JP2000017398A - Fe-Ni ALLOY FOR LEAD FRAME, EXCELLENT IN BANKABILITY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Fe-Ni alloy for lead frame, capable of reducing the anisotropy of shearing resistance at the time of blanking and also capable of inhibiting the occurrence of large-sized burr. SOLUTION: This alloy is an Fe-Ni alloy for lead frame, containing 30-50 wt.% Ni, and further, the prolonged length L of B type nonmetallic inclusions in a rolling direction is <=20 μm and also the size of individual nonmetallic inclusion is <=5 μm. By this method, the anisotropy of shearing resistance can be reduced and residual stress can be uniformized and also the size of burr can be uniformized, and blanking precision can be remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fe-Ni-based lead frame material having good punching characteristics, and controls the size, shape and composition of nonmetallic inclusions to improve the shearing characteristics at the time of punching. And a technique for obtaining good punching characteristics.

[0002]

2. Description of the Related Art In recent years, the number of pins in a lead frame has been increasing, as represented by a flat package, and the required level of miniaturization has been increasing. In general, lead frame materials are divided into punching applications in which the lead pattern is formed by punching and etching applications in which the lead pattern is formed by etching with a ferric chloride solution. Suitable for forming. In general, the characteristics required for lead frame materials include excellent punching characteristics, excellent workability in press working, good solderability, plating properties, and problems when bonding with semiconductor elements. No deformation, high strength after processing, low deformation, high electrical conductivity, and the actual operating temperature 2
Low thermal expansion coefficient at 00 ° C. or lower. The manufacturing process of an IC semiconductor package using a punched lead frame can be roughly divided as follows.

(1) Punching of a material (lead frame material) (2) Mounting step of mounting a lead frame on a resin mold (3) Bonding step of connecting a lead frame and a semiconductor element with a conductive wire

Here, the punching property is required in the step 1, the press formability is required in the step 2, and the plating property and the solderability are required in the step 3 respectively. The strength after the processing is required because it is necessary that deformation such as warpage or bending is less likely to occur at the time of bonding, and that the yield is prevented from lowering due to occurrence of defects due to deformation during handling. The electrical conductivity is
It affects the heat generated by the current flowing through the leads and affects the stability of the operation of the semiconductor element. Lead frame materials include
It is necessary that the thermal expansion coefficient of the semiconductor element or the mold resin be close to that of the semiconductor element or the mold resin in order to prevent the characteristic fluctuation of the semiconductor element due to the distortion caused by the difference in thermal expansion during the assembly process due to heating and the deterioration of the adhesion with the mold resin. Have been. As a typical metal material that meets such demands,
Fe-42Ni alloy, Fe-45Ni alloy, Fe-50
A material such as a Ni alloy is used.

[0005] In terms of heat conduction, copper alloys are more advantageous than Fe-Ni alloys. However, recently, the effective ratio due to the improvement of the stability of semiconductor elements, the improvement of heat dissipation, and the improvement of the shape of leads (thinning) has been improved. Due to individual improvements such as reduced resistance, the thermal conductivity of Fe-Ni alloys is not a technical bottleneck. On the other hand, regarding the punching performance, the quality variation in this process has a great effect on the product yield, and it is considered to be an important process along with the trend of higher definition and more pins in the future, so it has been a great process in the past. Are being considered. As an attempt to improve the punching performance so far, as disclosed in, for example, JP-A-61-44156, the size of inclusions having a cross section parallel to the rolling direction is set to 5 μm or less,
B-type inclusions having a total number of 20 or more per 1 mm ² or those in which fine non-metallic inclusions having a particle size of 3 μm or less are uniformly dispersed in the structure as shown in JP-A-60-255953. is there. Further, JP-A-9-87808, 24
9943, 10 to 1000 A- or B-type inclusions having a size of 10 μm or more per 1 mm ² of cross-sectional area parallel to the rolling and sheet pressure directions were used. The number is limited to 100 to 50,000, and the number of sulfide-based inclusion marks after etching is set to 1,000 to 200.
In many cases, inclusions are positively used to improve punchability, such as zero. Also, JP-A-63-24
By performing the refining temperature outside the furnace at 1700 ° C. or lower as shown in FIG. 010, the generation of inclusions of spinel-based oxides such as MgO—Al ₂ O ₃ having a size exceeding 10 μm, which is harmful to the punching property, is suppressed. Suppression techniques have also been proposed.
These facts show how important inclusion control is to punching performance.

