JPH10183274A - Copper alloy for electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper alloy for electronic equipment, excellent in strength, electric conductivity, bendability, and adhesion of an oxide film. SOLUTION: This copper alloy has a composition consisting of, by weight, 0.05-0.4% Cr, 0.03-0.25% Zr, 0.06-2.0% Zn, and the balance Cu with inevitable impurities and containing, if necessary, 0.1-1.8% Fe and 0.1-0.8% Ti or further containing, if necessary, 0.01-1.0%, in total, of one or more elements among Ni, Sn, In, Mn, P, Mg, and Si. Moreover, in this copper alloy, the size of inclusions is <=30μm and the number of inclusions of 0.5-30μm is regulated to <100 pieces/mm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy having the necessary strength, conductivity, bendability, and adhesion of an oxide film after an oxide film has been generated, and more particularly to an inclusion. A Cu—Cr—Zr—Zn-based electronic device copper alloy having a size of 30 μm or less and a number of inclusions of 0.5 to 30 μm of less than 100 / mm ² .

[0002]

2. Description of the Related Art Due to the demand for miniaturization of electronic equipment, the demand for high-density mounting of semiconductor elements on a substrate is increasing more and more. Recently, surface mount packages such as SOJ (for memory), SOP (for memory), and QFP (for logic), which are advantageous for improving the mounting density, have become mainstream. In these packages, further reduction in the lead pitch due to the demand for more pins and thinning such as TSOP and TQFP have been progressing. Most lead frames with many pins and narrow pitches are made by etching, but etching is not only in the thickness direction but also in the width direction, so the processing limits of the lead width and lead spacing are limited. Depending on the plate thickness, the thinner the plate, the more advantageous in the etching process. Also, due to the demand for thinner packages, it is necessary to reduce the thickness of the lead frame material, and as a result, the plate thickness has recently become 0.15 mm and 0.125 m.
Thin materials such as m have become mainstream. Such thinning of the lead frame and narrowing of the leads reduce the rigidity of the entire frame and the leads, causing deformation of the inner leads during the assembly process and deformation of the outer leads during device mounting. To prevent such troubles, higher strength is required for the lead frame material used. On the other hand, power consumption increases as the processing speed of the IC increases and the number of pins increases.
The measures to dissipate the heat generated from this become an important issue in IC design. Copper originally had a thermal conductivity of 42 alloy (Fe
-Ni alloy).
Copper alloys are advantageous in heat dissipation. Therefore, there is an increasing demand for a copper-based lead frame material having strength capable of coping with thinning and excellent heat dissipation.

[0003] Such lead frame materials for semiconductor devices are generally required to have a wide variety of characteristics such as the following: 1) Leads must have mechanical strength so that they are not easily deformed. 2) To have excellent etching and press workability in forming a lead frame pattern. 3) It has a high thermal conductivity capable of efficiently dissipating heat generated by the chip. 4) It has excellent current-carrying characteristics. 5) The solderability in mounting is excellent, and the reliability of the solder joint is high. 6) Excellent silver plating property for bonding. 7) The oxide layer on the alloy surface generated in the heating step is difficult to peel off. 8) Excellent workability during lead bending. 9) Appropriate price.

In a plastic semiconductor package, a semiconductor chip is bonded onto a die pad of a lead frame having an oxide film on the surface, and the semiconductor chip is connected to leads of the lead frame by bonding wires, and these are integrated. It is manufactured by sealing with a resin mold made of a thermosetting resin. The biggest problem regarding the reliability of these packages is the problem of package cracking and peeling occurring during surface mounting. When the adhesion between the resin and the die pad is weak after assembling the plastic semiconductor package, the peeling of the package is caused by thermal stress during the subsequent heat treatment. The mechanism of occurrence of package cracks is as follows. After assembling the plastic semiconductor package, the resin mold absorbs moisture from the atmosphere, so moisture evaporates during subsequent surface mounting heating, and if there is peeling inside the package, water vapor pressure is applied to the peeled surface and acts as internal pressure I do. This pressure causes swelling of the package and cracks due to the resin being unable to withstand the internal pressure. If cracks occur in the package after surface mounting, moisture and impurities penetrate and corrode the chip, thereby impairing the function as a semiconductor. In addition, when the package swells, the appearance becomes poor and the commercial value is lost. Such problems of package cracking and peeling have become remarkable with recent progress in thinning packages.

