metal in a narrow width is press-fitted to the base metal of a strip like thin metal sheet is subjected to a roll rolling within the range of 13-30% rolling reduction rate with 0.8-1.3S roll surface roughness and within the range lower than the curve that each coordinate of 13% rolling reduction rate in case of 1.1S roll surface roughness, 22% rolling reduction rate in case of 1.18S roll surface roughness, 25% rolling reduction rate in case of 1.23S roll surface roughness and 27% rolling reduction rate in case of 1.35 roll surface roughness is plotted, in the perpendicularly intersecting coordinate that the roll surface roughness is taken on (y) axis and the rolling reduction rate on (x) axis. In this case, the inconve nience of the finishing accuracy being spoiled with the bend of the metal piece by the release of the residual deflection can be avoided in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for adjusting residual strain in a metal strip, and more particularly, to a method for crimping dissimilar metals, which is preferably used as a lead frame molding material for an integrated circuit element, for example. The present invention relates to a method for adjusting the residual strain inherent in a metal strip to such an extent that it does not cause any problem when it is processed into a lead frame.

BACKGROUND OF THE INVENTION For example, as shown in FIG. 2, a metal strip 10 that is a press punched material has an aluminum strip of a predetermined width at the center of the surface of a base material 12 made of a strip-shaped thin metal plate made of 42% nickel steel. The piece 14 is crimped (clad) in the longitudinal direction. Then, by subjecting this metal strip 1o to the required punching press and bending processes, a lead frame 16 for an integrated circuit element having the shape shown in FIG. 3 is obtained.

The fence-like legs 16a that are bent and extend on both sides of the lead frame 16 are cut in the direction of line A-A at the end of the integrated circuit (IC) manufacturing process to form a large number of lead pieces for board connection. It will be one day.

Problems to be Solved by the Invention However, in the manufacturing process of the metal strip 1o, mechanical strain is generated and this strain inevitably remains inside the strip. Therefore, if the residual amount of strain exceeds the allowable limit, there is a problem that the lead piece 18 will be distorted or deformed.

For example, in order to manufacture the metal strip 1o, multiple strips of aluminum are crimped (clad) at predetermined intervals on a wide metal plate that has been expanded to a desired product thickness in advance, and the metal plate is clad with a slitting shear. Longitudinal shearing is commonly employed to obtain multiple aluminum clad metal strips.

However, the shear strain imparted by the slitting shear remains as internal stress in the metal structure of the sheared edge of the metal strip 10 that has been subjected to this shearing process. That is, significant elongation deformation occurs at the edge of the sheared metal strip 1o, and based on this elongation deformation, large compressive stress is generated in the width direction of the sheet. Furthermore, the enormous pressure stress applied to the metal base material 12 during pressure bonding of the aluminum 14 often remains as it is.

Therefore, when the aluminum clad metal strip 10 with these residual strains is pressed as a raw material, the residual strains are released in each lead piece 18 formed on the lead frame 16, and the tendency to deform in the width direction is reduced. show. For example, as shown in FIG. 3, a situation arises in which the distances a1 and a2 between the opposing ends of each lead piece 18 become uneven. If the spacing between the lead ends becomes uneven in this way, the aluminum lead wires (not shown) of the integrated circuit chip
Automatic positioning of the lead end so as to face the aluminum crimping part 14 becomes difficult, and this causes a serious hindrance to automatic bonding work in a subsequent process.

Therefore, in order to easily observe the tendency of internal strain remaining at the edge of the metal strip 1o, as shown in FIG. A large number of pieces 20 are formed.

It is generally practiced to determine the degree and distribution of strain based on the degree of deformation of each strip 20. For example, when the metal strip 10 is photo-etched, the strain remaining in the metal structure of the strip 20 on the edge side is released.
As shown in FIG. 4(a) or FIG. 4(b), it generally shows a tendency to curve inwardly or outwardly, respectively. Further, when there is almost no residual strain, each strip 20 extends linearly without being deformed, as shown in FIG. 4(c).

According to users' long-standing knowledge, the most suitable lead frame for integrated circuit devices is the 4th one.
The metal strip 10 exhibits a linear tendency as shown in FIG. 4(c), and then, depending on the degree of deformation, the metal strip 10 exhibits a tendency to curve inward as shown in FIG. 4(a). And Figure 4 (b
) metal strips 10 that exhibit a tendency to deform outwardly are often unsuitable for use as lead frames. Note that this photoetching inspection is carried out for each coil of the metal strip 10 in each production lot, and is used to determine whether or not the coil can be shipped to a user.

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, aluminum 1 adhered to the base material 12 of the metal strip 10
4 has a low melting point of 660℃, and the material has a melting point of 550℃.
When exposed to temperatures above, an aluminum-iron intermetallic compound is formed at the interface between the aluminum and the 42% nickel steel base material, and this compound exhibits significant brittleness and has the disadvantage of causing cracks during post-processing.

For this reason, annealing must be carried out at a temperature below 550'C, but temperatures below 550'C are not sufficient to reduce the residual strain inherent in the metal strip. Therefore, there is a need to establish a method for reducing residual strain at or near room temperature without exposing the metal strip to high temperatures.

