JPH06192793A - Metal sheet for fe-cu alloy lead frame minimal in inplane anisotropy of bending and its production therefor - Google Patents

Abstract

PURPOSE:To provide superior bendability and excellent stiffness and heat dissipation property by subjecting an Fe-Cu alloy stock to cold rolling, annealing, and aging treatment under respectively specified conditions and then applying residual stress uniformizing treatment. CONSTITUTION:A molten Fe-Cu alloy of 10-90wt.% Cu content is cast into a metal plate of 0.5-8mm thickness at (10 to 1000) deg.C/sec solidification cooling rate. If necessary, after softening at 500-900 deg.C, surface grinding is done. Subsequently, cold rolling is performed while regulating the ratio between the rolling draft in a longitudinal direction of a stock and that in a width direction to 1-10 and also regulating the total draft to >=30%. The resulting cold rolled stock is annealed at 600-1100 deg.C and aged at 300-650 deg.C. Then, residual stress uniformizing treatment is performed by using a tension leveler and a tension annealer. By this method, the metal sheet for lead frame, where the number of 90 deg. repeated bending times in the longitudinal and vertical directions of coil is regulated to >=3 and which has minimal inplane anisotropy and >=15000 kgf/mm<2> Young's modulus, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal plate used for a highly integrated semiconductor lead frame and the like and a method for manufacturing the same. The material of the present invention has a small in-plane anisotropy of bending and has a better balance of stiffness and electrical conductivity than conventional materials, and is therefore a material suitable for a highly integrated thin multi-pin packaging lead frame. .

[0002]

2. Description of the Related Art In order to meet the recent demand for extremely high integration of semiconductors, a thin lead pin material having a large number of pins and good heat dissipation is required. In order to meet these requirements, (1) the pins are taken from four directions of the lead frame, so that the in-plane anisotropy of the characteristics is small, and (2) the rigidity (hereinafter referred to as stiffness) is not reduced even if the thickness is reduced. Therefore, it is essential to have high strength, and (3) to have high thermal conductivity (in other words, electrical conductivity) in order to ensure excellent heat dissipation.

In order to meet such requirements, Fe-42Ni, which has been conventionally used as a lead frame material, is used.
In the field of alloys or Cu-based alloys, high-strength lead frame materials have been earnestly developed for the purpose of improving stiffness. For example, in the field of Fe-Ni alloys, Kovar alloy containing Fe- (26-30)% Ni- (11-16)% Co disclosed in JP-A-59-198741, or JP-A-SHO-I. An example thereof is an alloy containing Fe- (30-50)% Ni disclosed in JP-A-60-11147.

[0004] These Fe-Ni alloys are currently widely used because their thermal expansion characteristics match Si and their performance and quality are extremely stable. % IACS, which has a problem of poor heat dissipation. In addition, the manufacturing cost is extremely high. On the other hand, in the field of Cu-based alloys, development of high-strength materials is being actively conducted. For example, JP-A-60-218442
In the alloy described in the publication, Sn, Fe, Si, P, Ni,
Cr, Ti, Co, etc. are added to increase the strength. However, addition of these elements causes problems such as increase in alloy cost and deterioration of electric conductivity, and at the same time, C
With u-based alloys, it is basically extremely difficult to achieve the same high strength as Fe-Ni alloys, and there is a problem that there is a limit to thinning from the viewpoint of stiffness.

[0005]

In order to solve the above problems, the present inventors have been working on the development of a Fe-Cu alloy in which the amount of Cu has changed in a wide range from 10% to 90%. . The main point is the Japanese Patent Publication 3-591
As disclosed in Japanese Patent No. 31 and Japanese Patent Publication No. 04-024420, an Fe-Cu alloy is a two-phase alloy consisting of an Fe phase and a Cu phase, and the Fe phase has the strength and the electrical conductivity the Cu.
It is the responsibility of each phase to maximize the characteristics of each phase. From this viewpoint, these alloys have an excellent balance between strength and electrical conductivity. However, because it is a two-phase alloy, when it is manufactured through a unidirectional cold rolling / annealing process, even if it is recrystallized and annealed, the structure has an elongated shape in the rolling direction, so the in-plane characteristics are different. It has the drawback that the in-plane anisotropy of the directionality, especially bendability, becomes large.