[0006]

In a lead frame material, not only does the performance of the product deteriorate due to burrs and scum generated at the time of press punching, but also the mold is damaged or warped or bent due to residual stress. Trouble occurs in handling. For this reason, in a semiconductor manufacturing process, it may hinder stable manufacturing or lower the yield, which may cause a serious trouble. Further, recently, as the precision of the leads has been increased, the clearance of the mold has been set smaller, so that the shear resistance tends to be larger. For this reason, materials having better punching properties are increasingly required for extending the life of the mold. However, in order to satisfy such demands, control of inclusions as described above was not sufficient.

[0007]

Means for Solving the Problems The present inventor has proposed Fe-Ni
As a result of examining the punching properties of lead alloys for lead frames, we classified them into factors that affect the processing accuracy during punching and factors that affect the punching resistance (shear resistance). I paid attention. Then, the respective effects were individually grasped based on the morphology and distribution of the oxide-based inclusions, the morphology and distribution of the sulfide-based inclusions, and the presence or absence of fine carbide precipitation. The basic knowledge on which it is based is as follows.

First, factors that affect the processing accuracy at the time of punching are mainly the occurrence of burrs and the occurrence of sagging due to the flow of material. These are related to the ratio between the fracture surface and the shear surface at the time of punching. When the ratio of the shear surface increases, the generation of burrs increases, and at the same time, the generation of scum increases. Is known to increase. These are naturally influenced by the punching conditions such as the clearance between the die and the punch. However, when the punching conditions are the same, these differences come up as good or bad materials.

Another factor affecting the processing accuracy is the uniformity of the shear surface and the fracture surface. If the ratio between the shear surface and the fracture surface is not uniform, the size of the burr and the size of the sag become uneven depending on the location, and as a result, the variation in the shape increases depending on the location, and the processing accuracy deteriorates. If burrs or sagging occur at a certain size, it can be improved by changing the punching conditions such as clearance, but if the size of burrs or sagging varies, it is difficult to cope with the punching conditions Therefore, the material needs to be improved.

As shown by the hatched portion in FIG. 2, when the integrated value of the stress generated during the punch stroke during punching and the breaking strain is defined as the shear resistance, the magnitude of the shear resistance is generally determined by the tensile strength of the material. Although it is thought to be related to mechanical properties such as pod elongation, even if the same material is used, the mechanical properties differ between the rolling direction and the direction perpendicular to the rolling direction. Is recognized. When this anisotropy increases, for example, burrs are often generated in the rolling direction, but burrs are not generated in the direction perpendicular to the rolling direction. This leads to an adverse effect on the yield of lead frame material products.

From the above viewpoints, the present inventor divided the factors related to the processing accuracy at the time of punching into three: anisotropy of shear resistance, non-uniformity of burrs and sagging, and sizes of burrs and sagging. Considered individually. Then, as a result of conducting various studies on how the influence on the processing accuracy and the inclusions included in the material are related to each other, the following knowledge was obtained.

Regarding the anisotropy of the shear resistance, it has been found that B-based inclusions extending in the rolling direction are the cause. Specifically, when the length of the B-based inclusion exceeds 20 μm,
It has been found that the anisotropy of the shear resistance increases and the uniformity of the fracture surface and the shear surface deteriorates. Here, the B-based inclusions refer to those defined in JIS0555, and are shown in FIG.
As shown in the figure, a plurality of inclusions are arranged in the rolling direction. In the present invention, the interval P between the individual inclusions is 10
Those lined up within μm are defined as one B-based inclusion, and the symbol L in the figure is its length. When the size of each of the inclusions constituting the B-based inclusions and the size of the A-based inclusions and the C-based inclusions exceeds 5 μm, similarly, the anisotropy of the shear resistance is large, and the fracture surface and the shear surface It was found that the uniformity was poor. In addition, regarding the uniformity of burrs, the size and distribution of inclusions are the controlling factors, and the size of inclusions is particularly 10%.
In the case of a distribution form in which large ones exceeding μm are sparsely present, it has been found that the boundary between the fractured surface and the sheared surface is easily disturbed, and the generation of burrs and sagging becomes uneven.

The first Fe—Ni based alloy for a lead frame of the present invention has been made based on the above findings.
In the Fe-Ni-based lead frame alloy containing 30 to 50% by weight of i, the size of each nonmetallic inclusion is 5%.
μm or less, and the extended length of the B-based nonmetallic inclusion among the nonmetallic inclusions by rolling is 20 μm or less. In such Fe—Ni based alloys for lead frames, the anisotropy of shear resistance is reduced by limiting the size of inclusions, particularly the size of inclusions in the rolling direction. As a result, the residual stress after punching becomes uniform, so that temporal deformation of the punched product can be reduced. In addition, since the size of each inclusion is limited to 5 μm or less, the anisotropy of the shear resistance is reduced, and burrs and sagging are uniformly generated to greatly improve the punching accuracy. Becomes possible.

