JP2000109958A - MATERIAL FOR Fe-Ni LEAD FRAME EXCELLENT IN ETCHING WORKABILITY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the material for an Fe-Ni lead frame excellent in etching characteristics such as etching working precision, working velocity or the like. SOLUTION: This material is composed of an alloy contg., by weight, 30 to 80% Ni, and the balance substantial Fe, in which, in the regions of the center of the sheet thickness and at least to >=80% of the sheet thickness, the X-ray intensity ratio between (100)<001> which is the cubic orientation in the (111) pole figur in the normal direction of the sheet face and (221)<212> which is the twin direction thereof (X-ray count number ratio) Ir: (100)<001>/(221)<212> is 1.0 to 15. The main componental compsn. of the alloy is desirably composed of, by weight, <=0.1% C, <=0.5% Si, <=1.0% Mn, <=0.5% Cr, 40 to 60% Ni, and the balance essential Fe with inevitable impuritis.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention has good etching characteristics.
The present invention relates to a material for an Fe-Ni-based lead frame, and in particular, a cubic orientation (10
0) By suitably controlling the ratio of <001> and its twin orientation (221) <212>, it is intended to provide a lead frame material having excellent etching characteristics such as processing accuracy and processing speed. Is what you do. The present invention can also be used as a shadow mask material.

[0002]

2. Description of the Related Art In recent years, as represented by a flat package, the number of pins of a lead frame has been increased, and the required level of miniaturization processing has been increasingly higher. In general, lead frame materials are classified into two types, one for punching manufactured by punching and the other for etching with a ferric chloride solution. The latter is used for finer uses. You.

An IC semiconductor package using a lead frame is generally manufactured through the following steps. 1. 1. Photo-etching of the material (lead frame material), 2. a mounting process for mounting the lead frame on a resin mold; Bonding step for connecting the lead frame and the semiconductor element with a conductive wire. In the above step 1, good etching properties are required, in step 2, press moldability is required, and in step 3, plating properties and solderability are required. You. Further, the strength after processing is also necessary, which is necessary in order to prevent deformation such as warpage or bending at the time of bonding and to prevent a decrease in yield due to deformation during handling. Moreover,
Electric conductivity is also required to suppress heat generation due to current flowing through the leads and to ensure the operation stability of the semiconductor element.

[0004] For these reasons, a lead frame material to be subjected to an etching process has excellent etching characteristics, excellent workability at the time of press working, good solderability and plating property, and has good compatibility with semiconductor elements. There is no problem during bonding, the strength after processing is high and it is difficult to deform, the electric conductivity is high,
It is required to have excellent properties such as a low coefficient of thermal expansion at 200 ° C or lower, which is the actual operating temperature.

[0005]

In recent years, Fe-Ni alloys have high electric conductivity, and have been found to improve the stability of semiconductor elements, improve heat dissipation, and reduce the effective specific resistance by improving the shape (thinning) of leads. It has made great strides in terms of point, and furthermore, the improvements in pressability, plating properties, solderability, etc. are remarkable.
However, the fact is that much less study has been made on the improvement of the etching property of the Fe—Ni-based alloy. However, this etching process has a great effect on product quality variation and product yield, and is considered to be an important research topic in the future, along with the trend toward higher definition of mounting technology and increase in the number of pins.

An object of the present invention is to provide a Fe-Ni-based lead frame material having excellent etching characteristics such as etching accuracy and processing speed.

[0007]

Means for Solving the Problems In examining the above problems, the present inventors have observed an etched surface obtained at the time of etching and an observation result such as an etching factor which is an index of an etching speed. For the etching accuracy, it is important that the facets observed on the inner wall surface of the etched surface are dense and uniform,
It was also found that a large etching factor was important in terms of the etching rate. further,
Etching has an angle dependency (anisotropic) of the etching rate depending on the angle from the rolling direction, and it is effective to suppress this angle dependency as much as possible within the range of processing accuracy.
It has been found that a material having a high etching rate is required to perform etching more quickly.

[0008] The inventors of the present invention have conducted intensive studies based on the above findings. As a result, regarding the etching property of the lead frame material of the Fe-Ni-based alloy, factors affecting the processing accuracy at the time of etching and the etching rate were determined. It was effective to classify and understand the influencing factors, and it was concluded that it was effective to control the texture by the component composition, especially the crystal grain orientation. That is, the present invention relates to an alloy containing 30 to 80 wt% of Ni and the balance substantially consisting of Fe, wherein the center of the sheet thickness and at least 80% of the sheet thickness
In the above region, (100) <001>, which is the cubic orientation in the (111) pole figure in the normal direction of the plate surface, and its twin orientation
(221) X-ray intensity ratio with <212> (X-ray count number ratio) Ir: (1
(00) <001> / (221) <212> is a Fe-Ni-based lead frame material excellent in etching workability, characterized by being 1.0 to 15. In the present invention, the X-ray intensity ratio Ir
Can be said to be in the range of 1.5 to 10, more preferably 3.0 to 10.