Here, the oxide film adhesion of the lead frame material has the greatest effect on the adhesion between the mold resin and the die pad. In a semiconductor assembling process, the lead frame material undergoes various heating processes, and an oxide film is formed on the surface thereof. Therefore, since the mold resin and the die pad of the lead frame are in contact with each other via the oxide film, the adhesion of the oxide film to the lead frame base material determines the adhesion between the resin and the die pad. However, the Cu alloy lead frame is inferior to the Fe-Ni-based alloy in the adhesiveness of the oxide film described above, so that peeling is likely to occur between the resin and the die pad, and thus problems such as package cracking and peeling are likely to occur. For this reason, there was a problem that a highly reliable package could not be manufactured.

Conventionally, for electronic parts such as various terminals, connectors, relays or switches, inexpensive "brass", "phosphor bronze" having excellent spring characteristics, or "white steel" having excellent spring characteristics and corrosion resistance have conventionally been used. Such materials were applied. However, in recent years, electronic devices and their components have been required to be reduced in size and thickness, and in cases where they are used in high-temperature environments, such as electrical components of automobiles, they can withstand severe environments. There is a demand for highly reliable components. In response to such demands, such electronic component materials include: a) having sufficient strength to generate a high contact pressure even at a small thickness; b) having a low stress relaxation rate and being used for a long time at a high temperature. C) High conductivity, hard to generate Joule heat when energized, and easy to dissipate the generated heat. D) Cracks in the bent part even after severe bending E) Even if the bending deformation is repeatedly performed many times within the elastic range,
There are many demands for such properties that the material does not undergo fatigue failure, and f) the oxide film generated during the assembling process does not easily peel off from the base material.

In recent years, precipitation-type copper alloys are often used for applications requiring high strength and conductivity, such as copper alloys for electronic devices. A Cu-Cr-Zr-based alloy is a typical precipitation-type copper alloy having both high strength and high electrical conductivity, and its practical use as a material for electronic devices has been attempted.
According to the results of research on this alloy, the strength and electrical conductivity increase due to the formation of fine Cr and Cu ₃ Zr precipitate particles in the copper matrix during the aging precipitation process, and the size of the precipitate particles contributing to the strength increase Is 0.5μ
m or less.

[0008] For example, Patent Publication No. 2501275 (registered date: March 13, 1996) discloses a chromium 0.
One or both of 0.01 to 2 wt% and zirconium of 0.005 to 1 wt% are selected, oxygen is 60 ppm or less, the balance is substantially made of copper, the size of the precipitate is 50 μm or less, and 0.5 to 50 μm 100 to 100 precipitates
It describes a copper alloy having both conductivity and strength characterized by being present at 000 pieces / mm ² . In this alloy,
It also describes adding a specified amount of Ni, Sn, Fe, Co, Zn, Ti, and many other additional elements.

[0009]

SUMMARY OF THE INVENTION In a Cu-Cr-Zr alloy, fine Cr and Cu ₃ Zr are contained in a copper matrix.
The property that the strength and the electrical conductivity increase due to the formation of precipitated particles can be realized because the added elements Cr and Zr are difficult to form a solid solution with the copper of the matrix, but on the other hand, they contribute to the improvement of the strength. Coarse crystals or precipitates are likely to remain in the matrix, and oxides, sulfides, silicides, etc. are likely to be generated due to the high activity of these additional elements. The result is that the target tends to have a structure in which extremely large particles are dispersed. In fact, the above-mentioned Patent No. 2,501,275 discloses that a precipitate of 0.5 to 50 μm has 1
It is described that it exists as much as 100-100,000 pieces / mm ² .