Therefore, the first problem to be solved by the present invention is to improve the in-plane anisotropy of bendability of the Fe-Cu alloy, and the second problem is to improve the stiffness of the alloy. To improve.

[0007]

The present invention has been constructed to solve the above problems, and the gist thereof is as follows. (1) Fe-Cu containing 10 to 90% by weight of Cu
Alloy and in the longitudinal and vertical direction of the coil 9
The number of 0-degree repeated bendings (n _L and n _C , respectively) is 3 times or more, and the ratio (n _C / n _L ) of these has a small in-plane anisotropy of 1 to 3, and further Young's in each direction Rate is 15
000 kgf / mm ² or more, electrical conductivity at room temperature is 10% IACS
A metal plate for a lead frame, which has the above and has an excellent balance between stiffness and heat dissipation. (2) Fe-Cu containing 10 to 90% by weight of Cu
The molten metal is cast into a metal plate having a plate thickness of 0.5 to 8 mm at a solidification cooling rate of 10 to 1000 ° C./s, and if necessary, the obtained slab is softened and annealed in a temperature range of 500 to 900 ° C. Surface grinding is performed, and then the ratio of the rolling reduction (r _L ) in the longitudinal direction of the material to the rolling reduction (r _C ) in the width direction (r _L /
r _C ) is 1 to 10 and cold rolling is performed at a total reduction of 30% or more, and the cold rolled material is annealed at a temperature range of 600 to 1100 ° C., and then at a temperature range of 300 to 650 ° C. A lead frame metal that has a small in-plane anisotropy of bending and a good balance between stiffness and heat dissipation, which is subjected to an aging treatment and then a residual stress is made uniform using a tension leveler and / or a tension annealer. Method of manufacturing a plate.

In order to complete the above invention, the present inventors have
First of all, intensive research and development were carried out on improvement of bendability. As a result, in order to improve the in-plane anisotropy of the bending characteristics of an alloy having a two-phase structure such as an Fe-Cu alloy, it is essential to make the structure isotropic, By rolling not only in one direction but also in a direction perpendicular to this, that is, when cross rolling is performed, the structure becomes more uniform, so the in-plane anisotropy of bending properties is significantly improved. We obtained an extremely important finding industrially. It is considered that the in-plane anisotropy is reduced because the metal structure is not expanded only in one direction by the cross rolling but is also expanded in the direction perpendicular thereto. Cross-rolling can be performed simply by using a cutting plate to set the rolling directions in two directions orthogonal to each other. However, even in the coil shape, the method disclosed in Japanese Patent Publication No. 62-45007 can be used. If used, it will be possible continuously.

Secondly, a method for improving stiffness is also researched, and it is newly revealed that increasing the Young's modulus (improving the longitudinal elastic modulus) is the most effective, rather than the conventional strengthening. I chose That is, the stiffness is measured from the relationship between the bending measurement (M) and the displacement (δ) when one end of the strip-shaped test piece 1 is fixed and a load is applied to the other end as shown in FIG. The smaller the displacement for the same bending moment, the better the stiffness. This is a problem of so-called cantilever bending deformation, and the following expression (1) is established between M and δ.

M = w · t ³ / (4 · l ² ) · E · δ (1) Here, E is the Young's modulus, w is the width of the test piece, and l is the distance from the fixed point to the load point. FIG. 2 shows Fe within the scope of the present invention.
-Cu alloy, current high strength Fe-42% Ni alloy, Cu
The results of actual measurement of the relationship between M and δ for various materials such as base alloys are shown. As is clear from the figure, the relationship between M and δ can be arranged by the above equation (1). Therefore, it became clear that stiffness is determined by Young's modulus rather than strength.

