JPH1197609A - Copper alloy for lead frame superior in oxide film adhesion and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the characteristics for lead frames and oxide film adhesion by preparing a Cu alloy composed of P, Co, Cu and inevitable impurities where the P to Co wt.% ratio is specified. SOLUTION: P is used as a molten metal deoxidizer and compounds with other element to produce a precipitate which improves the strength, heat resistance, etc., without deteriorating the electric-terminal conductivity and contained 0.001-0.25 wt.%. Co forms a dispersed and precipitated Co-P compd. with P to reduce the amt. of P solidified in a matrix, and to improve the oxide film adhesion, heat resistance, electrical conductivity and mechanical strength, and a total content of 0.01-0.50 wt.%. When a Co to P ratio is 1.5 or less, suppression effect of P segregation by Co cannot be expected, resulting in a larger reduction of the oxide film adhesion. Hence, this ratio is set to a range of 1.5-10.

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 good adhesion to an oxide film used for a lead frame of a semiconductor device and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, 42 alloy (Fe-42Ni) has been used as a lead frame of a semiconductor device. At present, with the miniaturization and high density of semiconductor circuits, excellent heat conductivity has been achieved. Copper-based materials have come to be used.

In general, lead frames of semiconductor devices are required to have the following characteristics. (1) Excellent heat and electric conductivity. The function of the lead frame is to dissipate the heat generated by the chip in order to prevent the deterioration of the chip. In order to increase the efficiency of heat dissipation and reduce the heat generation of the lead portion, good thermal conductivity and electrical conductivity are required.

(2) High strength. The lead frame needs sufficient strength to support the chip in the manufacturing process or after the manufacturing.

(3) Good heat resistance. Lead frames are subjected to various types of heating during the manufacturing process. Therefore, heat resistance is required so that the strength does not deteriorate due to a thermal load.

(4) Good moldability. In most cases, lead frames are often subjected to press forming. Therefore, good moldability is required.

(5) Good plating and soldering properties. The lead frame is often plated or soldered such as Ag plating or solder plating. For this reason, good plating properties, solderability, and weather resistance are required.

[0008] In addition to the above-mentioned characteristics, another characteristic that has recently attracted attention is the adhesion between a material and an oxide film.
In the manufacturing process, the lead frame is 300 to 4 in die bonding, wire bonding, resin sealing, etc.
Although heat treatment is performed at a high temperature of 00 ° C., the adhesion between the oxide film and the material generated on the material surface during these heat treatments is often inferior to the adhesion between the oxide film and the resin.

Usually, the lead frame is sealed with a resin in a state in which the oxide film after the heat treatment has grown, so that when the adhesion between the oxide film and the material is poor, the adhesion between the lead frame and the resin is directly deteriorated. As a result, the wiring connecting the chip and the lead frame corrodes due to the ingress of moisture from the gap, causing poor moisture resistance. In addition, it causes process contamination, poor wire bonding, and package cracks.

In recent years, the size of semiconductors has been reduced in size, the number of pins has been increased, and the number of surface mounting types has been increasing. The proportion of the area that is being used is increasing. At the same time, the adhesion between the material and the oxide film has been increasing its importance as a characteristic relating to the reliability of the semiconductor device. In the manufacturing process, the temperature of heat treatment such as soldering and bonding has been increasing in order to increase the speed, and lead frames are required to have not only heat resistance but also oxide film adhesion at high temperatures. ing. Specifically, it is required that the oxide film adheres even when heated at 350 ° C. or higher, preferably 380 ° C. or higher.

By the way, copper-based materials are expensive, workable,
Although it has characteristics superior to 42 alloy in electric and thermal conductivity, an oxide film on the material surface is easily formed and easily peeled off during heat treatment.

Among the copper-based materials, oxygen-free copper has the best adhesion to an oxide film, but does not satisfy the properties required for a lead frame such as heat resistance and tensile strength. On the other hand, for phosphorus deoxidized copper to which P was added in order to improve heat resistance and tensile strength, it was found that P dissolved in the matrix greatly reduced the oxide film adhesion.

Also, copper alloys such as Cu-Fe-P-based and Cu-Sn-P-based to which other additive elements are added for improving the mechanical properties are considered to have good oxide film adhesion. I can't say it. For this reason, a copper alloy having good adhesion between a material and an oxide film while having characteristics such as strength and heat resistance sufficient for a lead frame has been demanded.