However, when a Cu—Cr—Zr alloy is put to practical use as a material for electronic equipment, the presence of these coarse particles causes a crack starting point when severe bending deformation is applied to the material. Becomes a problem. Therefore, solving these problems while maintaining the strength and conductivity as a material for electronic devices has become a problem of the alloy system. In addition, in applications such as lead frames used for plastic semiconductor packages, it is urgently necessary to ensure the adhesion of the generated oxide film.

[0011]

Means for Solving the Problems The present inventors have proposed Cu-C
As a result of repeated research on r-Zr alloys, Zn was added to Cr and Zr.
In addition to adjusting the alloy composition by adding, the production conditions are strictly controlled and selected to control the distribution of inclusions such as precipitates, crystallization, oxides, sulfides, and silicides in the matrix. By doing so, it is possible to balance the strength, conductivity, bendability, and adhesion of the oxide film at a high level, and to this, Fe and Ti, Ni, Sn,
It has been found that the strength characteristics can be further improved by adding one or more of In, Mn, P, Mg and Si. Unlike the disclosure of Patent No. 2501275, the size of the inclusion is 30 μm or less,
By setting the number of inclusions having a size of 5 to 30 μm to less than 100 / mm ^2, the bendability becomes good for the first time.
r and Zr can improve the adhesion between the oxide film formed on the surface and the base material by being co-added.
It has been found that by adding Zn, Zn has a function of improving the adhesion between the oxide film and the base material, and it is possible to obtain more favorable adhesion of the oxide film.

That is, according to the present invention, C
r: 0.05 to 0.4%, Zr: 0.03 to 0.25%
And Zn: 0.06 to 2.0%, and if necessary, Fe: 0.1 to 1.8% and Ti: 0.1
0.8%, and if necessary, Ni, Sn, I
at least one of n, Mn, P, Mg and Si: 0.
0.1 to 1.0%, the balance being Cu and unavoidable impurities, the size of inclusions is 30 μm or less, and the number of inclusions of 0.5 to 30 μm is 100 /
less than mm ² , the strength required as a material for electronic devices,
Provided is a copper alloy characterized by having improved conductivity, bendability, and adhesion of an oxide film after the oxide film is generated.

In the present invention, the term "inclusion" refers to the precipitation reaction in the solid phase matrix after the solidification process during casting, ie, the cooling process after solidification, the cooling process after hot rolling, and the aging annealing. Precipitates (particles) generated by segregation in the solidification process during casting and generally coarse precipitates (particles)
In addition, oxides, sulfides, silicides, and the like, which are impurities generated by a reaction in the molten metal at the time of melting, are used to cover particles observed in the matrix by microscopic observation of the copper alloy. "Size of inclusions" refers to the diameter of the smallest circle enclosing the inclusions under microscopic observation. The “number of inclusions” is the average number of inclusions per unit square mm actually counted at a number of locations under microscopic observation.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy of the present invention is used for electronic devices such as lead frames and various electronic components such as terminals, connectors, relays and switches. The reason for limiting the component composition and inclusion conditions of the alloy of the present invention,
The operation will be described in detail below.

A. The components Cr and ZrCr function to precipitate in the matrix by aging after liquefaction of the alloy, thereby improving the strength. When the content is less than 0.05% by weight, desired effects due to this effect are obtained. No effect is obtained, while if it exceeds 0.4% by weight, coarse Cr remains in the matrix after commercialization. As a result, the bending property and the etching property deteriorate. For the above reasons, the Cr content is determined to be 0.05 to 4% by weight. Zr has a function of forming a compound with Cu by aging treatment and precipitating in the base material to strengthen it.
If the content is less than 3% by weight, the desired effect due to the above-mentioned effects cannot be obtained, while if the content exceeds 0.25% by weight, Zr contains
After the solution treatment, coarse undissolved Zr is left in the base material, resulting in deterioration of bendability and etching property. Therefore, the Zr content is set to 0.03 to 0.25% by weight. .
In addition, when Cr and Zr are co-added, the adhesion between the oxide film formed on the alloy surface and the base material can be improved, which is effective as a measure against occurrence of package cracks and peeling. This is because when Cr and Zr are added together,
This is because segregation of Zr itself, other additive elements, and impurity elements to the oxide film-base material interface by heating is suppressed.