The method for improving the Young's modulus of Fe-Cu alloys is as follows.
Describe the method. Young's modulus has the same composition even if it has the same composition.
It is well known that the crystal orientation varies greatly. for example
For example, Young's modulus of random orientation of Fe is about 2100 kgf.
/ Mm²And the maximum direction <111> is 29000 k.
gf / mm²Becomes In addition, Young's modulus is the addition of a small amount of elements
However, it is known that it hardly changes. However, Fe
Add 42% Ni as much as -42Ni alloy
And Young's modulus is about 1500 kgf / mm²Drop to a degree
It On the other hand, since Cu has a lower melting point than Fe, its Young's modulus is about
1300 kgf / mm ²And significantly lower than Fe. like this
In addition, the Young's modulus of the conventional material is significantly lower than that of Fe.
have.

Therefore, a large amount of C, such as Fe--Cu alloy, is used.
In order to maintain the Young's modulus as high as that of Fe even if u is added, the following new idea was taken. That is,
The present inventors have found that Fe-C containing 10 to 90% of Cu.
It was noted that the u alloy has a two-phase structure of a Fe phase having a high Young's modulus and a Cu phase having a low Young's modulus. If the Fe phase having a high Young's modulus is spread in the four directions in which the leads are collected, the stiffness anisotropy in the four directions should be significantly improved. Therefore, they found that cross rolling is effective as a concrete means. That is, in the Fe-Cu alloy produced by the basic steps of cross rolling and annealing, the Fe phase is expanded in the rolling direction and the direction perpendicular to the rolling direction, so the Young's modulus in these directions is a high value close to that of Fe. Will be obtained. This is Fe consisting of a single phase with an fcc structure.
This is a point essentially different from the case of -42Ni, Cu-based alloy.

The basic composition of Cu in the present invention is Cu.
In order to produce a Fe-Cu alloy containing 10 to 90% of Fe, it is essential to quench the molten metal and directly cast it into a steel strip having a plate thickness of 0.5 mm to 8 mm. That is, as described in JP-B-4-024420, when hot rolling, which is a conventional basic process, is applied to the alloy of the present invention, since the Cu phase is still in the melt state in that temperature range, hot brittleness occurs. Occurs. In order to prevent this drastically, a method for manufacturing thin cast pieces called a strip casting method using a so-called twin roll casting machine in which hot rolling is omitted is applied. If the steel strip having the above-mentioned thickness is directly cast, the Fe-Cu alloy can be extremely thinned to the region of the metal foil of 0.1 mm or less by cold rolling by only performing softening annealing as necessary. Is possible. In addition, the width can be increased simultaneously by cross rolling.

The present invention has been made based on such a novel idea and knowledge as never before.

[0015]

The reason for limiting the material properties, steel composition and manufacturing conditions as described above in the present invention will be explained in detail. (1) Bendability: In a QFP type lead frame in which leads are taken from four directions, it is required that the bendability is good and there is no in-plane anisotropy. First, in order to satisfy the bending workability, it is necessary that the number of repeated bendings in the case of bending 90 degrees perpendicular (n _C ) and parallel (n _L ) to the coil longitudinal direction is 3 times or more. Next, these ratios (n _C / n _L ) are limited to 1 to 3. If it exceeds 3, the in-plane anisotropy becomes too large.

(2) Young's modulus: In order to maintain the stiffness even if the thickness is reduced, it is essential to improve the Young's modulus.
The Young's modulus of the current high-strength Fe-Ni alloy is about 15,000.
Since it is more than kgf / mm ² , the lower limit of Young's modulus is 1500
It shall be 0 kgf / mm ² . (3) Electric conductivity: In the present invention, the material characteristics having the above-mentioned high Young's modulus and having an electric conductivity of 10% IACS or more are defined. In the field of Fe-Ni alloys, the electrical conductivity is at most 5% IACS. On the other hand, in the field of Cu-based alloys, the electrical conductivity is good, but the Young's modulus is at most 13000 kgf / mm.
² is low. Therefore, in the present application, both alloys have excellent properties, and a Young's modulus of 15,000 kgf / mm ² or more and an electrical conductivity of 10% IACS or more are specified at the same time.

(4) Composition: The basic composition is 10% by weight.
An Fe-Cu alloy containing 90% Cu is used, but as described in JP-B-3-59131 and JP-B-4-024420, Cr may be added thereto for the purpose of maintaining corrosion resistance. For the purpose of improving strength and electric conductivity, Ti, Zr, etc. may be added.