[0014] Under such circumstances, attempts have been made to improve the adhesion of the oxide film by various methods. For example, Japanese Patent No. 2564633 discloses a production method in which copper plating is applied to a material surface, and then cold rolling and heat treatment are performed to obtain oxide film adhesion equivalent to oxygen-free copper and tough pitch copper. But in this case,
Extra steps such as plating, cold rolling, and heat treatment are performed, and the manufacturing cost is increased as compared with a normal copper alloy.

In Japanese Patent Application Laid-Open No. 2-173248, the surface after intermediate heat treatment or after final rolling is polished,
By removing the concentrated layer of the added element by heat treatment,
A method for improving adhesion is disclosed. However, in the polishing step for removing a sufficient concentration layer by this method, the surface roughness becomes rough, and the thickness of the oxide film on the material surface becomes larger than usual due to frictional heat during polishing. It has been found that the properties such as direct bonding and soldering are adversely affected. Further, in these prior applications, the thickness of the oxide film is not specified, and the adhesion of the oxide film after the high-temperature heat treatment is inferior.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has been developed without adversely affecting characteristics such as direct bonding and solderability. An object of the present invention is to propose a copper alloy for lead frames having excellent film adhesion and a method for producing the same.

[0017]

Means for Solving the Problems The present inventors have conducted intensive studies on various material factors affecting oxide film adhesion, and found that the distribution of added elements in the surface layer of the material and the oxide film formed at room temperature were obtained. It has been found that controlling the thickness of the material is important.

P which is often used as an additive element in copper alloys
Is an important element having a deoxidizing effect and an effect of improving properties by being combined with and precipitated with other elements, and is very useful in actually producing a copper alloy. However,
It was found that the addition of a small amount of P adversely affects the adhesion of the oxide film, and that the addition of elements other than P deteriorates the adhesion of the oxide film, although the degree of difference is different.

That is, an alloy in which an additive element such as P is dissolved is:
At a high temperature, P segregated in the oxide film on the surface of the material, and it was found that this reduced the adhesion of the oxide film generated at the high temperature.

Therefore, the present inventor has reduced the amount of additional elements such as P dissolved in the copper matrix.
That is, an attempt was made to improve the oxide film adhesion by bringing the matrix closer to the state of oxygen-free copper.

Then, as a result of investigating various alloy systems, it was found that Co, which is an additive element of the present invention, is one of the elements forming precipitates with P, such as Fe and Ni, which is the most effective element for preventing solid solution of P in the matrix. The effect that Co near the oxide film-metal interface inhibits the diffusion of P into the oxide film and prevents segregation into the oxide film, even for a small amount of P that is solid solution without being completely precipitated. It was found that he had.

An alloy in which a Co-P compound is precipitated in a copper matrix to improve mechanical properties is disclosed, for example, in Japanese Patent Application Laid-Open No. 3-180437. However, these patents do not specify the thickness of the oxide film, so that the adhesion of the oxide film at a high temperature is insufficient.

Further, as a technique relating to an alloy in which a thickness of an oxide film is specified in a lead frame material, for example, Japanese Patent Application Laid-Open No. Sho 60-225455 is disclosed. However, these techniques are stipulated from the viewpoint of improving the direct bonding property, and do not disclose the adhesion of an oxide film formed after heating.

Therefore, the added amount of Co and P, the Co / P ratio,
By controlling the range of the thickness of the oxide film formed at room temperature to an appropriate value, it has the same mechanical properties and heat resistance required for lead frames, but has the same oxide film adhesion as oxygen-free copper. It has become possible to obtain a good copper alloy.

That is, the present invention relates to the following copper alloy for lead frames and a method for producing the same. 1) In weight%, P:
0.001 to 0.25%, Co: 0.01 to 0.50
%, The balance being Cu and unavoidable impurities, wherein the ratio of the weight percentage of Co and P is Co / P = 1.5-10, the copper alloy for lead frames having excellent oxide film adhesion.

2) In weight%, P: 0.001 to
0.25%, Co: 0.01 to 0.50%, balance Cu and unavoidable impurities, the ratio of the weight percentage of Co and P is Co / P = 1.5 to 10, and the oxide film thickness A copper alloy for lead frames having excellent adhesion to an oxide film, having a thickness of 10 nm or less.