In the present invention, the main component composition of the alloy is as follows: C: 0.1 wt% or less, Si: 0.5 wt% or less, Mn:
1.0 wt% or less, Cr: 0.5 wt% or less, Ni: 40 to 60 wt%, and the balance is preferably made mainly of Fe and unavoidable impurities.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration of the present invention will be described below in detail from both the processing accuracy during etching and the etching rate. Regarding the processing accuracy at the time of etching As a method of improving the processing accuracy at the time of etching, that is, the etching accuracy, first, there is a method of controlling the crystal grain size, that is, a method of making the crystal grains fine and uniform to suppress the roughness of the etched surface. This is because the larger the crystal grain, the larger the facet size that constitutes the etched surface,
As a result, the unevenness of the etched surface becomes large, and the shape of the lead portion, particularly the interface between the etched surface and the base material, becomes undesirably zigzag. For example, controlling the GS number according to JIS G 0551 within an appropriate range (6 to 12) is also considered to be an effective method.

In order to improve the accuracy of the etching, it is also effective to control the texture. This is not intended to suppress the roughness of the etched surface and improve the processing accuracy as in the control of the crystal grain size. This is an attempt to improve the cross-sectional shape itself after etching. Such a cross-sectional shape is affected by an index called an etching factor. That is, the etching factor is a measure for knowing how much the etching depth has progressed with respect to the etching that proceeds in the lateral direction (side etching). The larger this value is, the easier the etching progresses in the thickness direction. This is desirable in terms of accuracy. Factors affecting this etching factor include, from the etching conditions, specific gravity of the etching solution, temperature, pressure of the etching spray, and the like.
Texture, surface properties (adhesion with the resist film) and the like.

[0012] Based on such knowledge, the inventors of the present invention have focused on a texture that has a great influence as a factor on the material side and studied. As a result, the etching factor is
It was found that it increased when the cube orientation (100) <001> was developed. It was also found that the etching factor was strongly affected by the ratio (ratio) of the (100) <001> cubic orientation and the (221) <212> twin orientation in the pole figure. That is, as shown in FIG. 1, the etching factor is determined by this ratio (X-ray intensity ratio Ir: (100) <001> / (221) <
212>) gradually increased (etching factor F = kln (Ir), where k = 0.12), and was found to be linear with the logarithm of Ir. Therefore, the higher the X-ray intensity ratio Ir, the better the etching accuracy.

However, if the X-ray intensity ratio Ir is made extremely large, another problem occurs. That is, a phenomenon (anisotropy) in which the etching rate depends on the angle dependence of the etching, that is, the angle from the rolling direction, occurs. For example, if there is an extremely high accumulation of (100) <001>, the etchability tends to progress in the rolling direction and the direction perpendicular to the rolling direction, the facet shape has a specific direction, and the entire shape does not follow the processing shape , The roundness defined in Figure 1
(1 to 5 steps). This effect on the roundness is particularly pronounced when the X-ray intensity ratio: Ir is 15 or more. Therefore, the appropriate range of the X-ray intensity ratio Ir from the viewpoint of etching processing accuracy is 1.0 to 15, preferably
The range is from 1.5 to 10, more preferably from 3.0 to 10.

Regarding the etching rate (FIG. 2) The improvement of the etching rate not only shortens the time for obtaining the target processing shape and contributes to the improvement of the productivity, but also increases the etching amount in the plate thickness direction. Factor is increased, and as a result, it contributes to improvement of processing accuracy. Here, in order to increase the processing rate (etching rate) at the time of etching, the controlling factors of the etching rate, that is, the etching conditions (specific gravity of the etching solution, temperature, spray pressure, etc.), material factors (influence of chemical components, aggregation Organization)
Need to be controlled. Among these factors, C, Si, and Cr affect the chemical components. However, since all of them have an effect of lowering the etching rate, it is desirable that they be as low as possible. On the other hand, as described above, the control of the texture is also an important factor that affects the etching rate. That is, the accumulation of the (100) <001> orientation, which is the preferred dissolution orientation, is a necessary element for increasing the etching rate, and it is necessary to increase the accumulation of this orientation in order to improve the etching rate.