(5) Manufacturing method (a) Solidification cooling rate and cast plate thickness: 10 to 10 molten metal
Cast into a metal plate having a plate thickness of 0.5 to 8 mm at a solidification cooling rate of 00 ° C./s. When the solidification cooling rate is less than 10 ° C / s, the solidification structure composed of the Fe phase and the Cu phase becomes extremely rough,
The so-called rapid solidification effect disappears. On the other hand, if the solidification cooling rate exceeds 1000 ° C./s, the solidification shell is not sufficiently developed, so that casting becomes extremely unstable. Also,
From the relationship with the solidification cooling rate, the casting thickness is 0.5 to
It will be 8.0 mm.

(B) Softening annealing, pickling, surface polishing: The above-mentioned cast plate is softened annealing, pickling or surface-ground as required. Above all, the softening annealing is effective for facilitating cold rolling to be performed later, and is preferably 500 to 900 ° C. (C) Cold rolling condition: The cold rolling condition is the most important structural requirement in the present invention in order to secure good bendability with small in-plane anisotropy. First, the total rolling reduction is 30% or more in order to obtain the required product thickness and strength. Next, the rolling reduction (r _L ) in the material longitudinal direction and the rolling reduction (r _L in the width direction
_C) the ratio of (r _L / r _C) is in a range such that 10 performs cross rolling. If the value of r _L / r _C is less than 1 or more than 10, the effect of cross rolling is lost and the in-plane anisotropy of bendability does not satisfy the target. The order of rolling in the longitudinal direction of the material and rolling in the width direction does not matter because it does not basically affect the in-plane anisotropy of bendability, but from the viewpoint of the surface properties of the final product, the final 5% The above cold rolling is preferably performed in the longitudinal direction of the material. Such cross rolling can be applied not only to cut plates, but also to coils, in Japanese Patent Publication No. 62-45.
This is possible by using the method disclosed in Japanese Patent Publication No. 007.

(D) Annealing condition after cold rolling: The cold rolled material is in the range of 600 to 1100 ° C., particularly preferably 8
Anneal in the range of 00 to 1050 ° C. Annealing temperature is 600
When the temperature is lower than 0 ° C, the ductility is insufficient and the bendability is poor. On the other hand, if the annealing is performed at a temperature higher than 1100 ° C., the melting point of Cu is exceeded, so that a defect in quality occurs, and in the case of continuous annealing, there is a problem of plate breakage.

(E) Aging treatment temperature condition: 300 to 650
The aging treatment is carried out in the temperature range of 400C, particularly preferably in the temperature range of 400 to 550C. The role of the aging treatment is to finely precipitate the solid solution Cu in the Fe phase to increase the strength, and to fix the solid solution Fe with Ti, Zr or the like in the Cu phase to improve the electric conductivity. If the aging temperature is less than 300 ° C, the above-mentioned precipitation and fixing reactions do not occur. If the aging treatment temperature exceeds 650 ° C, overaging will occur and the strength will decrease.

(F) Conditions for surface polishing and temper rolling: After the above annealing, surface polishing and temper rolling are performed if necessary.
The surface polishing has the purpose of removing the surface film formed on the surface of the steel sheet, and then has the role of adjusting the surface roughness. Further, temper rolling with a reduction rate of 1 to 10% has (a) a role of improving the plate shape deteriorated by the above-described annealing, and (b) a role of further adjusting the surface roughness. If the temper rolling ratio is less than 1%, the above-mentioned two roles cannot be achieved. On the other hand, if it exceeds 10%, the bendability deteriorates.

(G) Uniformization of residual stress: The residual stress is uniformized in the plate thickness direction by using at least one of a tension leveler and a tension annealer for the purpose of eliminating warpage after etching. Thus, according to the present invention, it has good bendability and its in-plane anisotropy is small,
Fe-having a Young's modulus of 15000 kgf / mm ² or more and an electric conductivity of 10% IACS or more, and having an excellent balance between stiffness and heat dissipation, containing 10 to 90% Cu by weight%
A Cu alloy highly integrated thin lead frame application metal plate can be obtained.