3) In weight%, P: 0.001 to
0.25%, Co: 0.01 to 0.50%, balance Cu and unavoidable impurities, the ratio of the weight percentage of Co and P is Co / P = 1.5 to 10, and the oxide film thickness A copper alloy for a lead frame having excellent adhesion to an oxide film, wherein the heating temperature at which the oxide film peeling rate is 10% or more is 380 ° C. or more.

4) In weight%, P: 0.001 to
0.25%, Co: 0.01 to 0.50%, further Fe,
Ni, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance Cu
A copper alloy for lead frames having excellent adhesion to an oxide film, wherein the copper alloy is composed of unavoidable impurities and has a Co / P weight percentage ratio of Co / P = 1.5 to 10.

5) In weight%, P: 0.001 to
0.25%, Co: 0.01 to 0.50%, further Fe,
Ni, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance Cu
And an unavoidable impurity, wherein the ratio of the weight percentage of Co and P is Co / P = 1.5-10 and the oxide film thickness is 10 nm or less. Copper alloy for lead frame.

6) In weight%, P: 0.001 to
0.25%, Co: 0.01 to 0.50%, further Fe,
Ni, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance Cu
Heating in which the ratio of the weight percentage of Co and P is Co / P = 1.5-10, the oxide film thickness is 10 nm or less, and the oxide film peeling rate is 10% or more. A copper alloy for lead frames having excellent oxide film adhesion, wherein the temperature is 380 ° C. or higher.

7) In the above 1) to 6), in order to control the thickness of the oxide film, chemical and / or chemical treatment after the heat treatment at the final thickness is performed.
Alternatively, the oxide film is removed by a mechanical method, and the oxide film thickness is reduced to 10 n.
m or less, and a method for producing a copper alloy for lead frames having excellent oxide film adhesion.

8) In the above item 7), the chemical treatment method is cleaning with an acid, and the mechanical treatment method is surface polishing with a buff or a brush. Production method.

[0033]

The contents of the present invention will be specifically described below. First, the selection of the additive element of the copper alloy according to the present invention and the reason for limiting the range of the content will be described.

(1) PP is used not only as a deoxidizing agent for molten metal, but also as a precipitate by being combined with other elements to improve strength and heat resistance without lowering electric and thermal conductivity. Element. However, if the P content is less than 0.001% by weight, the strength, heat resistance, and elasticity are insufficiently improved, and the effect of forming a compound with another additive element and dispersing and precipitating cannot be sufficiently obtained. On the other hand, if the content exceeds 0.25% by weight, the adhesion of the oxide film is deteriorated even in the presence of Co, and the electrical conductivity and the solder weather resistance are reduced. Therefore, the content of P is set to 0.001 to 0.25% by weight. More preferably, 0.001 to 0.15
% By weight.

(2) Co Co forms a Co—P-based compound with P to be dispersed and precipitated, so that the amount of P dissolved in the matrix is reduced, and the adhesion of the oxide film, heat resistance, and electric conductivity are reduced. Improve mechanical properties and mechanical properties. In addition, even for a very small amount of P, which cannot be completely precipitated and is dissolved in the matrix, Co near the oxide film-metal interface prevents the diffusion of P into the oxide film and prevents segregation into the oxide film. This has the effect of improving the adhesion of the oxide film. In order to exert these effects, the content of 0.01% by weight or more is necessary. However, if the content exceeds 0.50% by weight, the electric conductivity is remarkably reduced, and Co itself adheres to the oxide film. Not only does it have a negative effect on sex, but it is also disadvantageous economically. Therefore, the total amount of these contents is in the range of 0.01 to 0.50% by weight. More preferably, it is 0.25 to 0.45% by weight.

(3) Sub-components Further, as sub-components, Fe, Ni, Sn, Zn, Ti,
Mg, Zr, Ca, Si, Mn, Cd, Al, Pb, B
e, Te, In, Ag, B, Y, La, Cr, Ce, A
one or more selected from the group of u in a total amount of 0.0
When it is contained in an amount of from 0.01 to 2.0%, the above various characteristics required for the lead frame are further improved. That is, the addition of these elements improves the strength, elasticity, and heat resistance of the copper alloy according to the present invention without lowering the electrical conductivity.