A technique that focuses on the crystal orientation for the etching processability has also been mentioned in Japanese Unexamined Patent Application Publication No. 3-97831, for example, "Relative X-ray intensity ratio of crystal plane by X-ray diffraction." Has a (200) plane strength of 50% or more
Fe-Ni system ". However, the diffraction line intensity based on Bragg's law with this diffractometer can only obtain specific information from the texture of the polycrystalline structure.
Generally, only diffraction intensities of specific low index planes such as (111), (200), (220), and (311) planes can be obtained. For example, the (221) plane, which is the twin orientation that is actually important for the etching properties, does not appear (due to various intensity factors of X-ray diffraction) in the diffraction of a face-centered cubic lattice such as an Fe-Ni alloy. Therefore, in the present invention, in consideration of such a point, two orientations in the pole figure considered to be important for the etching characteristics, namely, (100) <001> and its twin orientation (221) <21.
2>, the etchability is arranged and used as a more effective index.

The above material is, for example, Ni: 30 to 80 wt.
%, And the balance consisting essentially of Fe is subjected to annealing according to a conventional method, and before the final rolling, annealing temperature: 900 to 1150 ° C., soaking time: 5 Intermediate annealing for ~ 60 seconds, then cold rolling at least 50% or more, annealing temperature: 700-900 ° C, soaking time: 60-600 seconds for final production Can be. After that, if necessary, the hardness of the product is adjusted by performing temper rolling within a range of several percent to 20% according to the application. The reason for increasing the soaking time in the final annealing condition is to promote the development of (100) <001>, which is the preferential etching direction. In the above-described manufacturing method, it is preferable that each annealing condition is performed within a range illustrated in a, b, c, and d of FIG.

According to the findings of the present inventors, there is a correspondence between the etching rate and the etching factor affecting the etching accuracy, which also depends on the same index: X-ray intensity ratio Ir as described above. As the Ir increases, the etching rate increases. Therefore, when evaluating the etching property of the lead frame material, it is expected that there will be no problem if only the etching factor is considered as the evaluation criterion, but it is necessary to limit the appropriate range from the viewpoint of the etching rate for the following reasons. come. That is, as shown in FIG. 2, similarly to the etching factor, the etching rate increases in proportion to the logarithm of the X-ray intensity ratio Ir, and when the X-ray intensity ratio Ir becomes 1 or less, the etching rate sharply decreases. Therefore, to ensure a stable etching rate,
It is desirable to use a material having an X-ray intensity ratio Ir of 3 or more.
However, if the intensity ratio Ir becomes larger than a certain value, a problem occurs, and local uniformity of the etching rate is lost. For example, a region having a high etching rate and a region having a low etching rate are locally formed, thereby deteriorating the shape accuracy. For this reason, in order to suppress this, the existence of twin orientation (221) <212> which plays a role of an appropriate inhibitor is required, and the upper limit thereof is almost 15 at Ir.

As described above, the elements to be provided as a lead frame material having a good etching processing accuracy and an excellent etching rate include that the crystal grains are sufficiently fine and uniform, and that a trace component that hinders etching is used. Suppression, and that the X-ray intensity ratio Ir: (100) <001> / (221) <212> in the pole figure in the texture is in an appropriate range.

Accordingly, the present invention limits the following range as a range having favorable etching characteristics as a lead frame material from both the etching processing accuracy and the etching rate. That is, the present invention is an alloy containing 30 to 80 wt% of Ni, and the balance being substantially Fe, and in the center of the plate thickness and at least 80% or more of the plate thickness, in the normal direction of the plate surface. (111) Cube orientation in pole figure (1
The X-ray intensity ratio Ir (X-ray count number ratio) of (00) <001> and its twin orientation (221) <212> is 1. (100) <001> / (221) <212> is 1.
That is, a lead frame material of 0 to 15 was used.

In the present invention, the measurement conditions and definition of the X-ray intensity ratio Ir are as follows. That is, the (100) pole measurement was performed on the sample plate surface by the Schulz reflection method under the measurement conditions shown in Table 1, and (1) was obtained based on the pole figure obtained thereby.
00) The X-ray intensity in the <001> direction and the X-ray intensity in the (221) <212> direction are obtained. Here, each X-ray intensity is the maximum X-ray intensity
(Maximum X-ray count), the intensity is divided into 15 equal parts, and the contour line intensity corresponding to the intensities corresponding to (100) <001> and (221) <212> is read from the obtained pole figure. The intensity is defined as the respective X-ray intensity. The X-ray intensity ratio Ir is calculated based on the following formula based on the X-ray intensities of the (100) <001> direction and the (221) <212> direction thus obtained. It is. Ir = X-ray intensity of cubic orientation (100) <001> / twin orientation (221) <
X-ray intensity of 212>