[0024]

【Example】

 [Example 1] Fe-30% Cu having the composition shown in Table 1
The alloy was vacuum melted in a laboratory. That is, the basic composition is
Fe-30% Cu alloy, but to ensure corrosion resistance
Cr and Mo to improve the balance between strength and electrical conductivity
Zr and Ti in order to improve castability
Al is added. Using a twin roll caster, 320
A plate thickness of 2.0 mm was cast at a surface cooling rate of ° C / s. Furthermore
In addition, in order to improve the cold rolling property,
Softening annealing at 00 ℃ for 1 hour, then 1.9mm thick
Both sides of the coil were ground with a coil grinder. Then 0.
When performing cold rolling to a thickness of 13 mm, the longitudinal direction of the material
Reduction ratio r_LAnd its vertical rolling reduction r _CRatio of (r_L/
r_C) Was changed variously as shown in Table 2. Still simple
First, in the longitudinal direction of the material (1- (1-r_L)^1/2)
Rolling at a rolling reduction of_Cof
Rolling is performed, and finally, the reduction ratio (1- (1-
r _L)^1/2) Was rolled. Cold produced in this way
The rolled plate was annealed in a bright annealing furnace. The annealing condition is 100
It is 0 ° C-60s. Then, in a vacuum furnace at 500 ℃ 3
Time aging annealing, after surface polishing, rolling reduction 5%
The surface roughness and shape were adjusted by temper rolling. And residual
Tension annealing at 450 ° C to homogenize stress
did.

[0025]

[Table 1]

[0026]

[Table 2]

The tensile properties were evaluated using a JIS No. 13 B test piece at a crosshead displacement rate of 10 mm / min. Repeated bending test is MIL-STD-883 / 2004
The test piece having a width of 0.5 mm, a length of 30 mm and a plate thickness is repeatedly subjected to 90 ° bending by applying a load of 225 gf. 9
One bend at 0 ° was considered as one bend. The electrical conductivity was evaluated using the 4-terminal method. The Young's modulus was obtained using the resonance method. As the surface roughness, R _max in the roughness measurement over a length of 25 mm was adopted. Table 2 collectively shows these measurement results. Further, for comparison in the table, a commercially available high-strength Fe-Ni alloy (HT42) and high-strength Cu are used.
The results for the alloy (KLF185) are also shown.

As is clear from Table 2, the material of the present invention utilizing the cross rolling technique has good bendability and its in-plane anisotropy is small. Furthermore, it has an excellent balance between Young's modulus and electrical conductivity, and balances stiffness and heat dissipation at unprecedentedly high levels. Also, the surface roughness is sufficiently small. Further, the corrosion resistance was evaluated from the red rust generation rate by a salt spray test for 48 hours.
There was no problem because it had the same ability as e-42Ni. In addition, it was confirmed that the material of the present invention had good solderability evaluated from the wet area ratio. [Example 2] Based on the findings of Example 1, Steel B (Fe-50% Cu alloy) and Steel C (Fe having the chemical compositions shown in Table 3)
-75% Cu) was melted in the laboratory. Cr, Mo, Zr, Ti, and Al are added to these steels as in the first embodiment. Further, a twin roll casting machine was used to cast a slab having a plate thickness of 2.0 mm. Both sides of the cast coil are 1.9
It was ground to a thickness of mm. Subsequently, in performing cold rolling to a thickness of 0.13 mm, the ratio (r _L / r _C ) of the reduction ratio r _{L in} the longitudinal direction of the material and the reduction ratio r _{C in} the vertical direction is shown in Table 4. Various changes were made. For simplicity, first, the material is rolled in the rolling direction at a rolling reduction of (1- (1-r _L ) ^1/2 ),
Subsequently, rolling with a reduction ratio r _C was performed in the vertical direction, and finally, reduction with a reduction ratio (1- (1-r _L ) ^1/2 ) was performed in the longitudinal direction of the material.