(4) Co / P ratio When the Co / P ratio is 1.5 or less, the effect of suppressing the segregation of P due to Co cannot be expected, and as a result, the adhesion of the oxide film is greatly reduced. Further, when the Co / P ratio is 10 or more, since Co forms a solid solution in the copper matrix, the electric conductivity is significantly reduced. Therefore, the range of the Co / P ratio is 1.5 to
10, preferably in the range of 3-5.

Further, from the viewpoint of the oxide film adhesion, the copper matrix containing these elements has a low solid solution element content,
That is, it is required to be in a state close to oxygen-free copper. Therefore, the conductivity is 70% IACS or more, and more preferably 7% IACS.
5% IACS or more.

Next, the oxide film will be described. The copper alloy forms an oxide film of 8 to 10 nm under a normal storage atmosphere. This oxide film is susceptible to changes in the surrounding environment, particularly humidity, even at room temperature, and easily grows beyond 10 nm. In this case, the adhesion of the oxide film after heating is greatly reduced. Therefore, the oxide film thickness is set to 10 nm or less, preferably 7 nm or less. Here, as a definition of the oxide film thickness, a value obtained by converting the amount of reduction electricity of an oxide by a constant current electrolysis method into CuO was used.

However, in a normal process, after working to the final thickness, annealing is performed for the purpose of removing strain, improving characteristics, and the like. At this time, the thickness of the oxide film on the surface of the material may exceed 10 nm. Therefore, the thickness of the oxide film on the material surface is controlled by a method such as mechanically or chemically removing the oxide film, and
nm or less. Here, as a mechanical removal method, surface polishing with a buff brush or the like is performed, and as a chemical removal method, cleaning with an acid is performed.

Here, when removing the oxide film by the mechanical removal method, if the surface roughness exceeds 1 μm in the maximum surface roughness (Rmax) and 0.1 μm in the center line average roughness (Ra). And the direct bonding property is reduced.
Therefore, Rmax: 1 μm or less and Ra: 0.1 μm
m or less.

As another method of controlling the oxide film thickness, a method of controlling the oxygen concentration in the atmosphere during annealing is also effective. Next, embodiments of the present invention will be described more specifically with reference to examples.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION

Example An alloy having the composition shown in Table 1 was melted using a high-frequency melting furnace.
After heating to 850 ° C., it was hot-rolled to a thickness of 5.0 mm. Next, the surface was polished to 4.8 mm, and cold rolling and heat treatment were repeated to obtain a sheet having a sheet thickness of 0.25 mm.

Therefore, the hardness, tensile strength, electrical conductivity, heat resistance temperature, oxide film thickness, and oxide film adhesion of the above materials were examined. The measurement of hardness, tensile strength, and electrical conductivity was performed in accordance with JIS-Z-2244, JIS-Z-2241, and JIS-H-0505, respectively.

The heat resistance was measured by heating the sample for 30 minutes and then measuring the hardness.
The temperature was set to 0%.

For the measurement of the oxide film thickness, an electrolytic solution: 0.1 NK
Constant current electrolysis was performed under the conditions of Cl and a current density of 0.25 mA / cm ² , and the amount of reduction electricity was converted to an oxide film thickness (cathode reduction method). The calculations were performed on the assumption that all oxides were CuO.

Regarding the oxide film adhesion, the sample was heated in air at 200 to 500 ° C. for 5 minutes and then allowed to cool for 1 minute.
Cooled to room temperature. After a while, 18mm x 20m on the surface
m, and the presence or absence of an oxide film adhering to the peeled tape was investigated.

At this time, the ratio of the area of the oxide film peeled off from the base material and adhered to the tape to the area of the attached tape is defined as the oxide film peeling rate, and the heating temperature when the oxide film peeling rate becomes 10% or more is defined as the heating temperature. The oxide film peeling temperature of the alloy was used. Here, the reason why the peeling rate is set to 10% or more is that when the peeling rate exceeds 10%, a slight increase in the heating temperature causes the entire peeling to proceed abruptly, causing the peeling of the oxide film almost entirely over the tape. Furthermore, the oxide film stripping rate was measured for the sample after heating at 360 ° C. for 5 minutes. Table 1 shows the test results.

[0049]

[Table 1]

The alloys 1 to 8 of the present invention have an oxide film peeling temperature of 38.
0 ° C. or higher, and the oxide film peeling rate after heating at 360 ° C. is 10% or less, excellent oxide film adhesion at high temperatures, high tensile strength and heat resistance temperature, and lead It is a suitable material for frames.