[0021]

[Table 1]

Based on the X-ray intensity ratios of the (100) <001> direction and the (221) <212> direction obtained under the above conditions,
It is obtained based on the following equation. Ir = X-ray intensity of cubic orientation (100) <001> / twin orientation (221) <
X-ray intensity of 212>

Various representative pole figures based on these relationships are shown in FIGS. These figures are shown in Table 3
FIG. 3 is a pole figure corresponding to samples,,, and alloys. For example, the sample alloy shown in FIG. 3 has an X-ray intensity ratio Ir of 1.4 and is an example conforming to the present invention. The properties of the etched holes after etching are rough and the roundness is good. However, the etching factor and the etching rate are rather small and the processing accuracy is not optimal, and the processing accuracy is slightly poor. The sample alloy of FIG. 4 is also an example conforming to the present invention, and the X-ray intensity ratio Ir is 3.5, which is an appropriate range. The properties of the etched holes after the etching are rough and the roundness is good, the etching factor and the etching rate are sufficient, and no defects in processing accuracy occur. However, the sample alloy of FIG. 5 has an X-ray intensity ratio Ir of 0.79.
This is an example in which the present invention is incompatible with the present invention.

On the other hand, the alloy of the sample shown in FIG.
Since Ir is too large as 21.2, this is an example of non-compliance with the present invention, and the roundness of the etching hole is poor, and the roughened surface of the etched surface is not suitable as a lead frame material.

The present invention is intended to define an appropriate range of the azimuth component based on the pole figure and thereby improve the etching accuracy of the lead frame material. It is effective to adopt First, an alloy material having a predetermined composition is cast,
This is hot-rolled according to a conventional method, and if necessary, recrystallization annealing is subjected to pickling or the like, for example, intermediate cold rolling,
Thereafter, intermediate annealing is performed before final rolling in which at least 50% or more of cold rolling is performed. This intermediate annealing is performed in the cube orientation (1
00) This is to control the development of <001>. This intermediate annealing is performed at a temperature of 900 to 1150 ° C. If the temperature is too low (<900 ° C), the cubic orientation in the final product will develop too much and the proportion of twin orientation (221) <212> will be low, resulting in rough surfaces on the etched surface. This causes a problem that the circularity is disturbed. It is considered that such a phenomenon occurs because the effect of a so-called inhibitor of etching disappears when the ratio of the twin orientation is relatively small, and the etching proceeds rapidly in the direction of a specific surface. On the other hand, when the temperature of the intermediate annealing is high (>
1150 ° C.), the cubic orientation is poorly developed, the etching rate is reduced, and the processing accuracy is reduced during photofabrication etching on the lead frame.

The soaking time in the intermediate annealing is as follows:
The range of 5 to 60 seconds is preferable. If this time is shorter than 5 seconds, recovery and recrystallization are not sufficiently performed, and the structure of a mixed particle state is maintained, thereby lowering the etching accuracy. On the other hand, if this time is longer than 60 seconds, coarse grains are formed, the development of the cubic orientation is reduced, and a mixed grain structure is also formed, resulting in a decrease in etching processing accuracy.

Next, in the present invention, it is effective to regulate not only the conditions of the intermediate annealing described above but also the conditions of the final annealing. That is, the final annealing is (1
00) To promote the development of <001> and to finely and uniformly arrange the crystal grains of the product, maintain the etching rate and do not impair the processing accuracy, 700-900 ° C
It is effective to perform the treatment at an annealing temperature of 60 to 600 seconds. The reason is that, in the final annealing, if the annealing temperature is lower than 700 ° C., the recrystallization becomes insufficient, while if it is higher than 900 ° C., the grains are coarsened and the etching accuracy is reduced.

Note that the soaking time for this annealing depends on the degree of growth of individual crystal grains and development of crystal orientation.
It is preferably within the range of ~ 600 seconds. For example, if the soaking time is short (<60 seconds), the cubic orientation will be insufficiently developed, and the processing speed will be deteriorated due to a decrease in the etching rate. On the other hand, when the soaking time is long (> 60 seconds), the crystal grains become coarse, and the twin orientation develops too much with respect to the cubic orientation, which also lowers the processing accuracy.

There is an appropriate range for these annealing conditions, and a region surrounded by a, b, c, and d in FIG. 7 is preferable.