[0029]

[Table 3]

[0030]

[Table 4]

The cold rolled sheet thus produced was annealed in a bright annealing furnace. The annealing condition is 1000 ° C.-60 s. Then, aging annealing was performed at 500 ° C. for 3 hours in a vacuum furnace. After the surface polishing, temper rolling with a rolling reduction of 3% was performed. Subsequently, the coil was put on a tension leveler for the purpose of making the residual stress uniform in the plate thickness direction. The material thus manufactured was subjected to a basic performance evaluation as a lead frame application. That is, a tensile test, a repeated bending test, an electric conductivity measurement, a Young's modulus measurement, a surface roughness measurement and the like were evaluated, and the evaluation measurement methods are exactly the same as in Example 1. The results are summarized in Table 4. Further, for comparison, the same table also shows a commercially available high-strength Fe-Ni alloy (HT
42) and high strength Cu alloy (KLF185) results are also shown. As is clear from the table, the material of the present invention has good bendability and small in-plane anisotropy due to the cross rolling technique, and further has excellent balance between Young's modulus and electrical conductivity, and stiffness and Excellent heat dissipation as never before. Also, the surface roughness is sufficiently small. Furthermore, corrosion resistance,
It was confirmed that the solderability was also good. Example 3 Steel A-2 of Example 1 and Steel B of Example 2
-2, the stiffness was measured using the high strength Fe-42% Ni alloy (HT42) and high strength Cu-based alloy (KLF185) materials used in Examples 1 and 2 as comparative materials. The measuring method was based on ASTM-F113-77.
As shown in FIG. 1, the material of the present invention had the smallest displacement amount with respect to the increase of the bending moment as compared with the conventional material, and had good stiffness. The relationship between the bending moment and the displacement amount obtained from the cantilever theory is in good agreement with the experimental results as shown in Fig. 1, and it became clear for the first time that Young's modulus determines stiffness. The alloy of the present invention has a significantly higher Young's modulus than that of the conventional material, and therefore has good stiffness.

[0032]

As described in detail above, since the material of the present invention has the characteristics of good bendability and small in-plane anisotropy,
It is suitable for highly integrated lead frames such as FP. Furthermore, since it has a better balance of Young's modulus and electrical conductivity than the conventional material, the stiffness and heat dissipation, which are important for practical use, are improved. Therefore, if the material of the present invention is applied to a lead frame, the semiconductor device can be highly integrated. Therefore, its industrial significance is extremely high, and since it affects many fields, its effect is remarkable.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method for measuring the stiffness of a material.

FIG. 2 is a diagram showing a relationship between a bending moment and a displacement amount.

[Explanation of symbols]

 1 ... Sample P ... Load δ ... Deflection amount

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C22C 9/00 38/20 C22F 1/08 B H01L 23/50 V 9272-4M

Claims (3)

[Claims] 1. An Fe-Cu alloy containing 10 to 90% by weight of Cu, and the number of times of repeated bending at 90 degrees in the coil longitudinal direction and the vertical direction (n _L , respectively ₎ .
n _C ) is 3 times or more, and the ratio (n _C / n _L ) of these is 1 to
3 has small in-plane anisotropy, Young's modulus in each direction is 15000 kgf / mm ² or more, and electric conductivity at room temperature is 10% IACS or more. Stiffness and heat dissipation Fe-Cu alloy lead frame metal plate with excellent in-plane bending and small in-plane anisotropy. 2. A Fe—Cu molten metal containing Cu: 10 to 90% by weight is cast at a solidification cooling rate of 10 to 1000 ° C./s into a metal plate having a thickness of 0.5 to 8 mm, and then, Cold rolling in which the ratio (r _L / r _C ) of the rolling reduction (r _L ) in the longitudinal direction of the material to the rolling reduction (r _C ) in the width direction is 1 to 10 and the total reduction is 30% or more. And annealing the cold rolled material in the temperature range of 600 to 1100 ° C., and then 300 to
Bending with excellent balance between stiffness and heat dissipation, characterized by performing aging treatment in a temperature range of 650 ° C and then performing residual treatment homogenization treatment using at least one of a tension leveler and a tension annealer. Of manufacturing a metal plate for a lead frame having a small in-plane anisotropy. 3. Following casting, the slab is 500 to 90
The manufacturing method according to claim 2, wherein the material is softened and annealed in a temperature range of 0 ° C and then cold-rolled.