Further, regarding the size of burrs and sagging,
Depending on the amount of relatively small inclusions (cleanness) of 10 μm or less, if the degree of cleanliness increases to some extent (increase in the amount of inclusions), the size of burrs decreases and the proportion of fractured surfaces increases. Conversely, as the cleanliness decreases (the amount of inclusions decreases), the generation of burrs increases, and the ratio of the shear surface increases. Therefore, it is not preferable that the amount of the inclusion is too large or extremely small, and it is necessary to set the amount to an appropriate range.

The second Fe-Ni alloy for lead frames of the present invention was quantitatively analyzed for sulfides mainly composed of MnS, which are known to contribute to free-cutting properties among inclusions. The size of each non-metallic inclusion is 5 μm or less in the Fe-Ni-based lead frame alloy containing 30 to 50% by weight of Ni obtained as a result.
In addition, among the nonmetallic inclusions, the extension length in the rolling direction of the B-based nonmetallic inclusions is not more than 20 μm, and the sulfide mainly composed of MnS having a particle size of 0.02 to 2 μm is 100%.
It is characterized by being dispersed at a rate of 0 to 10000 particles / mm ² . It has been confirmed that the presence of such inclusions imparts an appropriate degree of cleanliness and reduces the occurrence of burrs. The particle size of the MnS is preferably 0.05 to 2 μm, more preferably 0.1 to 2 μm.
μm, and more preferably 0.5 to 2 μm.

Next, as the elements relating to the resistance at the time of punching, the above-mentioned elements relating to the shear resistance, that is, the mechanical properties (tensile strength, elongation, hardness, rigidity, etc.) of the material, the distribution of inclusions in the rolling direction, etc. There is. Considering the life of the mold, the shear load is smaller and the breaking strain (stroke)
Is desirable as a material. The present inventor has conducted various studies on shear resistance, and found that fine carbide (mainly Fe ₃ C) dispersed in a tissue is most effective in reducing shear resistance. In addition, suitable precipitation conditions for carbides were found in the cooling conditions in hot rolling and the annealing conditions for hot strip.

A third Fe-Ni-based lead frame alloy according to the present invention is obtained by using the above alloy material at 900 ° C to 12 ° C.
Hot rolling in the range of 00 ° C, cooling after hot rolling is performed at a cooling rate of at least 5 ° C / sec from the hot rolling temperature to 650 ° C, and the hot rolled belt after cooling is cooled at a temperature of 500 ° C or less. The hot rolled belt is further wound in a coil annealing furnace at 70 ° C.
It is characterized in that fine carbides are precipitated in the alloy structure by holding at a temperature of 0 to 900 ° C. for 10 hours or more.

As described above, according to the present invention, first, the size of the oxide-based nonmetallic inclusion is specified to reduce the anisotropy of the shear resistance (first feature), and the predetermined sulfide is eliminated. Dispersion forms an appropriate ratio between the fracture surface and the shear surface (second characteristic), and further reduces the shear resistance by dispersing fine carbide (third characteristic). The process of the punching process when all of these features are provided is considered to be as follows.

First, in the vicinity of the punch, the individual size is 5 μm.
Cracks propagate from the following non-metallic inclusions such as A-type and B-type, and a fine M with a diameter of 2 μm or less
The nS generates a void, from which an infinite number of cracks are generated and punching proceeds. Further, in this process, fine carbides promote generation of the starting points, and contribute to lowering the resistance at the time of punching as a whole. However, this is merely an estimation, and it goes without saying that the present invention is not limited by the presence or absence of such an action. In addition, even if the total number of the oxide-based A-based and B-based inclusions was reduced, there was almost no difference in the shear resistance and the shear fracture surface. Therefore, the fine MnS itself was the starting point of the crack. It is thought that it has become.

Next, the preferred component composition of the present invention will be described. The preferred composition of the Fe—Ni-based lead frame alloy of the present invention is C: 0.005 to 0.5% by weight.
05%, Si: 0.005 to 0.5%, Mn: 0.1 to
1.0%, Cr: 0.5% or less, S: 0.0005 to
0.02%, the balance being substantially Fe, and the ratio Mn / S of the Mn content to the S content in the alloy is in the range of 50 to 150. Hereinafter, the grounds of the above limitation will be described. In the following description, “%” means “% by weight”.