Next, the reasons for limiting the component range of the present invention will be described. C: If C is contained in an amount of 0.01 wt% or more, carbides precipitate and the etching rate is reduced. In addition, since the proof stress increases and the springback increases, the workability during molding deteriorates. For this reason, C was limited to 0.01 wt% or less. Si: Si is one of the deoxidizing components. When the content of Si is large, the etching rate is reduced as in the case of C. In addition, the etching speed varies due to the non-uniformity of the etching due to the segregation itself, and the lead shape is deteriorated. Therefore, the amount of Si was limited to 0.5 wt% or less. Mn: Mn is one of the deoxidizing components similarly to Si, but since it combines with S which is harmful to hot workability to form MnS, the addition of an appropriate amount is effective for improving hot workability. . On the other hand, if the addition amount is too large, the coefficient of thermal expansion is increased, so that the difference in the coefficient of thermal expansion from the semiconductor element becomes large, making it unsuitable as a base material. Considering this, the appropriate range is 0.05-1.0 wt
%, Preferably 0.1 to 1.0 wt%, more preferably 0.5 to 1.0 wt%.
1.0 wt%. Ni: Ni is a main constituent element of the material of the present invention, and if its content is less than 30% by weight, the thermal expansion coefficient becomes large, and there is a possibility that martensitic transformation may occur and etching may become non-uniform. Processing accuracy deteriorates. However,
If it exceeds 80% by weight, the coefficient of thermal expansion also increases, which makes it unsuitable as a base material for semiconductor devices. The preferred range of the Ni content is 30 to 60 wt%, more preferably 40 to 50 wt%. Cr: Cr is an element inevitably mixed from raw materials such as refractories and scraps. When the Cr is high, the thermal expansion coefficient increases and the etching rate decreases. For this reason, the amount of Cr was limited to 0.5 wt% or less.

In the present invention, the X-ray intensity ratio Ir
The reason for limiting the thickness to the center and at least 80% of the sheet thickness (the sheet surface side is the center of the sheet thickness) is that the temper rolling (usually a rolling reduction of 20 to 40%) This is because specifying the degree of aggregation in a region excluding this part can better show the average of the entire board since the degree of aggregation of the element decreases. After temper rolling, SR treatment (stress relief annealing) is performed, but this does not affect the texture.

[0032]

EXAMPLE An ingot of the alloy of the present invention having the components shown in Table 2 was used.
After melting by vacuum degassing process, hot rolling
A hot-rolled sheet of 5 mm was manufactured by repeatedly performing cold rolling and annealing under the conditions shown in Table 4, adjusted to a product thickness of 0.22 t, and then formed into a lead frame product through an actual photo-etching process. An evaluation was performed. In the table, 1 to 5 are samples obtained under the production conditions of the present invention, and 6 to 10 are comparative materials. In Nos. 6 to 8, the value of the X-ray intensity ratio Ir is low, the etching factor is small, and the etching rate is low, so that poor etching accuracy often occurs. For 9, X
The line intensity ratio is too high, and the etched shape is defective (deterioration in roundness) and the etched surface is rough. further,
With respect to 10 and 11, the ranges of C and Si are out of the specified ranges, respectively, so that the etching rate is reduced and the etched surface is roughened, and the occurrence of poor etching accuracy is increasing. When the characteristics of the lead frame product obtained by the present invention after etching were evaluated, all of the pressability, plating property and solderability were good.

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

As described above, according to the present invention, it is possible to provide a Fe-Ni-based lead frame material having good etching characteristics such as etching accuracy and etching speed.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an X-ray intensity ratio (Ir) and an etching factor and an etching anisotropy (roundness).

FIG. 2 is a graph showing a relationship between an X-ray intensity ratio (Ir) and an etching rate.

FIG. 3 is a pole figure of Table 3, Sample No.

FIG. 4 is a pole figure of Table 3, Sample No.

FIG. 5 is a pole figure of Table 3, Sample No.

FIG. 6 is a pole figure of Table 3, Sample No.

FIG. 7 is a graph showing an appropriate range of annealing conditions used in the present invention.

Claims (2)

[Claims] 1. An alloy containing 30 to 80% by weight of Ni with the balance being substantially Fe, and in the center of the sheet thickness and at least 80% or more of the sheet thickness, the ( 111)
X-ray intensity ratio Ir of (100) <001> which is the cubic orientation in the pole figure and (221) <212> which is the twin orientation thereof: (100) <001> /
(221) A Fe-Ni-based lead frame material excellent in etching workability, wherein <212> is from 1.0 to 15. 2. The main component composition of the above alloy is C: 0.1 wt.
%, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, Cr: 0.
The lead frame material according to claim 1, wherein 5 wt% or less, Ni: 40 to 60 wt%, and the balance is mainly Fe and inevitable impurities.