Zn Zn has a function of improving the adhesion between the oxide film formed on the alloy surface by heating and the base material, and further improves the adhesion of the oxide film by co-adding with Cr and Zr. Can be. This is because Zn, like Cr and Zr, has an effect of suppressing the segregation of additional elements and impurity elements at the oxide film-base material interface by heating. Zn also has the function of improving the heat-peelability of the solder. If the content is less than 0.06% by weight, the desired effect due to the above-mentioned effect cannot be obtained. On the other hand, if Zn is contained in an amount exceeding 2.0% by weight, the electrical conductivity is deteriorated. It was determined to be 0.06 to 2.0% by weight.

Ti and Fe Ti and Fe contain T in the matrix when the alloy is aged.
They are added as necessary to form an intermetallic compound of i and Fe and consequently exert an effect of further improving the alloy strength.
%, The desired strength cannot be obtained by the above action.
On the other hand, if the Ti content exceeds 0.08% or the Fe content exceeds 1.80%, coarse inclusions containing Ti and Fe as main components remain, impairing bendability, and Significantly inhibits etchability.

Ni, Sn, In, Mn, P, Mg and
Si These components are all, without significantly decreasing the electrical conductivity of the alloy, primarily has the effect of improving the strength by solid solution strengthening, and thus one or more additives as necessary are made However, if the total content is less than 0.01% by weight, the desired effect cannot be obtained by the above effect, while if the total content exceeds 1.0% by weight, the conductivity of the alloy is significantly deteriorated. I do. Therefore, Ni, Sn, In, M, which are added alone or in combination of two or more kinds, are used.
The content of n, P, Mg and Si is 0.01 to a total amount.
It was determined to be 1.0% by weight.

B) Distribution of Inclusions As described above, in this alloy system, inclusion particles including precipitates, crystallized substances, oxides, sulfides, and silicides are present in the matrix. Inclusions (precipitated particles) for obtaining the strength required for this alloy are small, but 0.5 μm
Coarse inclusions not exceeding not only do not contribute to an increase in strength, but also degrade the bendability required as a copper alloy for electronic equipment.
In other words, strong tensile deformation occurs on the surface of the material subjected to bending deformation, but if coarse inclusions exist at this site, voids will be generated between the inclusions and the matrix, and these will eventually combine and reach the surface Since it becomes a crack in appearance and becomes apparent, it becomes a practical problem. In order to prevent such deterioration in bending property, the upper limit of the size of the coarse inclusion is set to 30 μm, and the number of inclusions having a size of 0.5 to 30 μm is set to less than 100 / mm ^2. Good.

Next, a manufacturing method for obtaining this alloy will be described.

(Melting / Casting) In the melting step, it is important to prevent formation of inclusions such as coarse oxides, sulfides and silicides. First, the material of the crucible is preferably carbon, and when a material containing an oxide such as magnesia, alumina, silica, etc. is used, the molten metal erodes these materials and is caught in the molten metal, or the furnace material is reduced by Zr to reduce the Zr oxide. Or it is not suitable. In addition, if the dissolved raw material used has an oily component, sulfide may be formed in the molten metal, which is not preferable. Therefore, the use of a return material should be avoided as much as possible, and the use of a return material requires degreasing. After the melted raw material is dropped, it is necessary to reduce the oxygen concentration by coating the surface of the molten metal with a reducing gas such as CO, or by providing a vacuum atmosphere. Thereby, it is desirable that the oxygen concentration be 20 ppm or less.