C: If C is contained in an amount exceeding 0.05%, coarse carbides are precipitated and the punching is reduced. Further, since the yield strength of the alloy increases and the springback increases, the workability at the time of molding is deteriorated. Conversely, 0.
If the content is less than 005%, fine carbides necessary for punching do not sufficiently precipitate, and the punching properties deteriorate. For the above reasons, the content of C is set to 0.005 to 0.05%.

Si: Si is added as a deoxidizing agent, but if its content is too high, the punching properties are reduced as in the case of C. On the other hand, the oxide of Si becomes a starting point of precipitation of sulfide such as MnS generated by heterogeneous nucleation in the structure,
An appropriate amount is desirable. From such a viewpoint, Si
Was 0.005 to 0.5%.

Mn: Mn is one of the deoxidizing components like Si, but it is effective for improving hot workability because it combines with S which is harmful to hot workability to form MnS. . Further, like Si, the Mn oxide becomes a starting point of precipitation of sulfides such as MnS generated by heterogeneous nucleation in the structure, and therefore, it is desirable to add an appropriate amount thereof. On the other hand, if the added amount of Mn is too large, the coefficient of thermal expansion becomes high, and the difference from the coefficient of thermal expansion with the semiconductor element becomes large, making it unsuitable as a base material. From the above viewpoint, the content of Mn is set to 0.1 to 1.0%.

S: S is a component harmful to hot workability, but is a component necessary for producing sulfides such as MnS useful for punching properties. is necessary. From such a viewpoint, the content of S is 0.000.
5 to 0.02%. Further, the ratio Mn / S of the amount of S to the amount of Mn is desirably set in the range of 50 to 150. According to the study of the present inventors, when Mn / S is less than 50, the content of Mn is relatively small, so that the amount of MnS becomes insufficient and the hot workability is deteriorated by S. When Mn / S exceeds 150, M
An excess of n causes an increase in the coefficient of thermal expansion. Note that Mn
The value of / S is preferably from 80 to 140, and more preferably from 90 to 130.

Ni: Ni is a main constituent element of the alloy of the present invention, and when its content is small, the coefficient of thermal expansion increases. In addition, since Ni is an element that promotes martensitic transformation, if the content is too large, inconsistency between precipitated martensite and a semiconductor element occurs, which makes it unsuitable as a base material and increases the thermal expansion coefficient. . From such a viewpoint, the content of Ni is set to 30 to 50%. Note that C
r is also an element that promotes martensitic transformation, and its allowable amount is 0.5%.

[0026]

Hereinafter, the present invention will be described in more detail with reference to specific examples.
This will be described in detail. Fe-Fe-42%
Ni-based alloy, vacuum degree 10^-1-10 ^-2invitation of torr
It was melted into a 5 kg steel ingot in a vacuum heating furnace of a conduction heating type. simultaneous
And CaO-SiO in an air melting furnace.₂-Al₂O₃The lord
Using slag as a component, the basicity of 0.5-2.0
In the same manner, a 5 kg steel ingot was melted.

As the raw materials for the above two kinds of dissolution, electrolytic iron, electrolytic nickel and electrolytic manganese, ferrosilicon, and iron sulfide were used. After hot forging these ingots to a thickness of 5 mm, heat treatment was performed at 1250 ° C. for 2 hours as homogenization annealing, and then hot rolling was performed at 1150 ° C. The cooling conditions at this time are as follows: rapid cooling to 650 ° C. or less after hot rolling (10
° C / min) and slow cooling (0.1 ° C / min). Some of these hot-rolled strips were annealed at 750 ° C. for 20 hours, cold-rolled to a thickness of 1.5 mm, and brightly annealed. Then, further cold-rolled to 0.25 mm,
The final bright baking was performed at 800 ° C. Further, samples subjected to temper rolling to 0.20 mm were used as test materials, and their component compositions are shown in Table 1. In Table 1, what was melted in the vacuum melting furnace was # 2, # 5, # 6, and # 7, and the other # 1, # 3, # 4, # 8, # 9, and # 10 were It was produced in an atmospheric melting furnace. Also, # 1 to # 6,
# 8 and # 9 are quenched after hot rolling and 750 ° C
For 20 hours.