On the other hand, comparative examples 9 to 13 show alloys generally used at present for lead frames. Comparative Example 9 is a so-called phosphorus deoxidized copper, Comparative Example 10 is a so-called oxygen-free copper, and Comparative Examples 11, 12, and 13 are Cu-
Fe-P system, Cu-Ni-Si-Mg system, Cu-Ni-
It is a Sn-Zn-P-based copper alloy. Except for Comparative Example 10, the oxide film adhesion was peeled at 350 ° C. or less, and the oxide film peeling rate after heating at 360 ° C. was 95% or more. It's hard to be there. In Comparative Example 10, the oxide film adhesion was good, but the mechanical properties and heat resistance were inferior.
It cannot be said that the characteristics required for the lead frame are satisfied.

Comparative Examples 14 to 17 are samples having the same composition as the alloy of the present invention, but having a thicker oxide film thickness than the alloy of the present invention. For these, the oxide film peeling temperature and 360 ° C.
Both the oxide film peeling rates after heating are inferior to the alloys of the present invention.

Comparative Example 18 is a sample having a Co / P ratio of 1.5 or less, and Comparative Example 19 is a sample having a Co / P ratio of 10 or more. Both have inferior oxide film adhesion and electrical conductivity characteristics. That is, only the product of the present invention, which contains specified amounts of P and Co as additional elements and has an oxide film thickness of 10 nm or less, has good oxide film adhesion and excellent mechanical properties comparable to conventional oxygen-free copper. You can have both.

[0054]

As described above, the present invention relates to a copper alloy,
By controlling the type and ratio of the added elements, especially the Co / P ratio, and further controlling the oxide film thickness, it is possible to simultaneously improve the characteristics for lead frames and the oxide film adhesion that could not be achieved until now. This is extremely practical value for semiconductor equipment requiring high reliability.

Claims (8)

[Claims] (1) P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, the balance being Cu and unavoidable impurities, wherein the ratio of the weight percentage of Co and P is Co / P = 1.5-10. Copper alloy for lead frames with excellent adhesion. 2. P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, balance Cu and inevitable impurities, the weight percentage ratio of Co and P is Co / P = 1.5 to 10, and the oxide film thickness is 1
A copper alloy for a lead frame having excellent oxide film adhesion, characterized in that the thickness is 0 nm or less. 3. The composition according to claim 1, wherein P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, balance Cu and inevitable impurities, the weight percentage ratio of Co and P is Co / P = 1.5 to 10, and the oxide film thickness is 1
A copper alloy for a lead frame having excellent adhesion to an oxide film, wherein the heating temperature is 0 nm or less and a heating temperature at which an oxide film peeling rate is 10% or more is 380 ° C. or more. 4. The method according to claim 1, wherein P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, Fe, N
i, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance C
A copper alloy for a lead frame having excellent adhesion to an oxide film, comprising u and unavoidable impurities, wherein a weight percentage ratio of Co and P is Co / P = 1.5-10. 5. The method according to claim 1, wherein P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, Fe, N
i, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance Cu
And an unavoidable impurity, wherein the ratio of the weight percentage of Co and P is Co / P = 1.5-10 and the oxide film thickness is 10 nm or less. Copper alloy for lead frame. 6. P: 0.001 to 0.
25%, Co: 0.01 to 0.50%, Fe, N
i, Sn, Zn, Ti, Mg, Zr, Ca, Si, M
n, Cd, Al, Pb, Be, Te, In, Ag, B,
One or more selected from the group consisting of Y, La, Cr, Ce, and Au are contained in a total amount of 0.01 to 2.0%, and the balance Cu
Heating in which the ratio of the weight percentage of Co and P is Co / P = 1.5-10, the oxide film thickness is 10 nm or less, and the oxide film peeling rate is 10% or more. A copper alloy for lead frames having excellent oxide film adhesion, wherein the temperature is 380 ° C. or higher. 7. The method according to claim 1, wherein the oxide film is removed by a chemical and / or mechanical method after the heat treatment at the final thickness in order to control the oxide film thickness. A method for producing a copper alloy for lead frames having excellent oxide film adhesion. 8. The copper alloy according to claim 7, wherein the chemical treatment method is cleaning with an acid, and the mechanical treatment method is surface polishing with a buff or a brush. Production method.