(Homogenizing Heat Treatment) Next, the homogenizing heat treatment conditions will be described. In the ingot, crystallized substances formed due to segregation of additional elements such as Cr and Zr during casting are present. In order to reduce these in the process up to the product, it is necessary to sufficiently reduce the crystallized matter at this stage by sufficiently performing the homogenizing heat treatment before hot rolling. Specifically, the temperature at the start of hot rolling needs to be 800 ° C. or higher, preferably 850 ° C. or higher.

(Hot Rolling) Next, the conditions for hot rolling will be described. If the temperature decreases during rolling, the precipitation reaction proceeds, and the particles become coarse. In such a case, large particles remain even at the product stage. Therefore, it is necessary that the temperature of the material does not drop during hot rolling, and the end temperature is desirably 700 ° C or higher, preferably 750 ° C or higher. In the cooling process after hot rolling, the slower the cooling rate, the more the precipitation reaction proceeds, and the larger the precipitates tend to be. Specifically, when the cooling rate is lower than 1 ° C./sec, the precipitates are excessively coarsened. Therefore, the cooling rate after the completion of hot rolling is set to 1 ° C./sec or more.

(Solution treatment) The solution treatment is performed in order to obtain a high-strength material by the subsequent aging treatment. The higher the treatment temperature, the higher the amount of solid solution in the matrix of Cr and Zr, and the higher the strength after aging. In order to obtain such an effect, the higher the processing temperature, the better, and it is preferable that the temperature be 700 ° C. or higher. Further, if the crystal grain size of the recrystallization at this time becomes large, the surface of the bent portion becomes rough when the product is subjected to bending, so that the crystal grain size is desirably 40 μm or less. In the solution treatment, the higher the cooling rate is, the higher the strength is easily obtained. Specifically, it is desirable to perform water cooling.

(Cold Rolling) If cold rolling is performed after the solution treatment, precipitation in the aging step is promoted, and high strength is obtained. In order to obtain this effect, it is desirable to set the working ratio of the cold rolling to 40% or more.

(Aging Treatment) The aging treatment is necessary to improve the strength and conductivity, but the aging treatment temperature is 300 ° C.
The temperature is preferably set to ℃ 700 ° C. If the temperature is lower than 300 ° C., it takes a long time to perform the aging treatment, which is not economical. If the temperature exceeds 700 ° C., Cr and Zr form a solid solution, and the strength and conductivity characteristic of the age hardening type alloy cannot be obtained. Thereafter, final cold rolling and strain relief annealing are performed.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, electrolytic copper or oxygen-free copper is used as a main material, and copper chromium mother alloy, copper zirconium mother alloy, zinc, titanium, nickel, tin, indium, manganese,
Magnesium mild steel, silicon, and copper-phosphorus mother alloy were used as auxiliary materials, and a carbon crucible was used in a high-frequency melting furnace.
Copper alloys having various component compositions shown in Table 1 were melted in a vacuum or in an Ar atmosphere, and cast into ingots having a thickness of 30 mm. Next, in accordance with the above-described steps, each of these ingots was subjected to hot working and solution treatment, first cold rolling, aging treatment, final cold rolling, and strain relief annealing, in the order of 0.1 mm in thickness.
A 5 mm plate was used, and the characteristics as a copper alloy for electronic devices were evaluated.

The properties were evaluated by investigating "strength", "elongation", "conductivity", and "bendability". "Strength" and "elongation" were measured by a tensile test, and "conductivity" was obtained by measuring conductivity. "Bendability"
Is evaluated by performing a W bending test with a bending radius of 0,
The case where a fine crack was formed on the surface of the bent portion was evaluated as “×”, and the case where no fine crack was formed was evaluated as “○”. The “number of inclusions” was measured by actually counting inclusions having a size of 0.5 to 30 μm by microscopic observation.