[0028]

[Table 1]

The obtained test material was evaluated by performing a punching test. In the punching test, a 3% clearance was set with respect to the plate thickness using a 3 ton precision mold press for a laboratory, and 5 m was used.
This was carried out by drilling five m-square holes at 10 mm intervals perpendicular to the rolling direction. The evaluation contents are the maximum burr height shown in FIG. 3, the fracture surface / shear surface ratio of the punched surface, the shear resistance (KN · mm), and the difference in the shear resistance newly defined in the present invention between the rolling direction and the direction perpendicular to the rolling direction. L, a measure of anisotropy
/ T value (shear resistance in the rolling direction / shear resistance in the direction perpendicular to the rolling direction), and the measured values are also shown in Table 1. Table 1 also shows the inclusion distribution of each test material together with the contents of the evaluation.

As can be seen from Table 1, the condition (B)
System inclusion length and individual inclusion size) #
1 to # 5, # 7 and # 10, the shear resistance anisotropy ratio L / T
Are close to 1 and the anisotropy is small, the value of the maximum burr height is small, and excellent punchability is exhibited. On the other hand, in # 8 and # 9 which do not satisfy the condition of claim 1,
It can be seen that L / T is much smaller than 1 and the anisotropy is large. Further, as is apparent from a comparison of the shear resistance between # 7 and # 10 and the other test materials, the shear resistance is small in the case where carbide is dispersed. In addition, about # 6, the condition of Claim 1 is not satisfied, and moreover, Mn / S
Is high and the number of MnS is extremely small, L /
T and the maximum burr height are very large.

For the measurement of the distribution state of MnS, the surface subjected to electrolysis by the SPEED method after buffing was subjected to X-ray irradiation.
Using a line microanalyzer, a range of 50 μm × 50 μm was observed in 10 visual fields of each sample, and the distribution of MnS was counted as points by mapping, and the average was determined as the number per 1 mm 2.

[0032]

As described above, according to the present invention, since the anisotropy of the shear resistance can be reduced, the material defect due to the occurrence of burrs in the punching step of the lead frame material and the defect due to the handling are eliminated. It is expected that the life of the mold can be greatly improved, and it is possible to supply parts that are excellent in improving the definition, reliability and production efficiency of lead frame materials for IC packages in recent years. Become.

[Brief description of the drawings]

FIG. 1 is a view showing a B-based inclusion.

FIG. 2 is a diagram for explaining a shear resistance.

FIG. 3 is a cross-sectional view showing a state of occurrence of burrs and a definition of the size thereof.

[Explanation of symbols]

 L: Rolling extension length of B-based nonmetallic inclusions.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidekazu Todoro 4-2 Kojimacho, Kawasaki-ku, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Metallurgical Industry Co., Ltd. Research and Development Headquarters Technical Research Institute (72) Inventor Jun Watanabe Kawasaki-shi, Kawasaki-shi, Kanagawa Prefecture 4-2 Kojima-cho, Ward Nihon Metallurgical Industry Co., Ltd.

Claims (4)

[Claims] 1. An Fe-containing alloy containing 30 to 50% by weight of Ni.
In the Ni-based lead frame alloy, the size of each non-metallic inclusion is 5 μm or less, and among the non-metallic inclusions, the extension length in the rolling direction of the B-based non-metallic inclusion is 20 μm or less. An Fe-Ni-based lead frame alloy excellent in punching workability. 2. An Fe-containing alloy containing 30 to 50% by weight of Ni.
In the Ni-based lead frame alloy, the size of each non-metallic inclusion is 5 μm or less, and among the non-metallic inclusions, the extension length in the rolling direction of the B-based non-metallic inclusion is 20 μm or less. In addition, 1,000 to 10,000 sulfides mainly composed of MnS having a particle size of 0.02 to 2 μm /
An alloy for a lead frame excellent in punching workability, characterized by being dispersed at a ratio of ² mm ² . 3. The alloy material is hot-rolled in a temperature range of 900 to 1200 ° C., and cooling after hot rolling is performed at a cooling rate of at least 5 ° C./sec from a hot rolling temperature to 650 ° C. Winding the hot strip after winding at a temperature of 500 ° C. or less,
Further, this hot-rolled strip is placed in a coil annealing furnace at 700 to 9%.
The lead-frame alloy according to claim 1 or 2, wherein fine carbides are precipitated in the alloy structure by maintaining the alloy at a temperature of 00 ° C for 10 hours or more. 4. In% by weight, C: 0.005 to 0.05
%, Si: 0.005 to 0.5%, Mn: 0.1 to 1.%.
0%, Cr: 0.5% or less, S: 0.0005 to 0.0
2%, the balance being substantially Fe, and the ratio Mn / S of the Mn content to the S content in the alloy is 50 to 50%.
The lead frame alloy according to any one of claims 1 to 3, wherein the alloy has excellent punching workability.