Introduction and Embodiments of the Invention The inventor of the present invention, as a result of considering various means in view of the above-mentioned request, came up with the idea of eliminating the residual strain by subjecting the sheared metal strip to machining rolling. We found that the degree can be adjusted.

As for the use of the lead frame, any residual strain that shows the linear trend shown in FIG. 4(c) or the residual strain that slightly deforms inward as shown in FIG. 4(a) is practical. Since there is no problem, when this roll rolling was carried out under various conditions, it was found that the amount of strain after rolling had a significantly changing correlation between the roughness of the roll surface and the rolling reduction ratio. It turns out.

For example, a metal strip 1o formed by crimping a narrow dissimilar metal 14 onto a metal base material 12 is rolled by passing it between a pair of upper and lower work rolls (not shown) in a roll-type cold rolling mill. Preferably, the metal base material 12 is a nickel-based alloy, and the dissimilar metal 14 is aluminum. At this time, the roll surface roughness of the work roll was set to 1.1S.
Various changes were made within the range of ~3.98, and the rolling reduction was changed to 13.
% to about 30%, and the tendency of residual strain developed in the metal strip after each rolling was determined by the photoetching method described above. Then, calculate this result as the roll surface roughness S
) on the y-axis and the rolling reduction rate (%) on the x-axis and plotted, the curve C shown in Figure 1 was plotted.
I got it.

This curve C indicates the boundary where the residual strain becomes zero (0), and in the area above this, the strips 20 tend to open outward as shown in FIG. 4(b).

The metal strip 1o is often unsuitable for the lead frame.

Furthermore, in the area A below the curve C, the strip 2o tends to open inward as shown in FIG. 4(a), and in this case, as described above, the metal strip 1o is Can be used as a lead frame. However, the surface roughness of the lead frame product is within the standard 1. Since the user specifications require that the lead frame be within O3, taking this into consideration, in area A of the graph shown in Figure 1, the area that can be effectively used as a lead frame is limited to the shaded area. It will be done. That is, the range in which the metal strip 10 can be used as a lead frame is within the range where the roll surface roughness is 0.8 to 1.3 S and the rolling reduction is 13 to 30%. The upper limit that can be used as a lead frame is the boundary defined by the curve C, and it has been confirmed through multiple experiments that this boundary line can be obtained by plotting the following coordinates.

Roll surface roughness 1. IS→Reduction rate 13% Roll surface roughness 1.12S→Reduction rate 16% Roll surface roughness 1
．． 18S→Reduction rate 22% Roll surface roughness 1.23S→Reduction rate 25% and Roll surface roughness 1.3S→Reduction rate 27% However, even in this case, the closer to the curve C, the smaller the residual strain. Therefore, it goes without saying that it can be suitably used as a lead frame.

Effects of the Invention As described above, according to the method for adjusting the residual strain of a metal strip according to the present invention, a metal strip formed by crimping a narrow dissimilar metal onto a base material of a strip-shaped thin metal plate (for example, a lead frame for an integrated circuit element) By rolling an aluminum crimped metal strip (used in aluminum crimped metal strips) with the required correlation between roll surface roughness and rolling reduction, the strain added during the manufacturing process and remaining in the metal structure of the strip can be reduced. can be reduced to an almost negligible level in processing. Therefore, for example, in the post-process of press-molding a lead frame of an integrated circuit element, the release of the residual strain causes the lead end to bend, resulting in a loss of finishing accuracy, and inconveniences such as making automatic bonding impossible. It has many beneficial advantages, such as being avoided.

[Brief explanation of drawings]

Figure 1 shows the roll surface roughness (S) on the y-axis and the rolling reduction rate (%).
It is a graph diagram consisting of a rectangular coordinate system with the X axis taken as
The correlation between roll surface roughness and rolling reduction rate is shown. Figure 2 is a perspective view of a metal strip crimped with aluminum, Figure 3 is a perspective view of a lead frame for integrated circuit elements, and Figures 4 (a) to 4. FIG. 4(c) is a schematic explanatory diagram showing elongation deformation occurring at the outer end of a strip-shaped strip obtained by photo-etching a sheared metal strip. 10...Metal strip 12...Base material 14...
Aluminum crimp part 16...Lead frame 18...Lead piece 20.
...Strip-shaped strip FIG, 2 FIG, 3, FIG, 4 +01 [bl(C1

Claims (2)

[Claims] (1) In an orthogonal coordinate system in which the roll surface roughness is taken as the y-axis and the rolling reduction is taken as the Saga 0
．． When the roll surface roughness is 1.1S, the rolling reduction is 13%, and when the roll surface roughness is 1.12S, the rolling reduction is 16%, and the roll surface roughness is in the range of 13 to 30% at 8 to 1.3S. Sa1
．． At 18S, rolling reduction rate is 22%, roll surface roughness is 1.23S
Residual strain of a metal strip characterized in that it is rolled within a range below the curve obtained by plotting the respective coordinates of a rolling reduction of 25% and a roll surface roughness of 1.3S and a rolling reduction of 27%. Adjustment method. (2) The method for adjusting residual strain in a metal strip according to claim 1, wherein the base material is a nickel-based alloy and the dissimilar metal is aluminum.