The results of these investigations are also shown in Table 1. The following is clear from the results shown in Table 1. The alloys 1 to 13 of the present invention have sufficiently good evaluations in all of the properties of strength, elongation, conductivity, and bendability. On the other hand, the comparative alloy 14 is inferior in strength because of insufficient Cr content. Comparative alloy 1
5, 16, 17, and 18 have Cr, Zr, Fe, and Ti contents exceeding the respective upper limit values, and the comparative alloy 19 has a high oxygen concentration, so that the number of inclusions is high and the bendability is inferior. . Next, Comparative Alloy 20 is an example in which the conductivity is inferior because the Zn content exceeds the upper limit.

[0030]

[Table 1]

The adhesiveness of the oxide film of a 0.15 mm thick plate having the composition shown in Table 2 separately produced in the same manner was evaluated by a tape peeling test. A test piece of 20 × 50 mm was cut out from each plate material and heated in air at a predetermined temperature for a predetermined time, and then a commercially available tape (3M # 851) was attached to the surface of the test piece on which the oxide film was formed and peeled off. At that time, the adhesiveness was evaluated based on the area of the oxide film adhered to the tape. The case where the oxide film was not peeled at all was evaluated as ○, the one where the oxide film was partially peeled was evaluated as Δ, and the one where the oxide film was completely peeled was evaluated as ×. At the same time, the strength and the conductivity were also evaluated as before.

Table 3 shows the evaluation results. Example 1
With regard to 13, good oxide film adhesion was obtained. On the other hand, Comparative Examples 15 to 27 have low adhesion of the oxide film. Comparative Example 14 had good adhesion to the oxide film, but was inferior in strength.

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

According to the present invention, it is possible to obtain a copper alloy having good strength, conductivity, bendability and adhesion of an oxide film after generation of the oxide film, which is great for miniaturization and thinning of electronic equipment. Industrially extremely useful effects such as contribution can be brought about.

Claims (4)

[Claims] 1. Cr: 0.05 to 0.4 in weight ratio.
%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0%, the balance consists of Cu and unavoidable impurities, and the size of inclusions is 30 μm or less,
And the number of inclusions of 0.5 to 30 μm is 100 / mm
A copper alloy having a strength of less than ² and having improved strength, conductivity, bendability, and adhesion of an oxide film after the oxide film is generated, which is required as a material for electronic devices. 2. Cr: 0.05 to 0.4 in weight ratio.
%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0% and further contains Ni, Sn, In, Mn, P,
One or more of Mg and Si: 0.01 to 1.0% in total amount
And the balance consists of Cu and unavoidable impurities, and the size of inclusions is 30 μm or less, and the number of inclusions of 0.5 to 30 μm is less than 100 / mm ² , Strength, conductivity,
A copper alloy characterized by improved bendability and adhesion of an oxide film after the oxide film is generated. 3. Cr: 0.05 to 0.4 in weight ratio.
%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0%, Fe: 0.1-1.8%, T
i: contains 0.1 to 0.8%, the balance consists of Cu and unavoidable impurities, and the size of inclusions is 30 μm
And the number of inclusions of 0.5 to 30 μm is 1
A copper alloy having a strength of less than 00 pieces / mm ² , and having good strength, conductivity, bendability, and adhesion of an oxide film after the oxide film is generated, which is necessary as a material for electronic devices. 4. Cr: 0.05 to 0.4 by weight ratio.
%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0%, Fe: 0.1-1.8%, T
i: contains 0.1 to 0.8%, and additionally contains Ni, Sn,
At least one of In, Mn, P, Mg, and Si: also contains 0.01 to 1.0% in total amount, the balance consists of Cu and unavoidable impurities, and the size of inclusions is 30 μm.
And the number of inclusions of 0.5 to 30 μm is 1
A copper alloy having a strength of less than 00 pieces / mm ² , and having good strength, conductivity, bendability, and adhesion of an oxide film after the oxide film is generated, which is necessary as a material for electronic devices.